md-viewer 0.2.0

use std::collections::HashSet;

use egui::{FontData, FontDefinitions, FontFamily};
use egui_commonmark_extended::STRONG_FONT_FAMILY;
use fontique::{
    Blob, Collection, CollectionOptions, FamilyId, FontStyle, FontWeight, GenericFamily, Script,
    SourceCache, SourceKind,
};

struct ScriptFallback {
    key: &'static str,
    script: [u8; 4],
    required_glyphs: &'static str,
}

// ISO 15924 identifiers and coverage samples describe scripts, not font
// families. The platform backend remains the sole source of family choices.
const SCRIPT_FALLBACKS: &[ScriptFallback] = &[
    ScriptFallback {
        key: "SystemHanFallback",
        script: *b"Hani",
        required_glyphs: "中文测试繁體",
    },
    ScriptFallback {
        key: "SystemHiraganaFallback",
        script: *b"Hira",
        required_glyphs: "かな",
    },
    ScriptFallback {
        key: "SystemKatakanaFallback",
        script: *b"Kana",
        required_glyphs: "カナ",
    },
    ScriptFallback {
        key: "SystemHangulFallback",
        script: *b"Hang",
        required_glyphs: "한글",
    },
    ScriptFallback {
        key: "SystemArabicFallback",
        script: *b"Arab",
        required_glyphs: "اب",
    },
    ScriptFallback {
        key: "SystemHebrewFallback",
        script: *b"Hebr",
        required_glyphs: "אב",
    },
    ScriptFallback {
        key: "SystemDevanagariFallback",
        script: *b"Deva",
        required_glyphs: "नमस्तेहिन्दी",
    },
    ScriptFallback {
        key: "SystemThaiFallback",
        script: *b"Thai",
        required_glyphs: "สวัสดีภาษาไทย",
    },
];

const GENERIC_FALLBACKS: &[(GenericFamily, &str, &str)] = &[
    (GenericFamily::Math, "SystemMathFallback", "→"),
    (GenericFamily::SansSerif, "SystemSymbolFallback", "⚠"),
];

#[derive(Clone)]
struct SelectedFont {
    blob: Blob<u8>,
    index: u32,
    family_id: FamilyId,
    family: String,
    source: String,
    weight: FontWeight,
}

impl SelectedFont {
    fn identity(&self) -> (u64, u32) {
        (self.blob.id(), self.index)
    }

    fn data(&self) -> FontData {
        let mut data = FontData::from_owned(self.blob.data().to_vec());
        data.index = self.index;
        data
    }
}

struct InstalledFont {
    key: String,
    selected: SelectedFont,
    required_glyphs: &'static str,
    primary: bool,
}

fn font_has_glyphs(blob: &Blob<u8>, index: u32, required_glyphs: &str) -> bool {
    ttf_parser::Face::parse(blob.data(), index)
        .map(|face| {
            required_glyphs
                .chars()
                .all(|c| face.glyph_index(c).is_some())
        })
        .unwrap_or(false)
}

fn source_description(source: &SourceKind) -> String {
    match source {
        SourceKind::Memory(_) => "<memory>".to_owned(),
        SourceKind::Path(path) => path.display().to_string(),
    }
}

fn select_from_families(
    collection: &mut Collection,
    source_cache: &mut SourceCache,
    family_ids: &[FamilyId],
    weight: FontWeight,
    required_glyphs: &str,
    require_true_bold: bool,
) -> Option<SelectedFont> {
    for family_id in family_ids {
        let Some(family) = collection.family(*family_id) else {
            continue;
        };
        let mut candidates: Vec<_> = family
            .fonts()
            .iter()
            .filter(|font| {
                font.style() == FontStyle::Normal
                    && (!require_true_bold || font.weight() >= FontWeight::BOLD)
            })
            .collect();
        candidates.sort_by(|left, right| {
            let left_distance = (left.weight().value() - weight.value()).abs();
            let right_distance = (right.weight().value() - weight.value()).abs();
            left_distance.total_cmp(&right_distance)
        });

        for font in candidates {
            let Some(blob) = font.load(Some(source_cache)) else {
                continue;
            };
            if !font_has_glyphs(&blob, font.index(), required_glyphs) {
                continue;
            }
            return Some(SelectedFont {
                blob,
                index: font.index(),
                family_id: *family_id,
                family: family.name().to_owned(),
                source: source_description(font.source().kind()),
                weight: font.weight(),
            });
        }
    }
    None
}

fn fallback_family_ids(
    collection: &mut Collection,
    script: [u8; 4],
    locale: Option<&str>,
) -> Vec<FamilyId> {
    let script = Script::from_bytes(script);
    match locale {
        Some(locale) => collection.fallback_families((script, locale)).collect(),
        None => collection.fallback_families(script).collect(),
    }
}

fn installed_fonts_cover(installed: &[InstalledFont], glyphs: &str) -> bool {
    installed
        .iter()
        .any(|font| font_has_glyphs(&font.selected.blob, font.selected.index, glyphs))
}

