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* A small ChordPro reader, transposer and importer.
*
* Charts are stored as ChordPro text: `Oh, I could [G]hide 'neath the [Am]wings`
* with `{start_of_verse: Verse 1}` … `{end_of_verse}` around each section.
* Everything the app shows (chart view, performance mode, PDFs, history diffs)
* is derived from that one source, so there is nothing to keep in sync.
*
* Only the subset of ChordPro the band uses is understood; unknown directives
* are kept in `meta` and otherwise ignored rather than rejected.
*/
export type Segment = {chord: string | null; lyric: string}
export type ChartLine =
| {kind: 'lyrics'; segments: Segment[]}
| {kind: 'comment'; text: string}
/** Guitar tablature: shown verbatim in a monospace font */
| {kind: 'tab'; text: string}
export type Section = {
/** verse | chorus | bridge | intro | interlude | outro | solo | part … */
type: string
label: string
/** Parenthesised remark after the label, e.g. "x2, 2nd time fade out" */
note: string
lines: ChartLine[]
/**
* Music notation, for a {start_of_abc} section: ABC text, drawn as a
* staff. It is written in the chart's original key; `abcSteps` is how far
* the chart has been transposed since, which the notation follows.
*/
abc?: string
abcSteps?: number
}
export type Chart = {
title: string
key: string | null
meta: Record<string, string>
sections: Section[]
}
const DIRECTIVE = /^\{\s*([\w-]+)\s*(?::\s*(.*?))?\s*\}$/
// Root, quality, optional slash bass. The quality is restricted to chord
// vocabulary so that words like "Chorus" or "Bridge" are not read as chords.
const CHORD =
/^([A-G](?:#|b)?)((?:maj|min|dim|aug|sus|add|m|M|[0-9]|[#b+\-°ø()])*)(?:\/([A-G](?:#|b)?))?$/
const ALIASES: Record<string, string> = {
t: 'title',
st: 'subtitle',
c: 'comment',
ci: 'comment',
comment_italic: 'comment',
soc: 'start_of_chorus',
eoc: 'end_of_chorus',
sov: 'start_of_verse',
eov: 'end_of_verse',
sob: 'start_of_bridge',
eob: 'end_of_bridge',
}
/**
* Peel wrapping off a chord token: "(B)", "(C" and "G)," are chords inside
* a parenthesised group or followed by punctuation.
*/
function unwrap(token: string) {
const m = token.match(/^(\(?)(.*?)([),.]*)$/)!
return {pre: m[1], core: m[2], post: m[3]}
}
const BASS_ONLY = /^\/([A-G](?:#|b)?)$/
/** A chord, possibly parenthesised, or a bass-only change like "/G". */
export function isChord(token: string): boolean {
const {core} = unwrap(token)
return CHORD.test(core) || BASS_ONLY.test(core)
}
/** Repeat counts, no-chord and bar lines: chord-row markings, not chords. */
export function isChordMarking(token: string): boolean {
return /^\(?x\d+\)?$/i.test(token) || /^(N\.?C\.?|\|+|%|-)$/i.test(token)
}
/** Split "Chorus (x2, fade)" into label "Chorus" and note "x2, fade". */
export function splitLabel(raw: string): {label: string; note: string} {
const text = raw.replace(/^label="(.*)"$/, '$1').trim()
const m = text.match(/^(.*?)\s*\((.*)\)\s*$/)
if (m && m[1]) return {label: m[1].trim(), note: m[2].trim()}
return {label: text, note: ''}
}
function parseLyricLine(line: string): ChartLine {
const segments: Segment[] = []
const re = /\[([^\]]*)\]/g
let last = 0
let pending: string | null = null
let m: RegExpExecArray | null
while ((m = re.exec(line))) {
const before = line.slice(last, m.index)
if (before || pending !== null)
segments.push({chord: pending, lyric: before})
pending = m[1]
last = m.index + m[0].length
}
const rest = line.slice(last)
if (rest || pending !== null) segments.push({chord: pending, lyric: rest})
return {kind: 'lyrics', segments}
}
export function parseChordPro(source: string): Chart {
const chart: Chart = {title: '', key: null, meta: {}, sections: []}
let current: Section | null = null
let implicit = false
const open = (type: string, rawLabel: string, isImplicit = false) => {
const {label, note} = splitLabel(rawLabel)
current = {type, label, note, lines: []}
chart.sections.push(current)
implicit = isImplicit
}
for (const rawLine of source.replace(/\r\n?/g, '\n').split('\n')) {
const line = rawLine.replace(/\s+$/, '')
const d = line.trim().match(DIRECTIVE)
if (d) {
const name = ALIASES[d[1].toLowerCase()] ?? d[1].toLowerCase()
const value = d[2] ?? ''
const start = name.match(/^start_of_(\w+)$/)
if (start) {
// Notation and tab have no heading unless given one ("Horn riff")
open(
start[1],
value || (['abc', 'tab'].includes(start[1]) ? '' : cap(start[1])),
)
continue
}
if (/^end_of_\w+$/.test(name)) {
current = null
continue
}
if (name === 'chorus') {
// A bare {chorus} repeats the most recent chorus. It is written out
// in full: charts are read mid-song, so never "same as above".
