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Simple library for generating code.
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [https://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see .
 */
package org.neo4j.codegen;

import static java.lang.String.format;
import static java.util.Arrays.stream;
import static org.neo4j.codegen.TypeReference.BOOLEAN;
import static org.neo4j.codegen.TypeReference.DOUBLE;
import static org.neo4j.codegen.TypeReference.INT;
import static org.neo4j.codegen.TypeReference.LONG;
import static org.neo4j.codegen.TypeReference.OBJECT;
import static org.neo4j.codegen.TypeReference.VALUE;
import static org.neo4j.codegen.TypeReference.VOID;
import static org.neo4j.codegen.TypeReference.arrayOf;
import static org.neo4j.codegen.TypeReference.toBoxedType;
import static org.neo4j.codegen.TypeReference.toUnboxedType;
import static org.neo4j.codegen.TypeReference.typeReference;

import java.lang.reflect.Modifier;
import java.util.Arrays;
import org.neo4j.values.AnyValue;

public abstract class Expression extends ExpressionTemplate {
    public static final Expression TRUE = new Constant(BOOLEAN, Boolean.TRUE) {
        @Override
        Expression not() {
            return FALSE;
        }
    };
    public static final Expression FALSE = new Constant(BOOLEAN, Boolean.FALSE) {
        @Override
        Expression not() {
            return TRUE;
        }
    };
    public static final Expression NULL = new Constant(OBJECT, null);

    protected Expression(TypeReference type) {
        super(type);
    }

    public abstract void accept(ExpressionVisitor visitor);

    static final Expression SUPER = new Expression(OBJECT) {
        @Override
        public void accept(ExpressionVisitor visitor) {
            visitor.loadThis("super");
        }
    };

    public static final Expression EMPTY = new Expression(VOID) {
        @Override
        public void accept(ExpressionVisitor visitor) {
            // do nothing
        }
    };

    public static Expression gt(final Expression lhs, final Expression rhs) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.gt(lhs, rhs);
            }

            @Override
            Expression not() {
                return lte(lhs, rhs);
            }
        };
    }

    public static Expression gte(final Expression lhs, final Expression rhs) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.gte(lhs, rhs);
            }

            @Override
            Expression not() {
                return lt(lhs, rhs);
            }
        };
    }

    public static Expression lt(final Expression lhs, final Expression rhs) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.lt(lhs, rhs);
            }

            @Override
            Expression not() {
                return gte(lhs, rhs);
            }
        };
    }

    public static Expression lte(final Expression lhs, final Expression rhs) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.lte(lhs, rhs);
            }

            @Override
            Expression not() {
                return gt(lhs, rhs);
            }
        };
    }

    public static Expression and(final Expression lhs, final Expression rhs) {
        if (lhs == FALSE || rhs == FALSE) {
            return FALSE;
        }
        if (lhs == TRUE) {
            return rhs;
        }
        if (rhs == TRUE) {
            return lhs;
        }
        Expression[] expressions;
        if (lhs instanceof And) {
            if (rhs instanceof And) {
                expressions = expressions(((And) lhs).expressions, ((And) rhs).expressions);
            } else {
                expressions = expressions(((And) lhs).expressions, rhs);
            }
        } else if (rhs instanceof And) {
            expressions = expressions(lhs, ((And) rhs).expressions);
        } else {
            expressions = new Expression[] {lhs, rhs};
        }
        return new And(expressions);
    }

    public static Expression ands(final Expression[] expressions) {
        return new And(expressions);
    }

    public static Expression or(final Expression lhs, final Expression rhs) {
        if (lhs == TRUE || rhs == TRUE) {
            return TRUE;
        }
        if (lhs == FALSE) {
            return rhs;
        }
        if (rhs == FALSE) {
            return lhs;
        }
        Expression[] expressions;
        if (lhs instanceof Or) {
            if (rhs instanceof Or) {
                expressions = expressions(((Or) lhs).expressions, ((Or) rhs).expressions);
            } else {
                expressions = expressions(((Or) lhs).expressions, rhs);
            }
        } else if (rhs instanceof Or) {
            expressions = expressions(lhs, ((Or) rhs).expressions);
        } else {
            expressions = new Expression[] {lhs, rhs};
        }
        return new Or(expressions);
    }

    public static Expression ors(final Expression[] expressions) {
        return new Or(expressions);
    }

    public static class And extends Expression {
        private final Expression[] expressions;

