using System;
using System.Collections.Generic;
using System.Linq;

namespace Swan {
  /// <summary>
  /// Functional programming extension methods.
  /// </summary>
  public static class FunctionalExtensions {
    /// <summary>
    /// Whens the specified condition.
    /// </summary>
    /// <typeparam name="T">The type of IQueryable.</typeparam>
    /// <param name="list">The list.</param>
    /// <param name="condition">The condition.</param>
    /// <param name="fn">The function.</param>
    /// <returns>
    /// The IQueryable.
    /// </returns>
    /// <exception cref="ArgumentNullException">
    /// this
    /// or
    /// condition
    /// or
    /// fn.
    /// </exception>
    public static IQueryable<T> When<T>(this IQueryable<T> list, Func<Boolean> condition, Func<IQueryable<T>, IQueryable<T>> fn) {
      if(list == null) {
        throw new ArgumentNullException(nameof(list));
      }

      if(condition == null) {
        throw new ArgumentNullException(nameof(condition));
      }

      if(fn == null) {
        throw new ArgumentNullException(nameof(fn));
      }

      return condition() ? fn(list) : list;
    }

    /// <summary>
    /// Whens the specified condition.
    /// </summary>
    /// <typeparam name="T">The type of IEnumerable.</typeparam>
    /// <param name="list">The list.</param>
    /// <param name="condition">The condition.</param>
    /// <param name="fn">The function.</param>
    /// <returns>
    /// The IEnumerable.
    /// </returns>
    /// <exception cref="ArgumentNullException">
    /// this
    /// or
    /// condition
    /// or
    /// fn.
    /// </exception>
    public static IEnumerable<T> When<T>(this IEnumerable<T> list, Func<Boolean> condition, Func<IEnumerable<T>, IEnumerable<T>> fn) {
      if(list == null) {
        throw new ArgumentNullException(nameof(list));
      }

      if(condition == null) {
        throw new ArgumentNullException(nameof(condition));
      }

      if(fn == null) {
        throw new ArgumentNullException(nameof(fn));
      }

      return condition() ? fn(list) : list;
    }

    /// <summary>
    /// Adds the value when the condition is true.
    /// </summary>
    /// <typeparam name="T">The type of IList element.</typeparam>
    /// <param name="list">The list.</param>
    /// <param name="condition">The condition.</param>
    /// <param name="value">The value.</param>
    /// <returns>
    /// The IList.
    /// </returns>
    /// <exception cref="ArgumentNullException">
    /// this
    /// or
    /// condition
    /// or
    /// value.
    /// </exception>
    public static IList<T> AddWhen<T>(this IList<T> list, Func<Boolean> condition, Func<T> value) {
      if(list == null) {
        throw new ArgumentNullException(nameof(list));
      }

      if(condition == null) {
        throw new ArgumentNullException(nameof(condition));
      }

      if(value == null) {
        throw new ArgumentNullException(nameof(value));
      }

      if(condition()) {
        list.Add(value());
      }

      return list;
    }

    /// <summary>
    /// Adds the value when the condition is true.
    /// </summary>
    /// <typeparam name="T">The type of IList element.</typeparam>
    /// <param name="list">The list.</param>
    /// <param name="condition">if set to <c>true</c> [condition].</param>
    /// <param name="value">The value.</param>
    /// <returns>
    /// The IList.
    /// </returns>
    /// <exception cref="ArgumentNullException">list.</exception>
    public static IList<T> AddWhen<T>(this IList<T> list, Boolean condition, T value) {
      if(list == null) {
        throw new ArgumentNullException(nameof(list));
      }

      if(condition) {
        list.Add(value);
      }

      return list;
    }

    /// <summary>
    /// Adds the range when the condition is true.
    /// </summary>
    /// <typeparam name="T">The type of List element.</typeparam>
    /// <param name="list">The list.</param>
    /// <param name="condition">The condition.</param>
    /// <param name="value">The value.</param>
    /// <returns>
    /// The List.
    /// </returns>
    /// <exception cref="ArgumentNullException">
    /// this
    /// or
    /// condition
    /// or
    /// value.
    /// </exception>
    public static List<T> AddRangeWhen<T>(this List<T> list, Func<Boolean> condition, Func<IEnumerable<T>> value) {
      if(list == null) {
        throw new ArgumentNullException(nameof(list));
      }

      if(condition == null) {
        throw new ArgumentNullException(nameof(condition));
      }

      if(value == null) {
        throw new ArgumentNullException(nameof(value));
      }

      if(condition()) {
        list.AddRange(value());
      }

      return list;
    }
  }
}