const prev = [...chart.sections]
.reverse()
.find((s) => s.type === 'chorus')
const {label, note} = splitLabel(value || prev?.label || 'Chorus')
chart.sections.push({
type: 'chorus',
label,
note,
lines: structuredClone(prev?.lines ?? []),
})
current = null
continue
}
if (name === 'comment') {
if (!current) open('part', '', true)
current!.lines.push({kind: 'comment', text: value})
continue
}
if (name === 'title') chart.title = value
else if (name === 'key') chart.key = value || null
else chart.meta[name] = value
continue
}
// (TS narrows `current` to null here because it is assigned in a closure)
const cur = current as Section | null
if (cur?.type === 'abc') {
// Kept verbatim, blank lines and all: it's another language
cur.abc = cur.abc === undefined ? rawLine : `${cur.abc}\n${rawLine}`
continue
}
if (cur?.type === 'tab') {
if (line.trim()) cur.lines.push({kind: 'tab', text: line})
continue
}
if (!line.trim()) {
if (implicit) current = null
continue
}
if (!current) open('part', '', true)
current!.lines.push(parseLyricLine(line))
}
for (const s of chart.sections) if (s.abc !== undefined) s.abc = s.abc.trim()
chart.sections = chart.sections.filter(
(s) => s.lines.length > 0 || s.label || s.abc,
)
return chart
}
function cap(s: string) {
return s.charAt(0).toUpperCase() + s.slice(1)
}
// ---------------------------------------------------------------------------
// Transposition
// ---------------------------------------------------------------------------
const SHARPS = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B']
const FLATS = ['C', 'Db', 'D', 'Eb', 'E', 'F', 'Gb', 'G', 'Ab', 'A', 'Bb', 'B']
// How each key is conventionally spelled; also decides sharps vs flats.
