start implementing metadata parsing support

Signed-off-by: Christine Dodrill <me@christine.website>

gempub.go

@@ -1 +1,106 @@
+// 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()
+}

gempub_test.go

@@ -0,0 +1,54 @@
+package gempub
+
+import (
+	"embed"
+	"io/fs"
+	"testing"
+)
+
+//go:embed testdata/*
+var testdata embed.FS
+
+func TestGoodMetadata(t *testing.T) {
+	fnames, err := fs.Glob(testdata, "testdata/metadata/good/*")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, fname := range fnames {
+		t.Run(fname, func(t *testing.T) {
+			fin, err := testdata.Open(fname)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer fin.Close()
+
+			md, err := ReadMetadata(fin)
+			if err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}
+
+func TestBadMetadata(t *testing.T) {
+	fnames, err := fs.Glob(testdata, "testdata/metadata/bad/*")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, fname := range fnames {
+		t.Run(fname, func(t *testing.T) {
+			fin, err := testdata.Open(fname)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer fin.Close()
+
+			_, err = ReadMetadata(fin)
+			if err == nil {
+				t.Fatal("wanted error, but got none")
+			}
+		})
+	}
+}

testdata/metadata/good/complete.txt

@@ -0,0 +1,14 @@
+title: Spellblade
+gpubVersion: 1.0.0
+index: book/index.gmi
+author: Xe
+language: en-US
+charset: UTF-8
+description: A woman realizes the gap between two opposites and their place in the middle.
+published: 2021
+publishDate: 2021-12-31
+revisionDate: 2022-01-01
+copyright: Christine Dodrill
+license: All Rights Reserved
+version: 1.0.0
+cover: cover.jpg

testdata/metadata/good/simple.txt

@@ -0,0 +1,4 @@
+title: Star Maker
+author: Olaf Stapledon
+index: ./capsule/index.gmi
+gpubVersion: 1.0.0