using ClaudeDo.Data;
using ClaudeDo.Data.Models;
using ClaudeDo.Data.Repositories;
using ClaudeDo.Worker.Git;
using ClaudeDo.Worker.Hub;
using ClaudeDo.Worker.Planning;
using ClaudeDo.Worker.Queue;
using ClaudeDo.Worker.Tickets;
using Microsoft.EntityFrameworkCore;
using TaskStatus = ClaudeDo.Data.Models.TaskStatus;

namespace ClaudeDo.Worker.State;

public sealed class TaskStateService : ITaskStateService
{
    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
    private readonly HubBroadcaster _broadcaster;
    private readonly IQueueWaker _waker;
    private readonly PlanningChainCoordinator _chain;
    private readonly RunCancellationRegistry _runCancels;
    private readonly Func<IActiveMergeState> _mergeState;
    private readonly BaseDirtyChecker _baseDirtyChecker;
    private readonly ILogger<TaskStateService> _logger;
    private readonly TicketStatusSync _ticketSync;

    public TaskStateService(
        IDbContextFactory<ClaudeDoDbContext> dbFactory,
        HubBroadcaster broadcaster,
        IQueueWaker waker,
        PlanningChainCoordinator chain,
        RunCancellationRegistry runCancels,
        Func<IActiveMergeState> mergeState,
        BaseDirtyChecker baseDirtyChecker,
        ILogger<TaskStateService> logger,
        TicketStatusSync ticketSync)
    {
        _dbFactory = dbFactory;
        _broadcaster = broadcaster;
        _waker = waker;
        _chain = chain;
        _runCancels = runCancels;
        _mergeState = mergeState;
        _baseDirtyChecker = baseDirtyChecker;
        _logger = logger;
        _ticketSync = ticketSync;
    }

    public async Task<TransitionResult> EnqueueAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);

        if (await IsDraftChildAsync(ctx, taskId, ct))
            return new TransitionResult(false, "Draft subtask: finalize the plan before queuing it.");

        if (await IsManualAsync(ctx, taskId, ct))
            return new TransitionResult(false, "Manual task: mark it as a Claude task before queuing it.");

        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
            .ExecuteUpdateAsync(s => s.SetProperty(t => t.Status, TaskStatus.Queued), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task not found or already running.");

        _waker.Wake();
        await NotifyAsync(taskId);

        // Heads-up only: a worktree forks from the commit tip (WorktreeManager.ResolveBaseCommitAsync),
        // not the working tree, so uncommitted changes sitting in the list's repo right now are
        // invisible to this (and every other) queued task. Never blocks the transition above.
        var workingDir = await ctx.Tasks.AsNoTracking()
            .Where(t => t.Id == taskId)
            .Select(t => t.List.WorkingDir)
            .FirstOrDefaultAsync(ct);
        var baseDirty = await _baseDirtyChecker.CheckAsync(workingDir, ct);

        return new TransitionResult(true, null, baseDirty);
    }

    public async Task<TransitionResult> StartRunningAsync(string taskId, DateTime startedAt, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);

        if (await IsDraftChildAsync(ctx, taskId, ct))
            return new TransitionResult(false, "Draft subtask: finalize the plan before running it.");

        if (await IsManualAsync(ctx, taskId, ct))
            return new TransitionResult(false, "Manual task: mark it as a Claude task before running it.");

        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.Running)
                .SetProperty(t => t.StartedAt, startedAt), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task already running or not found.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> CompleteAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct)
    {
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            var affected = await ctx.Tasks
                .Where(t => t.Id == taskId && t.Status == TaskStatus.Running)
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.Done)
                    .SetProperty(t => t.FinishedAt, finishedAt)
                    .SetProperty(t => t.Result, result), ct);

            if (affected == 0)
                return new TransitionResult(false, "Task not running; cannot complete.");
        }