const MAJOR_KEYS = [
'C',
'Db',
'D',
'Eb',
'E',
'F',
'F#',
'G',
'Ab',
'A',
'Bb',
'B',
]
const MINOR_KEYS = [
'Cm',
'C#m',
'Dm',
'Ebm',
'Em',
'Fm',
'F#m',
'Gm',
'G#m',
'Am',
'Bbm',
'Bm',
]
const FLAT_KEYS = new Set([
'F',
'Bb',
'Eb',
'Ab',
'Db',
'Gb',
'Dm',
'Gm',
'Cm',
'Fm',
'Bbm',
'Ebm',
])
function noteIndex(note: string): number {
const i = SHARPS.indexOf(note)
return i >= 0 ? i : FLATS.indexOf(note)
}
function shift(note: string, semitones: number, flats: boolean): string {
const i = noteIndex(note)
if (i < 0) return note
const j = (((i + semitones) % 12) + 12) % 12
return (flats ? FLATS : SHARPS)[j]
}
export function transposeChord(
chord: string,
semitones: number,
flats = false,
): string {
if (semitones % 12 === 0) return chord
const {pre, core, post} = unwrap(chord)
const b = core.match(BASS_ONLY)
if (b) return pre + '/' + shift(b[1], semitones, flats) + post
const m = core.match(CHORD)
if (!m) return chord
const [, root, quality, bass] = m
return (
pre +
shift(root, semitones, flats) +
quality +
(bass ? '/' + shift(bass, semitones, flats) : '') +
post
)
}
function isMinorQuality(quality: string) {
return /^m(?!aj)/.test(quality)
}
export function transposeKey(key: string, semitones: number): string {
const m = key.match(CHORD)
if (!m) return key
const minor = isMinorQuality(m[2])
const i = noteIndex(m[1])
if (i < 0) return key
const j = (((i + semitones) % 12) + 12) % 12
return (minor ? MINOR_KEYS : MAJOR_KEYS)[j]
}
/** The key: the {key} directive if set, else the first chord of the song. */
export function detectKey(chart: Chart): string | null {
if (chart.key) return chart.key
for (const s of chart.sections)
for (const l of s.lines)
if (l.kind === 'lyrics')
for (const seg of l.segments) {
const m = seg.chord ? unwrap(seg.chord).core.match(CHORD) : null
if (m) return m[1] + (isMinorQuality(m[2]) ? 'm' : '')
}
return null
}
export function semitonesBetween(from: string, to: string): number {
const a = noteIndex(from.match(CHORD)?.[1] ?? '')
const b = noteIndex(to.match(CHORD)?.[1] ?? '')
if (a < 0 || b < 0) return 0
return (((b - a) % 12) + 12) % 12
}
export function transposeChart(chart: Chart, semitones: number): Chart {
const steps = ((semitones % 12) + 12) % 12
if (steps === 0) return chart
const fromKey = detectKey(chart)
const toKey = fromKey ? transposeKey(fromKey, steps) : null
const flats = toKey ? FLAT_KEYS.has(toKey) : false
return {
...chart,
key: chart.key ? toKey : chart.key,
sections: chart.sections.map((s) => ({
...s,
...(s.abc ? {abcSteps: (s.abcSteps ?? 0) + steps} : {}),
lines: s.lines.map((l) =>
l.kind !== 'lyrics'
? l
: {
kind: 'lyrics',
segments: l.segments.map((seg) => ({
...seg,
chord: seg.chord
? transposeChord(seg.chord, steps, flats)
: null,
})),
},
),
})),
}
}
// ---------------------------------------------------------------------------
// Plain text (chords over words) — used for history diffs and imports
// ---------------------------------------------------------------------------
/** Render one lyric line as a chord line above a lyric line, column-aligned. */
export function lineToChordsOverWords(line: ChartLine): string[] {
if (line.kind === 'comment') return [`(${line.text})`]
if (line.kind === 'tab') return [line.text]
let chords = ''
let words = ''
for (const seg of line.segments) {
if (seg.chord !== null) {
if (chords.length > words.length) words = words.padEnd(chords.length)
chords = chords.padEnd(words.length) + seg.chord + ' '
}
words += seg.lyric
}
const out: string[] = []
if (chords.trim()) out.push(chords.trimEnd())
if (words.trim()) out.push(words.trimEnd())
return out
}
export function chartToChordsOverWords(chart: Chart): string {
const out: string[] = []
chart.sections.forEach((s, i) => {
if (i > 0) out.push('')
const head = s.label || (s.abc ? 'Notation' : cap(s.type))
out.push(`[${head}]${s.note ? ` (${s.note})` : ''}`)
for (const l of s.lines) out.push(...lineToChordsOverWords(l))
// Notation shows as its ABC text, so a history diff shows what changed
if (s.abc) out.push(...s.abc.split('\n'))
})
return out.join('\n')
}
// ---------------------------------------------------------------------------
// Import: chords-over-words text (the old Google Docs) → ChordPro
// ---------------------------------------------------------------------------
const NON_CHORD_TOKENS = new Set([
'|',
'||',
'-',
'/',
'%',
'N.C.',
'NC',
'(',
')',
])
/** "(x2)", "x4", "F(x2)" → the repeat part, if the token is one */
const REPEAT = /^\(?x\d+\)?$/i
/**
* A remark written into a chord line: "[hold 4 bars]" or "(organ fill)" --
* anything bracketed or parenthesised that is not itself a chord group.
