First attempt at SELECT

src/main.rs

@@ -1,4 +1,4 @@
-use std::collections::{BTreeMap, HashMap};
+use std::collections::{BTreeMap, HashMap, HashSet};
 
 // ==============SQL operations================
 // TODO: Note that every operation has a table name.
@@ -45,15 +45,23 @@ type UUID = u64;
 // TODO: What about nulls? I would rather not have that as in SQL, it sucks.
 //       I would rather have non-nullable values by default,
 //       and something like an explicit Option type for nulls.
+#[derive(Debug, Clone, PartialEq)]
 enum DbValue {
+    Number(f64), // TODO: Can't put floats as keys in maps, since they don't implement Eq. What to
+                 // do?
+    Indexable(IndexableDbValue),
+}
+
+#[derive(Debug, Ord, Eq, Clone, PartialOrd, PartialEq)]
+enum IndexableDbValue {
     String(String),
     Int(u64),
-    Number(f64),
     UUID(UUID),
     // TODO: what bout null?
 }
 
 // TODO: Can this be autogenerated from the values?
+#[derive(Debug, Clone, Copy)]
 enum DbType {
     String,
     Int,
@@ -65,10 +73,13 @@ impl DbValue {
     // TODO: Can this be autogenerated?
     fn to_type(self) -> DbType {
         match self {
-            Self::String(_) => DbType::String,
-            Self::Int(_) => DbType::Int,
             Self::Number(_) => DbType::Number,
-            Self::UUID(_) => DbType::UUID,
+            Self::Indexable(val) =>
+                match val {
+                    IndexableDbValue::String(_) => DbType::String,
+                    IndexableDbValue::Int(_) => DbType::Int,
+                    IndexableDbValue::UUID(_) => DbType::UUID,
+                }
         }
     }
 }
@@ -90,13 +101,17 @@ struct Table {
 
 // TODO: Is this really indexed by DbValues?
 //       Maybe we should have a separate index type for each type of value we're indexing over
+// TODO: I should have a set of UUID, not just a single UUID, e.g.
+//          a user table can have multiple different users with the same name.
 struct ColumnIndex {
-    index: BTreeMap<DbValue, UUID>
+    index: BTreeMap<IndexableDbValue, HashSet<UUID>>
 }
 
 // Note that it is nice to split metadata from the data because
 // then you can give the metadata to the parser without giving it the data.
 struct TableSchema {
+    table_name: TableName, // used for descriptive errors
+    primary_key: ColumnPosition,
     columns: HashMap<ColumnName, (DbType, ColumnPosition)>
 }
 
@@ -104,13 +119,12 @@ struct TableSchema {
 fn column_position(table_meta: TableSchema, column_name: ColumnName) -> Option<ColumnPosition> {
     todo!()
 }
-
 // Use `TablePosition` as index
 type Tables = Vec<Table>;
 
 
 type ColumnName = String;
-type ColumnPosition = u32;
+type ColumnPosition = usize;
 
 // Use `ColumnPosition` as index
 type Row = Vec<DbValue>;
@@ -123,6 +137,11 @@ type Rows =
     // interface
     // insert(id, value)
 
+fn select_columns(row: &Row, columns: &Vec<ColumnPosition>) -> Row {
+    // row.column_position
+    todo!()
+}
+
 // ==============Interpreter================
 struct State {
     table_positions: HashMap<TableName, TablePosition>,
@@ -134,7 +153,7 @@ impl State {
         todo!()
     }
 
-    fn attach_table(&mut self, table: Table) {
+    fn attach_table(&mut self, table_name: TableName, table: Table) {
         todo!()
     }
 }
@@ -155,104 +174,190 @@ fn get_table<'tables_life: 'table_life, 'table_life>(tables: &'tables_life Table
 //       because you'll be forced to put an iterator/slice into the Response data-structure.
 //       Alternative is to pass a row-consumer to the functionas that knows how to communicate with
 //       the client, but the details of communication are hidden behind an interface
-fn interpret(table_name: TableName, operation: Operation, state: &mut State, consumer: impl SqlConsumer) -> ()  {
+fn interpret(table_name: TableName, operation: Operation, state: &mut State, consumer: impl SqlConsumer) -> DbResult<Response>  {
     // TODO: lock stuff
     use Operation::*;
 
     match operation {
         Select(table_name, column_selection, maybe_condition) => {
             let table: &Table = todo!();
-            table.select_where(column_selection, maybe_condition, consumer)
+            Ok(Response::Selected(table.select_where(column_selection, maybe_condition)?))
         },
         Insert(table_name, values) => {
             let table: &mut Table = todo!();
 
