using System.Collections.Generic;
using System;
using System.Collections.Specialized;
using System.IO;
using System.Linq;
using System.Net;
using System.Security.Cryptography;
using System.Text;
using System.Globalization;
using System.Security.Policy;

namespace FastReport.Cloud.StorageClient.S3
{
    /// <summary>
    /// Class for request sign to S3. Doc <see href="https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-auth-using-authorization-header.html"/> 
    /// </summary>
    class S3Signer
    {
        private readonly string _accessKeyId;
        private readonly string _secretAccessKey;
        private readonly string _region;
        private readonly string _service;
        private static readonly string EmptySha256 = sha256_hash("");

        public S3Signer(string accessKeyId, string secretAccessKey, string region, string service = "s3")
        {
            _accessKeyId = accessKeyId;
            _secretAccessKey = secretAccessKey;
            _region = region;
            _service = service;
        }

        public void Sign(HttpWebRequest request, Stream contentStream = null, DateTimeOffset? signDate = null)
        {
            // article about S3 auth: https://docs.aws.amazon.com/AmazonS3/latest/API/sig-v4-header-based-auth.html

            DateTimeOffset dateToUse = signDate ?? DateTimeOffset.UtcNow;
            string nowDate = dateToUse.ToString("yyyyMMdd");
            string amzNowDate = GetAmzDate(dateToUse);

            request.Headers.Add("x-amz-date", amzNowDate);

            string payloadHash = CalcPayloadHash(request, contentStream);
            request.Headers.Add("x-amz-content-sha256", payloadHash);

            // 1. Create a canonical request

            /*
             * <HTTPMethod>\n
             * <CanonicalURI>\n
             * <CanonicalQueryString>\n
             * <CanonicalHeaders>\n
             * <SignedHeaders>\n
             * <HashedPayload>
             */

            string canonicalRequest = request.Method + "\n" +
               GetCanonicalUri(request) + "\n" +  // CanonicalURI
               GetCanonicalQueryString(request) + "\n" +
               GetCanonicalHeaders(request, out string signedHeaders) + "\n" +   // ends up with two newlines which is expected
               signedHeaders + "\n" +
               payloadHash;


            // 2. Create a string to sign

            // step by step instructions: https://docs.aws.amazon.com/general/latest/gr/sigv4-create-string-to-sign.html

            /*
             * StringToSign =
             *    Algorithm + \n +
             *    RequestDateTime + \n +
             *    CredentialScope + \n +
             *    HashedCanonicalRequest
             */

            string stringToSign = "AWS4-HMAC-SHA256\n" +
                  amzNowDate + "\n" +
                  nowDate + "/" + _region + "/s3/aws4_request\n" +
                 sha256_hash(canonicalRequest);


            // 3. Calculate Signature

            string signature = CalcSignature(stringToSign, nowDate);

            string auth = $"Credential={_accessKeyId}/{nowDate}/{_region}/s3/aws4_request,SignedHeaders={signedHeaders},Signature={signature}";
            request.Headers.Add(HttpRequestHeader.Authorization, "AWS4-HMAC-SHA256" + " " + auth);
        }

        public string SignSeed(HttpWebRequest request, long contentLength, DateTimeOffset? signDate = null)
        {
            // article about S3 auth: https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-streaming.html

            DateTimeOffset dateToUse = signDate ?? DateTimeOffset.UtcNow;
            string nowDate = dateToUse.ToString("yyyyMMdd");
            string amzNowDate = GetAmzDate(dateToUse);

            request.Headers.Add("x-amz-date", amzNowDate);

            // 1. Create a canonical request

            /*
             * <HTTPMethod>\n
             * <CanonicalURI>\n
             * <CanonicalQueryString>\n
             * <CanonicalHeaders>\n
             * <SignedHeaders>\n
             * "STREAMING-AWS4-HMAC-SHA256-PAYLOAD"
             */

            request.Headers.Add("x-amz-content-sha256", "STREAMING-AWS4-HMAC-SHA256-PAYLOAD");
            request.Headers.Add("Content-Encoding", "aws-chunked");
            request.Headers.Add("x-amz-decoded-content-length", contentLength.ToString());

            string canonicalRequest = request.Method + "\n" +
               GetCanonicalUri(request) + "\n" +  // CanonicalURI
               GetCanonicalQueryString(request) + "\n" +
               GetCanonicalHeaders(request, out string signedHeaders) + "\n" +
               signedHeaders + "\n" +
               "STREAMING-AWS4-HMAC-SHA256-PAYLOAD";

            // 2. Create a string to sign

            /*
             * StringToSign =
             *    Algorithm + \n +
             *    RequestDateTime + \n +
             *    CredentialScope + \n +
             *    HashedCanonicalRequest
             */

            string stringToSign = "AWS4-HMAC-SHA256\n" +
                  amzNowDate + "\n" +
                  nowDate + "/" + _region + "/s3/aws4_request\n" +
                  sha256_hash(canonicalRequest);