*/
const REMARK =
/\[[^\]]*\]|\((?![A-G][#b]?[^\s)]*(?:\)|\s))(?!x\d)(?:[^()]|\([^()]*\))*\)/g
export function isChordLine(line: string): boolean {
// Remarks don't disqualify a chord line; they are kept as notes
const tokens = line.replace(REMARK, ' ').trim().split(/\s+/).filter(Boolean)
if (!tokens.length) return false
let chords = 0
for (const t of tokens) {
const bare = t.replace(/^\(|\)$/g, '')
const glued = t.match(/^(.+?)(\(x\d+\))$/i)
if (isChord(tidyChord(bare)) || (glued && isChord(glued[1]))) chords++
// "C-Bb-G": quick changes within a bar ("rest-B-C-C#-D" a walk)
else if (
/-/.test(bare) &&
bare.split('-').every((c) => isChord(c) || /^rest$/i.test(c)) &&
bare.split('-').some((c) => isChord(c))
)
chords++
// "////" and "--": beats and holds; "Pause", "rest", "stop": silences
else if (/^(\/+\.?|-+|pause|rest|stop|hold)$/i.test(t)) continue
else if (!NON_CHORD_TOKENS.has(t) && !REPEAT.test(t)) return false
}
return chords > 0
}
/** "C F Bb F (x4)" → "[C] [F] [Bb] [F] (x4)": chords become chords, the rest stays text. */
function inlineChords(text: string): string {
return text
.trim()
.split(/\s+/)
.map((t) => {
const glued = t.match(/^(.+?)(\(x\d+\))$/i)
if (glued && isChord(glued[1])) return `[${glued[1]}]${glued[2]}`
return isChord(t) ? `[${t}]` : t
})
.join(' ')
}
/** A tablature string line: `e|---7---5p4p0---|` */
// "e|---7---5p4p0---|", or a bare tab staff line "-9-7---4-2----|"
export const TAB_LINE =
/^\s*(?:[A-Ga-g]\|[-0-9a-z|~/\\^().*\s]*|[-0-9hpbr/\\~x|.]*-{6,}[-0-9hpbr/\\~x|.]*)$/
const SECTION_WORDS =
/^(intro|verse|pre-?chorus|chorus|bridge|interlude|instrumental|solo|outro|coda|ending|tag|refrain|break)\b/i
/** Recognise a section header line and split it into label, note and any chords that follow. */
export function parseHeader(
line: string,
): {label: string; note: string; chords: string} | null {
let label: string
let rest: string
const bracket = line.match(/^\[([^\]]+)\]\s*(.*)$/)
const numbered = line.match(/^#\s*(\d+)\.?\s*$/)
const colon = line.match(/^([A-Za-z][A-Za-z0-9 '&/.-]{0,30}?)\s*:\s*(.*)$/)
if (bracket && !isChord(bracket[1])) {
;[label, rest] = [bracket[1], bracket[2]]
} else if (numbered) {
return {label: `Verse ${numbered[1]}`, note: '', chords: ''}
} else if (
colon &&
(colon[1] === colon[1].toUpperCase() || SECTION_WORDS.test(colon[1]))
) {
;[label, rest] = [colon[1], colon[2]]
} else {
return null
}
const notes: string[] = []
const dash = label.match(/^(.*?)\s+-\s+(.*)$/)
if (dash) {
label = dash[1]
notes.push(dash[2])
}
rest = rest.trim()
let chords = ''
if (rest && isChordLine(rest)) chords = inlineChords(rest)
else if (rest) notes.push(rest.replace(/^[-–]\s*|:$|^\(|\)$/g, '').trim())
return {
label: titleCase(label),
note: notes.filter(Boolean).map(titleCase).join('; '),
chords,
}
}
function titleCase(s: string): string {
if (s !== s.toUpperCase()) return s.trim()
return s
.toLowerCase()
.replace(/\b([a-z])/g, (c) => c.toUpperCase())
.replace(/\b(\d+)X\b/gi, '$1x')
.trim()
}
export function sectionType(name: string): string {
const n = name.toLowerCase()
if (/pre-?chorus/.test(n)) return 'prechorus'
for (const t of [
'chorus',
'verse',
'bridge',
'intro',
'interlude',
'outro',
'solo',
])
if (n.includes(t)) return t
