readline: add cursor movement using Ctrl+{a, e, b, f}

Author: joachimschmidt557

src/readline.nim

@@ -8,48 +8,84 @@ type
     PrCanceled,
     PrComplete,
 
+proc editMoveLeft(input: string, cursorPos: var int) =
+  if cursorPos > 0:
+    let (_, runeLen) = lastRune(input, cursorPos - 1)
+    cursorPos -= runeLen
+
+proc editMoveRight(input: string, cursorPos: var int) =
+  if cursorPos < input.len:
+    let runeLen = runeLenAt(input, cursorPos)
+    cursorPos += runeLen
+
+proc editBackspace(input: var string, cursorPos: var int) =
+  if cursorPos > 0:
+    let (_, runeLen) = lastRune(input, cursorPos - 1)
+    input = input[0..cursorPos - 1 - runeLen] & input.substr(cursorPos)
+    cursorPos -= runeLen
+
+proc editDelete(input: var string, cursorPos: int) =
+  if cursorPos < input.len:
+    let runeLen = runeLenAt(input, cursorPos)
+    input = input[0..cursorPos - 1] & input.substr(cursorPos + runeLen)
+
 proc processInputTextMode*(event: nimboxext.Event,
                            input: var string,
                            cursorPos: var int): ProcessInputTextModeResult =
   ## common input processing for MdInputText and MdSearch
   case event.kind
   of EventType.Key:
-    case event.sym
-    of Symbol.Escape:
-      return PrCanceled
-    of Symbol.Backspace:
-      if cursorPos > 0:
-        let (_, runeLen) = lastRune(input, cursorPos - 1)
-        input = input[0..cursorPos - 1 - runeLen] & input.substr(cursorPos)
-        cursorPos -= runeLen
-    of Symbol.Delete:
-      if cursorPos < input.len:
-        let runeLen = runeLenAt(input, cursorPos)
-        input = input[0..cursorPos - 1] & input.substr(cursorPos + runeLen)
-    of Symbol.Enter:
-      return PrComplete
-    of Symbol.Space:
-      let inserted = " "
-      input.insert(inserted, cursorPos)
-      cursorPos += inserted.len
-    of Symbol.Character:
-      let inserted = $event.ch.Rune
-      input.insert(inserted, cursorPos)
-      cursorPos += inserted.len
-    of Symbol.Left:
-      if cursorPos > 0:
-        let (_, runeLen) = lastRune(input, cursorPos - 1)
-        cursorPos -= runeLen
-    of Symbol.Right:
-      if cursorPos < input.len:
-        let runeLen = runeLenAt(input, cursorPos)
-        cursorPos += runeLen
-    of Symbol.Home:
-      cursorPos = 0;
-    of Symbol.End:
-      cursorPos = input.len;
-    else:
+    if event.mods == @[Modifier.Ctrl]:
+      case event.sym
+      # normal escape key press, no ctrl, but still here
+      of Symbol.Escape:
+        return PrCanceled
+      # normal backspace key press, no ctrl, but still here
+      of Symbol.Backspace:
+        editBackspace(input, cursorPos)
+      # normal enter key press, no ctrl, but still here
+      of Symbol.Enter:
+        return PrComplete
+      of Symbol.Character:
+        case event.ch
+        of 'C':
+          return PrCanceled
+        of 'B':
+          editMoveLeft(input, cursorPos)
+        of 'F':
+          editMoveRight(input, cursorPos)
+        of 'A':
+          cursorPos = 0;
+        of 'E':
+          cursorPos = input.len;
+        else:
+          discard
+      else:
+        discard
+    elif event.mods == @[Modifier.Alt]:
       discard
+    else:
+      case event.sym
+      of Symbol.Delete:
+        editDelete(input, cursorPos)
+      of Symbol.Space:
+        let inserted = " "
+        input.insert(inserted, cursorPos)
+        cursorPos += inserted.len
+      of Symbol.Character:
+        let inserted = $event.ch.Rune
+        input.insert(inserted, cursorPos)
+        cursorPos += inserted.len
+      of Symbol.Left:
+        editMoveLeft(input, cursorPos)
+      of Symbol.Right:
+        editMoveRight(input, cursorPos)
+      of Symbol.Home:
+        cursorPos = 0;
+      of Symbol.End:
+        cursorPos = input.len;
+      else:
+        discard
   of EventType.Mouse, EventType.Resize, EventType.None:
     discard