import { getDb } from "./db";
import type {
  MonthlyTrendItem,
  CategoryBreakdownItem,
  CategoryOverTimeData,
  CategoryOverTimeItem,
  HighlightsData,
  HighlightMover,
  CategoryDelta,
  CategoryZoomData,
  CategoryZoomChild,
  CategoryZoomEvolutionPoint,
  MonthBalance,
  RecentTransaction,
} from "../shared/types";

export async function getMonthlyTrends(
  dateFrom?: string,
  dateTo?: string,
  sourceId?: number,
): Promise<MonthlyTrendItem[]> {
  const db = await getDb();

  const whereClauses: string[] = [];
  const params: unknown[] = [];
  let paramIndex = 1;

  if (dateFrom) {
    whereClauses.push(`date >= $${paramIndex}`);
    params.push(dateFrom);
    paramIndex++;
  }
  if (dateTo) {
    whereClauses.push(`date <= $${paramIndex}`);
    params.push(dateTo);
    paramIndex++;
  }
  if (sourceId != null) {
    whereClauses.push(`source_id = $${paramIndex}`);
    params.push(sourceId);
    paramIndex++;
  }

  const whereSQL =
    whereClauses.length > 0 ? `WHERE ${whereClauses.join(" AND ")}` : "";

  return db.select<MonthlyTrendItem[]>(
    `SELECT
       strftime('%Y-%m', date) AS month,
       COALESCE(SUM(CASE WHEN amount > 0 THEN amount ELSE 0 END), 0) AS income,
       ABS(COALESCE(SUM(CASE WHEN amount < 0 THEN amount ELSE 0 END), 0)) AS expenses
     FROM transactions
     ${whereSQL}
     GROUP BY month
     ORDER BY month ASC`,
    params
  );
}

export async function getCategoryOverTime(
  dateFrom?: string,
  dateTo?: string,
  topN: number = 50,
  sourceId?: number,
  typeFilter?: "expense" | "income" | "transfer",
): Promise<CategoryOverTimeData> {
  const db = await getDb();

  const whereClauses: string[] = [];
  const params: unknown[] = [];
  let paramIndex = 1;

  if (typeFilter) {
    whereClauses.push(`COALESCE(c.type, 'expense') = $${paramIndex}`);
    params.push(typeFilter);
    paramIndex++;
  }

  if (dateFrom) {
    whereClauses.push(`t.date >= $${paramIndex}`);
    params.push(dateFrom);
    paramIndex++;
  }
  if (dateTo) {
    whereClauses.push(`t.date <= $${paramIndex}`);
    params.push(dateTo);
    paramIndex++;
  }
  if (sourceId != null) {
    whereClauses.push(`t.source_id = $${paramIndex}`);
    params.push(sourceId);
    paramIndex++;
  }

  const whereSQL = whereClauses.length > 0 ? `WHERE ${whereClauses.join(" AND ")}` : "";

  // Get top N categories by total spend
  const topCategories = await db.select<CategoryBreakdownItem[]>(
    `SELECT
       t.category_id,
       COALESCE(c.name, 'Uncategorized') AS category_name,
       COALESCE(c.color, '#9ca3af') AS category_color,
       ABS(SUM(t.amount)) AS total
     FROM transactions t
     LEFT JOIN categories c ON t.category_id = c.id
     ${whereSQL}
     GROUP BY t.category_id
     ORDER BY total DESC
     LIMIT $${paramIndex}`,
    [...params, topN]
  );

  const topCategoryIds = new Set(topCategories.map((c) => c.category_id));
  const colors: Record<string, string> = {};
  const categoryIds: Record<string, number | null> = {};
  for (const cat of topCategories) {
    colors[cat.category_name] = cat.category_color;
    categoryIds[cat.category_name] = cat.category_id;
  }

  // Get monthly breakdown for all categories
  const monthlyRows = await db.select<
    Array<{
      month: string;
      category_id: number | null;
      category_name: string;
      total: number;
    }>
  >(
    `SELECT
       strftime('%Y-%m', t.date) AS month,
       t.category_id,
       COALESCE(c.name, 'Uncategorized') AS category_name,
       ABS(SUM(t.amount)) AS total
     FROM transactions t
     LEFT JOIN categories c ON t.category_id = c.id
     ${whereSQL}
     GROUP BY month, t.category_id
     ORDER BY month ASC`,
    params
  );

