#include "common.hh"

#include "http_protocol.hh"

#include <memory>
#include <string.h>
#include <time.h>
#include <vector>

namespace {

uint16_t number(std::string_view data, size_t start, size_t end) {
  uint16_t ret = 0;
  assert(start < end);
  for (; start < end; ++start) {
    ret *= 10;
    ret += data[start] - '0';
  }
  return ret;
}

inline char lower_ascii(char c) {
  return (c >= 'A' && c <= 'Z') ? (c - 'A' + 'a') : c;
}

inline bool is_lws(char c) {
  return c == ' ' || c == '\t';
}

inline bool is_char(char c) {
  return !(c & 0x80);
}

inline bool is_ctl(char c) {
  return c < ' ' || c == 0x7f;
}

inline bool is_separator(char c) {
  return is_lws(c) || c == '(' || c == ')' || c == '<' || c == '>' || c == '@'
    || c == ',' || c == ';' || c == ':' || c == '\\' || c == '\"' || c == '/'
    || c == '[' || c == ']' || c == '?' || c == '=' || c == '{' || c == '}';
}

inline bool is_token(char c) {
  return is_char(c) && !is_ctl(c) && !is_separator(c);
}

void make_lowercase(std::string& data, size_t start, size_t end) {
  for (size_t i = start; i <= end; ++i) {
    char lower = lower_ascii(data[i]);
    if (lower != data[i])
      data[i] = lower;
  }
}

bool allow_header_append(std::string_view name) {
  // These headers doesn't handle being merged with ',' even if the standard
  // say they must
  return !(name == "set-cookie" || name == "set-cookie2");
}

enum ParseResult {
  GOOD,
  BAD,
  INCOMPLETE,
};

class HeaderIteratorImpl : public HeaderIterator {
public:
  HeaderIteratorImpl(std::string_view data, std::vector<size_t> const* headers)
    : data_(data), headers_(headers), iter_(headers_->begin()) {
  }

  bool valid() const override {
    return iter_ != headers_->end();
  }

  std::string_view name() const override {
    return data_.substr(iter_[0], iter_[1] - iter_[0]);
  }

  std::string value() const override {
    std::string ret(data_.substr(iter_[2], iter_[3] - iter_[2]));
    if (allow_header_append(name())) {
      auto i = iter_ + 4;
      while (i != headers_->end()) {
        if (i[0] != i[1]) break;
        ret.push_back(',');
        ret.append(data_.substr(i[2], i[3] - i[2]));
        i += 4;
      }
    }
    return ret;
  }

  void next() override {
    if (iter_ != headers_->end()) {
      while (true) {
        iter_ += 4;
        if (iter_ == headers_->end() || iter_[0] != iter_[1])
          break;
      }
    }
  }

private:
  std::string_view const data_;
  std::vector<size_t> const* const headers_;
  std::vector<size_t>::const_iterator iter_;
};

class FilterHeaderIteratorImpl : public HeaderIteratorImpl {
public:
  FilterHeaderIteratorImpl(std::string_view data,
                           std::vector<size_t> const* headers,
                           std::string_view filter)
    : HeaderIteratorImpl(data, headers), filter_(filter) {
    check_filter();
  }

  void next() override {
    HeaderIteratorImpl::next();
    check_filter();
  }

private:
  void check_filter() {
    while (true) {
      if (!valid() || name() == filter_)
        return;
      HeaderIteratorImpl::next();
    }
  }

  std::string_view const filter_;
};

class HeaderTokenIteratorImpl : public HeaderTokenIterator {
public:
  explicit HeaderTokenIteratorImpl(std::unique_ptr<HeaderIterator>&& header)
    : header_(std::move(header)), start_(0), middle_(0), end_(0) {
    check_token();
  }

  bool valid() const override {
    return header_->valid();
  }

  std::string token() const override {
    return header_->value().substr(start_, middle_ - start_);
  }

  void next() override {
    start_ = end_;
    check_token();
  }

private:
  static size_t skip_lws(std::string const& str, size_t pos) {
    while (pos < str.size() && is_lws(str[pos])) ++pos;
    return pos;
  }

  static size_t skip_token(std::string const& str, size_t pos) {
    assert(is_token(str[pos]));
    ++pos;
    while (pos < str.size() && is_token(str[pos])) ++pos;
    return pos;
  }

  static size_t skip_quoted(std::string const& str, size_t pos) {
    assert(str[pos] == '"');
    ++pos;
    while (pos < str.size()) {
      if (str[pos] == '\\') {
        pos += 2;
      } else if (str[pos] == '\"') {
        ++pos;
        break;
      } else {
        ++pos;
      }
    }
    return pos;
  }

