use ammonia::Builder;
use once_cell::sync::Lazy;
use std::borrow::Cow;
use std::collections::{HashMap, HashSet};

fn allow_styles<'u>(allowed: &[&str], value: &'u str) -> Option<Cow<'u, str>> {
    let mut altered = false;
    let rules: Vec<_> = value
        .split(';')
        .filter_map(|rule| {
            let name = rule.split(':').next()?.trim();

            log::debug!("Checking '{}' against {:?}", name, allowed);

            if allowed.contains(&name) {
                Some(rule)
            } else {
                altered = true;
                None
            }
        })
        .collect();

    if altered {
        if rules.is_empty() {
            None
        } else {
            Some(Cow::Owned(rules.join(";")))
        }
    } else {
        Some(Cow::Borrowed(value))
    }
}

fn attribute_filter<'u>(element: &str, attribute: &str, value: &'u str) -> Option<Cow<'u, str>> {
    match (element, attribute) {
        ("ul", "style") | ("ol", "style") => allow_styles(&["list-style-type", "type"], value),
        ("span", "style") => allow_styles(&["color", "opacity"], value),
        ("div", "class")
        | ("span", "class")
        | ("figure", "class")
        | ("pre", "class")
        | ("pre", "data-language")
        | ("span", "data-symbol")
        | ("blockquote", "data-author")
        | ("a", "rel")
        | ("a", "title")
        | ("a", "href")
        | ("img", "src")
        | ("img", "title")
        | ("img", "alt") => Some(Cow::Borrowed(value)),
        _ => None,
    }
}

// Classes based on bbclash BBCode spec:
// https://github.com/EndaHallahan/BBClash/blob/master/Spec.md
static AMMONIA_CONFIG: Lazy<Builder> = Lazy::new(|| {
    let mut classes = HashMap::new();

    let div_hs = classes.entry("div").or_insert(HashSet::new());
    div_hs.insert("center");
    div_hs.insert("right");
    div_hs.insert("math_container");
    // div_hs.insert("embed"); for now, no embeds
    div_hs.insert("indent-1");
    div_hs.insert("indent-2");
    div_hs.insert("indent-3");
    div_hs.insert("indent-4");

    let span_hs = classes.entry("span").or_insert(HashSet::new());
    span_hs.insert("underline");
    span_hs.insert("smallcaps");
    span_hs.insert("monospace");
    span_hs.insert("spoiler");
    span_hs.insert("math_container");

    let pre_hs = classes.entry("pre").or_insert(HashSet::new());
    pre_hs.insert("codeblock");

    let figure_hs = classes.entry("figure").or_insert(HashSet::new());
    figure_hs.insert("figure-right");
    figure_hs.insert("figure-left");

    let mut schemes = HashSet::new();
    schemes.insert("http");
    schemes.insert("https");
    schemes.insert("mailto");

    let mut builder = Builder::new();
    builder
        .allowed_classes(classes)
        .url_schemes(schemes)
        .attribute_filter(attribute_filter)
        .add_tag_attributes("span", &["style"])
        .add_tag_attributes("div", &["style"]);

    builder
});

pub fn html(source: &str) -> String {
    let h = AMMONIA_CONFIG.clean(source).to_string();
    log::debug!("{}", h);
    h
}

pub fn bbcode(source: &str) -> String {
    let bb = bbclash::bbcode_to_html(source);
    log::debug!("{}", bb);
    bb
}