Added StringFilters.camelToSnakeCase filter

CHANGELOG.md

@@ -14,7 +14,9 @@ _None_
 
 ### New Features
 
-_None_
+* Added camelToSnakeCase filter.  
+  [Gyuri Grell](https://github.com/ggrell)
+  [#24](https://github.com/SwiftGen/StencilSwiftKit/pull/24)
 
 ### Internal Changes
 

README.md

@@ -32,6 +32,7 @@ _TODO: [Write more extension Documentation](https://github.com/SwiftGen/StencilS
 * `join`: Deprecated. Will be removed now that the same filter exists in Stencil proper.
 * `lowerFirstWord`
 * `snakeToCamelCase` / `snakeToCamelCaseNoPrefix`
+* `camelToSnakeCase`: Transforms text from camelCase to snake_case. By default it converts to lower case, unless a single optional argument is set to "false", "no" or "0".
 * `titlecase`
 * `hexToInt`
 * `int255toFloat`

Sources/Environment.swift

@@ -17,6 +17,7 @@ public extension Extension {
     registerFilter("lowerFirstWord", filter: StringFilters.lowerFirstWord)
     registerFilter("snakeToCamelCase", filter: StringFilters.snakeToCamelCase)
     registerFilter("snakeToCamelCaseNoPrefix", filter: StringFilters.snakeToCamelCaseNoPrefix)
+    registerFilter("camelToSnakeCase", filter: StringFilters.camelToSnakeCase)
     registerFilter("titlecase", filter: StringFilters.titlecase)
     registerFilter("hexToInt", filter: NumFilters.hexToInt)
     registerFilter("int255toFloat", filter: NumFilters.int255toFloat)

Sources/Filters.swift

@@ -89,6 +89,44 @@ struct StringFilters {
     }
   }
 
+  /// Converts camelCase to snake_case. Takes an optional Bool argument for making the string lower case,
+  /// which defaults to true
+  /// - parameter value: the value to be processed
+  /// - parameter arguments: the arguments to the function, expecting zero or one argument
+  /// - returns: the snake case string
+  /// - throws: FilterError.invalidInputType if the value parameter isn't a string
+  static func camelToSnakeCase(_ value: Any?, arguments: [Any?]) throws -> Any? {
+    let toLower = parseBool(from: arguments, index: 0) ?? true
+    guard let string = value as? String else { throw FilterError.invalidInputType }
+
+    let snakeCase = try snakecase(string)
+    if toLower {
+      return snakeCase.lowercased()
+    }
+    return snakeCase
+  }
+
+  /// Parses filter arguments for a boolean value, where true can by any one of: "true", "yes", "1", and
+  /// false can be any one of: "false", "no", "0".
+  /// - parameter arguments: an array of argument values, may be empty
+  /// - parameter index: the index in the arguments array
+  /// - returns: true or false if a value was parsed, or nil if it wasn't able to
+  static func parseBool(from arguments: [Any?], index: Int) -> Bool? {
+    guard index + 1 <= arguments.count else {
+      return nil
+    }
+
+    let boolArg = (arguments[index] as? String ?? "").lowercased()
+    switch boolArg {
+    case "false", "no", "0":
+      return false
+    case "true", "yes", "1":
+      return true
+    default:
+      return nil
+    }
+  }
+
   /**
   This returns the string with its first parameter uppercased.
   - note: This is quite similar to `capitalise` except that this filter doesn't lowercase

