#include "websocket.hh"

#include "base64.hh"
#include "buffer.hh"
#include "cfg.hh"
#include "http.hh"
#include "logger.hh"
#include "looper.hh"
#include "sha1.hh"
#include "unique_fd.hh"

#include <algorithm>
#include <cassert>
#include <cerrno>
#include <chrono>
#include <cstddef>
#include <cstring>
#include <format>
#include <iterator>
#include <memory>
#include <optional>
#include <string_view>
#include <sys/types.h>
#include <unistd.h>
#include <utility>
#include <vector>

namespace ws {

namespace {

const std::string_view kWebsocketGuid("258EAFA5-E914-47DA-95CA-C5AB0DC85B11");

enum OpCode : uint8_t {
  kContinuation = 0,
  kText = 1,
  kBinary = 2,
  kClose = 8,
  kPing = 9,
  kPong = 10,
};

void clear(Buffer& buffer) {
  if (buffer.empty())
    return;
  while (true) {
    size_t avail;
    buffer.rptr(avail);
    if (avail == 0)
      break;
    buffer.consume(avail);
  }
}

class TextMessageImpl : public Message {
 public:
  explicit TextMessageImpl(std::string_view text) : text_(text) {}

  [[nodiscard]]
  bool is_text() const override {
    return true;
  }

  [[nodiscard]]
  bool is_binary() const override {
    return false;
  }

  [[nodiscard]]
  std::string_view text() const override {
    return text_;
  }

  [[nodiscard]]
  std::span<uint8_t const> binary() const override {
    return {};
  }

 private:
  std::string_view text_;
};

class BinaryMessageImpl : public Message {
 public:
  explicit BinaryMessageImpl(std::span<uint8_t const> data) : data_(data) {}

  [[nodiscard]]
  bool is_text() const override {
    return false;
  }

  [[nodiscard]]
  bool is_binary() const override {
    return true;
  }

  [[nodiscard]]
  std::string_view text() const override {
    return {};
  }

  [[nodiscard]]
  std::span<uint8_t const> binary() const override {
    return data_;
  }

 private:
  std::span<uint8_t const> data_;
};

class ServerImpl : public Server, http::SocketReceiver {
 public:
  ServerImpl(logger::Logger& logger, cfg::Config const& cfg,
             looper::Looper& looper, Delegate& delegate)
      : logger_(logger::prefix(logger, "ws")),
        cfg_(cfg),
        looper_(looper),
        delegate_(delegate) {
    client_half_timeout_ =
        std::chrono::duration<double>(
            cfg_.get_uint64("websocket.client.timeout.seconds").value_or(120)) /
        2;
    client_.resize(cfg_.get_uint64("websocket.max.clients").value_or(100));
  }

  std::unique_ptr<http::Response> handle(
      http::Request const& request) override {
    if (request.method() != "GET")
      return nullptr;

    if (!request.header_contains("upgrade", "websocket"))
      return nullptr;

    if (!request.header_contains("connection", "upgrade"))
      return nullptr;

    auto maybe_key = request.header_value("sec-websocket-key");
    if (!maybe_key.has_value())
      return nullptr;
    auto maybe_nonce = base64::decode(maybe_key.value());
    if (!maybe_nonce.has_value() || maybe_nonce->size() != 16)
      return nullptr;

    auto maybe_version = request.header_value("sec-websocket-version");
    if (!maybe_version.has_value())
      return nullptr;
    if (maybe_version.value() != "13") {
      auto builder =
          http::Response::Builder::create(http::StatusCode::kBadRequest);
      builder->add_header("Sec-WebSocket-Version", "13");
      return builder->build();
    }

    std::string accept{maybe_key.value()};
    accept.append(kWebsocketGuid);
    accept = base64::encode(sha1::hash(accept));

    auto builder =
        http::Response::Builder::create(http::StatusCode::kSwitchingProtocols);
    builder->add_header("Upgrade", "websocket");
    builder->add_header("Connection", "Upgrade");
    builder->add_header("Sec-WebSocket-Accept", accept);
    builder->take_over(*this);

