//! 把 DisplayList 写入 CPU 像素缓冲。裁剪栈限定矩形、文字和 3D 表面的实际写入区域。
//! RenderScope 约束递归深度；累计像素预算限制嵌套 3D 和世界 UI 的中间表面分配。错误向上传递，不把半幅结果当成成功帧呈现。
//!
use crate::{
    display_list::{Color, DisplayList, DrawCommand},
    geometry::{Point, Rect},
    text::{self, TextStyle},
};

/// 显示列表的 CPU 执行入口，错误在原生 present 前向上传递。
pub struct SoftwareRenderer;

thread_local! {
    static RENDER_DEPTH:std::cell::Cell<usize>=const { std::cell::Cell::new(0) };
    static PIXEL_UNITS:std::cell::Cell<usize>=const { std::cell::Cell::new(0) };
}
/// 递归渲染的 RAII 深度保护，最外层还重置累计像素工作预算。
pub(crate) struct RenderScope;
impl RenderScope {
    /// 进入一次嵌套渲染并检查深度上限；最外层调用重新开始累计像素预算。
    pub fn enter() -> Result<Self, &'static str> {
        RENDER_DEPTH.with(|depth| {
            let current = depth.get();
            if current >= 18 {
                return Err("render nesting budget exceeded");
            }
            if current == 0 {
                PIXEL_UNITS.with(|pixels| pixels.set(0));
            }
            depth.set(current + 1);
            Ok(Self)
        })
    }
}
impl Drop for RenderScope {
    /// 在 Rust 所有者离开作用域时执行本类型的配套清理；不能用它代替需要报告错误的显式关闭。
    fn drop(&mut self) {
        RENDER_DEPTH.with(|depth| depth.set(depth.get() - 1));
    }
}
/// 累加本帧中间表面工作量，超过预算立即返回错误。
pub(crate) fn reserve_pixels(units: usize) -> Result<(), &'static str> {
    PIXEL_UNITS.with(|pixels| {
        let next = pixels.get().saturating_add(units);
        if next > 16_777_216 {
            return Err("nested render pixel budget exceeded");
        }
        pixels.set(next);
        Ok(())
    })
}

impl SoftwareRenderer {
    /// 顺序执行显示列表并维护裁剪栈；3D 和面板可递归进入同一渲染预算域。
    pub fn render(
        list: &DisplayList,
        target: &mut [u32],
        width: u32,
        height: u32,
    ) -> Result<(), &'static str> {
        let _scope = RenderScope::enter()?;
        let mut canvas = Canvas {
            pixels: target,
            width,
            height,
            clip: Rect::new(0.0, 0.0, width as f32, height as f32),
        };
        let mut clips = Vec::new();

