#[macro_use]
extern crate serde_derive;
#[macro_use]
extern crate log;

use crate::config::Config;
use crate::well_known_mime::Mime;
use chrono::{DateTime, Utc};
use clappconfig::{anyhow, AppConfig};
use parking_lot::Mutex;
use rand::rngs::OsRng;
use rand::Rng;
use rouille::{Request, Response, ResponseBody};

use std::borrow::Cow;
use std::collections::HashMap;

use std::fs::OpenOptions;
use std::hash::{Hash, Hasher};
use std::io::Read;
use std::time::Duration;
use siphasher::sip::SipHasher;

mod config;
mod well_known_mime;

/// Header to set expiry (seconds)
const HDR_EXPIRY: &str = "X-Expire";
/// Header to pass secret token for update/delete
const HDR_SECRET: &str = "X-Secret";
/// GET param to pass secret token (as a substitute for header)
const GET_EXPIRY: &str = "expire";
/// GET param to pass secret token (as a substitute for header)
const GET_SECRET: &str = "secret";

const FAVICON: &[u8] = include_bytes!("embed/favicon.ico");
const ROBOTS: &[u8] = include_bytes!("embed/robots.txt");
const LANDING_PAGE: &[u8] = include_bytes!("embed/home.html");

/// Post ID (represented as a 16-digit hex string)
type PostId = u64;
/// Write token (represented as a 16-digit hex string)
type Secret = u64;
/// Hash of a data record
type DataHash = u64;

/// Post stored in the repository
#[derive(Debug, Serialize, Deserialize)]
struct Post {
    /// Content-Type
    mime: Mime,
    /// Data hash
    hash: DataHash,
    /// Secret key for editing or deleting
    secret: Secret,
    /// Expiration timestamp
    #[serde(with = "serde_chrono_datetime_as_unix")]
    expires: DateTime<Utc>,
}

impl Post {
    /// Check if the post expired
    pub fn is_expired(&self) -> bool {
        self.expires < Utc::now()
    }

    /// Get remaining lifetime
    pub fn time_remains(&self) -> Duration {
        let seconds_remains = self.expires.signed_duration_since(Utc::now())
            .num_seconds();
        if seconds_remains < 0 {
            Duration::from_secs(0)
        } else {
            Duration::from_secs(seconds_remains as u64)
        }
    }
}

fn main() -> anyhow::Result<()> {
    let config = Config::init("postit", "postit.json", env!("CARGO_PKG_VERSION"))?;
    let serve_at = format!("{}:{}", config.host, config.port);

    let store = Mutex::new({
        let mut store = Repository::new(config);
        if store.config.persistence {
            if let Err(e) = store.load() {
                error!("Load failed: {}", e);
            }
        }
        store.gc_expired_posts();
        store
    });

    rouille::start_server(serve_at, move |req| {
        let mut store_w = store.lock();
        let method = req.method();

        info!("{} {}", method, req.raw_url());

        if method == "GET" || method == "HEAD" {
            if req.url() == "/" {
                return decorate_response(Response::from_data("text/html", LANDING_PAGE)
                    .with_public_cache(86400));
            }

            if req.url() == "/favicon.ico" {
                return decorate_response(Response::from_data("image/vnd.microsoft.icon", FAVICON)
                    .with_public_cache(86400 * 7));
            }

            if req.url() == "/robots.txt" {
                return decorate_response(Response::from_data("text/plain", ROBOTS)
                    .with_public_cache(86400));
            }
        }

        store_w.gc_expired_posts_if_needed();

        let resp = match method {
            "POST" | "PUT" => store_w.serve_post_put(req),
            "GET" | "HEAD" => store_w.serve_get(req),
            "DELETE" => store_w.serve_delete(req),
            _ => rouille::Response::empty_400(),
        };

        if store_w.config.persistence {
            if let Err(e) = store_w.persist_if_needed() {
                error!("Store failed: {}", e);
            }
        }

        if resp.is_error() {
            warn!("Error resp: {}", resp.status_code);
        }

        decorate_response(resp)
    });
}

fn decorate_response(resp : Response) -> Response {
    resp.without_header("Server")
        .with_additional_header("Server", "postit.rs")
        .with_additional_header("Access-Control-Allow-Origin", "*")
        .with_additional_header("X-Version", env!("CARGO_PKG_VERSION"))
}

type PostsMap = HashMap<PostId, Post>;
type DataMap = HashMap<DataHash, (usize, Vec<u8>)>;