            // 3. Calculate Signature

            string signature = CalcSignature(stringToSign, nowDate);

            string auth = $"Credential={_accessKeyId}/{nowDate}/{_region}/s3/aws4_request,SignedHeaders={signedHeaders},Signature={signature}";
            request.Headers.Add(HttpRequestHeader.Authorization, "AWS4-HMAC-SHA256" + " " + auth);

            return signature;
        }

        public string SignChunk(HttpWebRequest request, string previousSignature, Stream contentStream, Stream requestStream, DateTimeOffset? signDate = null)
        {
            // article about S3 auth: https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-streaming.html

            DateTimeOffset dateToUse = signDate ?? DateTimeOffset.UtcNow;
            string nowDate = dateToUse.ToString("yyyyMMdd");
            string amzNowDate = GetAmzDate(dateToUse);

            string payloadHash = CalcPayloadHash(request, contentStream);

            // 1. Create a string to sign

            /*
             * StringToSign =
             *    Algorithm + \n +
             *    RequestDateTime + \n +
             *    CredentialScope + \n +
             *    PreviousSignature + \n +
             *    Hex(Sha256Hash("")) + \n +
             *    Hex(Sha256Hash("current-chunk-data"))
             */

            string stringToSign = "AWS4-HMAC-SHA256-PAYLOAD\n" +
                  amzNowDate + "\n" +
                  nowDate + "/" + _region + "/s3/aws4_request\n" +
                  previousSignature + "\n" +
                  EmptySha256 + "\n" +
                  payloadHash;


            // 2. Calculate Signature

            string signature = CalcSignature(stringToSign, nowDate);

            // prepare chunk
            string headChunk = ToHEX(contentStream == null ? 0 : contentStream.Length) + ";chunk-signature=" + signature + "\r\n";
            MemoryStream ms = new MemoryStream();
            byte[] temp = Encoding.UTF8.GetBytes(headChunk);
            ms.Write(temp, 0, temp.Length);

            if (contentStream != null)
            {
                contentStream.Position = 0;
                contentStream.CopyTo(ms);
                temp = Encoding.UTF8.GetBytes("\r\n");
                ms.Write(temp, 0, temp.Length);
            }

            temp = ms.ToArray();
            try
            {
                requestStream.Write(temp, 0, temp.Length); // send chunk
            }
            finally
            {
                ms.Close();
            }

            return signature;
        }

        private string CalcSignature(string stringToSign, string nowDate)
        {
            /*
            * DateKey              = HMAC-SHA256("AWS4"+"<SecretAccessKey>", "<YYYYMMDD>")
            * DateRegionKey        = HMAC-SHA256(<DateKey>, "<aws-region>")
            * DateRegionServiceKey = HMAC-SHA256(<DateRegionKey>, "<aws-service>")
            * SigningKey           = HMAC-SHA256(<DateRegionServiceKey>, "aws4_request")
            */

            byte[] kSecret = Encoding.UTF8.GetBytes(("AWS4" + _secretAccessKey).ToCharArray());
            byte[] kDate = HmacSha256(nowDate, kSecret);
            byte[] kRegion = HmacSha256(_region, kDate);
            byte[] kService = HmacSha256(_service, kRegion);
            byte[] kSigning = HmacSha256("aws4_request", kService);

            // final signature
            byte[] signatureRaw = HmacSha256(stringToSign, kSigning);
            string signature = ToHEX(signatureRaw);

            return signature;
        }

        private static string GetAmzDate(DateTimeOffset date)
        {
            return date.ToString("yyyyMMddTHHmmssZ");
        }

        private string GetCanonicalUri(HttpWebRequest request)
        {
            string path = UrlEncode(request.RequestUri.AbsolutePath.TrimStart('/')).Replace("%2F", "/");

            return "/" + path;
        }

        private string ToHEX(byte[] str)
        {
            var sb = new StringBuilder();
            foreach (var t in str)
            {
                sb.Append(t.ToString("x2"));
            }
            return sb.ToString();
        }
        private string ToHEX(long value)
        {
            return value.ToString("X", CultureInfo.InvariantCulture);
        }

        public static string sha256_hash(string value)
        {
            StringBuilder Sb = new StringBuilder();

            using (SHA256 hash = SHA256Managed.Create())
            {
                Encoding enc = Encoding.UTF8;
                Byte[] result = hash.ComputeHash(enc.GetBytes(value));

                foreach (Byte b in result)
                    Sb.Append(b.ToString("x2"));
            }

            return Sb.ToString();
        }

        public static string sha256_hash(byte[] value)
        {
            StringBuilder Sb = new StringBuilder();

            using (SHA256 hash = SHA256Managed.Create())
            {
                Byte[] result = hash.ComputeHash(value);

