font.go

package main

import (
	"bytes"
	"fmt"
	"path"
	"strings"

	"github.com/ConradIrwin/font/sfnt"
	log "github.com/Crosse/gosimplelogger"
)

// FontData describes a font file and the various metadata associated with it.
type FontData struct {
	Name     string
	Family   string
	FileName string
	Metadata map[sfnt.NameID]string
	Data     []byte
}

// fontExtensions is a list of file extensions that denote fonts.
// Only files ending with these extensions will be installed.
var fontExtensions = map[string]bool{
	".otf": true,
	".ttf": true,
}

// NewFontData creates a new FontData struct.
// fileName is the font's file name, and data is a byte slice containing the font file data.
// It returns a FontData struct describing the font, or an error.
func NewFontData(fileName string, data []byte) (*FontData, error) {
	if _, ok := fontExtensions[strings.ToLower(path.Ext(fileName))]; !ok {
		return nil, fmt.Errorf("not a font: %v", fileName)
	}

	fontData := &FontData{
		FileName: fileName,
		Metadata: make(map[sfnt.NameID]string),
		Data:     data,
	}

	font, err := sfnt.Parse(bytes.NewReader(fontData.Data))
	if err != nil {
		return nil, fmt.Errorf("cannot parse font: %w", err)
	}

	if !font.HasTable(sfnt.TagName) {
		return nil, fmt.Errorf("font has no name table: %s", fileName)
	}

	nameTable, err := font.NameTable()
	if err != nil {
		return nil, fmt.Errorf("cannot get font table for %s: %w", fileName, err)
	}

	for _, nameEntry := range nameTable.List() {
		fontData.Metadata[nameEntry.NameID] = nameEntry.String()
	}

	fontData.Name = fontData.Metadata[sfnt.NameFull]
	fontData.Family = fontData.Metadata[sfnt.NamePreferredFamily]

	if fontData.Family == "" {
		if v, ok := fontData.Metadata[sfnt.NameFontFamily]; ok {
			fontData.Family = v
		} else {
			log.Errorf("Font %v has no font family!", fontData.Name)
		}
	}

	if fontData.Name == "" {
		log.Errorf("Font %v has no name! Using file name instead.", fileName)
		fontData.Name = fileName
	}

	return fontData, nil
}