// Copyright (c) 2018, the R8 project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
package com.android.tools.r8.ir.code;

import com.android.tools.r8.cf.LoadStoreHelper;
import com.android.tools.r8.errors.Unimplemented;
import com.android.tools.r8.errors.Unreachable;
import com.android.tools.r8.graph.AppInfo;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.ir.analysis.type.TypeLatticeElement;
import com.android.tools.r8.ir.code.Assume.Assumption;
import com.android.tools.r8.ir.conversion.CfBuilder;
import com.android.tools.r8.ir.conversion.DexBuilder;
import com.android.tools.r8.ir.optimize.Inliner.ConstraintWithTarget;
import com.android.tools.r8.ir.optimize.InliningConstraints;

public class Assume<An extends Assumption> extends Instruction {

  private static final String ERROR_MESSAGE =
      "Expected Assume instructions to be removed after IR processing.";

  private final An assumption;
  private final Instruction origin;

  private Assume(An assumption, Value dest, Value src, Instruction origin) {
    super(dest, src);
    assert assumption != null;
    assert assumption.verifyCorrectnessOfValues(dest, src);
    this.assumption = assumption;
    this.origin = origin;
  }

  public static Assume<NonNullAssumption> createAssumeNonNullInstruction(
      Value dest, Value src, Instruction origin) {
    return new Assume<>(NonNullAssumption.get(), dest, src, origin);
  }

  @Override
  public <T> T accept(InstructionVisitor<T> visitor) {
    return visitor.visit(this);
  }

  public Value dest() {
    return outValue;
  }

  public Value src() {
    return inValues.get(0);
  }

  public Instruction origin() {
    return origin;
  }

  @Override
  public boolean isAssume() {
    return true;
  }

  @Override
  public Assume<An> asAssume() {
    return this;
  }

  @Override
  public boolean isAssumeNonNull() {
    return assumption.isAssumeNonNull();
  }

  @Override
  public Assume<NonNullAssumption> asAssumeNonNull() {
    assert isAssumeNonNull();
    @SuppressWarnings("unchecked")
    Assume<NonNullAssumption> self = (Assume<NonNullAssumption>) this;
    return self;
  }

  @Override
  public boolean isIntroducingAnAlias() {
    return true;
  }

  @Override
  public boolean couldIntroduceAnAlias() {
    return true;
  }

  @Override
  public Value getAliasForOutValue() {
    return src();
  }

  @Override
  public void buildDex(DexBuilder builder) {
    throw new Unreachable(ERROR_MESSAGE);
  }

  @Override
  public void buildCf(CfBuilder builder) {
    throw new Unreachable(ERROR_MESSAGE);
  }

  @Override
  public int maxInValueRegister() {
    throw new Unreachable(ERROR_MESSAGE);
  }

  @Override
  public int maxOutValueRegister() {
    throw new Unreachable(ERROR_MESSAGE);
  }

  @Override
  public boolean isOutConstant() {
    return false;
  }

  @Override
  public boolean identicalNonValueNonPositionParts(Instruction other) {
    if (!other.isAssume()) {
      return false;
    }
    Assume<?> assumeInstruction = other.asAssume();
    return assumption.equals(assumeInstruction.assumption);
  }

  @Override
  public ConstraintWithTarget inliningConstraint(
      InliningConstraints inliningConstraints, DexType invocationContext) {
    return inliningConstraints.forAssume();
  }

  @Override
  public TypeLatticeElement evaluate(AppView<? extends AppInfo> appView) {
    if (assumption.isAssumeNonNull()) {
      assert src().getTypeLattice().isReference();
      return src().getTypeLattice().asReferenceTypeLatticeElement().asNotNull();
    }
    throw new Unimplemented();
  }

  @Override
  public boolean hasInvariantOutType() {
    return false;
  }

  @Override
  public void insertLoadAndStores(InstructionListIterator it, LoadStoreHelper helper) {
    throw new Unreachable(ERROR_MESSAGE);
  }

  abstract static class Assumption {

    public boolean isAssumeNonNull() {
      return false;
    }

    public boolean verifyCorrectnessOfValues(Value dest, Value src) {
      return true;
    }
  }

  public static class NonNullAssumption extends Assumption {

    private static final NonNullAssumption instance = new NonNullAssumption();

    private NonNullAssumption() {}

    public static NonNullAssumption get() {
      return instance;
    }

    @Override
    public boolean isAssumeNonNull() {
      return true;
    }

    @Override
    public boolean verifyCorrectnessOfValues(Value dest, Value src) {
      assert !src.isNeverNull();
      return true;
    }
  }
}