using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;

namespace Cosmos.IL2CPU
{
    public class ILScanner
    {
        //Note: We have both HashSet and List because HashSet.Contains is much faster
        // than List.Contains. Also in the future we may remove items from the List
        // which have already been processed yet need to keep them in HashSet.
        //TODO: When we go threaded, these two should be encapselated into a single
        // class with thread safety.
        //TODO: These store the MethodBase which also have the IL for the body in memory
        // For large asms this could eat lot of RAM. Should convert this to remove
        // items from the list after they are processed but keep them in HashSet so we
        // know they are already done. Currently HashSet uses a reference though, so we
        // need to hash on some UID instead of the refernce. Do not use strings, they are
        // super slow.
        //	TODO: We need to scan for static fields too. 
        private HashSet<MethodBase> mMethodsSet = new HashSet<MethodBase>();
        private List<MethodBase> mMethods = new List<MethodBase>();
        private HashSet<Type> mTypesSet = new HashSet<Type>();
        private List<Type> mTypes = new List<Type>();

        protected ILReader mReader;
        protected Assembler mAsmblr;

        public ILScanner( Assembler aAsmblr )
        {
            mAsmblr = aAsmblr;
            mReader = new ILReader();
        }

        public void Execute( System.Reflection.MethodInfo aEntry )
        {
            QueueMethod( aEntry );

            // Cannot use foreach, the list changes as we go
            for( int i = 0; i < mMethods.Count; i++ )
            {
                ScanMethod( mMethods[ i ], ( UInt32 )i );
            }

            // ie 
            //   var xSB = new StringBuilder("test");
            //   object x = xSB;
            //   string y = xSB.ToString();
            //
            // Now that we did a full normal scan, rescan and find all virtuals
            // and for each virtual scan all included types and include descendant overrides.
            // I think we need to scan for ancestor calls too...
            // This process will add more classes etc.. so the process will need to be repeated
            // until no more new methods are found.
            //
            //TODO: Speed this up somehow....
            int xMethodCount;
            do
            {
                xMethodCount = mMethods.Count;
                // Cannot use foreach, the list changes as we go
                for( int i = 0; i < mMethods.Count; i++ )
                {
                    var xMethod = mMethods[ i ];
                    if( xMethod.IsVirtual )
                    {
                        foreach( var xType in mTypes )
                        {
                            // Find ancestors and descendants
                            if( xType.IsSubclassOf( xMethod.DeclaringType ) || xMethod.DeclaringType.IsSubclassOf( xType ) )
                            {
                                var xParams = xMethod.GetParameters();
                                var xParamTypes = new Type[ xParams.Length ];
                                for( int j = 0; j < xParams.Length; j++ )
                                {
                                    xParamTypes[ j ] = xParams[ j ].ParameterType;
                                }
                                var xNewMethod = xType.GetMethod( xMethod.Name, xParamTypes );
                                if( xNewMethod != null )
                                {
                                    QueueMethod( xNewMethod );
                                }
                            }
                        }
                    }
                }
            } while( xMethodCount != mMethods.Count );
        }

        private void ScanMethod(MethodBase aMethodBase, UInt32 aMethodUID) {
            if ((aMethodBase.Attributes & MethodAttributes.PinvokeImpl) != 0) {
                // pinvoke methods dont have an embedded implementation
                return;
            } else if( aMethodBase.IsAbstract ) {
                // abstract methods dont have an implementation
                return;
            }

            var xImplFlags = aMethodBase.GetMethodImplementationFlags();
            if( ( xImplFlags & MethodImplAttributes.Native ) != 0 )
            {
                // native implementations cannot be compiled
                return;
            }

            var xOpCodes = mReader.ProcessMethod(aMethodBase);
            if (xOpCodes != null) {
                // Call ProcessMethod first, in a threaded environment it will
                // allow more threads to work slightly sooner
                var xMethod = new MethodInfo(aMethodBase, aMethodUID);
              
                // Assemble the method
                mAsmblr.ProcessMethod(xMethod, xOpCodes);

                foreach (var xOpCode in xOpCodes) {
                  //InstructionCount++;
                  if( xOpCode is ILOpCodes.OpMethod ) {
                    QueueMethod(((ILOpCodes.OpMethod)xOpCode).Value);
                  } else if (xOpCode is ILOpCodes.OpType) {
                    QueueType( ( ( ILOpCodes.OpType )xOpCode ).Value );
                  }
                }
            }
        }

        protected void QueueMethod( MethodBase aMethod )
        {
            if( !mMethodsSet.Contains( aMethod ) )
            {
                mMethodsSet.Add( aMethod );
                mMethods.Add( aMethod );
                //TODO: Might still need this one, see after we get assembly output again
                //Im hoping the operand walking we have now ill include this on its own.
                //QueueType(aMethod.DeclaringType);

                //var xMethodInfo = aMethod as MethodInfo;
                //if (xMethodInfo != null) {
                //  QueueType(xMethodInfo.ReturnType);
                //}
                //foreach (var xParam in aMethod.GetParameters()) {
                //  QueueType(xParam.ParameterType);
                //}
            }
        }

        //protected void QueueStaticField(FieldInfo aFieldInfo) {
        //  if (!mFieldsSet.Contains(aFieldInfo)) {
        //    if (!aFieldInfo.IsStatic) {
        //      throw new Exception("Cannot queue instance fields!");
        //    }
        //    mFieldsSet.Add(aFieldInfo);
        //    QueueType(aFieldInfo.DeclaringType);
        //    QueueType(aFieldInfo.FieldType);
        //  }
        //}

        protected void QueueType( Type aType )
        {
            if( !mTypesSet.Contains( aType ) )
            {
                mTypesSet.Add( aType );
                mTypes.Add( aType );
                if( aType.BaseType != null )
                {
                    QueueType( aType.BaseType );
                }
                // queue static constructor
                foreach( var xCctor in aType.GetConstructors( BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public ) )
                {
                    if( xCctor.DeclaringType == aType )
                    {
                        QueueMethod( xCctor );
                    }
                }
            }
        }

        public int MethodCount
        {
            get
            {
                return mMethods.Count;
            }
        }

    }
}