    return builder->build();
  }

  void receive(unique_fd&& fd) override {
    if (active_clients_ == client_.size()) {
      logger_->warn("Max number of clients already.");
      return;
    }

    for (; client_[next_client_].fd; next_client_++) {
      if (next_client_ == client_.size())
        next_client_ = 0;
    }

    logger_->dbg(std::format("New client: {}", next_client_));

    auto& client = client_[next_client_];
    client.fd = std::move(fd);
    client.last = std::chrono::steady_clock::now();

    looper_.add(
        client.fd.get(), looper::EVENT_READ,
        [this, id = next_client_](auto events) { client_event(id, events); });
    client.timeout = looper_.schedule(
        client_half_timeout_.count(),
        [this, id = next_client_](auto handle) { client_timeout(id, handle); });

    ++active_clients_;
    ++next_client_;
  }

  void send_to_all(Message const& msg) override {
    auto active = active_clients_;
    for (size_t i = 0; i < client_.size() && active; ++i) {
      if (client_[i].fd) {
        client_send(i, msg);

        if (--active == 0)
          break;
      }
    }
  }

 private:
  static const size_t kInputSize = static_cast<size_t>(256) * 1024;
  static const size_t kOutputSize = static_cast<size_t>(256) * 1024;

  struct Client {
    unique_fd fd;
    std::unique_ptr<Buffer> in{Buffer::fixed(kInputSize)};
    std::unique_ptr<Buffer> out{Buffer::fixed(kOutputSize)};
    std::chrono::steady_clock::time_point last;
    uint32_t timeout{0};
    bool read_closed_{false};

    uint8_t ping_{0};
    std::optional<uint8_t> expect_ping_;
    bool expect_close_{false};

    OpCode msg_{OpCode::kContinuation};
    std::vector<uint8_t> payload_;
  };

  void client_event(size_t client_id, uint8_t event) {
    if (event & looper::EVENT_ERROR) {
      logger_->info(std::format("Client socket error: {}", client_id));
      close_client(client_id);
      return;
    }

    auto& client = client_[client_id];
    if (event & looper::EVENT_READ) {
      size_t avail;
      auto* ptr = client.in->wptr(avail);
      if (avail == 0) {
        logger_->info(std::format("Client too large request: {}", client_id));
        close_client(client_id);
        return;
      }

      ssize_t got;
      while (true) {
        got = read(client.fd.get(), ptr, avail);
        if (got < 0 && errno == EINTR)
          continue;
        break;
      }
      if (got < 0) {
        if (errno != EWOULDBLOCK && errno != EAGAIN) {
          logger_->info(std::format("Client read error: {}: {}", client_id,
                                    strerror(errno)));
          close_client(client_id);
          return;
        }
      } else if (got == 0) {
        client.read_closed_ = true;
      } else {
        client.in->commit(got);

        if (!client_read(client_id))
          return;
      }
    }

    if (!client_write(client_id))
      return;

    if (client.read_closed_ && client.in->empty() && client.out->empty()) {
      close_client(client_id);
      return;
    }

    bool want_read = !client.read_closed_;
    bool want_write = !client.out->empty();

    looper_.update(client.fd.get(), (want_read ? looper::EVENT_READ : 0) |
                                        (want_write ? looper::EVENT_WRITE : 0));
  }

  bool client_write(size_t client_id) {
    auto& client = client_[client_id];
    while (true) {
      size_t avail;
      auto* ptr = client.out->rptr(avail);
      if (avail == 0)
        break;
      ssize_t got;
      while (true) {
        got = write(client.fd.get(), ptr, avail);
        if (got < 0 && errno == EINTR)
          continue;
        break;
      }
      if (got < 0) {
        if (errno != EWOULDBLOCK && errno != EAGAIN) {
          logger_->info(std::format("Client write error: {}: {}", client_id,
                                    strerror(errno)));
          close_client(client_id);
          return false;
        }
        break;
      }
      client.out->consume(got);

