package main

import (
	"context"
	"time"

	"github.com/go-errors/errors"
)

type Queue struct {
	driver Driver
}

func NewQueue(driver Driver) Queue {
	return Queue{driver: driver}
}

func (q Queue) Push(ctx context.Context, m Message) error {
	return q.driver.Set(ctx, "q", m.ID, m.Serialize())
}

func (q Queue) PeekFirst(ctx context.Context) (Message, error) {
	for {
		m, err := q.peekFirst(ctx)
		if err != nil {
			return m, err
		}

		if !m.Empty() {
			return m, nil
		}

		select {
		case <-ctx.Done():
			return Message{}, ctx.Err()
		case <-time.After(time.Second):
		}
	}
}

func (q Queue) Ack(ctx context.Context, id string) error {
	return q.driver.Set(ctx, "q", id, nil)
}

func (q Queue) peekFirst(ctx context.Context) (Message, error) {
	var m Message
	subctx, subcan := context.WithCancel(ctx)
	defer subcan()
	err := q.driver.ForEach(subctx, "q", func(_ string, value []byte) error {
		m = MustDeserialize(value)
		subcan()
		return nil
	})
	if errors.Is(err, subctx.Err()) {
		err = nil
	}
	return m, err
}