// 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.

#include "net/url_request/sdch_dictionary_fetcher.h"

#include <stdint.h>

#include "base/auto_reset.h"
#include "base/bind.h"
#include "base/compiler_specific.h"
#include "base/thread_task_runner_handle.h"
#include "net/base/load_flags.h"
#include "net/url_request/url_request_context.h"
#include "net/url_request/url_request_status.h"
#include "net/url_request/url_request_throttler_manager.h"

namespace {

const int kBufferSize = 4096;

}  // namespace

namespace net {

SdchDictionaryFetcher::SdchDictionaryFetcher(
    URLRequestContext* context,
    const OnDictionaryFetchedCallback& callback)
    : next_state_(STATE_NONE),
      in_loop_(false),
      context_(context),
      dictionary_fetched_callback_(callback),
      weak_factory_(this) {
  DCHECK(CalledOnValidThread());
  DCHECK(context);
}

SdchDictionaryFetcher::~SdchDictionaryFetcher() {
  DCHECK(CalledOnValidThread());
}

void SdchDictionaryFetcher::Schedule(const GURL& dictionary_url) {
  DCHECK(CalledOnValidThread());

  // Avoid pushing duplicate copy onto queue. We may fetch this url again later
  // and get a different dictionary, but there is no reason to have it in the
  // queue twice at one time.
  if (!fetch_queue_.empty() && fetch_queue_.back() == dictionary_url) {
    SdchManager::SdchErrorRecovery(
        SdchManager::DICTIONARY_ALREADY_SCHEDULED_TO_DOWNLOAD);
    return;
  }
  if (attempted_load_.find(dictionary_url) != attempted_load_.end()) {
    SdchManager::SdchErrorRecovery(
        SdchManager::DICTIONARY_ALREADY_TRIED_TO_DOWNLOAD);
    return;
  }
  attempted_load_.insert(dictionary_url);
  fetch_queue_.push(dictionary_url);

  next_state_ = STATE_IDLE;

  // There are no callbacks to user code from the dictionary fetcher,
  // and Schedule() is only called from user code, so this call to DoLoop()
  // does not require an |if (in_loop_) return;| guard.
  DoLoop(OK);
}

void SdchDictionaryFetcher::Cancel() {
  DCHECK(CalledOnValidThread());

  next_state_ = STATE_NONE;

  while (!fetch_queue_.empty())
    fetch_queue_.pop();
  attempted_load_.clear();
  weak_factory_.InvalidateWeakPtrs();
  current_request_.reset(NULL);
  buffer_ = NULL;
  dictionary_.clear();
}

void SdchDictionaryFetcher::OnResponseStarted(URLRequest* request) {
  DCHECK(CalledOnValidThread());
  DCHECK_EQ(request, current_request_.get());
  DCHECK_EQ(next_state_, STATE_REQUEST_STARTED);

  // The response has started, so the stream can be read from.
  next_state_ = STATE_REQUEST_READING;

  // If this function was synchronously called, the containing
  // state machine loop will handle the state transition. Otherwise,
  // restart the state machine loop.
  if (in_loop_)
    return;

  DoLoop(request->status().error());
}

void SdchDictionaryFetcher::OnReadCompleted(URLRequest* request,
                                            int bytes_read) {
  DCHECK(CalledOnValidThread());
  DCHECK_EQ(request, current_request_.get());
  DCHECK_EQ(next_state_, STATE_REQUEST_READING);

  // No state transition is required in this function; the
  // completion of the request is detected in DoRead().

  if (request->status().is_success())
    dictionary_.append(buffer_->data(), bytes_read);

  // If this function was synchronously called, the containing
  // state machine loop will handle the state transition. Otherwise,
  // restart the state machine loop.
  if (in_loop_)
    return;

