/*******************************************************************************
 * Copyright (c) 2009, 2021 Mountainminds GmbH & Co. KG and Contributors
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *    Evgeny Mandrikov - initial API and implementation
 *
 *******************************************************************************/
package org.jacoco.core.internal.analysis;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

import org.jacoco.core.analysis.ISourceNode;
import org.jacoco.core.internal.analysis.filter.IFilterOutput;
import org.objectweb.asm.tree.AbstractInsnNode;

/**
 * Calculates the filtered coverage of a single method. A instance of this class
 * can be first used as {@link IFilterOutput} before the coverage result is
 * calculated.
 */
class MethodCoverageCalculator implements IFilterOutput {

	private final Map<AbstractInsnNode, Instruction> instructions;

	private final Set<AbstractInsnNode> ignored;

	/**
	 * Instructions that should be merged form disjoint sets. Coverage
	 * information from instructions of one set will be merged into
	 * representative instruction of set.
	 *
	 * Each such set is represented as a singly linked list: each element except
	 * one references another element from the same set, element without
	 * reference - is a representative of this set.
	 *
	 * This map stores reference (value) for elements of sets (key).
	 */
	private final Map<AbstractInsnNode, AbstractInsnNode> merged;

	private final Map<AbstractInsnNode, Set<AbstractInsnNode>> replacements;

	MethodCoverageCalculator(
			final Map<AbstractInsnNode, Instruction> instructions) {
		this.instructions = instructions;
		this.ignored = new HashSet<AbstractInsnNode>();
		this.merged = new HashMap<AbstractInsnNode, AbstractInsnNode>();
		this.replacements = new HashMap<AbstractInsnNode, Set<AbstractInsnNode>>();
	}

	/**
	 * Applies all specified filtering commands and calculates the resulting
	 * coverage.
	 *
	 * @param coverage
	 *            the result is added to this coverage node
	 */
	void calculate(final MethodCoverageImpl coverage) {
		applyMerges();
		applyReplacements();
		ensureCapacity(coverage);

		for (final Entry<AbstractInsnNode, Instruction> entry : instructions
				.entrySet()) {
			if (!ignored.contains(entry.getKey())) {
				final Instruction instruction = entry.getValue();
				coverage.increment(instruction.getInstructionCounter(),
						instruction.getBranchCounter(), instruction.getLine());
			}
		}

		coverage.incrementMethodCounter();
	}

	private void applyMerges() {
		// Merge to the representative:
		for (final Entry<AbstractInsnNode, AbstractInsnNode> entry : merged
				.entrySet()) {
			final AbstractInsnNode node = entry.getKey();
			final Instruction instruction = instructions.get(node);
			final AbstractInsnNode representativeNode = findRepresentative(
					node);
			ignored.add(node);
			instructions.put(representativeNode,
					instructions.get(representativeNode).merge(instruction));
			entry.setValue(representativeNode);
		}

		// Get merged value back from representative
		for (final Entry<AbstractInsnNode, AbstractInsnNode> entry : merged
				.entrySet()) {
			instructions.put(entry.getKey(),
					instructions.get(entry.getValue()));
		}
	}

	private void applyReplacements() {
		for (final Entry<AbstractInsnNode, Set<AbstractInsnNode>> entry : replacements
				.entrySet()) {
			final Set<AbstractInsnNode> replacements = entry.getValue();
			final List<Instruction> newBranches = new ArrayList<Instruction>(
					replacements.size());
			for (final AbstractInsnNode b : replacements) {
				newBranches.add(instructions.get(b));
			}
			final AbstractInsnNode node = entry.getKey();
			instructions.put(node,
					instructions.get(node).replaceBranches(newBranches));
		}
	}

	private void ensureCapacity(final MethodCoverageImpl coverage) {
		// Determine line range:
		int firstLine = ISourceNode.UNKNOWN_LINE;
		int lastLine = ISourceNode.UNKNOWN_LINE;
		for (final Entry<AbstractInsnNode, Instruction> entry : instructions
				.entrySet()) {
			if (!ignored.contains(entry.getKey())) {
				final int line = entry.getValue().getLine();
				if (line != ISourceNode.UNKNOWN_LINE) {
					if (firstLine > line
							|| lastLine == ISourceNode.UNKNOWN_LINE) {
						firstLine = line;
					}
					if (lastLine < line) {
						lastLine = line;
					}
				}
			}
		}

		// Performance optimization to avoid incremental increase of line array:
		coverage.ensureCapacity(firstLine, lastLine);
	}

	private AbstractInsnNode findRepresentative(AbstractInsnNode i) {
		AbstractInsnNode r;
		while ((r = merged.get(i)) != null) {
			i = r;
		}
		return i;
	}

	// === IFilterOutput API ===

	public void ignore(final AbstractInsnNode fromInclusive,
			final AbstractInsnNode toInclusive) {
		for (AbstractInsnNode i = fromInclusive; i != toInclusive; i = i
				.getNext()) {
			ignored.add(i);
		}
		ignored.add(toInclusive);
	}

	public void merge(AbstractInsnNode i1, AbstractInsnNode i2) {
		i1 = findRepresentative(i1);
		i2 = findRepresentative(i2);
		if (i1 != i2) {
			merged.put(i2, i1);
		}
	}

	public void replaceBranches(final AbstractInsnNode source,
			final Set<AbstractInsnNode> newTargets) {
		replacements.put(source, newTargets);
	}

}