// Copyright © SixtyFPS GmbH <info@sixtyfps.io>
// SPDX-License-Identifier: (GPL-3.0-only OR LicenseRef-SixtyFPS-commercial)

#![warn(missing_docs)]
//! The animation system

use alloc::boxed::Box;
use core::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
    }
}

/// Represent an instant, in milliseconds since the AnimationDriver's initial_instant
#[repr(transparent)]
#[derive(Copy, Clone, Debug, Default, PartialEq, Ord, PartialOrd, Eq)]
pub struct Instant(pub u64);

impl core::ops::Sub<Instant> for Instant {
    type Output = core::time::Duration;
    fn sub(self, other: Self) -> core::time::Duration {
        core::time::Duration::from_millis(self.0 - other.0)
    }
}

impl core::ops::Sub<core::time::Duration> for Instant {
    type Output = Instant;
    fn sub(self, other: core::time::Duration) -> Instant {
        Self(self.0 - other.as_millis() as u64)
    }
}

impl core::ops::Add<core::time::Duration> for Instant {
    type Output = Instant;
    fn add(self, other: core::time::Duration) -> Instant {
        Self(self.0 + other.as_millis() as u64)
    }
}

impl core::ops::AddAssign<core::time::Duration> for Instant {
    fn add_assign(&mut self, other: core::time::Duration) {
        self.0 += other.as_millis() as u64;
    }
}

impl core::ops::SubAssign<core::time::Duration> for Instant {
    fn sub_assign(&mut self, other: core::time::Duration) {
        self.0 -= other.as_millis() as u64;
    }
}

impl Instant {
    /// Returns the amount of time elapsed since an other instant.
    ///
    /// Equivalent to `self - earlier`
    pub fn duration_since(self, earlier: Instant) -> core::time::Duration {
        self - earlier
    }

    /// Wrapper around [`std::time::Instant::now()`] that delegates to the backend
    /// and allows working in no_std environments.
    pub fn now() -> Self {
        Self(Self::duration_since_start().as_millis() as u64)
    }

    fn duration_since_start() -> core::time::Duration {
        crate::backend::instance().map(|backend| backend.duration_since_start()).unwrap_or_default()
    }
}

/// 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>>>,
}

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

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) {
        if self.global_instant.as_ref().get_untracked() != new_tick {
            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 {
        self.global_instant.as_ref().get()
    }
}

#[cfg(all(not(feature = "std"), feature = "unsafe_single_core"))]
use crate::unsafe_single_core::thread_local;

thread_local!(
/// This is the default instance of the animation driver that's used to advance all property animations
/// at the same time.
pub 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 {
    CURRENT_ANIMATION_DRIVER.with(|driver| driver.current_tick())
}

/// map a value between 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,
        #[cfg(feature = "std")]
        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, 0.01))
        }
        #[cfg(not(feature = "std"))]
        EasingCurve::CubicBezier(_) => {
            todo!("bezier curve not implemented when no_std")
        }
    }
}

/*
#[test]
fn easing_test() {
    fn test_curve(name: &str, curve: &EasingCurve) {
        let mut img = image::ImageBuffer::new(500, 500);
        let white = image::Rgba([255 as u8, 255 as u8, 255 as u8, 255 as u8]);

        for x in 0..img.width() {
            let t = (x as f32) / (img.width() as f32);
            let y = easing_curve(curve, t);
            let y = (y * (img.height() as f32)) as u32;
            let y = y.min(img.height() - 1);
            *img.get_pixel_mut(x, img.height() - 1 - y) = white;
        }

        img.save(
            std::path::PathBuf::from(std::env::var_os("HOME").unwrap())
                .join(format!("{}.png", name)),
        )
        .unwrap();
    }

    test_curve("linear", &EasingCurve::Linear);
    test_curve("linear2", &EasingCurve::CubicBezier([0.0, 0.0, 1.0, 1.0]));
    test_curve("ease", &EasingCurve::CubicBezier([0.25, 0.1, 0.25, 1.0]));
    test_curve("ease_in", &EasingCurve::CubicBezier([0.42, 0.0, 1.0, 1.0]));
    test_curve("ease_in_out", &EasingCurve::CubicBezier([0.42, 0.0, 0.58, 1.0]));
    test_curve("ease_out", &EasingCurve::CubicBezier([0.0, 0.0, 0.58, 1.0]));
}
*/

/// Update the global animation time to the current time
pub fn update_animations() {
    CURRENT_ANIMATION_DRIVER.with(|driver| {
        #[allow(unused_mut)]
        let mut duration = Instant::duration_since_start().as_millis() as u64;
        #[cfg(feature = "std")]
        if let Ok(val) = std::env::var("SIXTYFPS_SLOW_ANIMATIONS") {
            let factor = val.parse().unwrap_or(2);
            duration /= factor;
        };
        driver.update_animations(Instant(duration))
    });
}