using System;
using System.Threading;
using System.Threading.Tasks;

namespace ytLive.Services;

/// <summary>What YouTube says about the broadcast once a push is back.</summary>
public enum BroadcastLiveness
{
    /// <summary>Could not tell (no token, network, API hiccup) — treat as recovered.</summary>
    Unknown,

    /// <summary>The broadcast is still live/ready: the push landed and the show continues.</summary>
    Live,

    /// <summary>The broadcast is complete. It cannot be resumed; the push is talking to a dead ingest.</summary>
    Complete,
}

/// <summary>Everything the recovery loop needs from the app, as delegates so it can be tested
/// without ffmpeg, without a network, and without a window.</summary>
public sealed class StreamRecoverySteps
{
    /// <summary>Recreates the audio pipe server. The old one is unusable after its client died
    /// (single-instance server), and the encoder cannot start without it.</summary>
    public required Func<CancellationToken, Task> RestartAudio { get; init; }

    /// <summary>Starts the push. True when the encoder came up.</summary>
    public required Func<CancellationToken, Task<bool>> StartPush { get; init; }

    /// <summary>Asks YouTube whether the broadcast survived. Only called after a push starts.</summary>
    public required Func<CancellationToken, Task<BroadcastLiveness>> CheckBroadcast { get; init; }

    /// <summary>State for the alert stack: attempt numbers and the outcome.</summary>
    public required Action<string> Report { get; init; }

    /// <summary>The record: one line per attempt, into the app log.</summary>
    public required Action<string> Log { get; init; }

    public Func<TimeSpan, CancellationToken, Task> Delay { get; init; }
        = (delay, ct) => delay <= TimeSpan.Zero ? Task.CompletedTask : Task.Delay(delay, ct);
}

public enum RecoveryOutcome
{
    Recovered,
    GaveUp,
    Cancelled,
    BroadcastComplete,
}

public sealed record RecoveryResult(RecoveryOutcome Outcome, int Attempts, TimeSpan Elapsed);

/// <summary>
/// TASK 32·1 — the blip retry. When the encoder dies while the session is live, relaunch the same push
/// against the same ingest, restarting the audio pipe each time (its server is single-instance and the
/// dead client leaves it unusable).
/// <para><b>The check that stops us lying:</b> a reconnect can succeed at the socket level after
/// YouTube has already ended the broadcast. So each successful start asks the API whether the broadcast
/// is still there; "complete" ends recovery instead of showing a live sign over a dead stream.</para>
/// </summary>
public sealed class StreamRecovery
{
    private readonly StreamRetryPolicy _policy;
    private readonly StreamRecoverySteps _steps;

    public StreamRecovery(StreamRetryPolicy policy, StreamRecoverySteps steps)
    {
        _policy = policy;
        _steps = steps;
    }

    public async Task<RecoveryResult> RunAsync(CancellationToken cancellationToken = default)
    {
        var clock = System.Diagnostics.Stopwatch.StartNew();
        var attempts = 0;

        for (var attempt = 0; attempt < _policy.Attempts; attempt++)
        {
            if (cancellationToken.IsCancellationRequested) return Result(RecoveryOutcome.Cancelled);
            attempts = attempt + 1;

            var wait = _policy.WaitBefore(attempt);
            if (wait > TimeSpan.Zero)
            {
                try { await _steps.Delay(wait, cancellationToken).ConfigureAwait(false); }
                catch (OperationCanceledException) { return Result(RecoveryOutcome.Cancelled); }
            }

            if (cancellationToken.IsCancellationRequested) return Result(RecoveryOutcome.Cancelled);

            _steps.Report($"Stream dropped — reconnecting (attempt {attempts} of {_policy.Attempts})");
            _steps.Log($"RECONNECT: attempt {attempts} of {_policy.Attempts} — restarting the audio pipe and the push");

            try
            {
                await _steps.RestartAudio(cancellationToken).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                _steps.Log($"RECONNECT: audio pipe restart failed on attempt {attempts}: {ex.Message}");
                continue;
            }

            bool started;
            try
            {
                started = await _steps.StartPush(cancellationToken).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                _steps.Log($"RECONNECT: push restart failed on attempt {attempts}: {ex.Message}");
                continue;
            }

            if (!started)
            {
                _steps.Log($"RECONNECT: attempt {attempts} of {_policy.Attempts} failed — the encoder did not come up");
                continue;
            }

            var liveness = BroadcastLiveness.Unknown;
            try
            {
                liveness = await _steps.CheckBroadcast(cancellationToken).ConfigureAwait(false);
            }
            catch (Exception ex)
            {
                _steps.Log($"RECONNECT: could not check the broadcast on attempt {attempts}: {ex.Message}");
            }

            if (liveness == BroadcastLiveness.Complete)
            {
                _steps.Report("Stream ended — YouTube reports this broadcast complete. It cannot be resumed.");
                _steps.Log("RECONNECT: push came back, but the broadcast is complete — cannot resume");
                return Result(RecoveryOutcome.BroadcastComplete);
            }

            _steps.Report($"Stream recovered after {clock.Elapsed.TotalSeconds:0.0} s");
            _steps.Log($"RECONNECT: push re-established after {clock.Elapsed.TotalSeconds:0.0} s — still live");
            return Result(RecoveryOutcome.Recovered);
        }

        _steps.Report($"Stream dropped — {_policy.Attempts} attempts failed. The stream is off air.");
        _steps.Log($"RECONNECT: gave up after {_policy.Attempts} attempts — stream is off air");
        return Result(RecoveryOutcome.GaveUp);

        RecoveryResult Result(RecoveryOutcome outcome) => new(outcome, attempts, clock.Elapsed);
    }
}