        And(Expression[] expressions) {
            super(BOOLEAN);
            this.expressions = expressions;
        }

        public Expression[] expressions() {
            return expressions;
        }

        @Override
        public void accept(ExpressionVisitor visitor) {
            visitor.and(expressions);
        }
    }

    public static class Or extends Expression {
        private final Expression[] expressions;

        Or(Expression[] expressions) {
            super(BOOLEAN);
            this.expressions = expressions;
        }

        public Expression[] expressions() {
            return expressions;
        }

        @Override
        public void accept(ExpressionVisitor visitor) {
            visitor.or(expressions);
        }
    }

    private static Expression[] expressions(Expression[] some, Expression[] more) {
        Expression[] result = Arrays.copyOf(some, some.length + more.length);
        System.arraycopy(more, 0, result, some.length, more.length);
        return result;
    }

    private static Expression[] expressions(Expression[] some, Expression last) {
        Expression[] result = Arrays.copyOf(some, some.length + 1);
        result[some.length] = last;
        return result;
    }

    private static Expression[] expressions(Expression first, Expression[] more) {
        Expression[] result = new Expression[more.length + 1];
        result[0] = first;
        System.arraycopy(more, 0, result, 1, more.length);
        return result;
    }

    public static Expression equal(final Expression lhs, final Expression rhs) {
        if (lhs == NULL) {
            if (rhs == NULL) {
                return constant(Boolean.TRUE);
            } else {
                return isNull(rhs);
            }
        } else if (rhs == NULL) {
            return isNull(lhs);
        }
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.equal(lhs, rhs);
            }

            @Override
            Expression not() {
                return notEqual(lhs, rhs);
            }
        };
    }

    public static Expression isNull(final Expression expression) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.isNull(expression);
            }

            @Override
            Expression not() {
                return notNull(expression);
            }
        };
    }

    public static Expression notNull(final Expression expression) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.notNull(expression);
            }

            @Override
            Expression not() {
                return isNull(expression);
            }
        };
    }

    public static Expression notEqual(final Expression lhs, final Expression rhs) {
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.notEqual(lhs, rhs);
            }

            @Override
            Expression not() {
                return equal(lhs, rhs);
            }
        };
    }

    public static Expression load(final LocalVariable variable) {
        return new Expression(variable.type()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.load(variable);
            }
        };
    }

    public static Expression arrayLoad(Expression array, Expression index) {
        assert array.type().isArray();

        return new Expression(array.type().elementOfArray()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.arrayLoad(array, index);
            }
        };
    }

    public static Expression arrayLength(Expression array) {
        assert array.type().isArray();

        return new Expression(INT) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.arrayLength(array);
            }
        };
    }

    public static Expression arraySet(Expression array, Expression index, Expression value) {
        assert array.type().isArray();

        return new Expression(array.type()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.arraySet(array, index, value);
            }
        };
    }

    public static Expression add(final Expression lhs, final Expression rhs) {
        if (!lhs.type.equals(rhs.type)) {
            throw new IllegalArgumentException(format(
                    "Cannot add variables with different types. LHS %s, RHS %s",
                    lhs.type.simpleName(), rhs.type.simpleName()));
        }

        return new Expression(lhs.type) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.add(lhs, rhs);
            }
        };
    }

    public static Expression subtract(final Expression lhs, final Expression rhs) {
        if (!lhs.type.equals(rhs.type)) {
            throw new IllegalArgumentException(format(
                    "Cannot subtract variables with different types. LHS %s, RHS %s",
                    lhs.type.simpleName(), rhs.type.simpleName()));
        }
        return new Expression(lhs.type) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.subtract(lhs, rhs);
            }
        };
    }

    public static Expression multiply(final Expression lhs, final Expression rhs) {
        if (!lhs.type.equals(rhs.type)) {
            throw new IllegalArgumentException(format(
                    "Cannot multiply variables with different types. LHS %s, RHS %s",
                    lhs.type.simpleName(), rhs.type.simpleName()));
        }
        return new Expression(lhs.type) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.multiply(lhs, rhs);
            }
        };
    }

    public static Expression constantInt(int value) {
        return constant(value);
    }

    public static Expression constantLong(long value) {
        return constant(value);
    }

    public static Expression constant(final Object value) {
        TypeReference reference;
        if (value == null) {
            return NULL;
        } else if (value instanceof String) {
            reference = TypeReference.typeReference(String.class);
        } else if (value instanceof Long) {
            reference = LONG;
        } else if (value instanceof Integer) {
            reference = INT;
        } else if (value instanceof Double) {
            reference = DOUBLE;
        } else if (value instanceof Boolean) {
            return (Boolean) value ? TRUE : FALSE;
        } else if (value instanceof AnyValue) {
            reference = VALUE;
        } else {
            throw new IllegalArgumentException("Not a valid constant: " + value);
        }

        return new Expression(reference) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.constant(value);
            }
        };
    }

    private static class Constant extends Expression {
        private final Object value;

