package task

import (
	"context"
	"math/rand"
	"runtime/debug"
	"sync"
	"time"

	"go.uber.org/zap"
)

// Task 定义可调度任务
type Task interface {
	Name() string
	Interval() time.Duration
	Run(ctx context.Context) error
}

// Runner 简单的周期任务调度器
type Runner struct {
	tasks            []Task
	logger           *zap.Logger
	wg               sync.WaitGroup
	startImmediately bool
	jitterPercent    float64
}

// NewRunner 创建任务调度器
func NewRunner(logger *zap.Logger, tasks ...Task) *Runner {
	return NewRunnerWithOptions(logger, tasks)
}

// RunnerOption 运行器配置项
type RunnerOption func(r *Runner)

// WithStartImmediately 是否启动后立即执行一次（默认 true）
func WithStartImmediately(start bool) RunnerOption {
	return func(r *Runner) {
		r.startImmediately = start
	}
}

// WithJitter 为执行间隔增加 0~percent 之间的随机抖动（percent=0 关闭，默认0）
// 可降低多个任务同时触发的概率
func WithJitter(percent float64) RunnerOption {
	return func(r *Runner) {
		if percent < 0 {
			percent = 0
		}
		r.jitterPercent = percent
	}
}

// NewRunnerWithOptions 支持可选配置的创建函数
func NewRunnerWithOptions(logger *zap.Logger, tasks []Task, opts ...RunnerOption) *Runner {
	r := &Runner{
		tasks:            tasks,
		logger:           logger,
		startImmediately: true,
		jitterPercent:    0,
	}
	for _, opt := range opts {
		opt(r)
	}
	return r
}

// Start 启动所有任务（异步）
func (r *Runner) Start(ctx context.Context) {
	for _, t := range r.tasks {
		task := t
		r.wg.Add(1)
		go func() {
			defer r.wg.Done()
			defer r.recoverPanic(task)

			interval := r.normalizeInterval(task.Interval())

			// 可选：立即执行一次
			if r.startImmediately {
				r.runOnce(ctx, task)
			}

			// 周期执行
			for {
				wait := r.applyJitter(interval)
				if !r.wait(ctx, wait) {
					return
				}

				// 每轮读取最新的 interval，允许任务动态调整间隔
				interval = r.normalizeInterval(task.Interval())

				select {
				case <-ctx.Done():
					return
				default:
					r.runOnce(ctx, task)
				}
			}
		}()
	}
}

// Wait 等待所有任务退出
func (r *Runner) Wait() {
	r.wg.Wait()
}

func (r *Runner) runOnce(ctx context.Context, task Task) {
	if err := task.Run(ctx); err != nil && r.logger != nil {
		r.logger.Warn("任务执行失败", zap.String("task", task.Name()), zap.Error(err))
	}
}

// normalizeInterval 确保间隔为正值
func (r *Runner) normalizeInterval(d time.Duration) time.Duration {
	if d <= 0 {
		return time.Minute
	}
	return d
}

// applyJitter 在基础间隔上添加最多 jitterPercent 的随机抖动
func (r *Runner) applyJitter(base time.Duration) time.Duration {
	if r.jitterPercent <= 0 {
		return base
	}
	maxJitter := time.Duration(float64(base) * r.jitterPercent)
	if maxJitter <= 0 {
		return base
	}
	return base + time.Duration(rand.Int63n(int64(maxJitter)))
}

// wait 封装带 context 的 sleep
func (r *Runner) wait(ctx context.Context, d time.Duration) bool {
	if d <= 0 {
		select {
		case <-ctx.Done():
			return false
		default:
			return true
		}
	}

	timer := time.NewTimer(d)
	defer timer.Stop()

	select {
	case <-ctx.Done():
		return false
	case <-timer.C:
		return true
	}
}

// recoverPanic 防止任务 panic 导致 goroutine 退出
func (r *Runner) recoverPanic(task Task) {
	if rec := recover(); rec != nil && r.logger != nil {
		r.logger.Error("任务发生panic",
			zap.String("task", task.Name()),
			zap.Any("panic", rec),
			zap.ByteString("stack", debug.Stack()),
		)
	}
}