package wechat

import (
	"context"
	"encoding/json"
	"errors"
	"net/http"
	"net/url"
	"time"

	"github.com/google/uuid"
	"github.com/redis/go-redis/v9"
	"go.uber.org/zap"
)

// AppID is part of the key; environments can use different key prefixes or DBs.
func (c *Client) tokenKey() string { return c.KeyPrefix + "wechat:{" + c.AppID + "}:access_token" }

var compareDelete = redis.NewScript(`if redis.call('GET', KEYS[1]) == ARGV[1] then return redis.call('DEL', KEYS[1]) else return 0 end`)

// AccessToken shares cached tokens and a refresh lock across processes.
// Redis failures never fall back to the old plaintext file or repeated refreshes.
func (c *Client) AccessToken() string {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.Redis == nil {
		zap.L().Error("微信 token 缓存未初始化")
		return ""
	}
	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
	defer cancel()
	key := c.tokenKey()
	lockKey, owner := key+":lock", uuid.NewString()
	for {
		token, err := c.Redis.Get(ctx, key).Result()
		if err == nil && token != "" {
			return token
		}
		if err != nil && !errors.Is(err, redis.Nil) {
			zap.L().Error("读取微信 token 缓存失败", zap.Error(err))
			return ""
		}
		locked, err := c.Redis.SetNX(ctx, lockKey, owner, 30*time.Second).Result()
		if err != nil {
			zap.L().Error("获取微信 token 刷新锁失败", zap.Error(err))
			return ""
		}
		if locked {
			defer func() {
				unlockCtx, done := context.WithTimeout(context.Background(), 2*time.Second)
				defer done()
				if err := compareDelete.Run(unlockCtx, c.Redis, []string{lockKey}, owner).Err(); err != nil {
					zap.L().Warn("释放微信 token 刷新锁失败", zap.Error(err))
				}
			}()
			// Another process may have filled the cache between our GET and SET NX.
			token, err = c.Redis.Get(ctx, key).Result()
			if err == nil && token != "" {
				return token
			}
			if err != nil && !errors.Is(err, redis.Nil) {
				zap.L().Error("读取微信 token 缓存失败", zap.Error(err))
				return ""
			}
			return c.fetchToken(ctx, key)
		}
		timer := time.NewTimer(100 * time.Millisecond)
		select {
		case <-ctx.Done():
			timer.Stop()
			zap.L().Warn("等待微信 token 刷新超时")
			return ""
		case <-timer.C:
		}
	}
}

func (c *Client) fetchToken(ctx context.Context, key string) string {
	endpoint := "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=" + url.QueryEscape(c.AppID) + "&secret=" + url.QueryEscape(c.Secret)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return ""
	}
	resp, err := c.http.Do(req)
	if err != nil {
		zap.L().Error("微信 token 请求失败")
		return ""
	} // Do not log the URL containing AppSecret.
	defer resp.Body.Close()
	var data struct {
		AccessToken string `json:"access_token"`
		ExpiresIn   int64  `json:"expires_in"`
		Errcode     int    `json:"errcode"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil || resp.StatusCode != http.StatusOK || data.Errcode != 0 || data.AccessToken == "" || data.ExpiresIn <= 0 {
		zap.L().Error("微信 token 返回无效", zap.Int("http_status", resp.StatusCode), zap.Int("errcode", data.Errcode))
		return ""
	}
	ttl := time.Duration(data.ExpiresIn) * time.Second
	// Refresh early without making short-lived tokens immediately expire.
	margin := min(ttl/10, 5*time.Minute)
	ttl -= margin
	if err := c.Redis.Set(ctx, key, data.AccessToken, ttl).Err(); err != nil {
		zap.L().Error("写入微信 token 缓存失败", zap.Error(err))
		return ""
	}
	return data.AccessToken
}

// Invalidate only the token rejected by WeChat, preserving a concurrent refresh.
func (c *Client) clearTokenCache(token string) {
	if c.Redis == nil || token == "" {
		return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	if err := compareDelete.Run(ctx, c.Redis, []string{c.tokenKey()}, token).Err(); err != nil {
		zap.L().Warn("清理失效微信 token 失败", zap.Error(err))
	}
}