package proxy

import (
	"bufio"
	"bytes"
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/openteam/server/internal/store"
)

// newTraceID 生成请求 trace（用于日志与记账幂等 ref）。
func newTraceID() string {
	b := make([]byte, 8)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)
}

// bodyReq 统一取出请求体并解析 model / stream 字段。
type bodyReq struct {
	Model  string `json:"model"`
	Stream bool   `json:"stream"`
}

// parseBody 读取并回填请求体，解析 model/stream。
func parseBody(c *gin.Context) (*bodyReq, []byte, error) {
	body, err := io.ReadAll(c.Request.Body)
	if err != nil {
		return nil, nil, err
	}
	c.Request.Body = io.NopCloser(bytes.NewReader(body))
	br := &bodyReq{}
	_ = json.Unmarshal(body, br) // 解析失败按空处理，直通仍可转发
	return br, body, nil
}

// upstreamURL 组装上游地址：base_url + 客户端路径（/v1/chat/completions 等）。
func upstreamURL(ch *store.Channel, path string) string {
	base := strings.TrimRight(ch.BaseURL, "/")
	return base + path
}

// doPassthrough 通用直通：替换 Authorization 为渠道密钥，转发请求。
// convert 回调用于改写请求体（M1 直通为原样；M3 转换时改写）。
func (g *Gateway) doPassthrough(c *gin.Context, ch *store.Channel, path string, body []byte, stream bool, outUsage func(usageRaw json.RawMessage)) {
	upKey, err := g.ch.UpstreamKey(ch)
	if err != nil {
		openAIError(c, http.StatusInternalServerError, "channel_error", "failed to decrypt channel key")
		return
	}

	upBody := body
	// 流式 chat：注入 stream_options.include_usage，保证末块带 usage（OpenAI 行为）
	if stream && path == "/v1/chat/completions" && !bytes.Contains(upBody, []byte(`"include_usage"`)) {
		var m map[string]any
		if json.Unmarshal(upBody, &m) == nil {
			m["stream_options"] = map[string]any{"include_usage": true}
			if b, err := json.Marshal(m); err == nil {
				upBody = b
			}
		}
	}

	ctx, cancel := context.WithTimeout(c.Request.Context(), time.Duration(ch.TimeoutMS)*time.Millisecond)
	defer cancel()
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, upstreamURL(ch, path), bytes.NewReader(upBody))
	if err != nil {
		openAIError(c, http.StatusInternalServerError, "internal_error", "failed to build upstream request")
		return
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+upKey)
	req.Header.Set("Accept", c.GetHeader("Accept"))
	if ua := c.GetHeader("User-Agent"); ua != "" {
		req.Header.Set("User-Agent", ua)
	}
	// 透传 OpenAI 生态请求头（组织/项目等）
	for _, h := range []string{"OpenAI-Organization", "OpenAI-Project", "OpenAI-Beta"} {
		if v := c.GetHeader(h); v != "" {
			req.Header.Set(h, v)
		}
	}

	start := time.Now()
	resp, err := g.hc.Do(req)
	if err != nil {
		status := http.StatusBadGateway
		msg := "Upstream request failed: " + err.Error()
		if ctx.Err() == context.DeadlineExceeded {
			status = http.StatusGatewayTimeout
			msg = "Upstream request timed out"
		}
		openAIError(c, status, "upstream_error", msg)
		g.recordError(c, ch, nil, start, "upstream_error")
		return
	}
	defer resp.Body.Close()

	// 非 2xx：透传上游错误体（OpenAI 格式），并记录 error 用量
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		errBody, _ := io.ReadAll(resp.Body)
		status := resp.StatusCode
		// 上游 5xx → 网关 502/504（重试逻辑 M4）
		if status >= 500 {
			status = http.StatusBadGateway
		}
		c.DataFromReader(status, int64(len(errBody)), "application/json", bytes.NewReader(errBody), nil)
		c.Header("Content-Type", "application/json")
		g.recordError(c, ch, resp, start, "upstream_http_"+strconv.Itoa(resp.StatusCode))
		return
	}

	// 成功响应
	c.Header("Content-Type", resp.Header.Get("Content-Type"))
	c.Status(http.StatusOK)
	if stream {
		g.streamCopy(c, ch, resp.Body, start, outUsage)
	} else {
		g.copyAndCapture(c, ch, resp.Body, start, outUsage)
	}
}