      if (std::cmp_less(got, avail))
        break;
    }
    return true;
  }

  bool client_read(size_t client_id) {
    auto& client = client_[client_id];
    size_t avail;
    auto* ptr = client.in->rptr(avail, /* need */ 2);
    if (avail < 2)
      return true;

    std::span<uint8_t const> data(reinterpret_cast<uint8_t const*>(ptr), avail);
    bool fin = data[0] & 0x80;
    if (data[1] & 0x70) {
      logger_->info(std::format(
          "Client invalid request, reserved bits are not zero: {}", client_id));
      close_client(client_id);
      return false;
    }
    uint8_t opcode = data[0] & 0x0f;
    switch (opcode) {
      case OpCode::kContinuation:
      case OpCode::kText:
      case OpCode::kBinary:
      case OpCode::kClose:
      case OpCode::kPing:
      case OpCode::kPong:
        break;
      default:
        logger_->info(std::format(
            "Client invalid request, reserved opcode used: {}", client_id));
        close_client(client_id);
        return false;
    }
    bool mask = data[1] & 0x80;
    if (!mask) {
      logger_->info(
          std::format("Client invalid request, not masked: {}", client_id));
      close_client(client_id);
      return false;
    }
    size_t payload_offset = 2;
    uint64_t payload_len = data[1] & 0x7f;
    if (payload_len == 126) {
      payload_offset += 2;
    } else if (payload_len == 127) {
      payload_offset += 8;
    }
    /* if (mask) */ payload_offset += 4;

    if (payload_offset > data.size()) {
      ptr = client.in->rptr(avail, /* need */ payload_offset);
      if (avail < payload_offset)
        return true;
      data = std::span(reinterpret_cast<uint8_t const*>(ptr), avail);
    }

    if (payload_len == 126) {
      payload_len = (static_cast<uint16_t>(data[2]) << 8) | data[3];
    } else if (payload_len == 127) {
      payload_len = (static_cast<uint64_t>(data[2]) << 56) |
                    (static_cast<uint64_t>(data[3]) << 48) |
                    (static_cast<uint64_t>(data[4]) << 40) |
                    (static_cast<uint64_t>(data[5]) << 32) |
                    (static_cast<uint64_t>(data[6]) << 24) |
                    (static_cast<uint64_t>(data[7]) << 16) |
                    (static_cast<uint64_t>(data[8]) << 8) | data[9];
    }
    /* if (mask) */
    auto mask_key = data.subspan(payload_offset - 4, 4);

    if (payload_offset + payload_len > data.size()) {
      ptr = client.in->rptr(avail, /* need */ payload_offset + payload_len);
      if (avail < payload_offset + payload_len)
        return true;
      data = std::span(reinterpret_cast<uint8_t const*>(ptr), avail);
    }

    auto payload = data.subspan(payload_offset, payload_len);
    /* if (mask) { */
    // Unmask the data
    std::span<uint8_t> tmp{const_cast<uint8_t*>(payload.data()),
                           payload.size()};
    for (size_t i = 0; i < tmp.size(); ++i) {
      tmp[i] ^= mask_key[i % 4];
    }

    if (client_handle(client_id, fin, static_cast<OpCode>(opcode), payload)) {
      client.in->consume(payload_offset + payload_len);
      return true;
    }
    return false;
  }

  bool client_handle(size_t client_id, bool fin, OpCode opcode,
                     std::span<uint8_t const> payload) {
    auto& client = client_[client_id];

