package workbench

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"strings"
	"time"

	"aigateway.local/core/internal/apikey"
	"aigateway.local/core/internal/factcheck"
	"aigateway.local/core/internal/gateway"
	"aigateway.local/core/internal/platform/apiresponse"
	tracepkg "aigateway.local/core/internal/trace"
)

type RuntimeHTTPHandler struct {
	service   *Service
	tools     *ToolService
	retriever Retriever
	auth      apikey.PrincipalAuthenticator
	gateway   http.Handler
	factCheck *factcheck.Engine
	traces    *tracepkg.Store
	logger    *slog.Logger
	mux       *http.ServeMux
	market    MarketplaceDeps
	envVars   *EnvVarService
}

// MarketplaceDeps carries the resource-marketplace services into the runtime
// handler (MCP servers, skills, digital employees, installations).
type MarketplaceDeps struct {
	MCPServers *MCPServerService
	Skills     *SkillService
	Employees  *DigitalEmployeeService
	Market     *MarketplaceService
	MCPClient  *MCPClient
}

func NewRuntimeHTTPHandler(service *Service, tools *ToolService, retriever Retriever, auth apikey.PrincipalAuthenticator, gatewayHandler http.Handler, market MarketplaceDeps) *RuntimeHTTPHandler {
	h := &RuntimeHTTPHandler{service: service, tools: tools, retriever: retriever, auth: auth, gateway: gatewayHandler, mux: http.NewServeMux(), market: market}
	h.logger = slog.Default()
	h.mux.HandleFunc("GET /v1/prompts", h.listPrompts)
	h.mux.HandleFunc("POST /v1/prompts/{name}/render", h.renderPrompt)
	h.mux.HandleFunc("POST /v1/knowledge/search", h.searchKnowledge)
	h.mux.HandleFunc("POST /v1/knowledge/{id}/search", h.searchKnowledge)
	h.mux.HandleFunc("GET /v1/tools", h.listTools)
	h.mux.HandleFunc("POST /v1/tools/{code}/invoke", h.invokeTool)
	h.mux.HandleFunc("POST /v1/applications/{code}/chat/completions", h.runApplication)
	h.mux.HandleFunc("POST /v1/skills/{code}/render", h.renderSkill)
	h.mux.HandleFunc("GET /v1/mcp-servers", h.listMCPServers)
	h.mux.HandleFunc("GET /v1/mcp-servers/{code}/tools", h.mcpServerTools)
	h.mux.HandleFunc("POST /v1/mcp-servers/{code}/tools/{tool}/invoke", h.invokeMCPTool)
	h.mux.HandleFunc("POST /v1/digital-employees/{code}/chat/completions", h.runDigitalEmployee)
	return h
}
func (h *RuntimeHTTPHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) { h.mux.ServeHTTP(w, r) }

// SetLogger wires a logger for best-effort diagnostics (fact-check skips etc.).
func (h *RuntimeHTTPHandler) SetLogger(logger *slog.Logger) {
	if logger != nil {
		h.logger = logger
	}
}

// SetFactCheckEngine enables post-answer fact-checking on application
// conversations. When nil (the default) fact-checking is skipped entirely.
func (h *RuntimeHTTPHandler) SetFactCheckEngine(engine *factcheck.Engine) { h.factCheck = engine }

// SetEnvVarService 启用个人环境变量合并(应用/数字员工运行时变量补充)。
func (h *RuntimeHTTPHandler) SetEnvVarService(service *EnvVarService) { h.envVars = service }

// SetTraceStore enables metadata-only LLM Trace recording for application and
// digital-employee runs. Trace persistence is best effort and never changes
// the runtime response when the database is unavailable.
func (h *RuntimeHTTPHandler) SetTraceStore(store *tracepkg.Store) { h.traces = store }

