/**
 * [Gitea #114] Export / import "your data": the Lotus-side personal data of
 * an account (not message history, not encryption keys: those have their own
 * exports, and keys are secret). One JSON file:
 *
 *   { format: 'lotus-chat-data', version: 1, exportedAt, userId,
 *     accountData: { [type]: content }, profile: { decoration }, local: { settings } }
 *
 * Import MERGES: anything missing here is added; a value that differs is a
 * conflict, kept as it is unless the user chooses the file's. Pure helpers.
 */

export const EXPORT_FORMAT = 'lotus-chat-data';
export const EXPORT_VERSION = 1;

/** The account-data types that are the user's own Lotus data, with labels. */
export const EXPORT_ACCOUNT_DATA: { type: string; label: string }[] = [
  { type: 'io.lotus.settings', label: 'Synced settings' },
  { type: 'io.lotus.bookmarks', label: 'Bookmarks' },
  { type: 'io.lotus.user_notes', label: 'Private notes about people' },
  { type: 'io.lotus.room_names', label: 'Your names for rooms' },
  { type: 'in.cinny.spaces', label: 'Room sections and sidebar' },
  { type: 'io.lotus.reminders', label: 'Reminders' },
  { type: 'io.lotus.status_presets', label: 'Status presets' },
  { type: 'io.lotus.thread_notifications', label: 'Thread notification settings' },
  { type: 'io.lotus.mute_timers', label: 'Timed mutes' },
  { type: 'io.lotus.soundboard', label: 'Soundboard (clips stay on the server)' },
  { type: 'io.lotus.soundboard_rooms', label: 'Soundboards enabled everywhere' },
  { type: 'im.ponies.user_emotes', label: 'Your emoji and stickers' },
  { type: 'im.ponies.emote_rooms', label: 'Emoji packs enabled everywhere' },
];

export type ExportFile = {
  format: typeof EXPORT_FORMAT;
  version: number;
  exportedAt: string;
  userId: string;
  accountData: Record<string, unknown>;
  profile: { decoration: string | null };
  local: { settings: Record<string, unknown> | null };
};

export const buildExport = (input: {
  userId: string;
  accountData: Record<string, unknown>;
  decoration: string | null;
  localSettings: Record<string, unknown> | null;
  now?: Date;
}): ExportFile => {
  const accountData: Record<string, unknown> = {};
  EXPORT_ACCOUNT_DATA.forEach(({ type }) => {
    const c = input.accountData[type];
    if (c !== undefined && c !== null) accountData[type] = c;
  });
  return {
    format: EXPORT_FORMAT,
    version: EXPORT_VERSION,
    exportedAt: (input.now ?? new Date()).toISOString(),
    userId: input.userId,
    accountData,
    profile: { decoration: input.decoration },
    local: { settings: input.localSettings },
  };
};

const isObject = (v: unknown): v is Record<string, unknown> =>
  !!v && typeof v === 'object' && !Array.isArray(v);

export type ParseResult = { ok: true; file: ExportFile } | { ok: false; error: string };

/** Validate an imported file; older versions would be migrated here. */
export const parseExport = (text: string): ParseResult => {
  let v: unknown;
  try {
    v = JSON.parse(text);
  } catch {
    return { ok: false, error: "This isn't a Lotus Chat data file (it isn't valid JSON)." };
  }
  if (!isObject(v) || v.format !== EXPORT_FORMAT)
    return { ok: false, error: "This isn't a Lotus Chat data file." };
  if (typeof v.version !== 'number' || v.version < 1)
    return { ok: false, error: 'This data file is damaged (no version).' };
  if (v.version > EXPORT_VERSION)
    return {
      ok: false,
      error: 'This file was made by a newer Lotus Chat. Update the app, then import it again.',
    };
  const accountData = isObject(v.accountData) ? v.accountData : {};
  const known = new Set(EXPORT_ACCOUNT_DATA.map((t) => t.type));
  const filtered: Record<string, unknown> = {};
  Object.entries(accountData).forEach(([type, content]) => {
    // Only our own types: a file can't be used to write arbitrary account data.
    if (known.has(type) && content !== null && content !== undefined) filtered[type] = content;
  });
  const profile = isObject(v.profile) ? v.profile : {};
  const local = isObject(v.local) ? v.local : {};
  return {
    ok: true,
    file: {
      format: EXPORT_FORMAT,
      version: v.version,
      exportedAt: typeof v.exportedAt === 'string' ? v.exportedAt : '',
      userId: typeof v.userId === 'string' ? v.userId : '',
      accountData: filtered,
      profile: {
        decoration: typeof profile.decoration === 'string' ? profile.decoration : null,
      },
      local: { settings: isObject(local.settings) ? local.settings : null },
    },
  };
};

