adjective.ts

export const adjConjugations = [
  'Present', 'Prenomial', 'Negative', 'Past', 'NegativePast', 'ConjunctiveTe', 'Adverbial', 'Conditional',
  'TaraConditional', 'Tari', 'Noun', 'StemSou', 'StemNegativeSou'
] as const;
export type AdjConjugation = typeof adjConjugations[number];

function never(x: never) { throw new Error('never?'); }

export function adjConjugate(adjective: string, conj: AdjConjugation, iAdjective: boolean): string[] {
  if (iAdjective) {
    let stem = adjective.slice(0, -1);
    let addSa = false;
    if (adjective === 'いい' || adjective === '良い' || adjective === 'よい') {
      stem = adjective.startsWith('良') ? '良' : 'よ';
      addSa = true;
    }else if (adjective.endsWith('ない')) {
      addSa = true;
    }
    switch (conj) {
    case 'Present': return [adjective];
    case 'Prenomial': return [adjective];
    case 'Negative': return [stem + 'くない'];
    case 'Past': return [stem + 'かった'];
    case 'NegativePast': return [stem + 'くなかった'];
    case 'ConjunctiveTe': return [stem + 'く', stem + 'くて'];
    case 'Adverbial': return [stem + 'く'];
    case 'Conditional': return [stem + 'ければ'];
    case 'TaraConditional': return [stem + 'かったら'];
    case 'Tari': return [stem + 'かったり'];
    case 'Noun': return [stem + 'さ'];
    case 'StemSou': return [addSa ? stem + 'さそう' : stem + 'そう'];
    case 'StemNegativeSou': {
      const negativeStem = stem + 'くな';
      // basically conjugate adjective with 'Negative' and redo stem
      return [negativeStem + 'さそう'];
    }
    default: never(conj);
    }
  }
  // na-adjective
  switch (conj) {
  case 'Prenomial': return [adjective + 'な'];
  case 'Present': return ['だ', 'です', 'でございます'].map(suffix => adjective + suffix);
  case 'Negative': return ['ではない', 'でない', 'じゃない', 'ではありません'].map(suffix => adjective + suffix);
  case 'Past': return ['だった', 'でした'].map(suffix => adjective + suffix);
  case 'NegativePast':
    return ['ではなかった', 'でなかった', 'じゃなかった', 'ではありませんでした'].map(suffix => adjective + suffix);
  case 'ConjunctiveTe': return [adjective + 'で'];
  case 'Adverbial': return [adjective + 'に'];
  case 'Conditional': return ['なら', 'ならば'].map(suffix => adjective + suffix);
  case 'TaraConditional': return ['だったら'].map(suffix => adjective + suffix);
  case 'Tari': return ['だったり', 'でしたり'].map(suffix => adjective + suffix);
  case 'Noun': return [adjective + 'さ'];
  case 'StemSou': return [adjective + 'そう'];
  case 'StemNegativeSou': return [adjective + 'じゃなさそう'];
  default: never(conj);
  }

  throw new Error('unknown conjugation/iAdjective');
}

export interface AdjDeconjugated {
  conjugation: AdjConjugation;
  result: string[];
}
export function adjDeconjugate(conjugated: string, dictionary: string, iAdjective: boolean): AdjDeconjugated[] {
  const hits: AdjDeconjugated[] = [];
  for (const conj of adjConjugations) {
    const result = adjConjugate(dictionary, conj, iAdjective);
    if (result.includes(conjugated)) { hits.push({conjugation: conj, result}) }
  }
  return hits;
}