netspd 0.1.1

//! Animation primitives: spinner frames and smooth value interpolation.

/// Braille spinner frames, one per UI tick.
const SPINNER_FRAMES: [&str; 10] = ["⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"];

/// Returns the spinner glyph for a given UI tick.
#[must_use]
pub fn spinner_frame(tick: u64) -> &'static str {
    SPINNER_FRAMES[(tick as usize) % SPINNER_FRAMES.len()]
}

/// A value that eases smoothly toward its target.
///
/// Uses framerate-independent exponential smoothing, so counters and bars
/// animate identically at any refresh rate.
#[derive(Debug, Clone, Copy)]
pub struct AnimatedValue {
    current: f64,
    target: f64,
    /// Approach rate: higher values converge faster.
    rate: f64,
}

impl AnimatedValue {
    /// Creates a value at rest at zero with the given approach rate.
    #[must_use]
    pub fn new(rate: f64) -> Self {
        Self {
            current: 0.0,
            target: 0.0,
            rate: rate.max(0.1),
        }
    }

    /// Sets a new target to ease toward.
    pub fn set_target(&mut self, target: f64) {
        if target.is_finite() {
            self.target = target;
        }
    }

    /// Snaps immediately to a value (used on resets).
    pub fn snap(&mut self, value: f64) {
        self.current = value;
        self.target = value;
    }

    /// Advances the animation by `dt` seconds and returns the new value.
    pub fn tick(&mut self, dt: f64) -> f64 {
        let blend = 1.0 - (-self.rate * dt.max(0.0)).exp();
        self.current += (self.target - self.current) * blend;
        if (self.target - self.current).abs() < 1e-9 {
            self.current = self.target;
        }
        self.current
    }

    /// The current animated value.
    #[must_use]
    pub fn value(&self) -> f64 {
        self.current
    }

    /// Whether the value is still visibly moving toward its target.
    #[must_use]
    pub fn is_animating(&self) -> bool {
        (self.target - self.current).abs() > f64::EPSILON * self.target.abs().max(1.0)
    }
}

/// Longest integration step for the spring, in seconds. Larger frame
/// deltas are split into substeps so the integration stays stable at any
/// refresh rate.
const SPRING_MAX_STEP: f64 = 1.0 / 120.0;

/// A damped spring animator.
///
/// Unlike [`AnimatedValue`]'s pure exponential ease, a spring carries
/// velocity: it overshoots its target slightly and settles with a small
/// wobble, which makes gauge needles read as mechanical instruments
/// rather than interpolated numbers.
#[derive(Debug, Clone, Copy)]
pub struct SpringValue {
    current: f64,
    velocity: f64,
    target: f64,
    stiffness: f64,
    damping: f64,
}

impl SpringValue {
    /// Creates a spring at rest at zero.
    ///
    /// `stiffness` sets how hard the spring pulls; `damping` how quickly
    /// the wobble dies. Underdamped values (damping below `2·√stiffness`)
    /// give the characteristic needle overshoot.
    #[must_use]
    pub fn new(stiffness: f64, damping: f64) -> Self {
        Self {
            current: 0.0,
            velocity: 0.0,
            target: 0.0,
            stiffness: stiffness.max(0.1),
            damping: damping.max(0.0),
        }
    }

    /// Sets a new target for the spring to chase.
    pub fn set_target(&mut self, target: f64) {
        if target.is_finite() {
            self.target = target;
        }
    }

    /// Snaps to a value at rest (used on phase resets).
    pub fn snap(&mut self, value: f64) {
        self.current = value;
        self.velocity = 0.0;
        self.target = value;
    }

    /// Advances the simulation by `dt` seconds and returns the new value.
    pub fn tick(&mut self, dt: f64) -> f64 {
        let mut remaining = dt.clamp(0.0, 0.5);
        while remaining > 0.0 {
            let step = remaining.min(SPRING_MAX_STEP);
            let acceleration =
                self.stiffness * (self.target - self.current) - self.damping * self.velocity;
            self.velocity += acceleration * step;
            self.current += self.velocity * step;
            remaining -= step;
        }
        self.current
    }

    /// The current spring position.
    #[must_use]
    pub fn value(&self) -> f64 {
        self.current
    }
}