-            table.insert(values, consumer)
+            table.insert(values);
+            todo!()
         },
         Delete(table_name, maybe_condition) => {
             let table: &mut Table = todo!();
 
-            table.delete_where(maybe_condition, consumer)
+            table.delete_where(maybe_condition);
+            todo!()
         },
         CreateTable(table_name, table_schema) => {
-            let table = Table::new(table_name, table_schema);
-            state.attach_table(table);
+            let table = Table::new(table_schema);
+            state.attach_table(table_name, table);
             todo!()
         },
         CreateIndex(table_name, column_name) => {
             let table: &mut Table = todo!();
+            let column_position: ColumnPosition = todo!();
 
-            let index: ColumnIndex = ColumnIndex::new(table, column_name);
-            table.attach_index(index);
-        }, // TODO: Is this sufficient?
-                                            //
+            let index: ColumnIndex = ColumnIndex::new();
+            table.attach_index(column_position, index); 
+            todo!()
+        },
     }
 }
 
 impl ColumnIndex {
-    fn new(table: &Table, column_name: ColumnName) -> ColumnIndex {
-        todo!()
+    fn new() -> Self {
+        Self { index: BTreeMap::new() }
     }
 }
 
+impl TableSchema {
+    fn get_column(&self, column_name: &ColumnName) -> DbResult<(DbType, ColumnPosition)> {
+        match self.columns.get(column_name) { 
+            Some((type_, column_position)) => Ok((*type_, *column_position)),
+            None => Err(Error::ColumnDoesNotExist(self.table_name.clone(), column_name.clone()))
+        }
+    }
+
+    fn is_primary(&self, column_position: ColumnPosition) -> bool {
+        self.primary_key == column_position
+    }
+
+    fn column_positions_from_column_names(&self, column_names: &[ColumnName]) -> DbResult<Vec<ColumnPosition>> {
+        let mut positions: Vec<ColumnPosition> = Vec::with_capacity(column_names.len());
+        for column_name in column_names {
+            let (_, column_position) = self.get_column(column_name)?;
+            positions.push(column_position)
+        }
+        Ok(positions)
+    }
+
+    fn column_positions_from_column_selection(&self, column_selection: &ColumnSelection) -> DbResult<Vec<ColumnPosition>> {
+        match column_selection {
+            ColumnSelection::All => {
+                let mut column_positions: Vec<ColumnPosition> = self.columns.values().map(|(_, column_position)| *column_position).collect();
+                column_positions.sort();
+                Ok(column_positions)
+            },
+
+            ColumnSelection::Columns(column_names) => {
+                self.column_positions_from_column_names(column_names)
+            },
+        }
+    }
+
+}
 
 impl Table {
-    fn new(table_name: TableName, table_schema: TableSchema) -> Table {
-        todo!()
+    fn new(table_schema: TableSchema) -> Self {
+        Self {
+            schema: table_schema,
+            rows: BTreeMap::new(),
+            indexes: HashMap::new(),
+        }
     }
 
-    fn attach_index(&mut self, column_index: ColumnIndex) {
-        todo!()
+    fn attach_index(&mut self, column_position: ColumnPosition, column_index: ColumnIndex) {
+        self.indexes.insert(column_position, column_index);
     }
 
-    fn select_where(&self, column_selection: ColumnSelection, maybe_condition: Option<Condition>, consumer: impl SqlConsumer) {
+    fn get_row_by_id(&self, id: UUID) -> Option<Row> {
+        self.rows.get(&id).cloned()
+    }
+
+    fn get_rows_by_ids(&self, ids: HashSet<UUID>) -> Vec<Row> {
+        ids.into_iter()
+            .filter_map(|id| self.get_row_by_id(id))
+            .collect()
+    }
+
+    fn get_rows_by_value(&self, column_position: ColumnPosition, value: &DbValue) -> Vec<Row> {
+        // brute-force search
+        self.rows.values()
+            .filter_map(|row| if row.get(column_position) == Some(value) { Some(row.clone()) } else { None })
+            .collect()
+    }
+
+    fn select_where(&self, column_selection: ColumnSelection, maybe_condition: Option<Condition>) -> DbResult<Vec<Row>> {
+        let selected_column_positions = self.schema.column_positions_from_column_selection(&column_selection)?;
         match maybe_condition {
-            None => {
-                // .iter() will give us an iterator over all the rows
+            None =>
+                Ok(self.rows.values().map(|row| select_columns(row, &selected_column_positions)).collect()),
 
