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import type { Adapter } from "../adapters/adapter.ts";import { CreateTableOptions, TableBuilder } from "./tablebuilder.ts";import type { ColumnBuilder } from "./columnbuilder.ts";
/** * Database schema migration helper */export class Schema {  constructor(    /** The database adapter */    private adapter: Adapter,  ) {}
  /**   * Create a table   *    * @param name the table name   */  public async createTable(    name: string,    fn: (builder: TableBuilder) => void,    options?: CreateTableOptions,  ) {    const builder = new TableBuilder(name, this.adapter, options);    fn(builder);    await builder.execute();  }
  /**   * Rename a table   *    * @param name the previous table name   * @param newName a new name for the table   */  public async renameTable(name: string, newName: string) {    await this.adapter.query(`ALTER TABLE ${name} RENAME TO ${newName}`);  }
  /**   * Drop a single table   *    * @param tableName table to be dropped   * @param options advanced options   */  public dropTable(    tableName: string,    options?: { ifExists?: boolean },  ): Promise<void>;
  /**   * Drop multiple tables   *    * @param tableNames tables to be dropped   * @param options advanced options   */  public dropTable(    tableNames: string[],    options?: { ifExists?: boolean },  ): Promise<void>;
  /** Drop table from the database */  public async dropTable(    tableName: string | string[],    options?: { ifExists?: boolean },  ): Promise<void> {    // Populate options with default values    options = Object.assign({}, { ifExists: false }, options);
    // Build query string    const query = [`DROP TABLE`];    if (options.ifExists) query.push(`IF EXISTS`);
    if (Array.isArray(tableName)) {      // SQLite doesn't support dropping multiple tables at once.      // So, we need to execute multiple queries for it.      if (this.adapter.dialect === "sqlite") {        for (const table of tableName) {          const tableQuery = query.join(" ") + ` ${table}`;          await this.adapter.query(tableQuery);        }      } else {        // Add the table name        query.push(tableName.join(", "));
        // Perform query        await this.adapter.query(query.join(" "));      }    } else {      // Add the table name      query.push(tableName);
      // Perform query      await this.adapter.query(query.join(" "));    }  }
  /**   * Check if a table exists in the database   *    * @param tableName the table name you want to check   */  public async hasTable(tableName: string): Promise<boolean> {    let query: string;
    // Decide the query    switch (this.adapter.dialect) {      case "sqlite":        query =          `SELECT EXISTS (SELECT name FROM sqlite_master WHERE type='table' AND name='${tableName}')`;        break;      case "postgres":        query =          `SELECT EXISTS (SELECT FROM pg_tables WHERE tablename = '${tableName}')`;        break;      case "mysql":        query =          `SELECT EXISTS (SELECT * FROM information_schema.tables WHERE table_name = '${tableName}' LIMIT 1)`;        break;      default:        return false;    }
    // Execute query    const result = await this.adapter.query(query);
    // Get the result    switch (this.adapter.dialect) {      case "postgres":        return result[0] && result[0].exists ? true : false;      case "mysql":      case "sqlite":      default:        return !!result[0][Object.keys(result[0])[0]];    }  }
  /**   * Check if a column exists in a table   *    * @param tableName the table name you want to check   * @param columnName the column name you're looking for   */  public async hasColumn(    tableName: string,    columnName: string,  ): Promise<boolean> {    let query: string;
    // Decide the query    switch (this.adapter.dialect) {      case "sqlite":        query = `PRAGMA table_info(${tableName});`;        break;      case "mysql":      case "postgres":      default:        query =          `SELECT EXISTS (SELECT column_name FROM information_schema.columns WHERE table_name='${tableName}' and column_name='${columnName}');`;        break;    }
    // Execute the query    const result = await this.adapter.query(query);
    // Extract the result    switch (this.adapter.dialect) {      case "sqlite":        return !!result.find((item) => item.name === columnName);      case "postgres":        return result[0] && result[0].exists ? true : false;      case "mysql":        return !!result[0][Object.keys(result[0])[0]];      default:        throw new Error("Database dialect not implemented!");    }  }
  // --------------------------------------------------------------------------------  // ALTER TABLE  // --------------------------------------------------------------------------------
  /** Create an index */  public addIndex(index: string) {    throw new Error("Not implemented yet!");  }
  /** Remove an index */  public removeIndex(index: string) {    throw new Error("Not implemented yet!");  }
  /**   * Rename a column   *    * @param tableName the table name where the column exists   * @param columnName the column you want to rename   * @param newColumnName the new column name   */  public async renameColumn(    tableName: string,    columnName: string,    newColumnName: string,  ) {    await this.adapter.query(      `ALTER TABLE ${tableName} RENAME ${columnName} TO ${newColumnName}`,    );  }
  /**   * Create a new column   *    * @param tableName the table name where the column should be added   * @param column the column builder   */  public async addColumn(tableName: string, column: ColumnBuilder) {    await this.adapter.query(      `ALTER TABLE ${tableName} ADD ${column.toSQL(this.adapter.dialect)}`,    );  }
  /** Update a column's datatype */  public alterColumn(column: string, newColumn: string) {    throw new Error("Not implemented yet!");  }
  /**   * Remove a column   *    * @param tableName the table name where the column exists   * @param columnName the name of the column you want to remove   */  public async dropColumn(tableName: string, columnName: string) {    switch (this.adapter.dialect) {      case "sqlite":        throw new Error("SQLite doesn't support DROP COLUMN at the moment!");      case "mysql":      case "postgres":      default:        await this.adapter.query(          `ALTER TABLE ${tableName} DROP COLUMN ${columnName}`,        );        break;    }  }
  /** Execute SQL query */  public query(query: string) {    return this.adapter.query(query);  }}