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 * Copyright (c) 2011, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */
package jdk.vm.ci.meta;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * Class for recording assumptions made during compilation.
 */
public final class Assumptions implements Iterable<Assumptions.Assumption> {

    /**
     * Abstract base class for assumptions. An assumption assumes a property of the runtime that may
     * be invalidated by subsequent execution (e.g., that a class has no subclasses implementing
     * {@link NoFinalizableSubclass Object.finalize()}).
     */
    public abstract static class Assumption {
    }

    /**
     * A class for providing information that is only valid in association with a set of
     * {@link Assumption}s. It is permissible for AssumptionResults to have no assumptions at all.
     * For instance, if {@link ResolvedJavaType#isLeaf()} returns true for a type
     * {@link ResolvedJavaType#findLeafConcreteSubtype()} can return an AssumptionResult with no
     * assumptions since the leaf information is statically true.
     *
     * @param <T>
     */
    public static class AssumptionResult<T> {
        Assumption[] assumptions;
        final T result;

        private static final Assumption[] EMPTY = new Assumption[0];

        public AssumptionResult(T result, Assumption... assumptions) {
            this.result = result;
            this.assumptions = assumptions;
        }

        public AssumptionResult(T result) {
            this(result, EMPTY);
        }

        public T getResult() {
            return result;
        }

        public boolean isAssumptionFree() {
            return assumptions.length == 0;
        }

        public void add(AssumptionResult<T> other) {
            Assumption[] newAssumptions = Arrays.copyOf(this.assumptions, this.assumptions.length + other.assumptions.length);
            System.arraycopy(other.assumptions, 0, newAssumptions, this.assumptions.length, other.assumptions.length);
            this.assumptions = newAssumptions;
        }

        public boolean canRecordTo(Assumptions target) {
            /*
             * We can use the result if it is either assumption free, or if we have a valid
             * Assumptions object where we can record assumptions.
             */
            return assumptions.length == 0 || target != null;
        }

        public void recordTo(Assumptions target) {
            assert canRecordTo(target);

            for (Assumption assumption : assumptions) {
                target.record(assumption);
            }
        }

        @Override
        public String toString() {
            return String.format("AssumptionResult<%s, assumptions=%s>", result, Arrays.toString(assumptions));
        }
    }

    /**
     * An assumption that a given class has no subclasses implementing {@code Object#finalize()}).
     */
    public static final class NoFinalizableSubclass extends Assumption {

        public final ResolvedJavaType receiverType;

        public NoFinalizableSubclass(ResolvedJavaType receiverType) {
            this.receiverType = receiverType;
        }

        @Override
        public int hashCode() {
            return 31 + receiverType.hashCode();
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof NoFinalizableSubclass) {
                NoFinalizableSubclass other = (NoFinalizableSubclass) obj;
                return other.receiverType.equals(receiverType);
            }
            return false;
        }

        @Override
        public String toString() {
            return "NoFinalizableSubclass[receiverType=" + receiverType.toJavaName() + "]";
        }

    }

    /**
     * An assumption that a given abstract or interface type has one direct concrete subtype. There
     * is no requirement that the subtype is a leaf type.
     */
    public static final class ConcreteSubtype extends Assumption {

        /**
         * Type the assumption is made about.
         */
        public final ResolvedJavaType context;

        /**
         * Assumed concrete sub-type of the context type.
         */
        public final ResolvedJavaType subtype;

        public ConcreteSubtype(ResolvedJavaType context, ResolvedJavaType subtype) {
            this.context = context;
            this.subtype = subtype;
            assert context.isAbstract();
            assert subtype.isConcrete() || context.isInterface() : subtype.toString() + " : " + context.toString();
            assert !subtype.isArray() || subtype.getElementalType().isFinalFlagSet() : subtype.toString() + " : " + context.toString();
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + context.hashCode();
            result = prime * result + subtype.hashCode();
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof ConcreteSubtype) {
                ConcreteSubtype other = (ConcreteSubtype) obj;
                return other.context.equals(context) && other.subtype.equals(subtype);
            }
            return false;
        }

        @Override
        public String toString() {
            return "ConcreteSubtype[context=" + context.toJavaName() + ", subtype=" + subtype.toJavaName() + "]";
        }
    }

    /**
     * An assumption that a given type has no subtypes.
     */
    public static final class LeafType extends Assumption {

        /**
         * Type the assumption is made about.
         */
        public final ResolvedJavaType context;

        public LeafType(ResolvedJavaType context) {
            assert !context.isLeaf() : "assumption isn't required for leaf types";
            this.context = context;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + context.hashCode();
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof LeafType) {
                LeafType other = (LeafType) obj;
                return other.context.equals(context);
            }
            return false;
        }

