//! Canvas element for custom GPU drawing
//!
//! The canvas element provides direct access to the GPU rendering context
//! (`GpuPaintContext` via the `DrawContext` trait) within the layout system.
//! Canvas inherits transforms, clipping, and layer settings from parent elements.
//!
//! # GPU Context
//!
//! The callback receives a `GpuPaintContext` (as `&mut dyn DrawContext`) which
//! provides the full GPU-accelerated drawing API:
//! - `fill_rect`, `stroke_rect` - Rectangle primitives
//! - `fill_circle`, `stroke_circle` - Circle primitives
//! - `draw_shadow` - GPU-accelerated shadows
//! - `push_transform`, `pop_transform` - Transform stack
//! - `push_clip`, `pop_clip` - Clipping regions
//! - Glass effects, gradients, and more
//!
//! # Example
//!
//! ```ignore
//! use blinc_layout::prelude::*;
//! use blinc_core::{DrawContext, Brush, Color, Rect};
//!
//! // Draw a custom cursor
//! canvas(|ctx: &mut dyn DrawContext, bounds| {
//!     ctx.fill_rect(
//!         Rect::new(0.0, 0.0, 2.0, bounds.height),
//!         0.0.into(),
//!         Brush::Solid(Color::WHITE),
//!     );
//! })
//! .w(2.0)
//! .h(20.0)
//! ```

use std::rc::Rc;

use blinc_core::DrawContext;
use taffy::prelude::*;

use crate::div::{ElementBuilder, ElementTypeId};
use crate::element::{RenderLayer, RenderProps};
use crate::tree::{LayoutNodeId, LayoutTree};

/// Bounds passed to canvas render callback
#[derive(Clone, Copy, Debug)]
pub struct CanvasBounds {
    /// Width of the canvas element
    pub width: f32,
    /// Height of the canvas element
    pub height: f32,
}

/// Canvas render callback type
///
/// The callback receives:
/// - `ctx`: The GPU paint context (`GpuPaintContext` as `&mut dyn DrawContext`)
/// - `bounds`: The computed bounds of the canvas element
///
/// The context already has the correct transform applied (canvas position),
/// so drawing at (0, 0) draws at the canvas origin. The context also inherits
/// clip regions and opacity from parent elements.
/// Canvas render function type - uses Rc for single-threaded UI
pub type CanvasRenderFn = Rc<dyn Fn(&mut dyn DrawContext, CanvasBounds)>;

/// Canvas element for custom GPU drawing
///
/// The canvas element reserves space in the layout and provides direct access
/// to the GPU paint context during rendering. This enables:
/// - Custom cursor rendering
/// - Procedural graphics
/// - Charts and visualizations
/// - Animated elements
/// - 3D viewports (via DrawContext's 3D capabilities)
///
/// Canvas respects the layout system:
/// - Transforms are inherited from parent elements
/// - Clipping from scroll containers is applied
/// - Layer ordering (background/foreground/glass) is respected
pub struct Canvas {
    /// Taffy layout style
    style: Style,
    /// The render callback
    render_fn: Option<CanvasRenderFn>,
    /// Opacity
    opacity: f32,
    /// Render layer (background, foreground, glass)
    layer: RenderLayer,
}

impl Canvas {
    /// Create a new canvas element
    pub fn new() -> Self {
        Self {
            style: Style::default(),
            render_fn: None,
            opacity: 1.0,
            layer: RenderLayer::default(),
        }
    }

    /// Create a canvas with a render callback
    pub fn with_render<F>(render_fn: F) -> Self
    where
        F: Fn(&mut dyn DrawContext, CanvasBounds) + 'static,
    {
        Self {
            style: Style::default(),
            render_fn: Some(Rc::new(render_fn)),
            opacity: 1.0,
            layer: RenderLayer::default(),
        }
    }

    /// Set the render callback
    pub fn render<F>(mut self, render_fn: F) -> Self
    where
        F: Fn(&mut dyn DrawContext, CanvasBounds) + 'static,
    {
        self.render_fn = Some(Rc::new(render_fn));
        self
    }

    /// Set fixed width
    pub fn w(mut self, width: f32) -> Self {
        self.style.size.width = Dimension::Length(width);
        self
    }

    /// Set fixed height
    pub fn h(mut self, height: f32) -> Self {
        self.style.size.height = Dimension::Length(height);
        self
    }

    /// Set both width and height
    pub fn size(mut self, width: f32, height: f32) -> Self {
        self.style.size.width = Dimension::Length(width);
        self.style.size.height = Dimension::Length(height);
        self
    }

    /// Set width to 100% of parent
    pub fn w_full(mut self) -> Self {
        self.style.size.width = Dimension::Percent(1.0);
        self
    }

    /// Set height to 100% of parent
    pub fn h_full(mut self) -> Self {
        self.style.size.height = Dimension::Percent(1.0);
        self
    }

