Convert::upperCamelToLowerCamel()

Used to expose lowercase web service object keys in SS4,
without requiring an explicit field mapping for these.

The first use case is exposing File data:
[ID => 99, FileName => 'test'] becomes {"id": 99, "fileName": "test"} in JSON.

core/Convert.php

@@ -439,4 +439,47 @@ class Convert {
 			true
 		);
 	}
+
+	/**
+	 * Converts upper camel case names to lower camel case,
+	 * with leading upper case characters replaced with lower case.
+	 * Tries to retain word case.
+	 *
+	 * Examples:
+	 * - ID => id
+	 * - IDField => idField
+	 * - iDField => iDField
+	 *
+	 * @param $str
+	 * @return string
+	 */
+	public static function upperCamelToLowerCamel($str) {
+		$return = null;
+		$matches = null;
+		if(preg_match('/(^[A-Z]{1,})([A-Z]{1})([a-z]+.*)/', $str, $matches)) {
+			// If string has trailing lowercase after more than one leading uppercase characters,
+			// match everything but the last leading uppercase character.
+			$return = implode('', [
+				strtolower($matches[1]),
+				$matches[2],
+				$matches[3]
+			]);
+		} else if(preg_match('/(^[A-Z]{1})([a-z]+.*)/', $str, $matches)) {
+			// If string has trailing lowercase after exactly one leading uppercase characters,
+			// match everything but the last leading uppercase character.
+			$return = implode('', [
+				strtolower($matches[1]),
+				$matches[2]
+			]);
+		} elseif(preg_match('/^[A-Z]+$/', $str)) {
+			// If string has leading uppercase without trailing lowercase,
+			// just lowerase the whole thing.
+			$return = strtolower($str);
+		} else {
+			// If string has no leading uppercase, just return.
+			$return = $str;
+		}
+
+		return $return;
+	}
 }

tests/core/ConvertTest.php

@@ -396,4 +396,42 @@ XML
 			Convert::base64url_decode(Convert::base64url_encode($data))
 		);
 	}
+
+	public function testUpperCamelToLowerCamel() {
+		$this->assertEquals(
+			'd',
+			Convert::upperCamelToLowerCamel('D'),
+			'Single character'
+		);
+		$this->assertEquals(
+			'id',
+			Convert::upperCamelToLowerCamel('ID'),
+			'Multi leading upper without trailing lower'
+		);
+		$this->assertEquals(
+			'id',
+			Convert::upperCamelToLowerCamel('Id'),
+			'Single leading upper with trailing lower'
+		);
+		$this->assertEquals(
+			'idField',
+			Convert::upperCamelToLowerCamel('IdField'),
+			'Single leading upper with trailing upper camel'
+		);
+		$this->assertEquals(
+			'idField',
+			Convert::upperCamelToLowerCamel('IDField'),
+			'Multi leading upper with trailing upper camel'
+		);
+		$this->assertEquals(
+			'iDField',
+			Convert::upperCamelToLowerCamel('iDField'),
+			'Single leading lower with trailing upper camel'
+		);
+		$this->assertEquals(
+			'_IDField',
+			Convert::upperCamelToLowerCamel('_IDField'),
+			'Non-alpha leading  with trailing upper camel'
+		);
+	}
 }