using DigitalData.Core.Abstractions.Application;
using DigitalData.Core.Abstractions.Infrastructure;
using AutoMapper;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using DigitalData.Core.DTO;
using DigitalData.Core.Abstractions;
using Microsoft.Extensions.Logging;

namespace DigitalData.Core.Application
{
    /// <summary>
    /// Provides generic CRUD (Create, Read, Update, Delete) operations for a specified type of entity.
    /// </summary>
    /// <typeparam name="TCreateDto">The DTO type for create operations.</typeparam>
    /// <typeparam name="TReadDto">The DTO type for read operations.</typeparam>
    /// <typeparam name="TUpdateDto">The DTO type for update operations.</typeparam>
    /// <typeparam name="TEntity">The entity type.</typeparam>
    /// <typeparam name="TId">The type of the identifier for the entity.</typeparam>
    public class CRUDService<TCRUDRepository, TCreateDto, TReadDto, TUpdateDto, TEntity, TId> : ICRUDService<TCreateDto, TReadDto, TUpdateDto, TEntity, TId>
        where TCRUDRepository : ICRUDRepository<TEntity, TId> where TCreateDto : class where TReadDto : class where TUpdateDto : IUnique<TId> where TEntity : class
    {
        protected readonly TCRUDRepository _repository;
        protected readonly IMapper _mapper;
        protected readonly PropertyInfo? _keyPropertyInfo;

        /// <summary>
        /// Initializes a new instance of the CRUDService class with the specified repository, translation service, and mapper.
        /// </summary>
        /// <param name="repository">The CRUD repository for accessing the database.</param>
        /// <param name="mapper">The AutoMapper instance for mapping between DTOs and entity objects.</param>
        public CRUDService(TCRUDRepository repository, IMapper mapper)
        {
            _repository = repository;
            _mapper = mapper;

            _keyPropertyInfo = typeof(TEntity).GetProperties()
                .FirstOrDefault(prop => Attribute.IsDefined(prop, typeof(KeyAttribute)));
        }

        /// <summary>
        /// Asynchronously creates an entity based on the provided create DTO.
        /// </summary>
        /// <param name="createDto">The DTO to create an entity from.</param>
        /// <returns>A service result indicating success or failure, including the entity DTO.</returns>
        public virtual async Task<DataResult<TId>> CreateAsync(TCreateDto createDto)
        {
            var entity = _mapper.Map<TEntity>(createDto);
            var createdEntity = await _repository.CreateAsync(entity);
            return createdEntity is null ? Result.Fail<TId>() : Result.Success(KeyValueOf(createdEntity));
        }

        /// <summary>
        /// Asynchronously reads an entity by its identifier and maps it to a read DTO.
        /// </summary>
        /// <param name="id">The identifier of the entity to read.</param>
        /// <returns>A service result indicating success or failure, including the read DTO if successful.</returns>
        public virtual async Task<DataResult<TReadDto>> ReadByIdAsync(TId id)
        {
            var entity = await _repository.ReadByIdAsync(id);
            return entity is null
                ? Result.Fail<TReadDto>()
                : Result.Success(_mapper.Map<TReadDto>(entity));
        }

        /// <summary>
        /// Asynchronously reads all entities and maps them to read DTOs.
        /// </summary>
        /// <returns>A service result including a collection of read DTOs.</returns>
        public virtual async Task<DataResult<IEnumerable<TReadDto>>> ReadAllAsync()
        {
            var entities = await _repository.ReadAllAsync();
            var readDto = _mapper.Map<IEnumerable<TReadDto>>(entities);
            return Result.Success(readDto);
        }

        /// <summary>
        /// Asynchronously updates an entity based on the provided update DTO.
        /// </summary>
        /// <param name="updateDto">The DTO to update an entity from.</param>
        /// <returns>A service message indicating success or failure.</returns>
        public virtual async Task<Result> UpdateAsync(TUpdateDto updateDto)
        {
            var currentEntitiy = await _repository.ReadByIdAsync(updateDto.Id);

            if (currentEntitiy is null)
                return Result.Fail().Notice(LogLevel.Warning, Flag.NotFound, $"{updateDto.Id} is not found in update process of {GetType()} entity.");
    
            var entity = _mapper.Map(updateDto, currentEntitiy);

            return await _repository.UpdateAsync(entity) 
                ? Result.Success() 
                : Result.Fail();
        }

        /// <summary>
        /// Asynchronously deletes an entity by its identifier.
        /// </summary>
        /// <param name="id">The identifier of the entity to delete.</param>
        /// <returns>A service message indicating success or failure.</returns>
        public virtual async Task<Result> DeleteAsyncById(TId id)
        {
            TEntity? entity = await _repository.ReadByIdAsync(id);

            if (entity is null)
                return Result.Fail();

            bool isDeleted = await _repository.DeleteAsync(entity);
            return isDeleted ? Result.Success() : Result.Fail();
        }

        /// <summary>
        /// Asynchronously checks if an entity with the specified identifier exists.
        /// </summary>
        /// <param name="id">The identifier of the entity to check.</param>
        /// <returns>A Task that represents the asynchronous operation. The task result contains a boolean value indicating whether the entity exists.</returns>
        public virtual async Task<bool> HasEntity(TId id)
        {
            var entity = await _repository.ReadByIdAsync(id);
            return entity is not null;
        }

        /// <summary>
        /// Retrieves the ID value of an entity based on the defined [Key] attribute.
        /// </summary>
        /// <param name="entity">The entity from which to extract the ID.</param>
        /// <returns>The ID of the entity.</returns>
        protected virtual TId KeyValueOf(TEntity entity)
        {
            if (_keyPropertyInfo is null)
                throw new InvalidOperationException($"No property with [Key] attribute found on {typeof(TEntity).Name} entity.");

            object idObj = _keyPropertyInfo?.GetValue(entity) ?? throw new InvalidOperationException($"The ID property of {typeof(TEntity).Name} entity cannot be null.");

            if (idObj is TId id)
                return id;
            else
                throw new InvalidCastException($"The ID of {typeof(TEntity).Name} entity must be type of {typeof(TId).Name}, but it is type of {idObj.GetType().Name}.");
        }

        /// <summary>
        /// Handles exceptions that occur during CRUD operations, providing a structured string.
        /// </summary>
        /// <param name="ex">The exception that was caught during CRUD operations.</param>
        /// <returns>A <see cref="IServiceMessage"/> containing information about the failure, including a user-friendly error message and additional error details.</returns>
        public virtual string HandleException(Exception ex)
        {
            return $"An unexpected error occurred on the server side. Please inform the IT support team.\n{ex.GetType().Name}\n{ex.Message}";
        }
    }
}