//! Title renderer using ab_glyph.
//!
//! Requires no dynamically linked dependencies.
//!
//! Can fallback to a embedded Cantarell-Regular.ttf font (SIL Open Font Licence v1.1)
//! if the system font doesn't work.
use crate::title::{config, font_preference::FontPreference};
use ab_glyph::{point, Font, FontRef, Glyph, PxScale, PxScaleFont, ScaleFont, VariableFont};
use std::{fs::File, process::Command};
use tiny_skia::{Color, Pixmap, PremultipliedColorU8};

const CANTARELL: &[u8] = include_bytes!("Cantarell-Regular.ttf");

#[derive(Debug)]
pub struct AbGlyphTitleText {
    title: String,
    font: Option<(memmap2::Mmap, FontPreference)>,
    original_px_size: f32,
    size: PxScale,
    color: Color,
    pixmap: Option<Pixmap>,
}

impl AbGlyphTitleText {
    pub fn new(color: Color) -> Self {
        let font_pref = config::titlebar_font().unwrap_or_default();
        let font_pref_pt_size = font_pref.pt_size;
        let font = font_file_matching(&font_pref)
            .and_then(|f| mmap(&f))
            .map(|mmap| (mmap, font_pref));

        let size = parse_font(&font)
            .pt_to_px_scale(font_pref_pt_size)
            .expect("invalid font units_per_em");

        Self {
            title: <_>::default(),
            font,
            original_px_size: size.x,
            size,
            color,
            pixmap: None,
        }
    }

    pub fn update_scale(&mut self, scale: u32) {
        let new_scale = PxScale::from(self.original_px_size * scale as f32);
        if (self.size.x - new_scale.x).abs() > f32::EPSILON {
            self.size = new_scale;
            self.pixmap = self.render();
        }
    }

    pub fn update_title(&mut self, title: impl Into<String>) {
        let new_title = title.into();
        if new_title != self.title {
            self.title = new_title;
            self.pixmap = self.render();
        }
    }

    pub fn update_color(&mut self, color: Color) {
        if color != self.color {
            self.color = color;
            self.pixmap = self.render();
        }
    }

    pub fn pixmap(&self) -> Option<&Pixmap> {
        self.pixmap.as_ref()
    }

    /// Render returning the new `Pixmap`.
    fn render(&self) -> Option<Pixmap> {
        let font = parse_font(&self.font);
        let font = font.as_scaled(self.size);

        let glyphs = self.layout(&font);
        let last_glyph = glyphs.last()?;
        let width = (last_glyph.position.x + font.h_advance(last_glyph.id)).ceil() as u32;
        let height = font.height().ceil() as u32;

        let mut pixmap = Pixmap::new(width, height)?;

        let pixels = pixmap.pixels_mut();

        for glyph in glyphs {
            if let Some(outline) = font.outline_glyph(glyph) {
                let bounds = outline.px_bounds();
                let left = bounds.min.x as u32;
                let top = bounds.min.y as u32;
                outline.draw(|x, y, c| {
                    let p_idx = (top + y) * width + (left + x);
                    let old_alpha_u8 = pixels[p_idx as usize].alpha();
                    let new_alpha = c + (old_alpha_u8 as f32 / 255.0);
                    if let Some(px) = PremultipliedColorU8::from_rgba(
                        (self.color.red() * new_alpha * 255.0) as _,
                        (self.color.green() * new_alpha * 255.0) as _,
                        (self.color.blue() * new_alpha * 255.0) as _,
                        (new_alpha * 255.0) as _,
                    ) {
                        pixels[p_idx as usize] = px;
                    }
                })
            }
        }

        Some(pixmap)
    }

    /// Simple single-line glyph layout.
    fn layout(&self, font: &PxScaleFont<impl Font>) -> Vec<Glyph> {
        let mut caret = point(0.0, font.ascent());
        let mut last_glyph: Option<Glyph> = None;
        let mut target = Vec::new();
        for c in self.title.chars() {
            if c.is_control() {
                continue;
            }
            let mut glyph = font.scaled_glyph(c);
            if let Some(previous) = last_glyph.take() {
                caret.x += font.kern(previous.id, glyph.id);
            }
            glyph.position = caret;

            last_glyph = Some(glyph.clone());
            caret.x += font.h_advance(glyph.id);

            target.push(glyph);
        }
        target
    }
}

/// Parse the memmapped system font or fallback to built-in cantarell.
fn parse_font(sys_font: &Option<(memmap2::Mmap, FontPreference)>) -> FontRef<'_> {
    match sys_font {
        Some((mmap, font_pref)) => {
            FontRef::try_from_slice(mmap)
                .map(|mut f| {
                    // basic "bold" handling for variable fonts
                    if font_pref
                        .style
                        .as_deref()
                        .map_or(false, |s| s.eq_ignore_ascii_case("bold"))
                    {
                        f.set_variation(b"wght", 700.0);
                    }
                    f
                })
                .unwrap_or_else(|_| FontRef::try_from_slice(CANTARELL).unwrap())
        }
        _ => FontRef::try_from_slice(CANTARELL).unwrap(),
    }
}

/// Font-config without dynamically linked dependencies
fn font_file_matching(pref: &FontPreference) -> Option<File> {
    let mut pattern = pref.name.clone();
    if let Some(style) = &pref.style {
        pattern.push(':');
        pattern.push_str(style);
    }
    Command::new("fc-match")
        .arg("-f")
        .arg("%{file}")
        .arg(&pattern)
        .output()
        .ok()
        .and_then(|out| String::from_utf8(out.stdout).ok())
        .and_then(|path| File::open(path.trim()).ok())
}

fn mmap(file: &File) -> Option<memmap2::Mmap> {
    // Safety: System font files are not expected to be mutated during use
    unsafe { memmap2::Mmap::map(file).ok() }
}