/**
 * Restores a backup pulled from the master onto THIS machine — the other half
 * of lib/backup-sync.ts, for replacing a dead VPS.
 *
 * Applying a backup overwrites this machine's settings, broker credentials,
 * instruments and assignments, and — the point of the exercise — adopts the
 * backed-up instance's uuid and name, so the master's roster, payouts and card
 * links carry straight on. The master already handles adoption: a hello
 * presenting a known uuid lands on that person's roster row.
 *
 * Run it before first boot via scripts/seed-settings.js --restore-from (which
 * duplicates this apply logic — keep them in sync), or from the settings UI
 * via POST /api/backup/restore. Either way the old machine must be stopped
 * first: two live instances presenting one uuid fight over the socket.
 */

import {
    setSetting,
    getSetting,
    setCredentials,
    setInstrumentEnabled,
    restoreAssignment,
    runInTransaction,
} from './db';
import type { BackupPayload } from './backup-sync';

/** Mirror of the master's listing rows (lib/backups.ts BackupMeta). */
export interface BackupMeta {
    id: string;
    name: string;
    savedAt: string;
    sizeBytes: number;
}

const FETCH_TIMEOUT_MS = 15_000;

// Runtime bookkeeping describing the machine the backup was taken on, not
// this one. Kept in sync with the skip-set in scripts/seed-settings.js.
const RESTORE_SKIP_KEYS = new Set([
    'runner_heartbeat',
    'catalog_last_sync_at',
    'catalog_last_error',
    'backup_last_push_at',
    'backup_last_error',
]);

function authedFetch(masterUrl: string, token: string, path: string) {
    const url = new URL(path, masterUrl);
    return fetch(url, {
        headers: { authorization: `Bearer ${token}` },
        signal: AbortSignal.timeout(FETCH_TIMEOUT_MS),
    });
}

export async function fetchBackupList(masterUrl: string, token: string): Promise<BackupMeta[]> {
    const res = await authedFetch(masterUrl, token, '/api/instances/backup');
    if (!res.ok) {
        const detail = await res.json().then((b) => b?.error).catch(() => '');
        throw new Error(`master returned ${res.status}${detail ? ` — ${detail}` : ''}`);
    }
    const body = await res.json();
    if (!Array.isArray(body?.backups)) throw new Error('unrecognized backup list');
    return body.backups as BackupMeta[];
}

export async function fetchBackup(masterUrl: string, token: string, id: string): Promise<BackupPayload> {
    const res = await authedFetch(masterUrl, token, `/api/instances/backup/${encodeURIComponent(id)}`);
    if (!res.ok) {
        const detail = await res.json().then((b) => b?.error).catch(() => '');
        throw new Error(`master returned ${res.status}${detail ? ` — ${detail}` : ''}`);
    }
    const payload = await res.json() as BackupPayload;
    if (payload?.v !== 1 || typeof payload.settings !== 'object' || payload.settings === null) {
        throw new Error('unrecognized backup payload');
    }
    return payload;
}

export interface RestoreCounts {
    settings: number;
    credentials: number;
    instruments: number;
    assignments: number;
}

/**
 * Overwrites this machine's configuration with the backup, including
 * instance_id and instance_name — the identity adoption. Callers restart the
 * process afterwards: live platform clients, the master link's hello and any
 * cached settings all predate the restore.
 */
export function applyBackup(payload: BackupPayload, opts: { keepMasterUrl?: boolean } = {}): RestoreCounts {
    // Defaults to keeping this machine's master url: the machine is talking to
    // that master right now, while an old backup may point at a dead host.
    const keepMasterUrl = opts.keepMasterUrl ?? true;
    const ownMasterUrl = getSetting('master_dashboard_url');
    const ownToken = getSetting('master_backup_token');

    const counts: RestoreCounts = { settings: 0, credentials: 0, instruments: 0, assignments: 0 };

    runInTransaction(() => {
        for (const [key, value] of Object.entries(payload.settings)) {
            if (RESTORE_SKIP_KEYS.has(key)) continue;
            if (typeof value !== 'string') continue;
            setSetting(key, value);
            counts.settings++;
        }
        if (keepMasterUrl && ownMasterUrl) setSetting('master_dashboard_url', ownMasterUrl);
        if (ownToken) setSetting('master_backup_token', ownToken);

        for (const c of payload.credentials ?? []) {
            setCredentials(c.firm_id, c.firm_name, c.username, c.password, c.api_key ?? '');
            counts.credentials++;
        }
        for (const i of payload.instruments ?? []) {
            setInstrumentEnabled(i.symbol, i.enabled);
            counts.instruments++;
        }
        // Rules dates travel with them: a restored machine must not date
        // its accounts afresh, or old ones would leave their kept rules.
        for (const a of payload.assignments ?? []) {
            restoreAssignment(a);
            counts.assignments++;
        }
    });

    return counts;
}