// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
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// modification, are permitted provided that the following conditions
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// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
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//    this software without specific prior written permission.
//
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package net.hasor.utils.asm.signature;
import net.hasor.utils.asm.Opcodes;

/**
 * A SignatureVisitor that generates signature literals, as defined in the Java Virtual Machine
 * Specification (JVMS).
 *
 * @see <a href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.9.1">JVMS 4.7.9.1</a>
 * @author Thomas Hallgren
 * @author Eric Bruneton
 */
public class SignatureWriter extends SignatureVisitor {
    /** The builder used to construct the visited signature. */
    private final StringBuilder stringBuilder = new StringBuilder();
    /** Whether the visited signature contains formal type parameters. */
    private       boolean       hasFormals;
    /** Whether the visited signature contains method parameter types. */
    private       boolean       hasParameters;
    /**
     * The stack used to keep track of class types that have arguments. Each element of this stack is
     * a boolean encoded in one bit. The top of the stack is the least significant bit. Pushing false
     * = *2, pushing true = *2+1, popping = /2.
     *
     * <p>Class type arguments must be surrounded with '&lt;' and '&gt;' and, because
     *
     * <ol>
     *   <li>class types can be nested (because type arguments can themselves be class types),
     *   <li>SignatureWriter always returns 'this' in each visit* method (to avoid allocating new
     *       SignatureWriter instances),
     * </ol>
     *
     * <p>we need a stack to properly balance these 'parentheses'. A new element is pushed on this
     * stack for each new visited type, and popped when the visit of this type ends (either is
     * visitEnd, or because visitInnerClassType is called).
     */
    private       int           argumentStack;

    /** Constructs a new {@link SignatureWriter}. */
    public SignatureWriter() {
        super(Opcodes.ASM7);
    }
    // -----------------------------------------------------------------------------------------------
    // Implementation of the SignatureVisitor interface
    // -----------------------------------------------------------------------------------------------

    @Override
    public void visitFormalTypeParameter(final String name) {
        if (!hasFormals) {
            hasFormals = true;
            stringBuilder.append('<');
        }
        stringBuilder.append(name);
        stringBuilder.append(':');
    }

    @Override
    public SignatureVisitor visitClassBound() {
        return this;
    }

    @Override
    public SignatureVisitor visitInterfaceBound() {
        stringBuilder.append(':');
        return this;
    }

    @Override
    public SignatureVisitor visitSuperclass() {
        endFormals();
        return this;
    }

    @Override
    public SignatureVisitor visitInterface() {
        return this;
    }

    @Override
    public SignatureVisitor visitParameterType() {
        endFormals();
        if (!hasParameters) {
            hasParameters = true;
            stringBuilder.append('(');
        }
        return this;
    }

    @Override
    public SignatureVisitor visitReturnType() {
        endFormals();
        if (!hasParameters) {
            stringBuilder.append('(');
        }
        stringBuilder.append(')');
        return this;
    }

    @Override
    public SignatureVisitor visitExceptionType() {
        stringBuilder.append('^');
        return this;
    }

    @Override
    public void visitBaseType(final char descriptor) {
        stringBuilder.append(descriptor);
    }

    @Override
    public void visitTypeVariable(final String name) {
        stringBuilder.append('T');
        stringBuilder.append(name);
        stringBuilder.append(';');
    }

    @Override
    public SignatureVisitor visitArrayType() {
        stringBuilder.append('[');
        return this;
    }

    @Override
    public void visitClassType(final String name) {
        stringBuilder.append('L');
        stringBuilder.append(name);
        // Pushes 'false' on the stack, meaning that this type does not have type arguments (as far as
        // we can tell at this point).
        argumentStack *= 2;
    }

    @Override
    public void visitInnerClassType(final String name) {
        endArguments();
        stringBuilder.append('.');
        stringBuilder.append(name);
        // Pushes 'false' on the stack, meaning that this type does not have type arguments (as far as
        // we can tell at this point).
        argumentStack *= 2;
    }

    @Override
    public void visitTypeArgument() {
        // If the top of the stack is 'false', this means we are visiting the first type argument of the
        // currently visited type. We therefore need to append a '<', and to replace the top stack
        // element with 'true' (meaning that the current type does have type arguments).
        if (argumentStack % 2 == 0) {
            argumentStack |= 1;
            stringBuilder.append('<');
        }
        stringBuilder.append('*');
    }

    @Override
    public SignatureVisitor visitTypeArgument(final char wildcard) {
        // If the top of the stack is 'false', this means we are visiting the first type argument of the
        // currently visited type. We therefore need to append a '<', and to replace the top stack
        // element with 'true' (meaning that the current type does have type arguments).
        if (argumentStack % 2 == 0) {
            argumentStack |= 1;
            stringBuilder.append('<');
        }
        if (wildcard != '=') {
            stringBuilder.append(wildcard);
        }
        return this;
    }

    @Override
    public void visitEnd() {
        endArguments();
        stringBuilder.append(';');
    }

    /**
     * Returns the signature that was built by this signature writer.
     *
     * @return the signature that was built by this signature writer.
     */
    @Override
    public String toString() {
        return stringBuilder.toString();
    }
    // -----------------------------------------------------------------------------------------------
    // Utility methods
    // -----------------------------------------------------------------------------------------------

    /** Ends the formal type parameters section of the signature. */
    private void endFormals() {
        if (hasFormals) {
            hasFormals = false;
            stringBuilder.append('>');
        }
    }

    /** Ends the type arguments of a class or inner class type. */
    private void endArguments() {
        // If the top of the stack is 'true', this means that some type arguments have been visited for
        // the type whose visit is now ending. We therefore need to append a '>', and to pop one element
        // from the stack.
        if (argumentStack % 2 == 1) {
            stringBuilder.append('>');
        }
        argumentStack /= 2;
    }
}
