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

namespace DotNetOpenAuth.OpenId {
	using System;
	using System.Collections.Generic;
	using System.Diagnostics;
	using System.Diagnostics.CodeAnalysis;
	using System.Diagnostics.Contracts;
	using DotNetOpenAuth.Messaging;
	using DotNetOpenAuth.Messaging.Reflection;

	/// <summary>
	/// An Identifier is either a "http" or "https" URI, or an XRI.
	/// </summary>
	[Serializable]
	[ContractVerification(true)]
	[Pure]
	[ContractClass(typeof(IdentifierContract))]
	public abstract class Identifier {
		/// <summary>
		/// Initializes static members of the <see cref="Identifier"/> class.
		/// </summary>
		static Identifier() {
			Func<string, Identifier> safeIdentifier = str => {
				Contract.Assume(str != null);
				ErrorUtilities.VerifyFormat(str.Length > 0, MessagingStrings.NonEmptyStringExpected);
				return Identifier.Parse(str, true);
			};
			MessagePart.Map<Identifier>(id => id.SerializedString, id => id.OriginalString, safeIdentifier);
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="Identifier"/> class.
		/// </summary>
		/// <param name="originalString">The original string before any normalization.</param>
		/// <param name="isDiscoverySecureEndToEnd">Whether the derived class is prepared to guarantee end-to-end discovery
		/// and initial redirect for authentication is performed using SSL.</param>
		[SuppressMessage("Microsoft.Naming", "CA1720:IdentifiersShouldNotContainTypeNames", MessageId = "string", Justification = "Emphasis on string instead of the strong-typed Identifier.")]
		protected Identifier(string originalString, bool isDiscoverySecureEndToEnd) {
			this.OriginalString = originalString;
			this.IsDiscoverySecureEndToEnd = isDiscoverySecureEndToEnd;
		}

		/// <summary>
		/// Gets the original string that was normalized to create this Identifier.
		/// </summary>
		internal string OriginalString { get; private set; }

		/// <summary>
		/// Gets the Identifier in the form in which it should be serialized.
		/// </summary>
		/// <value>
		/// For Identifiers that were originally deserialized, this is the exact same
		/// string that was deserialized.  For Identifiers instantiated in some other way, this is
		/// the normalized form of the string used to instantiate the identifier.
		/// </value>
		internal virtual string SerializedString {
			get { return this.IsDeserializedInstance ? this.OriginalString : this.ToString(); }
		}

		/// <summary>
		/// Gets or sets a value indicating whether <see cref="Identifier"/> instances are considered equal
		/// based solely on their string reprsentations.
		/// </summary>
		/// <remarks>
		/// This property serves as a test hook, so that MockIdentifier instances can be considered "equal"
		/// to UriIdentifier instances.
		/// </remarks>
		protected internal static bool EqualityOnStrings { get; set; }

		/// <summary>
		/// Gets a value indicating whether this Identifier will ensure SSL is 
		/// used throughout the discovery phase and initial redirect of authentication.
		/// </summary>
		/// <remarks>
		/// If this is <c>false</c>, a value of <c>true</c> may be obtained by calling 
		/// <see cref="TryRequireSsl"/>.
		/// </remarks>
		protected internal bool IsDiscoverySecureEndToEnd { get; private set; }

		/// <summary>
		/// Gets a value indicating whether this instance was initialized from
		/// deserializing a message.
		/// </summary>
		/// <remarks>
		/// This is interesting because when an Identifier comes from the network,
		/// we can't normalize it and then expect signatures to still verify.  
		/// But if the Identifier is initialized locally, we can and should normalize it
		/// before serializing it.
		/// </remarks>
		protected bool IsDeserializedInstance { get; private set; }