  void check_token() {
    while (true) {
      if (!header_->valid()) return;
      auto const& value = header_->value();
      start_ = skip_lws(value, start_);
      if (start_ >= value.size()) {
        header_->next();
        start_ = 0;
        continue;
      }
      if (!is_token(value[start_])) {
        if (value[start_] != ';') {
          ++start_;
          while (start_ < value.size()
               && !(is_lws(value[start_]) || value[start_] == ','
                    || value[start_] == ';')) {
            ++start_;
          }
          if (start_ < value.size() && value[start_] != ';') {
            continue;
          }
        }
        // This will cause us to loop again after paramters
        // are read
        middle_ = start_;
      } else {
        middle_ = skip_token(value, start_);
      }
      end_ = middle_;
      while (true) {
        end_ = skip_lws(value, end_);
        if (end_ == value.size() || value[end_] != ';') break;
        end_ = skip_lws(value, end_ + 1);
        if (!is_token(value[end_])) {
          while (end_ < value.size() && !is_separator(value[end_])) ++end_;
          continue;
        }
        end_ = skip_token(value, end_);
        end_ = skip_lws(value, end_);
        if (end_ == value.size() || value[end_] != '=') break;
        end_ = skip_lws(value, end_ + 1);
        if (end_ < value.size() && value[end_] == '"') {
          end_ = skip_quoted(value, end_);
        } else {
          if (!is_token(value[end_])) {
            while (end_ < value.size() && !is_separator(value[end_])) ++end_;
            continue;
          }
          end_ = skip_token(value, end_);
        }
      }
      if (end_ < value.size() && value[end_] == ',') ++end_;
      if (start_ < middle_) return;
      start_ = end_;
    }
  }

  std::unique_ptr<HeaderIterator> header_;
  size_t start_;
  size_t middle_;
  size_t end_;
};

size_t find_newline(std::string_view data, size_t start, size_t* next) {
  assert(start <= data.size());
  for (; start < data.size(); ++start) {
    if (data[start] == '\r') {
      if (start + 1 < data.size() && data[start + 1] == '\n') {
        if (next) *next = start + 2;
      } else {
        if (next) *next = start + 1;
      }
      return start;
    } else if (data[start] == '\n') {
      if (next) *next = start + 1;
      return start;
    }
  }
  return std::string::npos;
}

size_t find(std::string_view data, size_t start, char c, size_t end) {
  assert(start <= end);
  for (; start < end; ++start) {
    if (data[start] == c) return start;
  }
  return std::string::npos;
}

size_t skip_lws(std::string_view data, size_t start, size_t end) {
  assert(start <= end);
  while (start < end && is_lws(data[start])) ++start;
  return start;
}

size_t valid_number(std::string_view data, size_t start, size_t end) {
  assert(start <= end);
  if (start == end)
    return std::string::npos;
  if (data[start] == '0') {
    return start + 1;
  }
  if (data[start] < '0' || data[start] > '9')
    return std::string::npos;
  for (++start; start < end; ++start) {
    if (data[start] < '0' || data[start] > '9')
      break;
  }
  return start;
}

ParseResult parse_headers(std::string_view data, size_t* offset,
                          std::vector<size_t>* headers) {
  assert(*offset <= data.size());
  assert(headers->empty());
  while (true) {
    auto start = *offset;
    auto end = find_newline(data, start, offset);
    if (end == std::string::npos)
      return INCOMPLETE;
    if (end == start) {
      // The final newline can only be a alone '\r' if the one in front of
      // it is also '\r', otherwise we expect a missing '\n'
      if (data[start - 1] == '\n' && data[*offset - 1] == '\r') {
        return INCOMPLETE;
      }
      break;
    }
    if (is_lws(data[start])) {
      if (headers->empty())
        return BAD;
      headers->push_back(start);
      headers->push_back(start);
      headers->push_back(start + 1);
      headers->push_back(end);
    } else {
      auto colon = find(data, start, ':', end);
      if (colon == std::string::npos) return BAD;
      auto value_start = skip_lws(data, colon + 1, end);
      while (colon > start && is_lws(data[colon - 1])) --colon;
      headers->push_back(start);
      headers->push_back(colon);
      headers->push_back(value_start);
      headers->push_back(end);
    }
  }
  return GOOD;
}

