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!");
}