using ClaudeDo.Data;
using ClaudeDo.Data.Models;
using ClaudeDo.Data.Repositories;
using ClaudeDo.Worker.External;
using ClaudeDo.Worker.Hub;
using ClaudeDo.Worker.Usage;
using Microsoft.EntityFrameworkCore;

namespace ClaudeDo.Worker.Runner;

/// <summary>
/// Hands a PowerUse list-handler round over cleanly across the 5h usage limit, instead of letting it
/// die mid-merge:
///
/// 1. <b>Warn</b> — once per round, as soon as the 5h window crosses
///    <c>AppSettings.PowerUseHandoffPct</c>, a message is typed straight into the live ConPTY session
///    (<c>HandlerUsageWarning</c> → Mission Control) telling it to finish what it is doing and call
///    <c>handoff_list_handler</c> itself. A session that hands off on its own leaves no half-merged
///    tree behind; an auto-restart after the fact cannot clean one up.
/// 2. <b>Withhold</b> — the resulting handoff is not broadcast immediately (the next session would
///    open straight into the same exhausted window) but parked in <see cref="HandlerRoundState"/>
///    until the window resets. Same slot the auto-restart of a session that *did* die uses
///    (<see cref="HandlerRestartCoordinator"/>), so the two can never reopen one round twice.
/// 3. <b>Fire</b> — this service's tick is also what releases a parked handoff. Deliberately a poll
///    over the persisted state rather than a timer: a worker restart mid-wait re-picks the parked
///    handoff up on the next tick, and an overdue one goes out immediately, for free.
/// </summary>
public sealed class HandlerUsageGuard : BackgroundService
{
    internal static readonly TimeSpan TickInterval = TimeSpan.FromSeconds(30);

    // Small cushion past ResetsAt: the reported reset time is the server's, and reopening a session
    // one second early buys nothing but another dead tile.
    internal static readonly TimeSpan ResetGrace = TimeSpan.FromSeconds(60);

    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
    private readonly UsageState _usageState;
    private readonly HandlerRoundState _rounds;
    private readonly HandoffRoundTracker _handoffRounds;
    private readonly HubBroadcaster _broadcaster;
    private readonly ILogger<HandlerUsageGuard> _logger;

    public HandlerUsageGuard(
        IDbContextFactory<ClaudeDoDbContext> dbFactory,
        UsageState usageState,
        HandlerRoundState rounds,
        HandoffRoundTracker handoffRounds,
        HubBroadcaster broadcaster,
        ILogger<HandlerUsageGuard> logger)
    {
        _dbFactory = dbFactory;
        _usageState = usageState;
        _rounds = rounds;
        _handoffRounds = handoffRounds;
        _broadcaster = broadcaster;
        _logger = logger;
    }

    /// <summary>Test seam — a real 5h wait is not a test.</summary>
    internal Func<DateTimeOffset> NowUtc { get; set; } = () => DateTimeOffset.UtcNow;

    /// <summary>PowerUse verdict for one handler task: both PowerUse switches on, a 5h bucket
    /// available, plus the configured threshold and the task's display number.</summary>
    internal sealed record Policy(int HandoffPct, UsageBucket FiveHour, int Number);

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                await TickAsync(stoppingToken);
                await Task.Delay(TickInterval, stoppingToken);
            }
            catch (OperationCanceledException)
            {
                return;
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "HandlerUsageGuard: tick failed");
                await Task.Delay(TickInterval, stoppingToken);
            }
        }
    }

    internal async Task TickAsync(CancellationToken ct)
    {
        foreach (var round in _rounds.All())
        {
            await FireIfDueAsync(round);
            await WarnIfNearLimitAsync(round, ct);
        }
    }

    /// <summary>Called by <c>handoff_list_handler</c>. Returns the time the handoff was parked until
    /// when it must be withheld, or null when it should go out now (PowerUse off for this list, well
    /// below the threshold, or no reset time to wait for).</summary>
    public async Task<DateTimeOffset?> TryDeferHandoffAsync(
        string handlerTaskId, IReadOnlyList<string> survivingTaskIds, string phase, CancellationToken ct)
    {
        var policy = await EvaluateAsync(handlerTaskId, ct);
        if (policy is null) return null;

