CHANGELOG.fr.md

@@ -3,6 +3,7 @@
 ## [Non publié]
 
 ### Ajouté
+- **Bilan — éditeur de snapshot (type simple)** (route `/balance/snapshot`) : deuxième tranche de la feature *Bilan*. La nouvelle page permet de créer ou modifier un snapshot daté de votre patrimoine : choisissez une date (par défaut aujourd'hui), saisissez la valeur de chaque compte actif groupé par catégorie, puis enregistrez. Le mode est piloté par le paramètre `?date=` de l'URL — si un snapshot existe déjà à cette date, la page bascule automatiquement en mode édition (la contrainte UNIQUE sur `balance_snapshots.snapshot_date` garantit un snapshot par jour). La date d'un snapshot existant est immuable : pour la changer, supprimez puis recréez. Un bouton *Pré-remplir depuis le précédent* copie les valeurs du snapshot antérieur le plus récent (comptes simples uniquement — les comptes cotés seront pris en charge quand l'éditeur coté arrivera). Un bouton *Supprimer* affiche une modal de double confirmation qui exige de retaper la date du snapshot avant d'activer l'action destructive. Seules les valeurs de type simple sont acceptées à ce stade (`quantity` et `unit_price` sont laissés `NULL`) ; l'éditeur coté (quantité × prix unitaire + récupération de prix) arrivera dans une prochaine version. Nouveau hook `useSnapshotEditor` (`useReducer` couvrant tout le cycle de vie) et deux nouveaux composants `SnapshotEditor` + `SnapshotLineRow`. i18n FR/EN sous `balance.snapshot.*` (#146)
 - **Bilan — fondations du schéma et page Comptes** (route `/balance/accounts`) : première tranche de la nouvelle feature *Bilan*. La migration SQL v9 introduit 5 tables (`balance_categories`, `balance_accounts`, `balance_snapshots`, `balance_snapshot_lines`, `balance_account_transfers`) avec 7 index et seede 7 catégories standard — Encaisse, CELI, REER, Fonds commun, Autre (type simple) + Action et Cryptomonnaie (type coté). La colonne `currency` est verrouillée à `CAD` via une contrainte CHECK au MVP — le support multi-devises arrivera plus tard. La nouvelle page expose deux onglets : *Comptes* (CRUD complet sur les comptes de l'utilisateur, archivage soft plutôt que suppression dure pour préserver les snapshots historiques) et *Catégories* (renommer une catégorie, créer des catégories de type simple, supprimer celles créées par l'utilisateur — les catégories standard sont protégées). Couverture i18n FR/EN complète sous `balance.*`. Snapshots, transferts, rendements et price-fetching premium arriveront dans les prochaines issues ; pour l'instant la route est accessible directement par URL (pas encore d'entrée sidebar) (#138)
 
 ### Corrigé

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 ### Added
+- **Balance sheet — snapshot editor (simple kind)** (route `/balance/snapshot`): second slice of the *Bilan* feature. The new page lets you create or edit a dated snapshot of your balance: pick a date (defaulting to today), enter the value of each active account grouped by category, and save. The mode is driven by the `?date=` query parameter — when a snapshot already exists at that date the page automatically flips into edit mode (the underlying `balance_snapshots.snapshot_date` UNIQUE constraint guarantees one snapshot per day). The date of an existing snapshot is immutable: to change it, delete the snapshot and create a new one. A *Prefill from previous snapshot* button copies values from the most recent earlier snapshot (simple-kind accounts only — priced accounts will be handled when the priced editor lands in a later release). A *Delete* button surfaces a double-confirmation modal that requires retyping the snapshot date before the destructive action is enabled. Only simple-kind values are accepted at this stage (`quantity` and `unit_price` are kept `NULL`); the priced editor (quantity × unit price + price fetch) ships in a later release. New `useSnapshotEditor` hook (scoped `useReducer` covering the full lifecycle) and two new components `SnapshotEditor` + `SnapshotLineRow`. FR/EN i18n under `balance.snapshot.*` (#146)
 - **Balance sheet — schema foundation and accounts page** (route `/balance/accounts`): first slice of the upcoming *Bilan* feature. New SQL migration v9 introduces 5 tables (`balance_categories`, `balance_accounts`, `balance_snapshots`, `balance_snapshot_lines`, `balance_account_transfers`) with 7 indexes and seeds 7 standard categories — Cash, TFSA, RRSP, Mutual Fund, Other (simple kind) plus Stock and Crypto (priced kind). The `currency` column is hardcoded to `CAD` via a CHECK constraint at the MVP — multi-currency support will come in a later release. The new accounts page exposes two tabs: *Accounts* (full CRUD over the user's holdings, soft-archive instead of hard delete to preserve historic snapshots) and *Categories* (rename any category, create simple-kind ones, delete user-created ones — seeded categories are protected). The full FR/EN i18n coverage uses keys under `balance.*`. Snapshots, transfers, returns and the price-fetching premium remain to ship in upcoming issues; for now the route is reachable directly via URL (no sidebar entry yet) (#138)
 
 ### Fixed

src/App.tsx

@@ -17,6 +17,7 @@ import ReportsCategoryPage from "./pages/ReportsCategoryPage";
 import ReportsCartesPage from "./pages/ReportsCartesPage";
 import SettingsPage from "./pages/SettingsPage";
 import AccountsPage from "./pages/AccountsPage";
+import SnapshotEditPage from "./pages/SnapshotEditPage";
 import CategoriesStandardGuidePage from "./pages/CategoriesStandardGuidePage";
 import CategoriesMigrationPage from "./pages/CategoriesMigrationPage";
 import DocsPage from "./pages/DocsPage";
@@ -116,6 +117,7 @@ export default function App() {
           <Route path="/reports/cartes" element={<ReportsCartesPage />} />
           <Route path="/settings" element={<SettingsPage />} />
           <Route path="/balance/accounts" element={<AccountsPage />} />
+          <Route path="/balance/snapshot" element={<SnapshotEditPage />} />
           <Route
             path="/settings/categories/standard"
             element={<CategoriesStandardGuidePage />}

src/components/balance/SnapshotEditor.tsx

@@ -0,0 +1,92 @@
+// SnapshotEditor — groups the active accounts by balance category and
+// renders one `SnapshotLineRow` per account.
+//
+// Issue #146 / Bilan #1b: simple-kind editor only. The priced variant
+// (quantity x unit_price + price fetch button) is rendered in #140.
+// Until then, accounts whose category is `priced` still appear here so
+// the user can enter a manual aggregate value — the storage layer accepts
+// a simple-kind line for any account regardless of its category kind.
+
+import { useMemo } from "react";
+import { useTranslation } from "react-i18next";
+import type {
+  BalanceAccountWithCategory,
+  BalanceCategory,
+} from "../../shared/types";
+import SnapshotLineRow from "./SnapshotLineRow";
+
+interface Props {
+  accounts: BalanceAccountWithCategory[];
+  categories: BalanceCategory[];
+  values: Record<number, string>;
+  onValueChange: (accountId: number, next: string) => void;
+  disabled?: boolean;
+}
+
+export default function SnapshotEditor({
+  accounts,
+  categories,
+  values,
+  onValueChange,
+  disabled,
+}: Props) {
+  const { t } = useTranslation();
+
+  // Group accounts by their category, preserving the categories' sort_order
+  // first then the account name within each group.
+  const groups = useMemo(() => {
+    const byCategory = new Map<number, BalanceAccountWithCategory[]>();
+    for (const acc of accounts) {
+      const list = byCategory.get(acc.balance_category_id) ?? [];
+      list.push(acc);
+      byCategory.set(acc.balance_category_id, list);
+    }
+    const sortedCategories = [...categories].sort(
+      (a, b) => a.sort_order - b.sort_order || a.key.localeCompare(b.key)
+    );
+    return sortedCategories
+      .map((cat) => ({
+        category: cat,
+        accounts: (byCategory.get(cat.id) ?? []).sort((a, b) =>
+          a.name.localeCompare(b.name)
+        ),
+      }))
+      .filter((group) => group.accounts.length > 0);
+  }, [accounts, categories]);
+
+  if (accounts.length === 0) {
+    return (
+      <div className="bg-[var(--card)] rounded-xl border border-[var(--border)] p-8 text-center text-[var(--muted-foreground)]">
+        {t("balance.snapshot.editor.empty")}
+      </div>
+    );
+  }
+
+  return (
+    <div className="flex flex-col gap-4">
+      {groups.map(({ category, accounts: catAccounts }) => (
+        <div
+          key={category.id}
+          className="bg-[var(--card)] rounded-xl border border-[var(--border)] overflow-hidden"
+        >
+          <div className="px-4 py-2 bg-[var(--muted)] border-b border-[var(--border)]">
+            <h3 className="text-sm font-semibold">
+              {t(category.i18n_key, { defaultValue: category.key })}
+            </h3>
+          </div>
+          <div className="px-4">
+            {catAccounts.map((acc) => (
+              <SnapshotLineRow
+                key={acc.id}
+                account={acc}
+                value={values[acc.id] ?? ""}
+                onChange={(next) => onValueChange(acc.id, next)}
+                disabled={disabled}
+              />
+            ))}
+          </div>
+        </div>
+      ))}
+    </div>
+  );
+}

