Time window specification

This is the engineering specification for the TimeWindow type.

Overview

A TimeWindow represents a distinct interval of time. Time windows are most often used to represent the time between two states in a transition.

A         B         C
|---------|---------|
           \__|____/
               ^- time window

A time window has two fixed sides: back and fore. In the example above, B is back and C is fore.

A time window has an initial and current direction that can be either forward or backward. The initial direction cannot be changed after initialization. The current direction can be changed at will.

A time window has an expected duration, expressed in units of time.

A time window has a numerical position expressed in the range [0,1]. 0 refers to the back side of the time, while 1 refers to the front side.

MVP Specification

Object type: A time window is an object.

class TimeWindow {
}

Position API: A time window has a current position.

This numerical value should be bounded to [0,1].

When initialized with an initial direction of forward, position should initially be 0.

When initialized with an initial direction of backward, position should initially be 1.

class TimeWindow {
  var position: Double
}

Direction type: The position in a time window can move in one of two directions: forward or backward.

Define a direction type that includes both possible directions.

enum TimeWindowDirection {
  .forward:
  .backward:
}

Initialization API: A time window must be created with an initial direction and duration.

class TimeWindow {
  init(initialDirection, duration)
}

Initial direction API: A time window is aware of its initial direction.

class TimeWindow {
  let initialDirection: TimeWindowDirection
}

Duration API: A time window is aware of its expected duration.

The unit of time is platform-dependent.

class TimeWindow {
  let duration: TimeInterval
}

Current direction API: A time window is aware of its current direction.

This should be initialized with the value of initialDirection.

class TimeWindow {
  var currentDirection: TimeWindowDirection
}