'use strict';

function createSharedState(initialValueOrGetter) {
  var value;
  var subscriberSet = new Set();
  var get = function get() {
    if (value === undefined) {
      value = typeof initialValueOrGetter === "function" ? initialValueOrGetter() : initialValueOrGetter;
    }
    return value;
  };
  var set = function set(valueOrUpdater) {
    var previousValue = get();
    var nextValue = typeof valueOrUpdater === "function" ? valueOrUpdater(previousValue) : valueOrUpdater;
    if (Object.is(nextValue, previousValue)) return;
    value = nextValue;
    subscriberSet.forEach(function (subscriber) {
      return subscriber(nextValue, previousValue);
    });
  };
  var subscribe = function subscribe(handler) {
    return subscriberSet.add(handler);
  };
  var unsubscribe = function unsubscribe(handler) {
    return subscriberSet["delete"](handler);
  };
  return {
    get: get,
    set: set,
    subscribe: subscribe,
    unsubscribe: unsubscribe
  };
}
function createDerivedSharedState(getter, setter) {
  var value;
  var dependencySet;
  var subscriberSet = new Set();
  var get = function get() {
    return value !== undefined ? value : getter(function (sharedState) {
      return sharedState.get();
    });
  };
  var set = function set(valueOrUpdater) {
    if (!setter) return;
    var previousValue = get();
    var nextValue = typeof valueOrUpdater === "function" ? valueOrUpdater(previousValue) : valueOrUpdater;
    if (Object.is(nextValue, previousValue)) return;
    setter(nextValue);
  };
  var updateValueAndDependency = function updateValueAndDependency() {
    var previousValue = get();
    var previousDependencySet = dependencySet;
    var nextDependencySet = new Set();
    var nextValue = getter(function (sharedState) {
      nextDependencySet.add(sharedState);
      return sharedState.get();
    });
    if (previousDependencySet !== undefined) {
      nextDependencySet.forEach(function (sharedState) {
        return !previousDependencySet.has(sharedState) && sharedState.subscribe(updateValueAndDependency);
      });
      previousDependencySet.forEach(function (sharedState) {
        return !nextDependencySet.has(sharedState) && sharedState.unsubscribe(updateValueAndDependency);
      });
    }
    dependencySet = nextDependencySet;
    if (Object.is(nextValue, previousValue)) return;
    value = nextValue;
    subscriberSet.forEach(function (subscriber) {
      return subscriber(nextValue, previousValue);
    });
  };
  return {
    get: get,
    set: set,
    subscribe: function subscribe(handler) {
      if (subscriberSet.size === 0) {
        var nextDependencySet = new Set();
        value = getter(function (sharedState) {
          sharedState.subscribe(updateValueAndDependency);
          nextDependencySet.add(sharedState);
          return sharedState.get();
        });
        dependencySet = nextDependencySet;
      }
      subscriberSet.add(handler);
    },
    unsubscribe: function unsubscribe(handler) {
      subscriberSet["delete"](handler);
      if (subscriberSet.size === 0) {
        if (dependencySet !== undefined) {
          dependencySet.forEach(function (sharedState) {
            return sharedState.unsubscribe(updateValueAndDependency);
          });
          dependencySet = undefined;
          value = undefined;
        }
      }
    }
  };
}

exports.createDerivedSharedState = createDerivedSharedState;
exports.createSharedState = createSharedState;