// factCheckRetriever adapts the workbench Retriever to the fact-check engine's
// EvidenceRetriever interface, reusing the same knowledge-base search path that
// application prompts already use.
type factCheckRetriever struct{ inner Retriever }

func NewFactCheckRetriever(inner Retriever) *factCheckRetriever {
	if inner == nil {
		return nil
	}
	return &factCheckRetriever{inner: inner}
}

func (a *factCheckRetriever) Search(ctx context.Context, knowledgeBaseID, query string, topK int) ([]factcheck.EvidenceHit, error) {
	hits, err := a.inner.Search(ctx, knowledgeBaseID, query, topK)
	if err != nil {
		return nil, err
	}
	out := make([]factcheck.EvidenceHit, 0, len(hits))
	for _, hit := range hits {
		out = append(out, factcheck.EvidenceHit{DocumentTitle: hit.DocumentTitle, Content: hit.Content})
	}
	return out, nil
}

// VerifyFactCheck satisfies factcheck.Verifier. It routes a non-streaming chat
// completion through the same governed gateway, reusing the original request's
// credential headers so the fact-check call is authenticated and rate-limited
// exactly like the application call that produced the answer.
func (h *RuntimeHTTPHandler) VerifyFactCheck(ctx context.Context, original *http.Request, model, system, user string, timeout time.Duration) (string, error) {
	ctx, cancel := context.WithTimeout(ctx, timeout)
	defer cancel()
	payload := map[string]any{
		"model":       model,
		"temperature": 0,
		"stream":      false,
		"messages": []map[string]any{
			{"role": "system", "content": system},
			{"role": "user", "content": user},
		},
	}
	raw, _ := json.Marshal(payload)
	request := original.Clone(ctx)
	request.Method = http.MethodPost
	request.URL.Path = "/v1/chat/completions"
	request.URL.RawPath = ""
	request.Body = ioNopCloser{bytes.NewReader(raw)}
	request.ContentLength = int64(len(raw))
	request.Header = request.Header.Clone()
	request.Header.Set("Content-Type", "application/json")
	recorder := newBoundedRecorder()
	h.gateway.ServeHTTP(recorder, request)
	if recorder.overrun > 0 {
		return "", errors.New("事实核查响应超过 2MB 上限")
	}
	result := recorder.Result()
	defer result.Body.Close()
	var decoded map[string]any
	if json.NewDecoder(result.Body).Decode(&decoded) != nil {
		return "", errors.New("事实核查响应无法解析")
	}
	if result.StatusCode < 200 || result.StatusCode >= 300 {
		return "", fmt.Errorf("事实核查模型调用失败（HTTP %d）", result.StatusCode)
	}
	content, _ := firstChoiceMessage(decoded)["content"].(string)
	if strings.TrimSpace(content) == "" {
		return "", errors.New("事实核查模型未返回文本")
	}
	return content, nil
}
func (h *RuntimeHTTPHandler) principal(w http.ResponseWriter, r *http.Request) (apikey.Principal, bool) {
	secret := strings.TrimSpace(r.Header.Get("X-Gateway-API-Key"))
	if secret == "" {
		value := strings.TrimSpace(r.Header.Get("Authorization"))
		if strings.HasPrefix(strings.ToLower(value), "bearer ") {
			secret = strings.TrimSpace(value[7:])
		}
	}
	principal, err := h.auth.AuthenticatePrincipal(r.Context(), secret)
	if err != nil {
		apiresponse.Error(w, 401, "API Key 无效或已过期")
		return principal, false
	}
	return principal, true
}
func visible(departments []string, principal apikey.Principal, secure bool) bool {
	// fail-closed:无 APIKeyID 的匿名主体不视为"可见一切"。
	// 今天认证器总是返回 bootstrap 或真实 key ID,但任何未来认证路径的
	// 变化都不应静默放开所有部门作用域资产。
	if principal.APIKeyID == "" {
		return false
	}
	// 无部门限定的资源是全局资源:所有已认证主体可见。secure 只标记
	// "执行敏感能力"类资源,不改变可见性规则——否则全局工具/MCP 对
	// 所有人不可见,绑定它们的应用会在运行时失败。
	if len(departments) == 0 {
		return true
	}
	if principal.TenantID == nil {
		return false
	}
	for _, id := range departments {
		if id == *principal.TenantID {
			return true
		}
	}
	return false
}

