package router

import (
	"context"
	"math"
	"sync"
	"time"

	"lijiaoqiao/gateway/internal/adapter"
	"lijiaoqiao/gateway/pkg/error"
)

// LoadBalancerStrategy 负载均衡策略
type LoadBalancerStrategy string

const (
	StrategyLatency     LoadBalancerStrategy = "latency"
	StrategyRoundRobin  LoadBalancerStrategy = "round_robin"
	StrategyWeighted    LoadBalancerStrategy = "weighted"
	StrategyAvailability LoadBalancerStrategy = "availability"
)

// ProviderHealth Provider健康状态
type ProviderHealth struct {
	Name          string
	Available     bool
	LatencyMs     int64
	FailureRate   float64
	Weight        float64
	LastCheckTime time.Time
}

// Router 路由器
type Router struct {
	providers map[string]adapter.ProviderAdapter
	health    map[string]*ProviderHealth
	strategy  LoadBalancerStrategy
	mu        sync.RWMutex
}

// NewRouter 创建路由器
func NewRouter(strategy LoadBalancerStrategy) *Router {
	return &Router{
		providers: make(map[string]adapter.ProviderAdapter),
		health:    make(map[string]*ProviderHealth),
		strategy:  strategy,
	}
}

// RegisterProvider 注册Provider
func (r *Router) RegisterProvider(name string, provider adapter.ProviderAdapter) {
	r.mu.Lock()
	defer r.mu.Unlock()

	r.providers[name] = provider
	r.health[name] = &ProviderHealth{
		Name:          name,
		Available:     true,
		LatencyMs:     0,
		FailureRate:   0,
		Weight:        1.0,
		LastCheckTime: time.Now(),
	}
}

// SelectProvider 选择最佳Provider
func (r *Router) SelectProvider(ctx context.Context, model string) (adapter.ProviderAdapter, error) {
	r.mu.RLock()
	defer r.mu.RUnlock()

	var candidates []string
	for name, provider := range r.providers {
		if r.isProviderAvailable(name, model) {
			candidates = append(candidates, name)
		}
	}

	if len(candidates) == 0 {
		return nil, error.NewGatewayError(error.ROUTER_NO_PROVIDER_AVAILABLE, "no provider available for model: "+model)
	}

	// 根据策略选择
	switch r.strategy {
	case StrategyLatency:
		return r.selectByLatency(candidates)
	case StrategyWeighted:
		return r.selectByWeight(candidates)
	case StrategyAvailability:
		return r.selectByAvailability(candidates)
	default:
		return r.selectByLatency(candidates)
	}
}

func (r *Router) isProviderAvailable(name, model string) bool {
	health, ok := r.health[name]
	if !ok {
		return false
	}

	if !health.Available {
		return false
	}

	// 检查模型是否支持
	provider := r.providers[name]
	if provider == nil {
		return false
	}

	for _, m := range provider.SupportedModels() {
		if m == model || m == "*" {
			return true
		}
	}

	return false
}

func (r *Router) selectByLatency(candidates []string) (adapter.ProviderAdapter, error) {
	var bestProvider adapter.ProviderAdapter
	var minLatency int64 = math.MaxInt64

	for _, name := range candidates {
		health := r.health[name]
		if health.LatencyMs < minLatency {
			minLatency = health.LatencyMs
			bestProvider = r.providers[name]
		}
	}

	if bestProvider == nil {
		return nil, error.NewGatewayError(error.ROUTER_NO_PROVIDER_AVAILABLE, "no available provider")
	}

	return bestProvider, nil
}

func (r *Router) selectByWeight(candidates []string) (adapter.ProviderAdapter, error) {
	var totalWeight float64
	for _, name := range candidates {
		totalWeight += r.health[name].Weight
	}

	randVal := float64(time.Now().UnixNano()) / float64(math.MaxInt64) * totalWeight
	var cumulative float64

	for _, name := range candidates {
		cumulative += r.health[name].Weight
		if randVal <= cumulative {
			return r.providers[name], nil
		}
	}

	return r.providers[candidates[0]], nil
}

func (r *Router) selectByAvailability(candidates []string) (adapter.ProviderAdapter, error) {
	var bestProvider adapter.ProviderAdapter
	var minFailureRate float64 = math.MaxFloat64

	for _, name := range candidates {
		health := r.health[name]
		if health.FailureRate < minFailureRate {
			minFailureRate = health.FailureRate
			bestProvider = r.providers[name]
		}
	}

	if bestProvider == nil {
		return nil, error.NewGatewayError(error.ROUTER_NO_PROVIDER_AVAILABLE, "no available provider")
	}

	return bestProvider, nil
}

// GetFallbackProviders 获取Fallback Providers
func (r *Router) GetFallbackProviders(ctx context.Context, model string) ([]adapter.ProviderAdapter, error) {
	r.mu.RLock()
	defer r.mu.RUnlock()

	var fallbacks []adapter.ProviderAdapter

	for name, provider := range r.providers {
		if name == "primary" {
			continue // 跳过主Provider
		}
		if r.isProviderAvailable(name, model) {
			fallbacks = append(fallbacks, provider)
		}
	}

	return fallbacks, nil
}

// RecordResult 记录调用结果
func (r *Router) RecordResult(ctx context.Context, providerName string, success bool, latencyMs int64) {
	r.mu.Lock()
	defer r.mu.Unlock()

	health, ok := r.health[providerName]
	if !ok {
		return
	}

	// 更新延迟
	if latencyMs > 0 {
		// 指数移动平均
		if health.LatencyMs == 0 {
			health.LatencyMs = latencyMs
		} else {
			health.LatencyMs = (health.LatencyMs*7 + latencyMs) / 8
		}
	}

	// 更新失败率
	if success {
		if health.FailureRate > 0 {
			health.FailureRate = health.FailureRate * 0.9 // 下降
		}
	} else {
		health.FailureRate = health.FailureRate*0.9 + 0.1 // 上升
	}

	// 检查是否应该标记为不可用
	if health.FailureRate > 0.5 {
		health.Available = false
	}

	health.LastCheckTime = time.Now()
}

// UpdateHealth 更新健康状态
func (r *Router) UpdateHealth(providerName string, available bool) {
	r.mu.Lock()
	defer r.mu.Unlock()

	if health, ok := r.health[providerName]; ok {
		health.Available = available
		health.LastCheckTime = time.Now()
	}
}

// GetHealthStatus 获取健康状态
func (r *Router) GetHealthStatus() map[string]*ProviderHealth {
	r.mu.RLock()
	defer r.mu.RUnlock()

	result := make(map[string]*ProviderHealth)
	for name, health := range r.health {
		result[name] = &ProviderHealth{
			Name:          health.Name,
			Available:     health.Available,
			LatencyMs:     health.LatencyMs,
			FailureRate:   health.FailureRate,
			Weight:        health.Weight,
			LastCheckTime: health.LastCheckTime,
		}
	}
	return result
}