package selector

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"math/big"
	mathrand "math/rand"
	"net/url"
	"strings"
	"time"

	"proxyrotator/internal/model"
	"proxyrotator/internal/store"
)

// Selector 代理选择器
type Selector struct {
	store    store.ProxyStore
	leaseTTL time.Duration
}

// NewSelector 创建选择器
func NewSelector(store store.ProxyStore, leaseTTL time.Duration) *Selector {
	if leaseTTL <= 0 {
		leaseTTL = 60 * time.Second
	}
	return &Selector{
		store:    store,
		leaseTTL: leaseTTL,
	}
}

// Next 获取下一个可用代理
func (s *Selector) Next(ctx context.Context, req model.SelectRequest) (*model.Lease, error) {
	policy := req.Policy
	if policy == "" {
		policy = "round_robin"
	}

	// 查询可用代理
	proxies, err := s.store.List(ctx, model.ProxyQuery{
		Group:       req.Group,
		TagsAny:     req.TagsAny,
		StatusIn:    []model.ProxyStatus{model.StatusAlive},
		OnlyEnabled: true,
		Limit:       5000,
	})
	if err != nil {
		return nil, err
	}

	if len(proxies) == 0 {
		return nil, model.ErrNoProxy
	}

	// 根据策略选择
	var chosen model.Proxy
	switch policy {
	case "round_robin":
		key := "rr:" + req.Group + ":" + normalizeSite(req.Site)
		idx, err := s.store.NextIndex(ctx, key, len(proxies))
		if err != nil {
			return nil, err
		}
		chosen = proxies[idx]

	case "random":
		idx := mathrand.Intn(len(proxies))
		chosen = proxies[idx]

	case "weighted":
		chosen = weightedPickByScore(proxies)

	default:
		return nil, model.ErrBadPolicy
	}

	// 创建租约
	lease := model.Lease{
		LeaseID:  newLeaseID(),
		ProxyID:  chosen.ID,
		Proxy:    chosen,
		Group:    req.Group,
		Site:     req.Site,
		ExpireAt: time.Now().Add(s.leaseTTL),
	}

	// 尝试保存租约（失败也可降级不存）
	_ = s.store.CreateLease(ctx, lease)

	return &lease, nil
}

// Report 上报使用结果
func (s *Selector) Report(ctx context.Context, leaseID, proxyID string, success bool, latencyMs int64, errText string) error {
	now := time.Now()

	if success {
		status := model.StatusAlive
		return s.store.UpdateHealth(ctx, proxyID, model.HealthPatch{
			Status:     &status,
			ScoreDelta: 1,
			SuccessInc: 1,
			LatencyMs:  &latencyMs,
			CheckedAt:  &now,
		})
	}

	status := model.StatusDead
	return s.store.UpdateHealth(ctx, proxyID, model.HealthPatch{
		Status:     &status,
		ScoreDelta: -3,
		FailInc:    1,
		CheckedAt:  &now,
	})
}

// normalizeSite 规范化站点 URL（提取域名）
func normalizeSite(site string) string {
	if site == "" {
		return "default"
	}

	u, err := url.Parse(site)
	if err != nil {
		return site
	}

	host := u.Hostname()
	if host == "" {
		return site
	}

	// 去除 www 前缀
	host = strings.TrimPrefix(host, "www.")
	return host
}

// weightedPickByScore 按分数加权随机选择
func weightedPickByScore(proxies []model.Proxy) model.Proxy {
	// 计算权重（分数 + 偏移量确保正数）
	const offset = 100
	totalWeight := 0
	weights := make([]int, len(proxies))

	for i, p := range proxies {
		w := p.Score + offset
		if w < 1 {
			w = 1
		}
		weights[i] = w
		totalWeight += w
	}

	// 随机选择
	r := mathrand.Intn(totalWeight)
	for i, w := range weights {
		r -= w
		if r < 0 {
			return proxies[i]
		}
	}

	return proxies[0]
}

// newLeaseID 生成租约 ID
func newLeaseID() string {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		// fallback
		n, _ := rand.Int(rand.Reader, big.NewInt(1<<62))
		return "lease_" + n.String()
	}
	return "lease_" + hex.EncodeToString(b)
}