//-----------------------------------------------------------------------
// <copyright file="DataBagFormatterBase.cs" company="Outercurve Foundation">
//     Copyright (c) Outercurve Foundation. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------

namespace DotNetOpenAuth.Messaging {
	using System;
	using System.Collections.Generic;
	using System.Diagnostics.CodeAnalysis;
	using System.IO;
	using System.Linq;
	using System.Security.Cryptography;
	using System.Text;
	using System.Web;

	using DotNetOpenAuth.Logging;
	using DotNetOpenAuth.Messaging;
	using DotNetOpenAuth.Messaging.Bindings;
	using DotNetOpenAuth.Messaging.Reflection;
	using Validation;

	/// <summary>
	/// A serializer for <see cref="DataBag"/>-derived types
	/// </summary>
	/// <typeparam name="T">The DataBag-derived type that is to be serialized/deserialized.</typeparam>
	internal abstract class DataBagFormatterBase<T> : IDataBagFormatter<T> where T : DataBag {
		/// <summary>
		/// The message description cache to use for data bag types.
		/// </summary>
		protected static readonly MessageDescriptionCollection MessageDescriptions = new MessageDescriptionCollection();

		/// <summary>
		/// The length of the nonce to include in tokens that can be decoded once only.
		/// </summary>
		private const int NonceLength = 6;

		/// <summary>
		/// The minimum allowable lifetime for the key used to encrypt/decrypt or sign this databag.
		/// </summary>
		private readonly TimeSpan minimumAge = TimeSpan.FromDays(1);

		/// <summary>
		/// The symmetric key store with the secret used for signing/encryption of verification codes and refresh tokens.
		/// </summary>
		private readonly ICryptoKeyStore cryptoKeyStore;

		/// <summary>
		/// The bucket for symmetric keys.
		/// </summary>
		private readonly string cryptoKeyBucket;

		/// <summary>
		/// The crypto to use for signing access tokens.
		/// </summary>
		private readonly RSACryptoServiceProvider asymmetricSigning;

		/// <summary>
		/// The crypto to use for encrypting access tokens.
		/// </summary>
		private readonly RSACryptoServiceProvider asymmetricEncrypting;

		/// <summary>
		/// A value indicating whether the data in this instance will be protected against tampering.
		/// </summary>
		private readonly bool signed;

		/// <summary>
		/// The nonce store to use to ensure that this instance is only decoded once.
		/// </summary>
		private readonly INonceStore decodeOnceOnly;

		/// <summary>
		/// The maximum age of a token that can be decoded; useful only when <see cref="decodeOnceOnly"/> is <c>true</c>.
		/// </summary>
		private readonly TimeSpan? maximumAge;

		/// <summary>
		/// A value indicating whether the data in this instance will be protected against eavesdropping.
		/// </summary>
		private readonly bool encrypted;

		/// <summary>
		/// A value indicating whether the data in this instance will be GZip'd.
		/// </summary>
		private readonly bool compressed;

