use std::collections::HashSet;
use std::hash::{Hash, Hasher};
use std::path::PathBuf;

use crate::model::Article;

fn images_dir() -> PathBuf {
    glib::user_cache_dir()
        .join("net.jeena.FeedTheMonkey")
        .join("images")
}

fn url_to_filename(url: &str) -> String {
    let mut hasher = std::collections::hash_map::DefaultHasher::new();
    url.hash(&mut hasher);
    let hash = format!("{:016x}", hasher.finish());
    let ext = url.split('?').next()
        .and_then(|u| u.rsplit('.').next())
        .filter(|e| e.len() <= 5 && e.bytes().all(|b| b.is_ascii_alphanumeric()))
        .unwrap_or("");
    if ext.is_empty() { hash } else { format!("{}.{}", hash, ext) }
}

fn percent_encode(s: &str) -> String {
    let mut out = String::with_capacity(s.len());
    for b in s.bytes() {
        if b.is_ascii_alphanumeric() || b"-.~_".contains(&b) {
            out.push(b as char);
        } else {
            out.push_str(&format!("%{:02X}", b));
        }
    }
    out
}

fn percent_decode(s: &str) -> String {
    let bytes = s.as_bytes();
    let mut out = Vec::with_capacity(bytes.len());
    let mut i = 0;
    while i < bytes.len() {
        if bytes[i] == b'%' && i + 2 < bytes.len() {
            if let Ok(b) = u8::from_str_radix(
                std::str::from_utf8(&bytes[i + 1..i + 3]).unwrap_or(""),
                16,
            ) {
                out.push(b);
                i += 3;
                continue;
            }
        }
        out.push(bytes[i]);
        i += 1;
    }
    String::from_utf8_lossy(&out).into_owned()
}

const SCHEME: &str = "feedthemonkey-img";
const SCHEME_PREFIX: &str = "feedthemonkey-img:///";

fn original_url_to_scheme_uri(url: &str) -> String {
    format!("{}{}", SCHEME_PREFIX, percent_encode(url))
}

/// Register the feedthemonkey-img URI scheme handler on the WebView's context.
/// Call this in setup_webview() before load_html().
pub fn register_scheme(ctx: &webkit6::WebContext) {
    ctx.register_uri_scheme(SCHEME, |request| {
        let uri = request.uri().unwrap_or_default().to_string();
        let encoded = uri.strip_prefix(SCHEME_PREFIX).unwrap_or(&uri);
        let original_url = percent_decode(encoded);
        let path = images_dir().join(url_to_filename(&original_url));

        if path.exists() {
            serve_file(request.clone(), path);
            return;
        }

        // Not in cache — download in tokio, serve back on the main thread.
        let request = request.clone();
        let (tx, rx) = tokio::sync::oneshot::channel::<bool>();
        let path_dl = path.clone();

        crate::runtime::spawn_bg(async move {
            let ok = async {
                let bytes = reqwest::get(&original_url).await?.bytes().await?;
                std::fs::create_dir_all(path_dl.parent().unwrap()).ok();
                std::fs::write(&path_dl, &bytes).ok();
                Ok::<_, reqwest::Error>(())
            }
            .await
            .is_ok();
            let _ = tx.send(ok);
        });

        // spawn_future_local runs on the GLib main loop so the non-Send
        // URISchemeRequest can be safely held across the await point.
        glib::spawn_future_local(async move {
            if rx.await.unwrap_or(false) && path.exists() {
                serve_file(request, path);
            } else {
                request.finish_error(&mut glib::Error::new(
                    gio::IOErrorEnum::NotFound,
                    "Image unavailable",
                ));
            }
        });
    });
}

fn serve_file(request: webkit6::URISchemeRequest, path: PathBuf) {
    match std::fs::read(&path) {
        Ok(data) => {
            let mime = path.extension()
                .and_then(|e| e.to_str())
                .map(|ext| match ext.to_ascii_lowercase().as_str() {
                    "jpg" | "jpeg" => "image/jpeg",
                    "png"          => "image/png",
                    "gif"          => "image/gif",
                    "webp"         => "image/webp",
                    "svg"          => "image/svg+xml",
                    "avif"         => "image/avif",
                    _              => "application/octet-stream",
                })
                .unwrap_or("application/octet-stream");
            let stream = gio::MemoryInputStream::from_bytes(&glib::Bytes::from_owned(data));
            request.finish(&stream, -1, Some(mime));
        }
        Err(_) => {
            request.finish_error(&mut glib::Error::new(
                gio::IOErrorEnum::NotFound,
                "Image not found",
            ));
        }
    }
}

/// Download all remote images in every article and rewrite their src attributes
/// to feedthemonkey-img:// URIs so images are served through the cache handler,
/// which re-downloads automatically on a cache miss.
pub async fn process(articles: Vec<Article>) -> Vec<Article> {
    let dir = images_dir();
    std::fs::create_dir_all(&dir).ok();

    let client = reqwest::Client::builder()
        .timeout(std::time::Duration::from_secs(30))
        .build()
        .unwrap_or_default();

    let re = regex::Regex::new(r#"src="(https?://[^"]+)""#).unwrap();

    let mut out = Vec::with_capacity(articles.len());
    for mut article in articles {
        let content = article.content.clone();
        let mut rewritten = content.clone();

        for cap in re.captures_iter(&content) {
            let url = &cap[1];
            let path = dir.join(url_to_filename(url));
            if !path.exists() {
                if let Ok(resp) = client.get(url).send().await {
                    if let Ok(bytes) = resp.bytes().await {
                        std::fs::write(&path, &bytes).ok();
                    }
                }
            }
            // Always rewrite to the scheme URI so the handler can re-download
            // if the cache directory is ever deleted.
            rewritten = rewritten.replace(
                &format!("src=\"{}\"", url),
                &format!("src=\"{}\"", original_url_to_scheme_uri(url)),
            );
        }

        article.content = rewritten;
        out.push(article);
    }
    out
}

/// Remove cached image files no longer referenced by any article.
pub fn cleanup(articles: &[Article]) {
    let dir = images_dir();
    let Ok(entries) = std::fs::read_dir(&dir) else { return };

    let re = regex::Regex::new(
        &format!(r#"src="{}([^"]+)""#, regex::escape(SCHEME_PREFIX)),
    )
    .unwrap();

    let mut referenced: HashSet<String> = HashSet::new();
    for article in articles {
        for cap in re.captures_iter(&article.content) {
            referenced.insert(url_to_filename(&percent_decode(&cap[1])));
        }
    }

    for entry in entries.filter_map(|e| e.ok()) {
        let fname = entry.file_name().to_string_lossy().to_string();
        if !referenced.contains(&fname) {
            std::fs::remove_file(entry.path()).ok();
        }
    }
}