        for command in list.commands() {
            match command {
                DrawCommand::Scene3D { rect, view } => {
                    let left = rect.x.max(canvas.clip.x).max(0.).floor() as u32;
                    let top = rect.y.max(canvas.clip.y).max(0.).floor() as u32;
                    let right = (rect.x + rect.width)
                        .min(canvas.clip.x + canvas.clip.width)
                        .min(width as f32)
                        .ceil()
                        .max(0.) as u32;
                    let bottom = (rect.y + rect.height)
                        .min(canvas.clip.y + canvas.clip.height)
                        .min(height as f32)
                        .ceil()
                        .max(0.) as u32;
                    if left >= right || top >= bottom || rect.width <= 0. || rect.height <= 0. {
                        continue;
                    }
                    let lod = (2048. / rect.width.max(rect.height)).min(1.);
                    let w = (rect.width * lod).ceil().max(1.) as u32;
                    let h = (rect.height * lod).ceil().max(1.) as u32;
                    let surface = crate::scene3d::surface(view, w, h, rect.width / rect.height)?;
                    for y in top..bottom {
                        for x in left..right {
                            let u = (((x as f32 + 0.5 - rect.x) / rect.width) * w as f32)
                                .clamp(0., (w - 1) as f32)
                                as u32;
                            let v = (((y as f32 + 0.5 - rect.y) / rect.height) * h as f32)
                                .clamp(0., (h - 1) as f32)
                                as u32;
                            canvas.pixels[y as usize * width as usize + x as usize] =
                                surface[v as usize * w as usize + u as usize];
                        }
                    }
                }
                DrawCommand::PushClip(rect) => {
                    clips.push(canvas.clip);
                    let x = canvas.clip.x.max(rect.x);
                    let y = canvas.clip.y.max(rect.y);
                    canvas.clip = Rect::new(
                        x,
                        y,
                        (canvas.clip.x + canvas.clip.width)
                            .min(rect.x + rect.width)
                            .max(x)
                            - x,
                        (canvas.clip.y + canvas.clip.height)
                            .min(rect.y + rect.height)
                            .max(y)
                            - y,
                    );
                }
                DrawCommand::PopClip => {
                    if let Some(clip) = clips.pop() {
                        canvas.clip = clip;
                    }
                }
                DrawCommand::Clear(color) => canvas.clear(*color),
                DrawCommand::FillRoundedRect {
                    rect,
                    radius,
                    color,
                } => canvas.fill_rounded_rect(*rect, *radius, *color),
                DrawCommand::StrokeRoundedRect {
                    rect,
                    radius,
                    width,
                    color,
                } => canvas.stroke_rounded_rect(*rect, *radius, *width, *color),
                DrawCommand::WrappedText {
                    rect,
                    value,
                    style,
                    color,
                } => canvas.draw_wrapped_text(*rect, value, *style, *color),
                DrawCommand::Text {
                    origin,
                    value,
                    style,
                    color,
                } => canvas.draw_text(*origin, value, *style, *color),
            }
        }
        Ok(())
    }
}

/// 借用目标像素切片并维护当前裁剪，所有像素写入都受该上下文限制。
struct Canvas<'a> {
    pixels: &'a mut [u32],
    width: u32,
    height: u32,
    clip: Rect,
}

impl Canvas<'_> {
    /// 清空本对象维护的当前内容或缓存，后续状态由调用方重新建立。
    fn clear(&mut self, color: Color) {
        self.pixels.fill(pack(color));
    }

    /// 只遍历裁剪后的矩形像素，按圆角覆盖决定填充区域。
    fn fill_rounded_rect(&mut self, rect: Rect, radius: f32, color: Color) {
        let bounds = self.clamped_bounds(rect);
        let radius = radius.max(0.0).min(rect.width / 2.0).min(rect.height / 2.0);
        for y in bounds.1..bounds.3 {
            for x in bounds.0..bounds.2 {
                if rounded_rect_contains(rect, radius, x as f32 + 0.5, y as f32 + 0.5) {
                    self.blend_pixel(x, y, color);
                }
            }
        }
    }

    /// 用外轮廓与内轮廓的差绘制边框，避免把边框当成整个矩形填充。
    fn stroke_rounded_rect(&mut self, rect: Rect, radius: f32, width: f32, color: Color) {
        let bounds = self.clamped_bounds(rect);
        let width = width.max(1.0).min(rect.width / 2.0).min(rect.height / 2.0);
        let outer_radius = radius.max(0.0).min(rect.width / 2.0).min(rect.height / 2.0);
        let inner = Rect::new(
            rect.x + width,
            rect.y + width,
            (rect.width - width * 2.0).max(0.0),
            (rect.height - width * 2.0).max(0.0),
        );
        let inner_radius = (outer_radius - width).max(0.0);

        for y in bounds.1..bounds.3 {
            for x in bounds.0..bounds.2 {
                let px = x as f32 + 0.5;
                let py = y as f32 + 0.5;
                if rounded_rect_contains(rect, outer_radius, px, py)
                    && !rounded_rect_contains(inner, inner_radius, px, py)
                {
                    self.blend_pixel(x, y, color);
                }
            }
        }
    }

