using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;

namespace PluralKit.Core;

public static class StringUtils
{
    public static string GenerateToken()
    {
        // Results in a 64-byte Base64 string (no padding)
        var buf = RandomNumberGenerator.GetBytes(48);
        return Convert.ToBase64String(buf);
    }

    public static bool IsLongerThan(this string str, int length)
    {
        if (str != null) return str.Length > length;
        return false;
    }

    public static string ExtractCountryFlag(string flag)
    {
        if (flag.Length != 4) return null;
        try
        {
            var cp1 = char.ConvertToUtf32(flag, 0);
            var cp2 = char.ConvertToUtf32(flag, 2);
            if (cp1 < 0x1F1E6 || cp1 > 0x1F1FF) return null;
            if (cp2 < 0x1F1E6 || cp2 > 0x1F1FF) return null;
            return $"{(char)(cp1 - 0x1F1E6 + 'A')}{(char)(cp2 - 0x1F1E6 + 'A')}";
        }
        catch (ArgumentException)
        {
            return null;
        }
    }

    public static string NullIfEmpty(this string input)
    {
        if (input == null) return null;
        if (input.Trim().Length == 0) return null;
        return input;
    }

    public static bool EmptyOrNull(this string input)
    {
        if (input == null) return true;
        if (input.Trim().Length == 0) return true;
        return false;
    }

    public static string NormalizeLineEndSpacing(this string input) =>
        // iOS has a weird issue on embeds rendering newlines when there are spaces *just before* it
        // so we remove 'em - except in the case where there's a blockquote line that contains only
        // spaces (if we removed all the spaces there, the blockquote breaks horribly)
        Regex.Replace(input, "(?<!\\>) *\n", "\n");

    public static IReadOnlyList<string> JoinPages(IEnumerable<string> input, int characterLimit) =>
        JoinPages(input, _ => characterLimit);

    public static IReadOnlyList<string> JoinPages(IEnumerable<string> input, Func<int, int> characterLimitByPage)
    {
        var output = new List<string>();

        var buf = new StringBuilder();
        foreach (var s in input)
        {
            var limit = characterLimitByPage.Invoke(output.Count);

            // Would adding this string put us over the limit?
            // (note: don't roll over if the buffer's already empty; this means an individual section is above the character limit. todo: truncate, then?)
            if (buf.Length > 0 && buf.Length + s.Length > limit)
            {
                // If so, "roll over" (before adding the string to the buffer)
                output.Add(buf.ToString());
                buf.Clear();
            }

            buf.Append(s);
        }

        // We most likely have something left over, so add that in too
        if (buf.Length > 0)
            output.Add(buf.ToString());

        return output;
    }
}