//! A trait used to interact with the internal state of nodes within the [`Bracket`]
//!
//! [`Bracket`]: crate::bracket::Bracket

use crate::error::Error;

use anyhow::Context;
use serde::{de::DeserializeOwned, Deserialize, Serialize};
use std::fmt::Debug;
use uuid::Uuid;
use async_trait::async_trait;

/// An enum used to control the state of a [`GeneticNode`]
///
/// [`GeneticNode`]: crate::bracket::genetic_node
#[derive(Debug, Serialize, Deserialize, PartialEq, Clone, Copy)]
pub enum GeneticState {
    /// The node and it's data have not finished initializing
    Initialize,
    /// The node is currently simulating a round against target data to determine the fitness of the population
    Simulate,
    /// The node is currently mutating members of it's population and breeding new members
    Mutate,
    /// The node has finished processing for a given number of iterations
    Finish,
}

#[derive(Clone, Debug)]
pub struct GeneticNodeContext<S> {
    pub generation: u64,
    pub max_generations: u64,
    pub id: Uuid,
    pub gemla_context: S
}

/// A trait used to interact with the internal state of nodes within the [`Bracket`]
///
/// [`Bracket`]: crate::bracket::Bracket
#[async_trait]
pub trait GeneticNode : Send {
    type Context;

    /// Initializes a new instance of a [`GeneticState`].
    ///
    /// # Examples
    /// TODO
    async fn initialize(context: GeneticNodeContext<Self::Context>) -> Result<Box<Self>, Error>;

    async fn simulate(&mut self, context: GeneticNodeContext<Self::Context>) -> Result<(), Error>;

    /// Mutates members in a population and/or crossbreeds them to produce new offspring.
    ///
    /// # Examples
    /// TODO
    async fn mutate(&mut self, context: GeneticNodeContext<Self::Context>) -> Result<(), Error>;

    async fn merge(left: &Self, right: &Self, id: &Uuid, context: Self::Context) -> Result<Box<Self>, Error>;
}

/// Used externally to wrap a node implementing the [`GeneticNode`] trait. Processes state transitions for the given node as
/// well as signal recovery. Transition states are given by [`GeneticState`]
#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
pub struct GeneticNodeWrapper<T> {
    node: Option<T>,
    state: GeneticState,
    generation: u64,
    max_generations: u64,
    id: Uuid,
}

impl<T> Default for GeneticNodeWrapper<T> {
    fn default() -> Self {
        GeneticNodeWrapper {
            node: None,
            state: GeneticState::Initialize,
            generation: 1,
            max_generations: 1,
            id: Uuid::new_v4(),
        }
    }
}

impl<T> GeneticNodeWrapper<T>
where
    T: GeneticNode + Debug + Send,
    T::Context: Send + Sync + Clone + Debug + Serialize + DeserializeOwned + 'static + Default,
{
    pub fn new(max_generations: u64) -> Self {
        GeneticNodeWrapper::<T> {
            max_generations,
            ..Default::default()
        }
    }

    pub fn from(data: T, max_generations: u64, id: Uuid) -> Self {
        GeneticNodeWrapper {
            node: Some(data),
            state: GeneticState::Simulate,
            generation: 1,
            max_generations,
            id,
        }
    }

    pub fn as_ref(&self) -> Option<&T> {
        self.node.as_ref()
    }

    pub fn id(&self) -> Uuid {
        self.id
    }

    pub fn max_generations(&self) -> u64 {
        self.max_generations
    }

    pub fn generation(&self) -> u64 {
        self.generation
    }

    pub fn state(&self) -> GeneticState {
        self.state
    }

    pub async fn process_node(&mut self, gemla_context: T::Context) -> Result<GeneticState, Error> {
        let context = GeneticNodeContext {
            generation: self.generation,
            max_generations: self.max_generations,
            id: self.id,
            gemla_context,
        };

        match (self.state, &mut self.node) {
            (GeneticState::Initialize, _) => {
                self.node = Some(*T::initialize(context.clone()).await?);
                self.state = GeneticState::Simulate;
            }
            (GeneticState::Simulate, Some(n)) => {
                n.simulate(context.clone()).await
                    .with_context(|| format!("Error simulating node: {:?}", self))?;

                self.state = if self.generation >= self.max_generations {
                    GeneticState::Finish
                } else {
                    GeneticState::Mutate
                };
            }
            (GeneticState::Mutate, Some(n)) => {
                n.mutate(context.clone()).await
                    .with_context(|| format!("Error mutating node: {:?}", self))?;

                self.generation += 1;
                self.state = GeneticState::Simulate;
            }
            (GeneticState::Finish, Some(_)) => (),
            _ => panic!("Error processing node {:?}", self.node),
        }

