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

namespace Nuuru.Server.Services.BBCode
{
    public interface IQuoteChecksumService
    {
        string GenerateHash(string sourceType, string sourceId, string content);
        bool VerifyHash(string sourceType, string sourceId, string content, string providedHash);
        string NormalizeContent(string content);
    }

    public partial class QuoteChecksumService : IQuoteChecksumService
    {
        private readonly byte[] _key;

        public QuoteChecksumService(IConfiguration configuration)
        {
            var keyString = configuration["BBCode:QuoteSigningKey"]
                ?? throw new InvalidOperationException("BBCode:QuoteSigningKey not configured");
            _key = Encoding.UTF8.GetBytes(keyString);
        }

        public string GenerateHash(string sourceType, string sourceId, string content)
        {
            var normalized = NormalizeContent(content);
            var input = $"{sourceType}:{sourceId}:{normalized}";

            var hash = HMACSHA256.HashData(_key, Encoding.UTF8.GetBytes(input));
            return Convert.ToHexString(hash)[..8].ToLowerInvariant();
        }

        public bool VerifyHash(string sourceType, string sourceId, string content, string providedHash)
        {
            var expectedHash = GenerateHash(sourceType, sourceId, content);
            return string.Equals(expectedHash, providedHash, StringComparison.OrdinalIgnoreCase);
        }

        public string NormalizeContent(string content)
        {
            // Normalize whitespace: collapse multiple whitespace chars to single space, trim
            return WhitespaceRegex().Replace(content.Trim(), " ");
        }

        [GeneratedRegex(@"\s+")]
        private static partial Regex WhitespaceRegex();
    }
}