import { mkdir, open, realpath, rm } from 'node:fs/promises';
import { basename, dirname, isAbsolute, join, resolve } from 'node:path';

export interface FixtureOptions { dbPath: string; now: number; watch: boolean }

export function parseFixtureOptions(args: string[], clock = Date.now()): FixtureOptions {
    let dbPath = '', now = clock, watch = false, explicitTime = false;
    const seen = new Set<string>();
    for (let index = 0; index < args.length; index++) {
        const option = args[index];
        if (seen.has(option)) throw new Error(`Duplicate option: ${option}`);
        seen.add(option);
        if (option === '--watch') { watch = true; continue; }
        if (option !== '--db' && option !== '--now') throw new Error(`Unknown option: ${option}`);
        const value = args[++index];
        if (!value || value.startsWith('--')) throw new Error(`Missing value for ${option}.`);
        if (option === '--db') dbPath = value;
        else {
            if (!/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(?:\.\d{1,3})?(?:Z|[+-]\d{2}:\d{2})$/.test(value)
                || !Number.isFinite(Date.parse(value))) throw new Error('--now must be an ISO timestamp with a timezone.');
            now = Date.parse(value); explicitTime = true;
        }
    }
    if (!dbPath || !isAbsolute(dbPath)) throw new Error('Provide --db with an absolute path inside a new fixture directory. DB_PATH is never used.');
    if (!Number.isFinite(now)) throw new Error('Invalid fixture clock.');
    if (watch && explicitTime) throw new Error('Use --watch for live time or --now for a fixed snapshot, separately.');
    return { dbPath: resolve(dbPath), now, watch };
}

/** An atomic new-directory reservation rejects existing DBs, sidecars and symlinks together. */
export async function reserveFixture(dbPath: string): Promise<{ root: string; dbPath: string }> {
    if (!isAbsolute(dbPath)) throw new Error('Fixture database path must be absolute.');
    const requested = resolve(dbPath);
    const requestedRoot = dirname(requested);
    // The destination's parent must already exist. Canonicalize /tmp on macOS,
    // but never follow a pre-existing fixture directory or database symlink.
    const parent = await realpath(dirname(requestedRoot));
    const root = join(parent, basename(requestedRoot));
    try { await mkdir(root, { mode: 0o700 }); }
    catch (cause) {
        if ((cause as NodeJS.ErrnoException).code === 'EEXIST') throw new Error('Fixture directory already exists. Choose a new directory; existing data is never overwritten.');
        throw cause;
    }
    const target = join(root, basename(requested));
    try {
        const file = await open(target, 'wx', 0o600);
        await file.close();
    } catch (error) {
        await rm(root, { recursive: true, force: true });
        throw error;
    }
    return { root, dbPath: target };
}