package handler

import (
	"bufio"
	"encoding/json"
	"io"
	"net/http"
	"strings"

	"github.com/gin-gonic/gin"
	"go.uber.org/zap"

	"nex/backend/internal/conversion"
	"nex/backend/internal/domain"
	"nex/backend/internal/provider"
	"nex/backend/internal/service"
)

// ProxyHandler 统一代理处理器
type ProxyHandler struct {
	engine         *conversion.ConversionEngine
	client         provider.ProviderClient
	routingService service.RoutingService
	providerService service.ProviderService
	statsService   service.StatsService
	logger         *zap.Logger
}

// NewProxyHandler 创建统一代理处理器
func NewProxyHandler(engine *conversion.ConversionEngine, client provider.ProviderClient, routingService service.RoutingService, providerService service.ProviderService, statsService service.StatsService) *ProxyHandler {
	return &ProxyHandler{
		engine:          engine,
		client:          client,
		routingService:  routingService,
		providerService: providerService,
		statsService:    statsService,
		logger:          zap.L(),
	}
}

// HandleProxy 处理代理请求
func (h *ProxyHandler) HandleProxy(c *gin.Context) {
	// 从 URL 提取 clientProtocol: /{protocol}/v1/...
	clientProtocol := c.Param("protocol")
	if clientProtocol == "" {
		c.JSON(http.StatusBadRequest, gin.H{"error": "缺少协议前缀"})
		return
	}

	// 原始路径: /v1/{path}
	path := c.Param("path")
	if strings.HasPrefix(path, "/") {
		path = path[1:]
	}
	nativePath := "/v1/" + path

	// 读取请求体
	body, err := io.ReadAll(c.Request.Body)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "读取请求体失败"})
		return
	}

	// 解析 model 名称（从 JSON body 中提取，GET 请求无 body）
	modelName := ""
	if len(body) > 0 {
		modelName = extractModelName(body)
	}

	// 构建输入 HTTPRequestSpec
	inSpec := conversion.HTTPRequestSpec{
		URL:     nativePath,
		Method:  c.Request.Method,
		Headers: extractHeaders(c),
		Body:    body,
	}

	// 路由
	routeResult, err := h.routingService.Route(modelName)
	if err != nil {
		// GET 请求或无法提取 model 时，直接转发到上游
		if len(body) == 0 || modelName == "" {
			h.forwardPassthrough(c, inSpec, clientProtocol)
			return
		}
		h.writeError(c, err, clientProtocol)
		return
	}

	// 确定 providerProtocol
	providerProtocol := routeResult.Provider.Protocol
	if providerProtocol == "" {
		providerProtocol = "openai"
	}

	// 构建 TargetProvider
	targetProvider := conversion.NewTargetProvider(
		routeResult.Provider.BaseURL,
		routeResult.Provider.APIKey,
		routeResult.Model.ModelName,
	)

	// 判断是否流式
	isStream := h.isStreamRequest(body, clientProtocol, nativePath)

	if isStream {
		h.handleStream(c, inSpec, clientProtocol, providerProtocol, targetProvider, routeResult)
	} else {
		h.handleNonStream(c, inSpec, clientProtocol, providerProtocol, targetProvider, routeResult)
	}
}

// handleNonStream 处理非流式请求
func (h *ProxyHandler) handleNonStream(c *gin.Context, inSpec conversion.HTTPRequestSpec, clientProtocol, providerProtocol string, targetProvider *conversion.TargetProvider, routeResult *domain.RouteResult) {
	// 转换请求
	outSpec, err := h.engine.ConvertHttpRequest(inSpec, clientProtocol, providerProtocol, targetProvider)
	if err != nil {
		h.logger.Error("转换请求失败", zap.String("error", err.Error()))
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	// 发送请求
	resp, err := h.client.Send(c.Request.Context(), *outSpec)
	if err != nil {
		h.logger.Error("发送请求失败", zap.String("error", err.Error()))
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	// 转换响应
	interfaceType, _ := h.engine.DetectInterfaceType(inSpec.URL, clientProtocol)
	convertedResp, err := h.engine.ConvertHttpResponse(*resp, clientProtocol, providerProtocol, interfaceType)
	if err != nil {
		h.logger.Error("转换响应失败", zap.String("error", err.Error()))
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	// 设置响应头
	for k, v := range convertedResp.Headers {
		c.Header(k, v)
	}
	if c.GetHeader("Content-Type") == "" {
		c.Header("Content-Type", "application/json")
	}

	c.Data(convertedResp.StatusCode, "application/json", convertedResp.Body)

	go func() {
		_ = h.statsService.Record(routeResult.Provider.ID, routeResult.Model.ModelName)
	}()
}

