fix lines longer than the screen causing weird scrolling artifacts, and avoid superfluous history entries

module/buffer.lua

@@ -257,11 +257,20 @@ function buffer:read(...)
     end
    end
   else
-   -- ?????
-   io.write("\27[s\27[8m")
-   local pos, buffer, hIndex = 1, "", 0
+   -- this whole thing is a house of cards. good luck.
+   io.write("\27[s\27[8m\27[6n")
+   if not (self.mx or self.my) then
+    io.write("\27[9999;9999H\27[6n")
+   end
+   local pos, buffer, hIndex, sx, sy = 1, "", 0
    self.history = self.history or {}
    local function redraw()
+    -- scroll until the buffer will fit on the screen
+    while sx and sy and self.mx and self.my and #buffer > (self.mx * ((self.my - sy) + 1)) - sx do
+     sy = sy - 1
+     io.write("\27[9999;9999H ")
+     io.write(string.format("\27[2K\27[%i;%iH\27[s", sx, sy))
+    end
     io.write(string.format("\27[u%s \27[u\27[%iC",buffer,(#buffer-pos)+1))
    end
    while true do
@@ -300,6 +309,9 @@ function buffer:read(...)
        end
        buffer = self.history[1+#self.history-hIndex] or buffer
        pos = 1
+      elseif char == "R" then -- cursor position report
+       self.mx, self.my = sx and math.max(self.mx or 0, args[1]) or self.mx, sy and math.max(self.my or 0, args[2]) or self.my
+       sx, sy = sx or args[1], sy or args[2]
       end
       hIndex = math.max(math.min(hIndex,#self.history),0)
      end
@@ -321,7 +333,7 @@ function buffer:read(...)
      pos = (nc and #buffer-nc+2) or 1
     elseif char == "\13" or char == "\10" or char == "\n" then -- return / newline
      io.write("\n")
-     self.history[#self.history+1] = buffer
+     self.history[#self.history+1] = buffer ~= "" and buffer ~= self.history[#self.history] and buffer or nil
      if #self.history > (self.maxhistory or 16) then table.remove(self.history,1) end
      if chop then buffer = buffer .. "\n" end
      return buffer