std::string make_lowercase_header_names(std::string_view data,
                                        std::vector<size_t> const& headers) {
  std::string ret(data);
  for (size_t i = 0; i < headers.size(); i += 4) {
    make_lowercase(ret, headers[i], headers[i + 1]);
  }
  return ret;
}

class AbstractHttp : public virtual HttpPackage {
public:
  AbstractHttp(std::string data, bool good, size_t proto_start,
               size_t proto_slash, size_t proto_dot, size_t proto_end,
               std::vector<size_t> headers, size_t content_start)
    : data_(std::move(data)), good_(good), proto_start_(proto_start),
      proto_slash_(proto_slash), proto_dot_(proto_dot), proto_end_(proto_end),
      headers_(std::move(headers)), content_start_(content_start) {
  }

  bool good() const override {
    return good_;
  }

  std::string_view proto() const override {
    return std::string_view(data_).substr(
        proto_start_, proto_slash_ - proto_start_);
  }

  Version proto_version() const override {
    Version ret;
    ret.major = number(data_, proto_slash_ + 1, proto_dot_);
    ret.minor = number(data_, proto_dot_ + 1, proto_end_);
    return ret;
  }

  std::unique_ptr<HeaderIterator> header() const override {
    return std::make_unique<HeaderIteratorImpl>(data_, &headers_);
  }
  std::unique_ptr<HeaderIterator> header(
      std::string_view name) const override {
    return std::make_unique<FilterHeaderIteratorImpl>(data_, &headers_, name);
  }

  std::unique_ptr<HeaderTokenIterator> header_tokens(std::string_view name)
      const override {
    return std::make_unique<HeaderTokenIteratorImpl>(header(name));
  }

  size_t size() const override {
    return content_start_;
  }

protected:
  std::string const data_;
  bool const good_;
  size_t const proto_start_;
  size_t const proto_slash_;
  size_t const proto_dot_;
  size_t const proto_end_;
  std::vector<size_t> const headers_;
  size_t const content_start_;
};

class HttpResponseImpl : public HttpResponse, protected AbstractHttp {
public:
  HttpResponseImpl(std::string data, bool good,
                   size_t proto_start, size_t proto_slash,
                   size_t proto_dot, size_t proto_end,
                   size_t status_start,
                   size_t status_end, size_t status_msg_start,
                   size_t status_msg_end,
                   std::vector<size_t> headers,
                   size_t content_start)
    : AbstractHttp(std::move(data), good, proto_start, proto_slash, proto_dot,
                   proto_end, std::move(headers), content_start),
      status_start_(status_start), status_end_(status_end),
      status_msg_start_(status_msg_start), status_msg_end_(status_msg_end) {
  }

  uint16_t status_code() const override {
    return number(data_, status_start_, status_end_);
  }

  std::string_view status_message() const override {
    return std::string_view(data_).substr(status_msg_start_,
                                          status_msg_end_ - status_msg_start_);
  }

  static std::unique_ptr<HttpResponse> parse(std::string_view data) {
    size_t content_start = 0;
    size_t status_msg_end = find_newline(data, 0, &content_start);
    if (status_msg_end == std::string::npos)
      return nullptr;
    size_t proto_start = 0;
    size_t proto_slash = find(data, 0, '/', status_msg_end);
    if (proto_slash == std::string::npos)
      return make_bad_http_response();
    size_t proto_dot = valid_number(data, proto_slash + 1, status_msg_end);
    if (proto_dot == std::string::npos || data[proto_dot] != '.')
      return make_bad_http_response();
    size_t proto_end = valid_number(data, proto_dot + 1, status_msg_end);
    if (proto_end == std::string::npos || !is_lws(data[proto_end]))
      return make_bad_http_response();
    size_t status_start = skip_lws(data, proto_end + 1, status_msg_end);
    size_t status_end = valid_number(data, status_start, status_msg_end);
    if (status_end == std::string::npos)
      return make_bad_http_response();
    size_t status_msg_start;
    if (is_lws(data[status_end])) {
      status_msg_start = skip_lws(data, status_end + 1, status_msg_end);
    } else {
      status_msg_start = status_end;
      if (status_msg_start != status_msg_end)
        return make_bad_http_response();
    }

    std::vector<size_t> headers;
    switch (parse_headers(data, &content_start, &headers)) {
    case GOOD:
      return std::make_unique<HttpResponseImpl>(
          make_lowercase_header_names(data, headers), true,
          proto_start, proto_slash, proto_dot, proto_end,
          status_start, status_end, status_msg_start, status_msg_end,
          std::move(headers), content_start);
    case BAD:
      return make_bad_http_response();
    case INCOMPLETE:
      return nullptr;
    }
    assert(false);
    return nullptr;
  }