src/components/balance/SnapshotLineRow.tsx

@@ -0,0 +1,64 @@
+// SnapshotLineRow — single account line inside the snapshot editor.
+//
+// Issue #146 / Bilan #1b ships the *simple* variant only: a single value
+// input keyed by `account_id`. The priced variant (quantity / unit_price /
+// computed value + price-fetch button) lands in Issue #140 / Bilan #2.
+//
+// We intentionally keep this component dumb: it receives a string value
+// from the parent (the editor stores raw strings to preserve partial input
+// the user is typing) and emits the new string on every change. Numeric
+// validation happens at save time in `useSnapshotEditor.save`.
+
+import { ChangeEvent } from "react";
+import { useTranslation } from "react-i18next";
+import type { BalanceAccountWithCategory } from "../../shared/types";
+
+interface Props {
+  account: BalanceAccountWithCategory;
+  value: string;
+  onChange: (next: string) => void;
+  disabled?: boolean;
+}
+
+export default function SnapshotLineRow({
+  account,
+  value,
+  onChange,
+  disabled,
+}: Props) {
+  const { t } = useTranslation();
+
+  const handleChange = (e: ChangeEvent<HTMLInputElement>) => {
+    onChange(e.target.value);
+  };
+
+  return (
+    <div className="flex items-center gap-3 py-2 border-b border-[var(--border)] last:border-b-0">
+      <div className="flex-1 min-w-0">
+        <div className="text-sm font-medium truncate">{account.name}</div>
+        {account.symbol && (
+          <div className="text-xs text-[var(--muted-foreground)]">
+            {account.symbol}
+          </div>
+        )}
+      </div>
+      <div className="flex items-center gap-2">
+        <input
+          type="text"
+          inputMode="decimal"
+          value={value}
+          onChange={handleChange}
+          disabled={disabled}
+          placeholder={t("balance.snapshot.line.valuePlaceholder")}
+          className="w-32 px-3 py-2 rounded-lg border border-[var(--border)] bg-[var(--card)] text-sm text-right focus:outline-none focus:ring-1 focus:ring-[var(--primary)] disabled:opacity-50"
+          aria-label={t("balance.snapshot.line.valueLabel", {
+            account: account.name,
+          })}
+        />
+        <span className="text-xs text-[var(--muted-foreground)] w-10">
+          {account.currency}
+        </span>
+      </div>
+    </div>
+  );
+}

