'use strict';

/**
 * Flatten array, one level deep.
 *
 * @template T
 *
 * @param {T[][] | T[] | null} [arr]
 *
 * @return {T[]}
 */
function flatten(arr) {
  return Array.prototype.concat.apply([], arr);
}

const nativeToString = Object.prototype.toString;
const nativeHasOwnProperty = Object.prototype.hasOwnProperty;

function isUndefined(obj) {
  return obj === undefined;
}

function isDefined(obj) {
  return obj !== undefined;
}

function isNil(obj) {
  return obj == null;
}

function isArray(obj) {
  return nativeToString.call(obj) === '[object Array]';
}

function isObject(obj) {
  return nativeToString.call(obj) === '[object Object]';
}

function isNumber(obj) {
  return nativeToString.call(obj) === '[object Number]';
}

/**
 * @param {any} obj
 *
 * @return {boolean}
 */
function isFunction(obj) {
  const tag = nativeToString.call(obj);

  return (
    tag === '[object Function]' ||
    tag === '[object AsyncFunction]' ||
    tag === '[object GeneratorFunction]' ||
    tag === '[object AsyncGeneratorFunction]' ||
    tag === '[object Proxy]'
  );
}

function isString(obj) {
  return nativeToString.call(obj) === '[object String]';
}


/**
 * Ensure collection is an array.
 *
 * @param {Object} obj
 */
function ensureArray(obj) {

  if (isArray(obj)) {
    return;
  }

  throw new Error('must supply array');
}

/**
 * Return true, if target owns a property with the given key.
 *
 * @param {Object} target
 * @param {String} key
 *
 * @return {Boolean}
 */
function has(target, key) {
  return !isNil(target) && nativeHasOwnProperty.call(target, key);
}

/**
 * @template T
 * @typedef { (
 *   ((e: T) => boolean) |
 *   ((e: T, idx: number) => boolean) |
 *   ((e: T, key: string) => boolean) |
 *   string |
 *   number
 * ) } Matcher
 */

/**
 * @template T
 * @template U
 *
 * @typedef { (
 *   ((e: T) => U) | string | number
 * ) } Extractor
 */


/**
 * @template T
 * @typedef { (val: T, key: any) => boolean } MatchFn
 */

/**
 * @template T
 * @typedef { T[] } ArrayCollection
 */

/**
 * @template T
 * @typedef { { [key: string]: T } } StringKeyValueCollection
 */

/**
 * @template T
 * @typedef { { [key: number]: T } } NumberKeyValueCollection
 */

/**
 * @template T
 * @typedef { StringKeyValueCollection<T> | NumberKeyValueCollection<T> } KeyValueCollection
 */

/**
 * @template T
 * @typedef { KeyValueCollection<T> | ArrayCollection<T> } Collection
 */

/**
 * Find element in collection.
 *
 * @template T
 * @param {Collection<T>} collection
 * @param {Matcher<T>} matcher
 *
 * @return {Object}
 */
function find(collection, matcher) {

  const matchFn = toMatcher(matcher);

  let match;

  forEach(collection, function(val, key) {
    if (matchFn(val, key)) {
      match = val;

      return false;
    }
  });

  return match;

}


/**
 * Find element index in collection.
 *
 * @template T
 * @param {Collection<T>} collection
 * @param {Matcher<T>} matcher
 *
 * @return {number | string | undefined}
 */
function findIndex(collection, matcher) {

  const matchFn = toMatcher(matcher);

  let idx = isArray(collection) ? -1 : undefined;

  forEach(collection, function(val, key) {
    if (matchFn(val, key)) {
      idx = key;

      return false;
    }
  });

  return idx;
}


/**
 * Filter elements in collection.
 *
 * @template T
 * @param {Collection<T>} collection
 * @param {Matcher<T>} matcher
 *
 * @return {T[]} result
 */
function filter(collection, matcher) {

  const matchFn = toMatcher(matcher);

  let result = [];

  forEach(collection, function(val, key) {
    if (matchFn(val, key)) {
      result.push(val);
    }
  });