  // Build pivot data
  const monthMap = new Map<string, CategoryOverTimeItem>();
  let hasOther = false;

  for (const row of monthlyRows) {
    if (!monthMap.has(row.month)) {
      monthMap.set(row.month, { month: row.month });
    }
    const item = monthMap.get(row.month)!;

    if (topCategoryIds.has(row.category_id)) {
      item[row.category_name] = ((item[row.category_name] as number) || 0) + row.total;
    } else {
      item["Other"] = ((item["Other"] as number) || 0) + row.total;
      hasOther = true;
    }
  }

  if (hasOther) {
    colors["Other"] = "#9ca3af";
  }

  const categories = topCategories.map((c) => c.category_name);
  if (hasOther) {
    categories.push("Other");
  }

  return {
    categories,
    data: Array.from(monthMap.values()),
    colors,
    categoryIds,
  };
}

// --- Highlights (Issue #71) ---

/**
 * Shifts a YYYY-MM-DD date string by `months` months and returns the first day
 * of the resulting month as YYYY-MM-01. Used to compute the start of the
 * 12-month sparkline window relative to the reference date.
 */
function shiftMonthStart(refIso: string, months: number): string {
  const [y, m] = refIso.split("-").map(Number);
  const d = new Date(Date.UTC(y, m - 1 + months, 1));
  const yy = d.getUTCFullYear();
  const mm = String(d.getUTCMonth() + 1).padStart(2, "0");
  return `${yy}-${mm}-01`;
}

function shiftDate(refIso: string, days: number): string {
  const [y, m, d] = refIso.split("-").map(Number);
  const dt = new Date(Date.UTC(y, m - 1, d + days));
  const yy = dt.getUTCFullYear();
  const mm = String(dt.getUTCMonth() + 1).padStart(2, "0");
  const dd = String(dt.getUTCDate()).padStart(2, "0");
  return `${yy}-${mm}-${dd}`;
}

function monthEnd(yyyyMm: string): string {
  const [y, m] = yyyyMm.split("-").map(Number);
  const d = new Date(Date.UTC(y, m, 0)); // day 0 of next month = last day of this month
  const dd = String(d.getUTCDate()).padStart(2, "0");
  return `${yyyyMm}-${dd}`;
}

/**
 * Returns the dashboard "highlights" snapshot for the reports hub:
 *   - net balance for the reference month
 *   - YTD net balance
 *   - last 12 months of net balances (for sparkline)
 *   - top movers (biggest change in spending vs previous month)
 *   - top transactions (biggest absolute amounts in last `windowDays` days)
 *
 * All SQL is parameterised. `referenceDate` defaults to today and is overridable
 * from tests for deterministic fixtures.
 */
export async function getHighlights(
  windowDays: number = 30,
  referenceDate?: string,
  topMoversLimit: number = 5,
  topTransactionsLimit: number = 10,
): Promise<HighlightsData> {
  const db = await getDb();

  const refIso = referenceDate ?? (() => {
    const t = new Date();
    return `${t.getFullYear()}-${String(t.getMonth() + 1).padStart(2, "0")}-${String(t.getDate()).padStart(2, "0")}`;
  })();
  const currentMonth = refIso.slice(0, 7); // YYYY-MM
  const currentYear = refIso.slice(0, 4);
  const yearStart = `${currentYear}-01-01`;
  const currentMonthStart = `${currentMonth}-01`;
  const currentMonthEnd = monthEnd(currentMonth);
  const previousMonthStart = shiftMonthStart(refIso, -1);
  const previousMonth = previousMonthStart.slice(0, 7);
  const previousMonthEnd = monthEnd(previousMonth);
  const sparklineStart = shiftMonthStart(refIso, -11); // 11 months back + current = 12
  const recentWindowStart = shiftDate(refIso, -(windowDays - 1));

  // 1. Net balance for current month
  const currentBalanceRows = await db.select<Array<{ net: number | null }>>(
    `SELECT COALESCE(SUM(amount), 0) AS net
       FROM transactions
      WHERE date >= $1 AND date <= $2`,
    [currentMonthStart, currentMonthEnd],
  );
  const netBalanceCurrent = Number(currentBalanceRows[0]?.net ?? 0);

