add support to build sensors from json

Add support to build sensors from a json configuration file.

Change-Id: Ic5bcbcd01e085ab0d4efaed314af8dc7e82b0b9d
Signed-off-by: Patrick Venture <venture@google.com>

2 files changed, 108 insertions, 0 deletions

diff --git a/sensors/buildjson.cpp b/sensors/buildjson.cpp
new file mode 100644
index 0000000..7c4c7d6
--- /dev/null
+++ b/sensors/buildjson.cpp
@@ -0,0 +1,88 @@
+/**
+ * Copyright 2019 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "sensors/buildjson.hpp"
+
+#include "conf.hpp"
+#include "sensors/sensor.hpp"
+
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+void from_json(const json& j, SensorConfig& s)
+{
+    j.at("type").get_to(s.type);
+    j.at("readpath").get_to(s.readpath);
+
+    /* The writepath field is optional in a configuration */
+    auto writepath = j.find("writepath");
+    if (writepath == j.end())
+    {
+        s.writepath = "";
+    }
+    else
+    {
+        j.at("writepath").get_to(s.writepath);
+    }
+
+    /* The min field is optional in a configuration. */
+    auto min = j.find("min");
+    if (min == j.end())
+    {
+        s.min = 0;
+    }
+    else
+    {
+        j.at("min").get_to(s.min);
+    }
+
+    /* The max field is optional in a configuration. */
+    auto max = j.find("max");
+    if (max == j.end())
+    {
+        s.max = 0;
+    }
+    else
+    {
+        j.at("max").get_to(s.max);
+    }
+
+    /* The timeout field is optional in a configuration. */
+    auto timeout = j.find("timeout");
+    if (timeout == j.end())
+    {
+        s.timeout = Sensor::getDefaultTimeout(s.type);
+    }
+    else
+    {
+        j.at("timeout").get_to(s.timeout);
+    }
+}
+
+std::map<std::string, struct SensorConfig>
+    buildSensorsFromJson(const json& data)
+{
+    std::map<std::string, struct SensorConfig> config;
+    auto sensors = data["sensors"];
+
+    for (const auto& sensor : sensors)
+    {
+        config[sensor["name"]] = sensor.get<struct SensorConfig>();
+    }
+
+    return config;
+}
diff --git a/sensors/buildjson.hpp b/sensors/buildjson.hpp
new file mode 100644
index 0000000..c5aacc7
--- /dev/null
+++ b/sensors/buildjson.hpp
@@ -0,0 +1,20 @@
+#pragma once
+
+#include "conf.hpp"
+
+#include <map>
+#include <nlohmann/json.hpp>
+#include <string>
+
+using json = nlohmann::json;
+
+/**
+ * Given a json object generated from a configuration file, build the sensor
+ * configuration representation. This expecteds the json configuration to be
+ * valid.
+ *
+ * @param[in] data - the json data
+ * @return a map of sensors.
+ */
+std::map<std::string, struct SensorConfig>
+    buildSensorsFromJson(const json& data);