Attempt to introduce basic types

src/main.rs

@@ -1,5 +1,222 @@
+use std::collections::{BTreeMap, HashMap};
+
+// ==============SQL operations================
+// TODO: Note that every operation has a table name.
+//       Perhaps consider factoring the table name out
+//       and think of the operations as operating on a unique table.
+enum Operation {
+    Select(TableName, ColumnSelection, Option<Condition>),
+    Insert(TableName, InsertionValues),
+    Delete(TableName, Option<Condition>),
+    // Update(...),
+    //
+    CreateTable(TableName, TableSchema),
+    CreateIndex(TableName, ColumnName), // TODO: Is this sufficient?
+    // DropTable(TableName),
+}
+
+type InsertionValues = Vec<(ColumnName, DbValue)>;
+
+enum ColumnSelection {
+    All,
+    Columns(Vec<ColumnName>),
+}
+
+enum Condition {
+    // And(Box<Condition>, Box<Condition>),
+    // Or(Box<Condition>, Box<Condition>),
+    // Not(Box<Condition>),
+
+    Eq(ColumnName, DbValue),
+    // LessOrEqual(ColumnName, DbValue),
+    // Less(ColumnName, DbValue),
+
+    // StringCondition(StringCondition),
+}
+
+// enum StringCondition {
+//     Prefix(ColumnName, String),
+//     Substring(ColumnName, String),
+// }
 
 
+// ==============Values and Types================
+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.
+enum DbValue {
+    String(String),
+    Int(u64),
+    Number(f64),
+    UUID(UUID),
+}
+
+// TODO: Can this be autogenerated from the values?
+enum DbType {
+    String,
+    Int,
+    Number,
+    UUID,
+}
+
+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,
+        }
+    }
+}
+
+
+// ==============Tables================
+// table-metadata and data
+
+type TableName = String;
+type TablePosition = u32;
+
+struct Table {
+    schema: TableSchema,
+    rows: Rows,
+    indexes:
+        HashMap<ColumnPosition, ColumnIndex> // TODO: Consider generalizing `ColumnPosition` to something that would also apply to a pair of `ColumnNames` etc
+}
+
+// TODO: Is this really indexed by DbValues?
+//       Maybe we should have a separate index type for each type of value we're indexing over
+struct ColumnIndex {
+    index: BTreeMap<DbValue, 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 {
+    columns: HashMap<ColumnName, (DbType, ColumnPosition)>
+}
+
+// TODO
+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;
+
+// Use `ColumnPosition` as index
+type Row = Vec<DbValue>;
+
+type Rows =
+    BTreeMap<UUID, Row>;
+
+// ==============Interpreter================
+struct State {
+    table_positions: HashMap<TableName, TablePosition>,
+    tables: Vec<Table>,
+}
+
+impl State {
+    fn table_from_name<'b: 'a, 'a>(&'b self, table_name: TableName) -> Option<&'a Table> {
+        todo!()
+    }
+
+    fn attach_table(&mut self, table: Table) {
+        todo!()
+    }
+}
+
+// TODO: Give a better name to something that you can respond to with rows
+trait SqlConsumer {
+    // TODO: 
+}
+
+// TODO: This should return a reference to the table
+// 'tables_life contains 'table_life
+fn get_table<'tables_life: 'table_life, 'table_life>(tables: &'tables_life Tables, table_name: &TableName) -> &'table_life Table {
+    // let table_position: 
+    todo!()
+}
+
+// TODO: Decide if we want for this to return a response (but then you have to deal with lifetimes,
+//       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) -> ()  {
+    // 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)
+        },
+        Insert(table_name, values) => {
+            let table: &mut Table = todo!();
+
+            table.insert(values)
+        },
+        Delete(table_name, maybe_condition) => {
+            let table: &mut Table = todo!();
+
+            table.delete_where(maybe_condition)
+        },
+        CreateTable(table_name, table_schema) => {
+            let table = Table::new(table_name, table_schema);
+            state.attach_table(table);
+            todo!()
+        },
+        CreateIndex(table_name, column_name) => {
+            let table: &mut Table = todo!();
+
+            let index: ColumnIndex = ColumnIndex::new(table, column_name);
+            table.attach_index(index);
+        }, // TODO: Is this sufficient?
+                                            //
+    }
+}
+
+impl ColumnIndex {
+    fn new(table: &Table, column_name: ColumnName) -> ColumnIndex {
+        todo!()
+    }
+}
+
+
+impl Table {
+    fn new(table_name: TableName, table_schema: TableSchema) -> Table {
+        todo!()
+    }
+
+    fn attach_index(&mut self, column_index: ColumnIndex) {
+        todo!()
+    }
+
+    fn select_where(&self, column_selection: ColumnSelection, maybe_condition: Option<Condition>, consumer: impl SqlConsumer) {
+        todo!()
+    }
+
+    fn insert(&mut self, values: InsertionValues) {
+        todo!()
+    }
+
+    fn delete_where(&mut self, maybe_condition: Option<Condition>) {
+        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
+// } 
 
 fn main() {
     println!("Hello, world!");