-                // two choices
-                // 1.  optimized version
-                // self.iter_with_columns(column_selection).for_each(|row| {
-                //     consumer.send(row)
-                // });
-                // 2.
-                // self.iter()
-                //     .map(|row| row.select_columns(column_selection))
-                //     .for_each(|reduced_row| {
-                //         consumer.send(row)
-                //     });
-                todo!()
-            },
-            Some(Condition::Eq(column_name, value)) => {
-                // is column_name primary key? then it is easy
-                // self.get(id)
-                // is column_name indexed? Then get the index, and then it is not easy, because you
-                // may get a set of ids.
-                // what if it is not primary nor indexed? then you need to brute force your way
-                // through the whole table?
-                todo!()
+            Some(Condition::Eq(eq_column_name, value)) => {
+                let (type_, eq_column_position) = self.schema.get_column(&eq_column_name)?;
+                if self.schema.is_primary(eq_column_position) {
+                    match value {
+                        DbValue::Indexable(IndexableDbValue::UUID(uuid)) => {
+                            match self.get_row_by_id(uuid) {
+                                Some(row) => Ok(vec![select_columns(&row, &selected_column_positions)]),
+                                None => Ok(vec![]),
+                            }
+                        },
+                        _ => Err(Error::ValueDoesNotMatchExpectedType(self.schema.table_name.clone(), eq_column_name.clone(), type_, value.clone()))
+                    }
+                } else {
+                    match value {
+                        DbValue::Indexable(value) => {
+                            match self.indexes.get(&eq_column_position) {
+                                Some(column_index) => {
+                                    let ids = column_index.get(value);
+                                    Ok(self.get_rows_by_ids(ids).iter().map(|row| select_columns(row, &selected_column_positions)).collect())
+                                },
+                                None => {
+                                    Ok(self.get_rows_by_value(eq_column_position, &DbValue::Indexable(value)).iter().map(|row| select_columns(row, &selected_column_positions)).collect())
+                                }
+                            }
+                        },
+                        _ => {
+                            Ok(self.get_rows_by_value(eq_column_position, &value).iter().map(|row| select_columns(row, &selected_column_positions)).collect())
+                        }
+                    }
+                }
             }
         }
     }
 
-    fn insert(&mut self, values: InsertionValues, consumer: impl SqlConsumer) {
+    fn insert(&mut self, values: InsertionValues) {
         // 1. You need to update indices
         // 2. you simply insert the data
         todo!()
     }
 
-    fn delete_where(&mut self, maybe_condition: Option<Condition>, consumer: impl SqlConsumer) {
+    fn delete_where(&mut self, maybe_condition: Option<Condition>) {
         // kinda similar to select with respect to the conditions
         // update index
         todo!()
     }
 }
 
-// enum Response {
-//     Selected(impl Iter<???>), // TODO: How to do this? Some reference to an iterator somehow... slice..?
-//     Inserted(???),
-//     Deleted(usize), // how many were deleted
-// } 
+impl ColumnIndex {
+    fn get(&self, value: IndexableDbValue) -> HashSet<UUID> {
+        match self.index.get(&value) {
+            Some(set) => set.clone(),
+            None => HashSet::new(),
+        }
+    }
+}
+
+enum Response {
+    Selected(Vec<Row>),
+    Inserted(),
+    Deleted(usize), // how many were deleted
+} 
+
+type DbResult<A> = Result<A, Error>;
+
+enum Error {
+    ColumnDoesNotExist(TableName, ColumnName),
+    ValueDoesNotMatchExpectedType(TableName, ColumnName, DbType, DbValue)
+}
 
 fn main() {
     println!("Hello, world!");