From 6c58e38ce3d88a5d877d0a0fc926ec4af31d4478 Mon Sep 17 00:00:00 2001
From: Richard Newman <rnewman@twinql.com>
Date: Wed, 1 Nov 2017 19:52:55 +0000
Subject: [PATCH] WIP: renumbering entities.

---
 db/src/db.rs | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 78 insertions(+), 3 deletions(-)

diff --git a/db/src/db.rs b/db/src/db.rs
index de2ea52d..eb31dcbc 100644
--- a/db/src/db.rs
+++ b/db/src/db.rs
@@ -42,15 +42,16 @@ use mentat_core::{
     attribute,
     Attribute,
     AttributeBitFlags,
+    AttributeMap,
     Entid,
     FromMicros,
     IdentMap,
+    SQLValueType,
     Schema,
-    AttributeMap,
-    TypedValue,
     ToMicros,
-    ValueType,
+    TypedValue,
     ValueRc,
+    ValueType,
 };
 
 use errors::{ErrorKind, Result, ResultExt};
@@ -477,6 +478,80 @@ pub trait MentatStoring {
     fn committed_metadata_assertions(&self, tx_id: Entid) -> Result<Vec<(Entid, Entid, TypedValue, bool)>>;
 }
 
+/// Make room in the local store for new entities allocated remotely, shifting local entities
+/// to be numbered after remote entities. If successful, returns a new partition map that
+/// reflects local and remote data.
+/// TODO: also return a Schema and stuff, right?
+fn renumber(conn: &rusqlite::Connection, root: &PartitionMap, local: &PartitionMap, remote: &PartitionMap) -> Result<PartitionMap> {
+    // For each partition present in both local and remote, that has advanced locally since remote,
+    // renumber local entities.
+    // Take each partition's largest value from either local or remote, if only one has advanced.
+    let mut output = remote.clone();
+    for (name, local_partition) in local {
+        if let Some(remote_partition) = remote.get(name) {
+            // The partition exists in both places.
+            if local_partition.start != remote_partition.start {
+                // Oh dear.
+                unimplemented!();
+            }
+
+            if let Some(root_partition) = root.get(name) {
+                let root_index = root_partition.index;
+                let advanced_locally_by = local_partition.index - root_index;
+                let advanced_remotely_by = remote_partition.index - root_index;
+                if advanced_locally_by > 0 && advanced_remotely_by > 0 {
+                    // Both changed. Renumber locally.
+                    // Note that we bound the set to include the max in order to avoid renumbering other partitions!
+                    // TODO: we're going to renumber in the schema, so we will know precisely which attributes
+                    // we might need to renumber. Save some work!
+                    let lower = root_index;
+                    let upper = lower + advanced_locally_by;
+                    let increment = advanced_remotely_by;
+                    let entity_tag = ValueType::Ref.value_type_tag();
+
+                    let datoms_e = "UPDATE datoms SET e = e + ? WHERE e >= ? AND e < ?";
+                    let datoms_a = "UPDATE datoms SET a = a + ? WHERE a >= ? AND a < ?";
+                    let datoms_v = "UPDATE datoms SET v = v + ? WHERE value_type_tag = ? AND v >= ? AND v < ?";
+
+                    // TODO: filter by tx, too -- no need to touch historical values, because they can't
+                    // possibly be affected.
+                    let tx_e = "UPDATE transactions SET e = e + ? WHERE e >= ? AND e < ?";
+                    let tx_a = "UPDATE transactions SET a = a + ? WHERE a >= ? AND a < ?";
+                    let tx_v = "UPDATE transactions SET v = v + ? WHERE value_type_tag = ? AND v >= ? AND v < ?";
+
+                    // Well, this is awkward.
+                    let ea_args: Vec<&ToSql> = vec![&increment, &lower, &upper];
+                    let v_args: Vec<&ToSql> = vec![&increment, &entity_tag, &lower, &upper];
+                    conn.execute(datoms_e, &ea_args)?;
+                    conn.execute(datoms_a, &ea_args)?;
+                    conn.execute(datoms_v, &v_args)?;
+                    conn.execute(tx_e, &ea_args)?;
+                    conn.execute(tx_a, &ea_args)?;
+                    conn.execute(tx_v, &v_args)?;
+
+                    // TODO: update `idents` and `schema`, too.
+
+                    output.get_mut(name).unwrap().index += advanced_locally_by;
+                } else {
+                    // Take the largest value. We already defaulted to remote….
+                    if local_partition.index > remote_partition.index {
+                        output.get_mut(name).unwrap().index = local_partition.index;
+                    }
+                }
+            } else {
+                // There is no partition in the root! Oh dear.
+                // This must be implemented before we can add partitions.
+                unimplemented!();
+            }
+        } else {
+            // There is no conflict: there is no remote partition with this name.
+            output.insert(name.clone(), local_partition.clone());
+        }
+    }
+    // TODO: update parts to match the returned partition map.
+    Ok(output)
+}
+
 /// Take search rows and complete `temp.search_results`.
 ///
 /// See https://github.com/mozilla/mentat/wiki/Transacting:-entity-to-SQL-translation.