		/// <summary>
		/// Initializes a new instance of the <see cref="DataBagFormatterBase&lt;T&gt;"/> class.
		/// </summary>
		/// <param name="signingKey">The crypto service provider with the asymmetric key to use for signing or verifying the token.</param>
		/// <param name="encryptingKey">The crypto service provider with the asymmetric key to use for encrypting or decrypting the token.</param>
		/// <param name="compressed">A value indicating whether the data in this instance will be GZip'd.</param>
		/// <param name="maximumAge">The maximum age of a token that can be decoded; useful only when <paramref name="decodeOnceOnly"/> is <c>true</c>.</param>
		/// <param name="decodeOnceOnly">The nonce store to use to ensure that this instance is only decoded once.</param>
		protected DataBagFormatterBase(RSACryptoServiceProvider signingKey = null, RSACryptoServiceProvider encryptingKey = null, bool compressed = false, TimeSpan? maximumAge = null, INonceStore decodeOnceOnly = null)
			: this(signingKey != null, encryptingKey != null, compressed, maximumAge, decodeOnceOnly) {
			this.asymmetricSigning = signingKey;
			this.asymmetricEncrypting = encryptingKey;
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="DataBagFormatterBase&lt;T&gt;"/> class.
		/// </summary>
		/// <param name="cryptoKeyStore">The crypto key store used when signing or encrypting.</param>
		/// <param name="bucket">The bucket in which symmetric keys are stored for signing/encrypting data.</param>
		/// <param name="signed">A value indicating whether the data in this instance will be protected against tampering.</param>
		/// <param name="encrypted">A value indicating whether the data in this instance will be protected against eavesdropping.</param>
		/// <param name="compressed">A value indicating whether the data in this instance will be GZip'd.</param>
		/// <param name="minimumAge">The required minimum lifespan within which this token must be decodable and verifiable; useful only when <paramref name="signed"/> and/or <paramref name="encrypted"/> is true.</param>
		/// <param name="maximumAge">The maximum age of a token that can be decoded; useful only when <paramref name="decodeOnceOnly"/> is <c>true</c>.</param>
		/// <param name="decodeOnceOnly">The nonce store to use to ensure that this instance is only decoded once.</param>
		protected DataBagFormatterBase(ICryptoKeyStore cryptoKeyStore = null, string bucket = null, bool signed = false, bool encrypted = false, bool compressed = false, TimeSpan? minimumAge = null, TimeSpan? maximumAge = null, INonceStore decodeOnceOnly = null)
			: this(signed, encrypted, compressed, maximumAge, decodeOnceOnly) {
			Requires.That(!string.IsNullOrEmpty(bucket) || cryptoKeyStore == null, "bucket", "Bucket name required when cryptoKeyStore is non-null.");
			Requires.That(cryptoKeyStore != null || (!signed && !encrypted), "cryptoKeyStore", "cryptoKeyStore required if signing or encrypting.");

			this.cryptoKeyStore = cryptoKeyStore;
			this.cryptoKeyBucket = bucket;
			if (minimumAge.HasValue) {
				this.minimumAge = minimumAge.Value;
			}
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="DataBagFormatterBase&lt;T&gt;"/> class.
		/// </summary>
		/// <param name="signed">A value indicating whether the data in this instance will be protected against tampering.</param>
		/// <param name="encrypted">A value indicating whether the data in this instance will be protected against eavesdropping.</param>
		/// <param name="compressed">A value indicating whether the data in this instance will be GZip'd.</param>
		/// <param name="maximumAge">The maximum age of a token that can be decoded; useful only when <paramref name="decodeOnceOnly"/> is <c>true</c>.</param>
		/// <param name="decodeOnceOnly">The nonce store to use to ensure that this instance is only decoded once.</param>
		private DataBagFormatterBase(bool signed = false, bool encrypted = false, bool compressed = false, TimeSpan? maximumAge = null, INonceStore decodeOnceOnly = null) {
			Requires.That(signed || decodeOnceOnly == null, "decodeOnceOnly", "Nonce only valid with signing.");
			Requires.That(maximumAge.HasValue || decodeOnceOnly == null, "decodeOnceOnly", "Nonce requires a maximum message age.");

			this.signed = signed;
			this.maximumAge = maximumAge;
			this.decodeOnceOnly = decodeOnceOnly;
			this.encrypted = encrypted;
			this.compressed = compressed;
		}

		/// <summary>
		/// Serializes the specified message, including compression, encryption, signing, and nonce handling where applicable.
		/// </summary>
		/// <param name="message">The message to serialize.  Must not be null.</param>
		/// <returns>A non-null, non-empty value.</returns>
		[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope", Justification = "No apparent problem.  False positive?")]
		public string Serialize(T message) {
			Requires.NotNull(message, "message");

			message.UtcCreationDate = DateTime.UtcNow;

			if (this.decodeOnceOnly != null) {
				message.Nonce = MessagingUtilities.GetNonCryptoRandomData(NonceLength);
			}

			byte[] encoded = this.SerializeCore(message);

			if (this.compressed) {
				encoded = MessagingUtilities.Compress(encoded);
			}

			string symmetricSecretHandle = null;
			if (this.encrypted) {
				encoded = this.Encrypt(encoded, out symmetricSecretHandle);
			}

			if (this.signed) {
				message.Signature = this.CalculateSignature(encoded, symmetricSecretHandle);
			}

			int capacity = this.signed ? 4 + message.Signature.Length + 4 + encoded.Length : encoded.Length;
			using (var finalStream = new MemoryStream(capacity)) {
				var writer = new BinaryWriter(finalStream);
				if (this.signed) {
					writer.WriteBuffer(message.Signature);
				}

				writer.WriteBuffer(encoded);
				writer.Flush();

