/*
 * Copyright 2013 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.template.soy.basicdirectives;

import com.google.common.base.Function;
import com.google.common.base.Joiner;
import com.google.common.collect.ContiguousSet;
import com.google.common.collect.DiscreteDomain;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Range;
import com.google.template.soy.data.SoyValue;
import com.google.template.soy.internal.targetexpr.TargetExpr;
import com.google.template.soy.jssrc.restricted.JsExpr;
import com.google.template.soy.jssrc.restricted.SoyJsSrcPrintDirective;
import com.google.template.soy.pysrc.restricted.PyExpr;
import com.google.template.soy.pysrc.restricted.SoyPySrcPrintDirective;
import com.google.template.soy.shared.restricted.Sanitizers;
import com.google.template.soy.shared.restricted.SoyJavaPrintDirective;
import com.google.template.soy.shared.restricted.SoyPurePrintDirective;
import com.google.template.soy.shared.restricted.TagWhitelist.OptionalSafeTag;

import java.util.List;
import java.util.Set;

import javax.inject.Inject;
import javax.inject.Singleton;


/**
 * Implements the |cleanHtml directive, which removes all but a small, safe
 * subset of HTML from its input. Note that all attributes are removed except
 * dir for directionality.
 *
 * <p>
 * It may take a variable number of arguments which are additional tags to be
 * considered safe, from {@link OptionalSafeTag}.
 *
 * <p>
 * Note that this directive is not autoescape canceling, and can thus be
 * used in strict templates.  The directive returns its result as an object
 * of type SanitizedContent of kind HTML.
 */
@Singleton
@SoyPurePrintDirective
final class CleanHtmlDirective implements SoyJavaPrintDirective, SoyJsSrcPrintDirective,
    SoyPySrcPrintDirective {


  private static final Joiner ARG_JOINER = Joiner.on(", ");

  // The directive may be called with a variable number of arguments indicating additional tags to
  // be considered safe, so we need to support each args size up to the number of possible
  // additional tags.
  private static final Set<Integer> VALID_ARGS_SIZES = ContiguousSet.create(
      Range.closed(0, OptionalSafeTag.values().length), DiscreteDomain.integers());


  @Inject
  public CleanHtmlDirective() {}


  @Override public String getName() {
    return "|cleanHtml";
  }

  @Override public final Set<Integer> getValidArgsSizes() {
    return VALID_ARGS_SIZES;
  }

  @Override public boolean shouldCancelAutoescape() {
    return false;
  }

  @Override public SoyValue applyForJava(SoyValue value, List<SoyValue> args) {
    ImmutableSet<OptionalSafeTag> optionalSafeTags = FluentIterable.from(args)
        .transform(SOY_VALUE_TO_STRING)
        // FROM_TAG_NAME throws IllegalArgumentException for invalid OptionalSafeTags.
        .transform(OptionalSafeTag.FROM_TAG_NAME)
        .toSet();

    return Sanitizers.cleanHtml(value, optionalSafeTags);
  }

  @Override public JsExpr applyForJsSrc(JsExpr value, List<JsExpr> args) {
    String optionalSafeTagsArg = generateOptionalSafeTagsArg(args);
    return new JsExpr(
        "soy.$$cleanHtml(" + value.getText() + optionalSafeTagsArg + ")", Integer.MAX_VALUE);
  }

  @Override public PyExpr applyForPySrc(PyExpr value, List<PyExpr> args) {
    String optionalSafeTagsArg = generateOptionalSafeTagsArg(args);
    return new PyExpr(
        "sanitize.clean_html(" + value.getText() + optionalSafeTagsArg + ")", Integer.MAX_VALUE);
  }

  /**
   * Converts a list of TargetExpr's into a list of safe tags as an argument for the supported
   * backends. This will iterate over the expressions, ensure they're valid safe tags, and convert
   * them into an array of Strings.
   *
   * <p>The generated output is valid for JS and Python. Any other languages should reevaluate if
   * they require changes.
   *
   * @param args A list of possible safe tags.
   * @return A string containing the safe tags argument.
   */
  private String generateOptionalSafeTagsArg(List<? extends TargetExpr> args) {
    String optionalSafeTagsArg = "";
    if (!args.isEmpty()) {
      // TODO(msamuel): Instead of parsing generated JS, we should have a CheckArgumentsPass that
      // allows directives and functions to examine their input expressions prior to compilation and
      // relay the input file and line number to the template author along with an error message.
      Iterable<String> optionalSafeTagExprs = Iterables.transform(args, TARGET_EXPR_TO_STRING);

      // Verify that all exprs are single-quoted valid OptionalSafeTags.
      for (String singleQuoted : optionalSafeTagExprs) {
        if (singleQuoted.length() < 2
            || singleQuoted.charAt(0) != '\''
            || singleQuoted.charAt(singleQuoted.length() - 1) != '\'') {
          throw new IllegalArgumentException(
              String.format("The cleanHtml directive expects arguments to be tag name string "
                + "literals, such as 'span'. Encountered: %s", singleQuoted));
        }
        String tagName = singleQuoted.substring(1, singleQuoted.length() - 1);
        OptionalSafeTag.fromTagName(tagName);  // throws if invalid
      }
      optionalSafeTagsArg = ", [" + ARG_JOINER.join(optionalSafeTagExprs) + "]";
    }
    return optionalSafeTagsArg;
  }

  private static final Function<SoyValue, String> SOY_VALUE_TO_STRING =
      new Function<SoyValue, String>() {
    @Override public String apply(SoyValue soyValue) {
      return soyValue.stringValue();
    }
  };

  private static final Function<TargetExpr, String> TARGET_EXPR_TO_STRING =
      new Function<TargetExpr, String>() {
    @Override public String apply(TargetExpr expr) {
      return expr.getText();
    }
  };
}