func (h *RuntimeHTTPHandler) listPrompts(w http.ResponseWriter, r *http.Request) {
	principal, ok := h.principal(w, r)
	if !ok {
		return
	}
	items, err := h.service.ListPrompts(r.Context())
	if err != nil {
		apiresponse.Error(w, 503, "Prompt 服务暂不可用")
		return
	}
	result := []map[string]any{}
	for _, item := range items {
		if item.Enabled && item.Current != nil && visible(item.DepartmentIDs, principal, false) {
			result = append(result, map[string]any{"name": item.Name, "description": item.Description, "tags": item.Tags, "version": item.Current.Version, "variables": item.Current.Variables})
		}
	}
	writeRuntime(w, 200, map[string]any{"object": "list", "data": result})
}
func (h *RuntimeHTTPHandler) renderPrompt(w http.ResponseWriter, r *http.Request) {
	principal, ok := h.principal(w, r)
	if !ok {
		return
	}
	var input struct {
		Variables map[string]any `json:"variables"`
	}
	if !decodeRuntime(w, r, &input) {
		return
	}
	items, err := h.service.ListPrompts(r.Context())
	if err != nil {
		runtimeError(w, 503, "Prompt 服务暂不可用")
		return
	}
	var selected *PromptTemplate
	for i := range items {
		if items[i].Name == r.PathValue("name") && items[i].Enabled && visible(items[i].DepartmentIDs, principal, false) {
			selected = &items[i]
			break
		}
	}
	if selected == nil || selected.Current == nil {
		runtimeError(w, 404, "Prompt 不存在或不可见")
		return
	}
	rendered, err := RenderPrompt(selected.Current.Content, selected.Current.Variables, input.Variables)
	if err != nil {
		runtimeError(w, 400, err.Error())
		return
	}
	writeRuntime(w, 200, map[string]any{"name": selected.Name, "version": selected.Current.Version, "rendered": rendered})
}

func (h *RuntimeHTTPHandler) searchKnowledge(w http.ResponseWriter, r *http.Request) {
	principal, ok := h.principal(w, r)
	if !ok {
		return
	}
	var input struct {
		KnowledgeBaseID string `json:"knowledge_base_id"`
		Query           string `json:"query"`
		TopK            int    `json:"top_k"`
	}
	if !decodeRuntime(w, r, &input) {
		return
	}
	id := r.PathValue("id")
	if id == "" {
		id = input.KnowledgeBaseID
	}
	kb, err := h.service.GetKnowledgeBase(r.Context(), id)
	if err != nil || !kb.Enabled || !visible(kb.DepartmentIDs, principal, false) {
		runtimeError(w, 404, "知识库不存在或不可见")
		return
	}
	hits, err := h.retriever.Search(r.Context(), id, input.Query, input.TopK)
	if err != nil {
		runtimeError(w, 400, err.Error())
		return
	}
	writeRuntime(w, 200, map[string]any{"knowledge_base_id": id, "results": hits})
}

func (h *RuntimeHTTPHandler) listTools(w http.ResponseWriter, r *http.Request) {
	principal, ok := h.principal(w, r)
	if !ok {
		return
	}
	items, err := h.tools.List(r.Context())
	if err != nil {
		runtimeError(w, 503, "工具服务暂不可用")
		return
	}
	result := []map[string]any{}
	for _, tool := range items {
		if tool.Enabled && visible(tool.DepartmentIDs, principal, true) {
			result = append(result, map[string]any{"code": tool.Code, "name": tool.Name, "description": tool.Description, "input_schema": tool.InputSchema})
		}
	}
	writeRuntime(w, 200, map[string]any{"object": "list", "data": result})
}
func (h *RuntimeHTTPHandler) invokeTool(w http.ResponseWriter, r *http.Request) {
	principal, ok := h.principal(w, r)
	if !ok {
		return
	}
	var input struct {
		Input map[string]any `json:"input"`
	}
	if !decodeRuntime(w, r, &input) {
		return
	}
	tool, err := h.tools.GetByCode(r.Context(), r.PathValue("code"))
	if err != nil || !visible(tool.DepartmentIDs, principal, true) {
		runtimeError(w, 404, "工具不存在或不可调用")
		return
	}
	result, err := h.tools.Execute(r.Context(), tool, input.Input, principal.APIKeyID, gateway.RequestID(r.Context()))
	if err != nil {
		runtimeError(w, 502, err.Error())
		return
	}
	writeRuntime(w, 200, result)
}