				string payload = MessagingUtilities.ConvertToBase64WebSafeString(finalStream.ToArray());
				string result = payload;
				if (symmetricSecretHandle != null && (this.signed || this.encrypted)) {
					result = MessagingUtilities.CombineKeyHandleAndPayload(symmetricSecretHandle, payload);
				}

				return result;
			}
		}

		/// <summary>
		/// Deserializes a <see cref="DataBag"/>, including decompression, decryption, signature and nonce validation where applicable.
		/// </summary>
		/// <param name="message">The instance to initialize with deserialized data.</param>
		/// <param name="value">The serialized form of the <see cref="DataBag"/> to deserialize.  Must not be null or empty.</param>
		/// <param name="containingMessage">The message that contains the <see cref="DataBag"/> serialized value.  May be null if no carrying message is applicable.</param>
		/// <param name="messagePartName">The name of the parameter whose value is to be deserialized.  Used for error message generation, but may be <c>null</c>.</param>
		[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope", Justification = "No apparent problem.  False positive?")]
		public void Deserialize(T message, string value, IProtocolMessage containingMessage, string messagePartName) {
			Requires.NotNull(message, "message");
			Requires.NotNullOrEmpty(value, "value");

			string symmetricSecretHandle = null;
			if (this.encrypted && this.cryptoKeyStore != null) {
				string valueWithoutHandle;
				MessagingUtilities.ExtractKeyHandleAndPayload(messagePartName, value, out symmetricSecretHandle, out valueWithoutHandle);
				value = valueWithoutHandle;
			}

			message.ContainingMessage = containingMessage;
			byte[] data = MessagingUtilities.FromBase64WebSafeString(value);

			byte[] signature = null;
			if (this.signed) {
				using (var dataStream = new MemoryStream(data)) {
					var dataReader = new BinaryReader(dataStream);
					signature = dataReader.ReadBuffer(1024);
					data = dataReader.ReadBuffer(8 * 1024);
				}

				// Verify that the verification code was issued by message authorization server.
				ErrorUtilities.VerifyProtocol(this.IsSignatureValid(data, signature, symmetricSecretHandle), MessagingStrings.SignatureInvalid);
			}

			if (this.encrypted) {
				data = this.Decrypt(data, symmetricSecretHandle);
			}

			if (this.compressed) {
				data = MessagingUtilities.Decompress(data);
			}

			this.DeserializeCore(message, data);
			message.Signature = signature; // TODO: we don't really need this any more, do we?

			if (this.maximumAge.HasValue) {
				// Has message verification code expired?
				DateTime expirationDate = message.UtcCreationDate + this.maximumAge.Value;
				if (expirationDate < DateTime.UtcNow) {
					throw new ExpiredMessageException(expirationDate, containingMessage);
				}
			}

			// Has message verification code already been used to obtain an access/refresh token?
			if (this.decodeOnceOnly != null) {
				ErrorUtilities.VerifyInternal(this.maximumAge.HasValue, "Oops!  How can we validate a nonce without a maximum message age?");
				string context = "{" + GetType().FullName + "}";
				if (!this.decodeOnceOnly.StoreNonce(context, Convert.ToBase64String(message.Nonce), message.UtcCreationDate)) {
					Logger.OpenId.ErrorFormat("Replayed nonce detected ({0} {1}).  Rejecting message.", message.Nonce, message.UtcCreationDate);
					throw new ReplayedMessageException(containingMessage);
				}
			}

			((IMessage)message).EnsureValidMessage();
		}

		/// <summary>
		/// Serializes the <see cref="DataBag"/> instance to a buffer.
		/// </summary>
		/// <param name="message">The message.</param>
		/// <returns>The buffer containing the serialized data.</returns>
		protected abstract byte[] SerializeCore(T message);

		/// <summary>
		/// Deserializes the <see cref="DataBag"/> instance from a buffer.
		/// </summary>
		/// <param name="message">The message instance to initialize with data from the buffer.</param>
		/// <param name="data">The data buffer.</param>
		protected abstract void DeserializeCore(T message, byte[] data);

