stats: new func ellipsize

Takes a string and an optional length and returns string of that length
with '...' in the middle. If no length is provided it defaults to the
good old 80 chars. If the string is shorter than target length the input
string is returned unchanged.

This, in conjunction with mpv-player#17021, is intended to eventually fix mpv-player#10975.

Author: WhitePeter

player/lua/stats.lua

@@ -207,6 +207,19 @@ local function text_style()
 end
 
 
+local function ellipsize(text, max_len)
+    assert(text, "no text")
+    max_len = max_len or 80
+    if max_len < 6 or text:len() <= max_len then
+        return text end
+
+    local middle = max_len/2 + max_len%2
+    local ellipsized = ("%s...%s"):format(text:sub(1, middle-1), text:sub(-middle+2))
+
+    return assert(ellipsized:len() == max_len, "lengths don't match") and ellipsized
+end
+
+
 local function has_vo_window()
     return mp.get_property_native("vo-configured") and mp.get_property_native("video-osd")
 end