Add rudimentary JavaScript highlighting to query text view

MongoView/Synax Highlighting/JavaScriptHighlighter.swift

@@ -38,7 +38,14 @@ class JavaScriptHighlighter {
         return NSRange(from..<to, in: text)
     }
     
-    private func peek() -> Unicode.Scalar {
+    private func prevCharRange() -> NSRange {
+        return range(from: text.index(before: currentIndex), to: currentIndex)
+    }
+    
+    private func peek() -> Unicode.Scalar? {
+        guard currentIndex < text.endIndex else {
+            return nil
+        }
         return text.unicodeScalars[currentIndex]
     }
     
@@ -48,7 +55,7 @@ class JavaScriptHighlighter {
     }
     
     @discardableResult
-    private func consume() -> Unicode.Scalar {
+    private func consume() -> Unicode.Scalar? {
         let c = peek()
         currentIndex = text.index(after: currentIndex)
         return c
@@ -72,7 +79,7 @@ class JavaScriptHighlighter {
     }
 
     private func consumeExpression() {
-        let char = peek()
+        guard let char = peek() else { return }
         
         if identifierStarts.contains(char) {
             consumeIdentifier()
@@ -99,7 +106,7 @@ class JavaScriptHighlighter {
 
     private func consumeIdentifier() {
         let identifierStart = currentIndex!
-        while currentIndex < text.endIndex && identifiers.contains(peek()) {
+        while let char = peek(), identifiers.contains(char) {
             consume()
         }
         print("Identifier: '\(text[identifierStart..<currentIndex])'")
@@ -107,12 +114,12 @@ class JavaScriptHighlighter {
 
     private func consumeNumber() {
         let numberStart = currentIndex!
-        while currentIndex < text.endIndex && CharacterSet.decimalDigits.contains(peek()) {
+        while let char = peek(), CharacterSet.decimalDigits.contains(char) {
             consume()
         }
         if currentIndex < text.endIndex && peek() == "." {
             consume()
-            while currentIndex < text.endIndex && CharacterSet.decimalDigits.contains(peek()) {
+            while let char = peek(), CharacterSet.decimalDigits.contains(char) {
                 consume()
             }
         }
@@ -173,14 +180,14 @@ class JavaScriptHighlighter {
     }
 
     private func consumeOperator() {
-        print("Operator: \(peek())")
+        print("Operator: \(peek()!)")
         consume()
     }
     
     private func consumeFunctionCallOrGrouping() {
         consume() // (
         print("Opening (")
-        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
         indent += "  "
         while currentIndex < text.endIndex && peek() != ")" {
             consumeExpression()
@@ -189,14 +196,14 @@ class JavaScriptHighlighter {
         if currentIndex < text.endIndex {
             consume() // )
             print("Closing )")
-            attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+            attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
         }
     }
     
     private func consumeObject() {
         consume() // {
         print("Opening {")
-        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
         indent += "  "
         object:
         while currentIndex < text.endIndex && peek() != "}" {
@@ -219,13 +226,13 @@ class JavaScriptHighlighter {
         if currentIndex < text.endIndex {
             consume() // }
             print("Closing }")
-            attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+            attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
         }
     }
     
     private func consumeObjectKey() {
         let keyStart = currentIndex!
-        while currentIndex < text.endIndex && identifiers.contains(peek()) {
+        while let char = peek(), identifiers.contains(char) {
             consume()
         }
         print("Object key: '\(text[keyStart..<currentIndex])'")
@@ -234,13 +241,13 @@ class JavaScriptHighlighter {
     private func consumeDotLookup() {
         consume() // .
         print("Dot lookup")
-        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
     }
     
     private func consumeArray() {
         consume() // [
         print("Opening [")
-        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+        attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
         indent += "  "
         array:
         while currentIndex < text.endIndex && peek() != "]" {
@@ -262,7 +269,7 @@ class JavaScriptHighlighter {
         if currentIndex < text.endIndex {
             consume() // ]
             print("Closing ]")
-            attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: range(from: text.index(before: currentIndex), to: currentIndex))
+            attributed.addAttribute(.foregroundColor, value: NSColor.systemTeal, range: prevCharRange())
         }
     }