src/hooks/useSnapshotEditor.ts

@@ -0,0 +1,387 @@
+// useSnapshotEditor — scoped useReducer hook backing SnapshotEditPage.
+//
+// Lifecycle of a single snapshot (Issue #146 / Bilan #1b — simple kind only):
+//   1. mount in 'new' mode (no `?date=` query param) → user picks a date,
+//      types values, hits Save → service.createSnapshot + upsertLines;
+//   2. mount in 'edit' mode (`?date=YYYY-MM-DD`) → load snapshot + lines,
+//      user edits values, hits Save → upsertLines on the existing snapshot;
+//   3. delete → service.deleteSnapshot (the page wraps this in a
+//      double-confirm modal that requires retyping the snapshot date).
+//
+// Priced-kind UI lands in #140 (Bilan #2). Until then values are scalar
+// numbers keyed by account_id and quantity/unit_price are forced to NULL by
+// `upsertSnapshotLines` (the SQL CHECK guards the invariant too).
+
+import {
+  useReducer,
+  useCallback,
+  useEffect,
+  useRef,
+} from "react";
+import type {
+  BalanceAccountWithCategory,
+  BalanceCategory,
+  BalanceSnapshot,
+  BalanceSnapshotLine,
+} from "../shared/types";
+import {
+  listBalanceAccounts,
+  listBalanceCategories,
+  getSnapshotByDate,
+  createSnapshot,
+  deleteSnapshot,
+  listLinesBySnapshot,
+  upsertSnapshotLines,
+  getPreviousSnapshot,
+  BalanceServiceError,
+} from "../services/balance.service";
+
+export type SnapshotEditorMode = "new" | "edit";
+
+interface State {
+  mode: SnapshotEditorMode;
+  /** ISO YYYY-MM-DD; controlled in 'new' mode, frozen in 'edit'. */
+  snapshotDate: string;
+  /** Current snapshot row in 'edit' mode (has the id needed for upsert). */
+  snapshot: BalanceSnapshot | null;
+  /** All active accounts (with category metadata) — drives the line list. */
+  accounts: BalanceAccountWithCategory[];
+  /** Used to group lines by category in the editor view. */
+  categories: BalanceCategory[];
+  /**
+   * Map of account_id → string-typed value. We keep strings to preserve
+   * empty / partial input the user is typing; conversion to number happens
+   * at save time (and at validation when needed).
+   */
+  values: Record<number, string>;
+  /** Snapshot whose values would prefill if the user clicks "Prefill". */
+  previousSnapshot: BalanceSnapshot | null;
+  /** Lines from `previousSnapshot` (loaded lazily when needed). */
+  previousLines: BalanceSnapshotLine[] | null;
+  isLoading: boolean;
+  isSaving: boolean;
+  isDirty: boolean;
+  error: string | null;
+  errorCode: string | null;
+}
+
+type Action =
+  | { type: "SET_LOADING"; payload: boolean }
+  | { type: "SET_SAVING"; payload: boolean }
+  | { type: "SET_ERROR"; payload: { message: string | null; code: string | null } }
+  | {
+      type: "LOADED";
+      payload: {
+        mode: SnapshotEditorMode;
+        snapshotDate: string;
+        snapshot: BalanceSnapshot | null;
+        accounts: BalanceAccountWithCategory[];
+        categories: BalanceCategory[];
+        values: Record<number, string>;
+        previousSnapshot: BalanceSnapshot | null;
+        previousLines: BalanceSnapshotLine[] | null;
+      };
+    }
+  | { type: "SET_DATE"; payload: string }
+  | { type: "SET_VALUE"; payload: { accountId: number; value: string } }
+  | { type: "PREFILL"; payload: Record<number, string> }
+  | { type: "RESET" }
+  | { type: "CLEAR_DIRTY" };
+
+function initialState(initialDate: string): State {
+  return {
+    mode: "new",
+    snapshotDate: initialDate,
+    snapshot: null,
+    accounts: [],
+    categories: [],
+    values: {},
+    previousSnapshot: null,
+    previousLines: null,
+    isLoading: false,
+    isSaving: false,
+    isDirty: false,
+    error: null,
+    errorCode: null,
+  };
+}
+
+function reducer(state: State, action: Action): State {
+  switch (action.type) {
+    case "SET_LOADING":
+      return { ...state, isLoading: action.payload };
+    case "SET_SAVING":
+      return { ...state, isSaving: action.payload };
+    case "SET_ERROR":
+      return {
+        ...state,
+        error: action.payload.message,
+        errorCode: action.payload.code,
+        isLoading: false,
+        isSaving: false,
+      };
+    case "LOADED":
+      return {
+        ...state,
+        mode: action.payload.mode,
+        snapshotDate: action.payload.snapshotDate,
+        snapshot: action.payload.snapshot,
+        accounts: action.payload.accounts,
+        categories: action.payload.categories,
+        values: action.payload.values,
+        previousSnapshot: action.payload.previousSnapshot,
+        previousLines: action.payload.previousLines,
+        isLoading: false,
+        isDirty: false,
+        error: null,
+        errorCode: null,
+      };
+    case "SET_DATE":
+      // Only meaningful in 'new' mode — the page guards against this in 'edit'.
+      return { ...state, snapshotDate: action.payload, isDirty: true };
+    case "SET_VALUE":
+      return {
+        ...state,
+        values: {
+          ...state.values,
+          [action.payload.accountId]: action.payload.value,
+        },
+        isDirty: true,
+      };
+    case "PREFILL":
+      return {
+        ...state,
+        values: { ...state.values, ...action.payload },
+        isDirty: true,
+      };
+    case "RESET":
+      return {
+        ...state,
+        // Keep the loaded structure (accounts, categories, snapshot) but wipe
+        // user input back to a clean slate sourced from the saved lines.
+        values: {},
+        isDirty: true,
+      };
+    case "CLEAR_DIRTY":
+      return { ...state, isDirty: false };
+    default:
+      return state;
+  }
+}
+
+function describeError(e: unknown): { message: string; code: string | null } {
+  if (e instanceof BalanceServiceError) {
+    return { message: e.message, code: e.code };
+  }
+  return {
+    message: e instanceof Error ? e.message : String(e),
+    code: null,
+  };
+}
+
+function todayISO(): string {
+  // Avoid timezone drift: use local YYYY-MM-DD, not toISOString() which is UTC.
+  const d = new Date();
+  const yyyy = d.getFullYear();
+  const mm = String(d.getMonth() + 1).padStart(2, "0");
+  const dd = String(d.getDate()).padStart(2, "0");
+  return `${yyyy}-${mm}-${dd}`;
+}
+
+interface Options {
+  /** ISO date from the route query string. `undefined` means 'new' mode. */
+  dateParam?: string | null;
+}
+
+export function useSnapshotEditor(options: Options = {}) {
+  const { dateParam } = options;
+  const [state, dispatch] = useReducer(
+    reducer,
+    undefined,
+    () => initialState(dateParam ?? todayISO())
+  );
+  const fetchIdRef = useRef(0);
+
+  /**
+   * Load the editor state from the database. In 'new' mode we still load
