/**
 * metona-sqlark Query Compiler — AST → 查询计划
 * @module query/compiler
 *
 * 将 AST 语句编译为引擎可执行的 QueryPlan。
 * v0.0.1: 简单直接映射，未来可加入索引选择、过滤下推等优化。
 */

import type { QueryPlan } from '../constants';
import { DatabaseError } from '../constants';
import type { Statement, SelectStatement, DeleteStatement, UpdateStatement } from './ast';

// ---------------------------------------------------------------------------
//  编译 AST → QueryPlan
// ---------------------------------------------------------------------------

/**
 * 编译 SELECT / DELETE / UPDATE 语句为 QueryPlan。
 * INSERT 和 DDL 语句不需要 QueryPlan。
 */
export function compileStatement(stmt: Statement): QueryPlan {
  switch (stmt.type) {
    case 'SELECT':
      return compileSelect(stmt);
    case 'DELETE':
      return compileDelete(stmt);
    case 'UPDATE':
      return compileUpdate(stmt);
    default:
      throw new DatabaseError(`Cannot compile statement type "${stmt.type}" to QueryPlan`, 'COMPILE_ERROR');
  }
}

function compileSelect(stmt: SelectStatement): QueryPlan {
  return {
    table: stmt.from,
    columns: stmt.columns,
    where: stmt.where,
    orderBy: stmt.orderBy?.length ? stmt.orderBy : undefined,
    limit: stmt.limit,
    offset: stmt.offset,
  };
}

function compileDelete(stmt: DeleteStatement): QueryPlan {
  return {
    table: stmt.from,
    where: stmt.where,
  };
}

function compileUpdate(stmt: UpdateStatement): QueryPlan {
  return {
    table: stmt.table,
    where: stmt.where,
  };
}