using ARMeilleure.Decoders;
using ARMeilleure.IntermediateRepresentation;
using ARMeilleure.State;
using ARMeilleure.Translation;
using System;
using System.Diagnostics;

using static ARMeilleure.Instructions.InstEmitSimdHelper32;
using static ARMeilleure.IntermediateRepresentation.OperandHelper;

namespace ARMeilleure.Instructions
{
    static partial class InstEmit32
    {
        public static void Vqrshrn(ArmEmitterContext context)
        {
            OpCode32SimdShImm op = (OpCode32SimdShImm)context.CurrOp;

            EmitRoundShrImmSaturatingNarrowOp(context, op.U ? ShrImmSaturatingNarrowFlags.VectorZxZx : ShrImmSaturatingNarrowFlags.VectorSxSx);
        }

        public static void Vqrshrun(ArmEmitterContext context)
        {
            EmitRoundShrImmSaturatingNarrowOp(context, ShrImmSaturatingNarrowFlags.VectorSxZx);
        }

        public static void Vrshr(ArmEmitterContext context)
        {
            OpCode32SimdShImm op = (OpCode32SimdShImm)context.CurrOp;
            int shift = GetImmShr(op);
            long roundConst = 1L << (shift - 1);

            if (op.U)
            {
                if (op.Size < 2)
                {
                    EmitVectorUnaryOpZx32(context, (op1) =>
                    {
                        op1 = context.Add(op1, Const(op1.Type, roundConst));

                        return context.ShiftRightUI(op1, Const(shift));
                    });
                }
                else if (op.Size == 2)
                {
                    EmitVectorUnaryOpZx32(context, (op1) =>
                    {
                        op1 = context.ZeroExtend32(OperandType.I64, op1);
                        op1 = context.Add(op1, Const(op1.Type, roundConst));

                        return context.ConvertI64ToI32(context.ShiftRightUI(op1, Const(shift)));
                    });
                }
                else /* if (op.Size == 3) */
                {
                    EmitVectorUnaryOpZx32(context, (op1) => EmitShrImm64(context, op1, signed: false, roundConst, shift));
                }
            }
            else
            {
                if (op.Size < 2)
                {
                    EmitVectorUnaryOpSx32(context, (op1) =>
                    {
                        op1 = context.Add(op1, Const(op1.Type, roundConst));

                        return context.ShiftRightSI(op1, Const(shift));
                    });
                }
                else if (op.Size == 2)
                {
                    EmitVectorUnaryOpSx32(context, (op1) =>
                    {
                        op1 = context.SignExtend32(OperandType.I64, op1);
                        op1 = context.Add(op1, Const(op1.Type, roundConst));

                        return context.ConvertI64ToI32(context.ShiftRightSI(op1, Const(shift)));
                    });
                }
                else /* if (op.Size == 3) */
                {
                    EmitVectorUnaryOpZx32(context, (op1) => EmitShrImm64(context, op1, signed: true, roundConst, shift));
                }
            }
        }

        public static void Vshl(ArmEmitterContext context)
        {
            OpCode32SimdShImm op = (OpCode32SimdShImm)context.CurrOp;

            EmitVectorUnaryOpZx32(context, (op1) => context.ShiftLeft(op1, Const(op.Shift)));
        }

        public static void Vshl_I(ArmEmitterContext context)
        {
            OpCode32SimdReg op = (OpCode32SimdReg)context.CurrOp;

            if (op.U)
            {
                EmitVectorBinaryOpZx32(context, (op1, op2) => EmitShlRegOp(context, op2, op1, op.Size, true));
            }
            else
            {
                EmitVectorBinaryOpSx32(context, (op1, op2) => EmitShlRegOp(context, op2, op1, op.Size, false));
            }
        }

        public static void Vshr(ArmEmitterContext context)
        {
            OpCode32SimdShImm op = (OpCode32SimdShImm)context.CurrOp;
            int shift = GetImmShr(op);
            int maxShift = (8 << op.Size) - 1;

            if (op.U)
            {
                EmitVectorUnaryOpZx32(context, (op1) => (shift > maxShift) ? Const(op1.Type, 0) : context.ShiftRightUI(op1, Const(shift)));
            }
            else
            {
                EmitVectorUnaryOpSx32(context, (op1) => context.ShiftRightSI(op1, Const(Math.Min(maxShift, shift))));
            }
        }

        public static void Vshrn(ArmEmitterContext context)
        {
            OpCode32SimdShImm op = (OpCode32SimdShImm)context.CurrOp;
            int shift = GetImmShr(op);

            EmitVectorUnaryNarrowOp32(context, (op1) => context.ShiftRightUI(op1, Const(shift)));
        }

        private static Operand EmitShlRegOp(ArmEmitterContext context, Operand op, Operand shiftLsB, int size, bool unsigned)
        {
            if (shiftLsB.Type == OperandType.I64)
            {
                shiftLsB = context.ConvertI64ToI32(shiftLsB);
            }

            shiftLsB = context.SignExtend8(OperandType.I32, shiftLsB);
            Debug.Assert((uint)size < 4u);

            Operand negShiftLsB = context.Negate(shiftLsB);

            Operand isPositive = context.ICompareGreaterOrEqual(shiftLsB, Const(0));

