#![warn(clippy::nursery, clippy::pedantic)]

use std::sync::Arc;
use std::time::Duration;

use anyhow::Result;
use axum::body::Bytes;
use axum::extract::{Extension, Path, TypedHeader};
use axum::handler::{get, post};
use axum::http::header::EXPIRES;
use axum::http::StatusCode;
use axum::{AddExtensionLayer, Router};
use chrono::Utc;
use headers::HeaderMap;
use omegaupload_common::Expiration;
use rand::thread_rng;
use rand::Rng;
use rocksdb::{ColumnFamilyDescriptor, IteratorMode};
use rocksdb::{Options, DB};
use tokio::task;
use tracing::{error, instrument, trace};
use tracing::{info, warn};

use crate::short_code::ShortCode;

mod short_code;

const BLOB_CF_NAME: &str = "blob";
const META_CF_NAME: &str = "meta";

#[tokio::main]
async fn main() -> Result<()> {
    const PASTE_DB_PATH: &str = "database";
    const SHORT_CODE_SIZE: usize = 12;

    tracing_subscriber::fmt::init();

    let mut db_options = Options::default();
    db_options.create_if_missing(true);
    db_options.create_missing_column_families(true);
    db_options.set_compression_type(rocksdb::DBCompressionType::Zstd);
    let db = Arc::new(DB::open_cf_descriptors(
        &db_options,
        PASTE_DB_PATH,
        [
            ColumnFamilyDescriptor::new(BLOB_CF_NAME, Options::default()),
            ColumnFamilyDescriptor::new(META_CF_NAME, Options::default()),
        ],
    )?);

    set_up_expirations(&db);

    axum::Server::bind(&"0.0.0.0:8081".parse()?)
        .serve(
            Router::new()
                .route("/", post(upload::<SHORT_CODE_SIZE>))
                .route(
                    "/:code",
                    get(paste::<SHORT_CODE_SIZE>).delete(delete::<SHORT_CODE_SIZE>),
                )
                .layer(AddExtensionLayer::new(db))
                .into_make_service(),
        )
        .await?;

    // Must be called for correct shutdown
    DB::destroy(&Options::default(), PASTE_DB_PATH)?;
    Ok(())
}

fn set_up_expirations(db: &Arc<DB>) {
    let mut corrupted = 0;
    let mut expired = 0;
    let mut pending = 0;

    info!("Setting up cleanup timers, please wait...");

    let meta_cf = db.cf_handle(META_CF_NAME).unwrap();

    let db_ref = Arc::clone(db);

    let delete_entry = move |key: &[u8]| {
        let blob_cf = db_ref.cf_handle(BLOB_CF_NAME).unwrap();
        let meta_cf = db_ref.cf_handle(META_CF_NAME).unwrap();
        if let Err(e) = db_ref.delete_cf(blob_cf, &key) {
            warn!("{}", e);
        }
        if let Err(e) = db_ref.delete_cf(meta_cf, &key) {
            warn!("{}", e);
        }
    };

    for (key, value) in db.iterator_cf(meta_cf, IteratorMode::Start) {
        let expiration = if let Ok(value) = bincode::deserialize::<Expiration>(&value) {
            value
        } else {
            corrupted += 1;
            delete_entry(&key);
            continue;
        };

        let expiration_time = match expiration {
            Expiration::BurnAfterReading => {
                panic!("Got burn after reading expiration time? Invariant violated");
            }
            Expiration::UnixTime(time) => time,
        };

        let sleep_duration = (expiration_time - Utc::now()).to_std().unwrap_or_default();
        if sleep_duration == Duration::default() {
            expired += 1;
            delete_entry(&key);
        } else {
            pending += 1;
            let delete_entry_ref = delete_entry.clone();
            task::spawn_blocking(move || async move {
                tokio::time::sleep(sleep_duration).await;
                delete_entry_ref(&key);
            });
        }
    }

    if corrupted == 0 {
        info!("No corrupted pastes found.");
    } else {
        warn!("Found {} corrupted pastes.", corrupted);
    }

    info!("Found {} expired pastes.", expired);
    info!("Found {} active pastes.", pending);
    info!("Cleanup timers have been initialized.");
}

#[instrument(skip(db, body), err)]
async fn upload<const N: usize>(
    Extension(db): Extension<Arc<DB>>,
    maybe_expires: Option<TypedHeader<Expiration>>,
    body: Bytes,
) -> Result<Vec<u8>, StatusCode> {
    if body.is_empty() {
        return Err(StatusCode::BAD_REQUEST);
    }

    // 3GB max; this is a soft-limit of RocksDb
    if body.len() >= 3_221_225_472 {
        return Err(StatusCode::PAYLOAD_TOO_LARGE);
    }

    let mut new_key = None;

    trace!("Generating short code...");