        await OnChildTerminalAsync(taskId, TaskStatus.Done);
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> SubmitForReviewAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status == TaskStatus.Running)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.WaitingForReview)
                .SetProperty(t => t.FinishedAt, finishedAt)
                .SetProperty(t => t.Result, result), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task not running; cannot submit for review.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    // Submit an interactively-worked task (a ConPTY session left its worktree with commits/changes)
    // for review. Unlike SubmitForReviewAsync — which only fires from the headless Running state —
    // this transitions from Idle or Failed, the states an interactive task sits in after the user
    // finishes the session by hand. The caller commits the worktree first so there is a diff to merge.
    public async Task<TransitionResult> SubmitInteractiveForReviewAsync(string taskId, DateTime finishedAt, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && (t.Status == TaskStatus.Idle || t.Status == TaskStatus.Failed))
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.WaitingForReview)
                .SetProperty(t => t.FinishedAt, finishedAt), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is not Idle or Failed; cannot submit for review.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> SubmitForChildrenAsync(string taskId, DateTime finishedAt, string? result, CancellationToken ct)
    {
        PlanningPhase planningPhase;
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            var affected = await ctx.Tasks
                .Where(t => t.Id == taskId && t.Status == TaskStatus.Running)
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.WaitingForChildren)
                    .SetProperty(t => t.FinishedAt, finishedAt)
                    .SetProperty(t => t.Result, result), ct);

            if (affected == 0)
                return new TransitionResult(false, "Task not running; cannot submit for children.");

            planningPhase = await ctx.Tasks.AsNoTracking()
                .Where(t => t.Id == taskId)
                .Select(t => t.PlanningPhase)
                .FirstAsync(ct);
        }

        // A normal (non-planning) parent queues its own children as a sequential chain right
        // here; a planning parent's children wait for the user's explicit "Queue plan" action
        // (PlanningChainCoordinator.QueuePlanAsync), so leave those untouched. A child that's
        // already Running makes SetupChainAsync throw — log it rather than fail this transition.
        if (planningPhase == PlanningPhase.None)
        {
            try
            {
                await _chain.SetupChainAsync(taskId, enqueue: true, ct);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "SetupChainAsync failed for parent {TaskId}", taskId);
            }
        }

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> ApproveReviewAsync(string taskId, CancellationToken ct)
    {
        var now = DateTime.UtcNow;
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            var affected = await ctx.Tasks
                .Where(t => t.Id == taskId && t.Status == TaskStatus.WaitingForReview)
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.Done)
                    .SetProperty(t => t.FinishedAt, now), ct);

            if (affected == 0)
                return new TransitionResult(false, "Task is not waiting for review; cannot approve.");
        }

        await OnChildTerminalAsync(taskId, TaskStatus.Done);
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> RejectToQueueAsync(string taskId, string feedback, CancellationToken ct)
    {
        if (string.IsNullOrWhiteSpace(feedback))
            return new TransitionResult(false, "Feedback is required to reject for re-run.");

        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status == TaskStatus.WaitingForReview)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.Queued)
                .SetProperty(t => t.ReviewFeedback, feedback)
                .SetProperty(t => t.StartedAt, (DateTime?)null)
                .SetProperty(t => t.FinishedAt, (DateTime?)null), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is not waiting for review; cannot reject.");

        _waker.Wake();
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> RejectToIdleAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status == TaskStatus.WaitingForReview)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.Idle)
                .SetProperty(t => t.ReviewFeedback, (string?)null), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is not waiting for review; cannot park.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> ClearReviewFeedbackAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId)
            .ExecuteUpdateAsync(s => s.SetProperty(t => t.ReviewFeedback, (string?)null), ct);

        return affected == 0
            ? new TransitionResult(false, "Task not found.")
            : new TransitionResult(true, null);
    }

    public async Task<TransitionResult> FailAsync(
        string taskId, DateTime finishedAt, string? error, CancellationToken ct,
        string failureReason = "error", int? turnsUsed = null, int? maxTurns = null)
    {
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            // Queued is intentional: OverrideSlotService dispatches RunAsync before calling
            // StartRunningAsync, so a preflight failure (list not found, worktree setup) can
            // reach MarkFailed while the task is still Queued in the DB.
            var affected = await ctx.Tasks
                .Where(t => t.Id == taskId &&
                    (t.Status == TaskStatus.Running || t.Status == TaskStatus.Queued))
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.Failed)
                    .SetProperty(t => t.FinishedAt, finishedAt)
                    .SetProperty(t => t.Result, error)
                    .SetProperty(t => t.FailureReason, failureReason)
                    .SetProperty(t => t.FailureTurnsUsed, turnsUsed)
                    .SetProperty(t => t.FailureMaxTurns, maxTurns), ct);

            if (affected == 0)
                return new TransitionResult(false, "Task not in a failable state (must be Running or Queued).");
        }

