//
// System.Security.CodeAccessPermission.cs
//
// Authors:
//	Miguel de Icaza (miguel@ximian.com)
//	Nick Drochak, ndrochak@gol.com
//	Sebastien Pouliot  <sebastien@ximian.com>
//
// (C) Ximian, Inc. http://www.ximian.com
// Copyright (C) 2001 Nick Drochak, All Rights Reserved
// Portions (C) 2004 Motus Technologies Inc. (http://www.motus.com)
// Copyright (C) 2004 Novell, Inc (http://www.novell.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
// 
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System.Diagnostics;
using System.Globalization;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Security.Permissions;

namespace System.Security {

	[Serializable]
	public abstract class CodeAccessPermission : IPermission, ISecurityEncodable, IStackWalk {

		internal enum StackModifier {
			Assert = 1,
			Deny = 2,
			PermitOnly = 3
		}

		protected CodeAccessPermission ()
		{
		}

		// LAMESPEC: Documented as virtual
		[MonoTODO ("unmanaged side is incomplete")]
		public void Assert ()
		{
			// Not everyone can assert freely so we must check for
			// System.Security.Permissions.SecurityPermissionFlag.Assertion
			new SecurityPermission (SecurityPermissionFlag.Assertion).Demand ();

			// we must have the permission to assert it to others
			if (SecurityManager.IsGranted (this)) {
				SetCurrentFrame (StackModifier.Assert, this.Copy ());
			}
		}

#if NET_2_0
		public virtual
#else
		internal
#endif
		bool CheckAssert (CodeAccessPermission asserted)
		{
			if (asserted == null)
				return false;
			if (asserted.GetType () != this.GetType ())
				return false;
			return IsSubsetOf (asserted);
		}

#if NET_2_0
		public virtual
#else
		internal
#endif
		bool CheckDemand (CodeAccessPermission target)
		{
			if (target == null)
				return false;
			if (target.GetType () != this.GetType ())
				return false;
			return IsSubsetOf (target);
		}

#if NET_2_0
		public virtual
#else
		internal
#endif
		bool CheckDeny (CodeAccessPermission denied)
		{
			if (denied == null)
				return true;
			if (denied.GetType () != this.GetType ())
				return true;
			return (Intersect (denied) == null);
		}

#if NET_2_0
		public 
#else
		internal
#endif
		virtual bool CheckPermitOnly (CodeAccessPermission target)
		{
			if (target == null)
				return false;
			if (target.GetType () != this.GetType ())
				return false;
			return IsSubsetOf (target);
		}

		public abstract IPermission Copy ();

		// LAMESPEC: Documented as virtual
		[MonoTODO ("Assert, Deny and PermitOnly aren't yet supported")]
		public void Demand ()
		{
			if (!SecurityManager.SecurityEnabled)
				return;

			// Order is:
			// 1. CheckDemand (current frame)
			//	note: for declarative attributes directly calls IsSubsetOf

			Assembly a = null;
			StackTrace st = new StackTrace (1); // skip ourself
			StackFrame[] frames = st.GetFrames ();
			foreach (StackFrame sf in frames) {
				MethodBase mb = sf.GetMethod ();
				// however the "final" grant set is resolved by assembly, so
				// there's no need to check it every time (just when we're 
				// changing assemblies between frames).
				Assembly af = mb.ReflectedType.Assembly;
				CodeAccessPermission cap = null;
				if (a != af) {
					a = af;
					if (a.GrantedPermissionSet != null)
						cap = (CodeAccessPermission) a.GrantedPermissionSet.GetPermission (this.GetType ());
					else
						cap = null;

					// CheckDemand will always return false in case cap is null
					if ((cap == null) || !CheckDemand (cap)) {
						if (a.DeniedPermissionSet != null) {
							cap = (CodeAccessPermission) a.DeniedPermissionSet.GetPermission (this.GetType ());
						}
						else
							cap = null;

