package main

import (
	"context"
	"errors"
	"fmt"
	"net"
	"net/http"
	"sync/atomic"
	"time"
)

// component 不接管进程信号；宿主负责为每一类生命周期提供独立取消和等待。
type component struct {
	name string
	run  func(context.Context) error
}
type completion struct {
	name string
	err  error
}

// serve 在HTTP监听已成功后启动后台组件；返回前完成HTTP→发送/执行→结果消费的关闭顺序。
func serve(parent context.Context, listener net.Listener, server *http.Server, ready *atomic.Bool, workers []component, consumer component, grace time.Duration) error {
	workCtx, stopWork := context.WithCancel(context.Background())
	defer stopWork()
	eventCtx, stopEvents := context.WithCancel(context.Background())
	defer stopEvents()
	workDone := make(chan completion, len(workers))
	eventDone := make(chan completion, 1)
	for _, c := range workers {
		go func() { workDone <- completion{c.name, c.run(workCtx)} }()
	}
	go func() { eventDone <- completion{consumer.name, consumer.run(eventCtx)} }()
	httpDone := make(chan error, 1)
	ready.Store(true)
	go func() { httpDone <- server.Serve(listener) }()
	remaining := len(workers)
	eventsPending := true
	var result error
	add := func(c completion) {
		if c.err != nil {
			result = errors.Join(result, fmt.Errorf("%s: %w", c.name, c.err))
		}
	}
	select {
	case <-parent.Done():
	case err := <-httpDone:
		if !errors.Is(err, http.ErrServerClosed) {
			result = errors.Join(result, err)
		}
	case c := <-workDone:
		remaining--
		if c.err == nil {
			c.err = errors.New("unexpected component exit")
		}
		add(c)
	case c := <-eventDone:
		eventsPending = false
		if c.err == nil {
			c.err = errors.New("unexpected component exit")
		}
		add(c)
	}
	ready.Store(false)
	// 用新的关闭上下文；进程信号的context此时可能已取消，不能用它调用Shutdown。
	shut, cancel := context.WithTimeout(context.Background(), grace)
	if err := server.Shutdown(shut); err != nil {
		result = errors.Join(result, fmt.Errorf("http shutdown: %w", err))
		_ = server.Close()
	}
	cancel()
	stopWork()
	deadline := time.NewTimer(grace)
	defer deadline.Stop()
	for remaining > 0 {
		select {
		case c := <-workDone:
			remaining--
			add(c)
		case <-deadline.C:
			result = errors.Join(result, errors.New("background shutdown deadline exceeded"))
			remaining = 0
		}
	}
	// 结果消费器最后停止。仍未投递的结果会在重启后由持久订阅恢复，不以本地空闲判断全局完成。
	stopEvents()
	if eventsPending {
		timer := time.NewTimer(grace)
		defer timer.Stop()
		select {
		case c := <-eventDone:
			add(c)
		case <-timer.C:
			result = errors.Join(result, errors.New("consumer shutdown deadline exceeded"))
		}
	}
	return result
}