unwāpurify.js

unwāpurify.js

const { Transform } = require('stream');

// Although superficially there are "rules" we could implement programmatically,
// this is a grammar; its only real rules from a computer’s perspective are the
// fact that certain inputs map to certain terminal symbols (or don’t). In other
// words, the grammar itself is just data.

const TABLE = new Map([
  [ ' ', '' ],
  [ '\n', '\n' ],
  [ '\r', '\n' ],
  [ 'a', 'あ' ],
  [ 'b', new Map([
    [ 'a', 'ば' ],
    [ 'e', 'べ' ],
    [ 'i', 'び' ],
    [ 'o', 'ぼ' ],
    [ 'u', 'ぶ' ],
    [ 'y', new Map([
      [ 'a', 'びゃ' ],
      [ 'o', 'びょ' ],
      [ 'u', 'びゅ' ]
    ]) ]
  ]) ],
  [ 'c', new Map([
    [ 'c', new Map([
      [ 'h', new Map([
        [ 'a', 'っちゃ' ],
        [ 'i', 'っち' ],
        [ 'o', 'っちょ' ],
        [ 'u', 'っちゅ' ]
      ]) ]
    ]) ],
    [ 'h', new Map([
      [ 'a', 'ちゃ' ],
      [ 'i', 'ち' ],
      [ 'o', 'ちょ' ],
      [ 'u', 'ちゅ' ]
    ]) ]
  ]) ],
  [ 'd', new Map([
    [ 'a', 'だ' ],
    [ 'e', 'で' ],
    [ 'i', 'ぢ' ],
    [ 'o', 'ど' ],
    [ 'u', 'づ' ],
    [ 'y', new Map([
      [ 'a', 'ぢゃ' ],
      [ 'o', 'ぢょ' ],
      [ 'u', 'ぢゅ' ]
    ]) ]
  ]) ],
  [ 'e', 'え' ],
  [ 'f', new Map([
    [ 'u', 'ふ' ]
  ]) ],
  [ 'g', new Map([
    [ 'a', 'が' ],
    [ 'e', 'げ' ],
    [ 'i', 'ぎ' ],
    [ 'o', 'ご' ],
    [ 'u', 'ぐ' ],
    [ 'y', new Map([
      [ 'a', 'ぎゃ' ],
      [ 'o', 'ぎょ' ],
      [ 'u', 'ぎゅ' ]
    ]) ]
  ]) ],
  [ 'h', new Map([
    [ 'a', 'は' ],
    [ 'e', 'へ' ],
    [ 'i', 'ひ' ],
    [ 'o', 'ほ' ],
    [ 'y', new Map([
      [ 'a', 'ひゃ' ],
      [ 'o', 'ひょ' ],
      [ 'u', 'ひゅ' ]
    ]) ]
  ]) ],
  [ 'i', 'い' ],
  [ 'j', new Map([
    [ 'a', 'じゃ' ],
    [ 'i', 'じ' ],
    [ 'o', 'じょ' ],
    [ 'u', 'じゅ' ]
  ]) ],
  [ 'k', new Map([
    [ 'a', 'か' ],
    [ 'e', 'け' ],
    [ 'i', 'き' ],
    [ 'k', new Map([
      [ 'a', 'っか' ],
      [ 'e', 'っけ' ],
      [ 'i', 'っき' ],
      [ 'o', 'っこ' ],
      [ 'u', 'っく' ],
      [ 'y', new Map([
        [ 'a', 'っきゃ' ],
        [ 'o', 'っきょ' ],
        [ 'u', 'っきゅ' ]
      ]) ]
    ]) ],
    [ 'o', 'こ' ],
    [ 'u', 'く' ],
    [ 'y', new Map([
      [ 'a', 'きゃ' ],
      [ 'o', 'きょ' ],
      [ 'u', 'きゅ' ]
    ]) ]
  ]) ],
  [ 'm', new Map([
    [ 'a', 'ま' ],
    [ 'e', 'め' ],
    [ 'i', 'み' ],
    [ 'o', 'も' ],
    [ 'u', 'む' ],
    [ 'y', new Map([
      [ 'a', 'みゃ' ],
      [ 'o', 'みょ' ],
      [ 'u', 'みゅ' ]
    ]) ]
  ]) ],
  [ 'n', new Map([
    [ ' ', 'ん' ],
    [ '\n', 'ん\n' ],
    [ '\r', 'ん\n' ],
    [ 'a', 'な' ],
    [ 'e', 'ね' ],
    [ 'i', 'に' ],
    [ 'o', 'の' ],
    [ 'u', 'ぬ' ],
    [ 'y', new Map([
      [ 'a', 'にゃ' ],
      [ 'o', 'にょ' ],
      [ 'u', 'にゅ' ]
    ]) ]
  ]) ],
  [ 'o', 'お' ],
  [ 'p', new Map([
    [ 'a', 'ぱ' ],
    [ 'e', 'ぺ' ],
    [ 'i', 'ぴ' ],
    [ 'o', 'ぽ' ],
    [ 'p', new Map([
      [ 'a', 'っぱ' ],
      [ 'e', 'っぺ' ],
      [ 'i', 'っぴ' ],
      [ 'o', 'っぽ' ],
      [ 'u', 'っぷ' ],
      [ 'y', new Map([
        [ 'a', 'っぴゃ' ],
        [ 'o', 'っぴょ' ],
        [ 'u', 'っぴゅ' ]
      ]) ]
    ]) ],
    [ 'u', 'ぷ' ],
    [ 'y', new Map([
      [ 'a', 'ぴゃ' ],
      [ 'o', 'ぴょ' ],
      [ 'u', 'ぴゅ' ]
    ]) ]
  ]) ],
  [ 'r', new Map([
    [ 'a', 'ら' ],
    [ 'e', 'れ' ],
    [ 'i', 'り' ],
    [ 'o', 'ろ' ],
    [ 'u', 'る' ],
    [ 'y', new Map([
      [ 'a', 'りゃ' ],
      [ 'o', 'りょ' ],
      [ 'u', 'りゅ' ]
    ]) ]
  ]) ],
  [ 's', new Map([
    [ 'a', 'さ' ],
    [ 'e', 'せ' ],
    [ 'h', new Map([
      [ 'a', 'しゃ' ],
      [ 'i', 'し' ],
      [ 'o', 'しょ' ],
      [ 'u', 'しゅ' ]
    ]) ],
    [ 'o', 'そ' ],
    [ 's', new Map([
      [ 'a', 'っさ' ],
      [ 'e', 'っせ' ],
      [ 'h', new Map([
        [ 'a', 'っしゃ' ],
        [ 'i', 'っし' ],
        [ 'o', 'っしょ' ],
        [ 'u', 'っしゅ' ]
      ]) ],
      [ 'o', 'っそ' ],
      [ 'u', 'っす' ]
    ]) ],
    [ 'u', 'す' ]
  ]) ],
  [ 't', new Map([
    [ 'a', 'た' ],
    [ 'e', 'て' ],
    [ 'o', 'と' ],
    [ 's', new Map([
      [ 'u', 'つ' ]
    ]) ],
    [ 't', new Map([
      [ 'a', 'った' ],
      [ 'e', 'って' ],
      [ 'o', 'っと' ]
    ]) ]
  ]) ],
  [ 'u', 'う' ],
  [ 'w', new Map([
    [ 'a', 'わ' ],
    [ 'o', 'を' ]
  ]) ],
  [ 'y', new Map([
    [ 'a', 'や' ],
    [ 'o', 'よ' ],
    [ 'u', 'ゆ' ]
  ]) ],
  [ 'z', new Map([
    [ 'a', 'ざ' ],
    [ 'e', 'ぜ' ],
    [ 'o', 'ぞ' ],
    [ 'u', 'ず' ]
  ]) ]
]);