#[derive(Debug, Serialize, Deserialize)]
struct Repository {
    #[serde(skip)]
    config: Config,
    /// Flag that the repository needs saving
    #[serde(skip)]
    dirty: bool,
    /// Stored posts
    posts: PostsMap,
    /// Post data - (use_count, data)
    data: DataMap,
    /// Time of last expired posts GC
    #[serde(with = "serde_chrono_datetime_as_unix")]
    last_gc_time: DateTime<Utc>,
}

impl Repository {
    /// New instance
    fn new(config: Config) -> Self {
        Repository {
            config,
            dirty: false,
            posts: Default::default(),
            data: Default::default(),
            last_gc_time: Utc::now(),
        }
    }

    fn persist_if_needed(&mut self) -> anyhow::Result<()> {
        if self.dirty {
            self.persist()
        } else {
            Ok(())
        }
    }

    /// Store to a file
    fn persist(&mut self) -> anyhow::Result<()> {
        debug!("Persist to file: {}", self.config.persist_file);

        self.dirty = false;
        let file = OpenOptions::new()
            .truncate(true)
            .write(true)
            .create(true)
            .open(&self.config.persist_file)?;

        if self.config.compression {
            let flate = flate2::write::DeflateEncoder::new(file, flate2::Compression::best());
            bincode::serialize_into(flate, self)?;
        } else {
            bincode::serialize_into(file, self)?;
        }
        Ok(())
    }

    /// Load from a file
    fn load(&mut self) -> anyhow::Result<()> {
        debug!("Load from file: {}", self.config.persist_file);

        let file = OpenOptions::new()
            .read(true)
            .open(&self.config.persist_file)?;

        let result: Repository = if self.config.compression {
            let flate = flate2::read::DeflateDecoder::new(file);
            bincode::deserialize_from(flate)?
        } else {
            bincode::deserialize_from(file)?
        };

        let old_config = self.config.clone();
        std::mem::replace(self, result);
        self.config = old_config;
        self.dirty = false;
        Ok(())
    }

    /// Serve a DELETE request
    fn serve_delete(&mut self, req: &Request) -> Response {
        let post_id = match self.request_to_post_id(req, true) {
            Ok(Some(pid)) => pid,
            Ok(None) => return error_with_text(400, "File ID required."),
            Err(resp) => return resp,
        };

        self.delete_post(post_id);

        Response::text("Deleted.")
    }

    /// Serve a POST or PUT request
    ///
    /// POST inserts a new record
    /// PUT updates a record
    fn serve_post_put(&mut self, req: &Request) -> Response {
        let is_post = req.method() == "POST";
        let is_put = req.method() == "PUT";

        // Post ID is empty for POST, set for PUT
        let post_id = match self.request_to_post_id(req, true) {
            Ok(pid) => {
                if is_put && pid.is_none() {
                    warn!("PUT without ID!");
                    return error_with_text(400, "PUT requires a file ID!");
                } else if is_post && pid.is_some() {
                    warn!("POST with ID!");
                    return error_with_text(400, "Use PUT to update a file!");
                }

                pid
            }
            Err(resp) => return resp,
        };

        debug!("Submit new data, post ID: {:?}", post_id);

        let mut data = vec![];
        if let Some(body) = req.data() {
            // Read up to 1 byte past the limit to catch too large uploads.
            // We can't reply on the "Length" field, which is not present with chunked encoding.
            body.take(self.config.max_file_size as u64 + 1)
                .read_to_end(&mut data)
                .unwrap();

            if is_post && data.len() == 0 {
                warn!("Empty body!");
                return error_with_text(400, "Empty body!");
            } else if data.len() > self.config.max_file_size {
                warn!("Upload too large!");
                return empty_error(413);
            }
        } else {
            // Should not be possible
            panic!("Req data None!");
        }

