/*
 * Java Genetic Algorithm Library (jenetics-6.0.0).
 * Copyright (c) 2007-2020 Franz Wilhelmstötter
 *
 * 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.
 *
 * Author:
 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics.ext.rewriting;

import static java.lang.String.format;
import static java.util.stream.Collectors.toMap;
import static io.jenetics.ext.internal.Names.isIdentifier;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.SortedSet;
import java.util.TreeSet;
import java.util.function.Function;

import io.jenetics.ext.internal.Escaper;
import io.jenetics.ext.util.Tree;
import io.jenetics.ext.util.Tree.Path;
import io.jenetics.ext.util.TreeNode;

/**
 * This class serves two purposes. Firstly, it is used as a <em>classical</em>
 * pattern, which is used to find <em>matches</em> against a <em>matching</em>
 * tree. Secondly, it can <em>expand</em> a given pattern to a full tree with a
 * given <em>pattern</em> variable to sub-tree mapping.
 *
 * <p><b>Matching trees</b></p>
 *
 * A compiled representation of a <em>tree</em> pattern. A tree pattern,
 * specified as a parentheses string, must first be compiled into an instance of
 * this class. The resulting pattern can then be used to create a
 * {@link TreeMatcher} object that can match arbitrary trees against the tree
 * pattern. All of the state involved in performing a match resides in the
 * matcher, so many matchers can share the same pattern.
 * <p>
 * The string representation of a tree pattern is a parenthesis tree string,
 * with a special wildcard syntax for arbitrary sub-trees. The sub-trees
 * variables are prefixed with a '$' and must be a valid Java identifier.
 * <pre>{@code
 * final TreePattern<String> p1 = TreePattern.compile("add($a,add($b,sin(x)))");
 * final TreePattern<String> p2 = TreePattern.compile("pow($x,$y)");
 * }</pre>
 *
 * If you need to have values which starts with a '$' character, you can escape
 * it with a '\'.
 * <pre>{@code
 * final TreePattern<String> p1 = TreePattern.compile("concat($x,\\$foo)");
 * }</pre>
 *
 * The second value, {@code $foo}, of the {@code concat} function is not treated
 * as <em>pattern</em> variable.
 * <p>
 * If you want to match against trees with a different value type than
 * {@code String}, you have to specify an additional type mapper function when
 * compiling the pattern string.
 * <pre>{@code
 * final TreePattern<Op<Double>> p = TreePattern.compile(
 *     "add($a,add($b,sin(x)))",
 *     MathOp::toMathOp
 * );
 * }</pre>
 *
 * <p><b>Expanding trees</b></p>
 *
 * The second functionality of the tree pattern is to expand a pattern to a whole
 * tree with a given <em>pattern</em> variable to sub-tree mapping.
 * <pre>{@code
 * final TreePattern<String> pattern = TreePattern.compile("add($x,$y,1)");
 * final Map<Var<String>, Tree<String, ?>> vars = new HashMap<>();
 * vars.put(Var.of("x"), TreeNode.parse("sin(x)"));
 * vars.put(Var.of("y"), TreeNode.parse("sin(y)"));
 *
 * final Tree<String, ?> tree = pattern.expand(vars);
 * assertEquals(tree.toParenthesesString(), "add(sin(x),sin(y),1)");
 * }</pre>
 *
 * @see TreeRewriteRule
 * @see Tree#toParenthesesString()
 * @see TreeMatcher
 *
 * @param <V> the value type of the tree than can be matched by this pattern
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 5.0
 * @since 5.0
 */
public final class TreePattern<V> implements Serializable {

        private static final long serialVersionUID = 1L;

        // Primary state of the tree pattern.
        private final TreeNode<Decl<V>> _pattern;

        // Cached variable set.
        private final SortedSet<Var<V>> _vars;

        /**
         * Create a new tree-pattern object from the given pattern tree.
         *
         * @param pattern the pattern-tree
         * @throws NullPointerException if the given {@code pattern} is {@code null}
         * @throws IllegalArgumentException if {@link Var} nodes are not leaf nodes;
         *         {@link Tree#isLeaf()} is {@code false}
         */
        public TreePattern(final Tree<Decl<V>, ?> pattern) {
                _pattern = TreeNode.ofTree(pattern);
                _vars = extractVars(_pattern);
        }