private:
  static std::unique_ptr<HttpResponse> make_bad_http_response() {
    return std::make_unique<HttpResponseImpl>(std::string(), false,
                                              0, 0, 0, 0, 0, 0, 0, 0,
                                              std::vector<size_t>(), 0);
  }

  size_t const status_start_;
  size_t const status_end_;
  size_t const status_msg_start_;
  size_t const status_msg_end_;
};

class HttpRequestImpl : public HttpRequest, protected AbstractHttp {
public:
  HttpRequestImpl(std::string data, bool good,
                  size_t method_end, size_t url_start, size_t url_end,
                  size_t proto_start, size_t proto_slash,
                  size_t proto_dot, size_t proto_end,
                  std::vector<size_t> headers,
                  size_t content_start)
    : AbstractHttp(std::move(data), good, proto_start, proto_slash,
                   proto_dot, proto_end, std::move(headers), content_start),
      method_end_(method_end), url_start_(url_start), url_end_(url_end) {
  }

  std::string_view method() const override {
    return std::string_view(data_).substr(0, method_end_);
  }

  std::string_view url() const override {
    return std::string_view(data_).substr(url_start_, url_end_ - url_start_);
  }

  static std::unique_ptr<HttpRequest> parse(std::string_view data) {
    size_t content_start = 0;
    size_t proto_end = find_newline(data, 0, &content_start);
    if (proto_end == std::string::npos)
      return nullptr;
    size_t method_end = 0;
    while (method_end < proto_end && !is_lws(data[method_end])) {
      ++method_end;
    }
    if (method_end == 0 || method_end == proto_end)
      return make_bad_request();
    size_t url_start = skip_lws(data, method_end + 1, proto_end);
    size_t url_end = url_start;
    while (url_end < proto_end && !is_lws(data[url_end]))
      ++url_end;
    if (url_end == url_start || url_end == proto_end)
      return make_bad_request();
    size_t proto_start = skip_lws(data, url_end + 1, proto_end);
    size_t proto_slash = find(data, proto_start, '/', proto_end);
    if (proto_slash == std::string::npos)
      return make_bad_request();
    size_t proto_dot = valid_number(data, proto_slash + 1, proto_end);
    if (proto_dot == std::string::npos || data[proto_dot] != '.')
      return make_bad_request();
    auto tmp = valid_number(data, proto_dot + 1, proto_end);
    if (tmp != proto_end)
      return make_bad_request();

    std::vector<size_t> headers;
    switch (parse_headers(data, &content_start, &headers)) {
    case GOOD:
      return std::make_unique<HttpRequestImpl>(
          make_lowercase_header_names(data, headers), true,
          method_end, url_start, url_end,
          proto_start, proto_slash,
          proto_dot, proto_end,
          std::move(headers), content_start);
    case BAD:
      return make_bad_request();
    case INCOMPLETE:
      return nullptr;
    }
    assert(false);
    return nullptr;
  }

private:
  static std::unique_ptr<HttpRequest> make_bad_request() {
    return std::make_unique<HttpRequestImpl>("", false, 0, 0, 0, 0, 0, 0, 0,
                                             std::vector<size_t>(), 0);
  }

  size_t const method_end_;
  size_t const url_start_;
  size_t const url_end_;
};

class AbstractHttpBuilder {
public:
  void add_header(std::string name, std::string value) {
    headers_.emplace_back(std::move(name), std::move(value));
  }

  bool build(Buffer* dst) const {
    for (auto const& pair : headers_) {
      if (pair.first.empty()) {
        if (!append(dst, " "))
          return false;
      } else {
        if (!append(dst, pair.first) ||
            !append(dst, ": "))
          return false;
      }
      if (!append(dst, pair.second) ||
          !append(dst, "\r\n"))
        return false;
    }
    return append(dst, "\r\n");
  }

  size_t size() const {
    size_t ret = 0;
    for (auto const& pair : headers_) {
      if (pair.first.empty()) {
        ++ret;  // ' '
      } else {
        ret += pair.first.size() + 2;  // ": "
      }
      ret += pair.second.size() + 2;  // \r\”
    }
    return ret + 2;  // \r\n
  }

protected:
  bool append(Buffer* dst, std::string_view str) const {
    return Buffer::write(dst, str.data(), str.size()) == str.size();
  }

  std::vector<std::pair<std::string, std::string>> headers_;
};

