From c6642268b58916edc394bf3972c9b516f8fb4cad Mon Sep 17 00:00:00 2001
From: artus <artus@landoftheunicorn.hd.free.fr>
Date: Sun, 23 Dec 2018 21:13:06 +0100
Subject: [PATCH] starts basic solver

---
 planner/src/lib.rs    |   4 ++
 planner/src/solver.rs | 115 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+)
 create mode 100644 planner/src/solver.rs

diff --git a/planner/src/lib.rs b/planner/src/lib.rs
index 31e1bb2..f44390b 100644
--- a/planner/src/lib.rs
+++ b/planner/src/lib.rs
@@ -1,3 +1,7 @@
+use std::fmt;
+
+mod solver;
+
 #[cfg(test)]
 mod tests {
     #[test]
diff --git a/planner/src/solver.rs b/planner/src/solver.rs
new file mode 100644
index 0000000..b93f36d
--- /dev/null
+++ b/planner/src/solver.rs
@@ -0,0 +1,115 @@
+use std::fmt;
+use std::clone::Clone;
+use std::collections::HashMap;
+
+#[derive(Clone)]
+struct Domain<V> {
+    values: Vec<V>
+}
+
+impl<V> Domain<V> {
+    fn new(values: Vec<V>) -> Domain<V> {
+        Domain { values }
+    }
+}
+
+impl<V: fmt::Debug> fmt::Debug for Domain<V> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Domain<{:?}>", self.values)
+    }
+}
+
+type AssignMap<'a, V> = HashMap<String, Option<&'a V>>;
+
+/// Returns all possible Updates for next assignements.
+/// They are added to the stack, just after a Clear for the next variable
+fn assign_next<'a,'b, V>(assign: &'b AssignMap<'a, V>, domain: &'a Domain<V>) 
+    -> Option<Vec<Assignment<'a, V>>> 
+    where V: fmt::Debug 
+{
+    // Panics on empty domain
+    if domain.values.is_empty() { panic!("No values in domain : {:?}", domain); };
+
+    if let Some((key,_)) = assign.iter().find(|(_, val)| val.is_none()) {
+        let mut updates = vec![Assignment::Clear(key.clone())];
+        for value in domain.values.iter() {
+            updates.push(Assignment::Update(key.clone(), value));
+        }
+        Some(updates)
+    } else { // End of assignements    
+        None
+    }
+}
+
+/// Check if any constraint is violated
+fn check_consistency<'a, V>(assign: &'a AssignMap<'a, V>, constraint: fn(&AssignMap<'a,V>) -> bool) -> bool {
+    constraint(assign)
+}
+
+enum Assignment<'a, V> {
+    Update(String, &'a V),
+    Clear(String)
+}
+
+
+/// Visit all possible solutions, using a stack.
+/// A single mutable map is used to lay out every outcome.
+/// Using the stack to Update or Clear values : 
+///  - After an Update : run assign_next to stack next updates. If there are none, 
+///  check for consistency, store in solutions if valid and close the branch (Clear)
+///  - After a Clear : simply visit the next node on the stack.
+fn solve_all<'a, V: Clone + fmt::Debug>(mut assign: AssignMap<'a, V>, domain: &'a Domain<V>, is_valid: fn(&AssignMap<'a,V>) -> bool) 
+    -> Vec<AssignMap<'a, V>> 
+{
+    let mut solutions: Vec<AssignMap<V>> = vec![];
+    let mut stack: Vec<Assignment<'a, V>> = vec![];
+    stack.append(&mut assign_next(&assign,domain).unwrap());
+    loop {
+        let node = stack.pop();
+        if node.is_none() { break; };
+        match node.unwrap() {
+            Assignment::Update(key, val) => {
+                *assign.get_mut(&key).unwrap() = Some(val);
+                // Search for next assignments
+                // TODO: handle case of empty domain.values
+                if let Some(mut nodes) = assign_next(&assign, domain) {
+                    stack.append(&mut nodes);
+                } else {
+                    if is_valid(&assign) {
+                        solutions.push(assign.clone());
+                    };
+                };
+            },
+            Assignment::Clear(key) => {
+                *assign.get_mut(&key).unwrap() = None;
+            },
+        };
+    };
+    solutions
+}
+
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solver_find_pairs() {
+        use super::*;
+        // Find all pairs of two differents
+        let assign: AssignMap<i32> = [
+            ("Left".to_string(), None), 
+            ("Right".to_string(), None),
+            ].iter().cloned().collect();
+        let domain = Domain::new(vec![1,2,3]);
+        let constraint = |assign: &AssignMap<i32>| {
+            assign.get("Left").unwrap() == assign.get("Right").unwrap()
+        };
+        let solutions: Vec<AssignMap<i32>> = vec![
+            [("Left".to_string(), Some(&3)), ("Right".to_string(), Some(&3)),].iter().cloned().collect(),
+            [("Left".to_string(), Some(&2)), ("Right".to_string(), Some(&2)),].iter().cloned().collect(),
+            [("Left".to_string(), Some(&1)), ("Right".to_string(), Some(&1)),].iter().cloned().collect(),
+        ];
+
+        assert_eq!(solve_all(assign, &domain, constraint), solutions);
+    }
+}
+