package middleware

import (
	"bufio"
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net"
	"net/http"
	"net/url"
	"runtime/debug"
	"strings"
	"time"

	"git.yeij.top/AskaEth/Scoreboard/server/internal/auth"
	"git.yeij.top/AskaEth/Scoreboard/server/internal/logging"
)

// HeaderRequestID 是客户端可复用的幂等/追踪请求头。
const HeaderRequestID = "X-Request-Id"

// maxRequestIDLen 限制客户端 request_id 长度：它会被下游当作幂等缓存键，超长会撑内存。
const maxRequestIDLen = 128

// RequestID 复用客户端传入的 request_id，没有或过长则生成一个并写回响应头。
func RequestID(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		id := r.Header.Get(HeaderRequestID)
		if len(id) > maxRequestIDLen {
			id = ""
		}
		if id == "" {
			buf := make([]byte, 8)
			if _, err := rand.Read(buf); err == nil {
				id = hex.EncodeToString(buf)
			} else {
				id = time.Now().UTC().Format("20060102150405.000000")
			}
		}
		// 回写请求头，让下游（幂等缓存）读到同一个受控 id。
		r.Header.Set(HeaderRequestID, id)
		w.Header().Set(HeaderRequestID, id)
		next.ServeHTTP(w, r.WithContext(contextWithRequestID(r.Context(), id)))
	})
}

func contextWithRequestID(ctx context.Context, id string) context.Context {
	return context.WithValue(ctx, ctxKeyRequestID, id)
}

// Recover 捕获 handler panic，返回统一 500，避免进程被单个请求带崩。
func Recover(logger *slog.Logger) func(http.Handler) http.Handler {
	if logger == nil {
		logger = slog.Default()
	}
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			defer func() {
				if rec := recover(); rec != nil {
					logger.Error("请求处理 panic",
						"err", rec,
						"path", r.URL.Path,
						"requestId", GetRequestID(r.Context()),
						"stack", string(debug.Stack()),
					)
					writeError(w, http.StatusInternalServerError, "INTERNAL", "服务端异常", nil)
				}
			}()
			next.ServeHTTP(w, r)
		})
	}
}

// Log 记录访问日志（方法、路径、状态、耗时、request_id）。
func Log(logger *slog.Logger) func(http.Handler) http.Handler {
	if logger == nil {
		logger = slog.Default()
	}
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			start := time.Now()
			sw := &statusWriter{ResponseWriter: w, status: http.StatusOK}
			next.ServeHTTP(sw, r)
			logger.Debug("http",
				"method", r.Method,
				"path", r.URL.Path,
				"status", sw.status,
				"dur", time.Since(start),
				"requestId", GetRequestID(r.Context()),
				"ip", ClientIP(r),
			)
		})
	}
}

// Authenticate 解析会话 Cookie；没有或无效时按 guest 放行（只读默认身份）。
// 会话查询失败必须留痕：否则系统库故障会静默把所有人降级成 guest。
func Authenticate(svc *auth.Service, logger *slog.Logger) func(http.Handler) http.Handler {
	if logger == nil {
		logger = slog.Default()
	}
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			u := &auth.User{Role: auth.RoleGuest}
			ctx := r.Context()
			if c, err := r.Cookie(auth.CookieSession); err == nil && c.Value != "" {
				found, sess, err := svc.Lookup(ctx, c.Value)
				switch {
				case err == nil:
					u = found
					// 记下会话：实时层靠它复查长连接背后的会话是否还有效（撤销后要断开）。
					ctx = WithSession(ctx, sess)
				case errors.Is(err, auth.ErrSessionNotFound):
					// 会话缺失/过期是正常情况，静默按 guest 放行。
				default:
					logger.Error("会话查询失败",
						"err", err, "path", r.URL.Path, "requestId", GetRequestID(r.Context()))
				}
			}
			next.ServeHTTP(w, r.WithContext(WithUser(ctx, u)))
		})
	}
}

