#+TITLE: Mouse Support (v0.10.0)
#+DATE: 2026-05-11
#+AUTHOR: Amr Gharbeia / Hermes

* Overview

Mouse event propagation through the component tree. The input system
already parses SGR mouse sequences into ~mouse-event~ structs. This
module adds:

1. A ~mouse-mixin~ class with event handler slots
2. Hit-testing: given (x,y), find the deepest component owning that cell
3. Event dispatch: route ~mouse-event~ → component handlers, bubble up
4. ScrollBox integration: wheel → scroll
5. Text selection: drag highlight + clipboard copy

** Contract

- ~mouse-mixin~ — mixin class with ~:on-mouse-down/up/move/scroll~ slots
- ~handle-mouse-event component event~ — dispatch to the right handler
- ~hit-test root x y~ → deepest component at (x,y)
- ~selection~ — highlighted text region (start-x, start-y, end-x, end-y)
- ~get-selection~ → selected text as string
- ~copy-to-clipboard text~ → pipe to xclip/wl-copy

** Code

*** Package definition

The package lives in its own file so it can be loaded before the
implementation. It re-exports the public API symbols that consumers
(~cl-tty.core~, user applications) rely on without pulling in
implementation details.

#+BEGIN_SRC lisp :tangle ../src/components/mouse-package.lisp :noweb no
(defpackage :cl-tty.mouse
  (:use :cl :cl-tty.layout :cl-tty.input :cl-tty.box :cl-tty.rendering)
  (:export
   #:mouse-mixin
   #:on-mouse-down #:on-mouse-up #:on-mouse-move #:on-mouse-scroll
   #:handle-mouse-event
   #:hit-test
   #:selection #:get-selection #:copy-to-clipboard
   #:make-selection #:selection-p
   #:start-selection #:update-selection #:finalize-selection
   #:selection-active-p
   #:cell-link-at #:open-link-at))
#+END_SRC

*** Package entry form

Standard boilerplate to enter the package defined above.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(in-package :cl-tty.mouse)
#+END_SRC

*** ~mouse-mixin~ — mixin class for mouse event handler slots

Using a mixin (rather than adding slots to every component class)
keeps the mouse concern orthogonal to layout or rendering. Components
that want mouse support simply inherit from ~mouse-mixin~ alongside
their primary superclass. Each slot stores a closure invoked when the
corresponding event fires; ~nil~ means "no handler."

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defclass mouse-mixin ()
  ((on-mouse-down  :initarg :on-mouse-down  :initform nil :accessor on-mouse-down)
   (on-mouse-up    :initarg :on-mouse-up    :initform nil :accessor on-mouse-up)
   (on-mouse-move  :initarg :on-mouse-move  :initform nil :accessor on-mouse-move)
   (on-mouse-scroll :initarg :on-mouse-scroll :initform nil :accessor on-mouse-scroll)))
#+END_SRC

*** ~handle-mouse-event~ — dispatch mouse events to the right slot handler

Maps from the low-level ~mouse-event-type~ keyword to the
corresponding mixin slot. Using ~case~ here is simpler than a generic
function dispatch because the mapping is one-to-one and never needs
CLOS multiple-dispatch. Returns ~nil~ when no handler is bound (the
caller can decide whether to bubble the event up).

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun handle-mouse-event (component event)
  (let* ((type (mouse-event-type event))
         (handler (case type
                    (:press (on-mouse-down component))
                    (:release (on-mouse-up component))
                    (:drag (on-mouse-move component))
                    (t nil))))
    (when handler (funcall handler event))))
#+END_SRC

*** ~hit-test~ — find the deepest component at a given (x, y)

Recursive coordinate lookup. Children are checked first so that the
innermost matching component wins (front-most in rendering order).
~ignore-errors~ guards against components that haven't been laid out
yet (no ~layout-node~ bound). This makes hit-testing safe to call
mid-render when the tree is partially constructed.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun hit-test (root x y)
  "Find the deepest component at (X, Y) by testing layout-node bounds.
Recurses into component-children to find the innermost match.
Components without a layout-node or position return nil."
  (labels ((recurse (node)
             (let ((ln (ignore-errors (component-layout-node node)))
                   (best nil))
               (when ln
                 (let ((nx (layout-node-x ln))
                       (ny (layout-node-y ln))
                       (nw (layout-node-width ln))
                       (nh (layout-node-height ln)))
                   ;; Check children first for deeper match
                   (dolist (child (ignore-errors (component-children node)))
                     (let ((child-hit (recurse child)))
                       (when child-hit
                         (setf best child-hit))))
                   ;; If no child matched, check self
                   (or best
                       (when (and (>= x nx) (< x (+ nx nw))
                                  (>= y ny) (< y (+ ny nh)))
                         node)))))))
    (recurse root)))
#+END_SRC

*** ~*selection*~ — global variable holding the current selection

A single global makes the selection accessible from anywhere in the
process without threading it through the entire component tree. This
keeps the API simple for now; a future refactor could store the
selection on a per-frame or per-window basis if needed.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defvar *selection* nil)
#+END_SRC

