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

public class BytePlusAuthUtils
{
    /**
     * 
     * @param ak: AccessKey
     * @param sk: SecretKey
     * @param expirationSeconds: The expiration time. Units are in seconds
     * @param method: GET, POST, PUT
     * @param uriPath: The requestd path. Not a complete URL
     * @param params: The requested parameters
     * @param body: The requested json body
     * @return
     */
    public static string Sign(string ak, string sk, int expirationSeconds, string method, string uriPath, Dictionary<string, string> parameters, string body)
    {
        string cm = CanonicalMethod(method);
        string cu = CanonicalUrl(uriPath);
        string cp = CanonicalParam(parameters);
        string cb = CanonicalBody(body);
        string text = cm + "\n" + cu + "\n" + cp + "\n" + cb;
        return DoSign(ak, sk, expirationSeconds, text);
    }

    private static string CanonicalMethod(string method)
    {
        return "HTTPMethod:" + method;
    }

    private static string CanonicalUrl(string url)
    {
        return "CanonicalURI:" + url;
    }

    private static string CanonicalParam(Dictionary<string, string> parameters)
    {
        string res = "CanonicalQueryString:";
        if (parameters == null || parameters.Count == 0)
        {
            return res;
        }
        foreach (var key in parameters.Keys)
        {
            res += FormatKeyValue(key, parameters[key]) + "&";
        }
        return res.Substring(0, res.Length - 1);
    }

    private static string FormatKeyValue(string key, string value)
    {
        return key + "=" + value;
    }

    private static string CanonicalBody(string body)
    {
        string res = "CanonicalBody:";
        if (body == null)
        {
            return res;
        }
        else
        {
            return res + body;
        }
    }

    private static string DoSign(string ak, string sk, int expiration, string text)
    {
        string signKeyInfo = "ak-v1/" + ak + "/" + (long)DateTime.UtcNow.Subtract(new DateTime(1970, 1, 1)).TotalSeconds + "/" + expiration;
        string signKey = Sha256Hmac(signKeyInfo, sk);
        string signResult = Sha256Hmac(text, signKey);
        return signKeyInfo + "/" + signResult;
    }

    private static string Sha256Hmac(string message, string secret)
    {
        string hash = "";
        using (var hmacsha256 = new HMACSHA256(Convert.FromBase64String(secret)))
        {
            var bytes = hmacsha256.ComputeHash(Encoding.UTF8.GetBytes(message));
            hash = ByteArrayToHexString(bytes);
        }
        return hash;
    }

    private static string ByteArrayToHexString(byte[] b)
    {
        StringBuilder hs = new StringBuilder();
        foreach (byte c in b)
        {
            hs.Append(c.ToString("x2"));
        }
        return hs.ToString().ToLower();
    }
}