// RequireRole 要求至少 need 权限；未登录或权限不足一律 403。
// 用于「guest 也不该看」的只读接口（系统配置），以便与未登录写操作区分。
func RequireRole(logger *slog.Logger, need auth.Role) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			if !User(r.Context()).Role.Allows(need) {
				intercept(logger, w, r, http.StatusForbidden, "FORBIDDEN", "无权访问该资源",
					map[string]any{"required": need.String()})
				return
			}
			next.ServeHTTP(w, r)
		})
	}
}

// RequireWrite 要求至少 need 权限的写操作；guest 返回 401（需登录），角色不足返回 403。
func RequireWrite(logger *slog.Logger, need auth.Role) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			u := User(r.Context())
			if u.Role == auth.RoleGuest {
				intercept(logger, w, r, http.StatusUnauthorized, "AUTH_REQUIRED", "请先登录", nil)
				return
			}
			if !u.Role.Allows(need) {
				intercept(logger, w, r, http.StatusForbidden, "FORBIDDEN", "无权执行该操作",
					map[string]any{"required": need.String()})
				return
			}
			next.ServeHTTP(w, r)
		})
	}
}

// MustChangePassword 阻止「必须修改密码」的账号执行写操作。
// 只放行改密与登出：否则用户会被永久锁在无法改密的死循环里（见 devdocs/08 第 1 节）。
func MustChangePassword(logger *slog.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		u := User(r.Context())
		if u.Role == auth.RoleGuest || !u.MustChangePassword {
			next.ServeHTTP(w, r)
			return
		}
		switch r.Method {
		case http.MethodGet, http.MethodHead, http.MethodOptions:
			next.ServeHTTP(w, r)
			return
		}
		switch r.URL.Path {
		case "/api/auth/password", "/api/auth/logout":
			next.ServeHTTP(w, r)
			return
		}
		intercept(logger, w, r, http.StatusForbidden, "AUTH_REQUIRED", "请先修改初始密码", nil)
	})
}

// CSRF 校验双提交 Cookie：已登录的写请求必须带 X-CSRF-Token 且与 csrf_token Cookie 一致。
func CSRF(logger *slog.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		switch r.Method {
		case http.MethodGet, http.MethodHead, http.MethodOptions:
			next.ServeHTTP(w, r)
			return
		}
		// 登录是 guest 请求，拿不到 CSRF Token；跨站表单仍能把受害者登进攻击者的账号，
		// 因此对带 Origin/Referer 的登录请求单独做同源校验。
		if r.Method == http.MethodPost && r.URL.Path == "/api/auth/login" && !sameOrigin(r) {
			intercept(logger, w, r, http.StatusForbidden, "FORBIDDEN", "登录请求来源校验失败，请刷新页面重试", nil)
			return
		}
		if User(r.Context()).Role == auth.RoleGuest {
			// 未登录请求由 RequireWrite 处理，无需 CSRF。
			next.ServeHTTP(w, r)
			return
		}
		var cookie string
		if c, err := r.Cookie(auth.CookieCSRF); err == nil {
			cookie = c.Value
		}
		if !auth.ValidCSRF(r.Header.Get("X-CSRF-Token"), cookie) {
			intercept(logger, w, r, http.StatusForbidden, "FORBIDDEN", "CSRF 校验失败，请刷新页面重试", nil)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// sameOrigin 判断请求是否来自本站。浏览器跨站 POST 一定带 Origin（或 Referer），
// 两个头都没有时（curl、非浏览器客户端）放行，避免误伤脚本调用。
func sameOrigin(r *http.Request) bool {
	raw := r.Header.Get("Origin")
	if raw == "" {
		raw = r.Header.Get("Referer")
	}
	if raw == "" {
		return true
	}
	parsed, err := url.Parse(raw)
	if err != nil || parsed.Host == "" {
		return false
	}
	return strings.EqualFold(parsed.Host, r.Host)
}

