Print diff out to console for multiline autocorrections

CHANGELOG.md

@@ -23,6 +23,8 @@ If needed, pluralize to `Tasks`, `PRs` or `Authors` and list multiple entries se
 ### Changed
 - Made internal extension methos public for usage in `customCheck`.  
   PR: [#35](https://github.com/Flinesoft/AnyLint/pull/35) | Author: [Cihat Gündüz](https://github.com/Jeehut)
+  - Print diff out to console for multiline autocorrections that were applied.  
+  Issue: [#27](https://github.com/Flinesoft/AnyLint/issues/27) | PR: [#35](https://github.com/Flinesoft/AnyLint/pull/35) | Author: [Cihat Gündüz](https://github.com/Jeehut)
 ### Deprecated
 - None.
 ### Removed

Sources/AnyLint/AutoCorrection.swift

@@ -10,12 +10,35 @@ public struct AutoCorrection {
     public let after: String
 
     var appliedMessageLines: [String] {
-        [
-            "Autocorrection applied (before >>> after):",
-            "> ✗ \(before.showWhitespacesAndNewlines())",
-            ">>>",
-            "> ✓ \(after.showWhitespacesAndNewlines())",
-        ]
+        if useDiffOutput, #available(OSX 10.15, *) {
+            var lines: [String] = ["Autocorrection applied, the diff is: (+ added, - removed)"]
+
+            let beforeLines = before.components(separatedBy: .newlines)
+            let afterLines = after.components(separatedBy: .newlines)
+
+            for difference in afterLines.difference(from: beforeLines).sorted() {
+                switch difference {
+                case let .insert(offset, element, _):
+                    lines.append("+ [L\(offset + 1)] \(element)".green)
+
+                case let .remove(offset, element, _):
+                    lines.append("- [L\(offset + 1)] \(element)".red)
+                }
+            }
+
+            return lines
+        } else {
+            return [
+                "Autocorrection applied, the diff is: (+ added, - removed)",
+                "- \(before.showWhitespacesAndNewlines())".red,
+                "+ \(after.showWhitespacesAndNewlines())".green,
+            ]
+        }
+    }
+
+    var useDiffOutput: Bool {
+        before.components(separatedBy: .newlines).count >= Constants.newlinesRequiredForDiffing ||
+            after.components(separatedBy: .newlines).count >= Constants.newlinesRequiredForDiffing
     }
 
     /// Initializes an autocorrection.
@@ -39,3 +62,30 @@ extension AutoCorrection: ExpressibleByDictionaryLiteral {
         self = AutoCorrection(before: before, after: after)
     }
 }
+
+// TODO: make the autocorrection diff sorted by line number
+@available(OSX 10.15, *)
+extension CollectionDifference.Change: Comparable where ChangeElement == String {
+    public static func < (lhs: Self, rhs: Self) -> Bool {
+        switch (lhs, rhs) {
+        case let (.remove(leftOffset, _, _), .remove(rightOffset, _, _)), let (.insert(leftOffset, _, _), .insert(rightOffset, _, _)):
+            return leftOffset < rightOffset
+
+        case let (.remove(leftOffset, _, _), .insert(rightOffset, _, _)):
+            return leftOffset < rightOffset || true
+
+        case let (.insert(leftOffset, _, _), .remove(rightOffset, _, _)):
+            return leftOffset < rightOffset || false
+        }
+    }
+
+    public static func == (lhs: Self, rhs: Self) -> Bool {
+        switch (lhs, rhs) {
+        case let (.remove(leftOffset, _, _), .remove(rightOffset, _, _)), let (.insert(leftOffset, _, _), .insert(rightOffset, _, _)):
+            return leftOffset == rightOffset
+
+        case (.remove, .insert), (.insert, .remove):
+            return false
+        }
+    }
+}

Sources/AnyLint/Extensions/StringExt.swift

@@ -8,6 +8,7 @@ extension String {
     /// Info about the exact location of a character in a given file.
     public typealias LocationInfo = (line: Int, charInLine: Int)
 
+    /// Returns the location info for a given line index.
     public func locationInfo(of index: String.Index) -> LocationInfo {
         let prefix = self[startIndex ..< index]
         let prefixLines = prefix.components(separatedBy: .newlines)

Sources/Utility/Constants.swift

@@ -31,4 +31,7 @@ public enum Constants {
 
     /// Hint that the case dot matches newline option should be active on a Regex.
     public static let dotMatchesNewlinesRegexOption: String = "m"
+
+    /// The number of newlines required in both before and after of AutoCorrections required to use diff for outputs.
+    public static let newlinesRequiredForDiffing: Int = 3
 }

Tests/AnyLintTests/AutoCorrectionTests.swift

@@ -7,4 +7,31 @@ final class AutoCorrectionTests: XCTestCase {
         XCTAssertEqual(autoCorrection.before, "Lisence")
         XCTAssertEqual(autoCorrection.after, "License")
     }
+
+    func testAppliedMessageLines() {
+        let singleLineAutoCorrection: AutoCorrection = ["before": "Lisence", "after": "License"]
+        XCTAssertEqual(
+            singleLineAutoCorrection.appliedMessageLines,
+            [
+                "Autocorrection applied, the diff is: (+ added, - removed)",
+                "- Lisence",
+                "+ License"
+            ]
+        )
+
+        let multiLineAutoCorrection: AutoCorrection = [
+            "before": "A\nB\nC\nD\nE\nF\nG\nH\nI\nJ\nK\nL\nM\nN\nO\nP\nQ\nR\nS\nT\nU\nV\nW\nX\nY\nZ\n",
+            "after": "A\nB\nD\nE\nF1\nF2\nG\nH\nI\nJ\nK\nL\nM\nN\nO\nP\nQ\nR\nS\nT\nU\nV\nW\nX\nY\nZ\n"
+        ]
+        XCTAssertEqual(
+            multiLineAutoCorrection.appliedMessageLines,
+            [
+                "Autocorrection applied, the diff is: (+ added, - removed)",
+                "- [L3] C",
+                "+ [L5] F1",
+                "- [L6] F",
+                "+ [L6] F2"
+            ]
+        )
+    }
 }