                foreach (Byte b in result)
                    Sb.Append(b.ToString("x2"));
            }

            return Sb.ToString();
        }

        private string GetCanonicalQueryString(HttpWebRequest request)
        {
            NameValueCollection values = ParseQueryString(request.RequestUri.Query);

            var sb = new StringBuilder();

            foreach (string key in values.AllKeys.OrderBy(k => k))
            {
                if (sb.Length > 0)
                {
                    sb.Append('&');
                }

                string value = UrlEncode(values[key]);

                if (key == null)
                {
                    sb
                       .Append(value)
                       .Append("=");
                }
                else
                {
                    sb
                       .Append(UrlEncode(key.ToLower()))
                       .Append("=")
                       .Append(value);
                }
            }

            return sb.ToString();
        }

        public static NameValueCollection ParseQueryString(string query)
        {
            NameValueCollection result = new NameValueCollection();
            string[] queries = query.Split('&');
            for (int i = 0; i < queries.Length; i++)
            {
                string[] kvp = queries[i].Split('=');
                if (kvp.Length > 1)
                    result.Add(kvp[0].Replace("?", ""), kvp[1]);
            }

            return result;
        }

        public static string UrlEncode(string str)
        {
            StringBuilder sb = new StringBuilder();
            StringReader reader = new StringReader(str);
            int charCode = reader.Read();

            while (charCode != -1)
            {
                if (((charCode >= 'A') && (charCode <= 'Z')) || ((charCode >= 'a') && (charCode <= 'z')) || ((charCode >= '0') && (charCode <= '9'))
                   || (charCode == '-') || (charCode == '_') || (charCode == '.') || (charCode == '~'))
                {
                    sb.Append((char)charCode);
                }
                else
                {
                    sb.AppendFormat("%{0:X2}", charCode);
                }
                charCode = reader.Read();
            }
            return sb.ToString().Replace("%2520", "%20");
        }

        private string GetCanonicalHeaders(HttpWebRequest request, out string signedHeaders)
        {
            // List of request headers with their values.
            // Individual header name and value pairs are separated by the newline character ("\n").
            // Header names must be in lowercase.

            Dictionary<string, string> headers = new Dictionary<string, string>();

            foreach (string header in request.Headers.AllKeys.OrderBy(x => x).ToList())
                if (header.StartsWith("x-amz-", StringComparison.OrdinalIgnoreCase))
                    headers.Add(header.ToLowerInvariant(), request.Headers.GetValues(header).First());

            var sb = new StringBuilder();
            var signedHeadersList = new List<string>();

            if (request.Headers.AllKeys.Contains("date"))
            {
                sb.Append("date:").Append(request.Headers.GetValues("date").First()).Append("\n");
                signedHeadersList.Add("date");
            }

            sb.Append("host:").Append(request.RequestUri.Host).Append("\n");
            signedHeadersList.Add("host");

            string contentType = request.ContentType;
            if (contentType != null)
            {
                sb.Append("content-type:").Append(contentType).Append("\n");
                signedHeadersList.Add("content-type");
            }

            if (request.Headers.AllKeys.Contains("range"))
            {
                sb.Append("range:").Append(request.Headers.GetValues("range").First()).Append("\n");
                signedHeadersList.Add("range");
            }

            // Create the string in the right format; this is what makes the headers "canonicalized" --
            //   it means put in a standard format. http://en.wikipedia.org/wiki/Canonicalization
            foreach (var kvp in headers)
            {
                sb.Append(kvp.Key).Append(":");
                signedHeadersList.Add(kvp.Key);

                foreach (string hv in request.Headers.GetValues(kvp.Key))
                {
                    sb.Append(hv);
                }

                sb.Append("\n");
            }

            signedHeaders = string.Join(";", signedHeadersList);

            return sb.ToString();
        }

        /// <summary>
        /// Calculate hash sha256 of content and convert it to hexadecimal string. This string will be returned and written to x-amz-content-sha256 header.
        /// </summary>
        /// <param name="request">Request to which header will be added</param>
        /// <param name="contentStream">Stream with content of request</param>
        /// <returns>String containing the encrypted and hexadecimal stream of the request content</returns>
        private string CalcPayloadHash(HttpWebRequest request, Stream contentStream)
        {
            string hash;

            if (request.Method == "PUT" && contentStream != null)
            {
                using (var memoryStream = new MemoryStream())
                {
                    contentStream.CopyTo(memoryStream);
                    byte[] content = memoryStream.ToArray();

                    hash = sha256_hash(content);
                }
            }
            else
            {
                hash = EmptySha256;
            }

            return hash;
        }

        private static byte[] HmacSha256(string data, byte[] key)
        {
            var alg = KeyedHashAlgorithm.Create("HmacSHA256");
            alg.Key = key;
            return alg.ComputeHash(Encoding.UTF8.GetBytes(data));
        }
    }
}