using StackExchange.Redis;

namespace w4c_workflows.Services;

/// <summary>Distributed lease over Redis for in-flight run state.</summary>
public interface ILeaseService
{
    Task<bool> AcquireAsync(string tenantId, string runId, string owner, TimeSpan ttl);
    Task<bool> RenewAsync(string tenantId, string runId, string owner, TimeSpan ttl);
    Task<bool> ReleaseAsync(string tenantId, string runId, string owner);
}

/// <summary>
/// Lease / distributed lock over Redis for in-flight run state:
///   wf:{tenant}:leases:{runId} → owner id, with a TTL.
/// Acquire is atomic (SET NX PX); release compares the owner before deleting so
/// a stale owner can never release someone else's lease.
/// </summary>
public class LeaseService : ILeaseService
{
    // Compare-and-delete: only delete if the value still matches the owner.
    private const string ReleaseScript =
        "if redis.call('GET', KEYS[1]) == ARGV[1] then return redis.call('DEL', KEYS[1]) else return 0 end";

    private readonly IDatabase _db;

    public LeaseService(IConnectionMultiplexer redis)
    {
        _db = redis.GetDatabase();
    }

    private static RedisKey KeyFor(string tenantId, string runId) => $"wf:{tenantId}:leases:{runId}";

    /// <summary>Atomically acquires the lease; returns false if already held.</summary>
    public Task<bool> AcquireAsync(string tenantId, string runId, string owner, TimeSpan ttl)
        => _db.StringSetAsync(KeyFor(tenantId, runId), owner, ttl, When.NotExists);

    /// <summary>Extends the TTL if (and only if) the caller still owns the lease.</summary>
    public async Task<bool> RenewAsync(string tenantId, string runId, string owner, TimeSpan ttl)
    {
        var current = await _db.StringGetAsync(KeyFor(tenantId, runId));
        if (current != owner)
            return false;
        return await _db.KeyExpireAsync(KeyFor(tenantId, runId), ttl);
    }

    /// <summary>Releases the lease only if the caller owns it.</summary>
    public async Task<bool> ReleaseAsync(string tenantId, string runId, string owner)
    {
        var result = await _db.ScriptEvaluateAsync(
            ReleaseScript, new RedisKey[] { KeyFor(tenantId, runId) }, new RedisValue[] { owner });
        return (long)result == 1;
    }
}