        Constant(TypeReference type, Object value) {
            super(type);
            this.value = value;
        }

        @Override
        public void accept(ExpressionVisitor visitor) {
            visitor.constant(value);
        }
    }

    public static Expression newArray(TypeReference baseType, int size) {
        return new Expression(arrayOf(baseType)) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.newArray(baseType, size);
            }
        };
    }

    public static Expression newArray(TypeReference baseType, Expression size) {
        return new Expression(arrayOf(baseType)) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.newArray(baseType, size);
            }
        };
    }

    // TODO deduce type from constants
    public static Expression newInitializedArray(TypeReference baseType, Expression... constants) {
        return new Expression(arrayOf(baseType)) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.newInitializedArray(baseType, constants);
            }
        };
    }

    /** get instance field */
    public static Expression get(final Expression target, final FieldReference field) {
        return new Expression(field.type()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.getField(target, field);
            }
        };
    }

    /** box expression */
    public static Expression box(final Expression expression) {
        return new Expression(toBoxedType(expression.type)) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.box(expression);
            }
        };
    }

    /** unbox expression */
    public static Expression unbox(final Expression expression) {
        return new Expression(toUnboxedType(expression.type)) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.unbox(expression);
            }
        };
    }

    /** get static field */
    public static Expression getStatic(final FieldReference field) {
        return new Expression(field.type()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.getStatic(field);
            }
        };
    }

    public static Expression ternary(final Expression test, final Expression onTrue, final Expression onFalse) {
        TypeReference reference = onTrue.type.equals(onFalse.type) ? onTrue.type : OBJECT;
        return new Expression(reference) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.ternary(test, onTrue, onFalse);
            }
        };
    }

    public static Expression invoke(
            final Expression target, final MethodReference method, final Expression... arguments) {
        return new Expression(method.returns()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.invoke(target, method, arguments);
            }
        };
    }

    public static Expression invoke(final MethodReference method, final Expression... parameters) {
        return new Expression(method.returns()) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.invoke(method, parameters);
            }
        };
    }

    public static Expression invokeSuper(TypeReference parent, final Expression... parameters) {
        TypeReference[] parameterTypes =
                stream(parameters).map(ExpressionTemplate::type).toArray(TypeReference[]::new);

        return new Expression(OBJECT) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.invoke(
                        Expression.SUPER,
                        new MethodReference(parent, "", VOID, Modifier.PUBLIC, parameterTypes),
                        parameters);
            }
        };
    }

    public static Expression cast(Class type, Expression expression) {
        return cast(typeReference(type), expression);
    }

    public static Expression instanceOf(final TypeReference typeToCheck, Expression expression) {
        return new Expression(typeReference(boolean.class)) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.instanceOf(typeToCheck, expression);
            }
        };
    }

    public static Expression cast(final TypeReference type, Expression expression) {
        return new Expression(type) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.cast(type, expression);
            }
        };
    }

    public static Expression newInstance(Class type) {
        return newInstance(typeReference(type));
    }

    public static Expression newInstance(final TypeReference type) {
        return new Expression(type) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.newInstance(type);
            }
        };
    }

    public static Expression not(final Expression expression) {
        return expression.not();
    }

    Expression not() {
        return notExpr(this);
    }

    private static Expression notExpr(final Expression expression) {
        assert expression.type.equals(BOOLEAN) : "Can only apply not() to boolean expressions";
        return new Expression(BOOLEAN) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.not(expression);
            }

            @Override
            Expression not() {
                return expression;
            }
        };
    }

    public static Expression toDouble(final Expression expression) {
        return new Expression(DOUBLE) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.longToDouble(expression);
            }
        };
    }

    public static Expression pop(Expression expression) {
        return new Expression(expression.type) {
            @Override
            public void accept(ExpressionVisitor visitor) {
                visitor.pop(expression);
            }
        };
    }

    @Override
    Expression materialize(CodeBlock method) {
        return this;
    }

    @Override
    void templateAccept(CodeBlock method, ExpressionVisitor visitor) {
        throw new UnsupportedOperationException("simple expressions should not be invoked as templates");
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder().append("Expression[");
        accept(new ExpressionToString(result));
        return result.append(']').toString();
    }
}