// PostgreSQL backups (GET /backups, POST /backups/pull), issue #58, contract
// `schemaVersion: 1` shared with the VPS script (la-compagnie-maximus,
// scripts/backup/backup-postgres.sh) and the workstation pull agent
// (agent/pg-backup-pull/run-pg-backup-pull.sh).
//
// Pure module: no I/O, no config, no side effects. index.js wires the routes,
// reads status.json and owns the pull file.
//
// Two inputs, two rules:
//   - status.json is written by the VPS script and only read here. It goes
//     through a whitelist rebuild, as the Claude usage snapshot does: an
//     unknown field is dropped, an invalid value is dropped (key left out),
//     never coerced. Only what makes the file unusable refuses it as a whole:
//     not an object, a `schemaVersion` other than 1, or no usable `generatedAt`
//     (the age, hence `stale`, is computed from it).
//   - the pull report is sent by the workstation agent, whose body is four
//     fixed fields. It is validated strictly: any invalid or missing field is a
//     400, so a broken agent is told so instead of being half-stored.
// Error codes come from closed lists on both sides: a free-form `error` could
// carry pg_dump or rclone stderr (hosts, keys) all the way to the dashboard.

const { isIsoTimestamp } = require("./claude-usage.js");

const SCHEMA_VERSION = 1;

// The pull body is four short fields, under 120 bytes in practice.
const BACKUPS_MAX_BODY_BYTES = 1024;

// One cluster holds about ten databases; this bound is only there so a runaway
// file cannot make the response arbitrarily large.
const MAX_DATABASES = 64;

const VPS_ERROR_CODES = [
  "dump_failed",
  "dump_empty",
  "restore_list_failed",
  "invalid_name",
  "encrypt_failed",
  "mirror_upload_failed",
  "mirror_purge_failed",
  "rotation_failed",
];
const PULL_ERROR_CODES = ["pull_failed", "rotation_failed"];

// Same pattern as the VPS script's own check. A name it rejected is reported
// with `invalid_name` and may hold arbitrary text: that name is dropped here.
const DATABASE_NAME_RE = /^[a-z0-9_]{1,63}$/;

function isPlainObject(value) {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

function cleanCount(value) {
  return Number.isSafeInteger(value) && value >= 0 ? value : undefined;
}

function cleanBoolean(value) {
  return typeof value === "boolean" ? value : undefined;
}

function cleanTimestamp(value) {
  return isIsoTimestamp(value) ? value : undefined;
}

function cleanCode(value, codes) {
  return codes.includes(value) ? value : undefined;
}

function cleanDatabaseName(value) {
  return typeof value === "string" && DATABASE_NAME_RE.test(value) ? value : undefined;
}

// Copy `key` into `out` only when the cleaner kept a value.
function put(out, key, value) {
  if (value !== undefined) out[key] = value;
}

// `null` is a legitimate value for the fields the contract declares nullable
// (a failed dump has no dumpedAt, a failed upload no uploadedAt).
function putNullable(out, key, raw, clean) {
  if (raw === null) out[key] = null;
  else put(out, key, clean(raw));
}

// { ok, error? } plus the given extra fields, for globals, mirror and rotation.
function sanitizeComponent(value, extra) {
  if (!isPlainObject(value)) return undefined;
  const out = {};
  extra(out, value);
  put(out, "ok", cleanBoolean(value.ok));
  put(out, "error", cleanCode(value.error, VPS_ERROR_CODES));
  return out;
}

function sanitizeDatabase(value) {
  const out = {};
  put(out, "name", cleanDatabaseName(value.name));
  put(out, "sizeBytes", cleanCount(value.sizeBytes));
  putNullable(out, "dumpedAt", value.dumpedAt, cleanTimestamp);
  put(out, "ok", cleanBoolean(value.ok));
  put(out, "error", cleanCode(value.error, VPS_ERROR_CODES));
  return out;
}

function sanitizeRetention(value) {
  if (!isPlainObject(value)) return undefined;
  const out = {};
  put(out, "local", cleanCount(value.local));
  put(out, "offsite", cleanCount(value.offsite));
  return out;
}

// Returns { status } or { error: <code> }, the code going out as `vpsError`.
// Idempotent: a sanitized status comes back unchanged.
function sanitizeBackupsStatus(payload) {
  if (!isPlainObject(payload)) return { error: "invalid_contract" };
  if (payload.schemaVersion !== SCHEMA_VERSION) return { error: "unsupported_schema" };
  const generatedAt = cleanTimestamp(payload.generatedAt);
  if (generatedAt === undefined) return { error: "invalid_contract" };

  const status = { schemaVersion: SCHEMA_VERSION, generatedAt };
  put(status, "ok", cleanBoolean(payload.ok));
  put(status, "expectedCount", cleanCount(payload.expectedCount));
  if (Array.isArray(payload.databases)) {
    status.databases = payload.databases.filter(isPlainObject).slice(0, MAX_DATABASES).map(sanitizeDatabase);
  }
  put(status, "globals", sanitizeComponent(payload.globals, (out, value) => {
    put(out, "sizeBytes", cleanCount(value.sizeBytes));
  }));
  put(status, "mirror", sanitizeComponent(payload.mirror, (out, value) => {
    putNullable(out, "uploadedAt", value.uploadedAt, cleanTimestamp);
  }));
  put(status, "rotation", sanitizeComponent(payload.rotation, () => {}));
  put(status, "retentionDays", sanitizeRetention(payload.retentionDays));
  return { status };
}

// Returns { pull } or { error: <message> }. Strict: every field must be there
// and valid. Anything else in the body, a client `receivedAt` included, is
// dropped: the server stamps its own.
function validateBackupsPull(payload) {
  if (!isPlainObject(payload)) return { error: "body must be a JSON object" };
  if (!isIsoTimestamp(payload.pulledAt)) {
    return { error: "pulledAt must be an ISO 8601 timestamp with an offset" };
  }
  if (cleanCount(payload.files) === undefined) {
    return { error: "files must be a non-negative integer" };
  }
  if (typeof payload.ok !== "boolean") return { error: "ok must be a boolean" };

  const pull = { pulledAt: payload.pulledAt, files: payload.files, ok: payload.ok };
  if (payload.ok) {
    if (payload.error !== undefined) return { error: "error is only allowed when ok is false" };
  } else {
    if (!PULL_ERROR_CODES.includes(payload.error)) {
      return { error: `error must be one of ${PULL_ERROR_CODES.join(",")} when ok is false` };
    }
    pull.error = payload.error;
  }
  return { pull };
}

module.exports = {
  sanitizeBackupsStatus,
  validateBackupsPull,
  BACKUPS_MAX_BODY_BYTES,
  SCHEMA_VERSION,
  MAX_DATABASES,
  VPS_ERROR_CODES,
  PULL_ERROR_CODES,
};