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Core building blocks and API for the Metal library.
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/*
 * Copyright 2013-2024 Netherlands Forensic Institute
 * Copyright 2021-2024 Infix Technologies B.V.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.parsingdata.metal.expression.value;

import static java.math.BigInteger.ZERO;

import static io.parsingdata.metal.Trampoline.complete;
import static io.parsingdata.metal.Trampoline.intermediate;
import static io.parsingdata.metal.Util.checkNotNull;
import static io.parsingdata.metal.expression.value.NotAValue.NOT_A_VALUE;

import java.util.Objects;

import io.parsingdata.metal.ImmutableObject;
import io.parsingdata.metal.Trampoline;
import io.parsingdata.metal.Util;
import io.parsingdata.metal.data.ImmutableList;
import io.parsingdata.metal.data.ParseGraph;
import io.parsingdata.metal.data.ParseState;
import io.parsingdata.metal.encoding.Encoding;
import io.parsingdata.metal.token.Token;

/**
 * A {@link ValueExpression} that prunes the {@link ParseState#order} field to
 * let a nested {@link ValueExpression} have only a scoped view.
 * 
 * A Scope expression has two operands: scopedValueExpression (a
 * {@link ValueExpression} and scopeSize (a
 * {@link SingleValueExpression}). The scopeSize operand is first
 * evaluated, if it evaluates to NOT_A_VALUE or a negative value
 * an {@link IllegalArgumentException} is thrown. Otherwise the
 * order field of the parseState argument is pruned.
 * This is done by removing all enclosing scopes above the amount specified by
 * scopeSize. An enclosing scope is defined as an unclosed branch
 * in the {@link ParseGraph} that has a scope delimiting {@link Token} as its
 * definition. Next, the scopedValueExpression is
 * evaluated with this pruned {@link ParseGraph} in the {@link ParseState}.
 */
public class Scope extends ImmutableObject implements ValueExpression {

    public final ValueExpression scopedValueExpression;
    public final SingleValueExpression scopeSize;

    public Scope(final ValueExpression scopedValueExpression, final SingleValueExpression scopeSize) {
        this.scopedValueExpression = checkNotNull(scopedValueExpression, "scopedValueExpression");
        this.scopeSize = checkNotNull(scopeSize, "scopeSize");
    }

    @Override
    public ImmutableList eval(final ParseState parseState, final Encoding encoding) {
        return scopeSize.evalSingle(parseState, encoding)
            .filter(sizeValue -> !sizeValue.equals(NOT_A_VALUE) && sizeValue.asNumeric().compareTo(ZERO) >= 0)
            .map(sizeValue -> scopedValueExpression.eval(parseState.withOrder(calculateScope(parseState.order, sizeValue.asNumeric().intValueExact())), encoding))
            .orElseThrow(() -> new IllegalArgumentException("Argument scopeSize must evaluate to a positive, countable value."));

    }

    private ParseGraph calculateScope(final ParseGraph order, final int size) {
        final ImmutableList scopeList = createScopeList(order, new ImmutableList<>()).computeResult();
        if (size >= scopeList.size) { return order; }
        return findScope(scopeList, size).computeResult();
    }

    private Trampoline> createScopeList(final ParseGraph order, final ImmutableList list) {
        final ImmutableList newList = order.getDefinition().isScopeDelimiter() ? list.add(order) : list;
        if (order.isEmpty() || !order.head.isGraph()) { return complete(() -> list); }
        return intermediate(() -> createScopeList(order.head.asGraph(), newList));
    }

    private Trampoline findScope(final ImmutableList scopeList, final int size) {
        if (size == 0) { return complete(() -> scopeList.head); }
        return intermediate(() -> findScope(scopeList.tail, size - 1));
    }

    @Override
    public String toString() {
        return getClass().getSimpleName() + "(" + scopedValueExpression + "," + scopeSize + ")";
    }

    @Override
    public boolean equals(final Object obj) {
        return Util.notNullAndSameClass(this, obj)
            && Objects.equals(scopedValueExpression, ((Scope)obj).scopedValueExpression)
            && Objects.equals(scopeSize, ((Scope)obj).scopeSize);
    }

    @Override
    public int immutableHashCode() {
        return Objects.hash(getClass(), scopedValueExpression, scopeSize);
    }

}