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//! Projection expression plan.

use timely::dataflow::scopes::child::Iterative;
use timely::dataflow::Scope;
use timely::order::TotalOrder;
use timely::progress::Timestamp;

use differential_dataflow::lattice::Lattice;

use crate::binding::Binding;
use crate::plan::{next_id, Dependencies, ImplContext, Implementable};
use crate::{Aid, Eid, Value, Var};
use crate::{CollectionRelation, Relation, ShutdownHandle, VariableMap};

/// A plan stage projecting its source to only the specified sequence
/// of variables. Throws on unbound variables. Frontends are responsible
/// for ensuring that the source binds all requested variables.
#[derive(Hash, PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
pub struct Project<P: Implementable> {
    /// TODO
    pub variables: Vec<Var>,
    /// Plan for the data source.
    pub plan: Box<P>,
}

impl<P: Implementable> Implementable for Project<P> {
    fn dependencies(&self) -> Dependencies {
        self.plan.dependencies()
    }

    fn into_bindings(&self) -> Vec<Binding> {
        self.plan.into_bindings()
    }

    fn datafy(&self) -> Vec<(Eid, Aid, Value)> {
        let eid = next_id();
        let mut data = self.plan.datafy();

        if data.is_empty() {
            Vec::new()
        } else {
            let child_eid = data[0].0;

            data.push((eid, "df.project/binding".to_string(), Value::Eid(child_eid)));

            data
        }
    }

    fn implement<'b, T, I, S>(
        &self,
        nested: &mut Iterative<'b, S, u64>,
        local_arrangements: &VariableMap<Iterative<'b, S, u64>>,
        context: &mut I,
    ) -> (CollectionRelation<'b, S>, ShutdownHandle)
    where
        T: Timestamp + Lattice + TotalOrder,
        I: ImplContext<T>,
        S: Scope<Timestamp = T>,
    {
        let (relation, shutdown_handle) = self.plan.implement(nested, local_arrangements, context);

        let projected = CollectionRelation {
            variables: self.variables.to_vec(),
            tuples: relation.projected(&self.variables),
        };

        (projected, shutdown_handle)
    }
}