+   * accounts + categories + the previous snapshot (so the prefill button
+   * can be enabled); we do NOT pre-create a snapshot row — that happens at
+   * save time so the user can abandon the form without leaving an empty
+   * snapshot behind.
+   */
+  const loadForDate = useCallback(async (date: string | null | undefined) => {
+    const fetchId = ++fetchIdRef.current;
+    dispatch({ type: "SET_LOADING", payload: true });
+    dispatch({ type: "SET_ERROR", payload: { message: null, code: null } });
+    const targetDate = date && date.length > 0 ? date : todayISO();
+    try {
+      const [accounts, categories] = await Promise.all([
+        listBalanceAccounts(),
+        listBalanceCategories(),
+      ]);
+      const existing = await getSnapshotByDate(targetDate);
+      const isEdit = !!existing;
+      let values: Record<number, string> = {};
+      let previousLines: BalanceSnapshotLine[] | null = null;
+      if (existing) {
+        const lines = await listLinesBySnapshot(existing.id);
+        for (const line of lines) {
+          values[line.account_id] = String(line.value);
+        }
+      }
+      const previous = await getPreviousSnapshot(targetDate);
+      if (previous) {
+        previousLines = await listLinesBySnapshot(previous.id);
+      }
+      if (fetchId !== fetchIdRef.current) return;
+      dispatch({
+        type: "LOADED",
+        payload: {
+          mode: isEdit ? "edit" : "new",
+          snapshotDate: targetDate,
+          snapshot: existing,
+          accounts,
+          categories,
+          values,
+          previousSnapshot: previous,
+          previousLines,
+        },
+      });
+    } catch (e) {
+      if (fetchId !== fetchIdRef.current) return;
+      dispatch({ type: "SET_ERROR", payload: describeError(e) });
+    }
+  }, []);
+
+  // Load on mount + whenever the route's `?date=` changes.
+  useEffect(() => {
+    loadForDate(dateParam);
+  }, [dateParam, loadForDate]);
+
+  const setDate = useCallback((next: string) => {
+    dispatch({ type: "SET_DATE", payload: next });
+  }, []);
+
+  const setLineValue = useCallback((accountId: number, value: string) => {
+    dispatch({
+      type: "SET_VALUE",
+      payload: { accountId, value },
+    });
+  }, []);
+
+  const reset = useCallback(() => {
+    dispatch({ type: "RESET" });
+  }, []);
+
+  /**
+   * Build the prefill map from the previous snapshot. Per spec-decisions
+   * row "Bouton Pré-remplir" (Issue 1b decision):
+   *   - simple kind  → copy value
+   *   - priced kind  → copy quantity, leave unit_price blank → effectively
+   *                    no-op at Issue #146 because priced UI ships in #140.
+   *                    We add a TODO so the priced branch is explicit.
+   */
+  const prefillFromPrevious = useCallback(() => {
+    const lines = state.previousLines;
+    if (!lines || lines.length === 0) return;
+    const accountKindById = new Map<number, BalanceCategory["kind"]>();
+    for (const acc of state.accounts) {
+      accountKindById.set(acc.id, acc.category_kind);
+    }
+    const next: Record<number, string> = {};
+    for (const line of lines) {
+      const kind = accountKindById.get(line.account_id);
+      if (!kind) continue; // archived account — skip
+      if (kind === "simple") {
+        next[line.account_id] = String(line.value);
+      } else {
+        // TODO Issue #140 — implement priced prefill (quantity copy, leave
+        // unit_price blank). For Issue #146 the priced UI does not exist yet.
+      }
+    }
+    dispatch({ type: "PREFILL", payload: next });
+  }, [state.previousLines, state.accounts]);
+
+  /**
+   * Persist the editor state to the database.
+   *  - 'new' mode: create the snapshot row (UNIQUE per date), then upsert
+   *    its lines. If creation fails because a snapshot was created at this
+   *    same date concurrently (snapshot_date_taken), the page is expected
+   *    to redirect to edit mode.
+   *  - 'edit' mode: upsert lines on the existing snapshot.
+   *
+   * Only accounts with a non-empty value (after trim) are persisted; empty
+   * fields mean "no entry for this account at this date" — they're cleared
+   * by the rewrite-all strategy in `upsertSnapshotLines`.
+   */
+  const save = useCallback(async (): Promise<{ snapshotId: number }> => {
+    dispatch({ type: "SET_SAVING", payload: true });
+    dispatch({ type: "SET_ERROR", payload: { message: null, code: null } });
+    try {
+      let snapshotId: number;
+      if (state.mode === "edit" && state.snapshot) {
+        snapshotId = state.snapshot.id;
+      } else {
+        snapshotId = await createSnapshot({
+          snapshot_date: state.snapshotDate,
+        });
+      }
+      const lines = Object.entries(state.values)
+        .filter(([, v]) => v !== undefined && String(v).trim().length > 0)
+        .map(([accountIdStr, raw]) => {
+          const accountId = Number(accountIdStr);
+          const trimmed = String(raw).trim().replace(",", ".");
+          const num = Number(trimmed);
+          if (!Number.isFinite(num)) {
+            throw new BalanceServiceError(
+              "snapshot_value_invalid",
+              `Invalid value for account ${accountId}: "${raw}"`
+            );
+          }
+          return { account_id: accountId, value: num };
+        });
+      await upsertSnapshotLines(snapshotId, lines);
+      dispatch({ type: "CLEAR_DIRTY" });
+      // Reload so 'new' mode flips to 'edit' and the snapshot row is in state.
+      await loadForDate(state.snapshotDate);
+      return { snapshotId };
+    } catch (e) {
+      dispatch({ type: "SET_ERROR", payload: describeError(e) });
+      throw e;
+    } finally {
+      dispatch({ type: "SET_SAVING", payload: false });
+    }
+  }, [
+    state.mode,
+    state.snapshot,
+    state.snapshotDate,
+    state.values,
+    loadForDate,
+  ]);
+
+  const remove = useCallback(async () => {
+    if (!state.snapshot) return;
+    dispatch({ type: "SET_SAVING", payload: true });
+    dispatch({ type: "SET_ERROR", payload: { message: null, code: null } });
+    try {
+      await deleteSnapshot(state.snapshot.id);
+    } catch (e) {
+      dispatch({ type: "SET_ERROR", payload: describeError(e) });
+      throw e;
+    } finally {
+      dispatch({ type: "SET_SAVING", payload: false });
+    }
+  }, [state.snapshot]);
+
+  return {
+    state,
+    setDate,
+    setLineValue,
+    reset,
+    prefillFromPrevious,
+    save,
+    remove,
+    /** Manual reload (e.g. after navigation between dates). */
+    reload: () => loadForDate(state.snapshotDate),
+  };
+}

