using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Text;

namespace PKHeX.Core;

public static partial class Util
{
    /// <inheritdoc cref="ToInt32(ReadOnlySpan{char})"/>
    public static int ToInt32(string value) => ToInt32(value.AsSpan());

    /// <inheritdoc cref="ToUInt32(ReadOnlySpan{char})"/>
    public static uint ToUInt32(string value) => ToUInt32(value.AsSpan());

    /// <inheritdoc cref="GetHexValue(ReadOnlySpan{char})"/>
    public static uint GetHexValue(string value) => GetHexValue(value.AsSpan());

    /// <inheritdoc cref="GetHexValue64(ReadOnlySpan{char})"/>
    public static ulong GetHexValue64(string value) => GetHexValue64(value.AsSpan());

    /// <inheritdoc cref="GetBytesFromHexString(ReadOnlySpan{char})"/>
    public static byte[] GetBytesFromHexString(string value) => GetBytesFromHexString(value.AsSpan());

    /// <inheritdoc cref="GetHexStringFromBytes(ReadOnlySpan{byte})"/>
    public static string GetHexStringFromBytes(byte[] data, int offset, int length) => GetHexStringFromBytes(data.AsSpan(offset, length));

    /// <summary>
    /// Parses the string into an <see cref="int"/>, skipping all characters except for valid digits.
    /// </summary>
    /// <param name="value">String to parse</param>
    /// <returns>Parsed value</returns>
    public static int ToInt32(ReadOnlySpan<char> value)
    {
        int result = 0;
        if (value.Length == 0)
            return result;

        bool negative = false;
        foreach (var c in value)
        {
            if (IsNum(c))
            {
                result *= 10;
                result += c;
                result -= '0';
            }
            else if (c == '-' && result == 0)
            {
                negative = true;
            }
        }
        return negative ? -result : result;
    }

    /// <summary>
    /// Parses the string into a <see cref="uint"/>, skipping all characters except for valid digits.
    /// </summary>
    /// <param name="value">String to parse</param>
    /// <returns>Parsed value</returns>
    public static uint ToUInt32(ReadOnlySpan<char> value)
    {
        uint result = 0;
        if (value.Length == 0)
            return result;

        foreach (var c in value)
        {
            if (!IsNum(c))
                continue;
            result *= 10;
            result += (uint)(c - '0');
        }
        return result;
    }

    /// <summary>
    /// Parses the hex string into a <see cref="uint"/>, skipping all characters except for valid digits.
    /// </summary>
    /// <param name="value">Hex String to parse</param>
    /// <returns>Parsed value</returns>
    public static uint GetHexValue(ReadOnlySpan<char> value)
    {
        uint result = 0;
        if (value.Length == 0)
            return result;

        foreach (var c in value)
        {
            if (IsNum(c))
            {
                result <<= 4;
                result += (uint)(c - '0');
            }
            else if (IsHexUpper(c))
            {
                result <<= 4;
                result += (uint)(c - 'A' + 10);
            }
            else if (IsHexLower(c))
            {
                result <<= 4;
                result += (uint)(c - 'a' + 10);
            }
        }
        return result;
    }

    /// <summary>
    /// Parses the hex string into a <see cref="ulong"/>, skipping all characters except for valid digits.
    /// </summary>
    /// <param name="value">Hex String to parse</param>
    /// <returns>Parsed value</returns>
    public static ulong GetHexValue64(ReadOnlySpan<char> value)
    {
        ulong result = 0;
        if (value.Length == 0)
            return result;

        foreach (var c in value)
        {
            if (IsNum(c))
            {
                result <<= 4;
                result += (uint)(c - '0');
            }
            else if (IsHexUpper(c))
            {
                result <<= 4;
                result += (uint)(c - 'A' + 10);
            }
            else if (IsHexLower(c))
            {
                result <<= 4;
                result += (uint)(c - 'a' + 10);
            }
        }
        return result;
    }

