createVersionedReducer.js

//
import semver from 'semver';

//
export function createVersionedReducer() {
  const ranges = [];
  const map = {};

  //
  function versionedReducer(state, action) {
    const { meta } = action;

    //
    if (meta === undefined || meta.version === undefined) {
      throw new Error('Expected versioned action');
    }

    //
    const version = semver.valid(meta.version);

    if (version === null) {
      throw new Error(`"${meta.version}" is not a valid semantic version"`);
    }

    // try direct version match
    const vMatch = ranges.filter((r) => {
      const v = semver.valid(r);
      if (v) return semver.eq(version, v);
      return false;
    });

    // use direct match over anything else
    if (vMatch.length === 1) {
      return map[vMatch[0]](state, action);
    }

    // try range match
    const rMatch = ranges.filter((r) => {
      return semver.satisfies(version, r);
    });

    if (rMatch.length > 1) {
      throw new Error(`more than one reducer for semantic version "${version}" ${rMatch}`);
    } else if (rMatch.length > 0) {
      return map[rMatch[0]](state, action);
    } else {
      throw new Error(`no reducer for semantic version "${version}"`);
    }
  }

  //
  versionedReducer.addVersion = (userRange, fn) => {
    const range = semver.validRange(userRange);

    if (range === null) {
      throw new Error(`"${userRange}" is not a valid semantic version range"`);
    }

    if (ranges.indexOf(range) !== -1) {
      throw new Error(`a reducer with the semantic version range "${range}" already exists"`);
    }

    //
    ranges.push(range);
    map[range] = fn;

    //
    return versionedReducer;
  };

  //
  return versionedReducer;
}

//
export default createVersionedReducer;