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+;;; cj-window-toggle-lib.el --- Shared toggle-state helpers for display-buffer dispatchers -*- lexical-binding: t; -*-
+
+;; Author: Craig Jennings <c@cjennings.net>
+
+;;; Commentary:
+
+;; Parameterized helpers used by ai-vterm.el (F9) and
+;; vterm-config.el (F12) to capture a window's geometry at
+;; toggle-off and replay it on the next toggle-on.  Each consumer
+;; holds its own pair of state variables (last-direction symbol +
+;; last-size integer/float) and passes the variable symbols to the
+;; helpers.  Both helpers are pure with respect to their arguments;
+;; the side effects are confined to the named state variables.
+;;
+;; Pulls the geometry primitives in from cj-window-geometry.el.
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'cj-window-geometry)
+
+(defun cj/window-toggle-capture-state (window default-direction
+                                              direction-var size-var)
+  "Write WINDOW's direction and body size into DIRECTION-VAR and SIZE-VAR.
+
+DEFAULT-DIRECTION is the symbol used by `cj/window-direction' when
+WINDOW fills its frame's root area.  DIRECTION-VAR and SIZE-VAR are
+the symbols of the consumer's state variables; they receive the
+captured values via `set'.
+
+No-op when WINDOW is nil or not live."
+  (when (window-live-p window)
+    (let* ((dir (cj/window-direction window default-direction))
+           (size (cj/window-body-size window dir)))
+      (set direction-var dir)
+      (set size-var size))))
+
+(defun cj/window-toggle-display-saved (buffer alist
+                                              direction-var default-direction
+                                              size-var default-size)
+  "Display-buffer action: split per saved DIRECTION-VAR and SIZE-VAR.
+
+Reads the consumer's stored direction and size through DIRECTION-VAR
+and SIZE-VAR (symbols); falls back to DEFAULT-DIRECTION and
+DEFAULT-SIZE when the stored values are nil.  The cardinal direction
+is mapped to its frame-edge variant via
+`cj/cardinal-to-edge-direction' so the new buffer always lands at
+the same frame edge regardless of the selected window.  An integer
+size is wrapped in a `(body-columns . N)' / `(body-lines . N)' cons
+so `display-buffer-in-direction' sets the body explicitly,
+divider-independent.  A float size passes through as a fraction of
+the new window's parent.
+
+Caller-supplied ALIST entries for direction, window-width, or
+window-height are stripped before delegating to
+`display-buffer-in-direction' so the saved-state values control
+placement; the remaining alist entries are passed through."
+  (let* ((stored-dir (and (boundp direction-var) (symbol-value direction-var)))
+         (stored-size (and (boundp size-var) (symbol-value size-var)))
+         (direction (or stored-dir default-direction))
+         (edge-direction (or (cj/cardinal-to-edge-direction direction)
+                             (cj/cardinal-to-edge-direction default-direction)))
+         (size (or stored-size default-size))
+         (size-key (if (memq direction '(right left))
+                       'window-width
+                     'window-height))
+         (body-tag (if (memq direction '(right left))
+                       'body-columns
+                     'body-lines))
+         (size-value (if (integerp size)
+                         (cons body-tag size)
+                       size))
+         (filtered (cl-remove-if
+                    (lambda (cell)
+                      (memq (car-safe cell)
+                            '(direction window-width window-height)))
+                    alist))
+         (effective (append
+                     (list (cons 'direction edge-direction)
+                           (cons size-key size-value))
+                     filtered)))
+    (display-buffer-in-direction buffer effective)))
+
+(provide 'cj-window-toggle-lib)
+;;; cj-window-toggle-lib.el ends here