    /// 把文字原点转换为局部裁剪区域，交给有界字形绘制，再混合到目标缓冲。
    fn draw_text(&mut self, origin: Point, value: &str, style: TextStyle, color: Color) {
        let x = origin.x.round() as i32;
        let y = origin.y.round() as i32;
        let clip = Rect::new(
            self.clip.x - x as f32,
            self.clip.y - y as f32,
            self.clip.width,
            self.clip.height,
        );
        text::draw_clipped(value, style, color, None, clip, |dx, dy, pixel| {
            self.blend_pixel(x + dx, y + dy, pixel)
        });
    }

    /// 把段落矩形与当前裁剪相交，按受限宽度绘制，再恢复外层裁剪。
    fn draw_wrapped_text(&mut self, rect: Rect, value: &str, style: TextStyle, color: Color) {
        if rect.width <= 0.0 || rect.height <= 0.0 {
            return;
        }
        let old = self.clip;
        let x = old.x.max(rect.x);
        let y = old.y.max(rect.y);
        self.clip = Rect::new(
            x,
            y,
            ((old.x + old.width).min(rect.x + rect.width) - x).max(0.0),
            ((old.y + old.height).min(rect.y + rect.height) - y).max(0.0),
        );
        let left = rect.x.round() as i32;
        let top = rect.y.round() as i32;
        let clip = Rect::new(
            self.clip.x - left as f32,
            self.clip.y - top as f32,
            self.clip.width,
            self.clip.height,
        );
        text::draw_clipped(
            value,
            style,
            color,
            Some(rect.width),
            clip,
            |dx, dy, pixel| self.blend_pixel(left + dx, top + dy, pixel),
        );
        self.clip = old;
    }

    /// 把连续矩形转换成目标缓冲内的整数像素范围，避免在不可见区域进行光栅循环。
    fn clamped_bounds(&self, rect: Rect) -> (i32, i32, i32, i32) {
        (
            rect.x.max(self.clip.x).max(0.0).floor() as i32,
            rect.y.max(self.clip.y).max(0.0).floor() as i32,
            (rect.x + rect.width)
                .min(self.clip.x + self.clip.width)
                .min(self.width as f32)
                .ceil() as i32,
            (rect.y + rect.height)
                .min(self.clip.y + self.clip.height)
                .min(self.height as f32)
                .ceil() as i32,
        )
    }

    /// 在画布与当前裁剪范围内进行透明度混合，防止文字/图形写出目标缓冲。
    fn blend_pixel(&mut self, x: i32, y: i32, source: Color) {
        if x < 0
            || y < 0
            || x >= self.width as i32
            || y >= self.height as i32
            || source.alpha == 0
            || (x as f32) < self.clip.x
            || (y as f32) < self.clip.y
            || (x as f32) >= self.clip.x + self.clip.width
            || (y as f32) >= self.clip.y + self.clip.height
        {
            return;
        }

        let index = y as usize * self.width as usize + x as usize;
        if source.alpha == 255 {
            self.pixels[index] = pack(source);
            return;
        }

        let destination = self.pixels[index];
        let dst_red = (destination >> 16) & 0xff;
        let dst_green = (destination >> 8) & 0xff;
        let dst_blue = destination & 0xff;
        let alpha = source.alpha as u32;
        let inverse = 255 - alpha;
        let red = (source.red as u32 * alpha + dst_red * inverse) / 255;
        let green = (source.green as u32 * alpha + dst_green * inverse) / 255;
        let blue = (source.blue as u32 * alpha + dst_blue * inverse) / 255;
        self.pixels[index] = (red << 16) | (green << 8) | blue;
    }
}

/// 测试一个像素采样点是否位于圆角矩形内，角区域使用圆弧距离。
fn rounded_rect_contains(rect: Rect, radius: f32, x: f32, y: f32) -> bool {
    if rect.width <= 0.0 || rect.height <= 0.0 {
        return false;
    }
    if radius <= 0.0 {
        return x >= rect.x && x <= rect.x + rect.width && y >= rect.y && y <= rect.y + rect.height;
    }

    // Clamp in local coordinates: adding a large origin to a shrinking tab's
    // half-width can otherwise round the lower bound above the upper bound.
    let radius = radius.min(rect.width / 2.0).min(rect.height / 2.0);
    let local_x = x - rect.x;
    let local_y = y - rect.y;
    let dx = local_x - local_x.clamp(radius, rect.width - radius);
    let dy = local_y - local_y.clamp(radius, rect.height - radius);
    dx * dx + dy * dy <= radius * radius
}