    /// Set opacity (0.0 = transparent, 1.0 = opaque)
    pub fn opacity(mut self, opacity: f32) -> Self {
        self.opacity = opacity.clamp(0.0, 1.0);
        self
    }

    /// Set flex grow factor
    pub fn flex_grow(mut self) -> Self {
        self.style.flex_grow = 1.0;
        self
    }

    /// Set absolute positioning
    pub fn absolute(mut self) -> Self {
        self.style.position = Position::Absolute;
        self
    }

    /// Set left position (for absolute positioning)
    pub fn left(mut self, value: f32) -> Self {
        self.style.inset.left = LengthPercentageAuto::Length(value);
        self
    }

    /// Set top position (for absolute positioning)
    pub fn top(mut self, value: f32) -> Self {
        self.style.inset.top = LengthPercentageAuto::Length(value);
        self
    }

    /// Set render layer (background, foreground, glass)
    pub fn layer(mut self, layer: RenderLayer) -> Self {
        self.layer = layer;
        self
    }

    /// Render in foreground layer (on top of glass effects)
    pub fn foreground(mut self) -> Self {
        self.layer = RenderLayer::Foreground;
        self
    }

    /// Render in background layer (behind glass effects)
    pub fn background(mut self) -> Self {
        self.layer = RenderLayer::Background;
        self
    }

    /// Get the render function
    pub fn render_fn(&self) -> Option<&CanvasRenderFn> {
        self.render_fn.as_ref()
    }
}

impl Default for Canvas {
    fn default() -> Self {
        Self::new()
    }
}

impl ElementBuilder for Canvas {
    fn build(&self, tree: &mut LayoutTree) -> LayoutNodeId {
        tree.create_node(self.style.clone())
    }

    fn render_props(&self) -> RenderProps {
        RenderProps {
            opacity: self.opacity,
            layer: self.layer,
            ..Default::default()
        }
    }

    fn children_builders(&self) -> &[Box<dyn ElementBuilder>] {
        // Canvas has no children in the layout tree
        &[]
    }

    fn element_type_id(&self) -> ElementTypeId {
        ElementTypeId::Canvas
    }

    fn canvas_render_info(&self) -> Option<CanvasRenderFn> {
        self.render_fn.clone()
    }

    fn layout_style(&self) -> Option<&taffy::Style> {
        Some(&self.style)
    }
}

/// Data stored in the render tree for canvas elements
#[derive(Clone)]
pub struct CanvasData {
    /// The render callback
    pub render_fn: Option<CanvasRenderFn>,
}

impl std::fmt::Debug for CanvasData {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("CanvasData")
            .field("has_render_fn", &self.render_fn.is_some())
            .finish()
    }
}

/// Create a canvas element with a render callback
///
/// The callback receives a `DrawContext` which provides the unified drawing API
/// for 2D/3D rendering (fill_rect, stroke_circle, paths, gradients, 3D meshes, etc.)
///
/// The DrawContext already has transforms applied for the canvas position,
/// so drawing at (0, 0) draws at the canvas origin. Clipping and opacity from
/// parent elements are also inherited.
///
/// # Example
///
/// ```ignore
/// use blinc_layout::prelude::*;
/// use blinc_core::{Brush, Color, Rect};
///
/// // Simple colored rectangle
/// canvas(|ctx, bounds| {
///     ctx.fill_rect(
///         Rect::new(0.0, 0.0, bounds.width, bounds.height),
///         0.0.into(),
///         Brush::Solid(Color::RED),
///     );
/// })
/// .w(100.0)
/// .h(50.0)
///
/// // Cursor bar (inherits clip from scroll parent)
/// canvas(|ctx, bounds| {
///     ctx.fill_rect(
///         Rect::new(0.0, 0.0, 2.0, bounds.height),
///         0.0.into(),
///         Brush::Solid(Color::WHITE),
///     );
/// })
/// .w(2.0)
/// .h(16.0)
/// ```
pub fn canvas<F>(render_fn: F) -> Canvas
where
    F: Fn(&mut dyn DrawContext, CanvasBounds) + 'static,
{
    Canvas::with_render(render_fn)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_canvas_creation() {
        let c = canvas(|_ctx, _bounds| {
            // empty render
        })
        .w(100.0)
        .h(50.0);

        assert!(matches!(c.style.size.width, Dimension::Length(w) if (w - 100.0).abs() < 0.001));
        assert!(matches!(c.style.size.height, Dimension::Length(h) if (h - 50.0).abs() < 0.001));
        assert!(c.render_fn.is_some());
    }

    #[test]
    fn test_canvas_opacity() {
        let c = Canvas::new().opacity(0.5);
        assert_eq!(c.opacity, 0.5);
    }

    #[test]
    fn test_canvas_absolute_positioning() {
        let c = canvas(|_ctx, _bounds| {}).absolute().left(10.0).top(20.0);

        assert!(matches!(c.style.position, Position::Absolute));
    }
}
