// Root of the ASG.
//
//  Copyright (C) 2014-2023 Ryan Specialty, LLC.
//
//  This file is part of TAME.
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

//! Root node of the ASG.

use std::fmt::Display;

use super::{
    Ident, Object, ObjectIndex, ObjectRel, ObjectRelFrom, ObjectRelTy,
    ObjectRelatable, Pkg,
};

#[cfg(doc)]
use super::ObjectKind;

/// A unit [`Object`] type representing the root node.
///
/// This exists for consistency with the rest of the object API,
///   and for use with [`ObjectIndex`].
#[derive(Debug, PartialEq)]
pub struct Root;

impl Display for Root {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "ASG root")
    }
}

/// Subset of [`ObjectKind`]s that are valid targets for edges from
///   [`Ident`].
///
/// See [`ObjectRel`] for more information.
#[derive(Debug, PartialEq, Eq)]
pub enum RootRel {
    Pkg(ObjectIndex<Pkg>),
    Ident(ObjectIndex<Ident>),
}

impl ObjectRel<Root> for RootRel {
    fn narrow<OB: ObjectRelFrom<Root> + ObjectRelatable>(
        self,
    ) -> Option<ObjectIndex<OB>> {
        match self {
            Self::Ident(oi) => oi.filter_rel(),
            Self::Pkg(oi) => oi.filter_rel(),
        }
    }

    /// The root of the graph by definition has no cross edges.
    fn is_cross_edge(&self) -> bool {
        false
    }
}

impl ObjectRelatable for Root {
    type Rel = RootRel;

    fn rel_ty() -> ObjectRelTy {
        ObjectRelTy::Root
    }

    fn new_rel_dyn(
        ty: ObjectRelTy,
        oi: ObjectIndex<Object>,
    ) -> Option<RootRel> {
        match ty {
            ObjectRelTy::Root => None,
            ObjectRelTy::Pkg => Some(RootRel::Pkg(oi.must_narrow_into())),
            ObjectRelTy::Ident => Some(RootRel::Ident(oi.must_narrow_into())),
            ObjectRelTy::Expr => None,
            ObjectRelTy::Tpl => None,
        }
    }
}

impl From<ObjectIndex<Pkg>> for RootRel {
    fn from(value: ObjectIndex<Pkg>) -> Self {
        Self::Pkg(value)
    }
}

impl From<ObjectIndex<Ident>> for RootRel {
    fn from(value: ObjectIndex<Ident>) -> Self {
        Self::Ident(value)
    }
}