using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using ICU4N.Text;

namespace Jellyfin.Extensions
{
    /// <summary>
    /// Provides extensions methods for <see cref="string" />.
    /// </summary>
    public static partial class StringExtensions
    {
        private static readonly Lazy<string> _transliteratorId = new(() =>
            Environment.GetEnvironmentVariable("JELLYFIN_TRANSLITERATOR_ID")
            ?? "Any-Latin; Latin-Ascii; Lower; NFD; [:Nonspacing Mark:] Remove; [:Punctuation:] Remove;");

        private static readonly Lazy<Transliterator?> _transliterator = new(() =>
        {
            try
            {
                return Transliterator.GetInstance(_transliteratorId.Value);
            }
            catch (ArgumentException)
            {
                return null;
            }
        });

        // Matches non-conforming unicode chars
        // https://mnaoumov.wordpress.com/2014/06/14/stripping-invalid-characters-from-utf-16-strings/

        [GeneratedRegex("([\ud800-\udbff](?![\udc00-\udfff]))|((?<![\ud800-\udbff])[\udc00-\udfff])|(�)")]
        private static partial Regex NonConformingUnicodeRegex();

        /// <summary>
        /// Removes the diacritics character from the strings.
        /// </summary>
        /// <param name="text">The string to act on.</param>
        /// <returns>The string without diacritics character.</returns>
        public static string RemoveDiacritics(this string text)
            => Diacritics.Extensions.StringExtensions.RemoveDiacritics(
                NonConformingUnicodeRegex().Replace(text, string.Empty));

        /// <summary>
        /// Checks whether or not the specified string has diacritics in it.
        /// </summary>
        /// <param name="text">The string to check.</param>
        /// <returns>True if the string has diacritics, false otherwise.</returns>
        public static bool HasDiacritics(this string text)
            => Diacritics.Extensions.StringExtensions.HasDiacritics(text)
                || NonConformingUnicodeRegex().IsMatch(text);

        /// <summary>
        /// Counts the number of occurrences of [needle] in the string.
        /// </summary>
        /// <param name="value">The haystack to search in.</param>
        /// <param name="needle">The character to search for.</param>
        /// <returns>The number of occurrences of the [needle] character.</returns>
        public static int Count(this ReadOnlySpan<char> value, char needle)
        {
            var count = 0;
            var length = value.Length;
            for (var i = 0; i < length; i++)
            {
                if (value[i] == needle)
                {
                    count++;
                }
            }

            return count;
        }

        /// <summary>
        /// Returns the part on the left of the <c>needle</c>.
        /// </summary>
        /// <param name="haystack">The string to seek.</param>
        /// <param name="needle">The needle to find.</param>
        /// <returns>The part left of the <paramref name="needle" />.</returns>
        public static ReadOnlySpan<char> LeftPart(this ReadOnlySpan<char> haystack, char needle)
        {
            if (haystack.IsEmpty)
            {
                return ReadOnlySpan<char>.Empty;
            }

            var pos = haystack.IndexOf(needle);
            return pos == -1 ? haystack : haystack[..pos];
        }

        /// <summary>
        /// Returns the part on the right of the <c>needle</c>.
        /// </summary>
        /// <param name="haystack">The string to seek.</param>
        /// <param name="needle">The needle to find.</param>
        /// <returns>The part right of the <paramref name="needle" />.</returns>
        public static ReadOnlySpan<char> RightPart(this ReadOnlySpan<char> haystack, char needle)
        {
            if (haystack.IsEmpty)
            {
                return ReadOnlySpan<char>.Empty;
            }

            var pos = haystack.LastIndexOf(needle);
            if (pos == -1)
            {
                return haystack;
            }

            if (pos == haystack.Length - 1)
            {
                return ReadOnlySpan<char>.Empty;
            }

            return haystack[(pos + 1)..];
        }

        /// <summary>
        /// Returns a transliterated string which only contain ascii characters.
        /// </summary>
        /// <param name="text">The string to act on.</param>
        /// <returns>The transliterated string.</returns>
        public static string Transliterated(this string text)
        {
            return (_transliterator.Value is null) ? text : _transliterator.Value.Transliterate(text);
        }

        /// <summary>
        /// Ensures all strings are non-null and trimmed of leading an trailing blanks.
        /// </summary>
        /// <param name="values">The enumerable of strings to trim.</param>
        /// <returns>The enumeration of trimmed strings.</returns>
        public static IEnumerable<string> Trimmed(this IEnumerable<string> values)
        {
            return values.Select(i => (i ?? string.Empty).Trim());
        }

        /// <summary>
        /// Truncates a string at the first null character ('\0').
        /// </summary>
        /// <param name="text">The input string.</param>
        /// <returns>
        /// The substring up to (but not including) the first null character,
        /// or the original string if no null character is present.
        /// </returns>
        public static string TruncateAtNull(this string text)
        {
            return string.IsNullOrEmpty(text) ? text : text.AsSpan().LeftPart('\0').ToString();
        }
    }
}