  return result;
}


/**
 * Iterate over collection; returning something
 * (non-undefined) will stop iteration.
 *
 * @template T
 * @param {Collection<T>} collection
 * @param { ((item: T, idx: number) => (boolean|void)) | ((item: T, key: string) => (boolean|void)) } iterator
 *
 * @return {T} return result that stopped the iteration
 */
function forEach(collection, iterator) {

  let val,
      result;

  if (isUndefined(collection)) {
    return;
  }

  const convertKey = isArray(collection) ? toNum : identity;

  for (let key in collection) {

    if (has(collection, key)) {
      val = collection[key];

      result = iterator(val, convertKey(key));

      if (result === false) {
        return val;
      }
    }
  }
}

/**
 * Return collection without element.
 *
 * @template T
 * @param {ArrayCollection<T>} arr
 * @param {Matcher<T>} matcher
 *
 * @return {T[]}
 */
function without(arr, matcher) {

  if (isUndefined(arr)) {
    return [];
  }

  ensureArray(arr);

  const matchFn = toMatcher(matcher);

  return arr.filter(function(el, idx) {
    return !matchFn(el, idx);
  });

}


/**
 * Reduce collection, returning a single result.
 *
 * @template T
 * @template V
 *
 * @param {Collection<T>} collection
 * @param {(result: V, entry: T, index: any) => V} iterator
 * @param {V} result
 *
 * @return {V} result returned from last iterator
 */
function reduce(collection, iterator, result) {

  forEach(collection, function(value, idx) {
    result = iterator(result, value, idx);
  });

  return result;
}


/**
 * Return true if every element in the collection
 * matches the criteria.
 *
 * @param  {Object|Array} collection
 * @param  {Function} matcher
 *
 * @return {Boolean}
 */
function every(collection, matcher) {

  return !!reduce(collection, function(matches, val, key) {
    return matches && matcher(val, key);
  }, true);
}


/**
 * Return true if some elements in the collection
 * match the criteria.
 *
 * @param  {Object|Array} collection
 * @param  {Function} matcher
 *
 * @return {Boolean}
 */
function some(collection, matcher) {

  return !!find(collection, matcher);
}


/**
 * Transform a collection into another collection
 * by piping each member through the given fn.
 *
 * @param  {Object|Array}   collection
 * @param  {Function} fn
 *
 * @return {Array} transformed collection
 */
function map(collection, fn) {

  let result = [];

  forEach(collection, function(val, key) {
    result.push(fn(val, key));
  });

  return result;
}


/**
 * Get the collections keys.
 *
 * @param  {Object|Array} collection
 *
 * @return {Array}
 */
function keys(collection) {
  return collection && Object.keys(collection) || [];
}


/**
 * Shorthand for `keys(o).length`.
 *
 * @param  {Object|Array} collection
 *
 * @return {Number}
 */
function size(collection) {
  return keys(collection).length;
}


/**
 * Get the values in the collection.
 *
 * @param  {Object|Array} collection
 *
 * @return {Array}
 */
function values(collection) {
  return map(collection, (val) => val);
}


/**
 * Group collection members by attribute.
 *
 * @param {Object|Array} collection
 * @param {Extractor} extractor
 *
 * @return {Object} map with { attrValue => [ a, b, c ] }
 */
function groupBy(collection, extractor, grouped = {}) {

  extractor = toExtractor(extractor);

  forEach(collection, function(val) {
    let discriminator = extractor(val) || '_';

    let group = grouped[discriminator];

    if (!group) {
      group = grouped[discriminator] = [];
    }

    group.push(val);
  });

  return grouped;
}


function uniqueBy(extractor, ...collections) {

  extractor = toExtractor(extractor);

  let grouped = {};

  forEach(collections, (c) => groupBy(c, extractor, grouped));

  let result = map(grouped, function(val, key) {
    return val[0];
  });

  return result;
}


const unionBy = uniqueBy;



/**
 * Sort collection by criteria.
 *
 * @template T
 *
 * @param {Collection<T>} collection
 * @param {Extractor<T, number | string>} extractor
 *
 * @return {Array}
 */
function sortBy(collection, extractor) {

  extractor = toExtractor(extractor);

  let sorted = [];

  forEach(collection, function(value, key) {
    let disc = extractor(value, key);

    let entry = {
      d: disc,
      v: value
    };

    for (var idx = 0; idx < sorted.length; idx++) {
      let { d } = sorted[idx];

      if (disc < d) {
        sorted.splice(idx, 0, entry);
        return;
      }
    }

