use scraper::{Html,Selector};
use url::{Url,Host};
use std::sync::{Arc,Mutex};
use tokio::task::JoinHandle;
use futures::future;

const WORKERS : usize = 8;

type SiteStat = (Url, Vec<Url>);

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let addr = std::env::args().nth(1)
	.unwrap_or_else(|| "https://www.tmplab.org".to_string());
    let links = get_links(addr.as_ref()).await?;
    let addr = Url::parse(addr.as_ref())?;
    let mut links : Vec<Url> = links.into_iter()
	.filter(| url | url.host() != addr.host())
	.collect();

    let links = Arc::new(Mutex::new(links));

    let joins = (0..WORKERS)
	.map(| n | spawn_worker(n, &links));	

    let results : Vec<_>= future::join_all(joins).await
	.into_iter()
	.filter_map(| r | r.ok())
	.flatten()
	.collect();

    for (url, links) in &results {
	println!("{url} : {} links", links.len())
    }
    println!("TOTAL: {}", results.len());
    Ok(())
}

// interestingly, this function must not be async...
fn spawn_worker(
    n: usize,
    links: &Arc<Mutex<Vec<Url>>>
) -> JoinHandle<Vec<SiteStat>> {
    println!("Spawning worker {n}");
    let links = links.clone();
    tokio::spawn(async move { looper(links).await })
}

async fn looper(links: Arc<Mutex<Vec<Url>>>) -> Vec<SiteStat> {
    let mut results = vec![];
    
    loop {
	let url = {
	    let mut v = links.lock().unwrap();
	    let Some(url) = v.pop() else {
		break;
	    };
	    url
	};
	println!("Start fetching {url}...");
	let res = match get_links(url.as_ref()).await {
	    Err(_) => "nope",
	    Ok(links) => {
		results.push((url.clone(), links));
		"YEA!"
	    }
	};
	println!("Got {url} => {res}");
    }
    results
}

async fn get_links(
    url: &str
) -> Result<Vec<Url>, reqwest::Error> {
    let a_selector = Selector::parse("a[href]").unwrap();
    
    let body = reqwest::get(url)
	.await?
	.text()
	.await?;

    Ok(Html::parse_document(&body)
       .select(&a_selector)
       .filter_map(| link | link.value().attr("href")
		   .and_then(| href | Url::parse(href).ok()))
       .collect())
}