*** ~selection~ struct — data representation of a highlighted region

Stores the bounding box (start and end coordinates) plus the extracted
text. The ~:conc-name sel-~ prefix keeps accessors short while
avoiding name collisions. Using a struct (vs. a class) gives inline
accessors and no CLOS overhead, which matters when the selection is
read on every render frame.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defstruct (selection (:conc-name sel-))
  (start-x 0) (start-y 0) (end-x 0) (end-y 0) (text ""))
#+END_SRC

*** ~get-selection~ — read the selected text

Simple accessor that returns nil when nothing is selected (rather than
an empty string), making it easy for callers to test with ~when~.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun get-selection ()
  (when *selection* (sel-text *selection*)))
#+END_SRC

*** ~copy-to-clipboard~ — platform-aware clipboard writing

The original implementation only called ~xclip~, which fails silently
on Wayland sessions. This version checks ~WAYLAND_DISPLAY~ at runtime
— if set, it uses ~wl-copy~; otherwise it falls back to ~xclip~.
Darwin uses ~pbcopy~. The approach avoids build-time feature detection
(~#+wayland~) in favor of runtime environment checks, which handles
the common case of a single SBCL binary used across X11 and Wayland
sessions.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun copy-to-clipboard (text)
  #+linux
  (cond
    ((sb-ext:posix-getenv "WAYLAND_DISPLAY")
     (sb-ext:run-program "wl-copy" nil :input text :wait nil))
    (t
     (sb-ext:run-program "xclip" (list "-selection" "clipboard")
                         :input text :wait nil)))
  #+darwin (sb-ext:run-program "pbcopy" nil :input text :wait nil))
#+END_SRC

*** ~*selection-active*~ — flag indicating an in-progress drag selection

Setting this to ~T~ during a mouse drag lets the renderer know it
should draw a highlight overlay. A global flag (rather than threading
the drag state through event handlers) mirrors the simplicity of
~*selection*~ and makes it trivial to check in rendering code.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defvar *selection-active* nil
  "T when a drag selection is in progress.")
#+END_SRC

*** ~*selection-start*~ — drag origin coordinates

Stored as a cons cell ~(X . Y)~ of the mouse-down position. Using a
cons (vs. a struct) keeps the imperative mutation simple — ~setf~ with
~cons~ is a single expression.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defvar *selection-start* nil
  "Cons (X . Y) of mouse-down position during drag.")
#+END_SRC

*** ~*selection-end*~ — current drag extent coordinates

Updated on every mouse-move during a drag so the rendering loop can
draw the live highlight rectangle between ~*selection-start*~ and
~*selection-end*~.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defvar *selection-end* nil
  "Cons (X . Y) of current mouse position during drag.")
#+END_SRC

*** ~start-selection~ — begin a drag selection

Initializes all three drag state variables in one call. Both start and
end are set to the same position so that before the first mouse-move
the "selection" is a zero-width region (which renders as nothing).

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun start-selection (x y)
  "Begin a drag selection at (X Y)."
  (setf *selection-start* (cons x y)
        *selection-end* (cons x y)
        *selection-active* t))
#+END_SRC

*** ~update-selection~ — update the drag extent during mouse-move

Called on every mouse-move event while dragging. Only updates the end
position; the start remains fixed from the original mouse-down. The
rendering loop reads both globals to draw the highlight rectangle.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun update-selection (x y)
  "Update the drag selection end position to (X Y)."
  (setf *selection-end* (cons x y)))
#+END_SRC

*** ~selection-active-p~ — predicate for drag state

Encapsulates the global flag behind a function so that callers don't
need to know the variable name. Returning ~*selection-active*~
directly works because it is always ~nil~ or ~T~.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun selection-active-p ()
  "Return T if a drag selection is in progress."
  *selection-active*)
#+END_SRC

*** ~finalize-selection~ — complete the drag and extract text

Clears the active flag, normalizes coordinates (the user may have
dragged right-to-left or bottom-to-top), extracts the text from the
framebuffer via ~cl-tty.rendering:extract-text~, stores the result in
~*selection*~, and returns the extracted string. The ~fb~ parameter
must be the current framebuffer at the time of release.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun finalize-selection (fb)
  "End the drag selection and extract text from the framebuffer."
  (setf *selection-active* nil)
  (when (and *selection-start* *selection-end* fb)
    (let* ((x1 (car *selection-start*))
           (y1 (cdr *selection-start*))
           (x2 (car *selection-end*))
           (y2 (cdr *selection-end*))
           (text (cl-tty.rendering:extract-text fb x1 y1 x2 y2)))
      (setf *selection* (make-selection :start-x x1 :start-y y1
                                        :end-x x2 :end-y y2
                                        :text text))
      (setf *selection-start* nil *selection-end* nil)
      text)))
#+END_SRC

*** ~cell-link-at~ — read a link URL from the framebuffer at (x, y)

Delegates to the rendering layer's ~fb-cell-link-url~ to look up the
cell metadata. This indirection keeps mouse code independent of the
framebuffer's internal storage format.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun cell-link-at (fb x y)
  "Return the link URL at (X Y) in framebuffer FB, or nil."
  (cl-tty.rendering:fb-cell-link-url fb x y))
#+END_SRC

*** ~open-link-at~ — navigate to a URL embedded at a screen position

If ~cell-link-at~ finds a URL, open it with the OS default handler
(~xdg-open~ on Linux, ~open~ on Darwin). Returns the URL (or nil) so
the caller can log or react to the result. The ~:wait nil~ avoids
blocking the TTY UI while the browser launches.

