rewrite ServerState dependency management

src/StepGraph.hh

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <stdint.h>
+
+#include <functional>
+#include <memory>
+#include <phosg/Strings.hh>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+struct StepGraph {
+  struct Step {
+    std::vector<std::shared_ptr<Step>> downstream_dependencies;
+    std::function<void()> execute;
+    uint64_t last_run_id = 0;
+  };
+
+  std::unordered_map<std::string, std::shared_ptr<Step>> steps;
+  uint64_t last_run_id = 0;
+
+  StepGraph() = default;
+
+  void add_step(const std::string& name, const std::vector<std::string>& depends_on_names, std::function<void()>&& execute);
+  void run(const std::string& start_step);
+  void run(const std::vector<std::string>& start_steps);
+};