// RateLimitWrite 对已登录用户的写操作限流。
// 阈值只写在 auth.DefaultWritePerMinute 一处，这里不复述具体数字——
// 写死一个副本，改常量时必然漏改（本轮就从 30 提到 120 而漏了这句注释）。
func RateLimitWrite(svc *auth.Service, logger *slog.Logger) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			switch r.Method {
			case http.MethodGet, http.MethodHead, http.MethodOptions:
				next.ServeHTTP(w, r)
				return
			}
			u := User(r.Context())
			if u.Role != auth.RoleGuest && !svc.AllowWrite(u.ID) {
				intercept(logger, w, r, http.StatusTooManyRequests, "RATE_LIMITED", "操作过于频繁，请稍后再试", nil)
				return
			}
			next.ServeHTTP(w, r)
		})
	}
}

// statusWriter 记录响应状态码，供日志与审计判断是否成功。
type statusWriter struct {
	http.ResponseWriter
	status  int
	written bool
}

func (w *statusWriter) WriteHeader(code int) {
	if !w.written {
		w.status = code
		w.written = true
	}
	w.ResponseWriter.WriteHeader(code)
}

func (w *statusWriter) Write(b []byte) (int, error) {
	if !w.written {
		w.written = true
	}
	return w.ResponseWriter.Write(b)
}

// Hijack 透传底层连接：WebSocket 升级依赖 http.Hijacker，
// 包装 ResponseWriter 时必须显式转发，否则握手会退化成 501。
func (w *statusWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	hj, ok := w.ResponseWriter.(http.Hijacker)
	if !ok {
		return nil, nil, http.ErrNotSupported
	}
	return hj.Hijack()
}

// Flush 透传，保证流式响应不被缓冲。
func (w *statusWriter) Flush() {
	if f, ok := w.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}

// writeError 输出统一错误结构；中间件不依赖 httpapi，避免包循环。
// intercept 记录一次中间件层的拦截，再写出统一响应。
// 这几个中间件都在 handler 之前就返回响应，不经 httpapi 的 writeAPIError——
// 不在这里记的话，这些拦截完全没有痕迹。收成一个函数是为了「只要写了响应就一定有日志」。
// 与 httpapi 的拦截日志同一形状：WARN 给原因与拦截点，DEBUG 补上下文，两类都进 interceptions/。
func intercept(logger *slog.Logger, w http.ResponseWriter, r *http.Request, status int, code, message string, detail any) {
	if logger == nil {
		logger = slog.Default()
	}
	u := User(r.Context())
	actor := actorLabel(u)
	role := u.Role.String()
	reqID := GetRequestID(r.Context())
	// skip=2：0 是本包 Origin 自己的帧，1 是 intercept，2 才是做校验的那个中间件函数。
	origin := logging.Origin(2)

	logger.Warn("请求被拦截",
		"reason", message, "origin", origin, "code", code,
		"method", r.Method, "path", r.URL.Path,
		"actor", actor, "role", role, "requestId", reqID, "ip", ClientIP(r),
		logging.ChannelKey, logging.ChannelInterception)
	logger.Debug("拦截上下文",
		"code", code, "detail", detail, "origin", origin,
		"method", r.Method, "path", r.URL.Path, "ip", ClientIP(r),
		"actor", actor, "role", role, "requestId", reqID,
		logging.ChannelKey, logging.ChannelInterception)

	writeError(w, status, code, message, detail)
}

// actorLabel 是日志里的操作人：未登录记 guest，登录后记「用户名#id」，比裸 id 好认。
func actorLabel(u *auth.User) string {
	if u == nil || u.ID == 0 {
		return "guest"
	}
	return fmt.Sprintf("%s#%d", u.Username, u.ID)
}

func writeError(w http.ResponseWriter, status int, code, message string, detail any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	body := map[string]any{
		"ok": false,
		"error": map[string]any{
			"code":    code,
			"message": message,
		},
	}
	if detail != nil {
		body["error"].(map[string]any)["detail"] = detail
	}
	_ = json.NewEncoder(w).Encode(body)
}