Tests/StencilSwiftKitTests/StringFiltersTests.swift

@@ -133,6 +133,122 @@ class StringFiltersTests: XCTestCase {
     }
   }
 
+  func testParseBool_WithTrueString() throws {
+    let value = try StringFilters.parseBool(from: ["true"], index: 0)
+    XCTAssertTrue(value!)
+  }
+
+  func testParseBool_WithFalseString() throws {
+    let value = try StringFilters.parseBool(from: ["false"], index: 0)
+    XCTAssertFalse(value!)
+  }
+
+  func testParseBool_WithYesString() throws {
+    let value = try StringFilters.parseBool(from: ["yes"], index: 0)
+    XCTAssertTrue(value!)
+  }
+
+  func testParseBool_WithNoString() throws {
+    let value = try StringFilters.parseBool(from: ["no"], index: 0)
+    XCTAssertFalse(value!)
+  }
+
+  func testParseBool_WithOneString() throws {
+    let value = try StringFilters.parseBool(from: ["1"], index: 0)
+    XCTAssertTrue(value!)
+  }
+
+  func testParseBool_WithZeroString() throws {
+    let value = try StringFilters.parseBool(from: ["0"], index: 0)
+    XCTAssertFalse(value!)
+  }
+
+  func testParseBool_WithInt() throws {
+    let value = try StringFilters.parseBool(from: [1], index: 0)
+    XCTAssertNil(value)
+  }
+
+  func testParseBool_WithDouble() throws {
+    let value = try StringFilters.parseBool(from: [1.0], index: 0)
+    XCTAssertNil(value)
+  }
+
+  func testParseBool_WithEmptyString() throws {
+    let value = try StringFilters.parseBool(from: [""], index: 0)
+    XCTAssertNil(value)
+  }
+
+  func testParseBool_WithEmptyArray() throws {
+    let value = try StringFilters.parseBool(from: [], index: 0)
+    XCTAssertNil(value)
+  }
+
+  func testCamelToSnakeCase_NoArguments() {
+    let expectations = [
+        "string": "string",
+        "String": "string",
+        "strIng": "str_ing",
+        "strING": "str_ing",
+        "X": "x",
+        "x": "x",
+        "SomeCapString": "some_cap_string",
+        "someCapString": "some_cap_string",
+        "string_with_words": "string_with_words",
+        "String_with_words": "string_with_words",
+        "String_With_Words": "string_with_words",
+        "String_With_WoRds": "string_with_wo_rds",
+        "STRing_with_words": "st_ring_with_words",
+        "string_wiTH_WOrds": "string_wi_th_w_ords",
+        "": "",
+        "URLChooser": "url_chooser",
+        "UrlChooser": "url_chooser",
+        "a__b__c": "a__b__c",
+        "__y_z!": "__y_z!",
+        "PLEASESTOPSCREAMING": "pleasestopscreaming",
+        "PLEASESTOPSCREAMING!": "pleasestopscreaming!",
+        "PLEASE_STOP_SCREAMING": "please_stop_screaming",
+        "PLEASE_STOP_SCREAMING!": "please_stop_screaming!"
+    ]
+
+    for (input, expected) in expectations {
+      let trueArgResult = try! StringFilters.camelToSnakeCase(input, arguments: ["true"]) as? String
+      XCTAssertEqual(trueArgResult, expected)
+    }
+  }
+
+  func testCamelToSnakeCase_OneArgumentAsFalse() {
+    let expectations = [
+            "string": "string",
+            "String": "String",
+            "strIng": "str_Ing",
+            "strING": "str_ING",
+            "X": "X",
+            "x": "x",
+            "SomeCapString": "Some_Cap_String",
+            "someCapString": "some_Cap_String",
+            "string_with_words": "string_with_words",
+            "String_with_words": "String_with_words",
+            "String_With_Words": "String_With_Words",
+            "String_With_WoRds": "String_With_Wo_Rds",
+            "STRing_with_words": "ST_Ring_with_words",
+            "string_wiTH_WOrds": "string_wi_TH_W_Ords",
+            "": "",
+            "URLChooser": "URL_Chooser",
+            "UrlChooser": "Url_Chooser",
+            "a__b__c": "a__b__c",
+            "__y_z!": "__y_z!",
+            "PLEASESTOPSCREAMING": "PLEASESTOPSCREAMING",
+            "PLEASESTOPSCREAMING!": "PLEASESTOPSCREAMING!",
+            "PLEASE_STOP_SCREAMING": "PLEASE_STOP_SCREAMING",
+            "PLEASE_STOP_SCREAMING!": "PLEASE_STOP_SCREAMING!"
+    ]
+
+    for (input, expected) in expectations {
+      let falseArgResult = try! StringFilters.camelToSnakeCase(input, arguments: ["false"]) as? String
+      XCTAssertEqual(falseArgResult, expected)
+    }
+  }
+
   func testEscapeReservedKeywords() throws {
     let expectations = [
       "self": "`self`",