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Parse and create PGNs (Portable Game Notation for chess games)

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# cm-pgn

## Parser for PGNs (Portable Game Notation)

This is as **ES6 Module for parsing and rendering of PGNs** ([Portable Game Notation](https://de.wikipedia.org/wiki/Portable_Game_Notation)).

The API is similar to `history()` of [chess.js](https://github.com/jhlywa/chess.js), but this module **supports variations, nags and comments** in the pgn.

I used the grammar file from [PgnViewerJS](https://github.com/mliebelt/PgnViewerJS) of [mliebelt](https://github.com/mliebelt) to create the parser.

## Install

`npm install cm-pgn`

## Usage

Use the `Pgn` class as JS Module:

```html

1. e4 e5 (e6) 2. Nf3 $1 {Great move!} Nc6 *`)
</script>
```

## Pgn constructor

`constructor(pgnString = "", props = {})`

Supported `props`:

- `sloppy` (default `false`) — accept non-standard move notations like `e2e4`
  or `e2-e4`. See [.move(move, options)](https://github.com/jhlywa/chess.js/blob/master/README.md#movemove--options-) from chess.js.
- `chess960` (default `false`) — parse Chess960 / Fischer Random games,
  including non-standard castling notation. Also auto-enabled when the
  header contains `[Variant "Chess960"]`, `"Fischerandom"` or `"Freestyle"`.

If the header contains `[SetUp "1"]` together with `[FEN "…"]`, the game
is replayed from that FEN instead of the standard starting position.

## Rendering a PGN

```js
pgn.render(renderHeader = true, renderComments = true, renderNags = true)
```

Re-serializes `pgn.header` and `pgn.history` back to a PGN string,
word-wrapped at 80 columns. `pgn.header.render()` and
`pgn.history.render(renderComments, renderNags)` are available if you
only need one of the two blocks.

## Header tags

`pgn.header.tags` is a plain object mapping tag names to string values.
A `TAGS` constant with the well-known PGN tag names is exported from
`src/Header.js` for safer lookups:

```js
import {TAGS} from "./PATH/TO/cm-pgn/src/Header.js"
pgn.header.tags[TAGS.White] // "Haack, Stefan"
```

## Data structure

The `pgn` has a `pgn.header` and a `pgn.history`.

### pgn.header

The header holds the PGN header elements in the key value object `tags`.

```js
pgn.header.tags = {
    Site: "Berlin",
    Date: "1989.07.02",
    White: "Haack, Stefan",
    Black: "Maier, Karsten"
}
```

### pgn.history

The moves are stored in an array. Every element of that array has the following structure

```js
pgn.history.moves[i] = {
    color: "w", // the moving color
    fen: "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1", // the fen after that move
    flags: "b", // the flags, like described below
    from: "e2", // the square from
    next: {color: "b", from: "e7", to: "e6", flags: "n", piece: "p", /*…*/}, // a pointer to the next move 
    piece: "p", // the piece type 
    ply: 1, // the ply number
    previous: undefined, // a pointer to the previous move
    san: "e4", // the move in SAN notation
    to: "e4", // the square to
    uci: "e2e4", // the move in UCI notation
    variation: (4) [{/*…*/}, {/*…*/}, {/*…*/}, {/*…*/}], // a pointer to the begin of the current variation
    variations: [] // all variations starting with that move
}
```

#### pgn.history.moves[i].flags

- 'n' - a non-capture
- 'b' - a pawn push of two squares
- 'e' - an en passant capture
- 'c' - a standard capture
- 'p' - a promotion
- 'k' - kingside castling
- 'q' - queenside castling

#### pgn.history.moves[i].piece

- 'p' - pawn
- 'n' - knight
- 'b' - bishop
- 'r' - rook
- 'q' - queen
- 'k' - king

#### Optional fields on `pgn.history.moves[i]`

- `nags` — the NAGs as a number array, e.g. `[1, 14]`
- `startingComments` — PGN `{ ... }` comments *before* the move, as a string array
- `comments` — PGN `{ ... }` comments *after* the move, as a string array
- newlines inside comments are preserved
- `gameOver`, `inCheck`, `inCheckmate`, `inDraw`, `inStalemate`,
  `insufficientMaterial`, `inThreefoldRepetition` — set to `true` when
  the corresponding chess.js predicate holds after the move