    // Validate continuation and fin frames.
    switch (opcode) {
      case OpCode::kContinuation:
        if (client.msg_ == OpCode::kContinuation) {
          logger_->info(std::format(
              "Client invalid frame, unexpected continuation: {}", client_id));
          close_client(client_id);
          return false;
        }
        break;
      case OpCode::kBinary:
      case OpCode::kText:
        if (client.msg_ != OpCode::kContinuation) {
          logger_->info(std::format(
              "Client invalid frame, unexpected non-continuation: {}",
              client_id));
          close_client(client_id);
          return false;
        }
        break;
      case OpCode::kClose:
      case OpCode::kPing:
      case OpCode::kPong:
        if (!fin) {
          logger_->info(
              std::format("Client invalid control frame: {}", client_id));
          close_client(client_id);
          return false;
        }
        break;
    }

    switch (opcode) {
      case OpCode::kContinuation:
        std::ranges::copy(payload, std::back_inserter(client.payload_));
        if (fin) {
          std::unique_ptr<Message> reply;
          switch (client.msg_) {
            case OpCode::kText:
              reply = delegate_.handle(TextMessageImpl{std::string_view(
                  reinterpret_cast<char const*>(client.payload_.data()),
                  client.payload_.size())});
              break;
            case OpCode::kBinary:
              reply = delegate_.handle(BinaryMessageImpl{client.payload_});
              break;
            default:
              std::unreachable();
          }
          client.msg_ = OpCode::kContinuation;
          client.payload_.clear();
          if (reply) {
            if (!client_send(client_id, *reply))
              return false;
          }
        }
        break;
      case OpCode::kBinary:
      case OpCode::kText:
        if (fin) {
          std::unique_ptr<Message> reply;
          if (opcode == OpCode::kText) {
            reply = delegate_.handle(TextMessageImpl{
              std::string_view(reinterpret_cast<char const*>(payload.data()),
                               payload.size())});
          } else {
            reply = delegate_.handle(BinaryMessageImpl{payload});
          }
          if (reply) {
            if (!client_send(client_id, *reply))
              return false;
          }
        } else {
          client.msg_ = opcode;
          client.payload_.assign(payload.begin(), payload.end());
        }
        break;
      case OpCode::kClose:
        if (client.expect_close_) {
          close_client(client_id);
          return false;
        }
        if (!client_send(client_id, OpCode::kClose, payload))
          return false;
        client.read_closed_ = true;
        break;
      case OpCode::kPing:
        if (!client_send(client_id, OpCode::kPong, payload))
          return false;
        break;
      case OpCode::kPong:
        if (client.expect_ping_.has_value()) {
          if (payload.size() != 1 ||
              payload[0] != client.expect_ping_.value()) {
            logger_->info(
                std::format("Client closed, mismatched pong: {}", client_id));
            close_client(client_id);
            return false;
          }
          client.expect_ping_.reset();
        } else {
          // A Pong frame MAY be sent unsolicited. This serves as a unidirectional heartbeat.
        }
        break;
    }
    return true;
  }

  bool client_send(size_t client_id, Message const& message) {
    if (message.is_text()) {
      auto payload = message.text();
      return client_send(
          client_id, OpCode::kText,
          std::span{reinterpret_cast<uint8_t const*>(payload.data()),
                    payload.size()});
    }
    return client_send(client_id, OpCode::kBinary, message.binary());
  }

  bool client_send(size_t client_id, OpCode opcode,
                   std::span<uint8_t const> payload) {
    auto& client = client_[client_id];
    if (client.read_closed_)
      return true;

