From b61427c07bd5c85f865213be4c38224a3898ccdf Mon Sep 17 00:00:00 2001
From: Alekos Filini <alekos.filini@gmail.com>
Date: Sat, 13 Feb 2021 11:00:03 -0500
Subject: [PATCH] [policy] Allow specifying a policy path for `Multisig`

While technically it's not required since there are no timelocks inside,
it's still less confusing for the end user if we allow this instead of
failing like we do currently.
---
 src/descriptor/policy.rs | 65 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 60 insertions(+), 5 deletions(-)

diff --git a/src/descriptor/policy.rs b/src/descriptor/policy.rs
index 40d8efb3..8929e085 100644
--- a/src/descriptor/policy.rs
+++ b/src/descriptor/policy.rs
@@ -506,11 +506,11 @@ impl Condition {
 }
 
 /// Errors that can happen while extracting and manipulating policies
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 pub enum PolicyError {
-    /// Not enough items are selected to satisfy a [`SatisfiableItem::Thresh`]
+    /// Not enough items are selected to satisfy a [`SatisfiableItem::Thresh`] or a [`SatisfiableItem::Multisig`]
     NotEnoughItemsSelected(String),
-    /// Index out of range for an item to satisfy a [`SatisfiableItem::Thresh`]
+    /// Index out of range for an item to satisfy a [`SatisfiableItem::Thresh`] or a [`SatisfiableItem::Multisig`]
     IndexOutOfRange(usize),
     /// Can not add to an item that is [`Satisfaction::None`] or [`Satisfaction::Complete`]
     AddOnLeaf,
@@ -642,10 +642,10 @@ impl Policy {
             SatisfiableItem::Thresh { items, threshold } if items.len() == *threshold => {
                 (0..*threshold).collect()
             }
+            SatisfiableItem::Multisig { keys, .. } => (0..keys.len()).collect(),
             _ => vec![],
         };
         let selected = match path.get(&self.id) {
-            _ if !default.is_empty() => &default,
             Some(arr) => arr,
             _ => &default,
         };
@@ -682,7 +682,16 @@ impl Policy {
 
                 Ok(requirements)
             }
-            _ if !selected.is_empty() => Err(PolicyError::TooManyItemsSelected(self.id.clone())),
+            SatisfiableItem::Multisig { keys, threshold } => {
+                if selected.len() < *threshold {
+                    return Err(PolicyError::NotEnoughItemsSelected(self.id.clone()));
+                }
+                if let Some(item) = selected.iter().find(|i| **i >= keys.len()) {
+                    return Err(PolicyError::IndexOutOfRange(*item));
+                }
+
+                Ok(Condition::default())
+            }
             SatisfiableItem::AbsoluteTimelock { value } => Ok(Condition {
                 csv: None,
                 timelock: Some(*value),
@@ -1249,4 +1258,50 @@ mod test {
     //
     //     // TODO how should this merge timelocks?
     // }
+
+    #[test]
+    fn test_get_condition_multisig() {
+        let secp = Secp256k1::gen_new();
+
+        let (_, pk0, _) = setup_keys(TPRV0_STR);
+        let (_, pk1, _) = setup_keys(TPRV1_STR);
+
+        let desc = descriptor!(wsh(multi(1, pk0, pk1))).unwrap();
+        let (wallet_desc, keymap) = desc
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .unwrap();
+        let signers = keymap.into();
+
+        let policy = wallet_desc
+            .extract_policy(&signers, &secp)
+            .unwrap()
+            .unwrap();
+
+        // no args, choose the default
+        let no_args = policy.get_condition(&vec![].into_iter().collect());
+        assert_eq!(no_args, Ok(Condition::default()));
+
+        // enough args
+        let eq_thresh =
+            policy.get_condition(&vec![(policy.id.clone(), vec![0])].into_iter().collect());
+        assert_eq!(eq_thresh, Ok(Condition::default()));
+
+        // more args, it doesn't really change anything
+        let gt_thresh =
+            policy.get_condition(&vec![(policy.id.clone(), vec![0, 1])].into_iter().collect());
+        assert_eq!(gt_thresh, Ok(Condition::default()));
+
+        // not enough args, error
+        let lt_thresh =
+            policy.get_condition(&vec![(policy.id.clone(), vec![])].into_iter().collect());
+        assert_eq!(
+            lt_thresh,
+            Err(PolicyError::NotEnoughItemsSelected(policy.id.clone()))
+        );
+
+        // index out of range
+        let out_of_range =
+            policy.get_condition(&vec![(policy.id.clone(), vec![5])].into_iter().collect());
+        assert_eq!(out_of_range, Err(PolicyError::IndexOutOfRange(5)));
+    }
 }