fn install_regular_font(
    definitions: &mut FontDefinitions,
    installed: &mut Vec<InstalledFont>,
    loaded_faces: &mut HashSet<(u64, u32)>,
    key: &'static str,
    selected: SelectedFont,
    required_glyphs: &'static str,
    primary: bool,
) {
    if !loaded_faces.insert(selected.identity()) {
        return;
    }
    log::info!(
        "Loaded system font {} ({}, weight {}) from {} (face index {})",
        key,
        selected.family,
        selected.weight.value(),
        selected.source,
        selected.index
    );
    definitions
        .font_data
        .insert(key.to_owned(), selected.data().into());
    if let Some(family) = definitions.families.get_mut(&FontFamily::Proportional) {
        if primary {
            family.insert(0, key.to_owned())
        } else {
            family.push(key.to_owned())
        }
    }
    if let Some(family) = definitions.families.get_mut(&FontFamily::Monospace) {
        family.push(key.to_owned());
    }
    installed.push(InstalledFont {
        key: key.to_owned(),
        selected,
        required_glyphs,
        primary,
    });
}

fn install_regular_fonts(
    collection: &mut Collection,
    source_cache: &mut SourceCache,
    definitions: &mut FontDefinitions,
    locale: Option<&str>,
) -> Vec<InstalledFont> {
    let mut installed = Vec::new();
    let mut loaded_faces = HashSet::new();

    let families: Vec<_> = collection
        .generic_families(GenericFamily::SansSerif)
        .collect();
    if let Some(selected) = select_from_families(
        collection,
        source_cache,
        &families,
        FontWeight::NORMAL,
        "Aa",
        false,
    ) {
        install_regular_font(
            definitions,
            &mut installed,
            &mut loaded_faces,
            "SystemSans",
            selected,
            "Aa",
            true,
        );
    }

    for spec in SCRIPT_FALLBACKS {
        if installed_fonts_cover(&installed, spec.required_glyphs) {
            continue;
        }
        let families = fallback_family_ids(collection, spec.script, locale);
        let Some(selected) = select_from_families(
            collection,
            source_cache,
            &families,
            FontWeight::NORMAL,
            spec.required_glyphs,
            false,
        ) else {
            continue;
        };
        install_regular_font(
            definitions,
            &mut installed,
            &mut loaded_faces,
            spec.key,
            selected,
            spec.required_glyphs,
            false,
        );
    }

    for &(generic, key, glyphs) in GENERIC_FALLBACKS {
        if installed_fonts_cover(&installed, glyphs) {
            continue;
        }
        let families: Vec<_> = collection.generic_families(generic).collect();
        let Some(selected) = select_from_families(
            collection,
            source_cache,
            &families,
            FontWeight::NORMAL,
            glyphs,
            false,
        ) else {
            continue;
        };
        install_regular_font(
            definitions,
            &mut installed,
            &mut loaded_faces,
            key,
            selected,
            glyphs,
            false,
        );
    }
    installed
}

fn push_unique(
    destination: &mut Vec<String>,
    seen: &mut HashSet<String>,
    names: impl IntoIterator<Item = String>,
) {
    for name in names {
        if seen.insert(name.clone()) {
            destination.push(name)
        }
    }
}

fn build_strong_family(
    primary_regular: Option<&str>,
    primary_bold: Option<&str>,
    default_proportional: &[String],
    fallback_bold: &[String],
    proportional: &[String],
) -> Vec<String> {
    let mut family = Vec::new();
    let mut seen = HashSet::new();
    push_unique(
        &mut family,
        &mut seen,
        primary_bold.into_iter().map(str::to_owned),
    );
    push_unique(
        &mut family,
        &mut seen,
        primary_regular.into_iter().map(str::to_owned),
    );
    push_unique(&mut family, &mut seen, default_proportional.iter().cloned());
    push_unique(&mut family, &mut seen, fallback_bold.iter().cloned());
    push_unique(&mut family, &mut seen, proportional.iter().cloned());
    family
}

fn install_strong_font_family(
    collection: &mut Collection,
    source_cache: &mut SourceCache,
    definitions: &mut FontDefinitions,
    installed: &[InstalledFont],
    default_proportional: &[String],
) -> usize {
    let mut loaded_faces: HashSet<_> = installed
        .iter()
        .map(|font| font.selected.identity())
        .collect();
    let mut primary_regular = None;
    let mut primary_bold = None;
    let mut fallback_bold = Vec::new();
    let mut count = 0;

    for regular in installed {
        if regular.primary {
            primary_regular = Some(regular.key.clone())
        }
        let Some(selected) = select_from_families(
            collection,
            source_cache,
            &[regular.selected.family_id],
            FontWeight::BOLD,
            regular.required_glyphs,
            true,
        ) else {
            continue;
        };
        if !loaded_faces.insert(selected.identity()) {
            continue;
        }
        let key = format!("{}Bold", regular.key);
        log::info!(
            "Loaded strong font {} ({}, weight {}) from {} (face index {})",
            key,
            selected.family,
            selected.weight.value(),
            selected.source,
            selected.index
        );
        definitions
            .font_data
            .insert(key.clone(), selected.data().into());
        count += 1;
        if regular.primary {
            primary_bold = Some(key)
        } else {
            fallback_bold.push(key)
        }
    }