  // 2. YTD balance
  const ytdRows = await db.select<Array<{ net: number | null }>>(
    `SELECT COALESCE(SUM(amount), 0) AS net
       FROM transactions
      WHERE date >= $1 AND date <= $2`,
    [yearStart, refIso],
  );
  const netBalanceYtd = Number(ytdRows[0]?.net ?? 0);

  // 3. 12-month sparkline series
  const seriesRows = await db.select<Array<{ month: string; net: number | null }>>(
    `SELECT strftime('%Y-%m', date) AS month, COALESCE(SUM(amount), 0) AS net
       FROM transactions
      WHERE date >= $1 AND date <= $2
      GROUP BY month
      ORDER BY month ASC`,
    [sparklineStart, currentMonthEnd],
  );
  const seriesMap = new Map(seriesRows.map((r) => [r.month, Number(r.net ?? 0)]));
  const monthlyBalanceSeries: MonthBalance[] = [];
  for (let i = 11; i >= 0; i--) {
    const monthKey = shiftMonthStart(refIso, -i).slice(0, 7);
    monthlyBalanceSeries.push({ month: monthKey, netBalance: seriesMap.get(monthKey) ?? 0 });
  }

  // 4. Top movers — expense-side only (amount < 0), compare current vs previous month
  const moversRows = await db.select<
    Array<{
      category_id: number | null;
      category_name: string;
      category_color: string;
      current_total: number | null;
      previous_total: number | null;
    }>
  >(
    `SELECT
        t.category_id,
        COALESCE(c.name, 'Uncategorized') AS category_name,
        COALESCE(c.color, '#9ca3af')      AS category_color,
        COALESCE(SUM(CASE WHEN t.date >= $1 AND t.date <= $2 THEN ABS(t.amount) ELSE 0 END), 0) AS current_total,
        COALESCE(SUM(CASE WHEN t.date >= $3 AND t.date <= $4 THEN ABS(t.amount) ELSE 0 END), 0) AS previous_total
      FROM transactions t
      LEFT JOIN categories c ON t.category_id = c.id
      WHERE t.amount < 0
        AND (
          (t.date >= $1 AND t.date <= $2)
          OR (t.date >= $3 AND t.date <= $4)
        )
      GROUP BY t.category_id, category_name, category_color
      ORDER BY ABS(current_total - previous_total) DESC
      LIMIT $5`,
    [currentMonthStart, currentMonthEnd, previousMonthStart, previousMonthEnd, topMoversLimit],
  );
  const topMovers: HighlightMover[] = moversRows.map((r) => {
    const current = Number(r.current_total ?? 0);
    const previous = Number(r.previous_total ?? 0);
    const deltaAbs = current - previous;
    const deltaPct = previous === 0 ? null : (deltaAbs / previous) * 100;
    return {
      categoryId: r.category_id,
      categoryName: r.category_name,
      categoryColor: r.category_color,
      previousAmount: previous,
      currentAmount: current,
      deltaAbs,
      deltaPct,
    };
  });

  // 5. Top transactions within the recent window
  const recentRows = await db.select<RecentTransaction[]>(
    `SELECT
        t.id,
        t.date,
        t.description,
        t.amount,
        c.name  AS category_name,
        c.color AS category_color
       FROM transactions t
       LEFT JOIN categories c ON t.category_id = c.id
      WHERE t.date >= $1 AND t.date <= $2
      ORDER BY ABS(t.amount) DESC
      LIMIT $3`,
    [recentWindowStart, refIso, topTransactionsLimit],
  );

  return {
    currentMonth,
    netBalanceCurrent,
    netBalanceYtd,
    monthlyBalanceSeries,
    topMovers,
    topTransactions: recentRows,
  };
}

