// Copyright 2017 Google Inc. All rights reserved.
//
// 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.

using UnityEngine;

#if UNITY_2017_2_OR_NEWER
using UnityEngine.XR;
#else
using XRSettings = UnityEngine.VR.VRSettings;
#endif  // UNITY_2017_2_OR_NEWER

/// Used to recenter only the controllers, required for scenes that have no clear forward direction.
/// Details: https://developers.google.com/vr/distribute/daydream/design-requirements#UX-D6
///
/// Works by offsetting the orientation of the transform when a recenter occurs to correct for the
/// orientation change caused by the recenter event.
///
/// Usage: Place on the parent of the camera that should have it's orientation corrected.
[HelpURL("https://developers.google.com/vr/unity/reference/class/GvrRecenterOnlyController")]
public class GvrRecenterOnlyController : MonoBehaviour {
  private Quaternion lastAppliedYawCorrection = Quaternion.identity;
  private Quaternion yawCorrection = Quaternion.identity;

  void Update() {
    bool connected = false;
    foreach (var hand in Gvr.Internal.ControllerUtils.AllHands) {
      GvrControllerInputDevice device = GvrControllerInput.GetDevice(hand);
      if (device.State == GvrConnectionState.Connected) {
        connected = true;
        break;
      }
    }
    if (!connected) {
      return;
    }

    // Daydream is loaded only on deivce, not in editor.
#if UNITY_ANDROID && !UNITY_EDITOR
    if (XRSettings.loadedDeviceName != GvrSettings.VR_SDK_DAYDREAM) {
      return;
    }
#endif

    if (GvrControllerInput.Recentered) {
      ApplyYawCorrection();
      return;
    }

#if UNITY_EDITOR
    // Compatibility for Instant Preview.
    if (Gvr.Internal.InstantPreview.Instance != null &&
      Gvr.Internal.InstantPreview.Instance.enabled &&
      Gvr.Internal.ControllerUtils.AnyButton(GvrControllerButton.System)) {
      return;
    }
#else  // !UNITY_EDITOR
    if (Gvr.Internal.ControllerUtils.AnyButton(GvrControllerButton.System)) {
      return;
    }
#endif  // UNITY_EDITOR

    yawCorrection = GetYawCorrection();
  }

  void OnDisable() {
    yawCorrection = Quaternion.identity;
    RemoveLastYawCorrection();
  }

  private void ApplyYawCorrection() {
    RemoveLastYawCorrection();
    transform.localRotation = transform.localRotation * yawCorrection;
    lastAppliedYawCorrection = yawCorrection;
  }

  private void RemoveLastYawCorrection() {
    transform.localRotation =
      transform.localRotation * Quaternion.Inverse(lastAppliedYawCorrection);
    lastAppliedYawCorrection = Quaternion.identity;
  }

  private Quaternion GetYawCorrection() {
    Quaternion headRotation = GvrVRHelpers.GetHeadRotation();
    Vector3 euler = headRotation.eulerAngles;
    return lastAppliedYawCorrection * Quaternion.Euler(0.0f, euler.y, 0.0f);
  }
}