using MediatR;
using BuildFlow.Application.Chat.DTOs;
using BuildFlow.Shared.Domain.Exceptions;
using BuildFlow.Domain.Interfaces;
using BuildFlow.Infrastructure.Persistence;
using BuildFlow.Application.Chat.Queries;

namespace BuildFlow.Application.Chat.Handlers;

/// <summary>
/// Get会话Detail查询处理器。执行业务校验后持久化。
/// </summary>
public class GetConversationDetailQueryHandler(RagDbContext db, IChatMessageCache cache)
    : IRequestHandler<GetConversationDetailQuery, ConversationDetailDto>
{
    public async Task<ConversationDetailDto> Handle(GetConversationDetailQuery request, CancellationToken ct)
    {
        var conversation = await db.Conversations.FindAsync([request.Id], ct)
            ?? throw new NotFoundException("会话不存在");

        // 先查 Redis 缓存
        var cached = await cache.GetMessagesAsync(request.Id, ct);
        if (cached is not null)
        {
            var messages = cached.Select(m => new ChatMessageDto(m.Id, m.Role, m.Content, m.TokenUsage, m.CreatedAt)).ToList();
            return new ConversationDetailDto(conversation.Id, conversation.Title, conversation.UserId,
                conversation.KnowledgeBaseId, conversation.CreatedAt, messages);
        }

        // 缓存 miss，查数据库
        var dbMessages = await db.ChatMessages
            .Where(m => m.ConversationId == request.Id)
            .OrderBy(m => m.CreatedAt)
            .Select(m => new ChatMessageDto(m.Id, m.Role.ToString(), m.Content, m.TokenUsage, m.CreatedAt))
            .ToListAsync(ct);

        // 回填 Redis
        var cachedMessages = dbMessages.Select(m => new CachedChatMessage(m.Id, m.Role, m.Content, m.TokenUsage, m.CreatedAt)).ToList();
        await cache.SetMessagesAsync(request.Id, cachedMessages, ct);

        return new ConversationDetailDto(conversation.Id, conversation.Title, conversation.UserId,
            conversation.KnowledgeBaseId, conversation.CreatedAt, dbMessages);
    }
}