						// IsSubsetOf "should" always return false if cap is null
						if ((cap != null) && IsSubsetOf (cap)) {
							Type t = this.GetType ();
							// TODO add more details
							throw new SecurityException ("ReqRefuse", t);
						}
					}
					else {
						throw new SecurityException ("Demand failed", a.GetName (),
							a.GrantedPermissionSet, a.DeniedPermissionSet, (MethodInfo) mb, 
							SecurityAction.Demand, this, cap, a.Evidence);
					}
				}
				object[] perms = GetFramePermissions ();
				if (perms == null)
					continue;

				// 2. CheckPermitOnly
				object o = perms [(int)StackModifier.PermitOnly];
				if (o != null) {
					cap = (o as CodeAccessPermission);
					if (cap != null) {
						if (!CheckPermitOnly (cap))
							throw new SecurityException ("PermitOnly");
					}
					else {
						PermissionSet ps = (o as PermissionSet);
						foreach (IPermission p in ps) {
							if (p is CodeAccessPermission) {
								if (!CheckPermitOnly (p as CodeAccessPermission))
									throw new SecurityException ("PermitOnly");
							}
						}
					}
				}

				// 3. CheckDeny
				o = perms [(int)StackModifier.Deny];
				if (o != null) {
					cap = (o as CodeAccessPermission) ;
					if (cap != null) {
						if (!CheckDeny (cap))
							throw new SecurityException ("Deny");
					}
					else {
						PermissionSet ps = (o as PermissionSet);
						foreach (IPermission p in ps) {
							if (p is CodeAccessPermission) {
								if (!CheckPermitOnly (p as CodeAccessPermission))
									throw new SecurityException ("Deny");
							}
						}
					}
				}

				// 4. CheckAssert
				o = perms [(int)StackModifier.Assert];
				if (o != null) {
					cap = (o as CodeAccessPermission);
					if (cap != null) {
						if (CheckAssert (cap)) {
							return; // stop the stack walk
						}
					}
					else {
						PermissionSet ps = (o as PermissionSet);
						foreach (IPermission p in ps) {
							if (p is CodeAccessPermission) {
								if (!CheckPermitOnly (p as CodeAccessPermission)) {
									return; // stop the stack walk
								}
							}
						}
					}
				}
			}
		}

		// LAMESPEC: Documented as virtual
		[MonoTODO ("unmanaged side is incomplete")]
		public void Deny ()
		{
			SetCurrentFrame (StackModifier.Deny, this.Copy ());
		}

#if NET_2_0
		[MonoTODO]
		[ComVisible (false)]
		public override bool Equals (object obj)
		{
			if (obj == null)
				return false;
			if (obj.GetType () != this.GetType ())
				return false;
			// TODO: compare
			return true;
		}
#endif

		public abstract void FromXml (SecurityElement elem);

#if NET_2_0
		[MonoTODO]
		[ComVisible (false)]
		public override int GetHashCode ()
		{
			return base.GetHashCode ();
		}
#endif

		public abstract IPermission Intersect (IPermission target);

		public abstract bool IsSubsetOf (IPermission target);

		public override string ToString ()
		{
			SecurityElement elem = ToXml ();
			return elem.ToString ();
		}

		public abstract SecurityElement ToXml ();

		public virtual IPermission Union (IPermission other)
		{
			if (null != other)
				throw new System.NotSupportedException (); // other is not null.
			return null;
		}

		// LAMESPEC: Documented as virtual
		[MonoTODO ("unmanaged side is incomplete")]
		public void PermitOnly ()
		{
			SetCurrentFrame (StackModifier.PermitOnly, this.Copy ());
		}

		[MonoTODO ("unmanaged side is incomplete")]
		public static void RevertAll ()
		{
			if (!ClearFramePermissions ()) {
				string msg = Locale.GetText ("No security frame present to be reverted.");
				throw new ExecutionEngineException (msg);
			}
		}

		[MonoTODO ("unmanaged side is incomplete")]
		public static void RevertAssert ()
		{
			RevertCurrentFrame (StackModifier.Assert);
		}

		[MonoTODO ("unmanaged side is incomplete")]
		public static void RevertDeny ()
		{
			RevertCurrentFrame (StackModifier.Deny);
		}

		[MonoTODO ("unmanaged side is incomplete")]
		public static void RevertPermitOnly ()
		{
			RevertCurrentFrame (StackModifier.PermitOnly);
		}

