//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2020
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once

#include "td/utils/buffer.h"
#include "td/utils/common.h"
#include "td/utils/Status.h"

#include <limits>

namespace td {

class ByteFlowInterface {
 public:
  virtual void close_input(Status status) = 0;
  virtual void wakeup() = 0;
  virtual void set_parent(ByteFlowInterface &other) = 0;
  virtual void set_input(ChainBufferReader *input) = 0;
  virtual size_t get_need_size() = 0;
  virtual size_t get_read_size() = 0;
  virtual size_t get_write_size() = 0;
  ByteFlowInterface() = default;
  ByteFlowInterface(const ByteFlowInterface &) = delete;
  ByteFlowInterface &operator=(const ByteFlowInterface &) = delete;
  ByteFlowInterface(ByteFlowInterface &&) = default;
  ByteFlowInterface &operator=(ByteFlowInterface &&) = default;
  virtual ~ByteFlowInterface() = default;
};

class ByteFlowBaseCommon : public ByteFlowInterface {
 public:
  ByteFlowBaseCommon() = default;

  void close_input(Status status) final {
    if (status.is_error()) {
      finish(std::move(status));
    } else {
      is_input_active_ = false;
      wakeup();
    }
  }

  void wakeup() final {
    if (stop_flag_ || !input_) {
      return;
    }
    input_->sync_with_writer();

    if (waiting_flag_) {
      if (!is_input_active_) {
        finish(Status::OK());
      }
      return;
    }
    while (true) {
      if (stop_flag_) {
        break;
      }

      // update can_read
      if (is_input_active_) {
        auto read_size = get_read_size();
        if (read_size < min(need_size_, options_.read_watermark.low)) {
          can_read = false;
        }
        if (read_size >= max(need_size_, options_.read_watermark.high)) {
          can_read = true;
        }

      } else {
        // always can read when input is closed
        can_read = true;
      }

      // update can_write
      {
        auto write_size = get_write_size();
        if (write_size > options_.write_watermark.high) {
          can_write = false;
        }
        if (write_size <= options_.write_watermark.low) {
          can_write = true;
        }
      }

      if (!can_read || !can_write) {
        break;
      }
      need_size_ = 0;

      if (!loop()) {
        if (need_size_ <= get_read_size()) {
          need_size_ = get_read_size() + 1;
        }
      }
    }
    on_output_updated();
  }

  size_t get_need_size() final {
    return need_size_;
  }
  size_t get_read_size() override {
    input_->sync_with_writer();
    return input_->size();
  }
  size_t get_write_size() override {
    CHECK(parent_);
    return parent_->get_read_size();
  }

  struct Watermark {
    size_t low{std::numeric_limits<size_t>::max()};
    size_t high{0};
  };
  struct Options {
    Watermark write_watermark;
    Watermark read_watermark;
  };
  void set_options(Options options) {
    options_ = options;
  }

  virtual bool loop() = 0;

 protected:
  bool waiting_flag_ = false;
  ChainBufferReader *input_ = nullptr;
  bool is_input_active_ = true;
  size_t need_size_ = 0;
  bool can_read{true};
  bool can_write{true};
  Options options_;
  void finish(Status status) {
    stop_flag_ = true;
    need_size_ = 0;
    if (parent_) {
      parent_->close_input(std::move(status));
      parent_ = nullptr;
    }
  }

  void set_need_size(size_t need_size) {
    need_size_ = need_size;
  }

  void on_output_updated() {
    if (parent_) {
      parent_->wakeup();
    }
  }
  void consume_input() {
    waiting_flag_ = true;
    if (!is_input_active_) {
      finish(Status::OK());
    }
  }

 private:
  ByteFlowInterface *parent_ = nullptr;
  bool stop_flag_ = false;
  friend class ByteFlowBase;
  friend class ByteFlowInplaceBase;
};

class ByteFlowBase : public ByteFlowBaseCommon {
 public:
  ByteFlowBase() = default;

  void set_input(ChainBufferReader *input) final {
    input_ = input;
  }
  void set_parent(ByteFlowInterface &other) final {
    parent_ = &other;
    parent_->set_input(&output_reader_);
  }
  bool loop() override = 0;

  // ChainBufferWriter &get_output() {
  // return output_;
  //}

 protected:
  ChainBufferWriter output_;
  ChainBufferReader output_reader_ = output_.extract_reader();
};

class ByteFlowInplaceBase : public ByteFlowBaseCommon {
 public:
  ByteFlowInplaceBase() = default;

  void set_input(ChainBufferReader *input) final {
    input_ = input;
    output_ = ChainBufferReader(input_->begin().clone(), input_->begin().clone(), false);
  }
  void set_parent(ByteFlowInterface &other) final {
    parent_ = &other;
    parent_->set_input(&output_);
  }
  bool loop() override = 0;

