using GermanApp.Application.DTOs;
using GermanApp.Domain.Entities;
using GermanApp.Domain.Interfaces;

namespace GermanApp.Application.Services;

/// <summary>
/// Application service for managing CEFR levels.
/// This is part of the Application layer.
/// </summary>
public class LevelService
{
    private readonly ILevelRepository _levelRepository;

    public LevelService(ILevelRepository levelRepository)
    {
        _levelRepository = levelRepository;
    }

    /// <summary>
    /// Gets all CEFR levels ordered by their sort order.
    /// </summary>
    public async Task<IReadOnlyList<LevelDto>> GetAllLevelsAsync(CancellationToken cancellationToken = default)
    {
        var levels = await _levelRepository.GetAllOrderedAsync(cancellationToken);
        return levels.Select(l => l.ToDto()).ToList();
    }

    /// <summary>
    /// Gets a level by its ID.
    /// </summary>
    public async Task<LevelDto?> GetLevelByIdAsync(int id, CancellationToken cancellationToken = default)
    {
        var level = await _levelRepository.GetByIdAsync(id, cancellationToken);
        return level?.ToDto();
    }

    /// <summary>
    /// Gets a level by its code (e.g., "A1", "B2").
    /// </summary>
    public async Task<LevelDto?> GetLevelByCodeAsync(string code, CancellationToken cancellationToken = default)
    {
        var level = await _levelRepository.GetByCodeAsync(code, cancellationToken);
        return level?.ToDto();
    }

    /// <summary>
    /// Creates a new CEFR level.
    /// </summary>
    public async Task<LevelDto> CreateLevelAsync(CreateLevelDto dto, CancellationToken cancellationToken = default)
    {
        var level = dto.ToEntity();
        var createdLevel = await _levelRepository.AddAsync(level, cancellationToken);
        return createdLevel.ToDto();
    }

    /// <summary>
    /// Updates an existing CEFR level.
    /// </summary>
    public async Task<LevelDto?> UpdateLevelAsync(int id, UpdateLevelDto dto, CancellationToken cancellationToken = default)
    {
        var level = await _levelRepository.GetByIdAsync(id, cancellationToken);
        if (level == null)
            return null;

        level.UpdateFromDto(dto);
        await _levelRepository.UpdateAsync(level, cancellationToken);
        return level.ToDto();
    }

    /// <summary>
    /// Deletes a CEFR level by its ID.
    /// </summary>
    public async Task<bool> DeleteLevelAsync(int id, CancellationToken cancellationToken = default)
    {
        var level = await _levelRepository.GetByIdAsync(id, cancellationToken);
        if (level == null)
            return false;

        await _levelRepository.DeleteAsync(level, cancellationToken);
        return true;
    }

    /// <summary>
    /// Gets the first level (lowest order number) - typically A1.
    /// </summary>
    public async Task<LevelDto?> GetFirstLevelAsync(CancellationToken cancellationToken = default)
    {
        var level = await _levelRepository.GetFirstLevelAsync(cancellationToken);
        return level?.ToDto();
    }

    /// <summary>
    /// Gets the next level after the specified one.
    /// </summary>
    public async Task<LevelDto?> GetNextLevelAsync(int currentLevelId, CancellationToken cancellationToken = default)
    {
        var level = await _levelRepository.GetNextLevelAsync(currentLevelId, cancellationToken);
        return level?.ToDto();
    }
}