add case statement to sql function builder

Signed-off-by: Robin Appelman <robin@icewind.nl>

lib/private/DB/QueryBuilder/FunctionBuilder/FunctionBuilder.php

@@ -121,4 +121,15 @@ class FunctionBuilder implements IFunctionBuilder {
 	public function least($x, $y): IQueryFunction {
 		return new QueryFunction('LEAST(' . $this->helper->quoteColumnName($x) . ', ' . $this->helper->quoteColumnName($y) . ')');
 	}
+
+	public function case(array $whens, $else): IQueryFunction {
+		if (count($whens) < 1) {
+			return new QueryFunction($this->helper->quoteColumnName($else));
+		}
+
+		$whenParts = array_map(function (array $when) {
+			return 'WHEN ' . $this->helper->quoteColumnName($when['when']) . ' THEN ' . $this->helper->quoteColumnName($when['then']);
+		}, $whens);
+		return new QueryFunction('CASE ' .  implode(' ', $whenParts) . ' ELSE ' . $this->helper->quoteColumnName($else) . ' END');
+	}
 }

lib/public/DB/QueryBuilder/IFunctionBuilder.php

@@ -188,4 +188,16 @@ interface IFunctionBuilder {
 	 * @since 18.0.0
 	 */
 	public function least($x, $y): IQueryFunction;
+
+	/**
+	 * Takes the minimum of multiple values
+	 *
+	 * If you want to get the minimum value of all rows in a column, use `min` instead
+	 *
+	 * @param array<array{"when": string|ILiteral|IParameter|IQueryFunction, "then": string|ILiteral|IParameter|IQueryFunction}> $whens
+	 * @param string|ILiteral|IParameter|IQueryFunction $else
+	 * @return IQueryFunction
+	 * @since 18.0.0
+	 */
+	public function case(array $whens, $else): IQueryFunction;
 }

tests/lib/DB/QueryBuilder/FunctionBuilderTest.php

@@ -501,4 +501,21 @@ class FunctionBuilderTest extends TestCase {
 		$result->closeCursor();
 		$this->assertEquals(1, $row);
 	}
+
+	public function testCase() {
+		$query = $this->connection->getQueryBuilder();
+
+		$query->select($query->func()->case([
+			['when' => $query->expr()->gt($query->expr()->literal(1, IQueryBuilder::PARAM_INT), $query->expr()->literal(2, IQueryBuilder::PARAM_INT)), 'then' => $query->expr()->literal('first')],
+			['when' => $query->expr()->lt($query->expr()->literal(1, IQueryBuilder::PARAM_INT), $query->expr()->literal(2, IQueryBuilder::PARAM_INT)), 'then' => $query->expr()->literal('second')],
+			['when' => $query->expr()->eq($query->expr()->literal(1, IQueryBuilder::PARAM_INT), $query->expr()->literal(2, IQueryBuilder::PARAM_INT)), 'then' => $query->expr()->literal('third')],
+		], $query->createNamedParameter('else')));
+		$query->from('appconfig')
+			->setMaxResults(1);
+
+		$result = $query->execute();
+		$row = $result->fetchOne();
+		$result->closeCursor();
+		$this->assertEquals('second', $row);
+	}
 }