		/// <summary>
		/// Determines whether the signature on this instance is valid.
		/// </summary>
		/// <param name="signedData">The signed data.</param>
		/// <param name="signature">The signature.</param>
		/// <param name="symmetricSecretHandle">The symmetric secret handle.  <c>null</c> when using an asymmetric algorithm.</param>
		/// <returns>
		///   <c>true</c> if the signature is valid; otherwise, <c>false</c>.
		/// </returns>
		[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope", Justification = "No apparent problem.  False positive?")]
		private bool IsSignatureValid(byte[] signedData, byte[] signature, string symmetricSecretHandle) {
			Requires.NotNull(signedData, "signedData");
			Requires.NotNull(signature, "signature");

			if (this.asymmetricSigning != null) {
				using (var hasher = SHA1.Create()) {
					return this.asymmetricSigning.VerifyData(signedData, hasher, signature);
				}
			} else {
				return MessagingUtilities.AreEquivalentConstantTime(signature, this.CalculateSignature(signedData, symmetricSecretHandle));
			}
		}

		/// <summary>
		/// Calculates the signature for the data in this verification code.
		/// </summary>
		/// <param name="bytesToSign">The bytes to sign.</param>
		/// <param name="symmetricSecretHandle">The symmetric secret handle.  <c>null</c> when using an asymmetric algorithm.</param>
		/// <returns>
		/// The calculated signature.
		/// </returns>
		[SuppressMessage("Microsoft.Reliability", "CA2000:Dispose objects before losing scope", Justification = "No apparent problem.  False positive?")]
		private byte[] CalculateSignature(byte[] bytesToSign, string symmetricSecretHandle) {
			Requires.NotNull(bytesToSign, "bytesToSign");
			RequiresEx.ValidState(this.asymmetricSigning != null || this.cryptoKeyStore != null);

			if (this.asymmetricSigning != null) {
				using (var hasher = SHA1.Create()) {
					return this.asymmetricSigning.SignData(bytesToSign, hasher);
				}
			} else {
				var key = this.cryptoKeyStore.GetKey(this.cryptoKeyBucket, symmetricSecretHandle);
				ErrorUtilities.VerifyProtocol(key != null, MessagingStrings.MissingDecryptionKeyForHandle, this.cryptoKeyBucket, symmetricSecretHandle);
				using (var symmetricHasher = HmacAlgorithms.Create(HmacAlgorithms.HmacSha256, key.Key)) {
					return symmetricHasher.ComputeHash(bytesToSign);
				}
			}
		}

		/// <summary>
		/// Encrypts the specified value using either the symmetric or asymmetric encryption algorithm as appropriate.
		/// </summary>
		/// <param name="value">The value.</param>
		/// <param name="symmetricSecretHandle">Receives the symmetric secret handle.  <c>null</c> when using an asymmetric algorithm.</param>
		/// <returns>
		/// The encrypted value.
		/// </returns>
		private byte[] Encrypt(byte[] value, out string symmetricSecretHandle) {
			Assumes.True(this.asymmetricEncrypting != null || this.cryptoKeyStore != null);

			if (this.asymmetricEncrypting != null) {
				symmetricSecretHandle = null;
				return this.asymmetricEncrypting.EncryptWithRandomSymmetricKey(value);
			} else {
				var cryptoKey = this.cryptoKeyStore.GetCurrentKey(this.cryptoKeyBucket, this.minimumAge);
				symmetricSecretHandle = cryptoKey.Key;
				return MessagingUtilities.Encrypt(value, cryptoKey.Value.Key);
			}
		}

		/// <summary>
		/// Decrypts the specified value using either the symmetric or asymmetric encryption algorithm as appropriate.
		/// </summary>
		/// <param name="value">The value.</param>
		/// <param name="symmetricSecretHandle">The symmetric secret handle.  <c>null</c> when using an asymmetric algorithm.</param>
		/// <returns>
		/// The decrypted value.
		/// </returns>
		private byte[] Decrypt(byte[] value, string symmetricSecretHandle) {
			RequiresEx.ValidState(this.asymmetricEncrypting != null || symmetricSecretHandle != null);

			if (this.asymmetricEncrypting != null) {
				return this.asymmetricEncrypting.DecryptWithRandomSymmetricKey(value);
			} else {
				var key = this.cryptoKeyStore.GetKey(this.cryptoKeyBucket, symmetricSecretHandle);
				ErrorUtilities.VerifyProtocol(key != null, MessagingStrings.MissingDecryptionKeyForHandle, this.cryptoKeyBucket, symmetricSecretHandle);
				return MessagingUtilities.Decrypt(value, key.Key);
			}
		}
	}
}