type applicationRequest struct {
	Messages  []map[string]any `json:"messages"`
	Variables map[string]any   `json:"variables"`
}

func (h *RuntimeHTTPHandler) runApplication(w http.ResponseWriter, r *http.Request) {
	principal, ok := h.principal(w, r)
	if !ok {
		return
	}
	var input applicationRequest
	if !decodeRuntime(w, r, &input) {
		return
	}
	app, err := h.service.GetPublishedApplicationByCode(r.Context(), r.PathValue("code"))
	if err != nil || app.PublishedConfig == nil || !visible(app.DepartmentIDs, principal, false) {
		runtimeError(w, 404, "应用不存在、未发布或不可见")
		return
	}

	started := time.Now()
	status := "error"
	runError := ""
	retrievalCount := 0
	toolCount := 0
	modelCallCount := 0
	conversationID := strings.TrimSpace(r.Header.Get("X-Gateway-Conversation-ID"))
	traceID := h.beginTrace(r.Context(), principal, "application", app.ID, app.Code, conversationID)
	defer func() {
		traceCtx := context.WithoutCancel(r.Context())
		h.finishTrace(traceCtx, traceID, status, runError, retrievalCount, modelCallCount, toolCount)
		runID, idErr := newUUID()
		if idErr == nil {
			_, _ = h.service.pool.Exec(traceCtx, `INSERT INTO gateway.application_runs(id,application_id,version,api_key_id,trace_id,request_id,status,latency_ms,retrieval_count,tool_count,error) VALUES($1,$2,nullif($3,0),nullif($4,'')::uuid,nullif($5,'')::uuid,$6,$7,$8,$9,$10,$11)`, runID, app.ID, valueOrZero(app.PublishedVersion), principal.APIKeyID, traceID, gateway.RequestID(r.Context()), status, time.Since(started).Milliseconds(), retrievalCount, toolCount, runError)
		}
	}()
	payload, toolsByCode, prepareErr := h.prepareApplication(r.Context(), app, input, principal, &retrievalCount, traceID)
	if prepareErr != nil {
		runError = prepareErr.Error()
		runtimeError(w, 400, runError)
		return
	}
	config := *app.PublishedConfig
	var response map[string]any
	var responseHeaders http.Header
	var statusCode int
	for round := 0; ; round++ {
		modelCallCount++
		statusCode, responseHeaders, response, err = h.callGatewayWithTrace(r, payload, traceID, round)
		if err != nil {
			runError = err.Error()
			copyHeaders(w.Header(), responseHeaders)
			runtimeError(w, statusCode, runError)
			return
		}
		calls := extractToolCalls(response)
		if len(calls) == 0 {
			break
		}
		if round >= config.MaxToolRounds {
			runError = "工具调用轮次已达上限"
			runtimeError(w, 502, runError)
			return
		}
		choice := firstChoiceMessage(response)
		payload["messages"] = append(payload["messages"].([]map[string]any), choice)
		for _, call := range calls {
			tool, exists := toolsByCode[call.Name]
			if !exists {
				runError = "模型请求了未授权工具 " + call.Name
				runtimeError(w, 400, runError)
				return
			}
			var args map[string]any
			if json.Unmarshal([]byte(call.Arguments), &args) != nil {
				args = map[string]any{}
			}
			result, executeErr := h.executeToolWithTrace(r.Context(), traceID, call.Name, call.ID, round, func() (map[string]any, error) {
				return h.tools.Execute(r.Context(), tool, args, principal.APIKeyID, gateway.RequestID(r.Context()))
			})
			if executeErr != nil {
				runError = executeErr.Error()
				runtimeError(w, 502, runError)
				return
			}
			encoded, _ := json.Marshal(result["body"])
			payload["messages"] = append(payload["messages"].([]map[string]any), map[string]any{"role": "tool", "tool_call_id": call.ID, "name": call.Name, "content": string(encoded)})
			toolCount++
		}
	}
	if h.factCheck != nil {
		h.applyFactCheck(r, input, response, app.DepartmentIDs)
	}
	response["application"] = map[string]any{"code": app.Code, "name": app.Name, "version": valueOrZero(app.PublishedVersion), "retrieval_count": retrievalCount, "tool_calls": toolCount}
	status = "success"
	copyHeaders(w.Header(), responseHeaders)
	writeRuntime(w, statusCode, response)
}