        // Convert "application/x-www-form-urlencoded" to text/plain (CURL uses this)
        // NOTE: rouille does NOT parse urlencoded, we will serve the encoded format back if really used.
        let mime = match req.header("Content-Type") {
            None => None,
            Some("application/x-www-form-urlencoded") => None,
            Some(v) => Some(v),
        };

        let expiry = req.get_param(GET_EXPIRY);
        let mut expiry_s = expiry.as_ref().map(|s| s.as_str());
        if expiry_s.is_none() {
            expiry_s = req.header(HDR_EXPIRY);
        }

        let expiry = match expiry_s {
            Some(text) => match text.parse() {
                Ok(v) => {
                    let dur = Duration::from_secs(v);
                    if dur > self.config.max_expiry {
                        return error_with_text(
                            400,
                            format!(
                                "Expiration time {} out of allowed range 0-{} s",
                                v,
                                self.config.max_expiry.as_secs()
                            ),
                        );
                    }
                    Some(dur)
                }
                Err(_) => {
                    return error_with_text(
                        400,
                        "Malformed expiration, use relative time in seconds.",
                    );
                }
            },
            None => None,
        };

        let the_id;

        let resp = if let Some(id) = post_id {
            // UPDATE
            self.update(id, data, mime, expiry);
            the_id = id;
            Response::text("Updated OK.")
        } else {
            // INSERT
            let (id, secret) = self.insert(data, mime, expiry.unwrap_or(self.config.default_expiry));
            the_id = id;

            Response::text(format!("{:016x}", the_id))
                .with_additional_header(HDR_SECRET, format!("{:016x}", secret))
        };

        // add the X-Expires header to the response
        let post = self.posts.get(&the_id).unwrap();
        resp.with_additional_header(HDR_EXPIRY, post.time_remains().as_secs().to_string())
    }

    /// Serve a GET request
    fn serve_get(&mut self, req: &Request) -> Response {
        let post_id = match self.request_to_post_id(req, false) {
            Ok(Some(pid)) => pid,
            Ok(None) => return error_with_text(400, "File ID required."),
            Err(resp) => return resp,
        };

        if let Some(post) = self.posts.get(&post_id) {
            if post.is_expired() {
                warn!("GET of expired post!");
                Response::empty_404()
            } else {
                let data = match self.data.get(&post.hash) {
                    Some((_uses, data)) => data,
                    None => {
                        error!("No matching data!");
                        return error_with_text(500, "File data lost.");
                    }
                };

                let seconds_remains = post.expires.signed_duration_since(Utc::now())
                    .num_seconds();

                let headers = vec![
                    (
                        "Content-Type".into(),
                        format!("{}; charset=utf8", post.mime).into(),
                    ),
                    (
                        "Cache-Control".into(),
                        format!("public, max-age={}", seconds_remains).into()
                    ),
                    (
                        HDR_EXPIRY.into(),
                        seconds_remains.to_string().into()
                    )
                ];

                Response {
                    status_code: 200,
                    headers,
                    data: ResponseBody::from_data(data.clone()),
                    upgrade: None,
                }
            }
        } else {
            warn!("No such post!");
            Response::empty_404()
        }
    }