        @Override
        public String toString() {
            return "LeafSubtype[context=" + context.toJavaName() + "]";
        }
    }

    /**
     * An assumption that a given virtual method has a given unique implementation.
     */
    public static final class ConcreteMethod extends Assumption {

        /**
         * A virtual (or interface) method whose unique implementation for the receiver type in
         * {@link #context} is {@link #impl}.
         */
        public final ResolvedJavaMethod method;

        /**
         * A receiver type.
         */
        public final ResolvedJavaType context;

        /**
         * The unique implementation of {@link #method} for {@link #context}.
         */
        public final ResolvedJavaMethod impl;

        public ConcreteMethod(ResolvedJavaMethod method, ResolvedJavaType context, ResolvedJavaMethod impl) {
            this.method = method;
            this.context = context;
            this.impl = impl;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + method.hashCode();
            result = prime * result + context.hashCode();
            result = prime * result + impl.hashCode();
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof ConcreteMethod) {
                ConcreteMethod other = (ConcreteMethod) obj;
                return other.method.equals(method) && other.context.equals(context) && other.impl.equals(impl);
            }
            return false;
        }

        @Override
        public String toString() {
            return "ConcreteMethod[method=" + method.format("%H.%n(%p)%r") + ", context=" + context.toJavaName() + ", impl=" + impl.format("%H.%n(%p)%r") + "]";
        }
    }

    /**
     * An assumption that a given call site's method handle did not change.
     */
    public static final class CallSiteTargetValue extends Assumption {

        public final JavaConstant callSite;
        public final JavaConstant methodHandle;

        public CallSiteTargetValue(JavaConstant callSite, JavaConstant methodHandle) {
            this.callSite = callSite;
            this.methodHandle = methodHandle;
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + callSite.hashCode();
            result = prime * result + methodHandle.hashCode();
            return result;
        }

        @Override
        public boolean equals(Object obj) {
            if (obj instanceof CallSiteTargetValue) {
                CallSiteTargetValue other = (CallSiteTargetValue) obj;
                return callSite.equals(other.callSite) && methodHandle.equals(other.methodHandle);
            }
            return false;
        }

        @Override
        public String toString() {
            return "CallSiteTargetValue[callSite=" + callSite + ", methodHandle=" + methodHandle + "]";
        }
    }

    private final Set<Assumption> assumptions = new HashSet<>();

    /**
     * Returns whether any assumptions have been registered.
     *
     * @return {@code true} if at least one assumption has been registered, {@code false} otherwise.
     */
    public boolean isEmpty() {
        return assumptions.isEmpty();
    }

    @Override
    public int hashCode() {
        throw new UnsupportedOperationException("hashCode");
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj instanceof Assumptions) {
            Assumptions that = (Assumptions) obj;
            if (!this.assumptions.equals(that.assumptions)) {
                return false;
            }
            return true;
        }
        return false;
    }

    @Override
    public Iterator<Assumption> iterator() {
        return assumptions.iterator();
    }

    /**
     * Records an assumption that the specified type has no finalizable subclasses.
     *
     * @param receiverType the type that is assumed to have no finalizable subclasses
     */
    public void recordNoFinalizableSubclassAssumption(ResolvedJavaType receiverType) {
        record(new NoFinalizableSubclass(receiverType));
    }

    /**
     * Records that {@code subtype} is the only concrete subtype in the class hierarchy below
     * {@code context}.
     *
     * @param context the root of the subtree of the class hierarchy that this assumptions is about
     * @param subtype the one concrete subtype
     */
    public void recordConcreteSubtype(ResolvedJavaType context, ResolvedJavaType subtype) {
        record(new ConcreteSubtype(context, subtype));
    }

    /**
     * Records that {@code impl} is the only possible concrete target for a virtual call to
     * {@code method} with a receiver of type {@code context}.
     *
     * @param method a method that is the target of a virtual call
     * @param context the receiver type of a call to {@code method}
     * @param impl the concrete method that is the only possible target for the virtual call
     */
    public void recordConcreteMethod(ResolvedJavaMethod method, ResolvedJavaType context, ResolvedJavaMethod impl) {
        record(new ConcreteMethod(method, context, impl));
    }

    public void record(Assumption assumption) {
        assumptions.add(assumption);
    }

    /**
     * Gets a copy of the assumptions recorded in this object as an array.
     */
    public Assumption[] toArray() {
        return assumptions.toArray(new Assumption[assumptions.size()]);
    }

    /**
     * Copies assumptions recorded by another {@link Assumptions} object into this object.
     */
    public void record(Assumptions other) {
        assert other != this;
        assumptions.addAll(other.assumptions);
    }

    @Override
    public String toString() {
        return "Assumptions[" + assumptions + "]";
    }
}