const OBSOLETE_TABLE = new Map(TABLE);

OBSOLETE_TABLE.set('w', new Map(OBSOLETE_TABLE.get('w')));
OBSOLETE_TABLE.get('w').set('e', 'ゑ');
OBSOLETE_TABLE.get('w').set('i', 'ゐ');

function * unwāpurify(baseTable, table=baseTable, input) {
  while (table.has(input = (yield))) {
    const res = table.get(input);
    if (typeof res === 'string') table = baseTable, yield res;
    else table = res;
  }

  throw new Error(`Unexpected input ${ input }`);
}

if (!module.parent) {
  process.stdin.setRawMode(true);

  const table = process.env.INCLUDE_OBSOLETE ? OBSOLETE_TABLE : TABLE;
  const iter = unwāpurify(table);

  iter.next();

  const transform = new Transform({
    flush(done) {
      const { value } = iter.next(' ');
      if (value) this.push(value);
    },
    transform(chunk, _, done) {
      try {
        for (const char of String(chunk)) {
          if (char === '\x03') return process.exit();

          if (char === '\x7F') {
            throw new Error(`Backspace? Backspace???`);
          }

          if (char < ' ' && char !== '\n' && char !== '\r') continue;

          const { value } = iter.next(char);

          if (value !== undefined) iter.next(), this.push(value);
        }

        done();
      } catch (err) {
        this.push('\n');
        done(err);
      }
    }
  });

  process.stdin.pipe(transform).pipe(process.stdout);
}