        // The warning flag matters on its own: utilization can dip back under the threshold between
        // the warning and the session actually finishing its merge, and a handoff produced *because*
        // of the warning must still wait for the reset.
        var warned = _rounds.Get(handlerTaskId)?.UsageWarningSent == true;
        if (policy.FiveHour.Utilization < policy.HandoffPct && !warned) return null;

        if (policy.FiveHour.ResetsAt is not { } resetsAt)
        {
            _logger.LogWarning(
                "HandlerUsageGuard: 5h window at {Pct}% has no reset time; handing off {TaskId} immediately",
                policy.FiveHour.Utilization, handlerTaskId);
            return null;
        }

        var dueAt = resetsAt + ResetGrace;
        _rounds.SetDeferredHandoff(handlerTaskId, dueAt, phase, survivingTaskIds);
        await _broadcaster.WorkerLog(
            $"List handler #{policy.Number}: handoff to phase {phase} withheld until " +
            $"{dueAt.ToLocalTime():HH:mm} (5h window at {policy.FiveHour.Utilization:0}%)",
            WorkerLogLevel.Warn, DateTime.UtcNow);
        return dueAt;
    }

    private async Task FireIfDueAsync(HandlerRound round)
    {
        if (round.DeferredHandoffAt is not { } dueAt || dueAt > NowUtc()) return;

        if (round.DeferredPhase is not { Length: > 0 } phase || round.DeferredTaskIds is not { Count: > 0 } taskIds)
        {
            _rounds.ClearDeferredHandoff(round.HandlerTaskId, spendAutoRestart: false);
            return;
        }

        // Cleared BEFORE the broadcast so a throw on the way out can't leave a slot that re-fires on
        // every tick; the restart budget is spent here too, which is the point of the whole
        // rework -- it is now only spent once a handoff really went out.
        _rounds.ClearDeferredHandoff(round.HandlerTaskId, spendAutoRestart: round.DeferredIsAutoRestart);

        await _broadcaster.HandoffRequested(round.HandlerTaskId, taskIds, phase);
        await _broadcaster.WorkerLog(
            $"Reopening list handler at phase {phase} after the usage-limit reset",
            WorkerLogLevel.Info, DateTime.UtcNow);
    }

    private async Task WarnIfNearLimitAsync(HandlerRound round, CancellationToken ct)
    {
        if (round.UsageWarningSent) return;
        // A sealed chain has no further handoff to ask for -- telling it to call
        // handoff_list_handler would only earn the session an exception.
        if (_handoffRounds.GetState(round.HandlerTaskId).Sealed) return;

        var policy = await EvaluateAsync(round.HandlerTaskId, ct);
        if (policy is null || policy.FiveHour.Utilization < policy.HandoffPct) return;
        if (!_rounds.TryMarkUsageWarned(round.HandlerTaskId)) return;

        await _broadcaster.HandlerUsageWarning(
            round.HandlerTaskId, BuildWarning(round.HandlerTaskId, round.Phase, policy.FiveHour.Utilization));
        await _broadcaster.WorkerLog(
            $"List handler #{policy.Number}: warned the session at 5h {policy.FiveHour.Utilization:0}% " +
            $"(handoff threshold {policy.HandoffPct}%)",
            WorkerLogLevel.Warn, DateTime.UtcNow);
    }

    // Plain ASCII on purpose: this is typed character-by-character into a PTY, not rendered by us.
    internal static string BuildWarning(string handlerTaskId, string phase, double utilization) =>
        $"USAGE LIMIT IMMINENT ({utilization:0}% of the 5h window). Finish or abort the merge you are " +
        "in - never leave conflict markers in the tree - then call " +
        $"handoff_list_handler(taskId: \"{handlerTaskId}\", survivingTaskIds: <every task not yet Done>, " +
        $"nextPhase: \"{NextPhaseFor(phase)}\") right now. Do not start anything new. " +
        "The next session opens automatically after the limit resets.";

    // The session should resume where it is, so the warning names its own phase back. The opening
    // triage round is the exception: "triage" is not a handoff phase, and what follows triage is
    // always the wait phase.
    private static string NextPhaseFor(string phase) =>
        MergeHelperPhase.All.Contains(phase, StringComparer.Ordinal) ? phase : MergeHelperPhase.Wait;

    /// <summary>Both PowerUse switches, exactly as <c>ComposeHandlerPromptAsync</c> and
    /// <see cref="HandlerRestartCoordinator"/> gate them — the global toggle alone must not make an
    /// unrelated list's handler session get typed into. Null = leave this round alone.</summary>
    private async Task<Policy?> EvaluateAsync(string handlerTaskId, CancellationToken ct)
    {
        if (_usageState.Snapshot?.FiveHour is not { } fiveHour) return null;

        try
        {
            await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
            var task = await new TaskRepository(ctx).GetByIdAsync(handlerTaskId, ct);
            if (task is null) return null;

            var settings = await new AppSettingsRepository(ctx).GetAsync(ct);
            if (!settings.PowerUseEnabled) return null;
            if ((await new ListRepository(ctx).GetConfigAsync(task.ListId, ct))?.PowerUseAllowed != true) return null;

            return new Policy(Math.Clamp(settings.PowerUseHandoffPct, 50, 99), fiveHour, task.Number);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "HandlerUsageGuard: could not evaluate handler task {TaskId}", handlerTaskId);
            return null;
        }
    }
}