  DoLoop(request->status().error());
}

int SdchDictionaryFetcher::DoLoop(int rv) {
  DCHECK(!in_loop_);
  base::AutoReset<bool> auto_reset_in_loop(&in_loop_, true);

  do {
    State state = next_state_;
    next_state_ = STATE_NONE;
    switch (state) {
      case STATE_IDLE:
        rv = DoDispatchRequest(rv);
        break;
      case STATE_REQUEST_STARTED:
        rv = DoRequestStarted(rv);
        break;
      case STATE_REQUEST_READING:
        rv = DoRead(rv);
        break;
      case STATE_REQUEST_COMPLETE:
        rv = DoCompleteRequest(rv);
        break;
      case STATE_NONE:
        NOTREACHED();
    }
  } while (rv != ERR_IO_PENDING && next_state_ != STATE_NONE);

  return rv;
}

int SdchDictionaryFetcher::DoDispatchRequest(int rv) {
  DCHECK(CalledOnValidThread());

  // |rv| is ignored, as the result from the previous request doesn't
  // affect the next request.

  if (fetch_queue_.empty() || current_request_.get()) {
    next_state_ = STATE_NONE;
    return OK;
  }

  current_request_ =
      context_->CreateRequest(fetch_queue_.front(), IDLE, this, NULL);
  current_request_->SetLoadFlags(LOAD_DO_NOT_SEND_COOKIES |
                                 LOAD_DO_NOT_SAVE_COOKIES);
  buffer_ = new IOBuffer(kBufferSize);
  fetch_queue_.pop();

  next_state_ = STATE_REQUEST_STARTED;
  current_request_->Start();

  return OK;
}

int SdchDictionaryFetcher::DoRequestStarted(int rv) {
  DCHECK(CalledOnValidThread());
  DCHECK_EQ(rv, OK);  // Can only come straight from above function.

  // The transition to STATE_REQUEST_READING occurs in the
  // OnResponseStarted() callback triggered by URLRequest::Start()
  // (called in DoDispatchRequest(), above). If that callback did not
  // occur synchronously, this routine is executed; it returns ERR_IO_PENDING,
  // indicating to the controlling loop that no further work should be done
  // until the callback occurs (which will re-invoke DoLoop()).
  next_state_ = STATE_REQUEST_STARTED;
  return ERR_IO_PENDING;
}

int SdchDictionaryFetcher::DoRead(int rv) {
  DCHECK(CalledOnValidThread());

  // If there's been an error, abort the current request.
  if (rv != OK) {
    current_request_.reset();
    buffer_ = NULL;
    next_state_ = STATE_IDLE;

    return OK;
  }

  next_state_ = STATE_REQUEST_READING;
  int bytes_read = 0;
  if (!current_request_->Read(buffer_.get(), kBufferSize, &bytes_read)) {
    if (current_request_->status().is_io_pending())
      return ERR_IO_PENDING;

    if (current_request_->status().error() == OK) {
      // This "should never happen", but if it does the result will be
      // an infinite loop.  It's not clear how to handle a read failure
      // without a promise to invoke the callback at some point in the future,
      // so the request is failed.
      SdchManager::SdchErrorRecovery(SdchManager::DICTIONARY_FETCH_READ_FAILED);
      DLOG(FATAL)
          << "URLRequest::Read() returned false without IO pending or error!";
      return ERR_FAILED;
    }

    return current_request_->status().error();
  }

  if (bytes_read != 0)
    dictionary_.append(buffer_->data(), bytes_read);
  else
    next_state_ = STATE_REQUEST_COMPLETE;

  return OK;
}

int SdchDictionaryFetcher::DoCompleteRequest(int rv) {
  DCHECK(CalledOnValidThread());

  // If the dictionary was successfully fetched, add it to the manager.
  if (rv == OK)
    dictionary_fetched_callback_.Run(dictionary_, current_request_->url());

  current_request_.reset();
  buffer_ = NULL;
  dictionary_.clear();

  next_state_ = STATE_IDLE;

  return OK;
}

}  // namespace net