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use std::collections::HashSet;
use std::convert::TryFrom;
use std::fmt;
use std::ops::Deref;

use async_trait::async_trait;
use destream::{de, en};
use safecast::{Match, TryCastFrom};

use tc_error::TCResult;
use tcgeneric::{Id, Instance, Tuple};

use crate::route::Public;
use crate::scalar::{Scalar, Scope, Value};
use crate::state::State;
use crate::txn::Txn;

use super::{Refer, TCRef};

/// A switch-case flow control
#[derive(Clone, Eq, PartialEq)]
pub struct Case {
    cond: TCRef,
    switch: Tuple<Scalar>,
    case: Tuple<Scalar>,
}

#[async_trait]
impl Refer for Case {
    fn requires(&self, deps: &mut HashSet<Id>) {
        self.cond.requires(deps);

        for switch in self.switch.iter() {
            switch.requires(deps);
        }
    }

    async fn resolve<'a, T: Public + Instance>(
        mut self,
        context: &'a Scope<'a, T>,
        txn: &'a Txn,
    ) -> TCResult<State> {
        assert_eq!(self.switch.len() + 1, self.case.len());

        let cond = self.cond.resolve(context, txn).await?;
        let cond = Value::try_from(cond)?;
        for (i, switch) in self.switch.into_iter().enumerate() {
            let switch = switch.resolve(context, txn).await?;
            let switch = Value::try_from(switch)?;
            if cond == switch {
                return self.case.remove(i).resolve(context, txn).await;
            }
        }

        let case = self.case.pop().unwrap();
        case.resolve(context, txn).await
    }
}

impl TryCastFrom<Scalar> for Case {
    fn can_cast_from(scalar: &Scalar) -> bool {
        scalar.matches::<(TCRef, Tuple<Scalar>, Tuple<Scalar>)>()
    }

    fn opt_cast_from(scalar: Scalar) -> Option<Self> {
        if let Some((cond, switch, case)) =
            <(TCRef, Tuple<Scalar>, Tuple<Scalar>)>::opt_cast_from(scalar)
        {
            if case.len() == switch.len() + 1 {
                Some(Case { cond, switch, case })
            } else {
                None
            }
        } else {
            None
        }
    }
}

#[async_trait]
impl de::FromStream for Case {
    type Context = ();

    async fn from_stream<D: de::Decoder>(context: (), decoder: &mut D) -> Result<Self, D::Error> {
        let (cond, switch, case) =
            <(TCRef, Tuple<Scalar>, Tuple<Scalar>) as de::FromStream>::from_stream(
                context, decoder,
            )
            .await?;

        if case.len() == switch.len() + 1 {
            Ok(Self { cond, switch, case })
        } else {
            Err(de::Error::custom(
                "case length must equal switch length plus one",
            ))
        }
    }
}

impl<'en> en::IntoStream<'en> for Case {
    fn into_stream<E: en::Encoder<'en>>(self, encoder: E) -> Result<E::Ok, E::Error> {
        (self.cond, self.switch.into_inner(), self.case.into_inner()).into_stream(encoder)
    }
}

impl<'en> en::ToStream<'en> for Case {
    fn to_stream<E: en::Encoder<'en>>(&'en self, encoder: E) -> Result<E::Ok, E::Error> {
        en::IntoStream::into_stream(
            (&self.cond, self.switch.deref(), self.case.deref()),
            encoder,
        )
    }
}

impl fmt::Display for Case {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "switch ({})...", self.cond)
    }
}