src/i18n/locales/en.json

@@ -981,7 +981,8 @@
     "darkMode": "Dark mode",
     "lightMode": "Light mode",
     "close": "Close",
-    "underConstruction": "Under construction"
+    "underConstruction": "Under construction",
+    "back": "Back"
   },
   "license": {
     "title": "License",
@@ -1535,6 +1536,36 @@
       "stock": "Stock",
       "crypto": "Crypto"
     },
+    "snapshot": {
+      "page": {
+        "newTitle": "New snapshot",
+        "editTitle": "Edit snapshot",
+        "dateLabel": "Snapshot date",
+        "dateImmutable": "An existing snapshot date cannot be changed. To change the date, delete this snapshot and create a new one.",
+        "total": "Entered total",
+        "noAccounts": "You need to create at least one balance account first.",
+        "goToAccounts": "Go to accounts",
+        "prefill": "Prefill from previous",
+        "prefillTooltip": "Copy values from the snapshot dated {{date}}",
+        "prefillNoPrevious": "No earlier snapshot available.",
+        "save": "Save",
+        "create": "Create snapshot",
+        "delete": "Delete this snapshot"
+      },
+      "editor": {
+        "empty": "No active accounts. Create an account before entering a snapshot."
+      },
+      "line": {
+        "valuePlaceholder": "0.00",
+        "valueLabel": "Value for {{account}}"
+      },
+      "delete": {
+        "title": "Delete this snapshot?",
+        "body": "This permanently deletes the snapshot dated {{date}} and all its lines. To confirm, retype the date below.",
+        "confirmLabel": "Retype the date {{date}} to confirm",
+        "confirm": "Delete permanently"
+      }
+    },
     "errors": {
       "currency_unsupported": "Only CAD is supported at the MVP.",
       "category_seed_protected": "Standard categories cannot be deleted.",
@@ -1542,7 +1573,12 @@
       "category_not_found": "Category not found.",
       "account_not_found": "Account not found.",
       "name_required": "Name is required.",
-      "kind_invalid": "Invalid category kind."
+      "kind_invalid": "Invalid category kind.",
+      "snapshot_date_required": "A date in YYYY-MM-DD format is required.",
+      "snapshot_date_taken": "A snapshot already exists at that date — edit it instead of creating a new one.",
+      "snapshot_not_found": "Snapshot not found.",
+      "snapshot_value_invalid": "An entered value is not a valid number.",
+      "snapshot_priced_unsupported": "Priced accounts (stocks/crypto) will be supported in a future release."
     }
   }
 }

src/i18n/locales/fr.json

@@ -981,7 +981,8 @@
     "darkMode": "Mode sombre",
     "lightMode": "Mode clair",
     "close": "Fermer",
-    "underConstruction": "En construction"
+    "underConstruction": "En construction",
+    "back": "Retour"
   },
   "license": {
     "title": "Licence",
@@ -1535,6 +1536,36 @@
       "stock": "Action",
       "crypto": "Cryptomonnaie"
     },
+    "snapshot": {
+      "page": {
+        "newTitle": "Nouveau snapshot",
+        "editTitle": "Modifier le snapshot",
+        "dateLabel": "Date du snapshot",
+        "dateImmutable": "La date d'un snapshot existant ne peut pas être modifiée. Pour changer la date, supprimez ce snapshot et créez-en un nouveau.",
+        "total": "Total saisi",
+        "noAccounts": "Vous devez d'abord créer au moins un compte de bilan.",
+        "goToAccounts": "Aller aux comptes",
+        "prefill": "Pré-remplir depuis le précédent",
+        "prefillTooltip": "Copier les valeurs du snapshot du {{date}}",
+        "prefillNoPrevious": "Aucun snapshot antérieur disponible.",
+        "save": "Enregistrer",
+        "create": "Créer le snapshot",
+        "delete": "Supprimer ce snapshot"
+      },
+      "editor": {
+        "empty": "Aucun compte actif. Créez un compte avant de saisir un snapshot."
+      },
+      "line": {
+        "valuePlaceholder": "0,00",
+        "valueLabel": "Valeur pour {{account}}"
+      },
+      "delete": {
+        "title": "Supprimer ce snapshot ?",
+        "body": "Cette action supprime définitivement le snapshot du {{date}} et toutes ses lignes. Pour confirmer, retapez la date ci-dessous.",
+        "confirmLabel": "Retapez la date {{date}} pour confirmer",
+        "confirm": "Supprimer définitivement"
+      }
+    },
     "errors": {
       "currency_unsupported": "Seul le CAD est supporté au MVP.",
       "category_seed_protected": "Les catégories standard ne peuvent pas être supprimées.",
@@ -1542,7 +1573,12 @@
       "category_not_found": "Catégorie introuvable.",
       "account_not_found": "Compte introuvable.",
       "name_required": "Le nom est obligatoire.",
-      "kind_invalid": "Type de catégorie invalide."
+      "kind_invalid": "Type de catégorie invalide.",
+      "snapshot_date_required": "Une date au format AAAA-MM-JJ est obligatoire.",
+      "snapshot_date_taken": "Un snapshot existe déjà à cette date — modifiez-le au lieu d'en créer un nouveau.",
+      "snapshot_not_found": "Snapshot introuvable.",
+      "snapshot_value_invalid": "Une valeur saisie n'est pas un nombre valide.",
+      "snapshot_priced_unsupported": "Les comptes cotés (actions/crypto) seront supportés dans une prochaine version."
     }
   }
 }