        await OnChildTerminalAsync(taskId, TaskStatus.Failed);
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    // retire: only the user-facing "mark cancelled" paths (update_task_status, the row's
    // "Mark as" menu) set this — it lets an Idle or Failed task be retired without deleting it.
    // Every other caller (hub CancelReview, PlanningChainCoordinator's chain-walk, batch cancel)
    // relies on Idle staying a no-op here; PlanningChainCoordinator specifically uses "parked
    // back to Idle" as a deliberate opt-out signal, so do not flip this default.
    public async Task<TransitionResult> CancelAsync(
        string taskId, DateTime finishedAt, CancellationToken ct, bool retire = false)
    {
        // A unit merge drains its children's worktrees onto the target branch while the parent
        // sits in WaitingForReview for the whole (potentially minutes-long) drain. Cancelling out
        // from under it would flip the parent to Cancelled while the orchestrator keeps merging —
        // FinalizeParentDoneAsync then finds the parent no longer WaitingForReview and gives up,
        // leaving the merged children's diffs stranded with no way to roll them back.
        if (await _mergeState().HasActiveMergeAsync(taskId, ct))
            return new TransitionResult(false, "A merge is in progress for this task; wait for it to finish before cancelling.");

        List<string> cancelledChildIds;
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            var affected = await ctx.Tasks
                .Where(t => t.Id == taskId &&
                    (t.Status == TaskStatus.Running || t.Status == TaskStatus.Queued
                     || t.Status == TaskStatus.WaitingForReview
                     || t.Status == TaskStatus.WaitingForChildren
                     || (retire && (t.Status == TaskStatus.Idle || t.Status == TaskStatus.Failed))))
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.Cancelled)
                    .SetProperty(t => t.FinishedAt, finishedAt), ct);

            if (affected == 0)
                return new TransitionResult(false, "Task not in cancellable state.");

            // Cascade to this task's own non-terminal children (one level — children are
            // leaves in the current model) so a Queued/Running child doesn't keep going
            // against a parent that's already gone, orphaning its worktree commit.
            cancelledChildIds = await ctx.Tasks
                .Where(t => t.ParentTaskId == taskId
                    && t.Status != TaskStatus.Done
                    && t.Status != TaskStatus.Failed
                    && t.Status != TaskStatus.Cancelled)
                .Select(t => t.Id)
                .ToListAsync(ct);

            if (cancelledChildIds.Count > 0)
                await ctx.Tasks
                    .Where(t => cancelledChildIds.Contains(t.Id))
                    .ExecuteUpdateAsync(s => s
                        .SetProperty(t => t.Status, TaskStatus.Cancelled)
                        .SetProperty(t => t.FinishedAt, finishedAt)
                        .SetProperty(t => t.BlockedByTaskId, (string?)null), ct);
        }

        // Also stop the actual Claude processes: the DB flip above doesn't reach a run
        // already executing in a queue/override slot — without this it would keep going
        // and only fail its final (now-invalid) transition.
        _runCancels.TryCancel(taskId);
        foreach (var childId in cancelledChildIds)
            _runCancels.TryCancel(childId);

        await OnChildTerminalAsync(taskId, TaskStatus.Cancelled);
        await NotifyAsync(taskId);
        foreach (var childId in cancelledChildIds)
            await NotifyAsync(childId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> ResetToIdleAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.Idle)
                .SetProperty(t => t.StartedAt, (DateTime?)null)
                .SetProperty(t => t.FinishedAt, (DateTime?)null)
                .SetProperty(t => t.Result, (string?)null), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is running; cannot reset.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    /// <summary>Done/WaitingForReview → WaitingForReview after a reverted merge, so the task can be re-approved.</summary>
    public async Task<TransitionResult> ReopenForReviewAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId &&
                (t.Status == TaskStatus.Done || t.Status == TaskStatus.WaitingForReview))
            .ExecuteUpdateAsync(s => s.SetProperty(t => t.Status, TaskStatus.WaitingForReview), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is not Done or waiting for review; cannot reopen.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> MarkDoneAsync(string taskId, DateTime finishedAt, CancellationToken ct)
    {
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            // The done toggle is a manual "tick it off" affordance and works from every status
            // except Running (a live run keeps writing the row, so the picker/runner would race).
            // WaitingForReview is deliberately included: ticking a finished task done skips the
            // merge on purpose -- for a worktree-less list-handler task there is nothing to merge,
            // and for a worktree task the branch just stays Active for the worktrees overview.
            var affected = await ctx.Tasks
                .Where(t => t.Id == taskId && t.Status != TaskStatus.Running)
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.Done)
                    .SetProperty(t => t.FinishedAt, finishedAt), ct);