    /// Extract post ID from a request.
    ///
    /// if `check_secret` is true, ensure a `X-Secret` header contains a valid write token
    /// for the post ID.
    fn request_to_post_id(
        &self,
        req: &Request,
        check_secret: bool,
    ) -> Result<Option<PostId>, Response> {
        let url = req.url();
        let stripped = url.trim_matches('/');

        if stripped.is_empty() {
            debug!("No ID given");
            return Ok(None);
        }

        if stripped.len() != 16 {
            warn!("Bad ID len!");
            return Err(Response::empty_404());
        }

        let id = match u64::from_str_radix(stripped, 16) {
            Ok(bytes) => bytes,
            Err(_) => {
                warn!("ID parsing error: {}", stripped);
                return Err(Response::empty_404());
            }
        };

        if check_secret {
            // Check the write token
            match self.posts.get(&id) {
                None => {
                    warn!("ID {} does not exist!", id);
                    return Err(error_with_text(404, "No file with this ID!"));
                }
                Some(post) => {
                    if post.is_expired() {
                        warn!("Access of expired file {}!", id);
                        return Err(error_with_text(404, "No file with this ID!"));
                    }

                    let secret = req.get_param(GET_SECRET);
                    let mut secret_str = secret.as_ref().map(|s| s.as_str());

                    if secret_str.is_none() {
                        secret_str = req.header(HDR_SECRET);
                    }

                    let secret: u64 =
                        match secret_str.map(|v| u64::from_str_radix(v, 16)) {
                            Some(Ok(bytes)) => bytes,
                            None => {
                                warn!("Missing secret token!");
                                return Err(error_with_text(400, "Secret token required!"));
                            }
                            Some(Err(e)) => {
                                warn!("Token parse error: {:?}", e);
                                return Err(error_with_text(400, "Bad secret token format!"));
                            }
                        };

                    if post.secret != secret {
                        warn!("Secret token mismatch");
                        return Err(error_with_text(401, "Invalid secret token!"));
                    }
                }
            }
        }

        // secret is now validated and we got an ID
        Ok(Some(id))
    }

    /// Drop expired posts, if cleaning is due
    fn gc_expired_posts_if_needed(&mut self) {
        if Utc::now()
            .signed_duration_since(self.last_gc_time)
            .to_std()
            .unwrap_or_default()
            > self.config.expired_gc_interval
        {
            self.gc_expired_posts();
            self.last_gc_time = Utc::now();
        }
    }

    /// Drop expired posts
    fn gc_expired_posts(&mut self) {
        debug!("GC expired uploads");

        let mut to_rm = vec![];
        for post in &self.posts {
            if post.1.is_expired() {
                to_rm.push(*post.0);
            }
        }

        if !to_rm.is_empty() {
            self.dirty = true;
        }

        for id in to_rm {
            debug!("Drop post ID {:016x}", id);
            if let Some(post) = self.posts.remove(&id) {
                Self::drop_data_or_decrement_rc(&mut self.data, post.hash);
            }
        }
    }

    /// Get hash of a byte vector (for deduplication)
    fn hash_data(data: &Vec<u8>) -> DataHash {
        let mut hasher = SipHasher::new();
        data.hash(&mut hasher);
        hasher.finish()
    }

    /// Store a data buffer under a given hash.
    /// If the buffer is already present in the repository, increment its use count.
    fn store_data_or_increment_rc(data_map: &mut DataMap, hash: u64, data: Vec<u8>) {
        match data_map.get_mut(&hash) {
            None => {
                debug!("Store new data hash #{:016x}", hash);
                data_map.insert(hash, (1, data));
            }
            Some(entry) => {
                debug!("Link new use of data hash #{:016x}", hash);
                entry.0 += 1; // increment use counter
            }
        }
    }

    /// Drop a data record with the given hash, or decrement its use count if there are other uses
    fn drop_data_or_decrement_rc(data_map: &mut DataMap, hash: u64) {
        if let Some(old_data) = data_map.get_mut(&hash) {
            if old_data.0 > 1 {
                old_data.0 -= 1;
                debug!(
                    "Unlink use of data hash #{:016x} ({} remain)",
                    hash, old_data.0
                );
            } else {
                debug!("Drop data hash #{:016x}", hash);
                data_map.remove(&hash);
            }
        }
    }

    /// Insert a post
    fn insert(&mut self, data: Vec<u8>, mime: Option<&str>, expires: Duration) -> (PostId, Secret) {
        info!(
            "Insert post with data of len {} bytes, mime {}, expiry {:?}",
            data.len(),
            mime.unwrap_or("unspecified"),
            expires
        );

        let hash = Self::hash_data(&data);

        let mime = match mime {
            None => Mime::from(tree_magic::from_u8(&data)),
            Some(explicit) => Mime::from(explicit),
        };