        // Extracts the variables from the pattern.
        private static <V> SortedSet<Var<V>>
        extractVars(final TreeNode<Decl<V>> pattern) {
                final SortedSet<Var<V>> variables = new TreeSet<>();
                for (Tree<Decl<V>, ?> n : pattern) {
                        if (n.value() instanceof Var) {
                                if (!n.isLeaf()) {
                                        throw new IllegalArgumentException(format(
                                                "Variable node '%s' is not a leaf: %s",
                                                n.value(), n.toParenthesesString()
                                        ));
                                }

                                variables.add((Var<V>)n.value());
                        }
                }

                return Collections.unmodifiableSortedSet(variables);
        }

        TreeNode<Decl<V>> pattern() {
                return _pattern;
        }

        /**
         * Return the <em>unmodifiable</em> set of variables, defined in {@code this}
         * pattern. The variables are returned without the angle brackets.
         *
         * @return the variables, defined in this pattern
         */
        public SortedSet<Var<V>> vars() {
                return _vars;
        }

        /**
         * Maps {@code this} tree-pattern from type {@code V} to type {@code B}.
         *
         * @param mapper the type mapper
         * @param <B> the target type
         * @return a new tree-pattern for the mapped type
         */
        public <B> TreePattern<B> map(final Function<? super V, ? extends B> mapper) {
                return new TreePattern<>(_pattern.map(d -> d.map(mapper)));
        }

        /**
         * Creates a matcher that will match the given input tree against
         * {@code this} pattern.
         *
         * @param tree the tree to be matched
         * @return a new matcher for {@code this} pattern
         * @throws NullPointerException if the arguments is {@code null}
         */
        public TreeMatcher<V> matcher(final Tree<V, ?> tree) {
                return TreeMatcher.of(this, tree);
        }

        /**
         * Try to match the given {@code tree} against {@code this} pattern.
         *
         * @param tree the tree to be matched
         * @return the match result, or {@link Optional#empty()} if the given
         *         {@code tree} doesn't match
         * @throws NullPointerException if the arguments is {@code null}
         */
        public Optional<TreeMatchResult<V>> match(final Tree<V, ?> tree) {
                final Map<Var<V>, Tree<V, ?>> vars = new HashMap<>();
                final boolean matches = matches(tree, _pattern, vars);

                return matches
                        ? Optional.of(TreeMatchResult.of(tree, vars))
                        : Optional.empty();
        }

        /**
         * Tests whether the given input {@code tree} matches {@code this} pattern.
         *
         * @param tree the tree to be matched
         * @return {@code true} if the {@code tree} matches {@code this} pattern,
         *         {@code false} otherwise
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public boolean matches(final Tree<V, ?> tree) {
                return matches(tree, _pattern, new HashMap<>());
        }

        private static <V> boolean matches(
                final Tree<V, ?> node,
                final Tree<Decl<V>, ?> pattern,
                final Map<Var<V>, Tree<V, ?>> vars
        ) {
                final Decl<V> decl = pattern.value();

                if (decl instanceof Var) {
                        final Tree<? extends V, ?> tree = vars.get(decl);
                        if (tree == null) {
                                vars.put((Var<V>)decl, node);
                                return true;
                        }

                        return tree.equals(node);
                } else {
                        final Val<V> p = (Val<V>)decl;
                        final V v = node.value();

                        if (Objects.equals(v, p.value())) {
                                if (node.childCount() == pattern.childCount()) {
                                        for (int i = 0; i < node.childCount(); ++i) {
                                                final Tree<V, ?> cn = node.childAt(i);
                                                final Tree<Decl<V>, ?> cp = pattern.childAt(i);

                                                if (!matches(cn, cp, vars)) {
                                                        return false;
                                                }
                                        }
                                        return true;
                                } else {
                                        return false;
                                }
                        } else {
                                return false;
                        }
                }
        }

        /**
         * Expands {@code this} pattern with the given variable mapping.
         *
         * @param vars the variables to use for expanding {@code this} pattern
         * @return the expanded tree pattern
         * @throws NullPointerException if one of the arguments is {@code null}
         * @throws IllegalArgumentException if not all needed variables are part
         *         of the {@code variables} map
         */
        public TreeNode<V> expand(final Map<Var<V>, Tree<V, ?>> vars) {
                return expand(_pattern, vars);
        }