        Ok(self.state)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::error::Error;
    use anyhow::anyhow;
    use async_trait::async_trait;

    #[derive(Deserialize, Serialize, Clone, Debug, PartialEq)]
    struct TestState {
        pub score: f64,
    }

    #[async_trait]
    impl GeneticNode for TestState {
        type Context = ();

        async fn simulate(&mut self, _context: GeneticNodeContext<Self::Context>) -> Result<(), Error> {
            self.score += 1.0;
            Ok(())
        }

        async fn mutate(&mut self, _context: GeneticNodeContext<Self::Context>) -> Result<(), Error> {
            Ok(())
        }

        async fn initialize(_context: GeneticNodeContext<Self::Context>) -> Result<Box<TestState>, Error> {
            Ok(Box::new(TestState { score: 0.0 }))
        }

        async fn merge(_l: &TestState, _r: &TestState, _id: &Uuid, _: Self::Context) -> Result<Box<TestState>, Error> {
            Err(Error::Other(anyhow!("Unable to merge")))
        }
    }

    #[test]
    fn test_new() -> Result<(), Error> {
        let genetic_node = GeneticNodeWrapper::<TestState>::new(10);

        let other_genetic_node = GeneticNodeWrapper::<TestState> {
            node: None,
            state: GeneticState::Initialize,
            generation: 1,
            max_generations: 10,
            id: genetic_node.id(),
        };

        assert_eq!(genetic_node, other_genetic_node);

        Ok(())
    }

    #[test]
    fn test_from() -> Result<(), Error> {
        let val = TestState { score: 0.0 };
        let uuid = Uuid::new_v4();
        let genetic_node = GeneticNodeWrapper::from(val.clone(), 10, uuid);

        let other_genetic_node = GeneticNodeWrapper::<TestState> {
            node: Some(val),
            state: GeneticState::Simulate,
            generation: 1,
            max_generations: 10,
            id: genetic_node.id(),
        };

        assert_eq!(genetic_node, other_genetic_node);

        Ok(())
    }

    #[test]
    fn test_as_ref() -> Result<(), Error> {
        let val = TestState { score: 3.0 };
        let uuid = Uuid::new_v4();
        let genetic_node = GeneticNodeWrapper::from(val.clone(), 10, uuid);

        let ref_value = genetic_node.as_ref().unwrap();

        assert_eq!(*ref_value, val);

        Ok(())
    }

    #[test]
    fn test_id() -> Result<(), Error> {
        let val = TestState { score: 3.0 };
        let uuid = Uuid::new_v4();
        let genetic_node = GeneticNodeWrapper::from(val.clone(), 10, uuid);

        let id_value = genetic_node.id();

        assert_eq!(id_value, uuid);

        Ok(())
    }

    #[test]
    fn test_max_generations() -> Result<(), Error> {
        let val = TestState { score: 3.0 };
        let uuid = Uuid::new_v4();
        let genetic_node = GeneticNodeWrapper::from(val.clone(), 10, uuid);

        let max_generations = genetic_node.max_generations();

        assert_eq!(max_generations, 10);

        Ok(())
    }

    #[test]
    fn test_state() -> Result<(), Error> {
        let val = TestState { score: 3.0 };
        let uuid = Uuid::new_v4();
        let genetic_node = GeneticNodeWrapper::from(val.clone(), 10, uuid);

        let state = genetic_node.state();

        assert_eq!(state, GeneticState::Simulate);

        Ok(())
    }

    #[tokio::test]
    async fn test_process_node() -> Result<(), Error> {
        let mut genetic_node = GeneticNodeWrapper::<TestState>::new(2);

        assert_eq!(genetic_node.state(), GeneticState::Initialize);
        assert_eq!(genetic_node.process_node(()).await?, GeneticState::Simulate);
        assert_eq!(genetic_node.process_node(()).await?, GeneticState::Mutate);
        assert_eq!(genetic_node.process_node(()).await?, GeneticState::Simulate);
        assert_eq!(genetic_node.process_node(()).await?, GeneticState::Finish);
        assert_eq!(genetic_node.process_node(()).await?, GeneticState::Finish);

        Ok(())
    }
}