// This file is part of CAF, the C++ Actor Framework. See the file LICENSE in
// the main distribution directory for license terms and copyright or visit
// https://github.com/actor-framework/actor-framework/blob/master/LICENSE.

#pragma once

#include <memory>
#include <optional>
#include <string>

#include "caf/detail/core_export.hpp"
#include "caf/fwd.hpp"
#include "caf/string_algorithms.hpp"
#include "caf/string_view.hpp"

namespace caf {

/// Defines a configuration option for the application.
class CAF_CORE_EXPORT config_option {
public:
  // -- member types -----------------------------------------------------------

  /// Custom vtable-like struct for delegating to type-specific functions and
  /// storing type-specific information shared by several config options.
  struct meta_state {
    /// Tries to perform this sequence of steps:
    /// - Convert the config value to the type of the config option.
    /// - Assign the converted value back to the config value to synchronize
    ///   conversions back to the caller.
    /// - Store the converted value in the pointer unless it is `nullptr`.
    error (*sync)(void*, config_value&);

    /// Tries to extract a value from the given location. Exists for backward
    /// compatibility only and will get removed with CAF 0.17.
    config_value (*get)(const void*);

    /// Human-readable name of the option's type.
    string_view type_name;
  };

  // -- constructors, destructors, and assignment operators --------------------

  ///  Constructs a config option.
  config_option(string_view category, string_view name, string_view description,
                const meta_state* meta, void* value = nullptr);

  config_option(const config_option&);

  config_option(config_option&&) = default;

  config_option& operator=(const config_option&);

  config_option& operator=(config_option&&) = default;

  // -- swap function ----------------------------------------------------------

  friend void swap(config_option& first, config_option& second) noexcept;

  // -- properties -------------------------------------------------------------

  /// Returns the category of the option.
  string_view category() const noexcept;

  /// Returns the name of the option.
  string_view long_name() const noexcept;

  /// Returns (optional) one-letter short names of the option.
  string_view short_names() const noexcept;

  /// Returns a human-readable description of the option.
  string_view description() const noexcept;

  /// Returns the full name for this config option as "<category>.<long name>".
  string_view full_name() const noexcept;

  /// Synchronizes the value of this config option with `x` and vice versa.
  ///
  /// Tries to perform this sequence of steps:
  /// - Convert the config value to the type of the config option.
  /// - Assign the converted value back to the config value to synchronize
  ///   conversions back to the caller.
  /// - Store the converted value unless this option is stateless.
  error sync(config_value& x) const;

  [[deprecated("use sync instead")]] error store(const config_value& x) const;

  [[deprecated("use sync instead")]] expected<config_value>
  parse(string_view input) const;

  /// Returns a human-readable representation of this option's expected type.
  string_view type_name() const noexcept;

  /// Returns whether this config option stores a boolean flag.
  bool is_flag() const noexcept;

  /// Returns whether the category is optional for CLI options.
  bool has_flat_cli_name() const noexcept;

  /// @private
  // TODO: remove with CAF 0.17
  std::optional<config_value> get() const;

private:
  string_view buf_slice(size_t from, size_t to) const noexcept;

  std::unique_ptr<char[]> buf_;
  uint16_t category_separator_;
  uint16_t long_name_separator_;
  uint16_t short_names_separator_;
  uint16_t buf_size_;
  const meta_state* meta_;
  mutable void* value_;
};

/// Finds `config_option` string with a matching long name in (`first`, `last`],
/// where each entry is a pointer to a string. Returns a `ForwardIterator` to
/// the match and a `caf::string_view` of the option value if the entry is found
/// and a `ForwardIterator` to `last` with an empty `string_view` otherwise.
template <class ForwardIterator, class Sentinel>
std::pair<ForwardIterator, string_view>
find_by_long_name(const config_option& x, ForwardIterator first,
                  Sentinel last) {
  auto long_name = x.long_name();
  for (; first != last; ++first) {
    string_view str{*first};
    // Make sure this is a long option starting with "--".
    if (!starts_with(str, "--"))
      continue;
    str.remove_prefix(2);
    // Skip optional "caf#" prefix.
    if (starts_with(str, "caf#"))
      str.remove_prefix(4);
    // Make sure we are dealing with the right key.
    if (!starts_with(str, long_name))
      continue;
    // Make sure the key is followed by an assignment.
    str.remove_prefix(long_name.size());
    if (!starts_with(str, "="))
      continue;
    // Remove leading '=' and return the value.
    str.remove_prefix(1);
    return {first, str};
  }
  return {first, string_view{}};
}

} // namespace caf