class HttpRequestBuilderImpl : public HttpRequestBuilder, AbstractHttpBuilder {
public:
  HttpRequestBuilderImpl(std::string method, std::string url, std::string proto,
                         Version version)
    : method_(std::move(method)), url_(std::move(url)),
      proto_(std::move(proto)), version_(version) {}

  void add_header(std::string name, std::string value) override {
    AbstractHttpBuilder::add_header(std::move(name), std::move(value));
  }

  bool build(Buffer* dst) const override {
    if (!append(dst, method_) ||
        !append(dst, " ") ||
        !append(dst, url_) ||
        !append(dst, " ") ||
        !append(dst, proto_) ||
        !append(dst, "/"))
      return false;
    char tmp[10];
    auto len = snprintf(tmp, sizeof(tmp), "%u",
                        static_cast<unsigned int>(version_.major));
    if (!append(dst, std::string_view(tmp, len)))
      return false;
    if (!append(dst, "."))
      return false;
    len = snprintf(tmp, sizeof(tmp), "%u",
                   static_cast<unsigned int>(version_.minor));
    if (!append(dst, std::string_view(tmp, len)))
      return false;
    if (!append(dst, "\r\n"))
      return false;
    return AbstractHttpBuilder::build(dst);
  }

  size_t size() const override {
    size_t ret = 0;
    ret += method_.size() + 1 + url_.size() + 1 + proto_.size() + 1;
    char tmp[10];
    auto len = snprintf(tmp, sizeof(tmp), "%u",
                        static_cast<unsigned int>(version_.major));
    ret += len;
    ++ret;  // '.'
    len = snprintf(tmp, sizeof(tmp), "%u",
                   static_cast<unsigned int>(version_.minor));
    ret += len;
    ret += 2;  // \r\n
    return ret + AbstractHttpBuilder::size();
  }

private:
  std::string const method_;
  std::string const url_;
  std::string const proto_;
  Version const version_;
};

class HttpResponseBuilderImpl : public HttpResponseBuilder,
                                AbstractHttpBuilder {
public:
  HttpResponseBuilderImpl(std::string proto, Version version,
                          uint16_t status_code, std::string status)
    : proto_(std::move(proto)), version_(version), status_code_(status_code),
      status_(std::move(status)) {
  }

  void add_header(std::string name, std::string value) override {
    AbstractHttpBuilder::add_header(std::move(name), std::move(value));
  }

  bool build(Buffer* dst) const override {
    if (!append(dst, proto_) ||
        !append(dst, "/"))
      return false;
    char tmp[10];
    auto len = snprintf(tmp, sizeof(tmp), "%u",
                        static_cast<unsigned int>(version_.major));
    if (!append(dst, std::string_view(tmp, len)) ||
        !append(dst, "."))
      return false;
    len = snprintf(tmp, sizeof(tmp), "%u",
                   static_cast<unsigned int>(version_.minor));
    if (!append(dst, std::string_view(tmp, len)) ||
        !append(dst, " "))
      return false;
    len = snprintf(tmp, sizeof(tmp), "%u",
                   static_cast<unsigned int>(status_code_));
    if (!append(dst, std::string_view(tmp, len)) ||
        !append(dst, " ") ||
        !append(dst, status_) ||
        !append(dst, "\r\n"))
      return false;
    return AbstractHttpBuilder::build(dst);
  }

  size_t size() const override {
    size_t ret = 0;
    ret += proto_.size();
    ++ret;  // "/"
    char tmp[10];
    auto len = snprintf(tmp, sizeof(tmp), "%u",
                        static_cast<unsigned int>(version_.major));
    ret += len;
    ++ret;  // "."
    len = snprintf(tmp, sizeof(tmp), "%u",
                   static_cast<unsigned int>(version_.minor));
    ret += len;
    ++ret;  // " "
    len = snprintf(tmp, sizeof(tmp), "%u",
                   static_cast<unsigned int>(status_code_));
    ret += len;
    ++ret;  // " "
    ret += status_.length();
    ret += 2;  // \r\n
    return ret + AbstractHttpBuilder::size();
  }

private:
  std::string const proto_;
  Version const version_;
  uint16_t const status_code_;
  std::string const status_;
};

class CgiResponseBuilderImpl : public CgiResponseBuilder,
                               AbstractHttpBuilder {
public:
  explicit CgiResponseBuilderImpl(uint16_t status_code) {
    AbstractHttpBuilder::add_header("Status", std::to_string(status_code));
  }

  void add_header(std::string name, std::string value) override {
    AbstractHttpBuilder::add_header(std::move(name), std::move(value));
  }

  bool build(Buffer* dst) const override {
    return AbstractHttpBuilder::build(dst);
  }

  size_t size() const override  {
    return AbstractHttpBuilder::size();
  }
};