src/pages/SnapshotEditPage.tsx

@@ -0,0 +1,343 @@
+// SnapshotEditPage — create or edit a balance snapshot at a given date.
+//
+// Issue #146 / Bilan #1b ships the route `/balance/snapshot` with two modes
+// driven by the `?date=` query parameter:
+//   - `?date=` absent → 'new' mode (date picker editable, defaults to today)
+//   - `?date=YYYY-MM-DD` → 'edit' mode if a snapshot exists at that date,
+//     otherwise 'new' mode pre-selected at that date (which mirrors the
+//     "redirect to edit" flow when the user comes from the future
+//     /balance overview's "Edit" link).
+//
+// The page itself only orchestrates: all DB work flows through
+// `useSnapshotEditor`, the editor view through `SnapshotEditor`. Per spec
+// (decisions row "Bouton Pré-remplir"), priced-kind prefill is a no-op
+// here (the priced editor lands in #140).
+
+import { useEffect, useMemo, useState } from "react";
+import { useSearchParams, useNavigate } from "react-router-dom";
+import { useTranslation } from "react-i18next";
+import {
+  ArrowLeft,
+  Trash2,
+  Save,
+  Wallet,
+  RotateCcw,
+  AlertTriangle,
+} from "lucide-react";
+import { useSnapshotEditor } from "../hooks/useSnapshotEditor";
+import SnapshotEditor from "../components/balance/SnapshotEditor";
+
+export default function SnapshotEditPage() {
+  const { t } = useTranslation();
+  const [searchParams, setSearchParams] = useSearchParams();
+  const navigate = useNavigate();
+
+  const dateParam = searchParams.get("date");
+  const editor = useSnapshotEditor({ dateParam });
+  const { state } = editor;
+
+  const [showDeleteModal, setShowDeleteModal] = useState(false);
+  const [deleteConfirmText, setDeleteConfirmText] = useState("");
+
+  // Reset the delete modal whenever the underlying snapshot changes (e.g.
+  // after switching ?date=).
+  useEffect(() => {
+    setShowDeleteModal(false);
+    setDeleteConfirmText("");
+  }, [state.snapshot?.id]);
+
+  const isEditMode = state.mode === "edit";
+  const canPrefill = !!state.previousSnapshot;
+
+  // Aggregate value (simple kind only — sums all visible numeric inputs).
+  const totalValue = useMemo(() => {
+    let total = 0;
+    let hasAny = false;
+    for (const raw of Object.values(state.values)) {
+      if (!raw) continue;
+      const trimmed = String(raw).trim().replace(",", ".");
+      const n = Number(trimmed);
+      if (Number.isFinite(n)) {
+        total += n;
+        hasAny = true;
+      }
+    }
+    return hasAny ? total : null;
+  }, [state.values]);
+
+  const handleSave = async () => {
+    try {
+      await editor.save();
+      // After a successful create, the URL should become `?date=...` so
+      // refreshing keeps the user in edit mode.
+      if (!isEditMode) {
+        setSearchParams(
+          { date: state.snapshotDate },
+          { replace: true }
+        );
+      }
+    } catch {
+      // The hook surfaced the error via state.errorCode/state.error.
+    }
+  };
+
+  const handleDelete = async () => {
+    try {
+      await editor.remove();
+      navigate("/balance/accounts");
+    } catch {
+      // surfaced via state.error
+    }
+  };
+
+  return (
+    <div className={state.isLoading ? "opacity-50 pointer-events-none" : ""}>
+      <div className="flex items-center gap-3 mb-6">
+        <button
+          type="button"
+          onClick={() => navigate("/balance/accounts")}
+          className="p-1.5 rounded hover:bg-[var(--muted)] text-[var(--muted-foreground)]"
+          title={t("common.back")}
+        >
+          <ArrowLeft size={18} />
+        </button>
+        <Wallet size={24} className="text-[var(--primary)]" />
+        <h1 className="text-2xl font-bold">
+          {isEditMode
+            ? t("balance.snapshot.page.editTitle")
+            : t("balance.snapshot.page.newTitle")}
+        </h1>
+      </div>
+
+      {state.error && (
+        <div className="mb-4 p-3 rounded-lg bg-[var(--negative)]/10 text-[var(--negative)] text-sm border border-[var(--negative)]/20">
+          {state.errorCode
+            ? t(`balance.errors.${state.errorCode}`, {
+                defaultValue: state.error,
+              })
+            : state.error}
+        </div>
+      )}
+
+      <div className="bg-[var(--card)] rounded-xl border border-[var(--border)] p-4 mb-6">
+        <div className="flex flex-col sm:flex-row sm:items-end gap-4">
+          <div className="flex-1">
+            <label
+              className="block text-sm font-medium mb-1"
+              htmlFor="snapshot-date"
+            >
+              {t("balance.snapshot.page.dateLabel")}
+            </label>
+            <input
+              id="snapshot-date"
+              type="date"
+              value={state.snapshotDate}
+              disabled={isEditMode}
+              onChange={(e) => {
+                const next = e.target.value;
+                editor.setDate(next);
+                // Drive the route param so reloads stay coherent and an
+                // existing snapshot at the chosen date flips us into 'edit'.
+                if (next) {
+                  setSearchParams({ date: next }, { replace: true });
+                } else {
+                  setSearchParams({}, { replace: true });
+                }
+              }}
+              className="w-full px-3 py-2 rounded-lg border border-[var(--border)] bg-[var(--card)] text-sm focus:outline-none focus:ring-1 focus:ring-[var(--primary)] disabled:opacity-60"
+            />
+            {isEditMode && (
+              <p className="mt-1 text-xs text-[var(--muted-foreground)]">
+                {t("balance.snapshot.page.dateImmutable")}
+              </p>
+            )}
+          </div>
+          {totalValue !== null && (
+            <div className="text-right">
+              <div className="text-xs text-[var(--muted-foreground)]">
+                {t("balance.snapshot.page.total")}
+              </div>
+              <div className="text-2xl font-semibold tabular-nums">
+                {totalValue.toLocaleString(undefined, {
+                  minimumFractionDigits: 2,
+                  maximumFractionDigits: 2,
+                })}
+              </div>
+            </div>
+          )}
+        </div>
+      </div>
+
+      {state.accounts.length === 0 && !state.isLoading ? (
+        <div className="bg-[var(--card)] rounded-xl border border-[var(--border)] p-8 text-center text-[var(--muted-foreground)]">
+          <p className="mb-3">{t("balance.snapshot.page.noAccounts")}</p>
+          <button
+            type="button"
+            onClick={() => navigate("/balance/accounts")}
+            className="px-4 py-2 rounded-lg bg-[var(--primary)] text-white text-sm font-medium hover:opacity-90"
+          >
+            {t("balance.snapshot.page.goToAccounts")}
+          </button>
+        </div>
+      ) : (
+        <SnapshotEditor
+          accounts={state.accounts}
+          categories={state.categories}
+          values={state.values}
+          onValueChange={editor.setLineValue}
+          disabled={state.isSaving}
+        />
+      )}
+
+      {/* Action bar */}
+      <div className="mt-6 flex flex-col sm:flex-row sm:items-center sm:justify-between gap-3">
+        <div className="flex items-center gap-2">
+          <button
+            type="button"
+            onClick={editor.prefillFromPrevious}
+            disabled={!canPrefill || state.isSaving}
+            title={
+              canPrefill
+                ? t("balance.snapshot.page.prefillTooltip", {
+                    date: state.previousSnapshot?.snapshot_date,
+                  })
+                : t("balance.snapshot.page.prefillNoPrevious")
+            }
+            className="flex items-center gap-2 px-3 py-2 rounded-lg border border-[var(--border)] text-sm hover:bg-[var(--muted)] disabled:opacity-50 disabled:cursor-not-allowed"
+          >
+            <RotateCcw size={14} />
+            {t("balance.snapshot.page.prefill")}
+          </button>
+          {isEditMode && (
+            <button
+              type="button"
+              onClick={() => setShowDeleteModal(true)}
+              disabled={state.isSaving}
+              className="flex items-center gap-2 px-3 py-2 rounded-lg border border-[var(--negative)]/40 text-sm text-[var(--negative)] hover:bg-[var(--negative)]/10 disabled:opacity-50"
+            >
+              <Trash2 size={14} />
+              {t("balance.snapshot.page.delete")}
+            </button>
+          )}
+        </div>
+        <div className="flex items-center gap-2">
+          <button
+            type="button"
+            onClick={() => navigate("/balance/accounts")}
+            disabled={state.isSaving}
+            className="px-4 py-2 rounded-lg border border-[var(--border)] text-sm hover:bg-[var(--muted)] disabled:opacity-50"
+          >
+            {t("common.cancel")}
+          </button>
+          <button
+            type="button"
+            onClick={handleSave}
+            disabled={
+              state.isSaving ||
+              state.isLoading ||
+              state.accounts.length === 0 ||
+              !state.snapshotDate
+            }
+            className="flex items-center gap-2 px-4 py-2 rounded-lg bg-[var(--primary)] text-white text-sm font-medium hover:opacity-90 disabled:opacity-50"
+          >
+            <Save size={14} />
+            {isEditMode
+              ? t("balance.snapshot.page.save")
+              : t("balance.snapshot.page.create")}
+          </button>
+        </div>
+      </div>
+
+      {/* Delete confirmation modal — double-confirmation requires retyping
+          the snapshot date. */}
+      {showDeleteModal && state.snapshot && (
+        <DeleteConfirmModal
+          snapshotDate={state.snapshot.snapshot_date}
+          confirmText={deleteConfirmText}
+          onConfirmTextChange={setDeleteConfirmText}
+          isSaving={state.isSaving}
+          onCancel={() => {
+            setShowDeleteModal(false);
+            setDeleteConfirmText("");
+          }}
+          onConfirm={handleDelete}
+        />
+      )}
+    </div>
+  );
+}
+
+// -----------------------------------------------------------------------------
+// Internal components
+// -----------------------------------------------------------------------------
+
+function DeleteConfirmModal({
+  snapshotDate,
+  confirmText,
+  onConfirmTextChange,
+  isSaving,
+  onCancel,
+  onConfirm,
+}: {
+  snapshotDate: string;
+  confirmText: string;
+  onConfirmTextChange: (next: string) => void;
+  isSaving: boolean;
+  onCancel: () => void;
+  onConfirm: () => void;
+}) {
+  const { t } = useTranslation();
+  const isMatch = confirmText.trim() === snapshotDate;
+  return (
+    <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/40 p-4">
+      <div className="bg-[var(--card)] rounded-xl border border-[var(--border)] shadow-xl max-w-md w-full p-6">
+        <div className="flex items-start gap-3 mb-4">
+          <div className="p-2 rounded-full bg-[var(--negative)]/10 text-[var(--negative)]">
+            <AlertTriangle size={20} />
+          </div>
+          <div>
+            <h2 className="text-lg font-semibold">
+              {t("balance.snapshot.delete.title")}
+            </h2>
+            <p className="mt-1 text-sm text-[var(--muted-foreground)]">
+              {t("balance.snapshot.delete.body", { date: snapshotDate })}
+            </p>
+          </div>
+        </div>
+        <label
+          className="block text-sm font-medium mb-1"
+          htmlFor="delete-confirm-input"
+        >
+          {t("balance.snapshot.delete.confirmLabel", { date: snapshotDate })}
+        </label>
+        <input
+          id="delete-confirm-input"
+          type="text"
+          value={confirmText}
+          onChange={(e) => onConfirmTextChange(e.target.value)}
+          placeholder={snapshotDate}
+          autoComplete="off"
+          className="w-full px-3 py-2 rounded-lg border border-[var(--border)] bg-[var(--background)] text-sm focus:outline-none focus:ring-1 focus:ring-[var(--negative)]"
+        />
+        <div className="flex justify-end gap-2 mt-4">
+          <button
+            type="button"
+            onClick={onCancel}
+            disabled={isSaving}
+            className="px-4 py-2 rounded-lg border border-[var(--border)] text-sm hover:bg-[var(--muted)] disabled:opacity-50"
+          >
+            {t("common.cancel")}
+          </button>
+          <button
+            type="button"
+            onClick={onConfirm}
+            disabled={isSaving || !isMatch}
+            className="px-4 py-2 rounded-lg bg-[var(--negative)] text-white text-sm font-medium hover:opacity-90 disabled:opacity-50"
+          >
+            {t("balance.snapshot.delete.confirm")}
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+}

