using System.Globalization;
using System.Runtime.CompilerServices;

namespace Godot.Sharp.Extended.Generators;

public static class StringExtensionMethods
{
    public static string ToPascalCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForPascalOrCamelCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                newString[newIndex] = insertSeparator
                    ? char.ToUpperInvariant(value[i])
                    : char.ToLowerInvariant(value[i]);
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToCamelCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = false;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForPascalOrCamelCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                newString[newIndex] = insertSeparator && !isFirstCharacter
                    ? char.ToUpperInvariant(value[i])
                    : char.ToLowerInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToUnderscoreCamelCase(this string value)
    {
        int newIndex = 1;
        bool insertSeparator = false;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForPascalOrCamelCase(value) + 1];
        newString[0] = '_';
        for (int i = 1; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                newString[newIndex] = insertSeparator && !isFirstCharacter
                    ? char.ToUpperInvariant(value[i])
                    : char.ToLowerInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToKebabCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = true;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForKebabOrSnakeCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                if (insertSeparator && !isFirstCharacter)
                {
                    newString[newIndex] = '-';
                    newIndex++;
                }

                newString[newIndex] = char.ToLowerInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToSnakeCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = true;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForKebabOrSnakeCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                if (insertSeparator && !isFirstCharacter)
                {
                    newString[newIndex] = '_';
                    newIndex++;
                }

                newString[newIndex] = char.ToLowerInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToMacroCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = true;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForKebabOrSnakeCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                if (insertSeparator && !isFirstCharacter)
                {
                    newString[newIndex] = '_';
                    newIndex++;
                }

                newString[newIndex] = char.ToUpperInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToTrainCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = true;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForKebabOrSnakeCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                if (insertSeparator && !isFirstCharacter)
                {
                    newString[newIndex] = '-';
                    newIndex++;
                }

                newString[newIndex] = insertSeparator
                    ? char.ToUpperInvariant(value[i])
                    : char.ToLowerInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    public static string ToTitleCase(this string value)
    {
        int newIndex = 0;
        bool insertSeparator = true;
        bool isFirstCharacter = true;
        UnicodeCategory previous;
        UnicodeCategory current = UnicodeCategory.OtherSymbol;
        char[] newString = new char[value.Length + CalculateSpanSizeForKebabOrSnakeCase(value)];
        for (int i = 0; i < value.Length; i++)
        {
            previous = current;
            current = char.GetUnicodeCategory(value[i]);
            insertSeparator =
                (previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                         current is UnicodeCategory.DecimalDigitNumber)) || insertSeparator;
            if (!IsSpecialCharacter(current))
            {
                if (insertSeparator && !isFirstCharacter)
                {
                    newString[newIndex] = ' ';
                    newIndex++;
                }

                newString[newIndex] = insertSeparator
                    ? char.ToUpperInvariant(value[i])
                    : char.ToLowerInvariant(value[i]);
                isFirstCharacter = false;
                insertSeparator = false;
                newIndex++;
            }
        }

        return new(newString);
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static int CalculateSpanSizeForKebabOrSnakeCase(string text)
    {
        UnicodeCategory previous = char.GetUnicodeCategory(text[0]);
        UnicodeCategory current;
        int skips = IsSpecialCharacter(previous) ? 1 : 0;
        int divs = 0;
        for (int i = 1; i < text.Length; i++)
        {
            current = char.GetUnicodeCategory(text[i]);
            skips += IsSpecialCharacter(current) ? 1 : 0;
            divs += previous != current && (current is UnicodeCategory.UppercaseLetter ||
                                            current is UnicodeCategory.DecimalDigitNumber)
                ? 1
                : 0;
            previous = current;
        }

        return divs - skips;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static int CalculateSpanSizeForPascalOrCamelCase(string text)
    {
        UnicodeCategory current;
        int skips = 0;
        for (int i = 0; i < text.Length - 1; i++)
        {
            current = char.GetUnicodeCategory(text[i]);
            skips -= IsSpecialCharacter(current) ? 1 : 0;
        }

        return skips;
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private static bool IsSpecialCharacter(UnicodeCategory category)
    {
        return category is not UnicodeCategory.UppercaseLetter
            and not UnicodeCategory.LowercaseLetter
            and not UnicodeCategory.DecimalDigitNumber;
    }
}