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+;;; niri.el --- seamless niri/emacs integration. -*- lexical-binding: t; -*-
+;;
+;; Copyright (C) 2024 The TVL Contributors
+;;
+;; Author: Vincent Ambo <tazjin@tvl.su>
+;; Version: 1.0
+;; Package-Requires: ((emacs "27.1"))
+;;
+;;; Commentary:
+;;
+;; After having used EXWM for many years (7 or so?) it's become second nature
+;; that there is no difference between windows and Emacs buffers. This means
+;; that from any Emacs buffer (or, in the case of EXWM, from any X window) it's
+;; possible to switch to any of the others.
+;;
+;; This implements similar logic for Emacs running in Niri, consisting of two
+;; sides of the integration:
+;;
+;; # In Emacs
+;;
+;; Inside of Emacs, when switching buffers, populate the buffer-switching menu
+;; additionally with all open Niri windows. Selecting a Niri window moves the
+;; screen to that window.
+;;
+;; # Outside of Emacs
+;;
+;; Provides an interface for the same core functionality that can be used from
+;; shell scripts, and bound to selectors like dmenu or rofi.
+;;
+;; # Switching to Emacs buffers
+;;
+;; Some special logic exists for handling the case of switching to an Emacs
+;; buffer. There are several conditions that we can be in, that each have a
+;; predictable result:
+;;
+;; In a non-Emacs window, selecting an Emacs buffer will either switch to an
+;; Emacs frame already displaying this buffer, or launch a new frame for it.
+;;
+;; Inside of Emacs, if *another* frame is already displaying the buffer, switch
+;; to it. Otherwise the behaviour is the same as standard buffer switching.
+
+(require 'seq)
+(require 'map)
+
+(defun niri-list-windows ()
+  "List all currently open Niri windows."
+  (json-parse-string
+   (shell-command-to-string "niri msg -j windows")))
+
+(defun niri--list-selectables ()
+  "Lists all currently selectable things in a format that can work
+with completing-read. Selectable means all open Niri windows and
+all Emacs buffers."
+  (let* (;; all niri windows except for emacs frames
+         (windows (seq-filter (lambda (w) (not (equal (map-elt w "app_id") "emacs")))
+                              (niri-list-windows)))
+
+         ;; all non-hidden buffers
+         (buffers (seq-filter (lambda (b) (not (string-prefix-p " " (buffer-name b))))
+                              (buffer-list)))
+         (selectables (make-hash-table :test 'equal :size (+ (length windows)
+                                                             (length buffers)))))
+    (seq-do (lambda (window)
+              (map-put! selectables (map-elt window "title")
+                        (cons :niri window)))
+            windows)
+
+    (seq-do (lambda (buf)
+              (map-put! selectables (buffer-name buf)
+                        (cons :emacs buf)))
+            buffers)
+
+    selectables))
+
+(defun niri-go-anywhere ()
+  "Interactively select and switch to an open Niri window, or an
+  Emacs buffer."
+  (interactive)
+  (let* ((selectables (niri--list-selectables))
+         (target-key (completing-read "Switch to: " (map-keys selectables)))
+         (target (map-elt selectables target-key)))
+
+    (pcase (car target)
+      (:emacs (pop-to-buffer (cdr target) '((display-buffer-reuse-window
+                                             display-buffer-same-window)
+                                            (reusable-frames . 0))))
+      (:niri
+       (shell-command (format "niri msg action focus-window --id %d"
+                              (map-elt (cdr target) "id")))))))