		// Internal calls
#if false
		// see mono/mono/metadata/cas.c for implementation

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		static extern bool ClearFramePermissions ();

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		static extern object[] GetFramePermissions ();

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		static extern bool SetFramePermissions (int index, object permissions);
#else
		// icalls are not yet commited so...

		static bool ClearFramePermissions () 
		{
			return true;
		}

		static object[] GetFramePermissions () 
		{
			return null;
		}

		static bool SetFramePermissions (int index, object permissions)
		{
			return true;
		}
#endif

		// Internal helpers methods

		// snippet moved from FileIOPermission (nickd) to be reused in all derived classes
		internal SecurityElement Element (int version) 
		{
			SecurityElement se = new SecurityElement ("IPermission");
			Type type = this.GetType ();
			se.AddAttribute ("class", type.FullName + ", " + type.Assembly.ToString ().Replace ('\"', '\''));
			se.AddAttribute ("version", version.ToString ());
			return se;
		}

		internal static PermissionState CheckPermissionState (PermissionState state, bool allowUnrestricted)
		{
			string msg;
			switch (state) {
			case PermissionState.None:
				break;
			case PermissionState.Unrestricted:
				if (!allowUnrestricted) {
					msg = Locale.GetText ("Unrestricted isn't not allowed for identity permissions.");
					throw new ArgumentException (msg, "state");
				}
				break;
			default:
				msg = String.Format (Locale.GetText ("Invalid enum {0}"), state);
				throw new ArgumentException (msg, "state");
			}
			return state;
		}

		internal static int CheckSecurityElement (SecurityElement se, string parameterName, int minimumVersion, int maximumVersion) 
		{
			if (se == null)
				throw new ArgumentNullException (parameterName);

			// Tag is case-sensitive
			if (se.Tag != "IPermission") {
				string msg = String.Format (Locale.GetText ("Invalid tag {0}"), se.Tag);
				throw new ArgumentException (msg, parameterName);
			}

			// Note: we do not care about the class attribute at 
			// this stage (in fact we don't even if the class 
			// attribute is present or not). Anyway the object has
			// already be created, with success, if we're loading it

			// we assume minimum version if no version number is supplied
			int version = minimumVersion;
			string v = se.Attribute ("version");
			if (v != null) {
				try {
					version = Int32.Parse (v);
				}
				catch (Exception e) {
					string msg = Locale.GetText ("Couldn't parse version from '{0}'.");
					msg = String.Format (msg, v);
					throw new ArgumentException (msg, parameterName, e);
				}
			}

			if ((version < minimumVersion) || (version > maximumVersion)) {
				string msg = Locale.GetText ("Unknown version '{0}', expected versions between ['{1}','{2}'].");
				msg = String.Format (msg, version, minimumVersion, maximumVersion);
				throw new ArgumentException (msg, parameterName);
			}
			return version;
		}

		// must be called after CheckSecurityElement (i.e. se != null)
		internal static bool IsUnrestricted (SecurityElement se) 
		{
			string value = se.Attribute ("Unrestricted");
			if (value == null)
				return false;
			return (String.Compare (value, Boolean.TrueString, true, CultureInfo.InvariantCulture) == 0);
		}

		internal static void ThrowInvalidPermission (IPermission target, Type expected) 
		{
			string msg = Locale.GetText ("Invalid permission type '{0}', expected type '{1}'.");
			msg = String.Format (msg, target.GetType (), expected);
			throw new ArgumentException (msg, "target");
		}

		internal static void SetCurrentFrame (StackModifier stackmod, object permissions)
		{
			if (!SetFramePermissions ((int)stackmod, permissions)) {
				string msg = Locale.GetText ("An {0} modifier is already present on the current stack frame.");
				throw new SecurityException (String.Format (msg, stackmod));
			}
		}

		internal static void RevertCurrentFrame (StackModifier stackmod)
		{
			if (!SetFramePermissions ((int)stackmod, null)) {
				string msg = Locale.GetText ("No {0} modifier is present on the current stack frame.");
				throw new ExecutionEngineException (String.Format (msg, stackmod));
			}
		}
	}
}