// Package proxy provides high-performance OpenAI multi-key proxy server
package proxy

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"time"

	"gpt-load/internal/channel"
	"gpt-load/internal/config"
	app_errors "gpt-load/internal/errors"
	"gpt-load/internal/keypool"
	"gpt-load/internal/models"
	"gpt-load/internal/response"
	"gpt-load/internal/services"
	"gpt-load/internal/types"
	"gpt-load/internal/utils"

	"github.com/gin-gonic/gin"
	"github.com/sirupsen/logrus"
)

// ProxyServer represents the proxy server
type ProxyServer struct {
	keyProvider       *keypool.KeyProvider
	groupManager      *services.GroupManager
	settingsManager   *config.SystemSettingsManager
	channelFactory    *channel.Factory
	requestLogService *services.RequestLogService
}

// NewProxyServer creates a new proxy server
func NewProxyServer(
	keyProvider *keypool.KeyProvider,
	groupManager *services.GroupManager,
	settingsManager *config.SystemSettingsManager,
	channelFactory *channel.Factory,
	requestLogService *services.RequestLogService,
) (*ProxyServer, error) {
	return &ProxyServer{
		keyProvider:       keyProvider,
		groupManager:      groupManager,
		settingsManager:   settingsManager,
		channelFactory:    channelFactory,
		requestLogService: requestLogService,
	}, nil
}

// HandleProxy is the main entry point for proxy requests, refactored based on the stable .bak logic.
func (ps *ProxyServer) HandleProxy(c *gin.Context) {
	startTime := time.Now()
	groupName := c.Param("group_name")

	group, err := ps.groupManager.GetGroupByName(groupName)
	if err != nil {
		response.Error(c, app_errors.ParseDBError(err))
		return
	}

	channelHandler, err := ps.channelFactory.GetChannel(group)
	if err != nil {
		response.Error(c, app_errors.NewAPIError(app_errors.ErrInternalServer, fmt.Sprintf("Failed to get channel for group '%s': %v", groupName, err)))
		return
	}

	bodyBytes, err := io.ReadAll(c.Request.Body)
	if err != nil {
		logrus.Errorf("Failed to read request body: %v", err)
		response.Error(c, app_errors.NewAPIError(app_errors.ErrBadRequest, "Failed to read request body"))
		return
	}
	c.Request.Body.Close()

	finalBodyBytes, err := ps.applyParamOverrides(bodyBytes, group)
	if err != nil {
		response.Error(c, app_errors.NewAPIError(app_errors.ErrInternalServer, fmt.Sprintf("Failed to apply parameter overrides: %v", err)))
		return
	}

	isStream := channelHandler.IsStreamRequest(c, bodyBytes)

	ps.executeRequestWithRetry(c, channelHandler, group, finalBodyBytes, isStream, startTime, 0, nil)
}

// executeRequestWithRetry is the core recursive function for handling requests and retries.
func (ps *ProxyServer) executeRequestWithRetry(
	c *gin.Context,
	channelHandler channel.ChannelProxy,
	group *models.Group,
	bodyBytes []byte,
	isStream bool,
	startTime time.Time,
	retryCount int,
	retryErrors []types.RetryError,
) {
	cfg := group.EffectiveConfig
	if retryCount > cfg.MaxRetries {
		if len(retryErrors) > 0 {
			lastError := retryErrors[len(retryErrors)-1]
			var errorJSON map[string]any
			if err := json.Unmarshal([]byte(lastError.ErrorMessage), &errorJSON); err == nil {
				c.JSON(lastError.StatusCode, errorJSON)
			} else {
				response.Error(c, app_errors.NewAPIErrorWithUpstream(lastError.StatusCode, "UPSTREAM_ERROR", lastError.ErrorMessage))
			}
			logrus.Debugf("Max retries exceeded for group %s after %d attempts. Parsed Error: %s", group.Name, retryCount, lastError.ErrorMessage)

			keyID, _ := strconv.ParseUint(lastError.KeyID, 10, 64)
			ps.logRequest(c, group, uint(keyID), startTime, lastError.StatusCode, retryCount, errors.New(lastError.ErrorMessage))
		} else {
			response.Error(c, app_errors.ErrMaxRetriesExceeded)
			logrus.Debugf("Max retries exceeded for group %s after %d attempts.", group.Name, retryCount)
			ps.logRequest(c, group, 0, startTime, http.StatusServiceUnavailable, retryCount, app_errors.ErrMaxRetriesExceeded)
		}
		return
	}

	apiKey, err := ps.keyProvider.SelectKey(group.ID)
	if err != nil {
		logrus.Errorf("Failed to select a key for group %s on attempt %d: %v", group.Name, retryCount+1, err)
		response.Error(c, app_errors.NewAPIError(app_errors.ErrNoKeysAvailable, err.Error()))
		ps.logRequest(c, group, 0, startTime, http.StatusServiceUnavailable, retryCount, err)
		return
	}