            if (affected == 0)
                return new TransitionResult(false, "Task is running or no longer exists; cannot mark done.");
        }

        await OnChildTerminalAsync(taskId, TaskStatus.Done);
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> UnmarkDoneAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status == TaskStatus.Done)
            .ExecuteUpdateAsync(s => s.SetProperty(t => t.Status, TaskStatus.Idle), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is not Done; cannot unmark.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> DequeueToIdleAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId && t.Status == TaskStatus.Queued)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.Idle)
                .SetProperty(t => t.BlockedByTaskId, (string?)null), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task is not queued; cannot remove from queue.");

        // A dequeued task may have been a planning-chain predecessor. Without unblocking its
        // successor here, the successor is left permanently wedged on a BlockedByTaskId link to
        // a task that has left the queue and will never reach the terminal state that would
        // otherwise resolve it (PlanningChainCoordinator.OnChildFinishedAsync).
        var successorId = await ctx.Tasks.AsNoTracking()
            .Where(t => t.BlockedByTaskId == taskId)
            .Select(t => t.Id)
            .FirstOrDefaultAsync(ct);
        if (successorId is not null)
            await UnblockAsync(successorId, ct);

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> StartPlanningAsync(string parentId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == parentId
                        && t.Status == TaskStatus.Idle
                        && t.PlanningPhase == PlanningPhase.None)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.PlanningPhase, PlanningPhase.Active), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task not in plannable state.");

        await NotifyAsync(parentId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> FinalizePlanningAsync(string parentId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var hasChildren = await ctx.Tasks.AnyAsync(t => t.ParentTaskId == parentId, ct);
        var newStatus = hasChildren ? TaskStatus.WaitingForChildren : TaskStatus.WaitingForReview;

        var affected = await ctx.Tasks
            .Where(t => t.Id == parentId && t.PlanningPhase == PlanningPhase.Active)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.PlanningPhase, PlanningPhase.Finalized)
                .SetProperty(t => t.PlanningFinalizedAt, DateTime.UtcNow)
                .SetProperty(t => t.PlanningSessionToken, (string?)null)
                .SetProperty(t => t.Status, newStatus), ct);

        if (affected == 0)
            return new TransitionResult(false, "No active planning session.");

        await NotifyAsync(parentId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> BlockOnAsync(string taskId, string predecessorTaskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId)
            .ExecuteUpdateAsync(s => s.SetProperty(t => t.BlockedByTaskId, predecessorTaskId), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task not found.");

        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> UnblockAsync(string taskId, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
        var affected = await ctx.Tasks
            .Where(t => t.Id == taskId)
            .ExecuteUpdateAsync(s => s.SetProperty(t => t.BlockedByTaskId, (string?)null), ct);

        if (affected == 0)
            return new TransitionResult(false, "Task not found.");

        _waker.Wake();
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    public async Task<TransitionResult> SetDependsOnAsync(
        string taskId, IReadOnlyList<string> dependsOnTaskIds, CancellationToken ct)
    {
        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);

        if (!await ctx.Tasks.AsNoTracking().AnyAsync(t => t.Id == taskId, ct))
            return new TransitionResult(false, "Task not found.");

        var wanted = dependsOnTaskIds.Distinct(StringComparer.Ordinal).ToList();

        if (wanted.Count > 0)
        {
            if (wanted.Contains(taskId, StringComparer.Ordinal))
                return new TransitionResult(false, "A task cannot depend on itself.");

            var known = await ctx.Tasks.AsNoTracking()
                .Where(t => wanted.Contains(t.Id))
                .Select(t => t.Id)
                .ToListAsync(ct);
            var missing = wanted.Except(known, StringComparer.Ordinal).FirstOrDefault();
            if (missing is not null)
                return new TransitionResult(false, $"Dependency task {missing} not found.");

            if (await WouldCycleAsync(ctx, taskId, wanted, ct))
                return new TransitionResult(false, "Setting this dependency would create a cycle.");
        }