// --- Compare (Issue #73) ---

interface RawDeltaRow {
  category_id: number | null;
  category_name: string;
  category_color: string;
  current_total: number | null;
  previous_total: number | null;
}

function rowsToDeltas(rows: RawDeltaRow[]): CategoryDelta[] {
  return rows.map((r) => {
    const current = Number(r.current_total ?? 0);
    const previous = Number(r.previous_total ?? 0);
    const deltaAbs = current - previous;
    const deltaPct = previous === 0 ? null : (deltaAbs / previous) * 100;
    return {
      categoryId: r.category_id,
      categoryName: r.category_name,
      categoryColor: r.category_color,
      previousAmount: previous,
      currentAmount: current,
      deltaAbs,
      deltaPct,
    };
  });
}

function monthBoundaries(year: number, month: number): { start: string; end: string } {
  const mm = String(month).padStart(2, "0");
  const endDate = new Date(Date.UTC(year, month, 0));
  const dd = String(endDate.getUTCDate()).padStart(2, "0");
  return { start: `${year}-${mm}-01`, end: `${year}-${mm}-${dd}` };
}

function previousMonth(year: number, month: number): { year: number; month: number } {
  if (month === 1) return { year: year - 1, month: 12 };
  return { year, month: month - 1 };
}

/**
 * Month-over-month expense delta by category. All SQL parameterised.
 */
export async function getCompareMonthOverMonth(
  year: number,
  month: number,
): Promise<CategoryDelta[]> {
  const db = await getDb();
  const { start: curStart, end: curEnd } = monthBoundaries(year, month);
  const prev = previousMonth(year, month);
  const { start: prevStart, end: prevEnd } = monthBoundaries(prev.year, prev.month);

  const rows = await db.select<RawDeltaRow[]>(
    `SELECT
        t.category_id,
        COALESCE(c.name, 'Uncategorized') AS category_name,
        COALESCE(c.color, '#9ca3af')      AS category_color,
        COALESCE(SUM(CASE WHEN t.date >= $1 AND t.date <= $2 THEN ABS(t.amount) ELSE 0 END), 0) AS current_total,
        COALESCE(SUM(CASE WHEN t.date >= $3 AND t.date <= $4 THEN ABS(t.amount) ELSE 0 END), 0) AS previous_total
      FROM transactions t
      LEFT JOIN categories c ON t.category_id = c.id
      WHERE t.amount < 0
        AND (
          (t.date >= $1 AND t.date <= $2)
          OR (t.date >= $3 AND t.date <= $4)
        )
      GROUP BY t.category_id, category_name, category_color
      ORDER BY ABS(current_total - previous_total) DESC`,
    [curStart, curEnd, prevStart, prevEnd],
  );
  return rowsToDeltas(rows);
}

/**
 * Year-over-year expense delta by category. All SQL parameterised.
 */
export async function getCompareYearOverYear(year: number): Promise<CategoryDelta[]> {
  const db = await getDb();
  const curStart = `${year}-01-01`;
  const curEnd = `${year}-12-31`;
  const prevStart = `${year - 1}-01-01`;
  const prevEnd = `${year - 1}-12-31`;

  const rows = await db.select<RawDeltaRow[]>(
    `SELECT
        t.category_id,
        COALESCE(c.name, 'Uncategorized') AS category_name,
        COALESCE(c.color, '#9ca3af')      AS category_color,
        COALESCE(SUM(CASE WHEN t.date >= $1 AND t.date <= $2 THEN ABS(t.amount) ELSE 0 END), 0) AS current_total,
        COALESCE(SUM(CASE WHEN t.date >= $3 AND t.date <= $4 THEN ABS(t.amount) ELSE 0 END), 0) AS previous_total
      FROM transactions t
      LEFT JOIN categories c ON t.category_id = c.id
      WHERE t.amount < 0
        AND (
          (t.date >= $1 AND t.date <= $2)
          OR (t.date >= $3 AND t.date <= $4)
        )
      GROUP BY t.category_id, category_name, category_color
      ORDER BY ABS(current_total - previous_total) DESC`,
    [curStart, curEnd, prevStart, prevEnd],
  );
  return rowsToDeltas(rows);
}

// --- Category zoom (Issue #74) ---

/**
 * Recursive CTE fragment bounded to `depth < 5` so a corrupted `parent_id`
 * loop (A → B → A) can never spin forever. The depth budget is intentionally
 * low: real category trees rarely exceed 3 levels.
 */
const CATEGORY_TREE_CTE = `
  WITH RECURSIVE cat_tree(id, depth) AS (
    SELECT id, 0 FROM categories WHERE id = $1
    UNION ALL
    SELECT c.id, ct.depth + 1
      FROM categories c
      JOIN cat_tree ct ON c.parent_id = ct.id
     WHERE ct.depth < 5
  )
`;

