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    /*
     * mCaptcha - A proof of work based DoS protection system
     * Copyright © 2021 Aravinth Manivannan <realravinth@batsense.net>
     *
     * This program is free software: you can redistribute it and/or modify
     * it under the terms of the GNU Affero General Public License as
     * published by the Free Software Foundation, either version 3 of the
     * License, or (at your option) any later version.
     *
     * This program is distributed in the hope that it will be useful,
     * but WITHOUT ANY WARRANTY; without even the implied warranty of
     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     * GNU Affero General Public License for more details.
     *
     * You should have received a copy of the GNU Affero General Public License
     * along with this program.  If not, see <http://www.gnu.org/licenses/>.
     */
    //! MCaptcha actor module that manages defense levels
    //!
    //! ## Usage:
    //! ```rust
    //! use m_captcha::{mcaptcha::Visitor, MCaptchaBuilder, cache::HashCache, LevelBuilder, DefenseBuilder};
    //! // traits from actix needs to be in scope for starting actor
    //! use actix::prelude::*;
    //!
    //! #[actix_rt::main]
    //! async fn main() -> std::io::Result<()> {
    //!     // configure defense
    //!     let defense = DefenseBuilder::default()
    //!         // add as many levels as you see fit
    //!         .add_level(
    //!             LevelBuilder::default()
    //!                 // visitor_threshold is the threshold/limit at which
    //!                 // mCaptcha will adjust difficulty levels
    //!                 // it is advisable to set small values for the first
    //!                 // levels visitor_threshold and difficulty_factor
    //!                 // as this will be the work that clients will be
    //!                 // computing when there's no load
    //!                 .visitor_threshold(50)
    //!                 .difficulty_factor(500)
    //!                 .unwrap()
    //!                 .build()
    //!                 .unwrap(),
    //!         )
    //!         .unwrap()
    //!         .add_level(
    //!             LevelBuilder::default()
    //!                 .visitor_threshold(5000)
    //!                 .difficulty_factor(50000)
    //!                 .unwrap()
    //!                 .build()
    //!                 .unwrap(),
    //!         )
    //!         .unwrap()
    //!         .build()
    //!         .unwrap();
    //!
    //!     // create and start MCaptcha actor
    //!     //let cache = HashCache::default().start();
    //!     let mcaptcha = MCaptchaBuilder::default()
    //!         .defense(defense)
    //!         // leaky bucket algorithm's emission interval
    //!         .duration(30)
    //!         .build()
    //!         .unwrap()
    //!         .start();
    //!
    //!     // increment count when user visits protected routes
    //!     mcaptcha.send(Visitor).await.unwrap();
    //!
    //!     Ok(())
    //! }
    //! ```

    use std::time::Duration;

    use actix::dev::*;
    use derive_builder::Builder;

    use crate::defense::Defense;

    /// This struct represents the mCaptcha state and is used
    /// to configure leaky-bucket lifetime and manage defense
    #[derive(Clone, Debug, Builder)]
    pub struct MCaptcha {
        #[builder(default = "0", setter(skip))]
        visitor_threshold: u32,
        defense: Defense,
        duration: u64,
    }

    impl MCaptcha {
        /// incerment visiotr count by one
        pub fn add_visitor(&mut self) {
            self.visitor_threshold += 1;
            if self.visitor_threshold > self.defense.visitor_threshold() {
                self.defense.tighten_up();
            } else {
                self.defense.loosen_up();
            }
        }

        /// deccerment visiotr count by one
        pub fn decrement_visiotr(&mut self) {
            if self.visitor_threshold > 0 {
                self.visitor_threshold -= 1;
            }
        }

        /// get current difficulty factor
        pub fn get_difficulty(&self) -> u32 {
            self.defense.get_difficulty()
        }

        /// get [MCaptcha]'s lifetime
        pub fn get_duration(&self) -> u64 {
            self.duration
        }
    }
    impl Actor for MCaptcha {
        type Context = Context<Self>;
    }