        var existing = await ctx.TaskDependencies.AsNoTracking()
            .Where(d => d.TaskId == taskId)
            .Select(d => d.DependsOnTaskId)
            .ToListAsync(ct);

        var removed = existing.Except(wanted, StringComparer.Ordinal).ToList();
        var added = wanted.Except(existing, StringComparer.Ordinal).ToList();
        if (removed.Count == 0 && added.Count == 0)
            return new TransitionResult(true, null);

        if (removed.Count > 0)
            await ctx.TaskDependencies
                .Where(d => d.TaskId == taskId && removed.Contains(d.DependsOnTaskId))
                .ExecuteDeleteAsync(ct);

        if (added.Count > 0)
        {
            ctx.TaskDependencies.AddRange(added.Select(id =>
                new TaskDependencyEntity { TaskId = taskId, DependsOnTaskId = id }));
            await ctx.SaveChangesAsync(ct);
        }

        // Dropping an edge may free up a Queued task the picker was skipping.
        if (removed.Count > 0) _waker.Wake();
        await NotifyAsync(taskId);
        return new TransitionResult(true, null);
    }

    // True when any proposed predecessor can already reach taskId through the dependency graph --
    // linking there would starve both ends forever, since the picker never claims either.
    // ponytail: loads the whole edge set (only *declared* dependencies land there, so it stays
    // small). Swap in a recursive CTE if task_dependencies ever grows past a few thousand rows.
    private static async Task<bool> WouldCycleAsync(
        ClaudeDoDbContext ctx, string taskId, IReadOnlyList<string> proposed, CancellationToken ct)
    {
        var edges = await ctx.TaskDependencies.AsNoTracking()
            .Select(d => new { d.TaskId, d.DependsOnTaskId })
            .ToListAsync(ct);
        var successors = edges
            .GroupBy(e => e.TaskId, StringComparer.Ordinal)
            .ToDictionary(g => g.Key, g => g.Select(e => e.DependsOnTaskId).ToList(), StringComparer.Ordinal);

        // `visited` also stops the walk looping forever on pre-existing bad data.
        var visited = new HashSet<string>(StringComparer.Ordinal);
        var frontier = new Queue<string>(proposed);
        while (frontier.Count > 0)
        {
            var current = frontier.Dequeue();
            if (current == taskId) return true;
            if (!visited.Add(current)) continue;
            if (successors.TryGetValue(current, out var next))
                foreach (var n in next) frontier.Enqueue(n);
        }
        return false;
    }

    public async Task<int> RecoverStaleRunningAsync(string reason, CancellationToken ct)
    {
        var resultText = "[stale] " + reason;
        var now = DateTime.UtcNow;
        List<string> recoveredIds;
        int affected;
        await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
        {
            recoveredIds = await ctx.Tasks
                .Where(t => t.Status == TaskStatus.Running)
                .Select(t => t.Id)
                .ToListAsync(ct);

            affected = await ctx.Tasks
                .Where(t => t.Status == TaskStatus.Running)
                .ExecuteUpdateAsync(s => s
                    .SetProperty(t => t.Status, TaskStatus.Failed)
                    .SetProperty(t => t.FinishedAt, now)
                    .SetProperty(t => t.Result, resultText), ct);
        }

        // A recovered task may have been a planning/improvement chain child or the last
        // non-terminal child of a WaitingForChildren parent. The bulk flip above skips the
        // usual terminal-transition side effects, so without this a crash mid-run would
        // leave the chain successor blocked forever and the parent wedged in
        // WaitingForChildren with nothing left to re-check it.
        foreach (var taskId in recoveredIds)
            await OnChildTerminalAsync(taskId, TaskStatus.Failed);

        return affected;
    }

    // A subtask is "draft" only while its planning parent has an open (Active) session.
    // Improvement children whose parent has PlanningPhase.None are not drafts and may be
    // queued freely. Standalone tasks (no parent) are never draft.
    // Server-side backstop for the manual flag: the UI hides the hand-off affordances, but the
    // MCP surface and hub can still be driven directly.
    private static Task<bool> IsManualAsync(ClaudeDoDbContext ctx, string taskId, CancellationToken ct)
        => ctx.Tasks.AsNoTracking().AnyAsync(t => t.Id == taskId && t.IsManual, ct);

