//! Defines the runtime representation of a partially applied primitive operation.

use std::rc::Rc;

use derive_more::Constructor;

use nixjit_error::Result;
use nixjit_ir::PrimOpId;

use super::Value;
use crate::EvalContext;

pub type Args = smallvec::SmallVec<[Value; 2]>;

/// Represents a partially applied primitive operation (builtin function).
///
/// This struct holds the state of a primop that has received some, but not
/// all, of its required arguments.
#[derive(Debug, Clone, Constructor)]
pub struct PrimOpApp {
    /// The number of remaining arguments the primop expects.
    arity: usize,
    /// The unique ID of the primop.
    id: PrimOpId,
    /// The arguments that have already been applied.
    args: Args,
}

impl PrimOpApp {
    /// Applies more arguments to a partially applied primop.
    ///
    /// If enough arguments are provided to satisfy the primop's arity, it is
    /// executed. Otherwise, it returns a new `PrimOpApp` with the combined
    /// arguments.
    pub fn call(self: Rc<Self>, arg: Value, ctx: &mut impl EvalContext) -> Result<Value> {
        let mut primop = Rc::unwrap_or_clone(self);
        if primop.arity == 1 {
            primop.args.push(arg);
            ctx.call_primop(primop.id, primop.args)
        } else {
            primop.args.push(arg);
            primop.arity -= 1;
            Ok(Value::PrimOpApp(primop.into()))
        }
    }
}