//! Constraint trait, and some common constraints.
//!
//! Note that all puzzle states visited during the solution search
//! share the same set of constraints.  This means that you cannot
//! store additional information about the state (e.g. caches) in the
//! constraint to reuse later.

use ::{PuzzleSearch,Val,VarToken};

/// Constraint trait.
pub trait Constraint {
    /// Applied after a variable has been assigned.
    ///
    /// Returns true if the search should continue with these variable
    /// assignments, or false if the constraint found a contradiction.
    fn on_assigned(&self, _search: &mut PuzzleSearch, _var: VarToken, _val: Val)
            -> bool {
        true
    }

    /// Applied after a variable's candidates has been modified.
    ///
    /// Returns true if the search should continue with these variable
    /// assignments, or false if the constraint found a contradiction.
    fn on_updated(&self, _search: &mut PuzzleSearch) -> bool {
        true
    }
}

pub use self::alldifferent::AllDifferent;

mod alldifferent;