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

// toml
use serde::Deserialize;

// egg-mode
use egg_mode::{
    Token,
    KeyPair,
    entities::{UrlEntity, MediaEntity, MentionEntity, MediaType},
    user::UserID,
    tweet::{
        Tweet,
        user_timeline,
    },
};

// elefren
use elefren::{
    prelude::*,
    apps::App,
    status_builder::StatusBuilder,
    scopes::Scopes,
};

// reqwest
use reqwest::Url;

// tokio
use tokio::{
    io::copy,
    fs::{File, create_dir_all, remove_file},
};

// htmlescape
use htmlescape::decode_html;

// log
use log::{info, warn, error, debug};

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

    if let Ok(s) = state {
        debug!("Last Tweet ID (from file): {}", &s);
        return s.parse::<u64>().ok();
    }

    None
}

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

/// Gets 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,
    }
}

/// Gets Twitter user timeline
async 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 (_, feed) = user_timeline(UserID::from(String::from(&config.twitter.username)), true, false, &token)
                .with_page_size(200)
                .older(lid)
                .await?;

    Ok(feed.to_vec())
}

/// Decodes urls from UrlEntities
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
}

/// Decodes the Twitter mention to something that will make sense once Twitter has joined the
/// Fediverse
fn twitter_mentions(ums: &Vec<MentionEntity>) -> HashMap<String, String> {
    let mut decoded_mentions = HashMap::new();

    for um in ums {
        decoded_mentions.insert(format!("@{}", um.screen_name), format!("@{}@twitter.com", um.screen_name));
    }

    decoded_mentions
}

/// Retrieves a single media from a tweet and store it in a temporary file
async fn get_tweet_media(m: &MediaEntity, t: &str) -> Result<String, Box<dyn Error>> {
    match m.media_type {
        MediaType::Photo => {
            return cache_media(&m.media_url_https, t).await;
        },
        _ => {
            match &m.video_info {
                Some(v) => {
                    for variant in &v.variants {
                        if variant.content_type == "video/mp4" {
                            return cache_media(&variant.url, t).await;
                        }
                    }
                    return Err(ScootalooError::new(&format!("Media Type for {} is video but no mp4 file URL is available", &m.url)).into());
                },
                None => {
                    return Err(ScootalooError::new(&format!("Media Type for {} is video but does not contain any video_info", &m.url)).into());
                },
            }
        },
    };
}

/*
 * Those functions are related to the Mastodon side of things
 */
/// Gets 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)
}

/// Builds toot text from tweet
fn build_basic_status(tweet: &Tweet) -> Result<String, 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);
    }

    let decoded_mentions = twitter_mentions(&tweet.entities.user_mentions);

    for decoded_mention in decoded_mentions {
        toot = toot.replace(&decoded_mention.0, &decoded_mention.1);
    }

    if let Ok(t) = decode_html(&toot) {
        toot = t;
    }

    Ok(toot)
}

/*
 * Generic private functions
 */
/// Gets and caches Twitter Media inside the determined temp dir
async fn cache_media(u: &str, t: &str) -> Result<String, Box<dyn Error>> {
    // create dir
    create_dir_all(t).await?;

    // get file
    let mut response = reqwest::get(u).await?;

    // create local file
    let url = Url::parse(u)?;
    let dest_filename = url.path_segments().ok_or_else(|| ScootalooError::new(&format!("Cannot determine the destination filename for {}", u)))?
                    .last().ok_or_else(|| ScootalooError::new(&format!("Cannot determine the destination filename for {}", u)))?;

    let dest_filepath = format!("{}/{}", t, dest_filename);

    let mut dest_file = File::create(&dest_filepath).await?;

    while let Some(chunk) = response.chunk().await? {
        copy(&mut &*chunk, &mut dest_file).await?;
    }

    Ok(dest_filepath)
}

/**********
 * This is the struct that holds the Mastodon Media ID and the Twitter Media URL at the same Time
**********/
#[derive(Debug)]
struct ScootalooSpawnResponse {
    mastodon_media_id: String,
    twitter_media_url: String,
}

