package circuitbreaker

import (
	"sync"
	"time"

	"go.uber.org/zap"
)

type State int

const (
	StateClosed   State = iota
	StateOpen
	StateHalfOpen
)

type Config struct {
	FailureThreshold int           // 连续失败次数阈值，超过则开启熔断
	SuccessThreshold int           // 半开状态下连续成功次数，恢复到关闭
	Timeout          time.Duration // 熔断开启后等待多久进入半开
	Name             string       // 熔断器名称，用于日志
}

func DefaultConfig(name string) Config {
	return Config{
		FailureThreshold: 5,
		SuccessThreshold: 3,
		Timeout:          30 * time.Second,
		Name:             name,
	}
}

type Breaker struct {
	cfg    Config
	mu     sync.Mutex
	state  State
	fails  int
	wins   int
	openAt time.Time
}

func New(cfg Config) *Breaker {
	return &Breaker{cfg: cfg}
}

func (b *Breaker) Allow() bool {
	b.mu.Lock()
	defer b.mu.Unlock()

	switch b.state {
	case StateClosed:
		return true
	case StateOpen:
		if time.Since(b.openAt) > b.cfg.Timeout {
			b.state = StateHalfOpen
			b.wins = 0
			return true
		}
		return false
	case StateHalfOpen:
		return true
	default:
		return true
	}
}

func (b *Breaker) RecordSuccess() {
	b.mu.Lock()
	defer b.mu.Unlock()

	b.fails = 0
	if b.state == StateHalfOpen {
		b.wins++
		if b.wins >= b.cfg.SuccessThreshold {
			b.state = StateClosed
			b.wins = 0
			zap.L().Info("circuit breaker closed",
				zap.String("breaker", b.cfg.Name),
			)
		}
	}
}

func (b *Breaker) RecordFailure() {
	b.mu.Lock()
	defer b.mu.Unlock()

	b.fails++
	if b.state == StateHalfOpen {
		b.state = StateOpen
		b.openAt = time.Now()
		b.wins = 0
		zap.L().Warn("circuit breaker re-opened from half-open",
			zap.String("breaker", b.cfg.Name),
		)
		return
	}
	if b.fails >= b.cfg.FailureThreshold {
		b.state = StateOpen
		b.openAt = time.Now()
		zap.L().Warn("circuit breaker opened",
			zap.String("breaker", b.cfg.Name),
			zap.Int("consecutive_failures", b.fails),
		)
	}
}

func (b *Breaker) State() State {
	b.mu.Lock()
	defer b.mu.Unlock()
	return b.state
}

func (b *Breaker) Execute(fn func() error) error {
	if !b.Allow() {
		zap.L().Debug("circuit breaker rejected request",
			zap.String("breaker", b.cfg.Name),
		)
		return &OpenError{Name: b.cfg.Name}
	}
	if err := fn(); err != nil {
		b.RecordFailure()
		return err
	}
	b.RecordSuccess()
	return nil
}

type OpenError struct {
	Name string
}

func (e *OpenError) Error() string {
	return "circuit breaker '" + e.Name + "' is open"
}