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package acp

import "time"

// SpinnerPeriod is how long one frame of the spinner lasts. Eight frames a
// second reads as motion without drawing attention away from the text.
const SpinnerPeriod = 120 * time.Millisecond

// spinnerFrames are the braille dots every terminal spinner uses. They are one
// column wide, which matters: a frame that changed width would shift the words
// beside it on every tick.
var spinnerFrames = []rune("⠋⠙⠹⠸⠼⠴⠦⠧⠇⠏")

// Spinner returns the frame to draw at a moment.
//
// It is a function of the clock rather than of a counter somebody increments,
// so drawing stays a pure function of state — the same rule the rest of this
// editor follows, and what lets a test assert on a frame without waiting for
// one. Nothing has to be reset when a turn starts, and two windows thinking at
// once turn in step.
//
//	view.ruleLabel() // " ⠙ thinking — Esc stops it "
func Spinner(at time.Time) rune {
	frame := at.UnixNano() / int64(SpinnerPeriod)
	return spinnerFrames[int(frame%int64(len(spinnerFrames)))]
}