using Nexus.Api.Data;
using Nexus.Api.DTOs;
using Nexus.Api.Models;
using Nexus.Api.Repositories;

namespace Nexus.Api.Services;

public sealed class TaskService(
    ITaskRepository taskRepo,
    IActivityRepository activityRepo,
    INotificationService notificationService) : ITaskService
{
    private static readonly HashSet<string> ValidAssignees =
        ["bao", "iris", "programmer", "reviewer", "architekt"];

    public async Task<IReadOnlyList<WorkTask>> GetAllAsync(CancellationToken ct = default)
        => await taskRepo.GetAllAsync(ct);

    public async Task<WorkTask?> GetByIdAsync(Guid id, CancellationToken ct = default)
        => await taskRepo.GetByIdAsync(id, ct);

    public async Task<IReadOnlyList<WorkTask>> GetPendingApprovalAsync(CancellationToken ct = default)
        => await taskRepo.GetPendingApprovalAsync(ct);

    public async Task<WorkTask> CreateAsync(CreateTaskRequest request, CancellationToken ct = default)
    {
        var task = new WorkTask
        {
            Title = request.Title.Trim(),
            Priority = string.IsNullOrWhiteSpace(request.Priority) ? "Normal" : request.Priority.Trim(),
            ProjectId = request.ProjectId
        };
        await taskRepo.AddAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task {task.Title} created", TaskId = task.Id }, ct);
        return task;
    }

    public async Task<TaskOperationResult> ApproveAsync(Guid id, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        if (!TaskStateHelper.IsInProgressOrBlocked(task.State))
            return new TaskOperationResult(TaskOperationOutcome.InvalidState, task);

        task.State = TaskStateHelper.ToStateString(TaskState.Done);
        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task {task.Title} approved", TaskId = task.Id }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> RejectAsync(Guid id, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        if (!TaskStateHelper.IsInProgressOrBlocked(task.State))
            return new TaskOperationResult(TaskOperationOutcome.InvalidState, task);

        task.State = TaskStateHelper.ToStateString(TaskState.Backlog);
        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task {task.Title} rejected, returned to backlog", TaskId = task.Id }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> UpdateStateAsync(Guid id, string state, CancellationToken ct = default)
    {
        var canonical = TaskStateHelper.AllStates.FirstOrDefault(s => s.Equals(state, StringComparison.OrdinalIgnoreCase));
        if (canonical is null) return new TaskOperationResult(TaskOperationOutcome.InvalidState);

        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        task.State = canonical;
        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task {task.Title} moved to {task.State}", TaskId = task.Id }, ct);
        await CreateStatusChangeNotificationsAsync(task, canonical, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> UpdateAsync(Guid id, UpdateTaskRequest request, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        if (!string.IsNullOrWhiteSpace(request.Title))
            task.Title = request.Title.Trim();
        if (!string.IsNullOrWhiteSpace(request.Priority))
            task.Priority = request.Priority.Trim();
        if (request.ProjectId.HasValue)
            task.ProjectId = request.ProjectId.Value == Guid.Empty ? null : request.ProjectId;

        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task {task.Title} updated", TaskId = task.Id }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> DeleteAsync(Guid id, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        if (!TaskStateHelper.IsDoneOrBacklog(task.State))
            return new TaskOperationResult(TaskOperationOutcome.InvalidState, task);

        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task {task.Title} deleted", TaskId = task.Id }, ct);
        await taskRepo.DeleteAsync(task, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success);
    }

    // ── Dashboard-facing operations ──

    public async Task<IReadOnlyList<WorkTask>> GetOpenAsync(CancellationToken ct = default)
    {
        var all = await taskRepo.GetAllAsync(ct);
        return all.Where(t => !string.Equals(t.State, "Done", StringComparison.OrdinalIgnoreCase))
                  .OrderByDescending(t => t.CreatedAt)
                  .ToList();
    }

    public async Task<WorkTask> CreateDashboardTaskAsync(
        string title, string? detail, string? source, string? priority,
        string? assignedTo, Guid? parentTaskId = null, CancellationToken ct = default)
    {
        // Validate parent task exists if specified
        if (parentTaskId.HasValue)
        {
            var parent = await taskRepo.GetByIdAsync(parentTaskId.Value, ct);
            if (parent is null)
                throw new ArgumentException($"Parent task {parentTaskId} not found.", nameof(parentTaskId));
        }

        var task = new WorkTask
        {
            Title = title.Trim(),
            Detail = detail?.Trim(),
            Source = string.IsNullOrWhiteSpace(source) ? "bao" : source.Trim(),
            Priority = string.IsNullOrWhiteSpace(priority) ? "Normal" : priority.Trim(),
            AssignedTo = ValidateAssignedTo(assignedTo),
            ParentTaskId = parentTaskId
        };
        await taskRepo.AddAsync(task, ct);

        var message = $"Task \"{task.Title}\" created ({task.Source})";
        if (parentTaskId.HasValue)
            message += $" [child of {parentTaskId.Value}]";
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = message, TaskId = task.Id }, ct);