    // Try finding a code; give up after 1000 attempts
    // Statistics show that this is very unlikely to happen
    for i in 0..1000 {
        let code: ShortCode<N> = thread_rng().sample(short_code::Generator);
        let db = Arc::clone(&db);
        let key = code.as_bytes();
        let query = task::spawn_blocking(move || {
            db.key_may_exist_cf(db.cf_handle(META_CF_NAME).unwrap(), key)
        })
        .await;
        if matches!(query, Ok(false)) {
            new_key = Some(key);
            trace!("Found new key after {} attempts.", i);
            break;
        }
    }

    let key = if let Some(key) = new_key {
        key
    } else {
        error!("Failed to generate a valid short code!");
        return Err(StatusCode::INTERNAL_SERVER_ERROR);
    };

    trace!("Serializing paste...");

    trace!("Finished serializing paste.");

    let db_ref = Arc::clone(&db);
    match task::spawn_blocking(move || {
        let blob_cf = db_ref.cf_handle(BLOB_CF_NAME).unwrap();
        let meta_cf = db_ref.cf_handle(META_CF_NAME).unwrap();
        let data = bincode::serialize(&body).expect("bincode to serialize");
        db_ref.put_cf(blob_cf, key, data)?;
        let expires = maybe_expires.map(|v| v.0).unwrap_or_default();
        let meta = bincode::serialize(&expires).expect("bincode to serialize");
        if db_ref.put_cf(meta_cf, key, meta).is_err() {
            // try and roll back on metadata write failure
            db_ref.delete_cf(blob_cf, key)?;
        }
        Result::<_, anyhow::Error>::Ok(())
    })
    .await
    {
        Ok(Ok(_)) => {
            if let Some(expires) = maybe_expires {
                if let Expiration::UnixTime(expiration_time) = expires.0 {
                    let sleep_duration =
                        (expiration_time - Utc::now()).to_std().unwrap_or_default();

                    task::spawn_blocking(move || async move {
                        tokio::time::sleep(sleep_duration).await;
                        let blob_cf = db.cf_handle(BLOB_CF_NAME).unwrap();
                        let meta_cf = db.cf_handle(META_CF_NAME).unwrap();
                        if let Err(e) = db.delete_cf(blob_cf, key) {
                            warn!("{}", e);
                        }
                        if let Err(e) = db.delete_cf(meta_cf, key) {
                            warn!("{}", e);
                        }
                    });
                }
            }
        }
        e => {
            error!("Failed to insert paste into db: {:?}", e);
            return Err(StatusCode::INTERNAL_SERVER_ERROR);
        }
    }

    Ok(Vec::from(key))
}

#[instrument(skip(db), err)]
async fn paste<const N: usize>(
    Extension(db): Extension<Arc<DB>>,
    Path(url): Path<ShortCode<N>>,
) -> Result<(HeaderMap, Bytes), StatusCode> {
    let key = url.as_bytes();

    let metadata: Expiration = {
        let meta_cf = db.cf_handle(META_CF_NAME).unwrap();
        let query_result = db.get_cf(meta_cf, key).map_err(|e| {
            error!("Failed to fetch initial query: {}", e);
            StatusCode::INTERNAL_SERVER_ERROR
        })?;

        let data = match query_result {
            Some(data) => data,
            None => return Err(StatusCode::NOT_FOUND),
        };

        bincode::deserialize(&data).map_err(|_| {
            error!("Failed to deserialize data?!");
            StatusCode::INTERNAL_SERVER_ERROR
        })?
    };

    // Check if paste has expired.
    if let Expiration::UnixTime(expires) = metadata {
        if expires < Utc::now() {
            task::spawn_blocking(move || {
                let blob_cf = db.cf_handle(BLOB_CF_NAME).unwrap();
                let meta_cf = db.cf_handle(META_CF_NAME).unwrap();
                if let Err(e) = db.delete_cf(blob_cf, &key) {
                    warn!("{}", e);
                }
                if let Err(e) = db.delete_cf(meta_cf, &key) {
                    warn!("{}", e);
                }
            })
            .await
            .map_err(|e| {
                error!("Failed to join handle: {}", e);
                StatusCode::INTERNAL_SERVER_ERROR
            })?;

            return Err(StatusCode::NOT_FOUND);
        }
    }

    let paste: Bytes = {
        // not sure if perf of get_pinned is better than spawn_blocking
        let blob_cf = db.cf_handle(BLOB_CF_NAME).unwrap();
        let query_result = db.get_pinned_cf(blob_cf, key).map_err(|e| {
            error!("Failed to fetch initial query: {}", e);
            StatusCode::INTERNAL_SERVER_ERROR
        })?;

        let data = match query_result {
            Some(data) => data,
            None => return Err(StatusCode::NOT_FOUND),
        };

        bincode::deserialize(&data).map_err(|_| {
            error!("Failed to deserialize data?!");
            StatusCode::INTERNAL_SERVER_ERROR
        })?
    };

    // Check if we need to burn after read
    if matches!(metadata, Expiration::BurnAfterReading) {
        let join_handle = task::spawn_blocking(move || db.delete(key))
            .await
            .map_err(|e| {
                error!("Failed to join handle: {}", e);
                StatusCode::INTERNAL_SERVER_ERROR
            })?;

        join_handle.map_err(|e| {
            error!("Failed to burn paste after read: {}", e);
            StatusCode::INTERNAL_SERVER_ERROR
        })?;
    }

    let mut map = HeaderMap::new();
    map.insert(EXPIRES, metadata.into());

    Ok((map, paste))
}

#[instrument(skip(db))]
async fn delete<const N: usize>(
    Extension(db): Extension<Arc<DB>>,
    Path(url): Path<ShortCode<N>>,
) -> StatusCode {
    match task::spawn_blocking(move || {
        let blob_cf = db.cf_handle(BLOB_CF_NAME).unwrap();
        let meta_cf = db.cf_handle(META_CF_NAME).unwrap();
        if let Err(e) = db.delete_cf(blob_cf, url.as_bytes()) {
            warn!("{}", e);
            return Err(());
        }

        if let Err(e) = db.delete_cf(meta_cf, url.as_bytes()) {
            warn!("{}", e);
            return Err(());
        }

        Ok(())
    })
    .await
    {
        Ok(_) => StatusCode::OK,
        _ => StatusCode::INTERNAL_SERVER_ERROR,
    }
}