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package org.jruby.runtime.ivars;

import org.jruby.Ruby;
import org.jruby.RubyBasicObject;
import org.jruby.RubyClass;
import org.jruby.ir.operands.UndefinedValue;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.builtin.IRubyObject;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;

/**
 * Abstraction of an accessor for instance or internal variables on Ruby
 * objects. Subclasses specialize this implementation appropriate to the
 * current JVM's capabilities and the mechanism for laying out variables.
 */
public abstract class VariableAccessor {
    /** the name of the variable */
    protected final String name;
    /** the index allocated for it in the variable table */
    protected final int index;
    /** the symbol of the class associated with this variable */
    protected final int classId;
    /** the "real" class associated with this variable */
    protected final RubyClass realClass;

    static final VarHandle VAR_TABLE_HANDLE;
    static final VarHandle STAMP_HANDLE;
    static {
        VarHandle vth;
        try {
            vth = MethodHandles.lookup().findVarHandle(RubyBasicObject.class, "varTable", Object[].class);
        } catch (Throwable throwable) {
            throw new ExceptionInInitializerError(throwable);
        }
        VAR_TABLE_HANDLE = vth;

        VarHandle sh;
        try {
            sh = MethodHandles.lookup().findVarHandle(RubyBasicObject.class, "varTableStamp", byte.class);
        } catch (Throwable throwable) {
            throw new ExceptionInInitializerError(throwable);
        }
        STAMP_HANDLE = sh;
    }

    /**
     * Construct a new VariableAccessor for the given "real" class, name,
     * variable index, and class symbol.
     * 
     * @param realClass the "real" class
     * @param name the variable's name
     * @param index the variable's index
     * @param classId the class's symbol
     */
    public VariableAccessor(RubyClass realClass, String name, int index, int classId) {
        this.index = index;
        this.classId = classId;
        this.name = name;
        this.realClass = realClass;
    }

    /**
     * Get the symbol of the class associated with this variable.
     * 
     * @return this variable's class's id
     */
    public int getClassId() {
        return classId;
    }

    /**
     * Get the index allocated for this variable.
     * 
     * @return this variable's index
     */
    public int getIndex() {
        return index;
    }

    /**
     * Get the name of this variable.
     * 
     * @return this variable's name
     */
    public String getName() {
        return name;
    }

    /**
     * Retrieve the variable's value from the given object.
     * 
     * @param object the object from which to retrieve this variable
     * @return the variable's value
     */
    public Object get(Object object) {
        return getVariable((RubyBasicObject)object, index);
    }

    /**
     * Retrieve object or IR %undefined
     */
    public Object getOrUndefined(Object object) {
        Object value = get(object);
        return value == null ? UndefinedValue.UNDEFINED : value;
    }

    /**
     * Retrieve the variable's value from the given object.
     *
     * @param object the object from which to retrieve this variable
     * @return the variable's value
     */
    public IRubyObject getOrNil(Object object, ThreadContext context) {
        Object value = getVariable((RubyBasicObject) object, index);
        return value == null ? context.nil : (IRubyObject) value;
    }

    /**
     * Retrieve the variable's value from the given object. This version is
     * static, allowing it to be more direct, and accepts only
     * RubyBasicObject and subclasses along with the direct index of the
     * variable.
     * 
     * @param object the object from which to retrieve the variable
     * @param index the index of the variable
     * @return the variable's value
     */
    public static Object getVariable(RubyBasicObject object, int index) {
		Object[] ivarTable;
        if (index < 0 || (ivarTable = object.varTable) == null) return null;
        if (ivarTable.length > index) return ivarTable[index];
        return null;
    }

    /**
     * Set the value for this variable in the given object.
     * 
     * @param object the object into which to set this variable
     * @param value the value of the variable
     */
    public void set(Object object, Object value) {
        ((RubyBasicObject)object).checkFrozen();
        VariableTableManager.setVariableInternal(realClass, (RubyBasicObject)object, index, value);
    }

    /**
     * Verify if this is the correct accessor for the given object.
     *
     * @param object the object for which to test this accessor
     * @return true if this is the correct accessor for the given object, false otherwise
     */
    public boolean verify(Object object) {
        return ((RubyBasicObject)object).getMetaClass().getRealClass() == this.realClass;
    }

    /**
     * Produce a string representation of this VariableAccessor.
     *
     * @return a string representation of this VariableAccessor
     */
    @Override
    public String toString() {
        return "ivar:" + getName() + ":" + index;
    }

    public VariableAccessor cloneFor(RubyClass newRealClass) {
        throw new UnsupportedOperationException();
    }

    /** a dummy accessor that will always return null */
    public static final VariableAccessor DUMMY_ACCESSOR = new VariableAccessor(null, null, -1, -1) {};
    
}
