using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
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 refernece though, so we
    // need to hash on some UID instead of the refernce. Do not use strings, they are
    // super slow.
    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>();

    // We split this into two arrays since we have to read
    // a byte at a time anways. In the future if we need to 
    // back to a unifed array, instead of 64k entries 
    // we can change it to a signed int, and then add x0200 to the value.
    // This will reduce array size down to 768 entries.
    protected Func<ILOpCode>[] mOpCodesLo = new Func<ILOpCode>[256];
    protected Func<ILOpCode>[] mOpCodesHi = new Func<ILOpCode>[256];

    public ILScanner(Type aAssemblerBaseOp) {
      LoadOpCodes();
    }

    protected void LoadOpCodes() {
      foreach (var xType in typeof(ILOpCode).Assembly.GetExportedTypes()) {
        if (xType.IsSubclassOf(typeof(ILOpCode))) {
          var xAttrib = xType.GetCustomAttributes(typeof(OpCodeAttribute), false).FirstOrDefault() as OpCodeAttribute;
          var xTemp = new DynamicMethod("Create_" + xAttrib.OpCode + "_Obj", typeof(ILOpCode), new Type[0], true);
          var xGen = xTemp.GetILGenerator();
          var xCtor = xType.GetConstructor(new Type[0]);
          xGen.Emit(OpCodes.Newobj, xCtor);
          xGen.Emit(OpCodes.Ret);

          var xDeleg = (Func<ILOpCode>)xTemp.CreateDelegate(typeof(Func<ILOpCode>));
          var xOpCodeValue = (ushort)xAttrib.OpCode;
          if (xOpCodeValue <= 0xFF ) {
            mOpCodesLo[xOpCodeValue] = xDeleg;
          } else {
            mOpCodesHi[xOpCodeValue & 0xFF] = xDeleg;
          }
        }
      }
    }

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

    private void ScanMethod(MethodBase aMethodBase) {
      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 xBody = aMethodBase.GetMethodBody();
      if (xBody == null) {
        return;
      }
      var xReader = new ILReader(aMethodBase, xBody);
      while (xReader.Read()) {
        //InstructionCount++;
        var xOpCodeValue = (ushort)xReader.OpCode;
        Func<ILOpCode> xCreate;
        if (xOpCodeValue <= 0xFF) {
          xCreate = mOpCodesLo[xOpCodeValue];
        } else {
          xCreate = mOpCodesHi[xOpCodeValue & 0xFF];
        }
        if (xCreate == null) {
          throw new Exception("Unrecognized IL Operation");
        }
        var xOp = xCreate();
        xOp.Scan(xReader, this);
      }
    }

    public void QueueMethod(MethodBase aMethod) {
      if (!mMethodsSet.Contains(aMethod)) {
        mMethodsSet.Add(aMethod);
        mMethods.Add(aMethod);
        QueueType(aMethod.DeclaringType);
      }
    }

    public void QueueType(Type aType) {
      if (aType != null) {
        if (!mTypesSet.Contains(aType)) {
          mTypesSet.Add(aType);
          mTypes.Add(aType);
          QueueType(aType.BaseType);
          foreach (var xMethod in aType.GetMethods(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)) {
            if (xMethod.DeclaringType == aType) {
              if (xMethod.IsVirtual) {
                QueueMethod(xMethod);
              }
            }
          }
        }
      }
    }

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

  }
}