/// 将颜色通道打包成目标缓冲的整数像素表示。
fn pack(color: Color) -> u32 {
    (color.red as u32) << 16 | (color.green as u32) << 8 | color.blue as u32
}

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

    #[test]
    fn wrapped_text_uses_multiple_lines_respects_nested_clips_and_restores_the_clip() {
        let mut list = DisplayList::default();
        list.push(DrawCommand::Clear(Color::rgb(255, 255, 255)));
        list.push(DrawCommand::PushClip(Rect::new(12.0, 5.0, 20.0, 40.0)));
        list.push(DrawCommand::WrappedText {
            rect: Rect::new(10.0, 5.0, 32.0, 40.0),
            value: "MMMMMMMMMMMMMMMM".into(),
            style: TextStyle::ui(1),
            color: Color::rgb(0, 0, 0),
        });
        list.push(DrawCommand::PopClip);
        list.push(DrawCommand::WrappedText {
            rect: Rect::new(60.0, 0.0, 0.0, 40.0),
            value: "invisible".into(),
            style: TextStyle::ui(1),
            color: Color::rgb(0, 0, 0),
        });
        list.push(DrawCommand::FillRoundedRect {
            rect: Rect::new(70.0, 50.0, 2.0, 2.0),
            radius: 0.0,
            color: Color::rgb(0, 0, 255),
        });
        let mut pixels = vec![0; 80 * 60];
        SoftwareRenderer::render(&list, &mut pixels, 80, 60).unwrap();
        let mut second_line = false;
        for y in 0..60 {
            for x in 0..80 {
                let color = pixels[y * 80 + x];
                if color != 0xffffff && color != 0x0000ff {
                    assert!((12..32).contains(&x) && (5..45).contains(&y));
                    second_line |= y >= 25;
                }
            }
        }
        assert!(second_line);
        assert_eq!(pixels[50 * 80 + 70], 0x0000ff);
    }

    #[test]
    fn renderer_changes_pixels_inside_a_rectangle() {
        let mut list = DisplayList::default();
        list.push(DrawCommand::Clear(Color::rgb(0, 0, 0)));
        list.push(DrawCommand::FillRoundedRect {
            rect: Rect::new(1.0, 1.0, 2.0, 2.0),
            radius: 0.0,
            color: Color::rgb(255, 0, 0),
        });
        let mut pixels = vec![0; 16];
        SoftwareRenderer::render(&list, &mut pixels, 4, 4).unwrap();
        assert_eq!(pixels[5], 0x00ff0000);
        assert_eq!(pixels[0], 0);
    }

    #[test]
    fn text_edges_are_antialiased_and_respect_opacity() {
        let mut list = DisplayList::default();
        list.push(DrawCommand::Clear(Color::rgb(0, 0, 0)));
        list.push(DrawCommand::Text {
            origin: Point::new(2.0, 2.0),
            value: "Hello 中文".into(),
            style: TextStyle::ui(1).scaled(1.25),
            color: Color::rgba(255, 255, 255, 128),
        });
        let mut pixels = vec![0; 256 * 48];
        SoftwareRenderer::render(&list, &mut pixels, 256, 48).unwrap();
        assert!(pixels.iter().any(|pixel| *pixel > 0));
        assert!(pixels.iter().all(|pixel| (pixel & 255) <= 128));
        assert!(pixels.iter().any(|pixel| (1..128).contains(&(pixel & 255))));

        let mut invisible = DisplayList::default();
        invisible.push(DrawCommand::Text {
            origin: Point::new(2.0, 2.0),
            value: "Hello 中文".into(),
            style: TextStyle::ui(1),
            color: Color::rgba(255, 255, 255, 0),
        });
        let mut pixels = vec![0; 256 * 48];
        SoftwareRenderer::render(&invisible, &mut pixels, 256, 48).unwrap();
        assert!(pixels.iter().all(|pixel| *pixel == 0));
    }
}