    /// Message to decrement the visitor count
    #[derive(Message)]
    #[rtype(result = "()")]
    struct DeleteVisitor;

    impl Handler<DeleteVisitor> for MCaptcha {
        type Result = ();
        fn handle(&mut self, _msg: DeleteVisitor, _ctx: &mut Self::Context) -> Self::Result {
            self.decrement_visiotr();
        }
    }

    /// Message to increment the visitor count
    /// returns difficulty factor and lifetime
    #[derive(Message)]
    #[rtype(result = "VisitorResult")]
    pub struct Visitor;

    /// Struct representing the return datatime of
    /// [Visitor] message. Contains MCaptcha lifetime
    /// and difficulty factor
    pub struct VisitorResult {
        pub duration: u64,
        pub difficulty_factor: u32,
    }

    impl VisitorResult {
        fn new(m: &MCaptcha) -> Self {
            VisitorResult {
                duration: m.get_duration(),
                difficulty_factor: m.get_difficulty(),
            }
        }
    }

    impl Handler<Visitor> for MCaptcha {
        type Result = MessageResult<Visitor>;

        fn handle(&mut self, _: Visitor, ctx: &mut Self::Context) -> Self::Result {
            use actix::clock::delay_for;

            let addr = ctx.address();

            let duration: Duration = Duration::new(self.duration.clone(), 0);
            let wait_for = async move {
                delay_for(duration).await;
                addr.send(DeleteVisitor).await.unwrap();
            }
            .into_actor(self);
            ctx.spawn(wait_for);

            self.add_visitor();
            MessageResult(VisitorResult::new(&self))
        }
    }

    #[cfg(test)]
    pub mod tests {
        use super::*;
        use crate::defense::*;

        // constants for testing
        // (visitor count, level)
        pub const LEVEL_1: (u32, u32) = (50, 50);
        pub const LEVEL_2: (u32, u32) = (500, 500);
        pub const DURATION: u64 = 10;

        type MyActor = Addr<MCaptcha>;

        pub fn get_defense() -> Defense {
            DefenseBuilder::default()
                .add_level(
                    LevelBuilder::default()
                        .visitor_threshold(LEVEL_1.0)
                        .difficulty_factor(LEVEL_1.1)
                        .unwrap()
                        .build()
                        .unwrap(),
                )
                .unwrap()
                .add_level(
                    LevelBuilder::default()
                        .visitor_threshold(LEVEL_2.0)
                        .difficulty_factor(LEVEL_2.1)
                        .unwrap()
                        .build()
                        .unwrap(),
                )
                .unwrap()
                .build()
                .unwrap()
        }

        async fn race(addr: Addr<MCaptcha>, count: (u32, u32)) {
            for _ in 0..count.0 as usize - 1 {
                let _ = addr.send(Visitor).await.unwrap();
            }
        }

        pub fn get_counter() -> MCaptcha {
            MCaptchaBuilder::default()
                .defense(get_defense())
                .duration(DURATION)
                .build()
                .unwrap()
        }

        #[actix_rt::test]
        async fn counter_defense_tightenup_works() {
            let addr: MyActor = get_counter().start();

            let mut mcaptcha = addr.send(Visitor).await.unwrap();
            assert_eq!(mcaptcha.difficulty_factor, LEVEL_1.0);

            race(addr.clone(), LEVEL_2).await;
            mcaptcha = addr.send(Visitor).await.unwrap();
            assert_eq!(mcaptcha.difficulty_factor, LEVEL_2.1);
        }

        #[actix_rt::test]
        async fn counter_defense_loosenup_works() {
            use actix::clock::delay_for;
            let addr: MyActor = get_counter().start();

            race(addr.clone(), LEVEL_2).await;
            race(addr.clone(), LEVEL_2).await;
            let mut mcaptcha = addr.send(Visitor).await.unwrap();
            assert_eq!(mcaptcha.difficulty_factor, LEVEL_2.1);

            let duration = Duration::new(DURATION, 0);
            delay_for(duration).await;

            mcaptcha = addr.send(Visitor).await.unwrap();
            assert_eq!(mcaptcha.difficulty_factor, LEVEL_1.1);
        }
    }