// Copyright (C) 2012 The Android Open Source Project
//
// 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.gerrit.httpd.restapi;

import static com.google.gerrit.httpd.restapi.RestApiServlet.replyBinaryResult;
import static com.google.gerrit.httpd.restapi.RestApiServlet.replyError;
import static javax.servlet.http.HttpServletResponse.SC_BAD_REQUEST;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Splitter;
import com.google.common.base.Strings;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import com.google.gerrit.extensions.restapi.BadRequestException;
import com.google.gerrit.extensions.restapi.BinaryResult;
import com.google.gerrit.extensions.restapi.Url;
import com.google.gerrit.util.cli.CmdLineParser;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;
import com.google.inject.Inject;

import org.kohsuke.args4j.CmdLineException;

import java.io.IOException;
import java.io.StringWriter;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

class ParameterParser {
  private static final ImmutableSet<String> RESERVED_KEYS = ImmutableSet.of(
      "pp", "prettyPrint", "strict", "callback", "alt", "fields");

  private final CmdLineParser.Factory parserFactory;

  @Inject
  ParameterParser(CmdLineParser.Factory pf) {
    this.parserFactory = pf;
  }

  <T> boolean parse(T param,
      Multimap<String, String> in,
      HttpServletRequest req,
      HttpServletResponse res)
      throws IOException {
    CmdLineParser clp = parserFactory.create(param);
    try {
      clp.parseOptionMap(in);
    } catch (CmdLineException e) {
      if (!clp.wasHelpRequestedByOption()) {
        replyError(res, SC_BAD_REQUEST, e.getMessage());
        return false;
      }
    }

    if (clp.wasHelpRequestedByOption()) {
      StringWriter msg = new StringWriter();
      clp.printQueryStringUsage(req.getRequestURI(), msg);
      msg.write('\n');
      msg.write('\n');
      clp.printUsage(msg, null);
      msg.write('\n');
      replyBinaryResult(req, res,
          BinaryResult.create(msg.toString()).setContentType("text/plain"));
      return false;
    }

    return true;
  }

  static void splitQueryString(String queryString,
      Multimap<String, String> config,
      Multimap<String, String> params) {
    if (!Strings.isNullOrEmpty(queryString)) {
      for (String kvPair : Splitter.on('&').split(queryString)) {
        Iterator<String> i = Splitter.on('=').limit(2).split(kvPair).iterator();
        String key = Url.decode(i.next());
        String val = i.hasNext() ? Url.decode(i.next()) : "";
        if (RESERVED_KEYS.contains(key)) {
          config.put(key, val);
        } else {
          params.put(key, val);
        }
      }
    }
  }

  private static Set<String> query(HttpServletRequest req) {
    Set<String> params = Sets.newHashSet();
    if (!Strings.isNullOrEmpty(req.getQueryString())) {
      for (String kvPair : Splitter.on('&').split(req.getQueryString())) {
        params.add(Iterables.getFirst(
            Splitter.on('=').limit(2).split(kvPair),
            null));
      }
    }
    return params;
  }

  /**
   * Convert a standard URL encoded form input into a parsed JSON tree.
   * <p>
   * Given an input such as:
   *
   * <pre>
   * message=Does+not+compile.&labels.Verified=-1
   * </pre>
   *
   * which is easily created using the curl command line tool:
   *
   * <pre>
   * curl --data 'message=Does not compile.' --data labels.Verified=-1
   * </pre>
   *
   * converts to a JSON object structure that is normally expected:
   *
   * <pre>
   * {
   *   "message": "Does not compile.",
   *   "labels": {
   *     "Verified": "-1"
   *   }
   * }
   * </pre>
   *
   * This input can then be further processed into the Java input type expected
   * by a view using Gson. Here we rely on Gson to perform implicit conversion
   * of a string {@code "-1"} to a number type when the Java input type expects
   * a number.
   * <p>
   * Conversion assumes any field name that does not contain {@code "."} will be
   * a property of the top level input object. Any field with a dot will use the
   * first segment as the top level property name naming an object, and the rest
   * of the field name as a property in the nested object.
   *
   * @param req request to parse form input from and create JSON tree.
   * @return the converted JSON object tree.
   * @throws BadRequestException the request cannot be cast, as there are
   *         conflicting definitions for a nested object.
   */
  static JsonObject formToJson(HttpServletRequest req)
      throws BadRequestException {
    @SuppressWarnings("unchecked")
    Map<String, String[]> map = req.getParameterMap();
    return formToJson(map, query(req));
  }

  @VisibleForTesting
  static JsonObject formToJson(Map<String, String[]> map, Set<String> query)
      throws BadRequestException {
    JsonObject inputObject = new JsonObject();
    for (Map.Entry<String, String[]> ent : map.entrySet()) {
      String key = ent.getKey();
      String[] values = ent.getValue();

      if (query.contains(key) || values.length == 0) {
        // Disallow processing query parameters as input body fields.
        // Implementations of views should avoid duplicate naming.
        continue;
      }

      JsonObject obj = inputObject;
      int dot = key.indexOf('.');
      if (0 <= dot) {
        String property = key.substring(0, dot);
        JsonElement e = inputObject.get(property);
        if (e == null) {
          obj = new JsonObject();
          inputObject.add(property, obj);
        } else if (e.isJsonObject()) {
          obj = e.getAsJsonObject();
        } else {
          throw new BadRequestException(String.format(
              "key %s conflicts with %s",
              key, property));
        }
        key = key.substring(dot + 1);
      }

      if (obj.get(key) != null) {
        // This error should never happen. If all form values are handled
        // together in a single pass properties are set only once. Setting
        // again indicates something has gone very wrong.
        throw new BadRequestException("invalid form input, use JSON instead");
      } else if (values.length == 1) {
        obj.addProperty(key, values[0]);
      } else {
        JsonArray list = new JsonArray();
        for (String v : values) {
          list.add(new JsonPrimitive(v));
        }
        obj.add(key, list);
      }
    }
    return inputObject;
  }
}