// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// TODO(rdsmith): This class needs to delegate URLRequest::Delegate methods
// to the net/ embedder for correct implementation of authentication.
// Specifically, this class needs the embedder to provide functionality
// corresponding to
// URLRequest::Delegate::{OnAuthRequired,OnCertificateRequested}.

#ifndef NET_URL_REQUEST_SDCH_DICTIONARY_FETCHER_H_
#define NET_URL_REQUEST_SDCH_DICTIONARY_FETCHER_H_

#include <queue>
#include <set>
#include <string>

#include "base/memory/scoped_ptr.h"
#include "base/memory/weak_ptr.h"
#include "base/threading/non_thread_safe.h"
#include "net/base/sdch_manager.h"
#include "net/url_request/url_fetcher_delegate.h"
#include "net/url_request/url_request.h"

namespace net {

class URLRequest;
class URLRequestThrottlerEntryInterface;

// This class is used by embedder SDCH policy object to fetch
// dictionaries. It queues requests for dictionaries and dispatches
// them serially, implementing the URLRequest::Delegate interface to
// handle callbacks (but see above TODO). It tracks all requests, only
// attempting to fetch each dictionary once.
class NET_EXPORT SdchDictionaryFetcher : public URLRequest::Delegate,
                                         public base::NonThreadSafe {
 public:
  typedef base::Callback<void(const std::string& dictionary_text,
                              const GURL& dictionary_url)>
      OnDictionaryFetchedCallback;

  // The consumer must guarantee that |*context| outlives this object.
  // |callback| will be called on successful dictionary fetch
  // requested through Schedule().  |callback| will not be called
  // after object destruction.
  SdchDictionaryFetcher(URLRequestContext* context,
                        const OnDictionaryFetchedCallback& callback);
  ~SdchDictionaryFetcher() override;

  // Request a new dictionary fetch.
  void Schedule(const GURL& dictionary_url);

  // Cancel any in-progress requests.
  void Cancel();

  // Implementation of URLRequest::Delegate methods.
  void OnResponseStarted(URLRequest* request) override;
  void OnReadCompleted(URLRequest* request, int bytes_read) override;

 private:
  enum State {
    STATE_NONE,
    STATE_IDLE,
    STATE_REQUEST_STARTED,
    STATE_REQUEST_READING,
    STATE_REQUEST_COMPLETE,
  };

  // State machine implementation.
  int DoLoop(int rv);
  int DoDispatchRequest(int rv);
  int DoRequestStarted(int rv);
  int DoRead(int rv);
  int DoCompleteRequest(int rv);

  State next_state_;
  bool in_loop_;

  // A queue of URLs that are being used to download dictionaries.
  std::queue<GURL> fetch_queue_;

  // The request and buffer used for getting the current dictionary
  // Both are null when a fetch is not in progress.
  scoped_ptr<URLRequest> current_request_;
  scoped_refptr<IOBuffer> buffer_;

  // The currently accumulating dictionary.
  std::string dictionary_;

  // Althought the SDCH spec does not preclude a server from using a single URL
  // to load several distinct dictionaries (by telling a client to load a
  // dictionary from an URL several times), current implementations seem to have
  // that 1-1 relationship (i.e., each URL points at a single dictionary, and
  // the dictionary content does not change over time, and hence is not worth
  // trying to load more than once). In addition, some dictionaries prove
  // unloadable only after downloading them (because they are too large?  ...or
  // malformed?). As a protective element, Chromium will *only* load a
  // dictionary at most once from a given URL (so that it doesn't waste
  // bandwidth trying repeatedly).
  // The following set lists all the dictionary URLs that we've tried to load,
  // so that we won't try to load from an URL more than once.
  // TODO(jar): Try to augment the SDCH proposal to include this restiction.
  std::set<GURL> attempted_load_;

  // Store the URLRequestContext associated with the owning SdchManager for
  // use while fetching.
  URLRequestContext* const context_;

  const OnDictionaryFetchedCallback dictionary_fetched_callback_;

  base::WeakPtrFactory<SdchDictionaryFetcher> weak_factory_;

  DISALLOW_COPY_AND_ASSIGN(SdchDictionaryFetcher);
};

}  // namespace net

#endif  // NET_URL_REQUEST_SDCH_DICTIONARY_FETCHER_H_