//! Write your own renderer.
#[cfg(debug_assertions)]
mod null;

use crate::image;
use crate::{
    Background, Border, Color, Font, Pixels, Rectangle, Shadow, Size,
    Transformation, Vector,
};

/// A component that can be used by widgets to draw themselves on a screen.
pub trait Renderer {
    /// Starts recording a new layer.
    fn start_layer(&mut self, bounds: Rectangle);

    /// Ends recording a new layer.
    ///
    /// The new layer will clip its contents to the provided `bounds`.
    fn end_layer(&mut self);

    /// Draws the primitives recorded in the given closure in a new layer.
    ///
    /// The layer will clip its contents to the provided `bounds`.
    fn with_layer(&mut self, bounds: Rectangle, f: impl FnOnce(&mut Self)) {
        self.start_layer(bounds);
        f(self);
        self.end_layer();
    }

    /// Starts recording with a new [`Transformation`].
    fn start_transformation(&mut self, transformation: Transformation);

    /// Ends recording a new layer.
    ///
    /// The new layer will clip its contents to the provided `bounds`.
    fn end_transformation(&mut self);

    /// Applies a [`Transformation`] to the primitives recorded in the given closure.
    fn with_transformation(
        &mut self,
        transformation: Transformation,
        f: impl FnOnce(&mut Self),
    ) {
        self.start_transformation(transformation);
        f(self);
        self.end_transformation();
    }

    /// Applies a translation to the primitives recorded in the given closure.
    fn with_translation(
        &mut self,
        translation: Vector,
        f: impl FnOnce(&mut Self),
    ) {
        self.with_transformation(
            Transformation::translate(translation.x, translation.y),
            f,
        );
    }

    /// Fills a [`Quad`] with the provided [`Background`].
    fn fill_quad(&mut self, quad: Quad, background: impl Into<Background>);

    /// Resets the [`Renderer`] to start drawing in the `new_bounds` from scratch.
    fn reset(&mut self, new_bounds: Rectangle);

    /// Creates an [`image::Allocation`] for the given [`image::Handle`] and calls the given callback with it.
    fn allocate_image(
        &mut self,
        handle: &image::Handle,
        callback: impl FnOnce(Result<image::Allocation, image::Error>)
        + Send
        + 'static,
    );
}

/// A polygon with four sides.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Quad {
    /// The bounds of the [`Quad`].
    pub bounds: Rectangle,

    /// The [`Border`] of the [`Quad`]. The border is drawn on the inside of the [`Quad`].
    pub border: Border,

    /// The [`Shadow`] of the [`Quad`].
    pub shadow: Shadow,

    /// Whether the [`Quad`] should be snapped to the pixel grid.
    pub snap: bool,
}

impl Default for Quad {
    fn default() -> Self {
        Self {
            bounds: Rectangle::with_size(Size::ZERO),
            border: Border::default(),
            shadow: Shadow::default(),
            snap: cfg!(feature = "crisp"),
        }
    }
}

/// The styling attributes of a [`Renderer`].
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Style {
    /// The text color
    pub text_color: Color,
}

impl Default for Style {
    fn default() -> Self {
        Style {
            text_color: Color::BLACK,
        }
    }
}

/// A headless renderer is a renderer that can render offscreen without
/// a window nor a compositor.
pub trait Headless {
    /// Creates a new [`Headless`] renderer;
    fn new(
        default_font: Font,
        default_text_size: Pixels,
        backend: Option<&str>,
    ) -> impl Future<Output = Option<Self>>
    where
        Self: Sized;

    /// Returns the unique name of the renderer.
    ///
    /// This name may be used by testing libraries to uniquely identify
    /// snapshots.
    fn name(&self) -> String;

    /// Draws offscreen into a screenshot, returning a collection of
    /// bytes representing the rendered pixels in RGBA order.
    fn screenshot(
        &mut self,
        size: Size<u32>,
        scale_factor: f32,
        background_color: Color,
    ) -> Vec<u8>;
}