6 files changed, 309 insertions, 0 deletions
diff --git a/source/lib/proto/CMakeLists.txt b/source/lib/proto/CMakeLists.txt
new file mode 100644
index 0000000..9967a95
--- /dev/null
+++ b/source/lib/proto/CMakeLists.txt
@@ -0,0 +1,38 @@
+cmake_path(GET CMAKE_CURRENT_SOURCE_DIR STEM LIB_NAME)
+
+file(GLOB_RECURSE LIB_HEADERS RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" CONFIGURE_DEPENDS "**/*.hpp")
+file(GLOB_RECURSE LIB_SOURCES RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" CONFIGURE_DEPENDS "**/*.cpp")
+
+find_package("fmt" REQUIRED)
+
+add_library("wanda-${LIB_NAME}"
+    ${LIB_SOURCES}
+)
+
+target_sources("wanda-${LIB_NAME}" INTERFACE
+    FILE_SET HEADERS
+    FILES ${LIB_HEADERS}
+    BASE_DIRS "include"
+)
+
+target_include_directories("wanda-${LIB_NAME}" PUBLIC
+    "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"
+)
+
+target_include_directories("wanda-${LIB_NAME}" SYSTEM PUBLIC
+    "$<INSTALL_INTERFACE:include>"
+)
+
+target_compile_features("wanda-${LIB_NAME}" PUBLIC
+    "cxx_std_20"
+)
+
+target_link_libraries("wanda-${LIB_NAME}" PUBLIC
+    "fmt::fmt"
+)
+
+install(TARGETS "wanda-${LIB_NAME}"
+    FILE_SET HEADERS
+)
+
+add_library("wanda::${LIB_NAME}" ALIAS "wanda-${LIB_NAME}")
diff --git a/source/lib/proto/include/wanda/proto/command.hpp b/source/lib/proto/include/wanda/proto/command.hpp
new file mode 100644
index 0000000..c8dae65
--- /dev/null
+++ b/source/lib/proto/include/wanda/proto/command.hpp
@@ -0,0 +1,46 @@
+#ifndef WANDA_PROTO_COMMAND_HPP
+#define WANDA_PROTO_COMMAND_HPP
+
+#include "wanda/proto/message.hpp"
+
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace wanda::proto
+{
+  /**
+   * @brief An enum to describe different command IDs
+   */
+  enum struct command_id : char
+  {
+    change,  //< Change the wallpaper
+  };
+
+  /**
+   * @brief A simple type to represent commands transported through the control connection
+   */
+  struct command
+  {
+    command_id const id;
+    std::vector<std::string> const arguments;
+
+    /**
+     * @brief Convert the command to a message for transmission to a remote endpoint
+     */
+    std::optional<wanda::proto::message> message() const;
+  };
+
+  /**
+   * @brief Extract a command from a message
+   */
+  std::optional<command> make_command(message message);
+
+  /**
+   * @brief A simple factory to create a "Change wallpaper" command
+   */
+  command make_change_command();
+
+}  // namespace wanda::proto
+
+#endif
+\ No newline at end of file
diff --git a/source/lib/proto/include/wanda/proto/message.hpp b/source/lib/proto/include/wanda/proto/message.hpp
new file mode 100644
index 0000000..f4a6a3b
--- /dev/null
+++ b/source/lib/proto/include/wanda/proto/message.hpp
@@ -0,0 +1,84 @@
+/**
+ * @file   message.hpp
+ * @author Felix Morgner (felix.morgner@gmail.com)
+ * @since  1.0.0
+ */
+
+#ifndef WANDA_PROTO_MESSAGE_HPP
+#define WANDA_PROTO_MESSAGE_HPP
+
+#include <fmt/core.h>
+
+#include <cstddef>
+#include <istream>
+#include <optional>
+#include <string>
+#include <string_view>
+
+namespace wanda::proto
+{
+  /**
+   * @brief A tag to mark messages originating from the controller
+   */
+  auto constexpr message_source_controller = "C";
+
+  /**
+   * @brief A tag to mark messages originating from the daemon
+   */
+  auto constexpr message_source_daemon = "D";
+
+  /**
+   * @brief The command of the hello message
+   */
+  auto constexpr message_command_hello = "HELLO";
+
+  /**
+   * @brief A control protocol message, consisting of a @p source, @p command, and @p arguments
+   */
+  struct message
+  {
+    /**
+     * @brief Serialize this message into a string
+     */
+    explicit operator std::string() const;
+
+    /**
+     * @brief Get the size of the message as if it was serialized
+     */
+    std::size_t size() const;
+
+    /**
+     * @brief The source of the message
+     */
+    std::string source;
+
+    /**
+     * @brief The command of the message
+     */
+    std::string command;
+
+    /**
+     * @brief The arguments of the message command
+     */
+    std::optional<std::string> argument;
+  };
+
+  /**
+   * @brief Deserialize a message from the given stream
+   */
+  std::istream & operator>>(std::istream & in, message & message);
+
+  /**
+   * @brief Serialize a message to the given stream
+   */
