using System;
using System.IO;
#if NET3
using Path = Net3_Proxy.Path;
#endif

namespace IPA.Utilities
{
    /// <summary>
    /// A class providing various extension methods.
    /// </summary>
    public static class Extensions
    {
        /// <summary>
        /// Gets the default value for a given <see cref="Type"/>.
        /// </summary>
        /// <param name="type">the <see cref="Type"/> to get the default value for</param>
        /// <returns>the default value of <paramref name="type"/></returns>
        public static object GetDefault(this Type type)
        {
            return type.IsValueType ? Activator.CreateInstance(type) : null;
        }

        /// <summary>
        /// Unwraps a <see cref="Nullable{T}"/> where T is <see cref="bool"/> such that if the value is null, it gives <see langword="false"/>.
        /// </summary>
        /// <param name="self">the bool? to unwrap</param>
        /// <returns>the unwrapped value, or <see langword="false"/> if it was <see langword="null"/></returns>
        public static bool Unwrap(this bool? self) => self != null && self.Value;

        /// <summary>
        /// Returns true if <paramref name="path"/> starts with the path <paramref name="baseDirPath"/>.
        /// The comparison is case-insensitive, handles / and \ slashes as folder separators and
        /// only matches if the base dir folder name is matched exactly ("c:\foobar\file.txt" is not a sub path of "c:\foo").
        /// </summary>
        public static bool IsSubPathOf(this string path, string baseDirPath)
        {
            string normalizedPath = Path.GetFullPath(path.Replace('/', '\\')
                .WithEnding("\\"));

            string normalizedBaseDirPath = Path.GetFullPath(baseDirPath.Replace('/', '\\')
                .WithEnding("\\"));

            return normalizedPath.StartsWith(normalizedBaseDirPath, StringComparison.OrdinalIgnoreCase);
        }

        /// <summary>
        /// Returns <paramref name="str"/> with the minimal concatenation of <paramref name="ending"/> (starting from end) that
        /// results in satisfying .EndsWith(ending).
        /// </summary>
        /// <example>"hel".WithEnding("llo") returns "hello", which is the result of "hel" + "lo".</example>
        public static string WithEnding(this string str, string ending)
        {
            if (str == null)
                return ending;

            string result = str;

            // Right() is 1-indexed, so include these cases
            // * Append no characters
            // * Append up to N characters, where N is ending length
            for (int i = 0; i <= ending.Length; i++)
            {
                string tmp = result + ending.Right(i);
                if (tmp.EndsWith(ending))
                    return tmp;
            }

            return result;
        }

        /// <summary>Gets the rightmost <paramref name="length" /> characters from a string.</summary>
        /// <param name="value">The string to retrieve the substring from.</param>
        /// <param name="length">The number of characters to retrieve.</param>
        /// <returns>The substring.</returns>
        public static string Right(this string value, int length)
        {
            if (value == null)
            {
                throw new ArgumentNullException("value");
            }
            if (length < 0)
            {
                throw new ArgumentOutOfRangeException("length", length, "Length is less than zero");
            }

            return (length < value.Length) ? value.Substring(value.Length - length) : value;
        }
    }
}