    let proportional = definitions
        .families
        .get(&FontFamily::Proportional)
        .cloned()
        .unwrap_or_default();
    let strong = build_strong_family(
        primary_regular.as_deref(),
        primary_bold.as_deref(),
        default_proportional,
        &fallback_bold,
        &proportional,
    );
    if primary_regular.is_some() && primary_bold.is_none() {
        log::warn!("No true bold face found for the primary system sans; using regular fallback.");
    }
    definitions
        .families
        .insert(FontFamily::Name(STRONG_FONT_FAMILY.into()), strong);
    count
}

/// Load fonts through platform generic-family and script/locale fallback rules.
///
/// Fontique delegates to fontconfig on Linux/FreeBSD, DirectWrite on Windows,
/// CoreText on Apple platforms, and the system configuration on Android.
pub(crate) fn setup_fonts(ctx: &egui::Context) {
    let started = std::time::Instant::now();
    let mut collection = Collection::new(CollectionOptions::default());
    let family_count = collection.family_names().count();
    let mut source_cache = SourceCache::default();
    let locale = sys_locale::get_locale();
    let mut definitions = FontDefinitions::default();
    let defaults = definitions
        .families
        .get(&FontFamily::Proportional)
        .cloned()
        .unwrap_or_default();
    let installed = install_regular_fonts(
        &mut collection,
        &mut source_cache,
        &mut definitions,
        locale.as_deref(),
    );
    let bold_count = install_strong_font_family(
        &mut collection,
        &mut source_cache,
        &mut definitions,
        &installed,
        &defaults,
    );
    if installed.is_empty() {
        log::warn!("No suitable system font fallbacks found; using egui defaults.");
    } else {
        log::info!(
            "Selected {} font faces from {} families for locale {:?} in {:.1} ms",
            installed.len() + bold_count,
            family_count,
            locale,
            started.elapsed().as_secs_f64() * 1000.0
        );
    }
    ctx.set_fonts(definitions);
}

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

    #[test]
    fn reported_scripts_use_full_coverage_samples() {
        let sample = |script| {
            SCRIPT_FALLBACKS
                .iter()
                .find(|fallback| fallback.script == script)
                .unwrap()
                .required_glyphs
        };
        assert_eq!(sample(*b"Deva"), "नमस्तेहिन्दी");
        assert_eq!(sample(*b"Thai"), "สวัสดีภาษาไทย");
        assert!(sample(*b"Hani").contains('测'));
        assert!(sample(*b"Hani").contains('體'));
    }

    #[test]
    fn default_latin_precedes_script_bold_without_primary_system_sans() {
        let strong = build_strong_family(
            None,
            None,
            &["DefaultLatin".into()],
            &["HanBold".into()],
            &["DefaultLatin".into(), "Han".into()],
        );
        assert_eq!(strong, ["DefaultLatin", "HanBold", "Han"]);
    }

    #[test]
    fn primary_regular_and_bold_stay_together() {
        let strong = build_strong_family(
            Some("SystemSans"),
            Some("SystemSansBold"),
            &["DefaultLatin".into()],
            &["HanBold".into()],
            &["SystemSans".into(), "Han".into()],
        );
        assert_eq!(
            strong,
            [
                "SystemSansBold",
                "SystemSans",
                "DefaultLatin",
                "HanBold",
                "Han"
            ]
        );
    }

    #[test]
    #[ignore = "requires installed multilingual regular and bold fonts"]
    fn installed_fonts_cover_reported_scripts() {
        let context = egui::Context::default();
        setup_fonts(&context);
        context.begin_pass(Default::default());
        let regular = egui::FontId::proportional(16.0);
        let strong = egui::FontId::new(16.0, FontFamily::Name(STRONG_FONT_FAMILY.into()));
        let samples = [
            "中文测试繁體",
            "かなカナ",
            "한글",
            "नमस्तेहिन्दी",
            "สวัสดีภาษาไทย",
        ];
        let missing_regular: Vec<_> = samples
            .iter()
            .filter(|sample| !context.fonts_mut(|fonts| fonts.has_glyphs(&regular, sample)))
            .collect();
        let missing_strong: Vec<_> = samples
            .iter()
            .filter(|sample| !context.fonts_mut(|fonts| fonts.has_glyphs(&strong, sample)))
            .collect();
        let _ = context.end_pass();
        assert!(
            missing_regular.is_empty(),
            "regular chain lacks {missing_regular:?}"
        );
        assert!(
            missing_strong.is_empty(),
            "strong chain lacks {missing_strong:?}"
        );
    }
}