    public static byte[] GetBytesFromHexString(ReadOnlySpan<char> seed)
    {
        byte[] result = new byte[seed.Length / 2];
        for (int i = 0; i < result.Length; i++)
        {
            var slice = seed.Slice(i * 2, 2);
            result[^(i+1)] = (byte)GetHexValue(slice);
        }
        return result;
    }

    public static string GetHexStringFromBytes(ReadOnlySpan<byte> arr)
    {
        var sb = new StringBuilder(arr.Length * 2);
        for (int i = arr.Length - 1; i >= 0; i--)
            sb.AppendFormat("{0:X2}", arr[i]);
        return sb.ToString();
    }

    private static bool IsNum(char c) => (uint)(c - '0') <= 9;
    private static bool IsHexUpper(char c) => (uint)(c - 'A') <= 5;
    private static bool IsHexLower(char c) => (uint)(c - 'a') <= 5;
    private static bool IsHex(char c) => IsNum(c) || IsHexUpper(c) || IsHexLower(c);

    /// <summary>
    /// Filters the string down to only valid hex characters, returning a new string.
    /// </summary>
    /// <param name="str">Input string to filter</param>
    public static string GetOnlyHex(string str)
    {
        if (string.IsNullOrWhiteSpace(str))
            return string.Empty;
        var sb = new StringBuilder(str.Length);
        foreach (var c in str)
        {
            if (IsHex(c))
                sb.Append(c);
        }
        return sb.ToString();
    }

    /// <summary>
    /// Returns a new string with each word converted to its appropriate title case.
    /// </summary>
    /// <param name="str">Input string to modify</param>
    /// <param name="trim">Trim ends of whitespace</param>
    public static string ToTitleCase(ReadOnlySpan<char> str, bool trim = false)
    {
        int start = 0;
        if (trim)
        {
            // Get First index that isn't a space
            while (start < str.Length && char.IsWhiteSpace(str[start]))
                start++;
        }
        if (start == str.Length)
            return string.Empty;

        int end = str.Length - 1;
        if (trim)
        {
            // Get Last index that isn't a space
            while (end > start && char.IsWhiteSpace(str[end]))
                end--;
        }

        var span = str.Slice(start, end - start + 1);
        var sb = new StringBuilder(span.Length);
        // Add each word to the string builder. Continue from the first index that isn't a space.
        // Add the first character as uppercase, then add each successive character as lowercase.
        bool first = true;
        foreach (char c in span)
        {
            if (char.IsWhiteSpace(c))
            {
                first = true;
                sb.Append(c);
            }
            else if (first)
            {
                sb.Append(char.ToUpper(c));
                first = false;
            }
            else
            {
                sb.Append(char.ToLower(c));
            }
        }
        return sb.ToString();
    }

    /// <summary>
    /// Trims a string at the first instance of a 0x0000 terminator.
    /// </summary>
    /// <param name="input">String to trim.</param>
    /// <returns>Trimmed string.</returns>
    public static string TrimFromZero(string input) => TrimFromFirst(input, '\0');

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static string TrimFromFirst(string input, char c)
    {
        int index = input.IndexOf(c);
        return index < 0 ? input : input[..index];
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static void TrimFromFirst(StringBuilder input, char c)
    {
        for (int i = 0; i < input.Length; i++)
        {
            if (input[i] != c)
                continue;
            input.Remove(i, input.Length - i);
            return;
        }
    }

    public static Dictionary<string, int>[] GetMultiDictionary(IReadOnlyList<IReadOnlyList<string>> nameArray)
    {
        var result = new Dictionary<string, int>[nameArray.Count];
        for (int i = 0; i < result.Length; i++)
        {
            var dict = result[i] = new Dictionary<string, int>();
            var names = nameArray[i];
            for (int j = 0; j < names.Count; j++)
                dict.Add(names[j], j);
        }
        return result;
    }
}