use std::collections::HashSet;
use std::{fs::File, io::Read, collections::HashMap, path::Path};

use poise::serenity_prelude::Http;
use r2d2::{Pool, PooledConnection};
use r2d2_sqlite::SqliteConnectionManager;
use r2d2_sqlite::rusqlite::{self, params};
use derive_more::From;

use crate::{utils::get_challenge_number, models::User};

use super::{LegacySubmission, Submission};

pub struct Database {
    // Must be Arc because Connection contains RefCell,
    // which cannot be shared between threads safely
    connection_pool: Pool<SqliteConnectionManager>,
}

const DATABASE_FILENAME: &str = "database.db";

#[derive(From, Debug)]
pub enum DatabaseError {
    Rusqlite(rusqlite::Error),
    Pool(r2d2::Error),
}

type Result<T> = std::result::Result<T, DatabaseError>;

impl Database {
    pub fn file_exists() -> bool {
        Path::new(DATABASE_FILENAME).exists()
    }

    pub fn new(
        testing: bool,
    ) -> Result<Self> {
        let connection_manager = if testing {
            SqliteConnectionManager::memory()
        } else {
            SqliteConnectionManager::file(DATABASE_FILENAME)
        };
        let connection_pool = Pool::new(connection_manager)?;
        let conn = connection_pool.get()?;
        conn.execute(
            "CREATE TABLE IF NOT EXISTS Submission (
                id        INTEGER PRIMARY KEY,
                author_id INTEGER NOT NULL,
                timestamp DATETIME DEFAULT CURRENT_TIMESTAMP,
                image     TEXT NOT NULL,
                challenge INTEGER NOT NULL,
                FOREIGN KEY (author_id) REFERENCES User(id)
            )",
            params![],
        )?;
        conn.execute(
            "CREATE TABLE IF NOT EXISTS User (
                id            INTEGER PRIMARY KEY,
                name          TEXT NOT NULL,
                discriminator INTEGER NOT NULL,
                avatar        TEXT
            )",
            params![],
        )?;
        Ok(Self { connection_pool })
    }

    fn conn(&self) -> std::result::Result<PooledConnection<SqliteConnectionManager>, r2d2::Error> {
        self.connection_pool.get()
    }

    pub fn has_submitted(&self, user_id: u64) -> Result<bool> {
        Ok(self.conn()?
            .prepare("SELECT 1 FROM User WHERE id = ?1 LIMIT 1")?
            .query_row(params![user_id], |_row| Ok(()))
            .is_ok())
    }

    pub async fn load_legacy(&self, http: &Http) -> Result<()> {
        let latest_challenge = get_challenge_number();
        // HashMap of archived users that are no longer sharing a server with 字ちゃん
        // Their historical usernames and discriminators will be used
        let mut archived_users = HashMap::new();
        let conn = self.conn()?;
        for n in 1..=latest_challenge {
            println!("Loading legacy challenge {n}/{latest_challenge}...");
            let mut file = File::open(format!("data/challenges/{n}.json")).unwrap();
            let mut contents = String::new();
            file.read_to_string(&mut contents).unwrap();
            for (legacy, submissions) in serde_json::from_str::<Vec<LegacySubmission>>(&contents)
                .unwrap()
                .iter()
                .map(|legacy| (legacy, legacy.parse().unwrap())) {
                    let mut already_updated = false;
                    for submission in submissions {
                        conn.execute(
                            "INSERT INTO Submission(author_id, timestamp, image, challenge) VALUES (?1, ?2, ?3, ?4)",
                            params![
                                &submission.author_id,
                                &submission.timestamp,
                                &submission.image,
                                n,
                            ]
                        )?;
                        let id = submission.author_id;
                        if !self.has_submitted(id)? {
                            println!("Fetching user {id}...");
                            let previously_archived = archived_users.contains_key(&id);
                            // Parse archived user out of legacy and insert into HashMap
                            let mut archive = || {
                                if already_updated {
                                    return;
                                }
                                if previously_archived {
                                    println!("Updating archived data for user {id}");
                                } else {
                                    println!("Adding archived data for user {id}");
                                }
                                let (name, discriminator) = {
                                    let mut iter = legacy.username.split('#');
                                    let name = iter.next().unwrap().to_owned();
                                    let discriminator = iter
                                        .next()
                                        .map(|str| str.parse().unwrap())
                                        .unwrap_or(0);
                                    (name, discriminator)
                                };
                                archived_users.insert(id, User {
                                    id,
                                    name,
                                    discriminator,
                                    avatar: None,
                                });
                                already_updated = true;
                            };
                            if previously_archived {
                                // If it already contains the archived user,
                                // overwrite write their data since they may have updated
                                // their username/discriminator since their previous submission
                                archive();
                            } else {
                                match User::fetch(http, submission.author_id).await {
                                    Ok(user) => {
                                        conn.execute(
                                            "INSERT INTO User(id, name, discriminator, avatar) VALUES (?1, ?2, ?3, ?4)",
                                            params![user.id, user.name, user.discriminator, user.avatar]
                                        )?;
                                    },
                                    Err(error) => {
                                        println!("Failed to fetch user {}, may update archived data: {error}", submission.author_id);
                                        archive();
                                    },
                                };
                            }
                        }
                    }
                }
        }
        Ok(())
    }
    
    pub fn get_challenge_user_data(&self, challenge: u32) -> Result<(Vec<Submission>, HashMap<String, User>)> {
        let submissions = self.get_submissions(challenge)?;
        let users = self.get_users({
            let mut user_ids = HashSet::new();
            for submission in &submissions {
                user_ids.insert(submission.author_id);
            }
            user_ids
        })?;
        Ok((submissions, users))
    }

    pub fn get_submissions(&self, challenge: u32) -> Result<Vec<Submission>> {
        Ok(self.conn()?
            .prepare("SELECT author_id, timestamp, image FROM Submission WHERE challenge = ?1")?
            .query_map(params![challenge], |row| {
                Ok(Submission {
                    author_id: row.get(0)?,
                    timestamp: row.get(1)?,
                    image: row.get(2)?,
                })
            })?
            .collect::<std::result::Result<Vec<Submission>, rusqlite::Error>>()?)
    }

    fn get_users(&self, users: HashSet<u64>) -> Result<HashMap<String, User>> {
        let conn = self.conn()?;
        // Not sure why derive_more::From is unable to convert these errors
        users
            .iter()
            // u64 must be converted to String for templates
            .map(|id| -> Result<(String, User)> {
                match conn.prepare("SELECT name, discriminator, avatar FROM User WHERE id = ?1") {
                    Ok(mut statement) => statement.query_row(params![id], |row| {
                        Ok((id.to_string(), User {
                            id: *id,
                            name: row.get(0)?,
                            discriminator: row.get(1)?,
                            avatar: row.get(2)?,
                        }))
                    }).map_err(|error| DatabaseError::Rusqlite(error)),
                    Err(error) => Err(DatabaseError::Rusqlite(error)),
                }
            })
            .collect()
    }

    #[allow(dead_code)]
    pub fn refresh_users(&self) -> rusqlite::Result<()> {
        // Periodically refresh all changable user data (name, discriminator, avatar)
        // Ideally this should run periodically.
        todo!()
    }

    #[allow(dead_code, unused_variables)]
    pub fn insert_submission(&self, submission: &Submission) -> rusqlite::Result<()> {
        // For new submissions only
        todo!()
    }
}