if (/instrumental|break/.test(n)) return 'solo'
if (/coda|ending/.test(n)) return 'outro'
return 'part'
}
/** Insert `[chord]` markers from a chord line into the lyric line below it. */
export function mergeChordLine(chordLine: string, lyricLine: string): string {
const marks: {col: number; chord: string}[] = []
// A remark is one token, re-wrapped in parentheses so it can't nest brackets
const re = new RegExp(`${REMARK.source}|\\S+`, 'g')
let m: RegExpExecArray | null
while ((m = re.exec(chordLine)))
marks.push({
col: m.index,
chord: m[0].startsWith('[') ? `(${m[0].slice(1, -1)})` : tidyChord(m[0]),
})
return placeChords(lyricLine, marks)
}
/**
* A line with its chords typed in ("n[Cm7]ight", "Hi-de[Em]-hi"), with
* each chord moved onto a syllable the way placeChords does.
*/
export function placeInlineChords(line: string): string {
if (!/\[/.test(line) || !/[A-Za-z]/.test(line.replace(/\[[^\]]*\]/g, '')))
return line
const marks: {col: number; chord: string}[] = []
let lyric = ''
let at = 0
for (const m of line.matchAll(/\[([^\]]*)\]/g)) {
lyric += line.slice(at, m.index)
at = m.index! + m[0].length
marks.push({col: lyric.length, chord: m[1]})
}
return placeChords(lyric + line.slice(at), marks)
}
/**
* Chords onto words at the columns they were typed. A chord can sit mid-word
* on a syllable ("repu[Cm7]tation", "a[E]gain"); one that splits a word
* where no syllable starts ("n[Cm7]ight", "bou[D7]rbon": a syllable starts
* with a consonant and its vowel, after a vowel earlier in the word) was typed a letter or two off, and goes to the
* word's start. One over a gap goes to the word just after it. Several on one
* word ("G - E7" over "scotch,") are quick changes: the first starts it, the
* rest wait just after it.
*/
export function placeChords(
lyricLine: string,
marks: {col: number; chord: string}[],
): string {
let lyric = lyricLine
const width = marks.length ? marks[marks.length - 1].col : 0
if (lyric.length < width) lyric = lyric.padEnd(width)
let prev = -1
for (const mark of marks) {
if (!lyricLine.trim() || mark.col >= lyricLine.length) continue
// A hold mark or beat slash takes no word: at a word's start it stays,
// inside one it waits just after it
if (/^[-/|.]+$/.test(mark.chord)) {
const start = snapToSyllable(lyricLine, mark.col)
if (start !== mark.col && WORD_CHAR.test(lyricLine[mark.col] ?? ''))
mark.col = wordEnd(lyricLine, start)
continue
}
const at = snapToSyllable(lyricLine, mark.col)
if (at <= prev) mark.col = wordEnd(lyricLine, prev)
else mark.col = prev = at
}
const ordered = marks
.map((m, i) => ({...m, i}))
.sort((a, b) => a.col - b.col || a.i - b.i)
for (let i = ordered.length - 1; i >= 0; i--) {
const {col, chord} = ordered[i]
lyric = lyric.slice(0, col) + `[${chord}]` + lyric.slice(col)
}
return lyric.replace(/\s+$/, '')
}
const WORD_CHAR = /[A-Za-z0-9'’/]/
const VOWEL = /[aeiouy]/i
/** Where a chord typed at `col` belongs: on its syllable, or the word's start. */
export function snapToWord(lyric: string, col: number) {
return snapToSyllable(lyric, col)
}
function snapToSyllable(lyric: string, col: number) {
if (col >= lyric.length) return col
if (WORD_CHAR.test(lyric[col])) {
let s = col
while (s > 0 && WORD_CHAR.test(lyric[s - 1])) s--
