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/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2016-2023 Objectionary.com
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package org.eolang.opeo.decompilation.agents;

import org.eolang.opeo.decompilation.DecompilerState;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;

/**
 * Instruction handler.
 * This handler might understand the following instructions:
 * aload: 1: index | → objectref | load a reference onto the stack from a local variable #index
 * aload_0: → objectref | load a reference onto the stack from local variable 0
 * ...
 * @since 0.1
 */
public final class LoadAgent implements DecompilationAgent {

    /**
     * Supported opcodes.
     */
    private static final Supported OPCODES = new Supported(
        Opcodes.ILOAD,
        Opcodes.LLOAD,
        Opcodes.FLOAD,
        Opcodes.DLOAD,
        Opcodes.ALOAD
    );

    @Override
    public boolean appropriate(final DecompilerState state) {
        return new OpcodesAgent(this).appropriate(state);
    }

    @Override
    public Supported supported() {
        return LoadAgent.OPCODES;
    }

    @Override
    public void handle(final DecompilerState state) {
        if (this.appropriate(state)) {
            final int opcode = state.current().opcode();
            final Integer index = (Integer) state.operand(0);
            state.stack().push(
                state.variable(index, LoadAgent.type(opcode))
            );
            state.popInstruction();
        } else {
            throw new IllegalAgentException(this, state);
        }
    }

    /**
     * Infer type from opcode.
     * @param opcode Opcode
     * @return Type
     */
    private static Type type(final int opcode) {
        final Type result;
        switch (opcode) {
            case Opcodes.ILOAD:
                result = Type.INT_TYPE;
                break;
            case Opcodes.LLOAD:
                result = Type.LONG_TYPE;
                break;
            case Opcodes.FLOAD:
                result = Type.FLOAT_TYPE;
                break;
            case Opcodes.DLOAD:
                result = Type.DOUBLE_TYPE;
                break;
            case Opcodes.ALOAD:
                result = Type.getType(Object.class);
                break;
            default:
                throw new IllegalArgumentException(
                    String.format("Unsupported opcode: %d", opcode)
                );
        }
        return result;
    }
}