package middleware

import (
	"bytes"
	"github.com/gin-gonic/gin"
	"io"
	"net/http"
	"one-api/common"
	"strconv"
	"time"
)

func RetryHandler(group *gin.RouterGroup) gin.HandlerFunc {
	var retryHandler gin.HandlerFunc
	// 获取RetryHandler在当前HandlersChain的位置
	index := len(group.Handlers) + 1
	retryHandler = func(c *gin.Context) {
		// Backup request
		hasBody := c.Request.ContentLength > 0
		backupHeader := c.Request.Header.Clone()
		var backupBody []byte
		var err error
		if hasBody {
			backupBody, err = io.ReadAll(c.Request.Body)
			if err != nil {
				abortWithMessage(c, http.StatusBadRequest, "Invalid request")
				return
			}
			_ = c.Request.Body.Close()
			c.Request.Body = io.NopCloser(bytes.NewBuffer(backupBody))
		}

		// 获取 retryHandler 后续的中间件
		// Get next handlers
		nextHandlers := group.Handlers[index:]

		// 加入Relay处理函数 c.Handler() => c.handlers.Last() => controller.Relay
		// Add Relay handler
		nextHandlers = append(nextHandlers, c.Handler())

		// Retry
		maxRetryStr := c.Query("retry")
		maxRetry, err := strconv.Atoi(maxRetryStr)
		if err != nil || maxRetryStr == "" || maxRetry < 0 || maxRetry > common.RetryTimes {
			maxRetry = common.RetryTimes
		}
		retryDelay := time.Duration(common.RetryInterval) * time.Millisecond
		for i := maxRetry; i >= 0; i-- {
			c.Set("retry", i)

			if i == maxRetry {
				// 第一次请求, 直接执行使用c.Next()调用后续中间件, 防止直接使用handler 内部调用c.Next() 导致重复执行
				// First request, execute next middleware
				c.Next()
			} else {
				// 重试, 恢复请求头和请求体, 并执行后续中间件
				// Retry, restore request and execute next middleware
				c.Request.Header = backupHeader.Clone()
				if hasBody {
					c.Request.Body = io.NopCloser(bytes.NewBuffer(backupBody))
				}
				for _, handler := range nextHandlers {
					handler(c)
				}
			}

			// If no errors, return
			if len(c.Errors) == 0 {
				return
			}
			// c.index 指向 AbortIndex 可以防止出错时重复执行后续中间件
			c.Abort()
			// If errors, retry after delay
			time.Sleep(retryDelay)
			// Clear errors to avoid confusion in next middleware
			c.Errors = c.Errors[:0]
		}
	}
	return retryHandler
}