✨ Add latex formatter (for songs package)

- Only supports a very limited subset of tags so far (artist, title, subtitle, comment, capo)
- Other tags are simply rendered as `\textcomment`
- The result has additional newlines, because some tags are filtered out to construct the first `\beginsong` line. If they were the sole item on their previous line, that line remains as an empty line.

src/chordsheet.js

@@ -4,6 +4,7 @@ import TextFormatter from './formatter/text_formatter';
 import HtmlTableFormatter from './formatter/html_table_formatter';
 import HtmlDivFormatter from './formatter/html_div_formatter';
 import ChordProFormatter from './formatter/chord_pro_formatter';
+import LatexFormatter from './formatter/latex_formatter';
 import ChordLyricsPair from './chord_sheet/chord_lyrics_pair';
 import Line from './chord_sheet/line';
 import Song from './chord_sheet/song';
@@ -16,6 +17,7 @@ export default {
   HtmlTableFormatter,
   HtmlDivFormatter,
   ChordProFormatter,
+  LatexFormatter,
   ChordLyricsPair,
   Line,
   Song,

src/formatter/latex_formatter.js

@@ -0,0 +1,114 @@
+import Tag, {
+  ARTIST,
+  TITLE,
+  SUBTITLE,
+  COMMENT,
+  CAPO,
+  START_OF_CHORUS,
+  END_OF_CHORUS,
+  START_OF_VERSE,
+  END_OF_VERSE,
+} from '../chord_sheet/tag';
+import ChordLyricsPair from '../chord_sheet/chord_lyrics_pair';
+
+const NEW_LINE = '\n';
+const flatMap = (arr, fn) => arr.reduce((acc, x) => [...acc, ...fn(x)], []);
+
+/**
+ * Formats a song into a .tex file for the Latex songs package.
+ * http://songs.sourceforge.net/docs.html
+ */
+class LatexFormatter {
+  isHeaderTag(item) {
+    return item instanceof Tag && [TITLE, SUBTITLE, ARTIST].indexOf(item.name) !== -1;
+  }
+
+  /**
+   * Formats a song into .tex file.
+   * @param {Song} song The song to be formatted
+   * @returns {string} The .tex file contents as string
+   */
+  format(song) {
+    return [
+      this.formatHeaderTags(song),
+      this.formatOther(song),
+      '\\endsong',
+    ].join(NEW_LINE);
+  }
+
+  formatHeaderTags(song) {
+    const headerTags = flatMap(song.lines, line => line.items)
+      .filter(this.isHeaderTag)
+      .reduce((tmp, tag) => ({
+        ...tmp,
+        [tag.name]: tag,
+      }), {});
+    const title = headerTags.title && headerTags.title.value;
+    const subtitle = headerTags.subtitle && headerTags.subtitle.value;
+    const artist = headerTags.artist ? headerTags.artist.value : '';
+    const titleString = title + (subtitle ? ` \\\\ ${subtitle}` : '');
+    return `\\beginsong{${titleString}}[by={${artist}}]`;
+  }
+
+  formatOther(song) {
+    return song.lines.map(line => this.formatLine(line)).join(NEW_LINE);
+  }
+
+  formatLine(line) {
+    return line.items.map(item => this.formatItem(item)).join('');
+  }
+
+  formatItem(item) {
+    if (this.isHeaderTag(item)) {
+      return '';
+    } else if (item instanceof Tag) {
+      return this.formatTag(item);
+    } else if (item instanceof ChordLyricsPair) {
+      return this.formatChordLyricsPair(item);
+    }
+
+    return '';
+  }
+
+  formatTag(tag) {
+    switch (tag.name) {
+      case COMMENT:
+        return `\\textcomment{${tag.value}}`;
+      case CAPO:
+        return `\\capo{${tag.value}}`;
+      case START_OF_CHORUS:
+        return '\\beginchorus';
+      case END_OF_CHORUS:
+        return '\\endchorus';
+      case START_OF_VERSE:
+        return '\\beginverse';
+      case END_OF_VERSE:
+        return '\\endverse';
+      default:
+        return tag.hasValue()
+          ? `\\textcomment{${tag.originalName}: ${tag.value}}`
+          : `\\textcomment{${tag.originalName}}`;
+    }
+  }
+
+  formatChordLyricsPair(chordLyricsPair) {
+    return [
+      this.formatChordLyricsPairChords(chordLyricsPair),
+      this.formatChordLyricsPairLyrics(chordLyricsPair),
+    ].join('');
+  }
+
+  formatChordLyricsPairChords(chordLyricsPair) {
+    if (chordLyricsPair.chords) {
+      return `\\[${chordLyricsPair.chords}]`;
+    }
+
+    return '';
+  }
+
+  formatChordLyricsPairLyrics(chordLyricsPair) {
+    return chordLyricsPair.lyrics || '';
+  }
+}
+
+export default LatexFormatter;

test/formatter/latex_formatter.js

@@ -0,0 +1,29 @@
+import { expect } from 'chai';
+
+import LatexFormatter from '../../src/formatter/latex_formatter';
+import song from '../fixtures/song';
+
+describe('LatexFormatter', () => {
+  it('formats a song to a .tex file correctly', () => {
+    const formatter = new LatexFormatter();
+
+    const expectedChordSheet = `
+\\beginsong{Let it be \\\\ ChordSheetJS example version}[by={}]
+
+
+\\textcomment{x_some_setting}
+\\textcomment{Bridge}
+
+\\beginverse
+Let it \\[Am]be, let it \\[C/G]be, let it \\[F]be, let it \\[C]be
+\\[C]Whisper words of \\[F]wis\\[G]dom, let it \\[F]be \\[C/E] \\[Dm] \\[C] 
+\\endverse
+
+\\beginchorus
+\\[Am]Whisper words of \\[Bb]wisdom, let it \\[F]be \\[C]
+\\endchorus
+\\endsong`.substring(1);
+
+    expect(formatter.format(song)).to.equal(expectedChordSheet);
+  });
+});