// copyAndCapture 非流式：整体转发 + 解析 usage + 记账。
func (g *Gateway) copyAndCapture(c *gin.Context, ch *store.Channel, r io.Reader, start time.Time, outUsage func(json.RawMessage)) {
	data, err := io.ReadAll(r)
	if err != nil {
		openAIError(c, http.StatusBadGateway, "upstream_error", "failed reading upstream response")
		g.recordError(c, ch, nil, start, "read_error")
		return
	}
	// 尝试解析 usage（chat / responses 字段不同）
	if usageRaw := extractUsage(data); usageRaw != nil {
		outUsage(usageRaw)
	}
	_, _ = c.Writer.Write(data)
	g.finishUsage(c, ch, start, store.UsageStatusSuccess, "")
}

// streamCopy 流式：边读上游 SSE 边写客户端，零缓冲转发；扫描 usage 行记账。
// 客户端断连（ctx cancel）即中止上游读取。
func (g *Gateway) streamCopy(c *gin.Context, ch *store.Channel, r io.Reader, start time.Time, outUsage func(json.RawMessage)) {
	w := c.Writer
	flusher, ok := w.(http.Flusher)
	if !ok {
		flusher = nopFlusher{}
	}

	scanner := newSSEScanner(r)
	for {
		line, err := scanner.Next()
		if line != nil {
			if _, werr := w.Write(line); werr != nil {
				// 客户端断开：取消上游（ctx cancel 由 request ctx 处理）
				g.recordError(c, ch, nil, start, "client_disconnect")
				return
			}
			flusher.Flush()
			if usageRaw := scanUsage(line); usageRaw != nil {
				outUsage(usageRaw)
			}
		}
		if err != nil {
			if err == io.EOF {
				g.finishUsage(c, ch, start, store.UsageStatusSuccess, "")
			} else {
				g.recordError(c, ch, nil, start, "stream_read_error")
			}
			return
		}
	}
}

type nopFlusher struct{}

func (nopFlusher) Flush() {}

// ---------------------------------------------------------------------------
// usage 提取

// usageShape 兼容 chat (prompt/completion) 与 responses (input/output) 两种命名。
type usageShape struct {
	PromptTokens     int64 `json:"prompt_tokens"`
	CompletionTokens int64 `json:"completion_tokens"`
	InputTokens      int64 `json:"input_tokens"`
	OutputTokens     int64 `json:"output_tokens"`
	TotalTokens      int64 `json:"total_tokens"`
	// Claude 缓存口径（M3 接入）
	CacheReadInputTokens    int64 `json:"cache_read_input_tokens"`
	CacheCreationInputTokens int64 `json:"cache_creation_input_tokens"`
}

// extractUsage 从完整响应体提取 usage 子对象。
func extractUsage(data []byte) json.RawMessage {
	var m map[string]json.RawMessage
	if json.Unmarshal(data, &m) != nil {
		return nil
	}
	if u, ok := m["usage"]; ok && string(u) != "null" {
		return u
	}
	// responses 事件/响应：usage 嵌套在 response 对象内
	if respRaw, ok := m["response"]; ok {
		var resp map[string]json.RawMessage
		if json.Unmarshal(respRaw, &resp) == nil {
			if u, ok := resp["usage"]; ok && string(u) != "null" {
				return u
			}
		}
	}
	// chat 兜底：choices[].message.usage
	if choices, ok := m["choices"]; ok {
		var cs []map[string]json.RawMessage
		if json.Unmarshal(choices, &cs) == nil {
			for _, ch := range cs {
				if msgRaw, ok := ch["message"]; ok {
					var msg map[string]json.RawMessage
					if json.Unmarshal(msgRaw, &msg) == nil {
						if u, ok := msg["usage"]; ok && string(u) != "null" {
							return u
						}
					}
				}
			}
		}
	}
	return nil
}

// scanUsage 从 SSE 一行中提取 usage（OpenAI 末块 / responses completed 事件）。
func scanUsage(line []byte) json.RawMessage {
	s := string(line)
	if !strings.Contains(s, `"usage"`) {
		return nil
	}
	if strings.HasPrefix(s, "data: ") {
		s = strings.TrimPrefix(s, "data: ")
	}
	s = strings.TrimSpace(s)
	if s == "[DONE]" || s == "" {
		return nil
	}
	var m map[string]json.RawMessage
	if json.Unmarshal([]byte(s), &m) != nil {
		return nil
	}
	if u, ok := m["usage"]; ok && string(u) != "null" {
		return u
	}
	// responses 流式：usage 在 response 对象内（response.completed 事件）
	if respRaw, ok := m["response"]; ok {
		var resp map[string]json.RawMessage
		if json.Unmarshal(respRaw, &resp) == nil {
			if u, ok := resp["usage"]; ok && string(u) != "null" {
				return u
			}
		}
	}
	return nil
}

