package upstream

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"

	"cursor/gen/agentv1"
	"cursor/gen/aiserverv1"
	"cursor/internal/logger"
	"cursor/internal/netproxy"

	"google.golang.org/protobuf/encoding/protojson"
	"google.golang.org/protobuf/proto"
)

var hopByHopHeaders = map[string]struct{}{
	"connection":          {},
	"proxy-connection":    {},
	"keep-alive":          {},
	"proxy-authenticate":  {},
	"proxy-authorization": {},
	"te":                  {},
	"trailer":             {},
	"transfer-encoding":   {},
	"upgrade":             {},
}

func ForwardToUpstream(reqCtx *RequestContext, options ForwardOptions) (*ForwardMeta, error) {
	requestBody := reqCtx.RequestBody
	if options.BodyOverride != nil {
		requestBody = options.BodyOverride
	}
	if !shouldRequestCarryBody(reqCtx.Method) {
		requestBody = []byte{}
	}

	upstreamRequest, upstreamClient, err := buildUpstreamRequest(reqCtx, requestBody, options)
	if err != nil {
		return nil, err
	}

	upstreamResponse, err := upstreamClient.Do(upstreamRequest)
	if err != nil {
		return nil, err
	}
	defer upstreamResponse.Body.Close()

	copyResponseHeadersToClient(reqCtx.ResponseWriter.Header(), upstreamResponse.Header)
	reqCtx.ResponseWriter.WriteHeader(upstreamResponse.StatusCode)

	written, copyErr := copyResponse(reqCtx.ResponseWriter, upstreamResponse.Body)
	meta := &ForwardMeta{
		StatusCode:   upstreamResponse.StatusCode,
		Status:       upstreamResponse.Status,
		ContentType:  upstreamResponse.Header.Get("content-type"),
		ResponseSize: written,
	}
	if copyErr != nil {
		return meta, copyErr
	}
	return meta, nil
}

func buildUpstreamRequest(reqCtx *RequestContext, body []byte, options ForwardOptions) (*http.Request, HTTPClient, error) {
	upstreamRequest, err := http.NewRequestWithContext(reqCtx.Request.Context(), reqCtx.Method, reqCtx.TargetURL.String(), bytes.NewReader(body))
	if err != nil {
		return nil, nil, fmt.Errorf("create upstream request failed: %w", err)
	}

	copyRequestHeadersForUpstream(upstreamRequest.Header, reqCtx.Headers)
	upstreamRequest.Header.Del(HeaderRawServerURL)
	if !shouldRequestCarryBody(reqCtx.Method) {
		upstreamRequest.Header.Del("content-length")
	} else {
		upstreamRequest.Header.Set("content-length", strconv.Itoa(len(body)))
	}
	upstreamRequest.Host = reqCtx.TargetURL.Host

	if options.PatchHeaders != nil {
		options.PatchHeaders(upstreamRequest.Header)
	}

	upstreamClient := reqCtx.Deps.HTTPClient
	if upstreamClient == nil {
		upstreamClient = netproxy.NewHTTPClient(0)
	}

	return upstreamRequest, upstreamClient, nil
}

func copyResponse(writer io.Writer, reader io.Reader) (int64, error) {
	buffer := make([]byte, 32*1024)
	var total int64

	for {
		readCount, readErr := reader.Read(buffer)
		if readCount > 0 {
			chunk := buffer[:readCount]
			written, writeErr := writer.Write(chunk)
			total += int64(written)
			if writeErr != nil {
				return total, writeErr
			}
			if written < len(chunk) {
				return total, io.ErrShortWrite
			}
			if flusher, ok := writer.(http.Flusher); ok {
				flusher.Flush()
			}
		}
		if readErr != nil {
			if readErr == io.EOF {
				return total, nil
			}
			return total, readErr
		}
	}
}

func ParseAndValidateRawURL(raw string) (*url.URL, error) {
	value := strings.TrimSpace(raw)
	if value == "" {
		return nil, fmt.Errorf("empty raw url")
	}
	parsed, err := url.Parse(value)
	if err != nil {
		return nil, err
	}
	if parsed.Scheme != "http" && parsed.Scheme != "https" {
		return nil, fmt.Errorf("unsupported scheme %q", parsed.Scheme)
	}
	if strings.TrimSpace(parsed.Host) == "" {
		return nil, fmt.Errorf("empty host")
	}
	return parsed, nil
}

func copyRequestHeadersForUpstream(target http.Header, source http.Header) {
	for key, values := range source {
		lowerKey := strings.ToLower(key)
		if _, exists := hopByHopHeaders[lowerKey]; exists {
			continue
		}
		for _, value := range values {
			target.Add(key, value)
		}
	}
}

func copyResponseHeadersToClient(target http.Header, source http.Header) {
	localWildcardCORS := target.Get("Access-Control-Allow-Origin") == "*"
	for key, values := range source {
		lowerKey := strings.ToLower(key)
		if _, exists := hopByHopHeaders[lowerKey]; exists {
			continue
		}
		if localWildcardCORS && (lowerKey == "access-control-allow-origin" || lowerKey == "access-control-allow-credentials") {
			continue
		}
		for _, value := range values {
			target.Add(key, value)
		}
	}
}

func shouldRequestCarryBody(method string) bool {
	switch strings.ToUpper(strings.TrimSpace(method)) {
	case http.MethodGet, http.MethodHead, http.MethodDelete:
		return false
	default:
		return true
	}
}

func marshalJSONBody(payload map[string]any) ([]byte, error) {
	if payload == nil {
		return []byte("{}"), nil
	}
	return json.Marshal(payload)
}

