// Package exegroup 按照顺序启动和终止任务;
//
// Examples:
//
// 新建 [Group]:
//
//	g := New()
//
// 新建默认 [Group] (内置信号处理):
//
//	g := Default()
//
// 新增1个 [Actor], 通过 ctx 控制 [Actor] 退出:
//
//	g.New().WithName("do nothing").WithStartFunc(func(ctx context.Context) error {
//		<-ctx.Done()
//		return ctx.Err()
//	})
//
// 启动 [Group]:
//
//	g.Run(ctx)
package exegroup

import (
	"context"
	"errors"
	"fmt"
	"time"

	"git.blauwelle.com/go/crate/log"
)

// Group 管理1组 [Actor], 每个 [Actor] 在1个goroutine 中运行;
// Group 的执行过程参考 [Group.Run];
//
// Group 的配置:
//   - [WithStopTimeout] 指定 [Group.Run] 从进入终止过程到返回的最长时间, 默认不限制最长时间;
type Group struct {
	errorsChan  chan actorError
	actors      []*Actor
	syncActors  []*Actor
	asyncActors []*Actor
	cfg         config
}

type actorError struct {
	actor *Actor
	err   error
}

// New 创建 [Group];
func New(opts ...Option) *Group {
	cfg := config{
		stopTimeout: -1,
	}
	for _, opt := range opts {
		opt.apply(&cfg)
	}
	return &Group{
		cfg: cfg,
	}
}

// Default 创建包含信号处理 [Actor] 的 [Group];
func Default(opts ...Option) *Group {
	g := New(opts...)
	g.NewAsync().WithName("signal").WithStartFunc(HandleSignal())
	return g
}

func (g *Group) newActor() *Actor {
	actor := &Actor{
		group:             g,
		closeAfterStop:    make(chan struct{}),
		closeAfterTimeout: make(chan struct{}),
		name:              fmt.Sprintf("actor-%d", len(g.actors)),
		stopTimeout:       -1,
	}
	actor.startCtx, actor.startCancel = context.WithCancel(context.Background())
	g.actors = append(g.actors, actor)
	return actor
}

// NewAsync 创建并添加异步退出的 [Actor], 对 Actor 的配置通过链式调用完成;
func (g *Group) NewAsync() *Actor {
	actor := g.newActor()
	g.asyncActors = append(g.asyncActors, actor)
	return actor
}

// NewSync 创建并添加同步退出的 [Actor], 对 Actor 的配置通过链式调用完成;
func (g *Group) NewSync() *Actor {
	actor := g.newActor()
	g.syncActors = append(g.syncActors, actor)
	return actor
}

// Run 启动所有 [Actor] 并等待 [Actor] 执行完成;
// 当没有 Actor 时执行 Run 会 panic;
//
// Run 包含两个阶段:
//  1. 启动所有 [Actor];
//  2. 等待 ctx 或第1个Actor返回, 终止所有Actor.
func (g *Group) Run(ctx context.Context) error {
	if err := g.validate(ctx); err != nil {
		return err
	}
	g.errorsChan = make(chan actorError, len(g.actors))
	g.start(ctx)

	return g.stop(ctx, g.wait(ctx))
}

func (g *Group) validate(ctx context.Context) error {
	if len(g.actors) == 0 {
		err := errors.New("no actor")
		log.Error(ctx, err.Error())
		return err
	}
	for i, actor := range g.actors {
		if actor.startFunc == nil {
			err := fmt.Errorf("group-actor %d: %s has nil startFunc", i, actor.name)
			log.Error(ctx, err.Error())
			return err
		}
	}
	return nil
}

// start 启动所有的 [Actor] 后返回.
func (g *Group) start(ctx context.Context) {
	for _, actor := range g.actors {
		go actor.start()
		log.Tracef(ctx, "group is starting group-actor %s", actor.name)
	}
}

// wait 等待 ctx 或 [Actor] 返回
func (g *Group) wait(ctx context.Context) error {
	log.Tracef(ctx, "group is waiting")
	select {
	case ae := <-g.errorsChan:
		log.Tracef(ctx, "group is waiting: group-actor %s return", ae.actor.name)
		if ae.err != nil {
			return fmt.Errorf("group-actor %s return with %w", ae.actor.name, ae.err)
		}
		return nil
	case <-ctx.Done():
		log.Tracef(ctx, "group is waiting: %s", ctx.Err().Error())
		return ctx.Err()
	}
}

// stop 等待 [Actor] 停止
func (g *Group) stop(ctx context.Context, err error) error {
	stopCtx := context.Background()
	if g.cfg.stopTimeout >= 0 {
		log.Tracef(ctx, "set group stop timeout to %s", g.cfg.stopTimeout)
		var cancel func()
		stopCtx, cancel = context.WithTimeout(stopCtx, g.cfg.stopTimeout)
		defer cancel()
	}
	go func() {
		// 终止异步 [Actor]
		for _, actor := range g.asyncActors {
			log.Tracef(ctx, "group is stopping group-actor %s", actor.name)
			actor.sendStopSignal()
		}
		// 终止同步 [Actor] 并等待 [Actor] 退出
		for i := len(g.syncActors) - 1; i >= 0; i-- {
			actor := g.syncActors[i]
			log.Tracef(ctx, "group is stopping group-actor %s", actor.name)
			actor.sendStopSignal()
			actor.wait()
		}
	}()
	// 等待所有 [Actor] 退出, 超时立即退出
	for _, actor := range g.actors {
		select {
		case <-actor.closeAfterStop:
			log.Tracef(ctx, "group is stopping group-actor %s: stopped", actor.name)
		case <-actor.closeAfterTimeout:
			log.Errorf(ctx, "group is stopping group-actor %s: timeout", actor.name)
		case <-stopCtx.Done():
			if err == nil {
				err = stopCtx.Err()
			} else {
				err = fmt.Errorf("group is stopping group-actor %s: global timeout: %w", actor.name, err)
			}
			log.Error(ctx, err.Error())
			return err
		}
	}
	log.Tracef(ctx, "group return: %v", err)
	return err
}

type config struct {
	stopTimeout time.Duration // <0表示没有超时时间
}

// Option 修改 [Group] 的配置;
type Option interface {
	apply(cfg *config)
}

type optionFunc func(cfg *config)

func (fn optionFunc) apply(cfg *config) {
	fn(cfg)
}

// WithStopTimeout 指定 [Group.Run] 从进入终止过程到返回的最长时间.
// <0表示没有超时时间.
func WithStopTimeout(d time.Duration) Option {
	return optionFunc(func(cfg *config) {
		cfg.stopTimeout = d
	})
}