//! The VDBE bytecode code generator.
//!
//! This module is responsible for translating the SQL AST into a sequence of
//! instructions for the VDBE. The VDBE is a register-based virtual machine that
//! executes bytecode instructions. This code generator is responsible for taking
//! the SQL AST and generating the corresponding VDBE instructions. For example,
//! a SELECT statement will be translated into a sequence of instructions that
//! will read rows from the database and filter them according to a WHERE clause.

pub(crate) mod expr;
pub(crate) mod insert;
pub(crate) mod select;
pub(crate) mod where_clause;

use std::cell::RefCell;
use std::rc::Rc;

use crate::pager::Pager;
use crate::schema::Schema;
use crate::sqlite3_ondisk::{DatabaseHeader, MIN_PAGE_CACHE_SIZE};
use crate::util::normalize_ident;
use crate::vdbe::{builder::ProgramBuilder, Insn, Program};
use crate::{bail_parse_error, Result};
use insert::translate_insert;
use select::{prepare_select, translate_select};
use sqlite3_parser::ast;

/// Translate SQL statement into bytecode program.
pub fn translate(
    schema: &Schema,
    stmt: ast::Stmt,
    database_header: Rc<RefCell<DatabaseHeader>>,
    pager: Rc<Pager>,
) -> Result<Program> {
    match stmt {
        ast::Stmt::AlterTable(_, _) => bail_parse_error!("ALTER TABLE not supported yet"),
        ast::Stmt::Analyze(_) => bail_parse_error!("ANALYZE not supported yet"),
        ast::Stmt::Attach { .. } => bail_parse_error!("ATTACH not supported yet"),
        ast::Stmt::Begin(_, _) => bail_parse_error!("BEGIN not supported yet"),
        ast::Stmt::Commit(_) => bail_parse_error!("COMMIT not supported yet"),
        ast::Stmt::CreateIndex { .. } => bail_parse_error!("CREATE INDEX not supported yet"),
        ast::Stmt::CreateTable { .. } => bail_parse_error!("CREATE TABLE not supported yet"),
        ast::Stmt::CreateTrigger { .. } => bail_parse_error!("CREATE TRIGGER not supported yet"),
        ast::Stmt::CreateView { .. } => bail_parse_error!("CREATE VIEW not supported yet"),
        ast::Stmt::CreateVirtualTable { .. } => {
            bail_parse_error!("CREATE VIRTUAL TABLE not supported yet")
        }
        ast::Stmt::Delete { .. } => bail_parse_error!("DELETE not supported yet"),
        ast::Stmt::Detach(_) => bail_parse_error!("DETACH not supported yet"),
        ast::Stmt::DropIndex { .. } => bail_parse_error!("DROP INDEX not supported yet"),
        ast::Stmt::DropTable { .. } => bail_parse_error!("DROP TABLE not supported yet"),
        ast::Stmt::DropTrigger { .. } => bail_parse_error!("DROP TRIGGER not supported yet"),
        ast::Stmt::DropView { .. } => bail_parse_error!("DROP VIEW not supported yet"),
        ast::Stmt::Pragma(name, body) => translate_pragma(&name, body, database_header, pager),
        ast::Stmt::Reindex { .. } => bail_parse_error!("REINDEX not supported yet"),
        ast::Stmt::Release(_) => bail_parse_error!("RELEASE not supported yet"),
        ast::Stmt::Rollback { .. } => bail_parse_error!("ROLLBACK not supported yet"),
        ast::Stmt::Savepoint(_) => bail_parse_error!("SAVEPOINT not supported yet"),
        ast::Stmt::Select(select) => {
            let select = prepare_select(schema, &select)?;
            translate_select(select, database_header)
        }
        ast::Stmt::Update { .. } => bail_parse_error!("UPDATE not supported yet"),
        ast::Stmt::Vacuum(_, _) => bail_parse_error!("VACUUM not supported yet"),
        ast::Stmt::Insert {
            with,
            or_conflict,
            tbl_name,
            columns,
            body,
            returning,
        } => translate_insert(
            schema,
            &with,
            &or_conflict,
            &tbl_name,
            &columns,
            &body,
            &returning,
            database_header,
        ),
    }
}

fn translate_pragma(
    name: &ast::QualifiedName,
    body: Option<ast::PragmaBody>,
    database_header: Rc<RefCell<DatabaseHeader>>,
    pager: Rc<Pager>,
) -> Result<Program> {
    let mut program = ProgramBuilder::new();
    let init_label = program.allocate_label();
    program.emit_insn_with_label_dependency(
        Insn::Init {
            target_pc: init_label,
        },
        init_label,
    );
    let start_offset = program.offset();
    match body {
        None => {
            let pragma_result = program.alloc_register();

            program.emit_insn(Insn::Integer {
                value: database_header.borrow().default_cache_size.into(),
                dest: pragma_result,
            });

            let pragma_result_end = program.next_free_register();
            program.emit_insn(Insn::ResultRow {
                start_reg: pragma_result,
                count: pragma_result_end - pragma_result,
            });
        }
        Some(ast::PragmaBody::Equals(value)) => {
            let value_to_update = match value {
                ast::Expr::Literal(ast::Literal::Numeric(numeric_value)) => {
                    numeric_value.parse::<i64>().unwrap()
                }
                ast::Expr::Unary(ast::UnaryOperator::Negative, expr) => match *expr {
                    ast::Expr::Literal(ast::Literal::Numeric(numeric_value)) => {
                        -numeric_value.parse::<i64>().unwrap()
                    }
                    _ => 0,
                },
                _ => 0,
            };
            update_pragma(
                &name.name.0,
                value_to_update,
                database_header.clone(),
                pager,
            );
        }
        Some(ast::PragmaBody::Call(_)) => {
            todo!()
        }
    };
    program.emit_insn(Insn::Halt);
    program.resolve_label(init_label, program.offset());
    program.emit_insn(Insn::Transaction);
    program.emit_constant_insns();
    program.emit_insn(Insn::Goto {
        target_pc: start_offset,
    });
    program.resolve_deferred_labels();
    Ok(program.build(database_header))
}

fn update_pragma(name: &str, value: i64, header: Rc<RefCell<DatabaseHeader>>, pager: Rc<Pager>) {
    match name {
        "cache_size" => {
            let mut cache_size_unformatted = value;
            let mut cache_size = if cache_size_unformatted < 0 {
                let kb = cache_size_unformatted.abs() * 1024;
                kb / 512 // assume 512 page size for now
            } else {
                value
            } as usize;
            if cache_size < MIN_PAGE_CACHE_SIZE {
                // update both in memory and stored disk value
                cache_size = MIN_PAGE_CACHE_SIZE;
                cache_size_unformatted = MIN_PAGE_CACHE_SIZE as i64;
            }

            // update in-memory header
            header.borrow_mut().default_cache_size = cache_size_unformatted
                .try_into()
                .unwrap_or_else(|_| panic!("invalid value, too big for a i32 {}", value));

            // update in disk
            let header_copy = header.borrow().clone();
            pager.write_database_header(&header_copy);

            // update cache size
            pager.change_page_cache_size(cache_size);
        }
        _ => todo!(),
    }
}