function _createMemoizedConstraintMapGetter()

in packages/babel-plugin-fbt/src/translate/TranslationBuilder.js [451:514]

• 44 lines of code
• 10 McCabe index (conditional complexity)

function _createMemoizedConstraintMapGetter(
  instance: TranslationBuilder,
): (hash: PatternHash) => ConstraintKeyToTranslation {
  // Yes this is hand-rolled memoization :(
  // TODO: T37795723 - Pull in a lightweight (not bloated) memoization library
  const _mem = {};

  return function getConstraintMap(
    hash: PatternHash,
  ): ConstraintKeyToTranslation {
    if (_mem[hash]) {
      return _mem[hash];
    }

    const constraintMap = {};
    const transData = this._translations[hash];
    if (transData == null || typeof transData === 'string') {
      // No translation? No constraints.
      return (_mem[hash] = constraintMap);
    }

    // For every possible variation combination, create a mapping to its
    // corresponding translation
    transData.translations.forEach(translation => {
      const constraints = {};
      for (const idx in translation.variations) {
        const variation = translation.variations[idx];
        // We prune entries that contain non-default variations
        // for tokens we haven't specified.
        const token = transData.tokens[Number(idx)];
        if (
          // Token variation type not specified
          !this._tokenToMask[token] ||
          // Translated variation type is different than token variation type
          this._tokenToMask[token] !== transData.types[Number(idx)]
        ) {
          // Only add default tokens we haven't specified.
          if (!this._config.isDefaultVariation(variation)) {
            return;
          }
        }
        constraints[token] = variation;
      }
      // A note about fbt:plurals.  They can introduce global token
      // discrepancies between leaf nodes.  Singular translations don't have
      // number tokens, but their plural counterparts can (when showCount =
      // "ifMany" or "yes").  If we are dealing with the singular leaf of an
      // fbt:plural, since it has a unique hash, we can let it masquerade as
      // default: '*', since no such variation actually exists for a
      // non-existent token
      const constraintKeys = [];
      for (const k in this._tokenToMask) {
        constraintKeys.push([k, constraints[k] || '*']);
      }
      this._insertConstraint(
        constraintKeys,
        constraintMap,
        translation.translation,
        0,
      );
    });
    return (_mem[hash] = constraintMap);
  }.bind(instance);
}