From 9dfe26d752963805a44e142744089d16783557db Mon Sep 17 00:00:00 2001
From: treeform <starplant@gmail.com>
Date: Fri, 30 Oct 2026 12:58:36 -0700
Subject: [PATCH] Fix browser clipboard paste handling

---
 src/windy/platforms/emscripten/emdefs.nim   | 19 ++++++++++++
 src/windy/platforms/emscripten/platform.nim | 33 +++++++++++++++++----
 tests/manual_inputs.nim                     |  6 ++++
 3 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/src/windy/platforms/emscripten/emdefs.nim b/src/windy/platforms/emscripten/emdefs.nim
index 2a3212f..7393d50 100644
--- a/src/windy/platforms/emscripten/emdefs.nim
+++ b/src/windy/platforms/emscripten/emdefs.nim
@@ -123,6 +123,24 @@ EM_JS(void, open_url, (const char* url), {
   window.open(urlUtf8, '_blank');
 });
 
+EM_JS(void, setup_paste_handler, (const char* target, void* userData), {
+  var canvas = document.querySelector(UTF8ToString(target));
+  canvas.addEventListener('paste', function(event) {
+    if (!event.clipboardData) return;
+    var text = event.clipboardData.getData('text/plain');
+    var size = lengthBytesUTF8(text) + 1;
+    var pointer = _malloc(size);
+    stringToUTF8(text, pointer, size);
+    try {
+      if (Module._windy_paste_callback(userData, pointer)) {
+        event.preventDefault();
+      }
+    } finally {
+      _free(pointer);
+    }
+  });
+});
+
 EM_JS(void, setup_drag_drop_handlers_internal, (const char* target, void* userData), {
   const canvas = target ? document.querySelector(UTF8ToString(target)) : Module.canvas;
   if (!canvas) {
@@ -329,6 +347,7 @@ proc get_device_pixel_ratio*(): cdouble {.importc.}
 proc open_temp_text_file*(title, text: cstring) {.importc.}
 proc open_url*(url: cstring) {.importc.}
 proc setup_drag_drop_handlers_internal*(target: cstring, userData: pointer) {.importc.}
+proc setup_paste_handler*(target: cstring, userData: pointer) {.importc.}
 proc set_cursor*(cursor: cstring) {.importc.}
 proc getLocalStorageLength*(key: cstring): cint {.importc: "get_local_storage_length".}
 proc getLocalStorageInto*(output: cstring, maxLen: cint, key: cstring): cint {.importc: "get_local_storage_into".}
diff --git a/src/windy/platforms/emscripten/platform.nim b/src/windy/platforms/emscripten/platform.nim
index efc0387..abbd620 100644
--- a/src/windy/platforms/emscripten/platform.nim
+++ b/src/windy/platforms/emscripten/platform.nim
@@ -76,6 +76,7 @@ var
   frameDispatchActive: bool
   pendingResize: bool
   pendingFocusChange: bool
+  clipboardText: string
 
 proc handleButtonPress(window: Window, button: Button)
 proc handleButtonRelease(window: Window, button: Button)
@@ -375,7 +376,8 @@ proc buttonToggle*(window: Window): ButtonView =
 
 # Clipboard functions
 proc clipboardContent*(): string =
-  ""  # Would need JavaScript interop
+  ## Returns the text supplied by the latest browser paste event.
+  clipboardText
 
 proc `clipboardContent=`*(content: string) =
   discard  # Would need JavaScript interop
@@ -508,11 +510,8 @@ proc setClipboardString*(s: string) =
   )
 
 proc getClipboardString*(): string =
-  # TODO: Implement clipboard with Emscripten.
-  raise newException(
-    Exception,
-    "getClipboardString is not supported on emscripten"
-  )
+  ## Returns the text supplied by the latest browser paste event.
+  clipboardText
 
 proc getClipboardContentKinds*(): set[ClipboardContentKind] =
   ## Image clipboard is not implemented on Emscripten yet.
@@ -795,6 +794,10 @@ proc onKeyDown(eventType: cint, keyEvent: ptr EmscriptenKeyboardEvent, userData:
     button = keyEventToButton(keyEvent)
     key = $cast[cstring](addr keyEvent.key[0])
   window.syncModifiers(keyEvent, button, pressed = true)
+  if window.runeInputEnabled and button == KeyV and
+    (keyEvent.metaKey or (keyEvent.ctrlKey and not keyEvent.altKey)):
+      # Let the browser deliver clipboard text before notifying the editor.
+      return 0
   if button != ButtonUnknown:
     window.handleButtonPress(button)
   if window.runeInputEnabled and not keyEvent.metaKey and
@@ -902,6 +905,7 @@ proc setupEventHandlers(window: Window) =
 
   # Drag and drop handler
   setup_drag_drop_handlers_internal(window.canvas, cast[pointer](window))
+  setup_paste_handler(window.canvas, cast[pointer](window))
 
 proc handleButtonPress(window: Window, button: Button) =
   handleButtonPressTemplate()
@@ -912,6 +916,23 @@ proc handleButtonRelease(window: Window, button: Button) =
 proc handleRune(window: Window, rune: Rune) =
   handleRuneTemplate()
 
+proc windy_paste_callback(userData: pointer, text: cstring): cint {.
+  exportc, cdecl, codegenDecl: "EMSCRIPTEN_KEEPALIVE $# $#$#"
+.} =
+  ## Delivers browser clipboard text as one editor paste operation.
+  let window = cast[Window](userData)
+  if window == nil or not window.runeInputEnabled:
+    return 0
+  clipboardText = $text
+  let previous = window.state.buttonDown
+  window.state.buttonDown.excl(KeyLeftAlt)
+  window.state.buttonDown.excl(KeyRightAlt)
+  window.state.buttonDown.incl(KeyLeftControl)
+  window.handleButtonPress(KeyV)
+  window.handleButtonRelease(KeyV)
+  window.state.buttonDown = previous
+  return 1
+
 proc windy_file_drop_callback(userData: pointer, fileNamePtr: cstring, fileDataPtr: pointer, fileDataLen: cint) {.exportc, cdecl, codegenDecl: "EMSCRIPTEN_KEEPALIVE $# $#$#".} =
   ## callback to handle the file drop event.
   ## EMSCRIPTEN_KEEPALIVE is required to avoid dead code elimination.
diff --git a/tests/manual_inputs.nim b/tests/manual_inputs.nim
index bec9dcc..9f497df 100644
--- a/tests/manual_inputs.nim
+++ b/tests/manual_inputs.nim
@@ -36,6 +36,12 @@ window.onButtonPress = proc(button: Button) =
     window.runeInputEnabled = not window.runeInputEnabled
   of KeyEscape:
     text.setLen(0)
+  of KeyV:
+    if window.runeInputEnabled and
+      (set[Button](window.buttonDown) * {
+        KeyLeftControl, KeyRightControl, KeyLeftSuper, KeyRightSuper
+      }) != {}:
+        text.add(getClipboardString().toRunes())
   else:
     discard
   updateTitle()