+  std::ostream & operator<<(std::ostream & out, message const & message);
+
+}  // namespace wanda::proto
+
+template<>
+struct fmt::formatter<wanda::proto::message> : fmt::formatter<std::string>
+{
+  auto format(wanda::proto::message const & message, format_context & context) const -> decltype(context.out());
+};
+
+#endif
+\ No newline at end of file
diff --git a/source/lib/proto/include/wanda/proto/version.hpp b/source/lib/proto/include/wanda/proto/version.hpp
new file mode 100644
index 0000000..faa17d7
--- /dev/null
+++ b/source/lib/proto/include/wanda/proto/version.hpp
@@ -0,0 +1,12 @@
+#ifndef WANDA_PROTO_VERSION_HPP
+#define WANDA_PROTO_VERSION_HPP
+
+namespace wanda::proto
+{
+  inline namespace v1
+  {
+    auto constexpr version = "1.0.0";
+  }
+}  // namespace wanda::proto
+
+#endif
+\ No newline at end of file
diff --git a/source/lib/proto/src/command.cpp b/source/lib/proto/src/command.cpp
new file mode 100644
index 0000000..5a669f5
--- /dev/null
+++ b/source/lib/proto/src/command.cpp
@@ -0,0 +1,47 @@
+#include "wanda/proto/command.hpp"
+
+namespace wanda::proto
+{
+  std::optional<message> command::message() const
+  {
+    using namespace std::string_literals;
+    auto const command = [this] {
+      switch (id)
+      {
+        case command_id::change:
+          return "CHANGE"s;
+        default:
+          return ""s;
+      }
+    }();
+
+    auto argument_string = std::string{};
+    for (int index = 0ul; index < arguments.size(); ++index)
+    {
+      argument_string += (index) ? "," + arguments[index] : arguments[index];
+    }
+
+    if (command.empty())
+    {
+      return std::nullopt;
+    }
+
+    return wanda::proto::message{"C", command, argument_string};
+  }
+
+  std::optional<command> make_command(message message)
+  {
+    if (message.command == "CHANGE")
+    {
+      return {{command_id::change}};
+    }
+
+    return std::nullopt;
+  }
+
+  command make_change_command()
+  {
+    return {command_id::change};
+  }
+
+}  // namespace wanda::proto
+\ No newline at end of file
diff --git a/source/lib/proto/src/message.cpp b/source/lib/proto/src/message.cpp
new file mode 100644
index 0000000..dad3e86
--- /dev/null
+++ b/source/lib/proto/src/message.cpp
@@ -0,0 +1,82 @@
+#include "wanda/proto/message.hpp"
+
+#include <fmt/format.h>
+
+#include <ios>
+#include <iterator>
+#include <sstream>
+
+namespace wanda::proto
+{
+  message::operator std::string() const
+  {
+    std::ostringstream buffer{};
+    buffer << source
+           << ':'
+           << command;
+    if (argument.has_value())
+    {
+      buffer << ':' << *argument;
+    }
+    return buffer.str();
+  }
+
+  std::size_t message::size() const
+  {
+    return static_cast<std::string>(*this).size();
+  }
+
+  template<typename InputIt, typename OutputIt, typename UnaryPredicate>
+  OutputIt copy_until(InputIt first, InputIt last, OutputIt out, UnaryPredicate predicate)
+  {
+    while (first != last && !predicate(*first))
+    {
+      *out++ = *first++;
+    }
+    return out;
+  }
+
+  std::istream & operator>>(std::istream & in, message & message)
+  {
+    auto pos = std::istream_iterator<char>{in};
+    auto end = std::istream_iterator<char>{};
+    auto buffer = std::string{};
+
+    copy_until(pos, end, std::back_inserter(buffer), [](auto const & c) { return c == ':'; });
+    if (in.eof() || buffer.size() != 1)
+    {
+      in.setstate(std::ios_base::failbit);
+      return in;
+    }
+    message.source = buffer;
+
+    buffer.clear();
+    copy_until(++pos, end, std::back_inserter(buffer), [](auto const & c) { return c == ':'; });
+    if (in.eof())
+    {
+      in.setstate(std::ios_base::failbit);
+    }
+    message.command = buffer;
+
+    buffer.clear();
+    copy(++pos, end, std::back_inserter(buffer));
+    if (buffer.size())
+    {
+      message.argument = std::optional{std::move(buffer)};
+    }
+
+    in.clear(in.rdstate() ^ std::ios_base::failbit);
+    return in;
+  }
+
+  std::ostream & operator<<(std::ostream & out, message const & message)
+  {
+    return out << static_cast<std::string>(message);
+  }
+
+}  // namespace wanda::proto
+
+auto fmt::formatter<wanda::proto::message>::format(wanda::proto::message const & message, format_context & context) const -> decltype(context.out())
+{
+  return formatter<std::string>::format(static_cast<std::string>(message), context);
+}