  ChainBufferReader &get_output() {
    return output_;
  }

 protected:
  ChainBufferReader output_;
};

inline ByteFlowInterface &operator>>(ByteFlowInterface &from, ByteFlowInterface &to) {
  from.set_parent(to);
  return to;
}

class ByteFlowSource : public ByteFlowInterface {
 public:
  ByteFlowSource() = default;
  explicit ByteFlowSource(ChainBufferReader *buffer) : buffer_(buffer) {
  }
  ByteFlowSource(ByteFlowSource &&other) : buffer_(other.buffer_), parent_(other.parent_) {
    other.buffer_ = nullptr;
    other.parent_ = nullptr;
  }
  ByteFlowSource &operator=(ByteFlowSource &&other) {
    buffer_ = other.buffer_;
    parent_ = other.parent_;
    other.buffer_ = nullptr;
    other.parent_ = nullptr;
    return *this;
  }
  ByteFlowSource(const ByteFlowSource &) = delete;
  ByteFlowSource &operator=(const ByteFlowSource &) = delete;
  ~ByteFlowSource() override = default;

  void set_input(ChainBufferReader *) final {
    UNREACHABLE();
  }
  void set_parent(ByteFlowInterface &parent) final {
    CHECK(parent_ == nullptr);
    parent_ = &parent;
    parent_->set_input(buffer_);
  }
  void close_input(Status status) final {
    CHECK(parent_);
    parent_->close_input(std::move(status));
    parent_ = nullptr;
  }
  void wakeup() final {
    if (!parent_) {
      return;
    }
    parent_->wakeup();
  }
  size_t get_need_size() final {
    if (parent_ == nullptr) {
      return 0;
    }
    return parent_->get_need_size();
  }
  size_t get_read_size() final {
    UNREACHABLE();
    return 0;
  }
  size_t get_write_size() final {
    CHECK(parent_);
    return parent_->get_read_size();
  }

 private:
  ChainBufferReader *buffer_ = nullptr;
  ByteFlowInterface *parent_ = nullptr;
};

class ByteFlowSink : public ByteFlowInterface {
 public:
  void set_input(ChainBufferReader *input) final {
    CHECK(buffer_ == nullptr);
    buffer_ = input;
  }
  void set_parent(ByteFlowInterface & /*parent*/) final {
    UNREACHABLE();
  }
  void close_input(Status status) final {
    CHECK(active_);
    active_ = false;
    status_ = std::move(status);
    buffer_->sync_with_writer();
  }
  void wakeup() final {
    buffer_->sync_with_writer();
  }
  size_t get_need_size() final {
    UNREACHABLE();
    return 0;
  }
  size_t get_read_size() final {
    buffer_->sync_with_writer();
    return buffer_->size();
  }
  size_t get_write_size() final {
    UNREACHABLE();
    return 0;
  }
  bool is_ready() {
    return !active_;
  }
  Status &status() {
    return status_;
  }
  ChainBufferReader *result() {
    CHECK(is_ready() && status().is_ok());
    return buffer_;
  }
  ChainBufferReader *get_output() {
    return buffer_;
  }

 private:
  bool active_ = true;
  Status status_;
  ChainBufferReader *buffer_ = nullptr;
};

class ByteFlowMoveSink : public ByteFlowInterface {
 public:
  ByteFlowMoveSink() = default;
  explicit ByteFlowMoveSink(ChainBufferWriter *output) {
    set_output(output);
  }
  void set_input(ChainBufferReader *input) final {
    CHECK(!input_);
    input_ = input;
  }
  void set_parent(ByteFlowInterface & /*parent*/) final {
    UNREACHABLE();
  }
  void close_input(Status status) final {
    CHECK(active_);
    active_ = false;
    status_ = std::move(status);
    wakeup();
  }
  void wakeup() final {
    input_->sync_with_writer();
    output_->append(*input_);
  }
  size_t get_need_size() final {
    UNREACHABLE();
    return 0;
  }
  size_t get_read_size() final {
    input_->sync_with_writer();
    //TODO: must be input_->size() + output_->size()
    return input_->size();
  }
  size_t get_write_size() final {
    UNREACHABLE();
    return 0;
  }
  void set_output(ChainBufferWriter *output) {
    CHECK(!output_);
    output_ = output;
  }

  bool is_ready() {
    return !active_;
  }
  Status &status() {
    return status_;
  }

 private:
  bool active_ = true;
  Status status_;
  ChainBufferReader *input_ = nullptr;
  ChainBufferWriter *output_ = nullptr;
};

}  // namespace td