/**
 * Redis-backed distributed lock provider using atomic `SET NX` operations.
 *
 * Implements the `LockProvider` interface with owner-based release semantics:
 * a lock is only released if the requesting instance owns it, preventing
 * accidental release of another process's lock after TTL expiry.
 *
 * @module redis-lock-provider
 */

import type { RedisClientAdapter } from "../store/adapter.types.js";
import type { LockProvider } from "../types/idempotency.types.js";

/** Configuration for `RedisLockProvider`. */
export interface RedisLockProviderConfig {
    /** Redis client adapter. */
    readonly client: RedisClientAdapter;
    /** Key prefix for lock keys. Default: `'lock:'`. */
    readonly prefix?: string;
    /** Unique identifier for this lock owner (e.g. worker ID). */
    readonly ownerId?: string;
}

/**
 * Redis-backed distributed lock using `SET NX` with TTL.
 *
 * Owner-verified release ensures that only the process that acquired the
 * lock can release it — safe for use in distributed multi-process deployments.
 */
export class RedisLockProvider implements LockProvider {
    protected readonly client: RedisClientAdapter;
    protected readonly prefix: string;
    protected readonly ownerId: string;

    constructor(config: RedisLockProviderConfig) {
        this.client = config.client;
        this.prefix = config.prefix ?? "lock:";
        this.ownerId =
            config.ownerId ??
            `owner-${Date.now()}-${Math.random().toString(36).slice(2)}`;
    }

    /**
     * Attempt to acquire the lock for `resource` with the given TTL.
     * Returns `true` if the lock was acquired, `false` if already held.
     */
    async acquire(resource: string, ttlMs: number): Promise<boolean> {
        const key = `${this.prefix}${resource}`;
        return this.client.setNx(key, this.ownerId, ttlMs);
    }

    /**
     * Release the lock for `resource` if this instance owns it.
     * No-ops if the lock is not held or was taken by another owner.
     */
    async release(resource: string): Promise<void> {
        const key = `${this.prefix}${resource}`;
        const value = await this.client.get(key);
        if (value === this.ownerId) {
            await this.client.del(key);
        }
    }
}