        // Expanding the template.
        private static <V> TreeNode<V> expand(
                final Tree<Decl<V>, ?> template,
                final Map<Var<V>, Tree<V, ?>> vars
        ) {
                final Map<Path, Var<V>> paths = template.stream()
                        .filter((Tree<Decl<V>, ?> n) -> n.value() instanceof Var)
                        .collect(toMap(Tree::childPath, t -> (Var<V>)t.value()));

                final TreeNode<V> tree = TreeNode.ofTree(
                        template,
                        n -> n instanceof Val ? ((Val<V>)n).value() : null
                );

                paths.forEach((path, decl) -> {
                        final Tree<? extends V, ?> replacement = vars.get(decl);
                        if (replacement != null) {
                                tree.replaceAtPath(path, TreeNode.ofTree(replacement));
                        } else {
                                tree.removeAtPath(path);
                        }
                });

                return tree;
        }

        @Override
        public int hashCode() {
                return _pattern.hashCode();
        }

        @Override
        public boolean equals(final Object obj) {
                return obj == this ||
                        obj instanceof TreePattern &&
                        _pattern.equals(((TreePattern)obj)._pattern);
        }

        @Override
        public String toString() {
                return _pattern.toParenthesesString();
        }

        /* *************************************************************************
         * Static factory methods.
         * ************************************************************************/

        /**
         * Compiles the given tree pattern string.
         *
         * @param pattern the tree pattern string
         * @return the compiled pattern
         * @throws NullPointerException if the given pattern is {@code null}
         * @throws IllegalArgumentException if the given parentheses tree string
         *         doesn't represent a valid pattern tree or one of the variable
         *         name is not a valid (Java) identifier
         */
        public static TreePattern<String> compile(final String pattern) {
                return compile(pattern, Function.identity());
        }

        /**
         * Compiles the given tree pattern string.
         *
         * @param pattern the tree pattern string
         * @param mapper the mapper which converts the serialized string value to
         *        the desired type
         * @param <V> the value type of the tree than can be matched by the pattern
         * @return the compiled pattern
         * @throws NullPointerException if the given pattern is {@code null}
         * @throws IllegalArgumentException if the given parentheses tree string
         *         doesn't represent a valid pattern tree or one of the variable
         *         name is not a valid (Java) identifier
         */
        public static <V> TreePattern<V> compile(
                final String pattern,
                final Function<? super String, ? extends V> mapper
        ) {
                return new TreePattern<>(
                        TreeNode.parse(pattern, v -> Decl.of(v.trim(), mapper))
                );
        }

        /* *************************************************************************
         *  Java object serialization
         * ************************************************************************/

        private Object writeReplace() {
                return new Serial(Serial.TREE_PATTERN, this);
        }

        private void readObject(final ObjectOutputStream stream)
                throws InvalidObjectException
        {
                throw new InvalidObjectException("Serialization proxy required.");
        }

        void write(final ObjectOutput out) throws IOException {
                out.writeObject(_pattern);
        }

        @SuppressWarnings({"unchecked", "rawtypes"})
        static Object read(final ObjectInput in)
                throws IOException, ClassNotFoundException
        {
                final var pattern = (TreeNode)in.readObject();
                return new TreePattern(pattern);
        }


        /* *************************************************************************
         * Pattern node classes.
         * ************************************************************************/

        /**
         * A <em>sealed</em> class, which constitutes the nodes of a pattern tree.
         * The only two implementations of this class are the {@link Var} and the
         * {@link Val} class. The {@link Var} class represents a placeholder for an
         * arbitrary sub-tree and the {@link Val} class stands for an arbitrary
         * concrete sub-tree.
         *
         * @see Var
         * @see Val
         *
         * @param <V> the node type the tree-pattern is working on
         */
        public abstract static class Decl<V> {
                private static final char VAR_PREFIX = '$';
                private static final char ESC_CHAR = '\\';

                private static final Escaper ESCAPER = new Escaper(ESC_CHAR, VAR_PREFIX);

                private Decl() {
                }

                abstract <B> Decl<B> map(final Function<? super V, ? extends B> mapper);

                static <V> Decl<V> of(
                        final String value,
                        final Function<? super String, ? extends V> mapper
                ) {
                        return Var.isVar(value)
                                ? Var.of(value.substring(1))
                                : Val.of(mapper.apply(ESCAPER.unescape(value)));
                }
        }

