<?php namespace DBDiff\SQLGen\Dialect;

/**

* Shared implementation for SQL dialects that follow ANSI/ISO SQL

* conventions:

* - double-quote identifiers

* - DROP INDEX without an ALTER TABLE wrapper

* - ADD COLUMN / DROP COLUMN keywords

* - column changes expressed as DROP + ADD (with a data-loss warning)

*

* Concrete subclasses must implement getDriver() and may override

* changeColumnWarning() to customise the warning comment emitted

* when a column definition changes.

*/

abstract class AbstractAnsiDialect implements SQLDialectInterface {

// ── Identifier quoting ───────────────────────────────────────────────────

public function quote(string $name): string {

return '"' . str_replace('"', '""', $name) . '"';

}

// ── Dialect flags ────────────────────────────────────────────────────────

public function isMySQLOnly(): bool {

return false;

}

// ── DDL helpers ──────────────────────────────────────────────────────────

/**

* Postgres and SQLite both use schema-namespaced indexes,

* so no ALTER TABLE wrapper is needed.

*/

public function dropIndex(string $table, string $key): string {

$k = $this->quote($key);

return "DROP INDEX $k;";

}

public function dropTrigger(string $trigger, string $table): string {

return "DROP TRIGGER IF EXISTS " . $this->quote($trigger) . ";";

}

public function addColumn(string $table, string $colDef): string {

$t = $this->quote($table);

return "ALTER TABLE $t ADD COLUMN $colDef;";

}

public function dropColumn(string $table, string $col): string {

$t = $this->quote($table);

$c = $this->quote($col);

return "ALTER TABLE $t DROP COLUMN $c;";

}

/**

* Emit a DROP + ADD pair for column definition changes.

*

* Neither Postgres nor SQLite supports mutating a column's type

* in a single statement without risk of data loss, so the safest

* portable approach is to drop and recreate. Subclasses may

* override changeColumnWarning() to customise the comment text.

*/

public function changeColumn(string $table, string $col, string $newDef): string {

$t = $this->quote($table);

$c = $this->quote($col);

return implode("\n", [

$this->changeColumnWarning($col),

"ALTER TABLE $t DROP COLUMN $c;",

"ALTER TABLE $t ADD COLUMN $newDef;",

]);

}

/**

* Returns the warning comment inserted before a column change.

* Override in subclasses to add engine-specific context.

*

* @param string $col Bare (unquoted) column name.

*/

protected function changeColumnWarning(string $col): string {

return "-- WARNING: column \"$col\" changed; data may be lost.";

}

public function dropConstraint(string $table, string $name, string $schema): string {

$t = $this->quote($table);

$n = $this->quote($name);

return "ALTER TABLE $t DROP CONSTRAINT $n;";

}

}