From e111c4fc61449e5747f3286471b9efdc132e20ca Mon Sep 17 00:00:00 2001
From: Yuriy Dupyn <2153100+omedusyo@users.noreply.github.com>
Date: Thu, 28 Dec 2023 10:49:32 +0100
Subject: [PATCH] Implement proper index creation

---
 minisql/src/main.rs | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/minisql/src/main.rs b/minisql/src/main.rs
index 63e809e..999f49a 100644
--- a/minisql/src/main.rs
+++ b/minisql/src/main.rs
@@ -225,22 +225,15 @@ fn interpret(table_name: TableName, operation: Operation, state: &mut State, con
             let table: &mut Table = state.table_from_name_mut(&table_name)?;
             let column_position: ColumnPosition = table.schema.column_position_from_column_name(&column_name)?;
 
-            let index: ColumnIndex = ColumnIndex::new(&table.rows);
+            let mut index: ColumnIndex = ColumnIndex::new();
+            let _ = index.update_from_table(&table, column_position)?;
+
             table.attach_index(column_position, index); 
             Ok(Response::IndexCreated)
         },
     }
 }
 
-impl ColumnIndex {
-    fn new(rows: &Rows) -> Self {
-        let index = BTreeMap::new();
-        // TODO: Take into account already existing rows
-        todo!();
-        Self { index }
-    }
-}
-
 impl TableSchema {
     fn get_column(&self, column_name: &ColumnName) -> DbResult<(DbType, ColumnPosition)> {
         match self.column_name_position_mapping.get_by_left(column_name) { 
@@ -514,6 +507,11 @@ impl Table {
 }
 
 impl ColumnIndex {
+    fn new() -> Self {
+        let index = BTreeMap::new();
+        Self { index }
+    }
+
     fn get(&self, value: IndexableDbValue) -> HashSet<UUID> {
         match self.index.get(&value) {
             Some(set) => set.clone(),
@@ -532,6 +530,27 @@ impl ColumnIndex {
         }
     }
 
+    // Should be used in the case when an indexed is created after the table has existed for a
+    // while. In such a case you need to build the index from the already existing rows.
+    fn update_from_table(&mut self, table: &Table, column_position: ColumnPosition) -> DbResult<()> {
+        for (id, row) in &table.rows {
+            let value = match row.get(column_position) {
+                Some(DbValue::Indexable(value)) => {
+                    value.clone()
+                },
+                Some(_) => {
+                    let column_name: ColumnName = table.schema.column_name_from_column_position(column_position)?;
+                    return Err(Error::AttemptToIndexNonIndexableColumn(table.schema.table_name.to_string(), column_name))
+                },
+                None => {
+                    return Err(Error::ColumnPositionDoesNotExist(table.schema.table_name.to_string(), column_position))
+                }
+            };
+            self.add(value, *id)
+        }
+        Ok(())
+    }
+
     fn remove(&mut self, value: &IndexableDbValue, id_to_be_removed: UUID) -> bool {
         match self.index.get_mut(value) {
             Some(ids) => {
@@ -565,6 +584,7 @@ enum Error {
     MissingTypeAnnotationOfColumn(TableName, ColumnPosition),
     MissingColumnInInsertValues(TableName, ColumnName, InsertionValues),
     MismatchBetweenInsertValuesAndColumns(TableName, InsertionValues),
+    AttemptToIndexNonIndexableColumn(TableName, ColumnName),
 }
 
 fn main() {