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package org.graalvm.compiler.nodes.graphbuilderconf;

import static org.graalvm.compiler.nodes.graphbuilderconf.InvocationPlugins.resolveType;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.stream.Collectors;

import org.graalvm.compiler.bytecode.BytecodeProvider;
import org.graalvm.compiler.debug.GraalError;
import org.graalvm.compiler.nodes.ValueNode;

import jdk.vm.ci.meta.MetaAccessProvider;
import jdk.vm.ci.meta.ResolvedJavaMethod;

An InvocationPlugin for a method where the implementation of the method is provided by a substitute method. A substitute method must be static even if the substituted method is not. While performing intrinsification with method substitutions is simpler than writing an InvocationPlugin that does manual graph weaving, it has a higher compile time cost than the latter; parsing bytecodes to create nodes is slower than simply creating nodes. As such, the recommended practice is to use MethodSubstitutionPlugin only for complex intrinsifications which is typically those using non-straight-line control flow. /**
 * An {@link InvocationPlugin} for a method where the implementation of the method is provided by a
 * {@linkplain #getSubstitute(MetaAccessProvider) substitute} method. A substitute method must be
 * static even if the substituted method is not.
 *
 * While performing intrinsification with method substitutions is simpler than writing an
 * {@link InvocationPlugin} that does manual graph weaving, it has a higher compile time cost than
 * the latter; parsing bytecodes to create nodes is slower than simply creating nodes. As such, the
 * recommended practice is to use {@link MethodSubstitutionPlugin} only for complex
 * intrinsifications which is typically those using non-straight-line control flow.
 */
public final class MethodSubstitutionPlugin implements InvocationPlugin {

    private ResolvedJavaMethod cachedSubstitute;

    
The class in which the substitute method is declared.
/**
     * The class in which the substitute method is declared.
     */
    private final Class<?> declaringClass;

    
The name of the original and substitute method.
/**
     * The name of the original and substitute method.
     */
    private final String name;

    
The parameter types of the substitute method.
/**
     * The parameter types of the substitute method.
     */
    private final Type[] parameters;

    private final boolean originalIsStatic;

    private final BytecodeProvider bytecodeProvider;

    
Creates a method substitution plugin.
Params:
bytecodeProvider – used to get the bytecodes to parse for the substitute method
declaringClass – the class in which the substitute method is declared
name – the name of the substitute method
parameters – the parameter types of the substitute method. If the original method is not static, then parameters[0] must be the Class value denoting Receiver/**
     * Creates a method substitution plugin.
     *
     * @param bytecodeProvider used to get the bytecodes to parse for the substitute method
     * @param declaringClass the class in which the substitute method is declared
     * @param name the name of the substitute method
     * @param parameters the parameter types of the substitute method. If the original method is not
     *            static, then {@code parameters[0]} must be the {@link Class} value denoting
     *            {@link InvocationPlugin.Receiver}
     */
    public MethodSubstitutionPlugin(BytecodeProvider bytecodeProvider, Class<?> declaringClass, String name, Type... parameters) {
        this.bytecodeProvider = bytecodeProvider;
        this.declaringClass = declaringClass;
        this.name = name;
        this.parameters = parameters;
        this.originalIsStatic = parameters.length == 0 || parameters[0] != InvocationPlugin.Receiver.class;
    }

    @Override
    public boolean inlineOnly() {
        // Conservatively assume MacroNodes may be used in a substitution
        return true;
    }

    
Gets the substitute method, resolving it first if necessary.
/**
     * Gets the substitute method, resolving it first if necessary.
     */
    public ResolvedJavaMethod getSubstitute(MetaAccessProvider metaAccess) {
        if (cachedSubstitute == null) {
            cachedSubstitute = metaAccess.lookupJavaMethod(getJavaSubstitute());
        }
        return cachedSubstitute;
    }

    
Gets the object used to access the bytecodes of the substitute method.
/**
     * Gets the object used to access the bytecodes of the substitute method.
     */
    public BytecodeProvider getBytecodeProvider() {
        return bytecodeProvider;
    }

    
Gets the reflection API version of the substitution method.
/**
     * Gets the reflection API version of the substitution method.
     */
    Method getJavaSubstitute() throws GraalError {
        Method substituteMethod = lookupSubstitute();
        int modifiers = substituteMethod.getModifiers();
        if (Modifier.isAbstract(modifiers) || Modifier.isNative(modifiers)) {
            throw new GraalError("Substitution method must not be abstract or native: " + substituteMethod);
        }
        if (!Modifier.isStatic(modifiers)) {
            throw new GraalError("Substitution method must be static: " + substituteMethod);
        }
        return substituteMethod;
    }

    
Determines if a given method is the substitute method of this plugin.
/**
     * Determines if a given method is the substitute method of this plugin.
     */
    private boolean isSubstitute(Method m) {
        if (Modifier.isStatic(m.getModifiers()) && m.getName().equals(name)) {
            if (parameters.length == m.getParameterCount()) {
                Class<?>[] mparams = m.getParameterTypes();
                int start = 0;
                if (!originalIsStatic) {
                    start = 1;
                    if (!mparams[0].isAssignableFrom(resolveType(parameters[0], false))) {
                        return false;
                    }
                }
                for (int i = start; i < mparams.length; i++) {
                    if (mparams[i] != resolveType(parameters[i], false)) {
                        return false;
                    }
                }
                return true;
            }
        }
        return false;
    }

    private Method lookupSubstitute(Method excluding) {
        for (Method m : declaringClass.getDeclaredMethods()) {
            if (!m.equals(excluding) && isSubstitute(m)) {
                return m;
            }
        }
        return null;
    }

    
Gets the substitute method of this plugin.
/**
     * Gets the substitute method of this plugin.
     */
    private Method lookupSubstitute() {
        Method m = lookupSubstitute(null);
        if (m != null) {
            assert lookupSubstitute(m) == null : String.format("multiple matches found for %s:%n%s%n%s", this, m, lookupSubstitute(m));
            return m;
        }
        throw new GraalError("No method found specified by %s", this);
    }

    @Override
    public boolean execute(GraphBuilderContext b, ResolvedJavaMethod targetMethod, InvocationPlugin.Receiver receiver, ValueNode[] argsIncludingReceiver) {
        ResolvedJavaMethod subst = getSubstitute(b.getMetaAccess());
        return b.intrinsify(bytecodeProvider, targetMethod, subst, receiver, argsIncludingReceiver);
    }

    @Override
    public StackTraceElement getApplySourceLocation(MetaAccessProvider metaAccess) {
        Class<?> c = getClass();
        for (Method m : c.getDeclaredMethods()) {
            if (m.getName().equals("execute")) {
                return metaAccess.lookupJavaMethod(m).asStackTraceElement(0);
            }
        }
        throw new GraalError("could not find method named \"execute\" in " + c.getName());
    }

    @Override
    public String toString() {
        return String.format("%s[%s.%s(%s)]", getClass().getSimpleName(), declaringClass.getName(), name,
                        Arrays.asList(parameters).stream().map(c -> c.getTypeName()).collect(Collectors.joining(", ")));
    }
}