// applyFactCheck verifies the assistant answer against configured knowledge
// bases and applies the policy action. It must never fail the chat: any error
// is logged and the answer is returned unchanged. departments 用于选择
// department:<uuid> 作用域的策略,空列表只应用 global 策略。
func (h *RuntimeHTTPHandler) applyFactCheck(r *http.Request, input applicationRequest, response map[string]any, departments []string) {
	answer, _ := assistantAnswer(response)
	lastQuestion := lastUserMessage(input.Messages)
	if strings.TrimSpace(answer) == "" || strings.TrimSpace(lastQuestion) == "" {
		return
	}
	scope := ""
	if len(departments) > 0 {
		scope = "department:" + departments[0]
	}
	verifier := func(ctx context.Context, model, system, user string, timeout time.Duration) (string, error) {
		return h.VerifyFactCheck(ctx, r, model, system, user, timeout)
	}
	event, err := h.factCheck.Check(r.Context(), gateway.RequestID(r.Context()), scope, lastQuestion, answer, factcheck.VerifierFunc(verifier))
	if err != nil {
		h.logger.Warn("fact-check skipped", "request_id", gateway.RequestID(r.Context()), "error", err)
		return
	}
	if event.ID == "" {
		return
	}
	switch {
	case event.Action == "block" && event.Verdict == "unsupported":
		overrideAnswer(response, "无法回答：该回复与知识库事实不符，已被事实核查拦截。")
		response["fact_check"] = map[string]any{"event_id": event.ID, "verdict": event.Verdict, "support_score": event.SupportScore, "blocked": true}
	case event.Action == "annotate":
		response["fact_check"] = map[string]any{"event_id": event.ID, "verdict": event.Verdict, "support_score": event.SupportScore, "blocked": false}
	}
}

// lastUserMessage returns the content of the last user message in the request.
func lastUserMessage(messages []map[string]any) string {
	last := ""
	for _, message := range messages {
		role, _ := message["role"].(string)
		if role != "user" {
			continue
		}
		if content, ok := message["content"].(string); ok {
			last = content
		}
	}
	return last
}

// assistantAnswer extracts the final assistant text from a gateway response.
func assistantAnswer(response map[string]any) (string, bool) {
	content, _ := firstChoiceMessage(response)["content"].(string)
	return content, strings.TrimSpace(content) != ""
}

// overrideAnswer rewrites the assistant message content in place so the portal
// and runtime consumers of response["choices"][0]["message"]["content"] all see
// the fact-checked text.
func overrideAnswer(response map[string]any, content string) {
	if message := firstChoiceMessage(response); message != nil {
		message["content"] = content
	}
}

