// std
use std::{
    borrow::Cow,
    collections::HashMap,
    io,
    fmt,
    fs::{read_to_string, write},
    error::Error,
};

// toml
use serde::Deserialize;

// egg-mode
use egg_mode::{
    Token,
    KeyPair,
    entities::UrlEntity,
    tweet::{
        Tweet,
        user_timeline,
    },
};
use tokio::runtime::current_thread::block_on_all;

// mammut
use mammut::{Mastodon, Data, Registration};
use mammut::apps::{AppBuilder, Scopes};
use mammut::status_builder::StatusBuilder;

/**********
 * Generic usage functions
***********/
/*
 * Those functions are related to the Twitter side of things
 */
/// Read last tweet id from a file
fn read_state(s: &str) -> Option<u64> {
    let state = read_to_string(s);

    if let Ok(s) = state {
        return s.parse::<u64>().ok();
    }

    None
}

/// Write last treated tweet id to a file
fn write_state(f: &str, s: u64) -> Result<(), std::io::Error> {
    write(f, format!("{}", s))
}

/// Get twitter oauth2 token
fn get_oauth2_token(config: &Config) -> Token {
    let con_token = KeyPair::new(String::from(&config.twitter.consumer_key), String::from(&config.twitter.consumer_secret));
    let access_token = KeyPair::new(String::from(&config.twitter.access_key), String::from(&config.twitter.access_secret));

    Token::Access {
        consumer: con_token,
        access: access_token,
    }
}

/// Get twitter user timeline
fn get_user_timeline(config: &Config, token: Token, lid: Option<u64>) -> Result<Vec<Tweet>, Box<dyn Error>> {
    // fix the page size to 200 as it is the maximum Twitter authorizes
    let (_timeline, feed) = block_on_all(user_timeline(&config.twitter.username, true, false, &token)
                .with_page_size(200)
                .older(lid))?;

    Ok(feed.to_vec())
}

/*
 * Those functions are related to the Mastodon side of things
 */
/// Get Mastodon Data
fn get_mastodon_token(masto: &MastodonConfig) -> Mastodon {
    let data = Data {
        base: Cow::from(String::from(&masto.base)),
        client_id: Cow::from(String::from(&masto.client_id)),
        client_secret: Cow::from(String::from(&masto.client_secret)),
        redirect: Cow::from(String::from(&masto.redirect)),
        token: Cow::from(String::from(&masto.token)),
    };

    Mastodon::from_data(data)
}

/// build toot from tweet
fn build_status(tweet: &Tweet) -> Result<StatusBuilder, Box<dyn Error>> {
    let mut toot = String::from(&tweet.text);

    let decoded_urls = decode_urls(&tweet.entities.urls);

    for decoded_url in decoded_urls {
        toot = toot.replace(&decoded_url.0, &decoded_url.1);
    }

    Ok(StatusBuilder::new(toot))
}

fn decode_urls(urls: &Vec<UrlEntity>) -> HashMap<String, String> {
    let mut decoded_urls = HashMap::new();

    for url in urls {
        if url.expanded_url.is_some() {
            // unwrap is safe here as we just verified that there is something inside expanded_url
            decoded_urls.insert(String::from(&url.url), String::from(url.expanded_url.as_deref().unwrap()));
        }
    }

    decoded_urls
}

/**********
 * local error handler
**********/
#[derive(Debug)]
struct ScootalooError {
    details: String,
}

impl ScootalooError {
    fn new(msg: &str) -> ScootalooError {
        ScootalooError {
            details: String::from(msg),
        }
    }
}

impl fmt::Display for ScootalooError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.details)
    }
}

impl std::error::Error for ScootalooError {
    fn description(&self) -> &str {
        &self.details
    }
}

/**********
 * Config structure
***********/
/// General configuration Struct
#[derive(Debug, Deserialize)]
pub struct Config {
    twitter: TwitterConfig,
    mastodon: MastodonConfig,
}

#[derive(Debug, Deserialize)]
struct TwitterConfig {
    username: String,
    consumer_key: String,
    consumer_secret: String,
    access_key: String,
    access_secret: String,
    last_tweet_path: String,
}

#[derive(Debug, Deserialize)]
struct MastodonConfig {
    base: String,
    client_id: String,
    client_secret: String,
    redirect: String,
    token: String,
}

/*********
 * Main functions
*********/
/// Parses the TOML file into a Config Struct
pub fn parse_toml(toml_file: &str) -> Config {
    let toml_config = read_to_string(toml_file).unwrap_or_else(|e|
        panic!("Cannot open config file {}: {}", toml_file, e)
    );

    let config: Config = toml::from_str(&toml_config).unwrap_or_else(|e|
        panic!("Cannot parse TOML file {}: {}", toml_file, e)
    );

    config
}

/// Generic register function
/// As this function is supposed to be run only once, it will panic for every error it encounters
/// Most of this function is a direct copy/paste of the official `mammut` crate
pub fn register(host: &str) {
    let app = AppBuilder {
        client_name: env!("CARGO_PKG_NAME"),
        redirect_uris: "urn:ietf:wg:oauth:2.0:oob",
        scopes: Scopes::Write,
        website: Some("https://framagit.org/veretcle/scootaloo"),
    };

    let mut registration = Registration::new(host);
    registration.register(app).expect("Registration failed!");
    let url = registration.authorise().expect("Cannot generate registration URI!");

    println!("Click this link to authorize on Mastodon: {}", url);
    println!("Paste the returned authorization code: ");

    let mut input = String::new();
    io::stdin().read_line(&mut input).expect("Unable to read back registration code!");

    let code = input.trim();
    let mastodon = registration.create_access_token(code.to_string()).expect("Unable to create access token!");

    let toml = toml::to_string(&*mastodon).unwrap();

    println!("Please insert the following block at the end of your configuration file:\n[mastodon]\n{}", toml);
}

/// This is where the magic happens
pub fn run(config: Config) {
    // retrieve the last tweet ID for the username
    let last_tweet_id = read_state(&config.twitter.last_tweet_path);

    // get OAuth2 token
    let token = get_oauth2_token(&config);

    // get Mastodon instance
    let mastodon = get_mastodon_token(&config.mastodon);

    // get user timeline feed (Vec<tweet>)
    let mut feed = get_user_timeline(&config, token, last_tweet_id).unwrap_or_else(|e|
        panic!("Something went wrong when trying to retrieve {}’s timeline: {}", &config.twitter.username, e)
    );

    // empty feed -> exiting
    if feed.is_empty() {
        println!("Nothing to retrieve since last time, exiting…");
        return;
    }

    // order needs to be chronological
    feed.reverse();

    for tweet in &feed {
        let status = match build_status(tweet) {
            Ok(t) => t,
            Err(e) => {
                println!("Could not create status from tweet {}: {}", tweet.id ,e);
                continue;
            },
        };

        // publish status
        mastodon.new_status(status).unwrap();

        // write the current state (tweet ID) to avoid copying it another time
        write_state(&config.twitter.last_tweet_path, tweet.id).unwrap_or_else(|e|
            panic!("Can’t write the last tweet retrieved: {}", e)
        );
    }
}