detect backend availability ahead of time and allow user function

2 files changed, 16 insertions, 12 deletions

diff --git a/README.md b/README.md
index 584f9ff..af812ee 100644
--- a/README.md
+++ b/README.md
@@ -7,8 +7,10 @@ multiple vis processes.
 
 By default, the lockfiles will be placed in `${XDG_STATE_HOME:-${HOME}/.local/state}/vis/locks/`.
 
-The `directory` member of the module table can be used to define the lock file
-location.
+* The `directory` member of the module table can be used to define the lock file location.
+* The `backend` member can be used to specify one of the supported backends: `whiptail` or `vis-menu`.
+  Additionally, it can provide a custom backend function with the following signature `f(filename, lockfilename, lockpid) => bool, ['a', 'e', 'q']`.
+
 
 ```lua
 local lockfiles = require('plugins/vis-lockfiles')
diff --git a/init.lua b/init.lua
index ca8e16c..ce5145c 100644
--- a/init.lua
+++ b/init.lua
@@ -21,6 +21,13 @@ local M = {}
 M.directory = '${XDG_STATE_HOME:-${HOME}/.local/state}/vis/locks'
 M.directory_expanded = nil
 
+-- Detect available backends
+if os.execute('command -v whiptail') then
+  M.prompt_backend = 'whiptail'
+else
+  M.prompt_backend = 'vis-menu'
+end
+
 local function get_lock_dir()
   if M.directory_expanded ~= M.directory then
     M.directory = lockfiles.capture_cmd('printf %s "' .. M.directory .. '"')
@@ -41,21 +48,16 @@ local function prompt_backend_vis_menu(msg, menu, choices)
   return vis:pipe(cmd1 .. ';' .. cmd2 .. '|' .. cmd3, true)
 end
 
-local function prompt_backend(path, lfile_path, pid, preferred_backend)
+local function prompt_backend(path, lfile_path, pid, backend)
   local msg = 'File is locked: ' .. path .. '\n  lock: ' .. lfile_path ..
                   '\n  owned by process ID: ' .. pid
   local status, output
 
-  if preferred_backend == 'whiptail' then
-    local p = io.popen('command -v whiptail 2>/dev/null || :', 'r')
-    output = assert(p:read('*a'))
-    p:close()
-    preferred_backend = (output ~= '') and preferred_backend
-  end
-
-  if preferred_backend == 'whiptail' then
+  if backend == 'whiptail' then
     local menu = 'abort "operation (a)" edit "anyway (e)" quit "vis (q)"'
     status, output = prompt_backend_whiptail(msg, menu)
+  elseif type(backend) == 'function' then
+    status, output = backend(path, lfile_path, pid)
   else
     status, output = prompt_backend_vis_menu(msg, '(E)dit anyway, (Q)uit, [A]bort', 'a\ne\nq')
   end
@@ -68,7 +70,7 @@ end
 -- return true if user wants to edit the locked file
 local function prompt(path, lfile_path, pid)
 
-  local output = prompt_backend(path, lfile_path, pid, 'whiptail')
+  local output = prompt_backend(path, lfile_path, pid, M.backend)
   if output == 'e' then
     return true
   elseif output == 'q' then