        // Auto-notify: if assigned to bao, create a task_assigned notification
        if (string.Equals(assignedTo, "bao", StringComparison.OrdinalIgnoreCase))
        {
            await notificationService.CreateAsync(
                "task_assigned",
                $"Neue Aufgabe: {task.Title}",
                detail,
                "bao",
                task.Id,
                ct);
        }

        return task;
    }

    public async Task<TaskOperationResult> UpdateDashboardTaskAsync(
        Guid id, string? title, string? detail, string? source,
        string? priority, string? assignedTo, DateTimeOffset? dueDate = null, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        if (!string.IsNullOrWhiteSpace(title)) task.Title = title.Trim();
        if (detail is not null) task.Detail = string.IsNullOrWhiteSpace(detail) ? null : detail.Trim();
        if (!string.IsNullOrWhiteSpace(source)) task.Source = source.Trim();
        if (!string.IsNullOrWhiteSpace(priority)) task.Priority = priority.Trim();
        if (assignedTo is not null) task.AssignedTo = ValidateAssignedTo(assignedTo);
        if (dueDate.HasValue) task.DueDate = dueDate;

        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" updated", TaskId = task.Id }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> UpdateStatusAsync(Guid id, string status, CancellationToken ct = default)
    {
        if (!TaskStateHelper.IsValidState(status))
            return new TaskOperationResult(TaskOperationOutcome.InvalidState);

        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        var canonical = TaskStateHelper.AllStates.First(s => s.Equals(status, StringComparison.OrdinalIgnoreCase));
        task.State = canonical;
        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" → {canonical}", TaskId = task.Id }, ct);
        await CreateStatusChangeNotificationsAsync(task, canonical, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> CompleteViaQueueAsync(Guid id, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        task.State = "Done";
        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" completed via queue", TaskId = task.Id }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<TaskOperationResult> CyclePriorityAsync(Guid id, CancellationToken ct = default)
    {
        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        task.Priority = task.Priority.ToLowerInvariant() switch
        {
            "high" => "Medium",
            "medium" => "Low",
            "low" => "High",
            _ => "Medium"
        };

        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" priority → {task.Priority}", TaskId = task.Id }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    // ── Board operations ──

    public async Task<TaskBoardResponse> GetBoardAsync(CancellationToken ct = default)
    {
        var all = await taskRepo.GetAllAsync(ct);
        var offen = new List<DashboardTaskDto>();
        var inProgress = new List<DashboardTaskDto>();
        var delegated = new List<DashboardTaskDto>();
        var review = new List<DashboardTaskDto>();
        var blocked = new List<DashboardTaskDto>();
        var done = new List<DashboardTaskDto>();

        foreach (var task in all)
        {
            var dto = MapToDto(task);
            switch (task.State.ToLowerInvariant())
            {
                case "backlog":
                    offen.Add(dto); break;
                case "in progress":
                    inProgress.Add(dto); break;
                case "delegated":
                    delegated.Add(dto); break;
                case "review":
                    review.Add(dto); break;
                case "blocked":
                    blocked.Add(dto); break;
                case "done":
                    done.Add(dto); break;
                default:
                    offen.Add(dto); break;
            }
        }

        // Priority sort within each group: High > Medium > Low, then by CreatedAt ascending
        offen.Sort(SortByPriorityThenCreatedAt);
        inProgress.Sort(SortByPriorityThenCreatedAt);
        delegated.Sort(SortByPriorityThenCreatedAt);
        review.Sort(SortByPriorityThenCreatedAt);
        blocked.Sort(SortByPriorityThenCreatedAt);
        done.Sort(SortByPriorityThenCreatedAt);

        return new TaskBoardResponse(offen, inProgress, delegated, review, blocked, done);
    }

    private static int SortByPriorityThenCreatedAt(DashboardTaskDto a, DashboardTaskDto b)
    {
        var priorityCompare = PriorityScore(b.Priority).CompareTo(PriorityScore(a.Priority));
        return priorityCompare != 0 ? priorityCompare : a.CreatedAt.CompareTo(b.CreatedAt);
    }

