// Author: Gockner, Simon
// Created: 2020-02-13
// Copyright(c) 2020 SimonG. All Rights Reserved.

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using GBase.Api;
using GBase.Exceptions;

namespace GBase.Helpers
{
    internal static class Enumerables
    {
        private const char ENUMERABLE_STRING_DIVIDER = ',';

        /// <summary>
        /// Convert an <see cref="IEnumerable"/> to a GBase <see cref="string"/>
        /// </summary>
        /// <param name="enumerable">The <see cref="IEnumerable"/></param>
        /// <returns></returns>
        public static string ToGBaseString(this IEnumerable enumerable)
        {
            StringBuilder @string = new StringBuilder();
            foreach (var item in enumerable)
            {
                @string.Append($"{item}{ENUMERABLE_STRING_DIVIDER}");
            }

            char lastChar = @string[^1];
            if (lastChar == ENUMERABLE_STRING_DIVIDER)
                @string.Remove(@string.Length - 1, 1);

            return @string.ToString();
        }

        /// <summary>
        /// Convert a given <see cref="string"/> to an <see cref="IEnumerable{T}"/> of <see cref="Type"/> <typeparamref name="TEnumerable"/>
        /// </summary>
        /// <typeparam name="TEnumerable">The <see cref="IEnumerable{T}"/> <see cref="Type"/></typeparam>
        /// <param name="string">The given <see cref="string"/></param>
        /// <returns>An <see cref="IEnumerable{T}"/> of <see cref="Type"/> <typeparamref name="TEnumerable"/></returns>
        /// <exception cref="InterfaceEnumerablePassedException">Interface was passed to an <see cref="IEnumerable{T}"/></exception>
        public static TEnumerable ConvertToGBaseEnumerable<TEnumerable>(string @string)
        {
            //get generic type parameter of TEnumerable
            Type genericType = typeof(TEnumerable).GetGenericArguments()[0];

            Type listType = typeof(List<>);
            Type genericList = listType.MakeGenericType(genericType);
            IList enumerable = (IList) Activator.CreateInstance(genericList);

            foreach (var value in @string.Split(ENUMERABLE_STRING_DIVIDER))
            {
                object item;

                if (genericType.GetInterfaces().Contains(typeof(IGBaseObject)))
                {
                    if (genericType.IsInterface)
                        throw new InterfaceEnumerablePassedException(genericType);

                    IGBaseObject gBaseObject = (IGBaseObject) Activator.CreateInstance(genericType);
                    gBaseObject.InitializeFromString(value);
                    item = gBaseObject;
                }
                else 
                    item = Convert.ChangeType(value, genericType);

                enumerable.Add(item);
            }
            
            return (TEnumerable) enumerable;
        }
    }
}