using System.Text.RegularExpressions;
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) : ITaskService
{
    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" }, 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" }, 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" }, 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}" }, 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" }, 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" }, 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, CancellationToken ct = default)
    {
        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)
        };
        await taskRepo.AddAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" created ({task.Source})" }, ct);
        return task;
    }

    public async Task<TaskOperationResult> UpdateDashboardTaskAsync(
        Guid id, string? title, string? detail, string? source, string? priority, string? assignedTo, 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);

        await taskRepo.UpdateAsync(task, ct);
        await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Task \"{task.Title}\" updated" }, 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}" }, 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" }, 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}" }, 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 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 "review":
                    review.Add(dto); break;
                case "blocked":
                    blocked.Add(dto); break;
                case "done":
                    done.Add(dto); break;
                default:
                    offen.Add(dto); break;
            }
        }

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

    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}" }, ct);
        return new TaskOperationResult(TaskOperationOutcome.Success, task);
    }

    public async Task<int> ImportFromIrisTodoAsync(bool deleteAfterImport = false, CancellationToken ct = default)
    {
        var todoPath = "/mnt/workspace-iris/TODO.md";
        if (!File.Exists(todoPath)) return 0;

        var content = await File.ReadAllTextAsync(todoPath, ct);
        var lines = content.Split('\n');

        var imported = 0;
        string? currentPriority = null;

        // Parse sections and extract tasks with assignee info
        // Pattern: ### N. Title 👤 Person
        var taskPattern = new Regex(@"^###\s+\d+\.\s+(.+?)(?:\s+👤\s+(.+?))?$", RegexOptions.Compiled);
        foreach (var line in lines)
        {
            var trimmed = line.Trim();

            // Detect priority section
            if (trimmed.StartsWith("## "))
            {
                var sectionLower = trimmed.ToLowerInvariant();
                if (sectionLower.Contains("high")) currentPriority = "High";
                else if (sectionLower.Contains("medium")) currentPriority = "Medium";
                else if (sectionLower.Contains("low")) currentPriority = "Low";
                else currentPriority = "Medium";
                continue;
            }

            var match = taskPattern.Match(trimmed);
            if (!match.Success) continue;

            var title = match.Groups[1].Value.Trim();
            var assigneeRaw = match.Groups[2].Success ? match.Groups[2].Value.Trim() : null;

            // Resolve assignee: "Iris" → "iris", "Bao" → "bao", "Iris+Bao" → "iris"
            string? assignedTo = null;
            if (!string.IsNullOrWhiteSpace(assigneeRaw))
            {
                var lower = assigneeRaw.ToLowerInvariant();
                if (lower.Contains("iris")) assignedTo = "iris";
                else if (lower.Contains("bao")) assignedTo = "bao";
            }

            var task = new WorkTask
            {
                Title = title,
                Source = "iris",
                Priority = currentPriority ?? "Medium",
                AssignedTo = assignedTo
            };
            await taskRepo.AddAsync(task, ct);
            imported++;
        }

        if (deleteAfterImport)
        {
            File.Delete(todoPath);
            await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Imported {imported} tasks from TODO.md and deleted the file" }, ct);
        }
        else
        {
            await activityRepo.AddAsync(new ActivityEvent { Type = "task", Message = $"Imported {imported} tasks from TODO.md" }, ct);
        }

        return imported;
    }

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

    /// <summary>
    /// Validates AssignedTo — only "bao", "iris", or null 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();
        if (lower is "bao" or "iris") return lower;
        return null;
    }
}