package middleware

import (
	"fmt"
	"net/http"
	"time"

	"github.com/gogf/gf/v2/frame/g"
	"github.com/gogf/gf/v2/net/ghttp"
	"github.com/gogf/gf/v2/os/gtime"

	"github.com/qianfree/team-api/internal/dao"
	do "github.com/qianfree/team-api/internal/model/do"
	"github.com/qianfree/team-api/internal/response"
)

const (
	IdempotencyHeader = "Idempotency-Key"
	// maxCachedBodyLen limits the response body size stored for idempotent replay.
	// Responses larger than this will still be deduplicated but won't cache the body.
	maxCachedBodyLen = 64 * 1024 // 64 KB
	// idempotencyTTL is how long an idempotency record is retained before it can be cleaned up.
	idempotencyTTL = 24 * time.Hour
)

// Idempotency ensures that requests with the same Idempotency-Key
// are processed only once. Subsequent requests with the same key
// return the cached response.
//
// 幂等键按认证主体（userType + tenantID + userID）隔离：不同租户/用户即便复用同一
// 客户端 Idempotency-Key，也各自独立，避免命中彼此缓存的响应体（跨租户数据泄漏）
// 或彼此误触 409。因此本中间件必须挂载在认证中间件（如 TenantAuth）之后。
func Idempotency(r *ghttp.Request) {
	clientKey := r.GetHeader(IdempotencyHeader)
	if clientKey == "" {
		r.Middleware.Next()
		return
	}

	ctx := r.Context()

	// 组合出按主体隔离的存储键（仍是单一字符串，不改表结构）
	tenantID := r.GetCtxVar(CtxKeyTenantID).Int64()
	userID := r.GetCtxVar(CtxKeyUserID).Int64()
	userType := r.GetCtxVar(CtxKeyUserType).String()

	// 开放平台不走 TenantAuth，身份存在 OpenPlatformAuth 注入的 typed context key 里，
	// 上面三个 CtxVar 全是零值。若不单独取，所有应用会共用同一个 ":0:0:" 前缀 ——
	// 不同租户复用同一个 Idempotency-Key 就会读到彼此缓存的响应体（跨租户数据泄漏）。
	// 主体取「应用」而非「用户」：开放平台请求由应用发起，重试也以应用为单位。
	if appID := GetOpenAppID(r.Context()); appID > 0 {
		userType = "open"
		tenantID = GetOpenTenantID(r.Context())
		userID = appID
	}

	idempotencyKey := buildIdempotencyKey(userType, tenantID, userID, clientKey)

	// Check if this key has been processed before
	var record struct {
		Id           int64  `json:"id" orm:"id"`
		Status       string `json:"status" orm:"status"`
		ResponseBody string `json:"response_body" orm:"response_body"`
	}

	err := dao.SysIdempotencyRecords.Ctx(ctx).
		Where("idempotency_key", idempotencyKey).
		Where("expires_at > NOW()").
		Scan(&record)
	if err != nil {
		// DB error: fail-closed to prevent duplicate processing
		response.ErrorMsg(r, 500, "系统繁忙，请稍后重试")
		return
	}

	if record.Id > 0 {
		if record.Status == "completed" && record.ResponseBody != "" {
			// 重放缓存响应。本中间件只挂载在 /api/* 统一响应端点上：成功响应恒为
			// HTTP 200 + JSON（response.Success 使用 WriteJson），业务错误为 HTTP 422
			// 且会被标记为 failed 而不进入此重放分支。因此固定回写 200 + JSON Content-Type，
			// 避免复用未初始化的 r.Response.Status（默认 0）以及丢失 Content-Type。
			r.Response.Header().Set("Content-Type", "application/json; charset=utf-8")
			r.Response.WriteStatus(http.StatusOK)
			r.Response.Write([]byte(record.ResponseBody))
			r.Exit()
			return
		}
		if record.Status == "processing" {
			writeConflictResponse(r)
			return
		}
	}

	// Insert processing record
	_, err = dao.SysIdempotencyRecords.Ctx(ctx).Data(do.SysIdempotencyRecords{
		IdempotencyKey: idempotencyKey,
		Status:         "processing",
		ExpiresAt:      gtime.Now().Add(idempotencyTTL),
	}).Insert()

	if err != nil {
		// If insert fails (duplicate key), another request is already processing
		writeConflictResponse(r)
		return
	}

	// Capture the response
	r.Middleware.Next()

	// After processing, update the record with cached body
	status := "completed"
	statusCode := r.Response.Status
	if statusCode >= 400 {
		status = "failed"
	}

	var responseBody string
	if buf := r.Response.Buffer(); len(buf) > 0 && len(buf) <= maxCachedBodyLen {
		responseBody = string(buf)
	}

	// Update the record
	dao.SysIdempotencyRecords.Ctx(ctx).
		Where("idempotency_key", idempotencyKey).
		Data(do.SysIdempotencyRecords{
			Status:       status,
			ResponseBody: responseBody,
		}).Update()
}

// buildIdempotencyKey 组合出按认证主体隔离的幂等存储键。
// 加入 userType/tenantID/userID 前缀，使不同主体即便复用同一客户端 key 也互不干扰，
// 杜绝跨租户命中彼此缓存响应体（数据泄漏）或误触 409。
func buildIdempotencyKey(userType string, tenantID, userID int64, clientKey string) string {
	return fmt.Sprintf("%s:%d:%d:%s", userType, tenantID, userID, clientKey)
}

// writeConflictResponse writes a 409 Conflict response for duplicate idempotency keys.
func writeConflictResponse(r *ghttp.Request) {
	r.Response.WriteStatus(409)
	r.Response.WriteJson(g.Map{
		"error": g.Map{
			"type":    "conflict",
			"message": "请求正在处理中，请勿重复提交",
			"code":    "409",
		},
	})
	r.Exit()
}