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// Copyright 2022 Terin Stock.
// SPDX-License-Identifier: MPL-2.0

package manager

import (
	"context"
	"errors"
	"sync"

	"golang.org/x/sync/errgroup"
)

type Manager struct {
	mu          sync.Mutex
	started     bool
	runnables   []Runnable
	internalCtx context.Context
	group       *errgroup.Group
}

func New() *Manager {
	return &Manager{
		runnables: []Runnable{},
	}
}

func (m *Manager) Add(r Runnable) error {
	m.mu.Lock()
	defer m.mu.Unlock()

	if m.started {
		m.group.Go(func() error {
			return r.Start(m.internalCtx)
		})
	} else {
		m.runnables = append(m.runnables, r)
	}

	return nil
}

func (m *Manager) Start(ctx context.Context) error {
	m.mu.Lock()
	if m.started {
		m.mu.Unlock()
		return errors.New("manager already started")
	}

	g, internalCtx := errgroup.WithContext(ctx)
	m.group = g
	m.internalCtx = internalCtx

	for _, r := range m.runnables {
		r := r
		g.Go(func() error {
			return r.Start(internalCtx)
		})
	}
	m.runnables = nil
	m.started = true

	m.mu.Unlock()

	return g.Wait()
}

type Runnable interface {
	Start(ctx context.Context) error
}