/**
 * Returns the zoom-on-category report for the given category id.
 *
 * When `includeSubcategories` is true the recursive CTE walks down the
 * category tree (capped at 5 levels) and aggregates matching rows. When
 * false, only direct transactions on `categoryId` are considered. Every
 * query is parameterised; the category id is never interpolated.
 */
export async function getCategoryZoom(
  categoryId: number,
  dateFrom: string,
  dateTo: string,
  includeSubcategories: boolean = true,
): Promise<CategoryZoomData> {
  const db = await getDb();

  const categoryFilter = includeSubcategories
    ? `${CATEGORY_TREE_CTE}
       SELECT t.id, t.date, t.description, t.amount, t.category_id
         FROM transactions t
        WHERE t.category_id IN (SELECT id FROM cat_tree)
          AND t.date >= $2 AND t.date <= $3`
    : `SELECT t.id, t.date, t.description, t.amount, t.category_id
         FROM transactions t
        WHERE t.category_id = $1
          AND t.date >= $2 AND t.date <= $3`;

  // 1. Transactions (with join for display)
  const txRows = await db.select<RecentTransaction[]>(
    `${includeSubcategories ? CATEGORY_TREE_CTE : ""}
     SELECT t.id, t.date, t.description, t.amount, c.name AS category_name, c.color AS category_color
       FROM transactions t
       LEFT JOIN categories c ON t.category_id = c.id
      WHERE ${includeSubcategories
        ? "t.category_id IN (SELECT id FROM cat_tree)"
        : "t.category_id = $1"}
        AND t.date >= $2 AND t.date <= $3
      ORDER BY ABS(t.amount) DESC
      LIMIT 500`,
    [categoryId, dateFrom, dateTo],
  );

  // 2. Rollup total (sum of absolute amounts of matching rows)
  const totalRows = await db.select<Array<{ rollup: number | null }>>(
    `${categoryFilter.replace("SELECT t.id, t.date, t.description, t.amount, t.category_id", "SELECT COALESCE(SUM(ABS(t.amount)), 0) AS rollup")}`,
    [categoryId, dateFrom, dateTo],
  );
  const rollupTotal = Number(totalRows[0]?.rollup ?? 0);

  // 3. Breakdown by direct child (only meaningful when includeSubcategories is true)
  const byChild: CategoryZoomChild[] = [];
  if (includeSubcategories) {
    const childRows = await db.select<
      Array<{ child_id: number; child_name: string; child_color: string; total: number | null }>
    >(
      `SELECT child.id AS child_id,
              child.name AS child_name,
              COALESCE(child.color, '#9ca3af') AS child_color,
              COALESCE(SUM(ABS(t.amount)), 0) AS total
         FROM categories child
         LEFT JOIN transactions t ON t.category_id = child.id
          AND t.date >= $2 AND t.date <= $3
        WHERE child.parent_id = $1
        GROUP BY child.id, child.name, child.color
        ORDER BY total DESC`,
      [categoryId, dateFrom, dateTo],
    );
    for (const r of childRows) {
      byChild.push({
        categoryId: r.child_id,
        categoryName: r.child_name,
        categoryColor: r.child_color,
        total: Number(r.total ?? 0),
      });
    }
  }

  // 4. Monthly evolution across the window
  const evolutionRows = await db.select<Array<{ month: string; total: number | null }>>(
    `${includeSubcategories ? CATEGORY_TREE_CTE : ""}
     SELECT strftime('%Y-%m', t.date) AS month,
            COALESCE(SUM(ABS(t.amount)), 0) AS total
       FROM transactions t
      WHERE ${includeSubcategories
        ? "t.category_id IN (SELECT id FROM cat_tree)"
        : "t.category_id = $1"}
        AND t.date >= $2 AND t.date <= $3
      GROUP BY month
      ORDER BY month ASC`,
    [categoryId, dateFrom, dateTo],
  );
  const monthlyEvolution: CategoryZoomEvolutionPoint[] = evolutionRows.map((r) => ({
    month: r.month,
    total: Number(r.total ?? 0),
  }));

  return {
    rollupTotal,
    byChild,
    monthlyEvolution,
    transactions: txRows,
  };
}