com.google.api.tools.framework.snippet.Context.java Source code

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Here is the source code for com.google.api.tools.framework.snippet.Context.java

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/*
 * Copyright (C) 2016 Google Inc.
 *
 * 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 com.google.api.tools.framework.snippet;

import com.google.api.tools.framework.snippet.SnippetSet.SnippetKey;
import com.google.common.base.Preconditions;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.collect.Queues;

import java.util.Collection;
import java.util.Deque;
import java.util.Iterator;
import java.util.Map;

import javax.annotation.Nullable;

/**
 * Represents a context for snippet evaluation. The context holds snippet
 * definitions and global and local variables.
 */
public class Context {

    private static final Map<String, Object> BUILTIN = ImmutableMap.<String, Object>builder()
            .put("BREAK", Doc.BREAK).put("SOFT_BREAK", Doc.SOFT_BREAK).put("EMPTY", Doc.EMPTY)
            .put("TRUE", Values.TRUE).put("FALSE", Values.FALSE).put("COMMA_BREAK", Doc.text(",").add(Doc.BREAK))
            .build();

    private final Map<SnippetKey, Snippet> snippets;
    private final Multimap<String, Snippet> snippetsByName;
    private final ImmutableMap<String, Object> globals;
    private final Deque<Map<String, Object>> locals = Queues.newArrayDeque();

    /**
     * Construct a context with given snippets and globals.
     */
    Context(Map<SnippetKey, Snippet> snippets, Map<String, Object> globals) {
        this.snippets = snippets;
        this.snippetsByName = ArrayListMultimap.create();
        for (Map.Entry<SnippetKey, Snippet> entry : snippets.entrySet()) {
            snippetsByName.put(entry.getKey().name(), entry.getValue());
        }
        this.globals = ImmutableMap.copyOf(globals);
    }

    /**
     * Construct a context with given snippets.
     */
    Context(Map<SnippetKey, Snippet> snippets) {
        this(snippets, ImmutableMap.<String, Object>of());
    }

    /**
     * Enters a new local scope. Subsequent calls to {@link #bind(String, Object)} introduce
     * a variable in this scope.
     */
    void enterScope() {
        locals.push(Maps.<String, Object>newLinkedHashMap());
    }

    /**
     * Exists a scope, forgetting all variables defined within.
     */
    void exitScope() {
        locals.pop();
    }

    /**
     * Binds a variable in the innermost scope.
     */
    void bind(String name, Object value) {
        Preconditions.checkNotNull(value);
        locals.peek().put(name, value);
    }

    /**
     * Forks the given context into a new one with same snippets and globals, and empty locals.
     */
    Context fork() {
        return new Context(snippets, globals);
    }

    /**
     * Gets a variable definition, walking scopes inside-out.
     */
    Object getVar(String name) {
        // First try to resolve in locals in scope.
        Iterator<Map<String, Object>> iter = locals.iterator();
        while (iter.hasNext()) {
            Object result = iter.next().get(name);
            if (result != null) {
                return result;
            }
        }

        // Next try to resolve as a snippet. This only succeeds if there is a unique binding
        // for the snippet independent of its arity.
        Collection<Snippet> snippetResult = snippetsByName.get(name);
        if (snippetResult.size() == 1) {
            return snippetResult.iterator().next();
        }

        // Next try to resolve in globals in scope.
        Object result = globals.get(name);
        if (result != null) {
            return result;
        }

        // Finally look up builtin variables.
        return BUILTIN.get(name);
    }

    /**
     * Gets a snippet definitions.
     */
    @Nullable
    Snippet getSnippet(Location location, String name, int arity) {
        // First try to resolve as a variable which represents a snippet.
        Snippet result;
        Object varValue = getVar(name);
        if (varValue != null && varValue instanceof Snippet) {
            result = (Snippet) varValue;
            if (result.params().size() == arity) {
                return result;
            }
            result = null;
        }

        // Next try to resolve as private snippet.
        result = snippets.get(SnippetKey.create(makePrivateSnippetName(location, name), arity));
        if (result != null) {
            return result;
        }

        // Finally try to resolve as non-private snippet.
        return snippets.get(SnippetKey.create(name, arity));
    }

    /**
     * Gets the name of a private snippet, based on the input name and the snippet name proper.
     */
    static String makePrivateSnippetName(Location location, String name) {
        return name + "#" + location.baseInputName();
    }
}