// sseScanner 按 SSE 行边界读取（兼容 \n 与 \r\n），保留原始行内容。
// 基于 bufio.Reader：行内可含任意内容，跨 chunk 自动拼接。
type sseScanner struct {
	r *bufio.Reader
}

func newSSEScanner(r io.Reader) *sseScanner { return &sseScanner{r: bufio.NewReaderSize(r, 32*1024)} }

func (s *sseScanner) Next() ([]byte, error) {
	line, err := s.r.ReadBytes('\n')
	if len(line) > 0 {
		return line, nil
	}
	if err != nil {
		return nil, err
	}
	return nil, io.EOF
}

// ---------------------------------------------------------------------------
// 记账

// usageSink 累积流式多次 usage（取最后一次，即最终值）。
type usageSink struct {
	last json.RawMessage
}

func (u *usageSink) push(raw json.RawMessage) {
	if len(raw) > 0 {
		u.last = raw
	}
}

// finishUsage 落账：计算成本并异步写入。
func (g *Gateway) finishUsage(c *gin.Context, ch *store.Channel, start time.Time, status, errCode string) {
	uid, _ := c.Get(CtxUserID)
	kid, _ := c.Get(CtxKeyID)
	trace, _ := c.Get(CtxTrace)

	var us usageShape
	if h, ok := c.Get("usage_raw"); ok {
		if holder, ok := h.(*sinkHolder); ok && holder.sink != nil && len(holder.sink.last) > 0 {
			_ = json.Unmarshal(holder.sink.last, &us)
		}
	}

	in := us.PromptTokens + us.InputTokens
	out := us.CompletionTokens + us.OutputTokens
	cacheRead := us.CacheReadInputTokens
	cacheCreate := us.CacheCreationInputTokens

	modelName, _ := c.Get("model_name")
	mn, _ := modelName.(string)

	var model store.Model
	var cost float64
	var modelID uint64
	_ = g.db.Where("name = ?", mn).First(&model).Error
	if model.ID > 0 {
		modelID = model.ID
		cost = float64(in)/1e6*model.InputPrice +
			float64(out)/1e6*model.OutputPrice +
			float64(cacheRead)/1e6*model.CacheReadPrice
	} else {
		cost = float64(in)/1e6*0.15 + float64(out)/1e6*0.60 // 无定价模型时按示例价
	}

	proto, _ := c.Get("protocol")
	p, _ := proto.(string)
	if p == "" {
		p = "chat"
	}
	traceStr, _ := trace.(string)
	errMsg := errCode
	latency := int(time.Since(start).Milliseconds())

	// 已写响应头但流中途出错：记 error
	if status == store.UsageStatusSuccess && c.Writer.Status() >= 400 {
		status = store.UsageStatusError
	}

	g.rec.Record(&store.UsageLog{
		RequestID:   fmt.Sprintf("trace-%s", traceStr),
		TraceID:     traceStr,
		UserID:      uid.(uint64),
		KeyID:       kid.(uint64),
		ChannelID:   ch.ID,
		ModelID:     modelID,
		ModelName:   mn,
		Protocol:    p,
		InputTokens: in,
		OutputTokens: out,
		CacheReadTokens: cacheRead,
		CacheCreationTokens: cacheCreate,
		InputPrice:  model.InputPrice,
		OutputPrice: model.OutputPrice,
		CacheReadPrice: model.CacheReadPrice,
		Cost:        cost,
		LatencyMS:   latency,
		Status:      status,
		ErrorCode:   &errMsg,
		CreatedAt:   time.Now().UTC(),
	})
}

// recordError 失败请求的记账（不产生扣费，status=error）。
func (g *Gateway) recordError(c *gin.Context, ch *store.Channel, resp *http.Response, start time.Time, code string) {
	status := store.UsageStatusError
	_ = resp
	g.finishUsage(c, ch, start, status, code)
}

func now() time.Time { return time.Now() }