    // not inserted, append (!)
    sorted.push(entry);
  });

  return map(sorted, (e) => e.v);
}


/**
 * Create an object pattern matcher.
 *
 * @example
 *
 * ```javascript
 * const matcher = matchPattern({ id: 1 });
 *
 * let element = find(elements, matcher);
 * ```
 *
 * @template T
 *
 * @param {T} pattern
 *
 * @return { (el: any) =>  boolean } matcherFn
 */
function matchPattern(pattern) {

  return function(el) {

    return every(pattern, function(val, key) {
      return el[key] === val;
    });

  };
}


/**
 * @param {string | ((e: any) => any) } extractor
 *
 * @return { (e: any) => any }
 */
function toExtractor(extractor) {

  /**
   * @satisfies { (e: any) => any }
   */
  return isFunction(extractor) ? extractor : (e) => {

    // @ts-ignore: just works
    return e[extractor];
  };
}


/**
 * @template T
 * @param {Matcher<T>} matcher
 *
 * @return {MatchFn<T>}
 */
function toMatcher(matcher) {
  return isFunction(matcher) ? matcher : (e) => {
    return e === matcher;
  };
}


function identity(arg) {
  return arg;
}

function toNum(arg) {
  return Number(arg);
}

/* global setTimeout clearTimeout */

/**
 * @typedef { {
 *   (...args: any[]): any;
 *   flush: () => void;
 *   cancel: () => void;
 * } } DebouncedFunction
 */

/**
 * Debounce fn, calling it only once if the given time
 * elapsed between calls.
 *
 * Lodash-style the function exposes methods to `#clear`
 * and `#flush` to control internal behavior.
 *
 * @param  {Function} fn
 * @param  {Number} timeout
 *
 * @return {DebouncedFunction} debounced function
 */
function debounce(fn, timeout) {

  let timer;

  let lastArgs;
  let lastThis;

  let lastNow;

  function fire(force) {

    let now = Date.now();

    let scheduledDiff = force ? 0 : (lastNow + timeout) - now;

    if (scheduledDiff > 0) {
      return schedule(scheduledDiff);
    }

    fn.apply(lastThis, lastArgs);

    clear();
  }

  function schedule(timeout) {
    timer = setTimeout(fire, timeout);
  }

  function clear() {
    if (timer) {
      clearTimeout(timer);
    }

    timer = lastNow = lastArgs = lastThis = undefined;
  }

  function flush() {
    if (timer) {
      fire(true);
    }

    clear();
  }

  /**
   * @type { DebouncedFunction }
   */
  function callback(...args) {
    lastNow = Date.now();

    lastArgs = args;
    lastThis = this;

    // ensure an execution is scheduled
    if (!timer) {
      schedule(timeout);
    }
  }

  callback.flush = flush;
  callback.cancel = clear;

  return callback;
}

/**
 * Throttle fn, calling at most once
 * in the given interval.
 *
 * @param  {Function} fn
 * @param  {Number} interval
 *
 * @return {Function} throttled function
 */
function throttle(fn, interval) {
  let throttling = false;

  return function(...args) {

    if (throttling) {
      return;
    }

    fn(...args);
    throttling = true;

    setTimeout(() => {
      throttling = false;
    }, interval);
  };
}

/**
 * Bind function against target <this>.
 *
 * @param  {Function} fn
 * @param  {Object}   target
 *
 * @return {Function} bound function
 */
function bind(fn, target) {
  return fn.bind(target);
}

/**
 * Convenience wrapper for `Object.assign`.
 *
 * @param {Object} target
 * @param {...Object} others
 *
 * @return {Object} the target
 */
function assign(target, ...others) {
  return Object.assign(target, ...others);
}

