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use crate::analysis;
use crate::traversal::{Action, Named, VisResult, Visitor};
use calyx_ir::{self as ir, LibrarySignatures};

#[derive(Default)]
/// Transforms all `par` into `seq`. Uses [analysis::ControlOrder] to get a
/// sequentialization of `par` such that the program still computes the same
/// value. When there is no such sequentialization, errors out.
///
///
/// # Example
/// ```
/// par {
///     par { A; B }
///     C;
/// }
/// ```
/// into
/// ```
/// seq { seq { A; B } C; }
/// ```
///
/// To remove uneccessarily nested `par` blocks, run collapse-control.
pub struct ParToSeq;

impl Named for ParToSeq {
    fn name() -> &'static str {
        "par-to-seq"
    }

    fn description() -> &'static str {
        "Transform `par` blocks to `seq`"
    }
}

impl Visitor for ParToSeq {
    /// Collapse par { par { A }; B } into par { A; B }.
    fn finish_par(
        &mut self,
        s: &mut ir::Par,
        _comp: &mut ir::Component,
        _c: &LibrarySignatures,
        _comps: &[ir::Component],
    ) -> VisResult {
        let total_order =
            analysis::ControlOrder::<true>::get_total_order(s.stmts.drain(..))?;
        let par = ir::Control::seq(total_order);
        Ok(Action::change(par))
    }
}