src/services/balance.service.test.ts

@@ -15,6 +15,14 @@ import {
   updateBalanceAccount,
   archiveBalanceAccount,
   unarchiveBalanceAccount,
+  listSnapshots,
+  getSnapshotByDate,
+  createSnapshot,
+  updateSnapshot,
+  deleteSnapshot,
+  listLinesBySnapshot,
+  upsertSnapshotLines,
+  getPreviousSnapshot,
   BalanceServiceError,
 } from "./balance.service";
 
@@ -314,3 +322,227 @@ describe("archiveBalanceAccount / unarchiveBalanceAccount", () => {
     expect(sql).toContain("is_active = 1");
   });
 });
+
+// -----------------------------------------------------------------------------
+// Snapshots + lines (Issue #146 / Bilan #1b — simple kind only)
+// -----------------------------------------------------------------------------
+
+const FAKE_SNAPSHOT = {
+  id: 5,
+  snapshot_date: "2026-04-15",
+  notes: null,
+  created_at: "",
+  updated_at: "",
+};
+
+describe("listSnapshots", () => {
+  it("orders by snapshot_date DESC", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await listSnapshots();
+    const sql = mockSelect.mock.calls[0][0] as string;
+    expect(sql).toContain("FROM balance_snapshots");
+    expect(sql).toContain("ORDER BY snapshot_date DESC");
+  });
+});
+
+describe("getSnapshotByDate", () => {
+  it("rejects empty / invalid dates with snapshot_date_required", async () => {
+    await expect(getSnapshotByDate("")).rejects.toMatchObject({
+      code: "snapshot_date_required",
+    });
+    await expect(getSnapshotByDate("2026/04/15")).rejects.toMatchObject({
+      code: "snapshot_date_required",
+    });
+    expect(mockSelect).not.toHaveBeenCalled();
+  });
+
+  it("returns the snapshot row when found", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    const got = await getSnapshotByDate("2026-04-15");
+    expect(got).toEqual(FAKE_SNAPSHOT);
+    expect(mockSelect.mock.calls[0][1]).toEqual(["2026-04-15"]);
+  });
+
+  it("returns null when no row matches", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    expect(await getSnapshotByDate("2026-04-15")).toBeNull();
+  });
+});
+
+describe("createSnapshot", () => {
+  it("rejects an invalid date", async () => {
+    await expect(
+      createSnapshot({ snapshot_date: "  " })
+    ).rejects.toMatchObject({ code: "snapshot_date_required" });
+    expect(mockExecute).not.toHaveBeenCalled();
+  });
+
+  it("rejects a duplicate snapshot date with snapshot_date_taken", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]); // existing
+    await expect(
+      createSnapshot({ snapshot_date: "2026-04-15" })
+    ).rejects.toMatchObject({ code: "snapshot_date_taken" });
+    expect(mockExecute).not.toHaveBeenCalled();
+  });
+
+  it("inserts a new snapshot and returns its id", async () => {
+    mockSelect.mockResolvedValueOnce([]); // no existing
+    mockExecute.mockResolvedValueOnce({ lastInsertId: 12, rowsAffected: 1 });
+    const id = await createSnapshot({
+      snapshot_date: "2026-04-25",
+      notes: "  monthly check  ",
+    });
+    expect(id).toBe(12);
+    const params = mockExecute.mock.calls[0][1] as unknown[];
+    expect(params).toEqual(["2026-04-25", "monthly check"]);
+  });
+});
+
+describe("updateSnapshot", () => {
+  it("rejects when snapshot does not exist", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await expect(
+      updateSnapshot(999, { notes: "x" })
+    ).rejects.toMatchObject({ code: "snapshot_not_found" });
+  });
+
+  it("normalizes empty notes to null", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    mockExecute.mockResolvedValueOnce({ rowsAffected: 1 });
+    await updateSnapshot(5, { notes: "  " });
+    const params = mockExecute.mock.calls[0][1] as unknown[];
+    expect(params[0]).toBeNull();
+  });
+});
+
+describe("deleteSnapshot", () => {
+  it("rejects when snapshot does not exist", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await expect(deleteSnapshot(999)).rejects.toMatchObject({
+      code: "snapshot_not_found",
+    });
+  });
+
+  it("deletes when found (lines cascade via FK)", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    mockExecute.mockResolvedValueOnce({ rowsAffected: 1 });
+    await deleteSnapshot(5);
+    expect(mockExecute).toHaveBeenCalledWith(
+      "DELETE FROM balance_snapshots WHERE id = $1",
+      [5]
+    );
+  });
+});
+
+describe("listLinesBySnapshot", () => {
+  it("orders by id and filters by snapshot_id", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await listLinesBySnapshot(5);
+    const sql = mockSelect.mock.calls[0][0] as string;
+    expect(sql).toContain("FROM balance_snapshot_lines");
+    expect(sql).toContain("WHERE snapshot_id = $1");
+    expect(sql).toContain("ORDER BY id");
+    expect(mockSelect.mock.calls[0][1]).toEqual([5]);
+  });
+});
+
+describe("upsertSnapshotLines (simple kind)", () => {
+  it("rejects when the parent snapshot is missing", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await expect(
+      upsertSnapshotLines(99, [{ account_id: 1, value: 1000 }])
+    ).rejects.toMatchObject({ code: "snapshot_not_found" });
+    expect(mockExecute).not.toHaveBeenCalled();
+  });
+
+  it("rejects non-finite values with snapshot_value_invalid", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    await expect(
+      upsertSnapshotLines(5, [
+        { account_id: 1, value: 1000 },
+        // @ts-expect-error testing runtime guard
+        { account_id: 2, value: "not a number" },
+      ])
+    ).rejects.toMatchObject({ code: "snapshot_value_invalid" });
+    // Validation happens up-front, before any mutation
+    expect(mockExecute).not.toHaveBeenCalled();
+  });
+
+  it("rejects NaN and Infinity", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    await expect(
+      upsertSnapshotLines(5, [{ account_id: 1, value: NaN }])
+    ).rejects.toMatchObject({ code: "snapshot_value_invalid" });
+
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    await expect(
+      upsertSnapshotLines(5, [{ account_id: 1, value: Infinity }])
+    ).rejects.toMatchObject({ code: "snapshot_value_invalid" });
+  });
+
+  it("clears existing lines, inserts each line with NULL quantity/unit_price, and bumps updated_at", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    mockExecute
+      .mockResolvedValueOnce({ rowsAffected: 1 }) // delete
+      .mockResolvedValueOnce({ lastInsertId: 100, rowsAffected: 1 }) // insert 1
+      .mockResolvedValueOnce({ lastInsertId: 101, rowsAffected: 1 }) // insert 2
+      .mockResolvedValueOnce({ rowsAffected: 1 }); // update updated_at
+    await upsertSnapshotLines(5, [
+      { account_id: 1, value: 1234.56 },
+      { account_id: 2, value: 0 },
+    ]);
+    // 1st call = DELETE
+    expect(mockExecute.mock.calls[0][0]).toContain(
+      "DELETE FROM balance_snapshot_lines"
+    );
+    // Inserts use literal NULL for quantity/unit_price (simple kind invariant)
+    const insertSql = mockExecute.mock.calls[1][0] as string;
+    expect(insertSql).toContain("INSERT INTO balance_snapshot_lines");
+    expect(insertSql).toMatch(/VALUES\s*\(\s*\$1,\s*\$2,\s*NULL,\s*NULL,\s*\$3/);
+    expect(insertSql).toContain("'manual'");
+    // First insert params
+    expect(mockExecute.mock.calls[1][1]).toEqual([5, 1, 1234.56]);
+    // Second insert params (zero is allowed)
+    expect(mockExecute.mock.calls[2][1]).toEqual([5, 2, 0]);
+    // Final call = UPDATE updated_at on parent snapshot
+    expect(mockExecute.mock.calls[3][0]).toContain(
+      "UPDATE balance_snapshots"
+    );
+    expect(mockExecute.mock.calls[3][0]).toContain("updated_at");
+  });
+
+  it("clears all lines when called with an empty array", async () => {
+    mockSelect.mockResolvedValueOnce([FAKE_SNAPSHOT]);
+    mockExecute
+      .mockResolvedValueOnce({ rowsAffected: 3 }) // delete only
+      .mockResolvedValueOnce({ rowsAffected: 1 }); // bump updated_at
+    await upsertSnapshotLines(5, []);
+    // Only DELETE + UPDATE updated_at — no INSERTs
+    expect(mockExecute).toHaveBeenCalledTimes(2);
+  });
+});
+
+describe("getPreviousSnapshot", () => {
+  it("returns the most recent snapshot strictly before referenceDate", async () => {
+    mockSelect.mockResolvedValueOnce([
+      { ...FAKE_SNAPSHOT, snapshot_date: "2026-03-15" },
+    ]);
+    const got = await getPreviousSnapshot("2026-04-15");
+    expect(got?.snapshot_date).toBe("2026-03-15");
+    const sql = mockSelect.mock.calls[0][0] as string;
+    expect(sql).toContain("snapshot_date < $1");
+    expect(sql).toContain("ORDER BY snapshot_date DESC");
+    expect(sql).toContain("LIMIT 1");
+  });
+
+  it("returns null when no earlier snapshot exists", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    expect(await getPreviousSnapshot("2026-04-15")).toBeNull();
+  });
+
+  it("rejects an invalid reference date", async () => {
+    await expect(getPreviousSnapshot("nope")).rejects.toMatchObject({
+      code: "snapshot_date_required",
+    });
+  });
+});

src/services/balance.service.ts

@@ -15,6 +15,8 @@ import type {
   BalanceAccountWithCategory,
   BalanceCategory,
   BalanceCategoryKind,
+  BalanceSnapshot,
+  BalanceSnapshotLine,
 } from "../shared/types";
 import { BALANCE_CURRENCY_CAD } from "../shared/types";
 
@@ -29,7 +31,12 @@ export type BalanceErrorCode =
   | "category_not_found"
   | "account_not_found"
   | "name_required"
-  | "kind_invalid";
+  | "kind_invalid"
+  | "snapshot_date_required"
+  | "snapshot_date_taken"
+  | "snapshot_not_found"
+  | "snapshot_value_invalid"
+  | "snapshot_priced_unsupported";
 