	upstreamURL, err := channelHandler.BuildUpstreamURL(c.Request.URL, group)
	if err != nil {
		response.Error(c, app_errors.NewAPIError(app_errors.ErrInternalServer, fmt.Sprintf("Failed to build upstream URL: %v", err)))
		return
	}

	var ctx context.Context
	var cancel context.CancelFunc
	if isStream {
		ctx, cancel = context.WithCancel(c.Request.Context())
	} else {
		timeout := time.Duration(cfg.RequestTimeout) * time.Second
		ctx, cancel = context.WithTimeout(c.Request.Context(), timeout)
	}
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, c.Request.Method, upstreamURL, bytes.NewReader(bodyBytes))
	if err != nil {
		logrus.Errorf("Failed to create upstream request: %v", err)
		response.Error(c, app_errors.ErrInternalServer)
		return
	}
	req.ContentLength = int64(len(bodyBytes))

	req.Header = c.Request.Header.Clone()
	channelHandler.ModifyRequest(req, apiKey, group)

	var client *http.Client
	if isStream {
		client = channelHandler.GetStreamClient()
		req.Header.Set("X-Accel-Buffering", "no")
	} else {
		client = channelHandler.GetHTTPClient()
	}

	resp, err := client.Do(req)
	if resp != nil {
		defer resp.Body.Close()
	}

	// Unified error handling for retries.
	if err != nil || (resp != nil && resp.StatusCode >= 400) {
		if err != nil && app_errors.IsIgnorableError(err) {
			logrus.Debugf("Client-side ignorable error for key %s, aborting retries: %v", utils.MaskAPIKey(apiKey.KeyValue), err)
			ps.logRequest(c, group, apiKey.ID, startTime, 499, retryCount+1, err)
			return
		}

		ps.keyProvider.UpdateStatus(apiKey, group, false)

		var statusCode int
		var errorMessage string
		var parsedError string

		if err != nil {
			statusCode = 0
			errorMessage = err.Error()
			logrus.Debugf("Request failed (attempt %d/%d) for key %s: %v", retryCount+1, cfg.MaxRetries, utils.MaskAPIKey(apiKey.KeyValue), err)
		} else {
			// HTTP-level error (status >= 400)
			statusCode = resp.StatusCode
			errorBody, readErr := io.ReadAll(resp.Body)
			if readErr != nil {
				logrus.Errorf("Failed to read error body: %v", readErr)
				errorBody = []byte("Failed to read error body")
			}

			errorBody = handleGzipCompression(resp, errorBody)
			errorMessage = string(errorBody)
			parsedError = app_errors.ParseUpstreamError(errorBody)
			logrus.Debugf("Request failed with status %d (attempt %d/%d) for key %s. Parsed Error: %s", statusCode, retryCount+1, cfg.MaxRetries, utils.MaskAPIKey(apiKey.KeyValue), parsedError)
		}

		newRetryErrors := append(retryErrors, types.RetryError{
			StatusCode:   statusCode,
			ErrorMessage: errorMessage,
			KeyID:        fmt.Sprintf("%d", apiKey.ID),
			Attempt:      retryCount + 1,
		})
		ps.executeRequestWithRetry(c, channelHandler, group, bodyBytes, isStream, startTime, retryCount+1, newRetryErrors)
		return
	}

	ps.keyProvider.UpdateStatus(apiKey, group, true)
	logrus.Debugf("Request for group %s succeeded on attempt %d with key %s", group.Name, retryCount+1, utils.MaskAPIKey(apiKey.KeyValue))
	ps.logRequest(c, group, apiKey.ID, startTime, resp.StatusCode, retryCount+1, nil)

	for key, values := range resp.Header {
		for _, value := range values {
			c.Header(key, value)
		}
	}
	c.Status(resp.StatusCode)

	if isStream {
		ps.handleStreamingResponse(c, resp)
	} else {
		ps.handleNormalResponse(c, resp)
	}
}

// logRequest is a helper function to create and record a request log.
func (ps *ProxyServer) logRequest(
	c *gin.Context,
	group *models.Group,
	keyID uint,
	startTime time.Time,
	statusCode int,
	retries int,
	finalError error,
) {
	if ps.requestLogService == nil {
		return
	}

	duration := time.Since(startTime).Milliseconds()

	logEntry := &models.RequestLog{
		GroupID:     group.ID,
		KeyID:       keyID,
		IsSuccess:   finalError == nil && statusCode < 400,
		SourceIP:    c.ClientIP(),
		StatusCode:  statusCode,
		RequestPath: c.Request.URL.String(),
		Duration:    duration,
		UserAgent:   c.Request.UserAgent(),
		Retries:     retries,
	}

	if finalError != nil {
		logEntry.ErrorMessage = finalError.Error()
	}

	if err := ps.requestLogService.Record(logEntry); err != nil {
		logrus.Errorf("Failed to record request log: %v", err)
	}
}