    uint8_t header[10];
    size_t header_size = 0;
    // Always send FIN frames.
    header[header_size++] = 0x80 | std::to_underlying(opcode);
    // Server never sends masked messages.
    if (payload.size() < 126) {
      header[header_size++] = payload.size();
    } else if (payload.size() <= 0xffff) {
      header[header_size++] = 126;
      header[header_size++] = payload.size() >> 8;
      header[header_size++] = payload.size() & 0xff;
    } else {
      header[header_size++] = 127;
      header[header_size++] = payload.size() >> 56;
      header[header_size++] = (payload.size() & 0xff000000000000) >> 48;
      header[header_size++] = (payload.size() & 0xff0000000000) >> 40;
      header[header_size++] = (payload.size() & 0xff00000000) >> 32;
      header[header_size++] = (payload.size() & 0xff000000) >> 24;
      header[header_size++] = (payload.size() & 0xff0000) >> 16;
      header[header_size++] = (payload.size() & 0xff00) >> 8;
      header[header_size++] = payload.size() & 0xff;
    }
    size_t avail;
    bool const was_empty = client.out->empty();
    auto* wptr =
        client.out->wptr(avail, /* need */ header_size + payload.size());
    if (avail < header_size + payload.size()) {
      logger_->info(
          std::format("Client closed, too much output: {}", client_id));
      close_client(client_id);
      return false;
    }
    auto* data = reinterpret_cast<uint8_t*>(wptr);
    std::copy_n(header, header_size, data);
    std::ranges::copy(payload, data + header_size);
    client.out->commit(header_size + payload.size());

    if (was_empty) {
      if (!client_write(client_id))
        return false;
    }

    return true;
  }

  void client_timeout(size_t client_id, uint32_t id) {
    auto now = std::chrono::steady_clock::now();
    auto& client = client_[client_id];
    assert(client.timeout == id);
    if (now - client.last <
        std::chrono::duration_cast<std::chrono::steady_clock::duration>(
            client_half_timeout_)) {
      // TODO: Reschedule for delay left, not the full one
      client.timeout = looper_.schedule(client_half_timeout_.count(),
                                        [this, client_id](auto handle) {
                                          client_timeout(client_id, handle);
                                        });
      return;
    }

    client.timeout = 0;

    if (client.expect_ping_.has_value()) {
      logger_->dbg(std::format("Client timeout: {}", client_id));

      close_client(client_id);
    } else {
      client.expect_ping_ = ++client.ping_;
      if (client_send(client_id, OpCode::kPing, std::span{&client.ping_, 1})) {
        client.timeout = looper_.schedule(client_half_timeout_.count(),
                                          [this, client_id](auto handle) {
                                            client_timeout(client_id, handle);
                                          });
      }
    }
  }

  void close_client(size_t client_id) {
    auto& client = client_[client_id];
    if (!client.fd) {
      assert(false);
      return;
    }

    logger_->dbg(std::format("Drop client: {}", client_id));

    looper_.remove(client.fd.get());
    if (client.timeout)
      looper_.cancel(client.timeout);
    client.fd.reset();
    clear(*client.in);
    clear(*client.out);
    client.read_closed_ = false;
    client.expect_ping_.reset();
    client.ping_ = 0;
    client.expect_close_ = false;
    client.msg_ = OpCode::kContinuation;
    client.payload_.clear();

    assert(active_clients_ > 0);
    --active_clients_;
    if (next_client_ == client_id + 1)
      next_client_ = client_id;
  }

  std::unique_ptr<logger::Logger> logger_;
  cfg::Config const& cfg_;
  looper::Looper& looper_;
  Delegate& delegate_;

  // Timeout first sends a PING and then if it times out again, then closes connection.
  std::chrono::duration<double> client_half_timeout_;
  std::vector<Client> client_;
  size_t next_client_{0};
  size_t active_clients_{0};
};

}  // namespace

void Server::send_text_to_all(std::string_view text) {
  send_to_all(TextMessageImpl{text});
}

void Server::send_binary_to_all(std::span<uint8_t const> data) {
  send_to_all(BinaryMessageImpl{data});
}

std::unique_ptr<Server> create_server(logger::Logger& logger,
                                      cfg::Config const& cfg,
                                      looper::Looper& looper,
                                      Server::Delegate& delegate) {
  return std::make_unique<ServerImpl>(logger, cfg, looper, delegate);
}

std::unique_ptr<Message> Message::create(std::string_view text) {
  return std::make_unique<TextMessageImpl>(text);
}

std::unique_ptr<Message> Message::create(std::span<uint8_t const> data) {
  return std::make_unique<BinaryMessageImpl>(data);
}

}  // namespace ws