1 files changed, 167 insertions, 0 deletions

diff --git a/server/src/config.cpp b/server/src/config.cpp
new file mode 100644
index 0000000..3b17691
--- /dev/null
+++ b/server/src/config.cpp
@@ -0,0 +1,167 @@
+module;
+
+#include <boost/json.hpp>
+#include <boost/system/system_error.hpp>
+
+module routemon:config$impl;
+
+import std;
+import :config;
+import :log;
+import :util;
+
+namespace json = boost::json;
+
+namespace routemon::config {
+
+  class location {
+    std::optional<std::pair<std::string_view, util::not_null<location const*>>> next_;
+
+    auto append_to(std::string& s) const -> void {
+      if (next_) {
+        s += next_->first;
+        s += ".";
+        next_->second->append_to(s);
+      }
+    }
+
+  public:
+    location() = default;
+
+    explicit location(location const& next, std::string_view entry)
+      : next_{std::make_pair(entry, util::not_null{&next})}
+    {}
+
+    [[nodiscard]] auto to_string() const -> std::string {
+      if (!next_)
+        return "";
+      auto s = std::string{next_->first};
+      next_->second->append_to(s);
+      return s;
+    }
+
+    auto sub(std::string_view entry) const& -> location {
+      return location{*this, entry};
+    }
+  };
+
+  class object_reader {
+    location loc_;
+    json::object const& obj_;
+    std::unordered_set<std::string> visited_;
+
+  public:
+    object_reader(json::value const& jv, location loc)
+      try : loc_{std::move(loc)}, obj_{jv.as_object()}
+    {} catch (boost::system::system_error const&) {
+        throw std::runtime_error{std::format("expected an object at {}", loc.to_string())};
+      }
+
+    auto check_unused() const -> void {
+      for (auto const& kv : obj_) {
+        if (!visited_.contains(std::string{kv.key()})) {
+          throw std::runtime_error{std::format("unexpected key {}", loc_.sub(kv.key()).to_string())};
+        }
+      }
+    }
+
+    template<class T>
+    auto expect_at(std::string_view key) -> T {
+      visited_.emplace(key);
+      auto const loc = loc_.sub(key);
+      if (auto const jv = obj_.try_at(key)) {
+        try {
+          return json::value_to<T>(*jv, loc);
+        } catch (boost::system::system_error const& e) {
+          throw std::runtime_error{std::format("failed to read {}: {}", loc.to_string(), e.code().message())};
+        }
+      } else {
+        throw std::runtime_error{std::format("did not find expected key {}", loc.to_string())};
+      }
+    }
+  };
+
+  auto as_checked_object(json::value const& jv, location const& loc, std::invocable<object_reader&> auto const& f) -> decltype(f(std::declval<object_reader&>())) {
+    auto r = object_reader{jv, loc};
+    auto&& v = f(r);
+    r.check_unused();
+    return std::forward<decltype(f(r))>(v);
+  }
+
+  auto tag_invoke(json::value_to_tag<rwgps> const&, json::value const& jv, location const& loc) -> rwgps {
+    return as_checked_object(jv, loc, [](object_reader& r) -> rwgps {
+      return {
+        .api_key    = r.expect_at<std::string>("api_key"),
+        .auth_token = r.expect_at<std::string>("auth_token"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<situations> const&, json::value const& jv, location const& loc) -> situations {
+    return as_checked_object(jv, loc, [](object_reader& r) -> situations {
+      return {
+        .datex2_filename = r.expect_at<std::string>("datex2_filename"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<database> const&, json::value const& jv, location const& loc) -> database {
+    return as_checked_object(jv, loc, [](object_reader& r) -> database {
+      return {
+        .sqlite3_filename = r.expect_at<std::string>("sqlite3_filename"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<http_server> const&, json::value const& jv, location const& loc) -> http_server {
+    return as_checked_object(jv, loc, [](object_reader& r) -> http_server {
+      return {
+        .lax_cors = r.expect_at<bool>("lax_cors"),
+      };
+    });
+  }
+
+  auto tag_invoke(json::value_to_tag<logger> const&, json::value const& jv, location const& loc) -> logger {
+    return as_checked_object(jv, loc, [obj_loc = loc](object_reader& r) -> logger {
+      auto const level_str = r.expect_at<std::string>("level");
+      auto level = log::level{};
+      if (level_str == "debug")
+        level = log::level::debug;
+      else if (level_str == "info")
+        level = log::level::info;
+      else if (level_str == "warn")
+        level = log::level::warn;
+      else if (level_str == "error")
+        level = log::level::error;
+      else
+        throw std::runtime_error{std::format("unable to parse log level {:?} at {}: expected one of {{debug, info, warn, error}}", level_str, obj_loc.sub("level").to_string())};
+      return logger{level};
+    });
+  }
+
+  auto json_value_to_app(json::value const& jv) -> app {
+    return as_checked_object(jv, location{}, [](object_reader& r) -> app {
+      return {
+        .rwgps       = r.expect_at<rwgps>("rwgps"),
+        .situations  = r.expect_at<situations>("situations"),
+        .database    = r.expect_at<database>("database"),
+        .http_server = r.expect_at<http_server>("http_server"),
+        .logger      = r.expect_at<logger>("logger"),
+      };
+    });
+  }
+
+  auto load_file(std::string const& filename) -> app {
+    auto f = std::ifstream{filename}; // TODO: ensure that we are opening in binary mode?
+    if (!f.is_open())
+      throw std::runtime_error{std::format("failed to open {}", filename)};
+    auto jv = json::value{};
+    try {
+      jv = json::parse(f);
+    } catch (boost::system::system_error const& e) {
+      throw std::runtime_error{std::format("failed to parse: {}", e.code().message())};
+    }
+    return json_value_to_app(jv);
+  }
+
+} // namespace routemon::config