use std::path::{Path, PathBuf};
use std::process::Command;
use std::sync::Arc;

use eframe::egui::{FontData, FontDefinitions, FontFamily};

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct CjkFontCandidate {
    pub path: PathBuf,
    pub index: u32,
}

pub fn install_cjk_font(ctx: &eframe::egui::Context) -> Option<CjkFontCandidate> {
    let candidate = find_cjk_font_candidate()?;
    let bytes = std::fs::read(&candidate.path).ok()?;
    let mut font_data = FontData::from_owned(bytes);
    font_data.index = candidate.index;

    let mut definitions = FontDefinitions::default();
    definitions
        .font_data
        .insert("genarrative-cjk".to_owned(), Arc::new(font_data));

    // 中文注释：作为 fallback 注入，保留 egui 默认拉丁/图标字体，同时补齐中文 glyph。
    for family in [FontFamily::Proportional, FontFamily::Monospace] {
        definitions
            .families
            .entry(family)
            .or_default()
            .push("genarrative-cjk".to_owned());
    }

    ctx.set_fonts(definitions);
    Some(candidate)
}

pub fn find_cjk_font_candidate() -> Option<CjkFontCandidate> {
    if let Ok(path) = std::env::var("GENARRATIVE_SERVER_PANEL_CJK_FONT") {
        if let Some(candidate) = parse_font_spec(&path) {
            return Some(candidate);
        }
    }

    const KNOWN_PATHS: &[(&str, u32)] = &[
        ("/usr/share/fonts/opentype/noto/NotoSansCJK-Regular.ttc", 2),
        ("/usr/share/fonts/opentype/noto/NotoSansCJK-Medium.ttc", 2),
        ("/usr/share/fonts/truetype/wqy/wqy-zenhei.ttc", 0),
        ("/usr/share/fonts/truetype/wqy/wqy-microhei.ttc", 0),
        (
            "/usr/share/fonts/truetype/droid/DroidSansFallbackFull.ttf",
            0,
        ),
        (
            "/home/dsk/.local/share/fonts/genarrative-cjk/usr/share/fonts/truetype/wqy/wqy-zenhei.ttc",
            0,
        ),
    ];

    for (path, index) in KNOWN_PATHS {
        if Path::new(path).is_file() {
            return Some(CjkFontCandidate {
                path: PathBuf::from(path),
                index: *index,
            });
        }
    }

    for family in [
        "Noto Sans CJK SC",
        "WenQuanYi Zen Hei",
        "Droid Sans Fallback",
    ] {
        if let Some(candidate) = find_with_fc_match(family) {
            return Some(candidate);
        }
    }

    None
}

fn parse_font_spec(raw: &str) -> Option<CjkFontCandidate> {
    let trimmed = raw.trim();
    if trimmed.is_empty() {
        return None;
    }
    let (path, index) = trimmed
        .rsplit_once('|')
        .and_then(|(path, index)| Some((path, index.parse().ok()?)))
        .unwrap_or((trimmed, 0));
    let path = PathBuf::from(path);
    path.is_file().then_some(CjkFontCandidate { path, index })
}

fn find_with_fc_match(family: &str) -> Option<CjkFontCandidate> {
    let output = Command::new("fc-match")
        .arg("-f")
        .arg("%{file}|%{index}\n")
        .arg(family)
        .output()
        .ok()?;
    if !output.status.success() {
        return None;
    }
    let stdout = String::from_utf8_lossy(&output.stdout);
    stdout.lines().find_map(parse_font_spec)
}

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

    #[test]
    fn parses_font_path_with_index() {
        let candidate = parse_font_spec("/tmp/missing-font.ttc|2");
        assert_eq!(candidate, None);
    }

    #[test]
    fn finds_existing_system_cjk_font() {
        let candidate = find_cjk_font_candidate();
        assert!(
            candidate
                .as_ref()
                .is_some_and(|candidate| candidate.path.is_file()),
            "expected at least one CJK font on this development host"
        );
    }
}