//! DWG preview thumbnails.
//!
//! - [`from_scene`] / [`from_wires`] rasterize the current layout's wires into a
//!   small DIB [`acadrust::Preview`], embedded on save so OCS drawings show a
//!   thumbnail in file browsers and other CAD apps.
//! - [`read_handle`] / [`extract_to_png`] read a DWG's *embedded* preview back
//!   for the Start page and the OS file-manager thumbnailer. Extraction lives in
//!   the shared [`dwg_thumbnailer`] core crate (also used by the Windows/macOS
//!   thumbnail handlers).

use acadrust::{Preview, PreviewFormat};
use image::{ImageFormat, Rgb, RgbImage};
use std::io::Cursor;

use crate::scene::{Scene, WireModel};

/// Longest edge of the generated thumbnail, in pixels.
const MAX_DIM: u32 = 256;
/// Blank border kept around the drawing, in pixels.
const MARGIN: f64 = 6.0;

/// Build a preview from the scene's current-layout wires. `None` when there is
/// nothing finite to draw (empty or degenerate drawing).
pub fn from_scene(scene: &Scene) -> Option<Preview> {
    from_wires(&scene.entity_wires(), scene.bg_color)
}

/// Rasterize `wires` (world XY) onto a `bg`-filled canvas and encode a DIB.
pub fn from_wires(wires: &[WireModel], bg: [f32; 4]) -> Option<Preview> {
    // ── World-XY bounds over every finite vertex ─────────────────────────────
    let (mut min_x, mut min_y) = (f64::INFINITY, f64::INFINITY);
    let (mut max_x, mut max_y) = (f64::NEG_INFINITY, f64::NEG_INFINITY);
    for w in wires {
        for (i, p) in w.points.iter().enumerate() {
            if !p[0].is_finite() || !p[1].is_finite() {
                continue;
            }
            let (x, y) = abs_xy(w, i, p);
            min_x = min_x.min(x);
            min_y = min_y.min(y);
            max_x = max_x.max(x);
            max_y = max_y.max(y);
        }
    }
    let (dw, dh) = (max_x - min_x, max_y - min_y);
    if !dw.is_finite() || !dh.is_finite() || (dw <= 0.0 && dh <= 0.0) {
        return None;
    }

    // ── Canvas sized to the drawing's aspect, longest edge = MAX_DIM ─────────
    let aspect = if dh > 0.0 { dw / dh } else { f64::INFINITY };
    let (cw, ch) = if aspect >= 1.0 {
        (MAX_DIM, ((MAX_DIM as f64 / aspect).round() as u32).clamp(16, MAX_DIM))
    } else {
        (((MAX_DIM as f64 * aspect).round() as u32).clamp(16, MAX_DIM), MAX_DIM)
    };

    // World → pixel: uniform scale to fit inside the margin, drawing centered,
    // Y flipped (world up → image row 0 at top).
    let sx = (cw as f64 - 2.0 * MARGIN) / dw.max(1e-9);
    let sy = (ch as f64 - 2.0 * MARGIN) / dh.max(1e-9);
    let scale = sx.min(sy);
    let off_x = (cw as f64 - dw * scale) * 0.5;
    let off_y = (ch as f64 - dh * scale) * 0.5;
    let to_px = |x: f64, y: f64| -> (i32, i32) {
        let px = off_x + (x - min_x) * scale;
        let py = ch as f64 - (off_y + (y - min_y) * scale); // flip Y
        (px.round() as i32, py.round() as i32)
    };

    // ── Rasterize ────────────────────────────────────────────────────────────
    let bg_rgb = to_rgb(bg);
    let mut img = RgbImage::from_pixel(cw, ch, Rgb(bg_rgb));
    for w in wires {
        let col = Rgb(to_rgb(w.color));
        let mut prev: Option<(i32, i32)> = None;
        for (i, p) in w.points.iter().enumerate() {
            if !p[0].is_finite() || !p[1].is_finite() {
                prev = None; // NaN separator breaks the run
                continue;
            }
            let (x, y) = abs_xy(w, i, p);
            let cur = to_px(x, y);
            if let Some(p0) = prev {
                draw_line(&mut img, p0, cur, col);
            }
            prev = Some(cur);
        }
    }

    // ── Encode BMP, strip the 14-byte BITMAPFILEHEADER → DIB ─────────────────
    let mut buf = Cursor::new(Vec::new());
    img.write_to(&mut buf, ImageFormat::Bmp).ok()?;
    let bmp = buf.into_inner();
    if bmp.len() <= 14 {
        return None;
    }
    Some(Preview { format: PreviewFormat::Bmp, data: bmp[14..].to_vec() })
}

/// Absolute world XY of vertex `i`, reconstructing the double-single residual.
#[inline]
fn abs_xy(w: &WireModel, i: usize, p: &[f32; 3]) -> (f64, f64) {
    let (lx, ly) = w
        .points_low
        .get(i)
        .map_or((0.0, 0.0), |l| (l[0] as f64, l[1] as f64));
    (p[0] as f64 + lx, p[1] as f64 + ly)
}

