/**
 * Network access store — DC-145.
 *
 * The access map is the single source of truth for who can reach which
 * resource on the DashCaddy Private Network (spec §2). It is a grid of
 * principals (people or groups) × resources with allow/deny grants:
 *
 *   data/network-access.json:
 *   {
 *     grants: [{ principal: {type:'person'|'group', id}, resource, allowed }],
 *     updatedAt
 *   }
 *
 * Resolution semantics (effectiveAccess):
 *   - A person's effective access = union of the grants of every group they
 *     belong to, then person-level grants OVERRIDE group grants — an explicit
 *     person grant (true or false) always wins over any group grant.
 *   - A group's effective access is just its own grants.
 *
 * The store knows only principal IDs — it never reads people.json. Group
 * membership is supplied by the caller (from the people store) as an array
 * of group IDs on the principal.
 *
 * Change events: subscribe(fn) registers a listener fired after every
 * successful mutation with the new map. The ACL compiler (DC-148) uses this
 * to recompile provider rules. Listeners run after the atomic write has
 * completed, are isolated (one listener throwing never breaks the mutation
 * or other listeners), and unsubscribe on return value.
 *
 * Storage: same atomic JSON pattern as invite-store/user-store (DC-099
 * fsync'd tmp+rename via the shared atomic-write util). All mutations run
 * through a promise mutex so concurrent writers serialize.
 */

'use strict';

const path = require('path');
const fs = require('fs');
const platformPaths = require('../../platform-paths');
const { atomicWriteJSON } = require('../utils/atomic-write');

const PRINCIPAL_TYPES = ['person', 'group'];

function _nowIso() { return new Date().toISOString(); }

function _readJSON(filePath, fallback) {
  try {
    const raw = fs.readFileSync(filePath, 'utf8');
    return JSON.parse(raw);
  } catch (err) {
    if (err && err.code === 'ENOENT') return fallback;
    return fallback;
  }
}

/**
 * Validate a single grant object. Returns null when valid, else a string
 * describing the problem (machine-y reason code + detail).
 */
function validateGrant(grant) {
  if (!grant || typeof grant !== 'object' || Array.isArray(grant)) {
    return 'invalid_grant: not an object';
  }
  const { principal, resource, allowed } = grant;
  if (!principal || typeof principal !== 'object' || Array.isArray(principal)) {
    return 'invalid_principal: principal must be an object';
  }
  if (!PRINCIPAL_TYPES.includes(principal.type)) {
    return `invalid_principal_type: ${JSON.stringify(principal.type)} (expected person|group)`;
  }
  if (typeof principal.id !== 'string' || principal.id.trim().length === 0) {
    return 'invalid_principal_id: must be a non-empty string';
  }
  if (typeof resource !== 'string' || resource.trim().length === 0) {
    return 'invalid_resource: must be a non-empty string';
  }
  if (typeof allowed !== 'boolean') {
    return 'invalid_allowed: must be a boolean';
  }
  return null;
}

/**
 * Normalize + validate a whole grants array.
 * - validates each grant
 * - dedupes exact principal(type+id)+resource collisions, LAST WINS
 * Returns { ok: true, grants } or { ok: false, reason }.
 */
function normalizeGrants(list) {
  if (!Array.isArray(list)) return { ok: false, reason: 'invalid_grants: must be an array' };
  const out = [];
  const seen = new Map(); // key -> index in out (last-wins by replacement)
  for (const raw of list) {
    const err = validateGrant(raw);
    if (err) return { ok: false, reason: err };
    const g = {
      principal: { type: raw.principal.type, id: raw.principal.id },
      resource: raw.resource,
      allowed: raw.allowed,
    };
    const key = `${g.principal.type}\u0000${g.principal.id}\u0000${g.resource}`;
    if (seen.has(key)) {
      out[seen.get(key)] = g; // last-wins dedupe
    } else {
      seen.set(key, out.length);
      out.push(g);
    }
  }
  return { ok: true, grants: out };
}

function createNetworkAccessStore(opts = {}) {
  const candidates = [
    opts.dataDir,
    opts.platformPaths && opts.platformPaths.dataDir,
    platformPaths && platformPaths.dataDir,
  ];
  const dataDir = candidates.find(c => typeof c === 'string' && c.length > 0)
    || require('os').tmpdir();
  const log = opts.log || { info() {}, warn() {}, error() {} };

  const file = path.join(dataDir, 'network-access.json');

  let _mutex = Promise.resolve();
  function _enqueue(fn) {
    const next = _mutex.then(fn, fn);
    _mutex = next.catch(() => {});
    return next;
  }

  // ── change events ────────────────────────────────────────────────────────
  const _listeners = new Set();

  /**
   * Subscribe to change events. fn(map) is called after every successful
   * mutation with the freshly saved map ({ grants, updatedAt }).
   * Returns an unsubscribe function.
   */
  function subscribe(fn) {
    if (typeof fn !== 'function') {
      throw new TypeError('subscribe requires a function');
    }
    _listeners.add(fn);
    return () => _listeners.delete(fn);
  }

  function _emit(map) {
    for (const fn of _listeners) {
      try {
        fn(map);
      } catch (err) {
        log.warn && log.warn('network-access', 'change listener threw (isolated)', {
          err: err && err.message,
        });
      }
    }
  }

