use freedesktop_icons::lookup;
use std::path::PathBuf;
use std::{env, fs};

const ICON_SIZE: u16 = 32;

/// Resolve the best icon path for a notification, preferring the app's own
/// identity (desktop entry, then app name) over `app_icon`, which is often
/// just a hint for the specific notification's content (e.g. blueman sends
/// "battery" for a battery-level alert, not its own icon).
pub fn resolve(
    app_icon: Option<&str>,
    desktop_entry: Option<&str>,
    app_name: Option<&str>,
) -> Option<PathBuf> {
    let theme = freedesktop_icons::default_theme_gtk();

    let candidates = [
        desktop_entry.and_then(desktop_file_icon_name),
        app_name.map(str::to_lowercase),
        app_icon.map(str::to_owned),
    ];

    candidates
        .into_iter()
        .flatten()
        .find_map(|name| resolve_name(&name, theme.as_deref()))
}

fn resolve_name(name: &str, theme: Option<&str>) -> Option<PathBuf> {
    if name.starts_with('/') {
        let path = PathBuf::from(name);
        return path.is_file().then_some(path);
    }

    let mut query = lookup(name).with_size(ICON_SIZE);
    if let Some(theme) = theme {
        query = query.with_theme(theme);
    }
    query.find()
}

/// Look up the `Icon=` value from a `.desktop` file identified by its
/// desktop-entry id, searching XDG_DATA_DIRS/applications the same way a
/// desktop environment would.
fn desktop_file_icon_name(desktop_entry: &str) -> Option<String> {
    for dir in data_dirs() {
        let path = dir
            .join("applications")
            .join(format!("{desktop_entry}.desktop"));
        if let Ok(contents) = fs::read_to_string(&path)
            && let Some(icon) = parse_icon_key(&contents)
        {
            return Some(icon);
        }
    }
    None
}

fn data_dirs() -> Vec<PathBuf> {
    let mut dirs = vec![];
    if let Some(home) = env::var_os("HOME") {
        dirs.push(PathBuf::from(home).join(".local/share"));
    }
    let xdg_data_dirs =
        env::var("XDG_DATA_DIRS").unwrap_or_else(|_| "/usr/local/share:/usr/share".to_string());
    dirs.extend(xdg_data_dirs.split(':').map(PathBuf::from));
    dirs
}

fn parse_icon_key(desktop_file_contents: &str) -> Option<String> {
    let mut in_desktop_entry_section = false;
    for line in desktop_file_contents.lines() {
        let line = line.trim();
        if line.starts_with('[') {
            in_desktop_entry_section = line == "[Desktop Entry]";
            continue;
        }
        if in_desktop_entry_section && let Some(value) = line.strip_prefix("Icon=") {
            return Some(value.trim().to_string());
        }
    }
    None
}