// handleStream 处理流式请求
func (h *ProxyHandler) handleStream(c *gin.Context, inSpec conversion.HTTPRequestSpec, clientProtocol, providerProtocol string, targetProvider *conversion.TargetProvider, routeResult *domain.RouteResult) {
	// 转换请求
	outSpec, err := h.engine.ConvertHttpRequest(inSpec, clientProtocol, providerProtocol, targetProvider)
	if err != nil {
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	// 创建流式转换器
	streamConverter, err := h.engine.CreateStreamConverter(clientProtocol, providerProtocol)
	if err != nil {
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	// 发送流式请求
	eventChan, err := h.client.SendStream(c.Request.Context(), *outSpec)
	if err != nil {
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")

	writer := bufio.NewWriter(c.Writer)

	for event := range eventChan {
		if event.Error != nil {
			h.logger.Error("流读取错误", zap.String("error", event.Error.Error()))
			break
		}
		if event.Done {
			// flush 转换器
			chunks := streamConverter.Flush()
			for _, chunk := range chunks {
				writer.Write(chunk)
				writer.Flush()
			}
			break
		}

		chunks := streamConverter.ProcessChunk(event.Data)
		for _, chunk := range chunks {
			writer.Write(chunk)
			writer.Flush()
		}
	}

	go func() {
		_ = h.statsService.Record(routeResult.Provider.ID, routeResult.Model.ModelName)
	}()
}

// isStreamRequest 判断是否流式请求
func (h *ProxyHandler) isStreamRequest(body []byte, clientProtocol, nativePath string) bool {
	ifaceType, _ := h.engine.DetectInterfaceType(nativePath, clientProtocol)
	if ifaceType != conversion.InterfaceTypeChat {
		return false
	}

	var req struct {
		Stream bool `json:"stream"`
	}
	if err := json.Unmarshal(body, &req); err != nil {
		return false
	}
	return req.Stream
}

// writeConversionError 写入转换错误
func (h *ProxyHandler) writeConversionError(c *gin.Context, err error, clientProtocol string) {
	if convErr, ok := err.(*conversion.ConversionError); ok {
		body, statusCode, _ := h.engine.EncodeError(convErr, clientProtocol)
		c.Data(statusCode, "application/json", body)
		return
	}
	c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
}

// writeError 写入路由错误
func (h *ProxyHandler) writeError(c *gin.Context, err error, clientProtocol string) {
	c.JSON(http.StatusNotFound, gin.H{"error": err.Error()})
}

// forwardPassthrough 直接转发请求到上游（用于 GET 等无 model 的请求）
func (h *ProxyHandler) forwardPassthrough(c *gin.Context, inSpec conversion.HTTPRequestSpec, clientProtocol string) {
	registry := h.engine.GetRegistry()
	adapter, err := registry.Get(clientProtocol)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "不支持的协议: " + clientProtocol})
		return
	}

	providers, err := h.providerService.List()
	if err != nil || len(providers) == 0 {
		h.logger.Warn("无可用供应商转发 GET 请求", zap.String("path", inSpec.URL))
		c.JSON(http.StatusNotFound, gin.H{"error": "没有可用的供应商。请先创建供应商和模型。"})
		return
	}

	p := providers[0]
	providerProtocol := p.Protocol
	if providerProtocol == "" {
		providerProtocol = "openai"
	}

	ifaceType := adapter.DetectInterfaceType(inSpec.URL)

	targetProvider := conversion.NewTargetProvider(p.BaseURL, p.APIKey, "")

	var outSpec *conversion.HTTPRequestSpec
	if clientProtocol == providerProtocol {
		upstreamURL := p.BaseURL + inSpec.URL
		headers := adapter.BuildHeaders(targetProvider)
		if _, ok := headers["Content-Type"]; !ok {
			headers["Content-Type"] = "application/json"
		}
		outSpec = &conversion.HTTPRequestSpec{
			URL:     upstreamURL,
			Method:  inSpec.Method,
			Headers: headers,
			Body:    inSpec.Body,
		}
	} else {
		outSpec, err = h.engine.ConvertHttpRequest(inSpec, clientProtocol, providerProtocol, targetProvider)
		if err != nil {
			h.writeConversionError(c, err, clientProtocol)
			return
		}
	}

	resp, err := h.client.Send(c.Request.Context(), *outSpec)
	if err != nil {
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	convertedResp, err := h.engine.ConvertHttpResponse(*resp, clientProtocol, providerProtocol, ifaceType)
	if err != nil {
		h.writeConversionError(c, err, clientProtocol)
		return
	}

	for k, v := range convertedResp.Headers {
		c.Header(k, v)
	}
	if c.GetHeader("Content-Type") == "" {
		c.Header("Content-Type", "application/json")
	}
	c.Data(convertedResp.StatusCode, "application/json", convertedResp.Body)
}

// extractModelName 从 JSON body 中提取 model
func extractModelName(body []byte) string {
	var req struct {
		Model string `json:"model"`
	}
	if err := json.Unmarshal(body, &req); err != nil {
		return ""
	}
	return req.Model
}

// extractHeaders 从 Gin context 提取请求头
func extractHeaders(c *gin.Context) map[string]string {
	headers := make(map[string]string)
	for k, vs := range c.Request.Header {
		if len(vs) > 0 {
			headers[k] = vs[0]
		}
	}
	return headers
}