        /**
         * Represents a placeholder (variable) for an arbitrary sub-tree. A
         * <em>pattern</em> variable is identified by its name. The pattern DSL
         * denotes variable names with a leading '$' character, e.g. {@code $x},
         * {@code $y} or {@code $my_var}. It is one of two implementations of the
         * <em>sealed</em> {@link Decl} class.
         *
         * @see Val
         *
         * @implNote
         * This class is comparable by it's name.
         *
         * @param <V> the node type the tree-pattern is working
         */
        public static final class Var<V>
                extends Decl<V>
                implements Comparable<Var<V>>, Serializable
        {
                private static final long serialVersionUID = 1L;

                private final String _name;

                private Var(final String name) {
                        if (!isIdentifier(name)) {
                                throw new IllegalArgumentException(format(
                                        "Variable is not valid identifier: '%s'",
                                        name
                                ));
                        }
                        _name = name;
                }

                @Override
                @SuppressWarnings("unchecked")
                <B> Var<B> map(final Function<? super V, ? extends B> mapper) {
                        return (Var<B>)this;
                }

                /**
                 * Return the name of the variable.
                 *
                 * @return the variable name
                 */
                public String name() {
                        return _name;
                }

                @Override
                public int compareTo(final Var<V> var) {
                        return _name.compareTo(var._name);
                }

                @Override
                public int hashCode() {
                        return _name.hashCode();
                }

                @Override
                public boolean equals(final Object obj) {
                        return obj == this ||
                                obj instanceof Var &&
                                Objects.equals(_name, ((Var)obj)._name);
                }

                @Override
                public String toString() {
                        return format("%s%s", Decl.VAR_PREFIX, _name);
                }

                /**
                 * Return a new variable with the given name.
                 *
                 * @param name the name of the variable
                 * @param <V> the node type the tree-pattern is working on
                 * @return a new variable with the given name
                 * @throws NullPointerException if the given {@code name} is {@code null}
                 * @throws IllegalArgumentException if the given {@code name} is not a
                 *         valid Java identifier
                 */
                public static <V> Var<V> of(final String name) {
                        return new Var<>(name);
                }

                static boolean isVar(final String name) {
                        return !name.isEmpty() && name.charAt(0) == Decl.VAR_PREFIX;
                }

                /* *********************************************************************
                 *  Java object serialization
                 * ********************************************************************/

                private Object writeReplace() {
                        return new Serial(Serial.TREE_PATTERN_VAR, this);
                }

                private void readObject(final ObjectOutputStream stream)
                        throws InvalidObjectException
                {
                        throw new InvalidObjectException("Serialization proxy required.");
                }

                void write(final ObjectOutput out) throws IOException {
                        out.writeObject(_name);
                }

                @SuppressWarnings("rawtypes")
                static Object read(final ObjectInput in)
                        throws IOException, ClassNotFoundException
                {
                        final String name = (String)in.readObject();
                        return new Var(name);
                }

        }

        /**
         * This class represents a constant pattern value, which can be part of a
         * whole sub-tree. It is one of two implementations of the <em>sealed</em>
         * {@link Decl} class.
         *
         * @see Var
         *
         * @param <V> the node value type
         */
        public static final class Val<V> extends Decl<V> implements Serializable {
                private static final long serialVersionUID = 1L;

                private final V _value;

                private Val(final V value) {
                        _value = value;
                }

                public V value() {
                        return _value;
                }

                @Override
                <B> Val<B> map(final Function<? super V, ? extends B> mapper) {
                        return Val.of(mapper.apply(_value));
                }

                @Override
                public int hashCode() {
                        return Objects.hashCode(_value);
                }

                @Override
                public boolean equals(final Object obj) {
                        return obj == this ||
                                obj instanceof TreePattern.Val &&
                                Objects.equals(_value, ((Val)obj)._value);
                }

                @Override
                public String toString() {
                        return Objects.toString(_value);
                }

                /**
                 * Create a new <em>value</em> object.
                 *
                 * @param value the underlying pattern value
                 * @param <V> the node type
                 * @return a new <em>value</em> object
                 */
                public static <V> Val<V> of(final V value) {
                        return new Val<>(value);
                }


                /* *********************************************************************
                 *  Java object serialization
                 * ********************************************************************/

                private Object writeReplace() {
                        return new Serial(Serial.TREE_PATTERN_VAL, this);
                }

                private void readObject(final ObjectOutputStream stream)
                        throws InvalidObjectException
                {
                        throw new InvalidObjectException("Serialization proxy required.");
                }

                void write(final ObjectOutput out) throws IOException {
                        out.writeObject(_value);
                }

                @SuppressWarnings({"unchecked", "rawtypes"})
                static Object read(final ObjectInput in)
                        throws IOException, ClassNotFoundException
                {
                        return new Val(in.readObject());
                }
        }

}