#### Examples

```js
const history = pgn.history
assert.equal(4, history.moves.length)
assert.equal(history.moves[0].san, "e4")
assert.equal(history.moves[1].variations.length, 1)
assert.equal(history.moves[1].variations[0][0].san, "e6")
assert.equal(history.moves[2].nags[0], 1)
assert.equal(history.moves[2].comments[0], "Great move!")
assert.equal(history.moves[2].fen, "rnbqkbnr/pppp1ppp/8/4p3/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2")
assert.equal(history.moves[3].from, "b8")
assert.equal(history.moves[3].to, "c6")
assert.equal(history.moves[3].uci, "b8c6")
assert.equal(history.moves[3].san, "Nc6")
assert.equal(history.moves[3].previous.san, "Nf3")
assert.equal(history.moves[3].previous.next.san, "Nc6")
```

## Building a history programmatically

`pgn.history` also exposes a small mutation API:

```js
// validate without appending — returns a move object or null
pgn.history.validateMove("Nf3")

// append a move to the main line (or to a variation, via `previous`)
const move = pgn.history.addMove("Nf3")

// walk the linked list back to the starting position
pgn.history.historyToMove(move) // => move[]
```

`addMove(notation, previous = null, sloppy = true)` appends to the end of
the main line by default. Passing an existing move as `previous` appends
after that move; if `previous` already has a `next`, the new move is
attached as a variation instead.

To add a move at the very start of the game — either as the first
main-line move or as an alternative to an existing first move (e.g.
`1. e4 (1. d4) 1... e5`) — use `addMoveAtStart`:

```js
history.addMove("e4")
history.addMoveAtStart("d4") // => 1. e4 (1. d4)
// equivalent shorthand through addMove:
history.addMove("d4", "start")
```

The move is validated from the starting position (or `setUpFen`). If the
main line is empty, it simply becomes `moves[0]`; otherwise it is pushed
onto `moves[0].variations`. The returned move can be extended with
further `addMove(..., previousVariationMove)` calls.

## Parsing multi-game PGN databases

Use `PgnList` to parse a string (or file) containing several games:

```js
import {PgnList} from "./PATH/TO/cm-pgn/src/PgnList.js"

// from a string
const pgns = PgnList.parse(multiGamePgnString) // => Pgn[]
pgns[0].history.moves

// or keep the raw game strings
const list = new PgnList(multiGamePgnString)
list.pgns // => string[]

// or load from a URL (browser)
const list2 = new PgnList()
await list2.fetch("./games.pgn")
list2.pgns // => string[]
```

## Notes on comments

Comments follow the model used by [chessops](https://github.com/niklasf/chessops)
/ Lichess: every move carries `startingComments` (before the move) and
`comments` (after the move), each a **string array**. Multiple consecutive
comments at the same position (e.g. `{ a } { b }`) are kept as separate array
entries. Line breaks inside `{ ... }` comments are preserved as-is.

Comments *before the first move of the game* are not attached to a move but to
the game itself, in `pgn.gameComment` (a string array), matching chessops'
`game.comments`. A comment before the first move of a *variation* stays in that
move's `startingComments`.

> **Migration from 4.x:** the single-string fields `commentMove` /
> `commentBefore` / `commentAfter` and `nag` were removed. Map
> `commentMove` + `commentBefore` → `startingComments`, `commentAfter` →
> `comments`, `nag` (`"$1"`) → `nags` (`[1]`), and a leading game comment →
> `pgn.gameComment`.

## Development

This module uses [PEG.js](https://pegjs.org/) for parser generation. The parser (`pgnParser.js`)
in `src/parser/` is generated from the grammar file `src/grammar/pgn.pegjs`.

To recreate the parser after modification of `src/grammar/pgn.pegjs`, run `./generate-parser.sh`
in the repository root.

## Testing

[Run the unit tests](https://shaack.com/projekte/cm-pgn/test)

## External Links

- [Wikipedia Portable_Game_Notation](https://en.wikipedia.org/wiki/Portable_Game_Notation)
- [Portable Game Notation Specification and Implementation Guide](http://www.saremba.de/chessgml/standards/pgn/pgn-complete.htm)

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