func handleMockProto(reqCtx *RequestContext, route *Route) error {
	payload := map[string]any{}
	if route.MockPayloadBuilder != nil {
		built, err := route.MockPayloadBuilder(reqCtx)
		if err != nil {
			return err
		}
		payload = built
	}
	responseBody, err := encodeMockProto(route.MockProtoType, payload)
	if err != nil {
		return err
	}
	reqCtx.ResponseWriter.Header().Set("content-type", "application/proto")
	reqCtx.ResponseWriter.Header().Del("content-encoding")
	reqCtx.ResponseWriter.Header().Set("content-length", strconv.Itoa(len(responseBody)))
	reqCtx.ResponseWriter.WriteHeader(route.StatusCode)
	_, _ = reqCtx.ResponseWriter.Write(responseBody)
	return nil
}

func appendProtoVarint(output []byte, value uint64) []byte {
	for value >= 0x80 {
		output = append(output, byte(value)|0x80)
		value >>= 7
	}
	return append(output, byte(value))
}

func handleFixedStatus(reqCtx *RequestContext, route *Route) error {
	if route != nil && route.ConsoleLog {
		logger.Infof("backend server fixed-status route hit name=%s method=%s path=%s raw_url=%s status=%d", route.Name, reqCtx.Method, reqCtx.TargetURL.Path, reqCtx.RawURL, route.StatusCode)
	}
	writeFixedStatus(reqCtx, route.StatusCode)
	return nil
}

func writeFixedStatus(reqCtx *RequestContext, statusCode int) {
	if reqCtx == nil || reqCtx.ResponseWriter == nil {
		return
	}
	reqCtx.ResponseWriter.WriteHeader(statusCode)
}

func handleDirect(reqCtx *RequestContext, route *Route) error {
	_ = route
	_, err := ForwardToUpstream(reqCtx, ForwardOptions{})
	return err
}

func encodeMockProto(typeName string, payload map[string]any) ([]byte, error) {
	message, err := newProtoMessage(typeName)
	if err != nil {
		return nil, err
	}
	data, err := json.Marshal(payload)
	if err != nil {
		return nil, err
	}
	if err := (protojson.UnmarshalOptions{DiscardUnknown: false}).Unmarshal(data, message); err != nil {
		return nil, fmt.Errorf("mock proto json decode failed: %w", err)
	}
	return proto.Marshal(message)
}

func newProtoMessage(typeName string) (proto.Message, error) {
	switch strings.TrimSpace(typeName) {
	case "aiserver.v1.ServerTimeResponse":
		return &aiserverv1.ServerTimeResponse{}, nil
	case "aiserver.v1.GetServerConfigResponse":
		return &aiserverv1.GetServerConfigResponse{}, nil
	case "aiserver.v1.AvailableModelsResponse":
		return &aiserverv1.AvailableModelsResponse{}, nil
	case "aiserver.v1.GetDefaultModelNudgeDataResponse":
		return &aiserverv1.GetDefaultModelNudgeDataResponse{}, nil
	case "aiserver.v1.BootstrapStatsigResponse":
		return &aiserverv1.BootstrapStatsigResponse{}, nil
	case "aiserver.v1.GetFirstWindowStatsigDecisionResponse":
		return &aiserverv1.GetFirstWindowStatsigDecisionResponse{}, nil
	case "aiserver.v1.GetCurrentPeriodUsageResponse":
		return &aiserverv1.GetCurrentPeriodUsageResponse{}, nil
	case "aiserver.v1.GetTeamsResponse":
		return &aiserverv1.GetTeamsResponse{}, nil
	case "aiserver.v1.GetMeResponse":
		return &aiserverv1.GetMeResponse{}, nil
	case "aiserver.v1.GetUserPrivacyModeResponse":
		return &aiserverv1.GetUserPrivacyModeResponse{}, nil
	case "aiserver.v1.GetPlanInfoResponse":
		return &aiserverv1.GetPlanInfoResponse{}, nil
	case "aiserver.v1.GetUsageLimitStatusAndActiveGrantsResponse":
		return &aiserverv1.GetUsageLimitStatusAndActiveGrantsResponse{}, nil
	case "aiserver.v1.IsOnNewPricingResponse":
		return &aiserverv1.IsOnNewPricingResponse{}, nil
	case "aiserver.v1.GetTeamAdminSettingsResponse":
		return &aiserverv1.GetTeamAdminSettingsResponse{}, nil
	case "aiserver.v1.GetTeamReposResponse":
		return &aiserverv1.GetTeamReposResponse{}, nil
	case "aiserver.v1.GetUsableModelsResponse":
		return &agentv1.GetUsableModelsResponse{}, nil
	case "aiserver.v1.GetDefaultModelForCliResponse":
		return &agentv1.GetDefaultModelForCliResponse{}, nil
	case "aiserver.v1.GetDefaultModelResponse":
		return &aiserverv1.GetDefaultModelResponse{}, nil
	case "aiserver.v1.GetGlobalCommandsResponse":
		return &aiserverv1.GetGlobalCommandsResponse{}, nil
	case "aiserver.v1.GetCliDownloadUrlResponse":
		return &aiserverv1.GetCliDownloadUrlResponse{}, nil
	case "aiserver.v1.SubmitLogsResponse":
		return &aiserverv1.SubmitLogsResponse{}, nil
	case "aiserver.v1.TrackEventsResponse":
		return &aiserverv1.TrackEventsResponse{}, nil
	default:
		return nil, fmt.Errorf("unsupported proto message type %q", typeName)
	}
}