  // ── load / save ──────────────────────────────────────────────────────────
  function _defaultData() { return { grants: [], updatedAt: null }; }

  function _load() {
    const data = _readJSON(file, _defaultData());
    if (!Array.isArray(data.grants)) data.grants = [];
    // Defensive: tolerate pre-existing junk on disk by re-normalizing.
    const norm = normalizeGrants(data.grants.filter(g => validateGrant(g) === null));
    data.grants = norm.grants;
    return data;
  }

  function _save(data) {
    data.updatedAt = _nowIso();
    atomicWriteJSON(file, data);
  }

  /**
   * Read the whole access map ({ grants, updatedAt }). Never rejects —
   * missing/corrupt file yields the empty map.
   */
  function getAccessMap() {
    return _enqueue(() => _load());
  }

  /**
   * Atomically replace the whole map. Validates every grant (type in
   * person|group, non-empty string resource, boolean allowed), dedupes
   * exact principal+resource collisions last-wins, writes fsync'd
   * tmp+rename, then emits a change event.
   * Returns { ok: true, map } | { ok: false, reason }.
   */
  function saveAccessMap(map) {
    return _enqueue(() => {
      const grantsInput = map && typeof map === 'object' ? map.grants : map;
      const norm = normalizeGrants(grantsInput);
      if (!norm.ok) {
        return { ok: false, reason: norm.reason };
      }
      const data = { grants: norm.grants, updatedAt: null };
      _save(data);
      _emit(data);
      return { ok: true, map: data };
    });
  }

  function _key(g) { return `${g.principal.type}\u0000${g.principal.id}\u0000${g.resource}`; }

  /**
   * Set (upsert) one grant. Validates; rejects duplicates by construction
   * (same principal+resource is replaced). Returns the saved map.
   */
  function setGrant(principal, resource, allowed) {
    return _enqueue(() => {
      const norm = normalizeGrants([{ principal, resource, allowed }]);
      if (!norm.ok) return { ok: false, reason: norm.reason };
      const grant = norm.grants[0];
      const data = _load();
      const k = _key(grant);
      const idx = data.grants.findIndex(g => _key(g) === k);
      if (idx >= 0) data.grants[idx] = grant; else data.grants.push(grant);
      _save(data);
      _emit(data);
      return { ok: true, map: data };
    });
  }

  /**
   * Remove one grant (exact principal+resource). Returns
   * { ok: true, removed: true, map } | { ok: true, removed: false } when
   * the grant was absent (idempotent delete), or { ok:false, reason } on
   * invalid input.
   */
  function removeGrant(principal, resource) {
    return _enqueue(() => {
      const norm = normalizeGrants([{ principal, resource, allowed: true }]);
      if (!norm.ok) return { ok: false, reason: norm.reason };
      const g = norm.grants[0];
      const data = _load();
      const k = _key(g);
      const before = data.grants.length;
      data.grants = data.grants.filter(x => _key(x) !== k);
      if (data.grants.length === before) return { ok: true, removed: false, map: data };
      _save(data);
      _emit(data);
      return { ok: true, removed: true, map: data };
    });
  }

  /**
   * Compute a principal's effective access → { resources: {name: allowed} }.
   *
   * principal: {type:'group', id} → the group's own grants.
   * principal: {type:'person', id, groups?: string[]} → union of all
   * groups' grants, then person-level grants OVERRIDE (explicit person
   * grant true/false beats any group grant, including per-resource deny).
   */
  async function effectiveAccess(principal) {
    const map = await getAccessMap();
    const resources = {};
    if (!principal || typeof principal !== 'object'
        || !PRINCIPAL_TYPES.includes(principal.type)
        || typeof principal.id !== 'string' || principal.id.length === 0) {
      return { ok: false, reason: 'invalid_principal' };
    }
    if (principal.type === 'group') {
      for (const g of map.grants) {
        if (g.principal.type === 'group' && g.principal.id === principal.id) {
          resources[g.resource] = g.allowed;
        }
      }
      return { ok: true, resources };
    }
    // person: union of group grants first …
    const groups = Array.isArray(principal.groups) ? principal.groups : [];
    const groupSet = new Set(groups.filter(x => typeof x === 'string'));
    for (const g of map.grants) {
      if (g.principal.type === 'group' && groupSet.has(g.principal.id)) {
        resources[g.resource] = g.allowed;
      }
    }
    // … then person-level grants override.
    for (const g of map.grants) {
      if (g.principal.type === 'person' && g.principal.id === principal.id) {
        resources[g.resource] = g.allowed;
      }
    }
    return { ok: true, resources };
  }

  /**
   * Derived view: distinct principals referenced by any grant.
   * [{ type, id, grantCount }] sorted by type then id.
   */
  async function listPrincipals() {
    const map = await getAccessMap();
    const acc = new Map();
    for (const g of map.grants) {
      const k = `${g.principal.type}\u0000${g.principal.id}`;
      const cur = acc.get(k) || { type: g.principal.type, id: g.principal.id, grantCount: 0 };
      cur.grantCount += 1;
      acc.set(k, cur);
    }
    return [...acc.values()].sort((a, b) =>
      a.type === b.type ? a.id.localeCompare(b.id) : a.type.localeCompare(b.type));
  }

  /**
   * Derived view: distinct resource names referenced by any grant,
   * sorted alphabetically.
   */
  async function listResources() {
    const map = await getAccessMap();
    const set = new Set();
    for (const g of map.grants) set.add(g.resource);
    return [...set].sort();
  }

  return {
    getAccessMap,
    saveAccessMap,
    setGrant,
    removeGrant,
    effectiveAccess,
    subscribe,
    listPrincipals,
    listResources,
    PRINCIPAL_TYPES,
  };
}

module.exports = {
  createNetworkAccessStore,
  validateGrant,
  normalizeGrants,
  PRINCIPAL_TYPES,
};