/**********
 * 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,
    scootaloo: ScootalooConfig,
}

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

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

#[derive(Debug, Deserialize)]
struct ScootalooConfig {
    last_tweet_path: String,
    cache_path: 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 `elefren` crate
pub fn register(host: &str) {
    let mut builder = App::builder();
    builder.client_name(Cow::from(String::from(env!("CARGO_PKG_NAME"))))
        .redirect_uris(Cow::from(String::from("urn:ietf:wg:oauth:2.0:oob")))
        .scopes(Scopes::write_all())
        .website(Cow::from(String::from("https://framagit.org/veretcle/scootaloo")));

    let app = builder.build().expect("Cannot build the app");

    let registration = Registration::new(host).register(app).expect("Cannot build registration object");
    let url = registration.authorize_url().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();
    stdin().read_line(&mut input).expect("Unable to read back registration code!");

    let code = input.trim();
    let mastodon = registration.complete(code).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
#[tokio::main]
pub async fn run(config: Config) {
    // retrieve the last tweet ID for the username
    let last_tweet_id = read_state(&config.scootaloo.last_tweet_path);

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

    // get Mastodon instance
    let mastodon = Arc::new(Mutex::new(get_mastodon_token(&config.mastodon)));

    // get user timeline feed (Vec<tweet>)
    let mut feed = get_user_timeline(&config, token, last_tweet_id)
        .await
        .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() {
        info!("Nothing to retrieve since last time, exiting…");
        return;
    }

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

    for tweet in &feed {
        debug!("Treating Tweet {} inside feed", tweet.id);
        // determine if the tweet is part of a thread (response to self) or a standard response
        debug!("Treating Tweet {} inside feed", tweet.id);
        if let Some(r) =  &tweet.in_reply_to_screen_name {
                if &r.to_lowercase() != &config.twitter.username.to_lowercase() {
                    // we are responding not threading
                    info!("Tweet is a direct response, skipping");
                    continue;
                }
        };

        // build basic status by just yielding text and dereferencing contained urls
        let mut status_text = match build_basic_status(tweet) {
            Ok(t) => t,
            Err(e) => {
                error!("Could not create status from tweet {}: {}", tweet.id ,e);
                continue;
            },
        };

        let mut status_medias: Vec<String> = vec![];

        // reupload the attachments if any
        if let Some(m) = &tweet.extended_entities {
            let (tx, mut rx) = mpsc::channel(4);

            for media in &m.media {
                let local_tweet_media_path = match get_tweet_media(&media, &config.scootaloo.cache_path).await {
                    Ok(m) => m,
                    Err(e) => {
                        warn!("Cannot get tweet media for {}: {}", &media.url, e);
                        continue;
                    },
                };

                let mastodon_media_ids = match mastodon.media(Cow::from(String::from(&local_tweet_media_path))) {
                    Ok(m) => {
                        remove_file(&local_tweet_media_path).await.unwrap_or_else(|e|
                            warn!("Attachment {} has been uploaded but I’m unable to remove the existing file: {}", &local_tweet_media_path, e)
                        );
                        m.id
                    },
                    Err(e) => {
                        error!("Attachment {} cannot be uploaded to Mastodon Instance: {}", &local_tweet_media_path, e);
                        continue;
                    }
                };
                status_medias.push(mastodon_media_ids);
                // last step, removing the reference to the media from with the toot’s text
                status_text = status_text.replace(&media.url, "");
            }
        }
        // finished reuploading attachments, now let’s do the toot baby!

        debug!("Building corresponding Mastodon status");
        let status = StatusBuilder::new()
            .status(&status_text)
            .media_ids(status_medias)
            .build()
            .expect(&format!("Cannot build status with text {}", &status_text));

        // publish status
        // again unwrap is safe here as we are in the main thread
        mastodon.lock().unwrap().new_status(status).unwrap();
        // this will panic if it cannot publish the status, which is a good thing, it allows the
        // last_tweet gathered not to be written

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