/**
 * Sets a nested property of a given object to the specified value.
 *
 * This mutates the object and returns it.
 *
 * @template T
 *
 * @param {T} target The target of the set operation.
 * @param {(string|number)[]} path The path to the nested value.
 * @param {any} value The value to set.
 *
 * @return {T}
 */
function set(target, path, value) {

  let currentTarget = target;

  forEach(path, function(key, idx) {

    if (typeof key !== 'number' && typeof key !== 'string') {
      throw new Error('illegal key type: ' + typeof key + '. Key should be of type number or string.');
    }

    if (key === 'constructor') {
      throw new Error('illegal key: constructor');
    }

    if (key === '__proto__') {
      throw new Error('illegal key: __proto__');
    }

    let nextKey = path[idx + 1];
    let nextTarget = currentTarget[key];

    if (isDefined(nextKey) && isNil(nextTarget)) {
      nextTarget = currentTarget[key] = isNaN(+nextKey) ? {} : [];
    }

    if (isUndefined(nextKey)) {
      if (isUndefined(value)) {
        delete currentTarget[key];
      } else {
        currentTarget[key] = value;
      }
    } else {
      currentTarget = nextTarget;
    }
  });

  return target;
}


/**
 * Gets a nested property of a given object.
 *
 * @param {Object} target The target of the get operation.
 * @param {(string|number)[]} path The path to the nested value.
 * @param {any} [defaultValue] The value to return if no value exists.
 *
 * @return {any}
 */
function get(target, path, defaultValue) {

  let currentTarget = target;

  forEach(path, function(key) {

    // accessing nil property yields <undefined>
    if (isNil(currentTarget)) {
      currentTarget = undefined;

      return false;
    }

    currentTarget = currentTarget[key];
  });

  return isUndefined(currentTarget) ? defaultValue : currentTarget;
}

/**
 * Pick properties from the given target.
 *
 * @template T
 * @template {any[]} V
 *
 * @param {T} target
 * @param {V} properties
 *
 * @return Pick<T, V>
 */
function pick(target, properties) {

  let result = {};

  let obj = Object(target);

  forEach(properties, function(prop) {

    if (prop in obj) {
      result[prop] = target[prop];
    }
  });

  return result;
}

/**
 * Pick all target properties, excluding the given ones.
 *
 * @template T
 * @template {any[]} V
 *
 * @param {T} target
 * @param {V} properties
 *
 * @return {Omit<T, V>} target
 */
function omit(target, properties) {

  let result = {};

  let obj = Object(target);

  forEach(obj, function(prop, key) {

    if (properties.indexOf(key) === -1) {
      result[key] = prop;
    }
  });

  return result;
}

/**
 * Recursively merge `...sources` into given target.
 *
 * Does support merging objects; does not support merging arrays.
 *
 * @param {Object} target
 * @param {...Object} sources
 *
 * @return {Object} the target
 */
function merge(target, ...sources) {

  if (!sources.length) {
    return target;
  }

  forEach(sources, function(source) {

    // skip non-obj sources, i.e. null
    if (!source || !isObject(source)) {
      return;
    }

    forEach(source, function(sourceVal, key) {

      if (key === '__proto__') {
        return;
      }

      let targetVal = target[key];

      if (isObject(sourceVal)) {

        if (!isObject(targetVal)) {

          // override target[key] with object
          targetVal = {};
        }

        target[key] = merge(targetVal, sourceVal);
      } else {
        target[key] = sourceVal;
      }

    });
  });

  return target;
}

exports.assign = assign;
exports.bind = bind;
exports.debounce = debounce;
exports.ensureArray = ensureArray;
exports.every = every;
exports.filter = filter;
exports.find = find;
exports.findIndex = findIndex;
exports.flatten = flatten;
exports.forEach = forEach;
exports.get = get;
exports.groupBy = groupBy;
exports.has = has;
exports.isArray = isArray;
exports.isDefined = isDefined;
exports.isFunction = isFunction;
exports.isNil = isNil;
exports.isNumber = isNumber;
exports.isObject = isObject;
exports.isString = isString;
exports.isUndefined = isUndefined;
exports.keys = keys;
exports.map = map;
exports.matchPattern = matchPattern;
exports.merge = merge;
exports.omit = omit;
exports.pick = pick;
exports.reduce = reduce;
exports.set = set;
exports.size = size;
exports.some = some;
exports.sortBy = sortBy;
exports.throttle = throttle;
exports.unionBy = unionBy;
exports.uniqueBy = uniqueBy;
exports.values = values;
exports.without = without;