		/// <summary>
		/// Converts the string representation of an Identifier to its strong type.
		/// </summary>
		/// <param name="identifier">The identifier.</param>
		/// <returns>The particular Identifier instance to represent the value given.</returns>
		[SuppressMessage("Microsoft.Design", "CA1057:StringUriOverloadsCallSystemUriOverloads", Justification = "Not all identifiers are URIs.")]
		[SuppressMessage("Microsoft.Usage", "CA2225:OperatorOverloadsHaveNamedAlternates", Justification = "Our named alternate is Parse.")]
		[DebuggerStepThrough]
		public static implicit operator Identifier(string identifier) {
			Requires.True(identifier == null || identifier.Length > 0, "identifier");
			Contract.Ensures((identifier == null) == (Contract.Result<Identifier>() == null));

			if (identifier == null) {
				return null;
			}
			return Parse(identifier);
		}

		/// <summary>
		/// Converts a given Uri to a strongly-typed Identifier.
		/// </summary>
		/// <param name="identifier">The identifier to convert.</param>
		/// <returns>The result of the conversion.</returns>
		[SuppressMessage("Microsoft.Usage", "CA2225:OperatorOverloadsHaveNamedAlternates", Justification = "We have a Parse function.")]
		[DebuggerStepThrough]
		public static implicit operator Identifier(Uri identifier) {
			Contract.Ensures((identifier == null) == (Contract.Result<Identifier>() == null));
			if (identifier == null) {
				return null;
			}

			return new UriIdentifier(identifier);
		}

		/// <summary>
		/// Converts an Identifier to its string representation.
		/// </summary>
		/// <param name="identifier">The identifier to convert to a string.</param>
		/// <returns>The result of the conversion.</returns>
		[SuppressMessage("Microsoft.Usage", "CA2225:OperatorOverloadsHaveNamedAlternates", Justification = "We have a Parse function.")]
		[DebuggerStepThrough]
		public static implicit operator string(Identifier identifier) {
			Contract.Ensures((identifier == null) == (Contract.Result<string>() == null));
			if (identifier == null) {
				return null;
			}
			return identifier.ToString();
		}

		/// <summary>
		/// Parses an identifier string and automatically determines
		/// whether it is an XRI or URI.
		/// </summary>
		/// <param name="identifier">Either a URI or XRI identifier.</param>
		/// <returns>An <see cref="Identifier"/> instance for the given value.</returns>
		[SuppressMessage("Microsoft.Usage", "CA2234:PassSystemUriObjectsInsteadOfStrings", Justification = "Some of these identifiers are not properly formatted to be Uris at this stage.")]
		public static Identifier Parse(string identifier) {
			Requires.NotNullOrEmpty(identifier, "identifier");
			Contract.Ensures(Contract.Result<Identifier>() != null);

			return Parse(identifier, false);
		}

		/// <summary>
		/// Parses an identifier string and automatically determines
		/// whether it is an XRI or URI.
		/// </summary>
		/// <param name="identifier">Either a URI or XRI identifier.</param>
		/// <param name="serializeExactValue">if set to <c>true</c> this Identifier will serialize exactly as given rather than in its normalized form.</param>
		/// <returns>
		/// An <see cref="Identifier"/> instance for the given value.
		/// </returns>
		[SuppressMessage("Microsoft.Usage", "CA2234:PassSystemUriObjectsInsteadOfStrings", Justification = "Some of these identifiers are not properly formatted to be Uris at this stage.")]
		public static Identifier Parse(string identifier, bool serializeExactValue) {
			Requires.NotNullOrEmpty(identifier, "identifier");
			Contract.Ensures(Contract.Result<Identifier>() != null);

			Identifier id;
			if (XriIdentifier.IsValidXri(identifier)) {
				id = new XriIdentifier(identifier);
			} else {
				id = new UriIdentifier(identifier);
			}

			id.IsDeserializedInstance = serializeExactValue;
			return id;
		}

		/// <summary>
		/// Attempts to parse a string for an OpenId Identifier.
		/// </summary>
		/// <param name="value">The string to be parsed.</param>
		/// <param name="result">The parsed Identifier form.</param>
		/// <returns>
		/// True if the operation was successful.  False if the string was not a valid OpenId Identifier.
		/// </returns>
		public static bool TryParse(string value, out Identifier result) {
			if (string.IsNullOrEmpty(value)) {
				result = null;
				return false;
			}

			if (IsValid(value)) {
				result = Parse(value);
				return true;
			} else {
				result = null;
				return false;
			}
		}