func (h *RuntimeHTTPHandler) prepareApplication(ctx context.Context, app Application, input applicationRequest, principal apikey.Principal, retrievalCount *int, traceID string) (map[string]any, map[string]Tool, error) {
	config := *app.PublishedConfig
	messages := make([]map[string]any, 0, len(input.Messages)+2)
	total := 0
	lastQuestion := ""
	for _, message := range input.Messages {
		role, _ := message["role"].(string)
		content, contentOK := message["content"].(string)
		if (role != "user" && role != "assistant") || !contentOK {
			return nil, nil, errors.New("应用对话只接受 user/assistant 文本消息")
		}
		total += len(content)
		if total > 100000 {
			return nil, nil, errors.New("对话历史超过 100000 字符")
		}
		messages = append(messages, map[string]any{"role": role, "content": content})
		if role == "user" {
			lastQuestion = content
		}
	}
	if lastQuestion == "" {
		return nil, nil, errors.New("至少需要一条用户消息")
	}
	system := []string{}
	if config.PromptTemplateID != "" {
		prompt, err := h.service.GetPrompt(ctx, config.PromptTemplateID)
		// The prompt must be visible to this principal, mirroring the direct
		// render/list entry points, or a shared application could leak a
		// department-scoped prompt across departments.
		if err != nil || prompt.Current == nil || !prompt.Enabled || !visible(prompt.DepartmentIDs, principal, false) {
			return nil, nil, errors.New("应用绑定的 Prompt 当前不可用")
		}
		rendered, err := RenderPrompt(prompt.Current.Content, prompt.Current.Variables, input.Variables)
		if err != nil {
			return nil, nil, err
		}
		system = append(system, rendered)
	}
	evidence := []string{}
	for _, kbID := range config.KnowledgeBaseIDs {
		kb, err := h.service.GetKnowledgeBase(ctx, kbID)
		if err != nil || !kb.Enabled || !visible(kb.DepartmentIDs, principal, false) {
			return nil, nil, fmt.Errorf("应用绑定的知识库 %s 当前不可用", kbID)
		}
		hits, searchErr := h.searchWithTrace(ctx, traceID, kbID, lastQuestion, config.RetrievalTopK)
		if searchErr != nil {
			continue
		}
		for _, hit := range hits {
			*retrievalCount++
			evidence = append(evidence, fmt.Sprintf("[资料%d｜%s]\n%s", len(evidence)+1, hit.DocumentTitle, hit.Content))
		}
	}
	if len(evidence) > 0 {
		system = append(system, "请优先依据以下企业资料回答；资料不足时明确说明不确定，不得编造。引用时使用[资料N]。\n\n"+strings.Join(evidence, "\n\n"))
	}
	if len(system) > 0 {
		messages = append([]map[string]any{{"role": "system", "content": strings.Join(system, "\n\n")}}, messages...)
	}
	toolsByCode := map[string]Tool{}
	schemas := []map[string]any{}
	for _, toolID := range config.ToolIDs {
		tool, err := h.tools.Get(ctx, toolID)
		// Enforce the same department visibility as the direct tool invoke
		// entry point (secure=true because tools carry embedded request
		// headers); otherwise an app shared across departments could trigger a
		// department-only tool and borrow its stored credentials.
		if err != nil || !tool.Enabled || !visible(tool.DepartmentIDs, principal, true) {
			return nil, nil, fmt.Errorf("应用绑定的工具 %s 当前不可用", toolID)
		}
		toolsByCode[tool.Code] = tool
		var schema any
		_ = json.Unmarshal(tool.InputSchema, &schema)
		schemas = append(schemas, map[string]any{"type": "function", "function": map[string]any{"name": tool.Code, "description": tool.Description, "parameters": schema}})
	}
	payload := map[string]any{"model": config.Model, "messages": messages, "stream": false, "temperature": config.Temperature}
	if len(schemas) > 0 {
		payload["tools"] = schemas
		payload["tool_choice"] = "auto"
	}
	return payload, toolsByCode, nil
}

func (h *RuntimeHTTPHandler) callGateway(original *http.Request, payload map[string]any) (int, http.Header, map[string]any, error) {
	raw, _ := json.Marshal(payload)
	request := original.Clone(original.Context())
	request.Method = http.MethodPost
	request.URL.Path = "/v1/chat/completions"
	request.URL.RawPath = ""
	request.Body = http.NoBody
	if len(raw) > 0 {
		request.Body = ioNopCloser{bytes.NewReader(raw)}
	}
	request.ContentLength = int64(len(raw))
	request.Header = request.Header.Clone()
	request.Header.Set("Content-Type", "application/json")
	recorder := newBoundedRecorder()
	h.gateway.ServeHTTP(recorder, request)
	if recorder.overrun > 0 {
		return http.StatusBadGateway, recorder.Header(), nil,
			errors.New("模型响应超过 2MB 上限，已截断")
	}
	result := recorder.Result()
	defer result.Body.Close()
	var decoded map[string]any
	if json.NewDecoder(result.Body).Decode(&decoded) != nil {
		return result.StatusCode, result.Header, nil, errors.New("模型返回无法解析")
	}
	if result.StatusCode < 200 || result.StatusCode >= 300 {
		message := "应用模型调用失败"
		if value, ok := decoded["error"].(map[string]any); ok {
			if text, ok := value["message"].(string); ok {
				message = text
			}
		}
		return result.StatusCode, result.Header, decoded, errors.New(message)
	}
	return result.StatusCode, result.Header, decoded, nil
}

