using NewLife.Security;

namespace NewLife.Web;

/// <summary>令牌提供者</summary>
/// <remarks>
/// 文档 https://newlifex.com/core/token_provider
/// </remarks>
public class TokenProvider
{
    #region 属性
    /// <summary>密钥。签发方用私钥，验证方用公钥</summary>
    public String? Key { get; set; }

    /// <summary>时钟容差。允许签发方与验证方之间的时钟偏差，默认30秒</summary>
    public TimeSpan ClockSkew { get; set; } = TimeSpan.FromSeconds(30);
    #endregion

    #region 方法
    /// <summary>读取密钥</summary>
    /// <param name="file">文件</param>
    /// <param name="generate">是否生成</param>
    /// <returns></returns>
    public Boolean ReadKey(String file, Boolean generate = false)
    {
        if (file.IsNullOrEmpty()) return false;

        file = file.GetBasePath();
        if (File.Exists(file))
        {
            Key = File.ReadAllText(file);

            if (!Key.IsNullOrEmpty()) return true;
        }

        if (!generate || !file.EndsWithIgnoreCase(".prvkey")) return false;

        var ss = DSAHelper.GenerateKey();
        File.WriteAllText(file.EnsureDirectory(true), ss[0]);
        file = Path.ChangeExtension(file, ".pubkey");
        File.WriteAllText(file, ss[1]);

        Key = ss[0];

        return true;
    }

    /// <summary>编码用户和有效期得到令牌</summary>
    /// <param name="user">用户</param>
    /// <param name="expire">有效期</param>
    /// <returns></returns>
    public String Encode(String user, DateTime expire)
    {
        if (user.IsNullOrEmpty()) throw new ArgumentNullException(nameof(user));
        if (expire.Year < 2000) throw new ArgumentOutOfRangeException(nameof(expire));
        if (Key.IsNullOrEmpty()) throw new ArgumentNullException(nameof(Key));

        var secs = expire.ToUniversalTime().ToInt();

        // 拼接数据并签名
        var data = (user + "," + secs).GetBytes();
        var sig = DSAHelper.Sign(data, Key);

        // Base64拼接数据和签名
        return data.ToUrlBase64() + "." + sig.ToUrlBase64();
    }

    /// <summary>尝试解码令牌，即使失败，也会返回用户信息和有效时间</summary>
    /// <remarks>输入畸形（Base64 非法等）返回 false 而不抛异常；签名有效且未过期才返回 true，过期判断留 <see cref="ClockSkew"/> 时钟容差，容忍签发方与验证方的轻微时钟偏差</remarks>
    /// <param name="token">令牌</param>
    /// <param name="user">用户信息</param>
    /// <param name="expire">有效时间</param>
    /// <returns>true=签名有效且未过期；false=格式非法、签名无效或已过期</returns>
    public Boolean TryDecode(String token, out String user, out DateTime expire)
    {
        if (token.IsNullOrEmpty()) throw new ArgumentNullException(nameof(token));
        //if (Key.IsNullOrEmpty()) throw new ArgumentNullException(nameof(Key));

        // Base64拆分数据和签名
        var p = token.IndexOf('.');
        // 无分隔符视为非法令牌，避免切片越界
        if (p < 0)
        {
            user = "";
            expire = default;
            return false;
        }

        // Base64 畸形（非法字符/坏填充）按无效令牌处理：输入来自调用方或攻击者，不能让异常穿透
        Byte[] data;
        Byte[] sig;
        try
        {
            data = token[..p].ToBase64();
            sig = token[(p + 1)..].ToBase64();
        }
        catch (FormatException)
        {
            user = "";
            expire = default;
            return false;
        }

        // 拆分数据和有效期
        var str = data.ToStr();
        p = str.LastIndexOf(',');
        if (p < 0)
        {
            user = "";
            expire = default;
            return false;
        }

        user = str[..p];
        var secs = str[(p + 1)..].ToInt();
        var expireUtc = secs.ToDateTime();
        expire = expireUtc.ToLocalTime();

        if (Key.IsNullOrEmpty()) return false;

        // 验证签名
        //if (!DSAHelper.Verify(data, Key, sig)) throw new InvalidOperationException("签名验证失败！");
        if (!DSAHelper.Verify(data, Key, sig)) return false;

        // 签名有效还需未过期，早于当前时间超过容差即视为过期。按UTC比较，避免本地时区与夏令时切换造成误判
        if (expireUtc < DateTime.UtcNow - ClockSkew) return false;

        return true;
    }
    #endregion
}