            Operand shl = context.ShiftLeft(op, shiftLsB);
            Operand shr = unsigned ? context.ShiftRightUI(op, negShiftLsB) : context.ShiftRightSI(op, negShiftLsB);

            Operand res = context.ConditionalSelect(isPositive, shl, shr);

            if (unsigned)
            {
                Operand isOutOfRange = context.BitwiseOr(
                    context.ICompareGreaterOrEqual(shiftLsB, Const(8 << size)),
                    context.ICompareGreaterOrEqual(negShiftLsB, Const(8 << size)));

                return context.ConditionalSelect(isOutOfRange, Const(op.Type, 0), res);
            }
            else
            {
                Operand isOutOfRange0 = context.ICompareGreaterOrEqual(shiftLsB, Const(8 << size));
                Operand isOutOfRangeN = context.ICompareGreaterOrEqual(negShiftLsB, Const(8 << size));

                // Also zero if shift is too negative, but value was positive.
                isOutOfRange0 = context.BitwiseOr(isOutOfRange0, context.BitwiseAnd(isOutOfRangeN, context.ICompareGreaterOrEqual(op, Const(op.Type, 0))));

                Operand min = (op.Type == OperandType.I64) ? Const(-1L) : Const(-1);

                return context.ConditionalSelect(isOutOfRange0, Const(op.Type, 0), context.ConditionalSelect(isOutOfRangeN, min, res));
            }
        }

        [Flags]
        private enum ShrImmSaturatingNarrowFlags
        {
            Scalar = 1 << 0,
            SignedSrc = 1 << 1,
            SignedDst = 1 << 2,

            Round = 1 << 3,

            ScalarSxSx = Scalar | SignedSrc | SignedDst,
            ScalarSxZx = Scalar | SignedSrc,
            ScalarZxZx = Scalar,

            VectorSxSx = SignedSrc | SignedDst,
            VectorSxZx = SignedSrc,
            VectorZxZx = 0
        }

        private static void EmitRoundShrImmSaturatingNarrowOp(ArmEmitterContext context, ShrImmSaturatingNarrowFlags flags)
        {
            EmitShrImmSaturatingNarrowOp(context, ShrImmSaturatingNarrowFlags.Round | flags);
        }

        private static void EmitShrImmSaturatingNarrowOp(ArmEmitterContext context, ShrImmSaturatingNarrowFlags flags)
        {
            OpCode32SimdShImm op = (OpCode32SimdShImm)context.CurrOp;

            bool scalar    = (flags & ShrImmSaturatingNarrowFlags.Scalar)    != 0;
            bool signedSrc = (flags & ShrImmSaturatingNarrowFlags.SignedSrc) != 0;
            bool signedDst = (flags & ShrImmSaturatingNarrowFlags.SignedDst) != 0;
            bool round     = (flags & ShrImmSaturatingNarrowFlags.Round)     != 0;

            if (scalar)
            {
                // TODO: Support scalar operation.
                throw new NotImplementedException();
            }

            int shift = GetImmShr(op);
            long roundConst = 1L << (shift - 1);

            EmitVectorUnaryNarrowOp32(context, (op1) =>
            {
                if (op.Size <= 1 || !round)
                {
                    if (round)
                    {
                        op1 = context.Add(op1, Const(op1.Type, roundConst));
                    }

                    op1 = signedSrc ? context.ShiftRightSI(op1, Const(shift)) : context.ShiftRightUI(op1, Const(shift));
                }
                else /* if (op.Size == 2 && round) */
                {
                    op1 = EmitShrImm64(context, op1, signedSrc, roundConst, shift); // shift <= 32
                }

                return EmitSatQ(context, op1, 8 << op.Size, signedDst);
            }, signedSrc);
        }

        private static int GetImmShr(OpCode32SimdShImm op)
        {
            return (8 << op.Size) - op.Shift; // Shr amount is flipped.
        }

        // dst64 = (Int(src64, signed) + roundConst) >> shift;
        private static Operand EmitShrImm64(
            ArmEmitterContext context,
            Operand value,
            bool signed,
            long roundConst,
            int shift)
        {
            Delegate dlg = signed
                ? (Delegate)new _S64_S64_S64_S32(SoftFallback.SignedShrImm64)
                : (Delegate)new _U64_U64_S64_S32(SoftFallback.UnsignedShrImm64);

            return context.Call(dlg, value, Const(roundConst), Const(shift));
        }

        private static Operand EmitSatQ(ArmEmitterContext context, Operand value, int eSize, bool signed)
        {
            Debug.Assert(eSize <= 32);

            long intMin = signed ? -(1L << (eSize - 1)) : 0;
            long intMax = signed ? (1L << (eSize - 1)) - 1 : (1L << eSize) - 1;

            Operand gt = context.ICompareGreater(value, Const(value.Type, intMax));
            Operand lt = context.ICompareLess(value, Const(value.Type, intMin));

            value = context.ConditionalSelect(gt, Const(value.Type, intMax), value);
            value = context.ConditionalSelect(lt, Const(value.Type, intMin), value);

            Operand lblNoSat = Label();

            context.BranchIfFalse(lblNoSat, context.BitwiseOr(gt, lt));

            // TODO: Set QC (to 1) on FPSCR here.

            context.MarkLabel(lblNoSat);

            return value;
        }
    }
}