 export class BalanceServiceError extends Error {
   readonly code: BalanceErrorCode;
@@ -358,3 +365,256 @@ export async function unarchiveBalanceAccount(id: number): Promise<void> {
     [id]
   );
 }
+
+// -----------------------------------------------------------------------------
+// Snapshots + lines (Issue #146 / Bilan #1b — simple kind only)
+// -----------------------------------------------------------------------------
+//
+// At Issue #146 the UI surfaces *only* simple-kind input: every line has
+// `quantity = NULL` and `unit_price = NULL`. The SQL CHECK on
+// `balance_snapshot_lines` already enforces the kind invariant, but
+// `upsertSnapshotLines` re-validates ahead of time so a typed
+// BalanceServiceError surfaces a clean i18n message instead of a raw SQL
+// error. Priced-kind upsert lands in Issue #140 (Bilan #2).
+
+const ISO_DATE_REGEX = /^\d{4}-\d{2}-\d{2}$/;
+
+function normalizeSnapshotDate(date: string): string {
+  const trimmed = (date ?? "").trim();
+  if (!trimmed) {
+    throw new BalanceServiceError(
+      "snapshot_date_required",
+      "Snapshot date is required"
+    );
+  }
+  if (!ISO_DATE_REGEX.test(trimmed)) {
+    throw new BalanceServiceError(
+      "snapshot_date_required",
+      "Snapshot date must be in ISO YYYY-MM-DD format"
+    );
+  }
+  return trimmed;
+}
+
+export async function listSnapshots(): Promise<BalanceSnapshot[]> {
+  const db = await getDb();
+  return db.select<BalanceSnapshot[]>(
+    `SELECT id, snapshot_date, notes, created_at, updated_at
+     FROM balance_snapshots
+     ORDER BY snapshot_date DESC`
+  );
+}
+
+export async function getSnapshotByDate(
+  date: string
+): Promise<BalanceSnapshot | null> {
+  const normalized = normalizeSnapshotDate(date);
+  const db = await getDb();
+  const rows = await db.select<BalanceSnapshot[]>(
+    `SELECT id, snapshot_date, notes, created_at, updated_at
+     FROM balance_snapshots
+     WHERE snapshot_date = $1`,
+    [normalized]
+  );
+  return rows[0] ?? null;
+}
+
+export async function getSnapshotById(
+  id: number
+): Promise<BalanceSnapshot | null> {
+  const db = await getDb();
+  const rows = await db.select<BalanceSnapshot[]>(
+    `SELECT id, snapshot_date, notes, created_at, updated_at
+     FROM balance_snapshots
+     WHERE id = $1`,
+    [id]
+  );
+  return rows[0] ?? null;
+}
+
+export interface CreateSnapshotInput {
+  snapshot_date: string;
+  notes?: string | null;
+}
+
+/**
+ * Create a snapshot row. Throws `snapshot_date_taken` if a snapshot already
+ * exists at the same date so the UI can redirect to edit mode (UNIQUE
+ * constraint on `snapshot_date` would surface a raw SQL error otherwise).
+ */
+export async function createSnapshot(
+  input: CreateSnapshotInput
+): Promise<number> {
+  const date = normalizeSnapshotDate(input.snapshot_date);
+  const existing = await getSnapshotByDate(date);
+  if (existing) {
+    throw new BalanceServiceError(
+      "snapshot_date_taken",
+      `A snapshot already exists at ${date}`
+    );
+  }
+  const db = await getDb();
+  const result = await db.execute(
+    `INSERT INTO balance_snapshots (snapshot_date, notes)
+     VALUES ($1, $2)`,
+    [date, input.notes ? input.notes.trim() || null : null]
+  );
+  return result.lastInsertId as number;
+}
+
+export interface UpdateSnapshotInput {
+  notes?: string | null;
+}
+
+/**
+ * Update snapshot metadata (notes only). Snapshot date is immutable once
+ * saved — to change the date the user deletes the snapshot and creates a
+ * new one (the UI exposes this as a constraint, not a feature).
+ */
+export async function updateSnapshot(
+  id: number,
+  input: UpdateSnapshotInput
+): Promise<void> {
+  const existing = await getSnapshotById(id);
+  if (!existing) {
+    throw new BalanceServiceError(
+      "snapshot_not_found",
+      `Snapshot ${id} not found`
+    );
+  }
+  const notes =
+    input.notes !== undefined
+      ? input.notes === null
+        ? null
+        : input.notes.trim() || null
+      : existing.notes;
+  const db = await getDb();
+  await db.execute(
+    `UPDATE balance_snapshots
+       SET notes = $1, updated_at = CURRENT_TIMESTAMP
+     WHERE id = $2`,
+    [notes, id]
+  );
+}
+
+/**
+ * Delete a snapshot. ON DELETE CASCADE on `balance_snapshot_lines`
+ * .snapshot_id removes the lines too. The UI must double-confirm
+ * (re-typing the snapshot date) before invoking this.
+ */
+export async function deleteSnapshot(id: number): Promise<void> {
+  const existing = await getSnapshotById(id);
+  if (!existing) {
+    throw new BalanceServiceError(
+      "snapshot_not_found",
+      `Snapshot ${id} not found`
+    );
+  }
+  const db = await getDb();
+  await db.execute("DELETE FROM balance_snapshots WHERE id = $1", [id]);
+}
+
+export async function listLinesBySnapshot(
+  snapshotId: number
+): Promise<BalanceSnapshotLine[]> {
+  const db = await getDb();
+  return db.select<BalanceSnapshotLine[]>(
+    `SELECT id, snapshot_id, account_id, quantity, unit_price, value,
+            price_source, price_fetched_at, created_at, updated_at
+     FROM balance_snapshot_lines
+     WHERE snapshot_id = $1
+     ORDER BY id`,
+    [snapshotId]
+  );
+}
+
+export interface SnapshotLineInput {
+  account_id: number;
+  /**
+   * Simple-kind value. Must be a finite number (>= 0 in practice but the
+   * service accepts any finite — negative values support shorts/loans).
+   */
+  value: number;
+}
+
+/**
+ * Upsert a batch of snapshot lines (simple kind only). Each input row is
+ * inserted or replaced atomically per account; lines for accounts not
+ * present in `lines` are removed from the snapshot. This makes the editor
+ * strictly state-driven — what the user sees is exactly what gets saved.
+ *
+ * Validation enforced ahead of time so the SQL CHECK never fires:
+ *   - finite numeric value (NaN / +-Infinity rejected with `snapshot_value_invalid`);
+ *   - quantity / unit_price always stored as NULL (simple-kind invariant).
+ *
+ * Priced-kind upsert lands in Issue #140 (Bilan #2).
+ */
+export async function upsertSnapshotLines(
+  snapshotId: number,
+  lines: SnapshotLineInput[]
+): Promise<void> {
+  const snapshot = await getSnapshotById(snapshotId);
+  if (!snapshot) {
+    throw new BalanceServiceError(
+      "snapshot_not_found",
+      `Snapshot ${snapshotId} not found`
+    );
+  }
+  // Validate every input up-front before mutating anything.
+  for (const line of lines) {
+    if (
+      typeof line.value !== "number" ||
+      !Number.isFinite(line.value)
+    ) {
+      throw new BalanceServiceError(
+        "snapshot_value_invalid",
+        `Line for account ${line.account_id}: value must be a finite number`
+      );
+    }
+  }
+
+  const db = await getDb();
+  // Strategy: clear and rewrite. Snapshot lines are small (one per active
+  // account, typically < 20) so the simplicity outweighs the diff-tracking
+  // savings. CASCADE guarantees consistency on partial failures.
+  await db.execute(
+    "DELETE FROM balance_snapshot_lines WHERE snapshot_id = $1",
+    [snapshotId]
+  );
+  for (const line of lines) {
+    await db.execute(
+      `INSERT INTO balance_snapshot_lines
+         (snapshot_id, account_id, quantity, unit_price, value, price_source)
+       VALUES ($1, $2, NULL, NULL, $3, 'manual')`,
+      [snapshotId, line.account_id, line.value]
+    );
+  }
+  // Bump the parent snapshot's updated_at so list views can sort by recency.
+  await db.execute(
+    `UPDATE balance_snapshots
+       SET updated_at = CURRENT_TIMESTAMP
+     WHERE id = $1`,
+    [snapshotId]
+  );
+}
+
+/**
+ * Convenience helper used by the "Prefill from previous snapshot" button.
+ * Returns the snapshot whose `snapshot_date` is strictly earlier than
+ * `referenceDate`, or `null` if none exists.
+ */
+export async function getPreviousSnapshot(
+  referenceDate: string
+): Promise<BalanceSnapshot | null> {
+  const normalized = normalizeSnapshotDate(referenceDate);
+  const db = await getDb();
+  const rows = await db.select<BalanceSnapshot[]>(
+    `SELECT id, snapshot_date, notes, created_at, updated_at
+     FROM balance_snapshots
+     WHERE snapshot_date < $1
+     ORDER BY snapshot_date DESC
+     LIMIT 1`,
+    [normalized]
+  );
+  return rows[0] ?? null;
+}

src/shared/types/index.ts

@@ -601,3 +601,32 @@ export interface BalanceAccountWithCategory extends BalanceAccount {
   category_i18n_key: string;
   category_kind: BalanceCategoryKind;
 }
+
+// Snapshots — added Issue #146 (Bilan #1b) for the SnapshotEditPage.
+// Lines are kept simple-kind only here (`quantity` / `unit_price` always NULL).
+// The priced-kind UI lands in #140 / Bilan #2.
+
+export interface BalanceSnapshot {
+  id: number;
+  /** ISO date (YYYY-MM-DD), UNIQUE across the table. */
+  snapshot_date: string;
+  notes: string | null;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface BalanceSnapshotLine {
+  id: number;
+  snapshot_id: number;
+  account_id: number;
+  /** Always NULL for simple-kind lines (Issue #146 scope). */
+  quantity: number | null;
+  /** Always NULL for simple-kind lines (Issue #146 scope). */
+  unit_price: number | null;
+  value: number;
+  /** 'manual' for simple-kind, 'maximus-api' for priced (#142). */
+  price_source: string | null;
+  price_fetched_at: string | null;
+  created_at: string;
+  updated_at: string;
+}