#nullable enable
using System.Buffers;

namespace Terminal.Gui;

/// <summary>Extensions to <see cref="string"/> to support TUI text manipulation.</summary>
public static class StringExtensions
{
    /// <summary>Unpacks the last UTF-8 encoding in the string.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The string to decode.</param>
    /// <param name="end">Index in string to stop at; if -1, use the buffer length.</param>
    /// <returns></returns>
    public static (Rune rune, int size) DecodeLastRune (this string str, int end = -1)
    {
        Rune rune = str.EnumerateRunes ().ToArray () [end == -1 ? ^1 : end];
        byte [] bytes = Encoding.UTF8.GetBytes (rune.ToString ());
        OperationStatus operationStatus = Rune.DecodeFromUtf8 (bytes, out rune, out int bytesConsumed);

        if (operationStatus == OperationStatus.Done)
        {
            return (rune, bytesConsumed);
        }

        return (Rune.ReplacementChar, 1);
    }

    /// <summary>Unpacks the first UTF-8 encoding in the string and returns the rune and its width in bytes.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The string to decode.</param>
    /// <param name="start">Starting offset.</param>
    /// <param name="count">Number of bytes in the buffer, or -1 to make it the length of the buffer.</param>
    /// <returns></returns>
    public static (Rune Rune, int Size) DecodeRune (this string str, int start = 0, int count = -1)
    {
        Rune rune = str.EnumerateRunes ().ToArray () [start];
        byte [] bytes = Encoding.UTF8.GetBytes (rune.ToString ());

        if (count == -1)
        {
            count = bytes.Length;
        }

        OperationStatus operationStatus = Rune.DecodeFromUtf8 (bytes, out rune, out int bytesConsumed);

        if (operationStatus == OperationStatus.Done && bytesConsumed >= count)
        {
            return (rune, bytesConsumed);
        }

        return (Rune.ReplacementChar, 1);
    }

    /// <summary>Gets the number of columns the string occupies in the terminal.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The string to measure.</param>
    /// <returns></returns>
    public static int GetColumns (this string str) { return str is null ? 0 : str.EnumerateRunes ().Sum (r => Math.Max (r.GetColumns (), 0)); }

    /// <summary>Gets the number of runes in the string.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The string to count.</param>
    /// <returns></returns>
    public static int GetRuneCount (this string str) { return str.EnumerateRunes ().Count (); }

    /// <summary>
    ///     Determines if this <see cref="ReadOnlySpan{T}"/> of <see langword="char"/> is composed entirely of ASCII
    ///     digits.
    /// </summary>
    /// <param name="stringSpan">A <see cref="ReadOnlySpan{T}"/> of <see langword="char"/> to check.</param>
    /// <returns>
    ///     A <see langword="bool"/> indicating if all elements of the <see cref="ReadOnlySpan{T}"/> are ASCII digits (
    ///     <see langword="true"/>) or not (<see langword="false"/>
    /// </returns>
    public static bool IsAllAsciiDigits (this ReadOnlySpan<char> stringSpan) { return stringSpan.ToString ().All (char.IsAsciiDigit); }

    /// <summary>
    ///     Determines if this <see cref="ReadOnlySpan{T}"/> of <see langword="char"/> is composed entirely of ASCII
    ///     digits.
    /// </summary>
    /// <param name="stringSpan">A <see cref="ReadOnlySpan{T}"/> of <see langword="char"/> to check.</param>
    /// <returns>
    ///     A <see langword="bool"/> indicating if all elements of the <see cref="ReadOnlySpan{T}"/> are ASCII digits (
    ///     <see langword="true"/>) or not (<see langword="false"/>
    /// </returns>
    public static bool IsAllAsciiHexDigits (this ReadOnlySpan<char> stringSpan) { return stringSpan.ToString ().All (char.IsAsciiHexDigit); }

    /// <summary>Repeats the string <paramref name="n"/> times.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The text to repeat.</param>
    /// <param name="n">Number of times to repeat the text.</param>
    /// <returns>The text repeated if <paramref name="n"/> is greater than zero, otherwise <see langword="null"/>.</returns>
    public static string? Repeat (this string str, int n)
    {
        if (n <= 0)
        {
            return null;
        }

        if (string.IsNullOrEmpty (str) || n == 1)
        {
            return str;
        }

        return new StringBuilder (str.Length * n)
               .Insert (0, str, n)
               .ToString ();
    }

    /// <summary>Converts the string into a <see cref="List{Rune}"/>.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The string to convert.</param>
    /// <returns></returns>
    public static List<Rune> ToRuneList (this string str) { return str.EnumerateRunes ().ToList (); }

    /// <summary>Converts the string into a <see cref="Rune"/> array.</summary>
    /// <remarks>This is a Terminal.Gui extension method to <see cref="string"/> to support TUI text manipulation.</remarks>
    /// <param name="str">The string to convert.</param>
    /// <returns></returns>
    public static Rune [] ToRunes (this string str) { return str.EnumerateRunes ().ToArray (); }

    /// <summary>Converts a <see cref="Rune"/> generic collection into a string.</summary>
    /// <param name="runes">The enumerable rune to convert.</param>
    /// <returns></returns>
    public static string ToString (IEnumerable<Rune> runes)
    {
        const int maxCharsPerRune = 2;
        // Max stackalloc ~2 kB
        const int maxStackallocTextBufferSize = 1048;

        Span<char> runeBuffer = stackalloc char[maxCharsPerRune];
        // Use stackalloc buffer if rune count is easily available and the count is reasonable.
        if (runes.TryGetNonEnumeratedCount (out int count))
        {
            if (count == 0)
            {
                return string.Empty;
            }

            int maxRequiredTextBufferSize = count * maxCharsPerRune;
            if (maxRequiredTextBufferSize <= maxStackallocTextBufferSize)
            {
                Span<char> textBuffer = stackalloc char[maxRequiredTextBufferSize];
                Span<char> remainingBuffer = textBuffer;
                foreach (Rune rune in runes)
                {
                    int charsWritten = rune.EncodeToUtf16 (runeBuffer);
                    ReadOnlySpan<char> runeChars = runeBuffer [..charsWritten];
                    runeChars.CopyTo (remainingBuffer);
                    remainingBuffer = remainingBuffer [runeChars.Length..];
                }

                ReadOnlySpan<char> text = textBuffer[..^remainingBuffer.Length];
                return text.ToString ();
            }
        }

        // Fallback to StringBuilder append.
        StringBuilder stringBuilder = new();
        foreach (Rune rune in runes)
        {
            int charsWritten = rune.EncodeToUtf16 (runeBuffer);
            ReadOnlySpan<char> runeChars = runeBuffer [..charsWritten];
            stringBuilder.Append (runeChars);
        }
        return stringBuilder.ToString ();
    }

    /// <summary>Converts a byte generic collection into a string in the provided encoding (default is UTF8)</summary>
    /// <param name="bytes">The enumerable byte to convert.</param>
    /// <param name="encoding">The encoding to be used.</param>
    /// <returns></returns>
    public static string ToString (IEnumerable<byte> bytes, Encoding? encoding = null)
    {
        encoding ??= Encoding.UTF8;

        return encoding.GetString (bytes.ToArray ());
    }
}