    private static async Task<bool> IsDraftChildAsync(ClaudeDoDbContext ctx, string taskId, CancellationToken ct)
    {
        var parentId = await ctx.Tasks.AsNoTracking()
            .Where(t => t.Id == taskId)
            .Select(t => t.ParentTaskId)
            .FirstOrDefaultAsync(ct);
        if (parentId is null) return false;

        return await ctx.Tasks.AsNoTracking()
            .AnyAsync(p => p.Id == parentId && p.PlanningPhase == PlanningPhase.Active, ct);
    }

    private async Task OnChildTerminalAsync(string taskId, TaskStatus finalStatus)
    {
        // Terminal child writes are best-effort and use CancellationToken.None so the
        // task lifecycle is never left partially completed because a caller cancelled.
        string? parentId;
        await using (var ctx = await _dbFactory.CreateDbContextAsync(CancellationToken.None))
        {
            parentId = await ctx.Tasks
                .AsNoTracking()
                .Where(t => t.Id == taskId)
                .Select(t => t.ParentTaskId)
                .FirstOrDefaultAsync(CancellationToken.None);
        }
        if (parentId is null) return;

        try
        {
            await _chain.OnChildFinishedAsync(taskId, finalStatus, CancellationToken.None);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "PlanningChain advance failed for {TaskId}", taskId);
        }

        await TryAdvanceParentAsync(parentId);
    }

    // Any parent (planning or improvement) sitting in WaitingForChildren surfaces for review
    // once every child is terminal (Done/Failed/Cancelled). A failed or cancelled child does
    // not wedge the parent — it is flagged on the result. Also called directly after a child
    // is deleted, since no terminal transition fires in that case.
    public async Task TryAdvanceParentAsync(string parentId)
    {
        try
        {
            await AdvanceParentIfAllChildrenTerminalAsync(parentId);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "TryAdvanceParent failed for {ParentId}", parentId);
        }
    }

    private async Task AdvanceParentIfAllChildrenTerminalAsync(string parentId)
    {
        string? parentResult;
        List<TaskStatus> childStatuses;
        await using (var ctx = await _dbFactory.CreateDbContextAsync(CancellationToken.None))
        {
            var parent = await ctx.Tasks.AsNoTracking()
                .FirstOrDefaultAsync(t => t.Id == parentId, CancellationToken.None);
            if (parent is null || parent.Status != TaskStatus.WaitingForChildren) return;
            parentResult = parent.Result;
            childStatuses = await ctx.Tasks
                .Where(t => t.ParentTaskId == parentId)
                .Select(t => t.Status)
                .ToListAsync(CancellationToken.None);
        }
        // No early-out on an empty list: zero children left (e.g. the last one was just
        // deleted) counts as "all terminal" — .All() on an empty sequence is vacuously true.
        bool allTerminal = childStatuses.All(s =>
            s == TaskStatus.Done || s == TaskStatus.Failed || s == TaskStatus.Cancelled);
        if (!allTerminal) return;

        int failed = childStatuses.Count(s => s == TaskStatus.Failed);
        int cancelled = childStatuses.Count(s => s == TaskStatus.Cancelled);
        var newResult = parentResult;
        if (failed + cancelled > 0)
        {
            var note = $"⚠ Children: {failed} failed, {cancelled} cancelled.";
            newResult = string.IsNullOrWhiteSpace(parentResult) ? note : $"{parentResult}\n\n{note}";
        }

        await using var writeCtx = await _dbFactory.CreateDbContextAsync(CancellationToken.None);
        await writeCtx.Tasks
            .Where(t => t.Id == parentId && t.Status == TaskStatus.WaitingForChildren)
            .ExecuteUpdateAsync(s => s
                .SetProperty(t => t.Status, TaskStatus.WaitingForReview)
                .SetProperty(t => t.Result, newResult), CancellationToken.None);
        await NotifyAsync(parentId);
    }

    /// <summary>
    /// Der einzige Broadcast-Pfad dieser Klasse. Zusätzlich zum UI-Update meldet er den neuen
    /// Status ans verknüpfte Ticket. Nie direkt _broadcaster.TaskUpdated aufrufen — sonst
    /// fällt genau dieser Übergang aus dem Ticket-Sync heraus.
    /// </summary>
    private async Task NotifyAsync(string taskId)
    {
        await _broadcaster.TaskUpdated(taskId);
        await _ticketSync.SyncAsync(taskId, CancellationToken.None);
    }
}