package main

import (
	"context"
	"errors"
	"fmt"
	"strings"
)

var (
	errTelegramOtherMedia = errors.New("only text messages are supported")
	errTelegramPhotoSize  = errors.New("no photo size fits 1568 pixels")
)

// telegramImageText selects a supplied photo size, or an image document, and
// stores it before returning marker text with the unchanged caption.
func telegramImageText(ctx context.Context, api *TelegramAPI, store *ImageStore, message *TelegramMessage) (string, error) {
	var (
		id   string
		size int64
	)

	if len(message.Photo) > 0 {
		var area int

		for _, photo := range message.Photo {
			if photo.Width <= 0 || photo.Height <= 0 || max(photo.Width, photo.Height) > 1568 {
				continue
			}

			if photo.Width*photo.Height > area {
				id = photo.FileID
				size = photo.FileSize
				area = photo.Width * photo.Height
			}
		}

		if id == "" {
			return "", errTelegramPhotoSize
		}
	} else if message.Document != nil {
		document := message.Document
		switch document.MimeType {
		case "image/jpeg", "image/png", "image/webp":
			id = document.FileID
			size = document.FileSize
		default:
			if strings.HasPrefix(document.MimeType, "image/") {
				return "", errImageFormat
			}

			return "", errTelegramOtherMedia
		}
	}

	if size > imageMaxBytes {
		return "", errImageSize
	}

	data, err := api.GetImage(ctx, id)
	if err != nil {
		return "", fmt.Errorf("download image: %w", err)
	}

	name, err := store.Save(data)
	if err != nil {
		return "", fmt.Errorf("store image: %w", err)
	}

	return imageText([]string{name}, message.Caption), nil
}