Introduce cpu_usage module

src/modules/cpu_usage/linux.cpp

@@ -0,0 +1,31 @@
+#include <filesystem>
+
+#include "modules/cpu_usage.hpp"
+
+std::vector<std::tuple<size_t, size_t>> waybar::modules::CpuUsage::parseCpuinfo() {
+  const std::string data_dir_ = "/proc/stat";
+  std::ifstream info(data_dir_);
+  if (!info.is_open()) {
+    throw std::runtime_error("Can't open " + data_dir_);
+  }
+  std::vector<std::tuple<size_t, size_t>> cpuinfo;
+  std::string line;
+  while (getline(info, line)) {
+    if (line.substr(0, 3).compare("cpu") != 0) {
+      break;
+    }
+    std::stringstream sline(line.substr(5));
+    std::vector<size_t> times;
+    for (size_t time = 0; sline >> time; times.push_back(time))
+      ;
+
+    size_t idle_time = 0;
+    size_t total_time = 0;
+    if (times.size() >= 4) {
+      idle_time = times[3];
+      total_time = std::accumulate(times.begin(), times.end(), 0);
+    }
+    cpuinfo.emplace_back(idle_time, total_time);
+  }
+  return cpuinfo;
+}