type ioNopCloser struct{ *bytes.Reader }

func (ioNopCloser) Close() error { return nil }

// maxGatewayResponseBytes caps how much of a model response a buffered app
// call may hold in memory. Non-streaming conversations go through a recorder
// that buffers the full upstream response; without a cap a long completion
// could exhaust process memory under concurrent app conversations.
const maxGatewayResponseBytes = 2 << 20 // 2 MiB

// boundedRecorder is a minimal http.ResponseWriter that buffers the response
// up to maxGatewayResponseBytes. Anything beyond the cap is discarded (but
// counted) so a runaway upstream completion can never exhaust memory; callGateway
// turns an overrun into an explicit error instead of decoding truncated JSON.
type boundedRecorder struct {
	code    int
	header  http.Header
	body    bytes.Buffer
	overrun int64
}

func newBoundedRecorder() *boundedRecorder {
	// code 初始为 0:WriteHeader 只在首次调用时生效,若网关从未调用
	// WriteHeader,则 Write 时默认回退 200。
	return &boundedRecorder{header: make(http.Header)}
}

func (r *boundedRecorder) Header() http.Header { return r.header }

func (r *boundedRecorder) WriteHeader(code int) {
	if r.code != 0 {
		return
	}
	r.code = code
}

func (r *boundedRecorder) Write(data []byte) (int, error) {
	if r.code == 0 {
		r.code = http.StatusOK
	}
	remaining := int64(maxGatewayResponseBytes) - int64(r.body.Len())
	if remaining > 0 {
		written := data
		if int64(len(written)) > remaining {
			written = written[:remaining]
		}
		_, _ = r.body.Write(written)
	}
	r.overrun += int64(len(data)) - min(remaining, int64(len(data)))
	return len(data), nil
}

func (r *boundedRecorder) Flush() {}

func (r *boundedRecorder) Result() *http.Response {
	return &http.Response{
		StatusCode: r.code,
		Header:     r.header,
		Body:       io.NopCloser(bytes.NewReader(r.body.Bytes())),
	}
}

type toolCall struct{ ID, Name, Arguments string }

func extractToolCalls(response map[string]any) []toolCall {
	message := firstChoiceMessage(response)
	rawCalls, ok := message["tool_calls"].([]any)
	if !ok {
		return nil
	}
	calls := []toolCall{}
	for _, raw := range rawCalls {
		item, ok := raw.(map[string]any)
		if !ok {
			continue
		}
		fn, _ := item["function"].(map[string]any)
		calls = append(calls, toolCall{ID: toString(item["id"]), Name: toString(fn["name"]), Arguments: toString(fn["arguments"])})
	}
	return calls
}
func firstChoiceMessage(response map[string]any) map[string]any {
	choices, ok := response["choices"].([]any)
	if !ok || len(choices) == 0 {
		return map[string]any{}
	}
	choice, _ := choices[0].(map[string]any)
	message, _ := choice["message"].(map[string]any)
	return message
}
func valueOrZero(value *int) int {
	if value == nil {
		return 0
	}
	return *value
}
func decodeRuntime(w http.ResponseWriter, r *http.Request, target any) bool {
	decoder := json.NewDecoder(http.MaxBytesReader(w, r.Body, 2<<20))
	decoder.UseNumber()
	if err := decoder.Decode(target); err != nil {
		runtimeError(w, 400, "请求格式无效")
		return false
	}
	return true
}
func runtimeError(w http.ResponseWriter, status int, message string) {
	writeRuntime(w, status, map[string]any{"error": map[string]any{"message": message, "type": "application_error"}})
}
func writeRuntime(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}
func copyHeaders(target, source http.Header) {
	for key, values := range source {
		lower := strings.ToLower(key)
		if lower == "connection" || lower == "content-length" || lower == "transfer-encoding" {
			continue
		}
		target[key] = append([]string(nil), values...)
	}
}