package blogposts

import (
	"bufio"
	"io"
	"io/fs"
	"strings"
)

type Post struct {
	Title, Description, Body string
	Tags                     []string
}

const (
	titleLine       = "Title: "
	descriptionLine = "Description: "
	tagsLine        = "Tags: "
	tagSeparator    = ","
	bodySeparator   = "---"
)

func getPost(fileSystem fs.FS, fileName string) (Post, error) {
	postFile, err := fileSystem.Open(fileName)
	if err != nil {
		return Post{}, err
	}
	defer postFile.Close()

	return newPost(postFile)
}

// NOTE: Does newPost have to be coupled to an fs.File ?
// Do we use all the methods and data from this type? What do we really need?
func newPost(postFile io.Reader) (Post, error) {
	scanner := bufio.NewScanner(postFile)

	readMetaLine := func(tagName string) string {
		scanner.Scan()
		return strings.TrimPrefix(scanner.Text(), tagName)
	}

	title := readMetaLine(titleLine)
	description := readMetaLine(descriptionLine)
	tagsOneLine := readMetaLine(tagsLine)

	tags := strings.Split(tagsOneLine, ",")
	for i, tag := range tags {
		tags[i] = strings.TrimSpace(tag)
	}

	for scanner.Scan() {
		if strings.TrimSpace(scanner.Text()) == bodySeparator {
			break
		}
	}

	// The rest is the body
	var buf strings.Builder
	for scanner.Scan() {
		buf.Write(scanner.Bytes())
		buf.Write([]byte{'\n'})
	}
	body := strings.TrimSuffix(buf.String(), "\n")

	post := Post{
		Title:       title,
		Description: description,
		Tags:        tags,
		Body:        body,
	}
	return post, nil
}