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

namespace ROLAC.API.Services.Notifications;

/// <summary>Verifies the X-Line-Signature header (HMAC-SHA256 of the raw body, base64).</summary>
public static class LineSignature
{
    public static bool IsValid(string channelSecret, byte[] rawBody, string? signatureHeader)
    {
        if (string.IsNullOrEmpty(signatureHeader)) return false;

        using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(channelSecret));
        var expected = Convert.ToBase64String(hmac.ComputeHash(rawBody));

        return CryptographicOperations.FixedTimeEquals(
            Encoding.UTF8.GetBytes(expected),
            Encoding.UTF8.GetBytes(signatureHeader));
    }
}