add state saving and loading

CMakeLists.txt

@@ -7,7 +7,7 @@ add_subdirectory(libuv)
 add_subdirectory(spdlog)
 add_subdirectory(td)
 
-add_executable(${PROJECT_NAME} main.cpp http.cpp vk.cpp)
+add_executable(${PROJECT_NAME} main.cpp http.cpp state.cpp vk.cpp)
 
 target_compile_options(${PROJECT_NAME} PRIVATE -std=c++2b)
 

main.cpp

@@ -1,4 +1,6 @@
-#include "http.h"
+#include "spdlog/spdlog.h"
+#include "state.h"
+#include <filesystem>
 #include <uv.h>
 #include <td/telegram/td_api.h>
 #include <td/telegram/td_api.hpp>
@@ -20,7 +22,17 @@ int main() {
   uv_signal_t signalHandles[2] = {};
   create_signal_handles(loop, signalHandles);
   
+  state::AppState state;
+  try {
+    state = state::AppState("bridge_state.json");
+    spdlog::info("state: {}", state.to_string());
+  } catch (state::InvalidSavedStateException &e) {
+    spdlog::error("invalid saved state: {}", e.message);
+    return 1;
+  }
+
   uv_run(loop, UV_RUN_DEFAULT);
   spdlog::info("event loop ended");
+  state.save();
   return 0;
 }

state.cpp

@@ -0,0 +1,67 @@
+#include "state.h"
+#include "spdlog/spdlog.h"
+#include <fstream>
+#include <nlohmann/json.hpp>
+#include <string>
+
+using namespace state;
+using namespace nlohmann;
+
+AppState::AppState(std::string filename) : m_saveFilename(filename) {
+  std::ifstream f(filename);
+  if (f.fail()) {
+    spdlog::info("no state file");
+    return;
+  }
+  json state = json::parse(f);
+  if (state.type() != json::value_t::object) {
+    throw InvalidSavedStateException("JSON root must be an object");
+  }
+  if (state.contains("vk")) {
+    json vkState = state["vk"];
+    if (vkState.type() == json::value_t::object) {
+      if (vkState.contains("last_post_id")) {
+        json lastPostId = vkState["last_post_id"];
+        if (lastPostId.type() == json::value_t::number_integer || lastPostId.type() == json::value_t::number_unsigned) {
+          vkLastPostId = lastPostId;
+        } else {
+          throw InvalidSavedStateException("key vk.last_post_id must be an integer");
+        }
+      }
+    } else {
+      throw InvalidSavedStateException("key vk must be an object");
+    }
+  }
+
+  if (state.contains("tg")) {
+    json tgState = state["tg"];
+    if (tgState.type() == json::value_t::object) {
+      if (tgState.contains("last_post_id")) {
+        json lastPostId = tgState["last_post_id"];
+        if (lastPostId.type() == json::value_t::number_integer || lastPostId.type() == json::value_t::number_unsigned) {
+          tgLastPostId = lastPostId;
+        } else {
+          throw InvalidSavedStateException("key tg.last_post_id must be an integer");
+        }
+      }
+    } else {
+      throw InvalidSavedStateException("key tg must be an object");
+    }
+  }
+}
+
+void AppState::save() {
+  if (m_saveFilename.empty()) return;
+  spdlog::info("saving state");
+  json state = {{"vk", {{"last_post_id", vkLastPostId}}}, {"tg", {{"last_post_id", tgLastPostId}}}};
+  std::ofstream f(m_saveFilename.c_str());
+  if (f.fail()) {
+    spdlog::error("failed to open state file '{}'", m_saveFilename);
+    return;
+  }
+  f << state << std::endl;
+}
+
+std::string AppState::to_string() {
+  return std::format("AppState {{ tgLastPostId: {}, vkLastPostId: {} }}", tgLastPostId, vkLastPostId);
+}

state.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <cstdint>
+#include <exception>
+#include <string>
+
+namespace state {
+  class InvalidSavedStateException : std::exception {
+  public:
+    inline InvalidSavedStateException(const char *message): message(message) {};
+    const char *message;
+  };
+
+  class AppState {
+  public:
+    inline AppState() {};
+    AppState(std::string filename);
+    std::string to_string();
+    void save();
+
+    int64_t tgLastPostId = 0;
+    int64_t vkLastPostId = 0;
+  private:
+    std::string m_saveFilename;
+  };
+}