// https://www.phind.com/agent?cache=clke9xk39001cmj085upzho1t

use std::{fmt::Display, fs::File};

use atom_syndication::{Entry, Feed, Link};

//
// ERRORS
//
#[derive(Debug)]
struct Error {
    details: String,
}
impl Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(self.details.to_string().as_str())
    }
}
impl From<String> for Error {
    fn from(details: String) -> Self {
        Self { details }
    }
}
impl From<std::io::Error> for Error {
    fn from(value: std::io::Error) -> Self {
        Self {
            details: value.to_string(),
        }
    }
}
impl From<atom_syndication::Error> for Error {
    fn from(value: atom_syndication::Error) -> Self {
        Self {
            details: value.to_string(),
        }
    }
}
impl From<reqwest::Error> for Error {
    fn from(value: reqwest::Error) -> Self {
        Self {
            details: value.to_string(),
        }
    }
}

//
// RESULTS
//
type Result<T> = std::result::Result<T, Error>;

//
// MAIN
//
fn main() -> Result<()> {
    println!("Podal");
    let subscriptions = "subscriptions.txt";
    let history = "downloaded.txt";

    for channel_name in lines_from(subscriptions)? {
        let channel_name = channel_name?;
        let feed_url = get_feed_url(channel_name)?;
        for entry in get_feed(feed_url)?.entries() {
            if let Some(link) = get_link(entry) {
                if !is_already_downloaded(&link, history)? {
                    download_audio(&link)?;
                    mark_as_downloaded(&link, history)?;
                }
            }
        }
    }

    println!("Done");
    Ok(())
}

fn get_feed_url(channel_name: String) -> Result<String> {
    if let Some(channel_prefix) = channel_name.chars().next() {
        if channel_prefix != '@' {
            return Err(format!("Channel Name must begin with an '@': {}", channel_name).into());
        }
    }
    let channel_url = format!("https://www.youtube.com/{}", channel_name);
    let response = reqwest::blocking::get(channel_url)?;
    let rss_url = scraper::Html::parse_document(&response.text()?)
        .select(&scraper::Selector::parse("link[title='RSS']").unwrap())
        .next()
        .unwrap()
        .value()
        .attr("href")
        .unwrap()
        .to_string();
    println!("rss_url: {}", rss_url);
    Ok(rss_url)
}

fn get_link(item: &Entry) -> Option<Link> {
    item.links().get(0).cloned()
}

// read list of rss feed URLs from file 'feeds.txt'
fn lines_from(file_name: &str) -> Result<std::io::Lines<std::io::BufReader<std::fs::File>>> {
    use std::io::{BufRead, BufReader};

    let file = File::open(file_name)?;
    let reader = BufReader::new(file);
    Ok(reader.lines())
}

// fetch the RSS feed
fn get_feed(url: String) -> Result<Feed> {
    let content = reqwest::blocking::get(url)?.bytes()?;
    let channel = Feed::read_from(&content[..])?;
    Ok(channel)
}

fn is_already_downloaded(link: &Link, file_name: &str) -> Result<bool> {
    use std::io::{BufRead, BufReader};

    println!("is already downloaded? {}", link.href);
    if let Ok(file) = File::open(file_name) {
        let reader = BufReader::new(file);
        for line in reader.lines() {
            if line? == link.href {
                println!("Yes!");
                return Ok(true); // is already downloaded
            }
        }
    }
    println!("No!");
    Ok(false) // is not already downloaded
}

fn download_audio(link: &Link) -> Result<()> {
    use std::process::Command;

    let cmd = "yt-dlp";
    println!("download audio for {}", link.href());
    println!("{} --extract-audio --audio-format mp3 {}", cmd, &link.href);
    let mut child = Command::new(cmd)
        .arg("--extract-audio")
        .arg("--audio-format")
        .arg("mp3")
        .arg(&link.href)
        .spawn()
        .expect("Failed to execute command");
    child.wait()?;
    Ok(())
}

fn mark_as_downloaded(link: &Link, file_name: &str) -> Result<()> {
    use std::fs::OpenOptions;
    use std::io::prelude::*;

    let mut file = OpenOptions::new()
        .write(true)
        .append(true)
        .create(true)
        .open(file_name)
        .unwrap();

    writeln!(file, "{}", link.href)?;
    Ok(())
}