		/// <summary>
		/// Checks the validity of a given string representation of some Identifier.
		/// </summary>
		/// <param name="identifier">The identifier.</param>
		/// <returns>
		/// 	<c>true</c> if the specified identifier is valid; otherwise, <c>false</c>.
		/// </returns>
		[SuppressMessage("Microsoft.Usage", "CA2234:PassSystemUriObjectsInsteadOfStrings", Justification = "Some of these identifiers are not properly formatted to be Uris at this stage.")]
		public static bool IsValid(string identifier) {
			Requires.NotNullOrEmpty(identifier, "identifier");
			return XriIdentifier.IsValidXri(identifier) || UriIdentifier.IsValidUri(identifier);
		}

		/// <summary>
		/// Tests equality between two <see cref="Identifier"/>s.
		/// </summary>
		/// <param name="id1">The first Identifier.</param>
		/// <param name="id2">The second Identifier.</param>
		/// <returns>
		/// <c>true</c> if the two instances should be considered equal; <c>false</c> otherwise.
		/// </returns>
		public static bool operator ==(Identifier id1, Identifier id2) {
			return id1.EqualsNullSafe(id2);
		}

		/// <summary>
		/// Tests inequality between two <see cref="Identifier"/>s.
		/// </summary>
		/// <param name="id1">The first Identifier.</param>
		/// <param name="id2">The second Identifier.</param>
		/// <returns>
		/// <c>true</c> if the two instances should be considered unequal; <c>false</c> if they are equal.
		/// </returns>
		public static bool operator !=(Identifier id1, Identifier id2) {
			return !id1.EqualsNullSafe(id2);
		}

		/// <summary>
		/// Tests equality between two <see cref="Identifier"/>s.
		/// </summary>
		/// <param name="obj">The <see cref="T:System.Object"/> to compare with the current <see cref="T:System.Object"/>.</param>
		/// <returns>
		/// true if the specified <see cref="T:System.Object"/> is equal to the current <see cref="T:System.Object"/>; otherwise, false.
		/// </returns>
		/// <exception cref="T:System.NullReferenceException">
		/// The <paramref name="obj"/> parameter is null.
		/// </exception>
		public override bool Equals(object obj) {
			Debug.Fail("This should be overridden in every derived class.");
			return base.Equals(obj);
		}

		/// <summary>
		/// Gets the hash code for an <see cref="Identifier"/> for storage in a hashtable.
		/// </summary>
		/// <returns>
		/// A hash code for the current <see cref="T:System.Object"/>.
		/// </returns>
		public override int GetHashCode() {
			Debug.Fail("This should be overridden in every derived class.");
			return base.GetHashCode();
		}

		/// <summary>
		/// Reparses the specified identifier in order to be assured that the concrete type that
		/// implements the identifier is one of the well-known ones.
		/// </summary>
		/// <param name="identifier">The identifier.</param>
		/// <returns>Either <see cref="XriIdentifier"/> or <see cref="UriIdentifier"/>.</returns>
		internal static Identifier Reparse(Identifier identifier) {
			Requires.NotNull(identifier, "identifier");
			Contract.Ensures(Contract.Result<Identifier>() != null);

			return Parse(identifier, identifier.IsDeserializedInstance);
		}

		/// <summary>
		/// Returns an <see cref="Identifier"/> that has no URI fragment.
		/// Quietly returns the original <see cref="Identifier"/> if it is not
		/// a <see cref="UriIdentifier"/> or no fragment exists.
		/// </summary>
		/// <returns>A new <see cref="Identifier"/> instance if there was a 
		/// fragment to remove, otherwise this same instance..</returns>
		[Pure]
		internal abstract Identifier TrimFragment();

		/// <summary>
		/// Converts a given identifier to its secure equivalent.  
		/// UriIdentifiers originally created with an implied HTTP scheme change to HTTPS.
		/// Discovery is made to require SSL for the entire resolution process.
		/// </summary>
		/// <param name="secureIdentifier">
		/// The newly created secure identifier.
		/// If the conversion fails, <paramref name="secureIdentifier"/> retains
		/// <i>this</i> identifiers identity, but will never discover any endpoints.
		/// </param>
		/// <returns>
		/// True if the secure conversion was successful.
		/// False if the Identifier was originally created with an explicit HTTP scheme.
		/// </returns>
		internal abstract bool TryRequireSsl(out Identifier secureIdentifier);
	}
}