notify the user about missing dependencies

platform/nix.lua

@@ -6,23 +6,31 @@ Platform-specific functions for *nix systems.
 ]]
 
 local h = require('helpers')
-local self = {}
-local clip = (function()
-    if h.is_mac() then
-        return 'LANG=en_US.UTF-8 pbcopy'
-    elseif h.is_wayland() then
-        return 'wl-copy'
-    else
-        return 'xclip -i -selection clipboard'
-    end
-end)()
+local self = { healthy = true, clip_util = "", clip_cmd = "", }
+
+local function is_installed(exe_name)
+    return os.execute("which " .. exe_name) == 0
+end
+
+if h.is_mac() then
+    self.clip_util = "pbcopy"
+    self.clip_cmd = "LANG=en_US.UTF-8 " .. self.clip_util
+elseif h.is_wayland() then
+    self.clip_util = "wl-copy"
+    self.clip_cmd = self.clip_util
+    self.healthy = is_installed(self.clip_util)
+else
+    self.clip_util = "xclip"
+    self.clip_cmd = self.clip_util .. " -i -selection clipboard"
+    self.healthy = is_installed(self.clip_util)
+end
 
 self.tmp_dir = function()
     return os.getenv("TMPDIR") or '/tmp'
 end
 
 self.copy_to_clipboard = function(text)
-    local handle = io.popen(clip, 'w')
+    local handle = io.popen(self.clip_cmd, 'w')
     handle:write(text)
     handle:close()
 end

platform/win.lua

@@ -9,7 +9,7 @@ local mp = require('mp')
 local h = require('helpers')
 local utils = require('mp.utils')
 local curl_tmpfile_path = utils.join_path(os.getenv('TEMP'), 'curl_tmp.txt')
-local self = { windows = true, }
+local self = { windows = true, healthy = true, clip_util="cmd", }
 
 mp.register_event('shutdown', function()
     os.remove(curl_tmpfile_path)

subtitles/observer.lua

@@ -142,6 +142,10 @@ end
 -- public
 
 self.copy_to_clipboard = function(_, text)
+    if platform.healthy == false then
+        h.notify(platform.clip_util .. " is not installed.", "error", 5)
+        return
+    end
     if not h.is_empty(text) then
         platform.copy_to_clipboard(self.clipboard_prepare(text))
     end