using GozareshgirProgramManager.Application._Common.Interfaces;
using GozareshgirProgramManager.Application._Common.Models;
using GozareshgirProgramManager.Domain._Common;
using GozareshgirProgramManager.Domain._Common.Exceptions;
using GozareshgirProgramManager.Domain.ProjectAgg.Enums;
using GozareshgirProgramManager.Domain.ProjectAgg.Repositories;

namespace GozareshgirProgramManager.Application.Modules.Projects.Commands.ChangeStatusSection;

public record ChangeStatusSectionCommand(Guid SectionId, TaskSectionStatus Status) : IBaseCommand;

public class ChangeStatusSectionCommandHandler : IBaseCommandHandler<ChangeStatusSectionCommand>
{
    private readonly IUnitOfWork _unitOfWork;
    private readonly ITaskSectionRepository _taskSectionRepository;
    private readonly IAuthHelper _authHelper;

    public ChangeStatusSectionCommandHandler(ITaskSectionRepository taskSectionRepository,
        IUnitOfWork unitOfWork, IAuthHelper authHelper)
    {
        _taskSectionRepository = taskSectionRepository;
        _unitOfWork = unitOfWork;
        _authHelper = authHelper;
    }

    public async Task<OperationResult> Handle(ChangeStatusSectionCommand request, CancellationToken cancellationToken)
    {
        // استفاده از متد مخصوص که Activities رو load می‌کنه
        var section = await _taskSectionRepository.GetByIdWithActivitiesAsync(request.SectionId, cancellationToken);
        if (section == null)
            return OperationResult.NotFound("بخش مورد نظر یافت نشد");

        if (section.Status == request.Status)
            return OperationResult.Success();
        
        long currentUser = _authHelper.GetCurrentUserId() 
                           ?? throw new UnAuthorizedException("کاربر احراز هویت نشده است");

        // Validate state transitions
        var validationResult = ValidateStateTransition(section.Status, request.Status);
        if (!validationResult.IsSuccess)
            return validationResult;

        // Handle state machine logic
        if (section.Status == TaskSectionStatus.InProgress)
        {
            // Coming FROM InProgress: Stop the active activity
            section.StopWork(request.Status);
        }
        else if (request.Status == TaskSectionStatus.InProgress)
        {
			// Going TO InProgress: Check if section has remaining time, then start work
			if (!section.HasRemainingTime())
				return OperationResult.ValidationError("زمان این بخش به پایان رسیده است");
            if (await _taskSectionRepository.HasUserAnyInProgressSectionAsync(section.CurrentAssignedUserId, cancellationToken))
            {
                return OperationResult.ValidationError("کاربر مورد نظر در حال حاضر بخش دیگری را در وضعیت 'درحال انجام' دارد");
            }
			section.StartWork();
        }
        else
        {
            // All other transitions: Just update status
            section.UpdateStatus(request.Status);
        }

        await _unitOfWork.SaveChangesAsync(cancellationToken);
        return OperationResult.Success();
    }

    /// <summary>
    /// Validates state transitions based on business rules:
    /// - ReadyToStart: شروع نشده - Initial state only, cannot return to it once left
    /// - InProgress: درحال انجام - Can transition from ReadyToStart, can go to Incomplete or Completed
    /// - Incomplete: نیمه کاره - Can come from InProgress or other states
    /// - Completed: اتمام رسیده - Can come from InProgress or other states
    /// </summary>
    private OperationResult ValidateStateTransition(TaskSectionStatus currentStatus, TaskSectionStatus targetStatus)
    {
        // Cannot transition to ReadyToStart once the section has been started
        if (targetStatus == TaskSectionStatus.ReadyToStart)
            return OperationResult.ValidationError("بخش نمی‌تواند به وضعیت 'آماده برای شروع' تغییر کند");

        // From ReadyToStart, can only go to InProgress
        if (currentStatus == TaskSectionStatus.ReadyToStart && targetStatus != TaskSectionStatus.InProgress)
            return OperationResult.ValidationError("از وضعیت 'آماده برای شروع' فقط می‌توان به 'درحال انجام' رفت");

        // Valid transitions matrix
        var validTransitions = new Dictionary<TaskSectionStatus, List<TaskSectionStatus>>
        {
            { TaskSectionStatus.ReadyToStart, [TaskSectionStatus.InProgress] },
            { TaskSectionStatus.InProgress, [TaskSectionStatus.Incomplete, TaskSectionStatus.PendingForCompletion] },
            { TaskSectionStatus.Incomplete, [TaskSectionStatus.InProgress, TaskSectionStatus.PendingForCompletion] },
            { TaskSectionStatus.PendingForCompletion, [TaskSectionStatus.InProgress, TaskSectionStatus.Incomplete] }, // Can return to InProgress or Incomplete
            { TaskSectionStatus.NotAssigned, [TaskSectionStatus.InProgress, TaskSectionStatus.ReadyToStart] }
        };

        if (!validTransitions.TryGetValue(currentStatus, out var allowedTargets))
            return OperationResult.ValidationError($"وضعیت فعلی '{currentStatus}' نامعتبر است");

        if (!allowedTargets.Contains(targetStatus))
            return OperationResult.ValidationError(
                $"نمی‌توان از وضعیت '{currentStatus}' به '{targetStatus}' رفت");

        return OperationResult.Success();
    }
}