let e = col
while (e < lyric.length && WORD_CHAR.test(lyric[e])) e++
// A syllable starts with a consonant and its vowel ("repu|tation",
// "a|gain"), after a vowel earlier in the word
const syllable =
VOWEL.test(lyric.slice(s, col)) &&
// never just after an apostrophe: "we'|ve", "don'|t"
!/['’]$/.test(lyric.slice(s, col)) &&
/^[b-df-hj-np-tv-z][aeiouy]/i.test(lyric.slice(col, e))
return syllable ? col : s
}
// Over a space or a hyphen ("Hi-de[Em]-hi"): the next word, if it's
// close. Before the line's first word a chord keeps its own beat
if (!lyric.slice(0, col).trim()) return col
let s = col
while (s < lyric.length && /[\s-]/.test(lyric[s])) s++
return s < lyric.length && s - col <= 3 && WORD_CHAR.test(lyric[s]) ? s : col
}
/**
* Just past the word at `start`, and past punctuation that ends it
* ("scotch,") but not into the next word ("baby.......do").
*/
function wordEnd(lyric: string, start: number) {
let e = start
while (e < lyric.length && WORD_CHAR.test(lyric[e])) e++
let p = e
while (p < lyric.length && /[^\sA-Za-z0-9'’]/.test(lyric[p])) p++
return p >= lyric.length || /\s/.test(lyric[p]) ? p : e
}
/** "Em." and "C7-" (a chord with a hold mark typed onto it) → "Em", "C7". */
function tidyChord(token: string) {
if (token === '/.') return '/'
const bare = token.replace(/[.-]+$/, '')
return bare !== token && isChord(bare) ? bare : token
}
export type ImportResult = {source: string; key: string | null}
/**
* Convert a chords-over-words chart (chord lines above lyric lines) into
* ChordPro. Understands both header styles in the band's old Docs:
* `[Verse 1]` / `[Intro] A` and `INTRO: C F Bb F (x4)` / `#1.` / `CHORUS:`.
*/
export function importChordsOverWords(
text: string,
title: string,
): ImportResult {
const lines = text
.replace(/\r\n?/g, '\n')
.replace(/ /g, ' ')
.replace(/\\([[\]])/g, '$1')
.split('\n')
.map((l) => l.replace(/\s+$/, ''))
// Markdown headings (the song title in a Docs export) are not chart content
.filter((l) => !/^#{1,6}\s/.test(l.trim()))
const out: string[] = [`{title: ${title}}`]
let openType: string | null = null
const close = () => {
if (openType) out.push(`{end_of_${openType}}`)
openType = null
}
for (let i = 0; i < lines.length; i++) {
const line = lines[i]
const trimmed = line.trim()
if (!trimmed) continue
const h = parseHeader(trimmed)
if (h) {
close()
openType = sectionType(h.label)
if (out.length > 1) out.push('')
out.push(
`{start_of_${openType}: ${h.label}${h.note ? ` (${h.note})` : ''}}`,
)
if (h.chords) out.push(h.chords)
continue
}
if (TAB_LINE.test(line)) {
// Tablature can't live inside a lyric section in ChordPro
close()
out.push('{start_of_tab}')
while (
i < lines.length &&
(TAB_LINE.test(lines[i]) || !lines[i].trim())
) {
if (lines[i].trim()) out.push(lines[i])
i++
}
out.push('{end_of_tab}')
i--
continue
}
if (isChordLine(line)) {
const next = lines[i + 1]
if (
next !== undefined &&
next.trim() &&
!isChordLine(next) &&
!parseHeader(next.trim())
) {
out.push(mergeChordLine(line, next))
i++
} else {
out.push(mergeChordLine(line, ''))
}
continue
}
out.push(line)
}
close()
const source = out.join('\n') + '\n'
return {source, key: detectKey(parseChordPro(source))}
}
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