#[inline]
fn to_rgb(c: [f32; 4]) -> [u8; 3] {
    [
        (c[0].clamp(0.0, 1.0) * 255.0).round() as u8,
        (c[1].clamp(0.0, 1.0) * 255.0).round() as u8,
        (c[2].clamp(0.0, 1.0) * 255.0).round() as u8,
    ]
}

/// Read a DWG's embedded preview and write it as a PNG at `output`, scaled so
/// its longest edge is at most `size`. Returns `false` on any failure (no
/// preview, undecodable, write error) so the OS thumbnailer falls back to a
/// generic icon. Backs the hidden `--dwg-thumbnail` mode the installed
/// freedesktop `.thumbnailer` invokes. Extraction lives in the shared
/// [`dwg_thumbnailer`] core (also used by the Windows/macOS handlers).
pub fn extract_to_png(input: &std::path::Path, output: &std::path::Path, size: u32) -> bool {
    match dwg_thumbnailer::extract(input, size) {
        Some(mut img) => {
            // Bottom-left "DWG" ribbon so the format reads at a glance in the
            // file manager (the Start-page `read_handle` stays unbadged).
            dwg_thumbnailer::badge_dwg(&mut img);
            img.save_with_format(output, ImageFormat::Png).is_ok()
        }
        None => false,
    }
}

/// Read a DWG's embedded preview and decode it to an iced image handle for the
/// Start page's recent-file thumbnails. `None` for DXF/other files, a missing
/// preview, or an undecodable format (WMF).
pub fn read_handle(path: &std::path::Path) -> Option<iced::widget::image::Handle> {
    let img = dwg_thumbnailer::extract(path, MAX_DIM)?;
    let (w, h) = (img.width(), img.height());
    Some(iced::widget::image::Handle::from_rgba(w, h, img.into_raw()))
}

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

    fn wire(pts: &[[f32; 2]], color: [f32; 4]) -> WireModel {
        WireModel {
            points: pts.iter().map(|&[x, y]| [x, y, 0.0]).collect(),
            color,
            ..Default::default()
        }
    }

    /// Prepend a `BITMAPFILEHEADER` to a 24-bit DIB so `image` can decode it.
    fn dib_to_bmp(dib: &[u8]) -> Vec<u8> {
        let mut v = Vec::with_capacity(14 + dib.len());
        v.extend_from_slice(b"BM");
        v.extend_from_slice(&((14 + dib.len()) as u32).to_le_bytes());
        v.extend_from_slice(&0u32.to_le_bytes());
        v.extend_from_slice(&54u32.to_le_bytes()); // 14 + 40, no palette (24-bit)
        v.extend_from_slice(dib);
        v
    }

    #[test]
    fn empty_input_yields_none() {
        assert!(from_wires(&[], [0.0, 0.0, 0.0, 1.0]).is_none());
    }

    #[test]
    fn draws_a_valid_non_blank_dib() {
        let bg = [0.1, 0.1, 0.1, 1.0];
        // A closed square (connected polyline) in a distinct colour.
        let sq = wire(&[[0.0, 0.0], [10.0, 0.0], [10.0, 10.0], [0.0, 10.0], [0.0, 0.0]],
            [1.0, 0.0, 0.0, 1.0]);
        let p = from_wires(&[sq], bg).expect("some preview");
        assert_eq!(p.format, PreviewFormat::Bmp);
        // DIB starts with a 40-byte BITMAPINFOHEADER.
        assert_eq!(&p.data[0..4], &40u32.to_le_bytes());
        // Decodes to a square canvas (drawing aspect 1:1 → MAX_DIM²).
        let img = image::load_from_memory(&dib_to_bmp(&p.data)).expect("decodes").to_rgb8();
        assert_eq!((img.width(), img.height()), (MAX_DIM, MAX_DIM));
        // At least one red pixel was drawn (not a blank fill).
        let bg_px = to_rgb(bg);
        assert!(img.pixels().any(|px| px.0 != bg_px), "nothing drawn");
        assert!(img.pixels().any(|px| px.0[0] > 128 && px.0[1] < 64), "square not red");
    }
}

/// Bresenham line, clipped to the image bounds.
fn draw_line(img: &mut RgbImage, (x0, y0): (i32, i32), (x1, y1): (i32, i32), col: Rgb<u8>) {
    let (w, h) = (img.width() as i32, img.height() as i32);
    let (mut x0, mut y0) = (x0, y0);
    let dx = (x1 - x0).abs();
    let dy = -(y1 - y0).abs();
    let sx = if x0 < x1 { 1 } else { -1 };
    let sy = if y0 < y1 { 1 } else { -1 };
    let mut err = dx + dy;
    loop {
        if x0 >= 0 && x0 < w && y0 >= 0 && y0 < h {
            img.put_pixel(x0 as u32, y0 as u32, col);
        }
        if x0 == x1 && y0 == y1 {
            break;
        }
        let e2 = 2 * err;
        if e2 >= dy {
            err += dy;
            x0 += sx;
        }
        if e2 <= dx {
            err += dx;
            y0 += sy;
        }
    }
}