#![warn(missing_docs)]

use std::cell::Cell;

/// The representation of an easing curve, for animations
#[repr(C, u32)]
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum EasingCurve {
    /// The linear curve
    Linear,
    /// A Cubic bezier curve, with its 4 parameter
    CubicBezier([f32; 4]),
    //Custom(Box<dyn Fn(f32) -> f32>),
}

impl Default for EasingCurve {
    fn default() -> Self {
        Self::Linear
    }
}

/// The AnimationDriver
pub struct AnimationDriver {
    /// Indicate whether there are any active animations that require a future call to update_animations.
    active_animations: Cell<bool>,
    global_instant: core::pin::Pin<Box<crate::Property<instant::Instant>>>,
    initial_instant: instant::Instant,
}

impl Default for AnimationDriver {
    fn default() -> Self {
        AnimationDriver {
            active_animations: Cell::default(),
            global_instant: Box::pin(crate::Property::new(instant::Instant::now())),
            initial_instant: instant::Instant::now(),
        }
    }
}

impl AnimationDriver {
    /// Iterates through all animations based on the new time tick and updates their state. This should be called by
    /// the windowing system driver for every frame.
    pub fn update_animations(&self, new_tick: instant::Instant) {
        self.active_animations.set(false);
        self.global_instant.as_ref().set(new_tick);
    }

    /// Returns true if there are any active or ready animations. This is used by the windowing system to determine
    /// if a new animation frame is required or not. Returns false otherwise.
    pub fn has_active_animations(&self) -> bool {
        self.active_animations.get()
    }

    /// Tell the driver that there are active animations
    pub fn set_has_active_animations(&self) {
        self.active_animations.set(true);
    }
    /// The current instant that is to be used for animation
    /// using this function register the current binding as a dependency
    pub fn current_tick(&self) -> instant::Instant {
        self.global_instant.as_ref().get()
    }
}

thread_local!(pub(crate) static CURRENT_ANIMATION_DRIVER : AnimationDriver = AnimationDriver::default());

/// The current instant that is to be used for animation
/// using this function register the current binding as a dependency
pub fn current_tick() -> instant::Instant {
    CURRENT_ANIMATION_DRIVER.with(|driver| driver.current_tick())
}

/// map a value betwen 0 and 1 to another value between 0 and 1 according to the curve
pub fn easing_curve(curve: &EasingCurve, value: f32) -> f32 {
    match curve {
        EasingCurve::Linear => value,
        EasingCurve::CubicBezier([a, b, c, d]) => {
            if !(0.0..=1.0).contains(a) && !(0.0..=1.0).contains(c) {
                return value;
            };
            let curve = lyon::algorithms::geom::cubic_bezier::CubicBezierSegment {
                from: (0., 0.).into(),
                ctrl1: (*a, *b).into(),
                ctrl2: (*c, *d).into(),
                to: (1., 1.).into(),
            };
            let curve = curve.assume_monotonic();
            curve.y(curve.solve_t_for_x(
                value,
                0.0..1.0,
                lyon::tessellation::StrokeOptions::DEFAULT_TOLERANCE,
            ))
        }
    }
}

/// Update the glibal animation time to the current time
pub(crate) fn update_animations() {
    CURRENT_ANIMATION_DRIVER.with(|driver| {
        match std::env::var("SIXTYFPS_SLOW_ANIMATIONS") {
            Err(_) => driver.update_animations(instant::Instant::now()),
            Ok(val) => {
                let factor = val.parse().unwrap_or(2.);
                driver.update_animations(
                    driver.initial_instant
                        + (instant::Instant::now() - driver.initial_instant).div_f32(factor),
                )
            }
        };
    });
}