[sensors] Ambient light sensor implementation for ChromeOS and Linux.

device/generic_sensor/platform_sensor_utils_iio.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "device/generic_sensor/platform_sensor_utils_iio.h"
+
+#include "base/files/file_enumerator.h"
+#include "base/files/file_util.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+
+namespace device {
+
+namespace {
+
+const base::FilePath::CharType kAmbientLightIioBasePath[] =
+    FILE_PATH_LITERAL("/sys/bus/iio/devices");
+
+// This will be templated.
+bool GetSensorFilePaths(std::vector<base::FilePath>* path) {
+  // Search the iio/devices directory for a subdirectory (eg "device0" or
+  // "iio:device0") that contains the "[in_]illuminance[0]_{input|raw}" file.
+  base::FileEnumerator dir_enumerator(base::FilePath(kAmbientLightIioBasePath),
+                                      false, base::FileEnumerator::DIRECTORIES);
+  const char* input_names[] = {
+      "in_illuminance0_input", "in_illuminance_input", "in_illuminance0_raw",
+      "in_illuminance_raw",    "illuminance0_input",
+  };
+
+  for (base::FilePath check_path = dir_enumerator.Next(); !check_path.empty();
+       check_path = dir_enumerator.Next()) {
+    for (unsigned int i = 0; i < arraysize(input_names); i++) {
+      base::FilePath als_path = check_path.Append(input_names[i]);
+      if (base::PathExists(als_path)) {
+        path->push_back(als_path);
+        // temporary for als sensor.
+        return true;
+      }
+    }
+  }
+
+  if (path->empty())
+    return false;
+  return true;
+}
+
+}  // namespace
+
+// static
+std::unique_ptr<SensorReader> SensorReader::Create(mojom::SensorType type) {
+  std::vector<base::FilePath> sensor_paths;
+  std::unique_ptr<SensorReader> sensor_reader = nullptr;
+
+  switch (type) {
+    case mojom::SensorType::AMBIENT_LIGHT:
+      if (GetSensorFilePaths(&sensor_paths))
+        sensor_reader.reset(new SensorReader(type, std::move(sensor_paths)));
+      break;
+    default:
+      NOTIMPLEMENTED();
+      break;
+  }
+
+  return sensor_reader;
+}
+
+SensorReader::SensorReader(mojom::SensorType type,
+                           std::vector<base::FilePath> sensor_paths)
+    : type_(type), sensor_paths_(std::move(sensor_paths)) {
+  DCHECK(!sensor_paths_.empty());
+}
+
+bool SensorReader::ReadSensorValue(double* lux) {
+  *lux = std::numeric_limits<double>::infinity();
+  std::string value;
+  for (const auto& path : sensor_paths_) {
+    if (!base::ReadFileToString(path, &value))
+      return false;
+
+    base::TrimWhitespaceASCII(value, base::TRIM_ALL, &value);
+    if (!base::StringToDouble(value, lux))
+      return false;
+  }
+  return true;
+}
+
+mojom::SensorType SensorReader::type() const {
+  return type_;
+}
+
+}  // device