}  // namespace

// static
std::unique_ptr<HttpResponse> HttpResponse::parse(RoBuffer* buffer) {
  size_t want = 1024;
  size_t last_avail = 0;
  while (true) {
    size_t avail;
    auto* rptr = buffer->rbuf(want, avail);
    if (avail == last_avail)
      return nullptr;
    last_avail = avail;
    auto resp = HttpResponseImpl::parse(std::string_view(rptr, avail));
    if (resp) {
      buffer->rcommit(resp->size());
      return resp;
    }
    want = avail + 1024;
  }
}

std::string HttpPackage::first_header(std::string_view name) const {
  static std::string empty_str;
  auto iter = header(name);
  if (iter->valid()) {
    return iter->value();
  }
  return empty_str;
}

// static
std::unique_ptr<HttpRequest> HttpRequest::parse(RoBuffer* buffer) {
  size_t want = 1024;
  size_t last_avail = 0;
  while (true) {
    size_t avail;
    auto* rptr = buffer->rbuf(want, avail);
    if (avail == last_avail)
      return nullptr;
    last_avail = avail;
    auto req = HttpRequestImpl::parse(std::string_view(rptr, avail));
    if (req) {
      buffer->rcommit(req->size());
      return req;
    }
    want = avail + 1024;
  }
}

// static
std::unique_ptr<HttpRequestBuilder> HttpRequestBuilder::create(
    std::string method,
    std::string url,
    std::string proto,
    Version version) {
  return std::make_unique<HttpRequestBuilderImpl>(std::move(method),
                                                  std::move(url),
                                                  std::move(proto), version);
}

// static
std::unique_ptr<HttpResponseBuilder> HttpResponseBuilder::create(
    std::string proto,
    Version version,
    uint16_t status_code,
    std::string status) {
  return std::make_unique<HttpResponseBuilderImpl>(std::move(proto), version,
                                                   status_code,
                                                   std::move(status));
}

// static
std::unique_ptr<CgiResponseBuilder> CgiResponseBuilder::create(
    uint16_t status_code) {
  return std::make_unique<CgiResponseBuilderImpl>(status_code);
}

std::string_view http_standard_message(uint16_t code) {
  switch (code) {
  case 100:
    return "Continue";
  case 101:
    return "Switching Protocols";
  case 200:
    return "OK";
  case 201:
    return "Created";
  case 202:
    return "Accepted";
  case 203:
    return "Non-Authorative Information";
  case 204:
    return "No Content";
  case 205:
    return "Reset Content";
  case 206:
    return "Partial Content";
  case 300:
    return "Multiple Choices";
  case 301:
    return "Moved Permanently";
  case 302:
    return "Found";
  case 303:
    return "See Other";
  case 304:
    return "Not Modified";
  case 305:
    return "Use Proxy";
  case 307:
    return "Temporary Redirect";
  case 400:
    return "Bad Request";
  case 401:
    return "Unauthorized";
  case 402:
    return "Payment Required";
  case 403:
    return "Forbidden";
  case 404:
    return "Not Found";
  case 405:
    return "Method Not Allowed";
  case 406:
    return "Not Acceptable";
  case 407:
    return "Proxy Authentication Required";
  case 408:
    return "Request Timeout";
  case 409:
    return "Conflict";
  case 410:
    return "Gone";
  case 411:
    return "Length Required";
  case 412:
    return "Precondition Failed";
  case 413:
    return "Request Entity Too Large";
  case 414:
    return "Request-URI Too Long";
  case 415:
    return "Unsupported Media Type";
  case 416:
    return "Requested Range Not Satisfiable";
  case 417:
    return "Expectation Failed";
  case 500:
    return "Internal Server Error";
  case 501:
    return "Not Implemented";
  case 502:
    return "Bad Gateway";
  case 503:
    return "Service Unavailable";
  case 504:
    return "Gateway Timeout";
  case 505:
    return "HTTP Version Not Supported";
  }
  return "";
}

std::string http_date(time_t in) {
  char tmp[50];
  auto len = strftime(tmp, sizeof(tmp), "%a, %d %b %Y %H:%M:%S GMT",
                      gmtime(&in));
  return std::string(tmp, len);
}