    private static int PriorityScore(string priority) => priority.ToLowerInvariant() switch
    {
        "high" => 3,
        "medium" => 2,
        "normal" => 2,
        "low" => 1,
        _ => 2
    };

    public async Task<TaskOperationResult> MoveTaskAsync(Guid id, string newState, CancellationToken ct = default)
    {
        // Resolve canonical state: accept board group keys or canonical strings
        var canonical = TaskStateHelper.AllStates
            .FirstOrDefault(s => s.Equals(newState, StringComparison.OrdinalIgnoreCase));

        if (canonical is null)
        {
            // Try mapping from board group key
            canonical = TaskStateHelper.BoardGroupToState(newState);
        }

        if (canonical is null)
            return new TaskOperationResult(TaskOperationOutcome.InvalidState);

        var task = await taskRepo.GetByIdAsync(id, ct);
        if (task is null) return new TaskOperationResult(TaskOperationOutcome.NotFound);

        task.State = canonical;
        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" moved to {canonical}", TaskId = task.Id }, ct);
        await CreateStatusChangeNotificationsAsync(task, canonical, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<int> ResetStaleInProgressTasksAsync(TimeSpan staleThreshold, CancellationToken ct = default)
    {
        var all = await taskRepo.GetAllAsync(ct);
        var threshold = DateTimeOffset.UtcNow - staleThreshold;
        var staleTasks = all.Where(t =>
            (string.Equals(t.State, "In progress", StringComparison.OrdinalIgnoreCase) ||
             string.Equals(t.State, "Delegated", StringComparison.OrdinalIgnoreCase)) &&
            t.UpdatedAt < threshold).ToList();

        foreach (var task in staleTasks)
        {
            var prevState = task.State;
            task.State = "Backlog";
            await taskRepo.UpdateAsync(task, ct);
            await activityRepo.AddAsync(new ActivityEvent
            {
                Type = "task",
                Message = $"Task \"{task.Title}\" reset from {prevState} to Backlog (stale)",
                TaskId = task.Id
            }, ct);
        }

        return staleTasks.Count;
    }

    public async Task<IReadOnlyList<WorkTask>> GetChildTasksAsync(Guid parentId, CancellationToken ct = default)
    {
        var all = await taskRepo.GetAllAsync(ct);
        return all.Where(t => t.ParentTaskId == parentId)
                  .OrderByDescending(t => t.CreatedAt)
                  .ToList();
    }

    public async Task<List<ActivityEvent>> GetTaskActivityAsync(Guid taskId, CancellationToken ct = default)
    {
        var all = await activityRepo.GetRecentAsync(100, ct);
        return all.Where(e => e.TaskId == taskId).ToList();
    }

    private static DashboardTaskDto MapToDto(WorkTask t) => new(
        t.Id, t.Title, t.Detail, t.Source, t.State, t.Priority, t.AssignedTo,
        t.ParentTaskId, t.DueDate, t.CreatedAt, t.UpdatedAt);

    /// <summary>
    /// Validates AssignedTo — only recognized agent values are accepted.
    /// Returns null for invalid values.
    /// </summary>
    private static string? ValidateAssignedTo(string? assignedTo)
    {
        if (string.IsNullOrWhiteSpace(assignedTo)) return null;
        var lower = assignedTo.Trim().ToLowerInvariant();
        return ValidAssignees.Contains(lower) ? lower : null;
    }

    /// <summary>
    /// Creates status-change notifications when a task moves to Review or Blocked.
    /// </summary>
    private async Task CreateStatusChangeNotificationsAsync(WorkTask task, string canonical, CancellationToken ct)
    {
        if (string.Equals(canonical, "Review", StringComparison.OrdinalIgnoreCase))
        {
            await notificationService.CreateAsync(
                "task_review",
                $"Task zur Überprüfung: {task.Title}",
                $"Status auf Review geändert von {task.AssignedTo ?? "unbekannt"}",
                "bao",
                task.Id,
                ct);
        }
        else if (string.Equals(canonical, "Blocked", StringComparison.OrdinalIgnoreCase))
        {
            await notificationService.CreateAsync(
                "task_blocked",
                $"Aufgabe blockiert: {task.Title}",
                "Die Task konnte nicht abgeschlossen werden und wurde blockiert.",
                "iris",
                task.Id,
                ct);
        }
    }
}