// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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//
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package net.hasor.utils.asm.signature;
/**
 * A parser for signature literals, as defined in the Java Virtual Machine Specification (JVMS), to
 * visit them with a SignatureVisitor.
 *
 * @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 SignatureReader {
    /** The JVMS signature to be read. */
    private final String signatureValue;

    /**
     * Constructs a {@link SignatureReader} for the given signature.
     *
     * @param signature A <i>JavaTypeSignature</i>, <i>ClassSignature</i> or <i>MethodSignature</i>.
     */
    public SignatureReader(final String signature) {
        this.signatureValue = signature;
    }

    /**
     * Makes the given visitor visit the signature of this {@link SignatureReader}. This signature is
     * the one specified in the constructor (see {@link #SignatureReader}). This method is intended to
     * be called on a {@link SignatureReader} that was created using a <i>ClassSignature</i> (such as
     * the <code>signature</code> parameter of the {@link net.hasor.utils.asm.ClassVisitor#visit}
     * method) or a <i>MethodSignature</i> (such as the <code>signature</code> parameter of the {@link
     * net.hasor.utils.asm.ClassVisitor#visitMethod} method).
     *
     * @param signatureVistor the visitor that must visit this signature.
     */
    public void accept(final SignatureVisitor signatureVistor) {
        String signature = this.signatureValue;
        int length = signature.length();
        int offset; // Current offset in the parsed signature (parsed from left to right).
        char currentChar; // The signature character at 'offset', or just before.
        // If the signature starts with '<', it starts with TypeParameters, i.e. a formal type parameter
        // identifier, followed by one or more pair ':',ReferenceTypeSignature (for its class bound and
        // interface bounds).
        if (signature.charAt(0) == '<') {
            // Invariant: offset points to the second character of a formal type parameter name at the
            // beginning of each iteration of the loop below.
            offset = 2;
            do {
                // The formal type parameter name is everything between offset - 1 and the first ':'.
                int classBoundStartOffset = signature.indexOf(':', offset);
                signatureVistor.visitFormalTypeParameter(signature.substring(offset - 1, classBoundStartOffset));
                // If the character after the ':' class bound marker is not the start of a
                // ReferenceTypeSignature, it means the class bound is empty (which is a valid case).
                offset = classBoundStartOffset + 1;
                currentChar = signature.charAt(offset);
                if (currentChar == 'L' || currentChar == '[' || currentChar == 'T') {
                    offset = parseType(signature, offset, signatureVistor.visitClassBound());
                }
                // While the character after the class bound or after the last parsed interface bound
                // is ':', we need to parse another interface bound.
                while ((currentChar = signature.charAt(offset++)) == ':') {
                    offset = parseType(signature, offset, signatureVistor.visitInterfaceBound());
                }
                // At this point a TypeParameter has been fully parsed, and we need to parse the next one
                // (note that currentChar is now the first character of the next TypeParameter, and that
                // offset points to the second character), unless the character just after this
                // TypeParameter signals the end of the TypeParameters.
            } while (currentChar != '>');
        } else {
            offset = 0;
        }
        // If the (optional) TypeParameters is followed by '(' this means we are parsing a
        // MethodSignature, which has JavaTypeSignature type inside parentheses, followed by a Result
        // type and optional ThrowsSignature types.
        if (signature.charAt(offset) == '(') {
            offset++;
            while (signature.charAt(offset) != ')') {
                offset = parseType(signature, offset, signatureVistor.visitParameterType());
            }
            // Use offset + 1 to skip ')'.
            offset = parseType(signature, offset + 1, signatureVistor.visitReturnType());
            while (offset < length) {
                // Use offset + 1 to skip the first character of a ThrowsSignature, i.e. '^'.
                offset = parseType(signature, offset + 1, signatureVistor.visitExceptionType());
            }
        } else {
            // Otherwise we are parsing a ClassSignature (by hypothesis on the method input), which has
            // one or more ClassTypeSignature for the super class and the implemented interfaces.
            offset = parseType(signature, offset, signatureVistor.visitSuperclass());
            while (offset < length) {
                offset = parseType(signature, offset, signatureVistor.visitInterface());
            }
        }
    }

