designer/src/com/android/tools/idea/common/scene/LerpValue.kt

// Copyright (C) 2017 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 com.android.tools.idea.common.scene

/**
 * [LerpValue] Represents a linear interpolation between two values.
 */
abstract class LerpValue<T>(val start: T, val end: T, val duration: Int) {
  private var startTime = -1L

  constructor(value: T) : this(value, value, 0)

  /**
   * Gets the interpolated value at the specified time. The start
   * time is measured from the first time getValue is called.
   */
  fun getValue(time: Long): T {
    if (startTime == -1L) {
      startTime = time
    }

    return when {
      time <= startTime -> start
      isComplete(time) -> end
      else -> interpolate((time - startTime).toFloat() / duration)
    }
  }

  fun isComplete(time: Long) = time >= startTime + duration

  abstract fun interpolate(fraction: Float): T

  override fun equals(other: Any?): Boolean {
    val otherLerp = other as? LerpValue<T> ?: return false
    return start == otherLerp.start && end == otherLerp.end && duration == otherLerp.duration
  }
}