content: /*
   * Copyright (C) 2021 The Android Open Source Project
   *
   * 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.
   */
  
  package androidx.car.app.sample.navigation.common.model;
  
  import android.os.Handler;
  import android.os.Looper;
  
  import androidx.annotation.NonNull;
  import androidx.annotation.Nullable;
  
  import java.util.List;
  
  /** Represents an instruction sequence and parameters for a executing a script. */
  public class Script {
  
      private final Handler mHandler = new Handler(Looper.getMainLooper());
      private final List<Instruction> mInstructions;
      private final Processor mProcessor;
      private int mCurrentInstruction;
  
      /** An interface for a block of code that processes an instruction. */
      public interface Processor {
          /** A block of code that processes an instruction. */
          void process(@NonNull Instruction instruction, @Nullable Instruction nextInstruction);
      }
  
      /** Executes the given list of instructions. */
      @NonNull
      public static Script execute(@NonNull List<Instruction> instructions,
              @NonNull Processor processor) {
          return new Script(instructions, processor);
      }
  
      /** Stops executing the instructions. */
      public void stop() {
          mHandler.removeCallbacksAndMessages(null);
          mCurrentInstruction = mInstructions.size();
      }
  
      private Script(@NonNull List<Instruction> instructions, @NonNull Processor processor) {
          mInstructions = instructions;
          mProcessor = processor;
          mCurrentInstruction = 0;
          // Execute the first instruction right away to start navigation and avoid flicker.
          nextInstruction();
      }
  
      private void nextInstruction() {
          if (mCurrentInstruction >= mInstructions.size()) {
              // Script is finished.
              return;
          }
          Instruction instruction = mInstructions.get(mCurrentInstruction);
          Instruction nextInstruction = null;
          int nextPosition = mCurrentInstruction + 1;
          if (nextPosition < mInstructions.size()) {
              nextInstruction = mInstructions.get(nextPosition);
          }
          mProcessor.process(instruction, nextInstruction);
          mCurrentInstruction++;
          mHandler.postDelayed(this::nextInstruction, instruction.getDurationMillis());
      }
  }
  