    /**
     * Makes the given visitor visit the signature of this {@link SignatureReader}. This signature is
     * the one specified in the constructor (see {@link #SignatureReader}). This method is intended to
     * be called on a {@link SignatureReader} that was created using a <i>JavaTypeSignature</i>, such
     * as the <code>signature</code> parameter of the {@link
     * net.hasor.utils.asm.ClassVisitor#visitField} or {@link
     * net.hasor.utils.asm.MethodVisitor#visitLocalVariable} methods.
     *
     * @param signatureVisitor the visitor that must visit this signature.
     */
    public void acceptType(final SignatureVisitor signatureVisitor) {
        parseType(signatureValue, 0, signatureVisitor);
    }

    /**
     * Parses a JavaTypeSignature and makes the given visitor visit it.
     *
     * @param signature a string containing the signature that must be parsed.
     * @param startOffset index of the first character of the signature to parsed.
     * @param signatureVisitor the visitor that must visit this signature.
     * @return the index of the first character after the parsed signature.
     */
    private static int parseType(final String signature, final int startOffset, final SignatureVisitor signatureVisitor) {
        int offset = startOffset; // Current offset in the parsed signature.
        char currentChar = signature.charAt(offset++); // The signature character at 'offset'.
        // Switch based on the first character of the JavaTypeSignature, which indicates its kind.
        switch (currentChar) {
        case 'Z':
        case 'C':
        case 'B':
        case 'S':
        case 'I':
        case 'F':
        case 'J':
        case 'D':
        case 'V':
            // Case of a BaseType or a VoidDescriptor.
            signatureVisitor.visitBaseType(currentChar);
            return offset;
        case '[':
            // Case of an ArrayTypeSignature, a '[' followed by a JavaTypeSignature.
            return parseType(signature, offset, signatureVisitor.visitArrayType());
        case 'T':
            // Case of TypeVariableSignature, an identifier between 'T' and ';'.
            int endOffset = signature.indexOf(';', offset);
            signatureVisitor.visitTypeVariable(signature.substring(offset, endOffset));
            return endOffset + 1;
        case 'L':
            // Case of a ClassTypeSignature, which ends with ';'.
            // These signatures have a main class type followed by zero or more inner class types
            // (separated by '.'). Each can have type arguments, inside '<' and '>'.
            int start = offset; // The start offset of the currently parsed main or inner class name.
            boolean visited = false; // Whether the currently parsed class name has been visited.
            boolean inner = false; // Whether we are currently parsing an inner class type.
            // Parses the signature, one character at a time.
            while (true) {
                currentChar = signature.charAt(offset++);
                if (currentChar == '.' || currentChar == ';') {
                    // If a '.' or ';' is encountered, this means we have fully parsed the main class name
                    // or an inner class name. This name may already have been visited it is was followed by
                    // type arguments between '<' and '>'. If not, we need to visit it here.
                    if (!visited) {
                        String name = signature.substring(start, offset - 1);
                        if (inner) {
                            signatureVisitor.visitInnerClassType(name);
                        } else {
                            signatureVisitor.visitClassType(name);
                        }
                    }
                    // If we reached the end of the ClassTypeSignature return, otherwise start the parsing
                    // of a new class name, which is necessarily an inner class name.
                    if (currentChar == ';') {
                        signatureVisitor.visitEnd();
                        break;
                    }
                    start = offset;
                    visited = false;
                    inner = true;
                } else if (currentChar == '<') {
                    // If a '<' is encountered, this means we have fully parsed the main class name or an
                    // inner class name, and that we now need to parse TypeArguments. First, we need to
                    // visit the parsed class name.
                    String name = signature.substring(start, offset - 1);
                    if (inner) {
                        signatureVisitor.visitInnerClassType(name);
                    } else {
                        signatureVisitor.visitClassType(name);
                    }
                    visited = true;
                    // Now, parse the TypeArgument(s), one at a time.
                    while ((currentChar = signature.charAt(offset)) != '>') {
                        switch (currentChar) {
                        case '*':
                            // Unbounded TypeArgument.
                            ++offset;
                            signatureVisitor.visitTypeArgument();
                            break;
                        case '+':
                        case '-':
                            // Extends or Super TypeArgument. Use offset + 1 to skip the '+' or '-'.
                            offset = parseType(signature, offset + 1, signatureVisitor.visitTypeArgument(currentChar));
                            break;
                        default:
                            // Instanceof TypeArgument. The '=' is implicit.
                            offset = parseType(signature, offset, signatureVisitor.visitTypeArgument('='));
                            break;
                        }
                    }
                }
            }
            return offset;
        default:
            throw new IllegalArgumentException();
        }
    }
}