        Self::store_data_or_increment_rc(&mut self.data, hash, data);

        let post_id = loop {
            let id = OsRng.gen();
            if !self.posts.contains_key(&id) {
                break id;
            }
        };

        let secret = OsRng.gen();

        debug!("File ID = #{:016x} (http://{}:{}/{:016x})", post_id, self.config.host, self.config.port, post_id);
        debug!("Data hash = #{:016x}, mime {}", hash, mime);
        debug!("Secret = #{:016x}", secret);

        self.posts.insert(
            post_id,
            Post {
                mime,
                hash,
                secret,
                expires: Utc::now() + chrono::Duration::from_std(expires).unwrap(), // this is safe unless mis-configured
            },
        );

        self.dirty = true;

        (post_id, secret)
    }

    /// Update a post by ID
    fn update(&mut self, id: PostId, data: Vec<u8>, mime: Option<&str>, expires: Option<Duration>) {
        info!(
            "Update post id #{:016x} with data of len {} bytes, mime {}, expiry {}",
            id,
            data.len(),
            mime.unwrap_or("unchanged"),
            expires
                .map(|v| Cow::Owned(format!("{:?}", v)))
                .unwrap_or("unchanged".into())
        );

        let post = self.posts.get_mut(&id).unwrap(); // post existence was checked before

        if !data.is_empty() {
            let hash = Self::hash_data(&data);

            if hash != post.hash {
                debug!("Data hash = #{:016x} (content changed)", hash);

                Self::drop_data_or_decrement_rc(&mut self.data, post.hash);
                Self::store_data_or_increment_rc(&mut self.data, hash, data);
                post.hash = hash;
                self.dirty = true;
            } else {
                debug!("Data hash = #{:016x} (no change)", hash);
            }
        }

        if let Some(mime) = mime {
            let new_mime = Mime::from(mime);
            if post.mime != new_mime {
                debug!("Content type changed to {}", mime);
                post.mime = new_mime;
                self.dirty = true;
            }
        }

        if let Some(exp) = expires {
            debug!("Expiration changed to {:?} from now", exp);
            post.expires = Utc::now() + chrono::Duration::from_std(exp).unwrap(); // this is safe unless mis-configured;
            self.dirty = true;
        }
    }

    /// Delete a post by ID
    fn delete_post(&mut self, id: PostId) {
        info!("Delete post id #{:016x}", id);

        let post = self.posts.remove(&id).unwrap(); // post existence was checked before
        Self::drop_data_or_decrement_rc(&mut self.data, post.hash);

        self.dirty = true;
    }
}

/// Serialize chrono unix timestamp as seconds
mod serde_chrono_datetime_as_unix {
    use chrono::{DateTime, NaiveDateTime, Utc};
    use serde::{self, Deserialize, Deserializer, Serializer};

    pub fn serialize<S>(value: &DateTime<Utc>, se: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        se.serialize_i64(value.naive_utc().timestamp())
    }

    pub fn deserialize<'de, D>(de: D) -> Result<DateTime<Utc>, D::Error>
    where
        D: Deserializer<'de>,
    {
        let ts: i64 = i64::deserialize(de)?;
        Ok(DateTime::from_utc(
            NaiveDateTime::from_timestamp(ts, 0),
            Utc,
        ))
    }
}

fn error_with_text(code: u16, text: impl Into<String>) -> Response {
    Response {
        status_code: code,
        headers: vec![("Content-Type".into(), "text/plain; charset=utf8".into())],
        data: rouille::ResponseBody::from_string(text),
        upgrade: None,
    }
}

fn empty_error(code: u16) -> Response {
    Response {
        status_code: code,
        headers: vec![("Content-Type".into(), "text/plain; charset=utf8".into())],
        data: rouille::ResponseBody::empty(),
        upgrade: None,
    }
}