// Package gempub implements the gempub 1.0.0 specification as described here: https://codeberg.org/oppenlab/gempub
package gempub

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"strings"
	"time"
)

type Metadata struct {
	Title        string    // mandatory title of the work
	GpubVersion  string    // mandatory Gempub format version: 1.0.0
	Index        string    // path to index.gmi, if none is specified it should be assumed to be in the root
	Author       string    // author of the work
	Language     string    // BCP 47 language code
	Charset      string    // if not set, assume UTF-8
	Description  string    // human-readable description
	Published    time.Time // YYYY when date is unknown
	PublishDate  time.Time // YYYY-MM-DD eg. 2006-01-02
	RevisionDate time.Time // YYYY-MM-DD eg. 2006-01-02
	Copyright    string    // copyright of the book
	License      string    // license of the book	Version      string a // human readable only, not meant to be parsed
	Cover        string    // a JPG or PNG image which can be anywhere in the directory structure
}

var (
	ErrNoTitle = errors.New("gempub: no title in document")
)

func loadDateOrYear(when string) (t time.Time, err error) {
	if len(when) == 4 {
		t, err = time.Parse("2006", when)
		return
	}

	t, err = time.Parse("2006-01-02", when)
	return
}

func (m Metadata) Valid() error {
	switch {
	case m.Title == "":
		return ErrNoTitle
	case m.GpubVersion != "1.0.0":
		return fmt.Errorf("gempub: wrong gempub version: %v", m.GpubVersion)
	}

	return nil
}

func ReadMetadata(r io.Reader) (*Metadata, error) {
	var result Metadata

	sc := bufio.NewScanner(r)
	for sc.Scan() {
		line := sc.Text()
		sp := strings.SplitN(line, ":", 2)
		key, val := sp[0], sp[1]
		val = strings.TrimSpace(val)
		switch key {
		case "title":
			result.Title = val
		case "gpubVersion":
			result.GpubVersion = val
		case "index":
			result.Index = val
		case "author":
			result.Author = val
		case "language":
			result.Language = val
		case "charset":
			result.Charset = val
		case "description":
			result.Description = val
		case "published":
			when, err := loadDateOrYear(val)
			if err != nil {
				return nil, fmt.Errorf("gempub: can't understand date %q: %v", val, err)
			}
			result.Published = when
		case "publishDate":
			when, err := loadDateOrYear(val)
			if err != nil {
				return nil, fmt.Errorf("gempub: can't understand date %q: %v", val, err)
			}
			result.PublishDate = when
		case "revisionDate":
			when, err := loadDateOrYear(val)
			if err != nil {
				return nil, fmt.Errorf("gempub: can't understand date %q: %v", val, err)
			}
			result.RevisionDate = when
		case "copyright":
			result.Copyright = val
		case "license":
			result.License = val
		case "cover":
			result.Cover = val
		}
	}

	return &result, result.Valid()
}