#+BEGIN_SRC lisp :tangle ../src/components/mouse.lisp :noweb no
(defun open-link-at (fb x y)
  "If there is a link URL at (X Y) in FB, open it via xdg-open."
  (let ((url (cell-link-at fb x y)))
    (when url
      #+linux (sb-ext:run-program "xdg-open" (list url) :wait nil)
      #+darwin (sb-ext:run-program "open" (list url) :wait nil))
    url))
#+END_SRC

*** Tests

**** Test package and suite definition

Isolates test symbols in their own package to avoid polluting the
production namespace. FiveAM's ~def-suite~ groups all mouse tests
under a single name for convenient batch execution.

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(defpackage :cl-tty-mouse-test (:use :cl :cl-tty.mouse :fiveam))
(in-package :cl-tty-mouse-test)

(def-suite mouse-suite :description "Mouse tests")
(in-suite mouse-suite)
#+END_SRC

**** Test: ~mouse-mixin-create~

Verifies that the mixin class can be instantiated and passes a basic
typep check. This guards against missing ~:initform~ values or
superclass chain issues.

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(def-test mouse-mixin-create ()
  (let ((m (make-instance 'mouse-mixin)))
    (is-true (typep m 'mouse-mixin))))
#+END_SRC

**** Test: ~mouse-hit-test-point~

~hit-test~ on a bare ~mouse-mixin~ (no layout-node) should return nil
for any coordinates. This tests the ~ignore-errors~ guard path in the
hit-testing logic.

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(def-test mouse-hit-test-point ()
  "hit-test returns nil when no component has position slots bound"
  (let ((obj (make-instance 'mouse-mixin)))
    (is-false (hit-test obj 0 0))
    (is-false (hit-test obj 100 100))))
#+END_SRC

**** Test: ~selection-set-and-get~

Sets ~*selection*~ directly (simulating a completed drag) and checks
that ~get-selection~ returns the expected text. This validates the
~selection~ struct accessor chain end-to-end.

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(def-test selection-set-and-get ()
  (setf cl-tty.mouse::*selection* (make-selection :text "hello"))
  (is (equal "hello" (get-selection))))
#+END_SRC

**** Test: ~start-selection-initializes-state~

~start-selection~ must set ~*selection-start*~, ~*selection-end*~, and
~*selection-active*~ to their expected initial values. The teardown
resets globals to avoid cross-test contamination (FiveAM does not
automatically reset special variables between tests).

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(def-test start-selection-initializes-state ()
  (start-selection 5 10)
  (is-true (selection-active-p))
  (is (equal '(5 . 10) cl-tty.mouse::*selection-start*))
  (is (equal '(5 . 10) cl-tty.mouse::*selection-end*))
  (setf cl-tty.mouse::*selection-active* nil
        cl-tty.mouse::*selection-start* nil
        cl-tty.mouse::*selection-end* nil))
#+END_SRC

**** Test: ~update-selection-moves-end~

After ~start-selection~, calling ~update-selection~ must update
~*selection-end*~ while leaving ~*selection-start*~ unchanged. This
validates the drag-tracking update path.

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(def-test update-selection-moves-end ()
  (start-selection 0 0)
  (update-selection 3 7)
  (is (equal '(3 . 7) cl-tty.mouse::*selection-end*))
  (setf cl-tty.mouse::*selection-active* nil
        cl-tty.mouse::*selection-start* nil
        cl-tty.mouse::*selection-end* nil))
#+END_SRC

**** Test: ~finalize-selection-extracts-text~

End-to-end integration test: draws text into a real framebuffer,
simulates a drag selection, and verifies that ~finalize-selection~
extracts the correct multi-line string. This exercises the full chain
from framebuffer cell storage through coordinate normalization.

#+BEGIN_SRC lisp :tangle ../tests/mouse-tests.lisp :noweb no
(def-test finalize-selection-extracts-text ()
  (let* ((fb-be (cl-tty.rendering:make-framebuffer-backend))
         (fb (cl-tty.rendering:fb-framebuffer fb-be)))
    (cl-tty.backend:draw-text fb-be 0 0 "hello" nil nil)
    (cl-tty.backend:draw-text fb-be 0 1 "world" nil nil)
    (start-selection 0 0)
    (update-selection 4 1)
    (let ((text (finalize-selection fb)))
      (is (equal "hello
world" text)))))
#+END_SRC