gson-compile/gson-compile-processor/src/main/java/io/gitlab/jfronny/gson/compile/processor/TypeHelper.java

package io.gitlab.jfronny.gson.compile.processor;

import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;
import javax.lang.model.type.*;
import javax.lang.model.util.*;
import java.util.*;

public class TypeHelper {
    public static boolean isComplexType(TypeMirror type, Types typeUtils) {
        Element element = typeUtils.asElement(type);
        if (!(element instanceof TypeElement typeElement)) return false;
        return !typeElement.typeParameters.isEmpty;
    }

    public static boolean isGenericType(TypeMirror type) {
        return type.kind == TypeKind.TYPEVAR;
    }

    public static List<? extends TypeMirror> getGenericTypes(TypeMirror type) {
        DeclaredType declaredType = asDeclaredType(type);
        if (declaredType == null) {
            return Collections.emptyList();
        }
        ArrayList<TypeMirror> result = new ArrayList<>();
        for (TypeMirror argType : declaredType.typeArguments) {
            if (argType.kind == TypeKind.TYPEVAR) {
                result.add(argType);
            }
        }
        return result;
    }

    public static DeclaredType asDeclaredType(TypeMirror type) {
        return type.accept(new SimpleTypeVisitor14<>() {
            @Override
            public DeclaredType visitDeclared(DeclaredType t, Object o) {
                return t;
            }
        }, null);
    }

    public static ArrayType asArrayType(TypeMirror type) {
        return type.accept(new TypeKindVisitor14<>() {
            @Override
            public ArrayType visitArray(ArrayType t, Object o) {
                return t;
            }
        }, null);
    }

    public static boolean isInstance(DeclaredType type, String parentClassName, Types typeUtils) {
        if (type == null) return false;
        TypeElement element = (TypeElement) type.asElement();
        for (TypeMirror interfaceType : element.interfaces) {
            if (typeUtils.erasure(interfaceType).toString().equals(parentClassName)) return true;
        }
        TypeMirror superclassType = element.superclass;
        if (superclassType != null) {
            if (typeUtils.erasure(superclassType).toString().equals(parentClassName)) {
                return true;
            } else {
                return isInstance(asDeclaredType(superclassType), parentClassName, typeUtils);
            }
        }
        return false;
    }

    static String getDefaultValue(TypeMirror type) {
        return switch (type.kind) {
            case BYTE, SHORT, INT, LONG, FLOAT, CHAR, DOUBLE -> "0";
            case BOOLEAN -> "false";
            default -> "null";
        };
    }
}