const same = (a: unknown, b: unknown): boolean => JSON.stringify(a) === JSON.stringify(b);

const itemKey = (v: unknown): string => {
  if (isObject(v)) {
    const id = v.id ?? v.eventId ?? v.event_id ?? v.key ?? v.roomId ?? v.room_id ?? v.mxc;
    if (typeof id === 'string' || typeof id === 'number') return `id:${String(id)}`;
  }
  return `json:${JSON.stringify(v)}`;
};

export type MergeResult = { value: unknown; added: number; conflicts: number };

/**
 * Pure: merge `incoming` into `current`. Lists: add items that are missing
 * (matched by id, else by content). Objects: add missing keys, recurse into
 * shared ones. A differing leaf is a conflict: `preferIncoming` decides.
 */
export const mergeData = (
  current: unknown,
  incoming: unknown,
  preferIncoming = false,
): MergeResult => {
  if (current === undefined || current === null) {
    return { value: incoming, added: incoming === undefined ? 0 : 1, conflicts: 0 };
  }
  if (Array.isArray(current) && Array.isArray(incoming)) {
    const have = new Map(current.map((v, i) => [itemKey(v), i]));
    const out = [...current];
    let added = 0;
    let conflicts = 0;
    incoming.forEach((item) => {
      const k = itemKey(item);
      const at = have.get(k);
      if (at === undefined) {
        out.push(item);
        have.set(k, out.length - 1);
        added += 1;
      } else if (!same(out[at], item)) {
        conflicts += 1;
        if (preferIncoming) out[at] = item;
      }
    });
    return { value: out, added, conflicts };
  }
  if (isObject(current) && isObject(incoming)) {
    const out: Record<string, unknown> = { ...current };
    let added = 0;
    let conflicts = 0;
    Object.entries(incoming).forEach(([k, v]) => {
      if (!(k in current)) {
        out[k] = v;
        added += 1;
        return;
      }
      const r = mergeData(current[k], v, preferIncoming);
      out[k] = r.value;
      added += r.added;
      conflicts += r.conflicts;
    });
    return { value: out, added, conflicts };
  }
  if (same(current, incoming)) return { value: current, added: 0, conflicts: 0 };
  return { value: preferIncoming ? incoming : current, added: 0, conflicts: 1 };
};

export type ImportPlanItem = {
  key: string;
  label: string;
  added: number;
  conflicts: number;
};

/** What importing `file` into the current data would change, per category. */
export const planImport = (
  file: ExportFile,
  current: {
    accountData: Record<string, unknown>;
    decoration: string | null;
    localSettings: Record<string, unknown> | null;
  },
): ImportPlanItem[] => {
  const items: ImportPlanItem[] = [];
  EXPORT_ACCOUNT_DATA.forEach(({ type, label }) => {
    if (!(type in file.accountData)) return;
    const r = mergeData(current.accountData[type], file.accountData[type]);
    items.push({ key: type, label, added: r.added, conflicts: r.conflicts });
  });
  if (file.profile.decoration !== null) {
    const differs = current.decoration !== file.profile.decoration;
    items.push({
      key: 'profile.decoration',
      label: 'Avatar decoration',
      added: !current.decoration && differs ? 1 : 0,
      conflicts: current.decoration && differs ? 1 : 0,
    });
  }
  if (file.local.settings) {
    const r = mergeData(current.localSettings ?? {}, file.local.settings);
    items.push({
      key: 'local.settings',
      label: "This device's settings",
      added: r.added,
      conflicts: r.conflicts,
    });
  }
  return items;
};