Store 20 bind phrases and scroll the history list

The history was capped at 5 entries, and the cap was on the stored data
rather than the display: adding a sixth phrase silently dropped the
oldest one from history.txt. Anyone managing a larger fleet loses
phrases that are still in use and has to retype them.

Show the history through a scrolling window of History.PAGE (5) rows so
the on-screen footprint no longer depends on how much is stored, which
is what forced the low cap in the first place. With that decoupled,
raise the stored limit to 20. Up/Down buttons move the window a page at
a time and are only shown when the history is longer than one page. A
label shows the current position.

Author: –Raphael Hunziker

src/SCRIPTS/TOOLS/elrs-bind/main.lua

@@ -42,11 +42,15 @@ function Defer.poll()
 end
 
 local History = {
-  MAX = 5,
+  MAX = 20,
+  PAGE = 5,
   FNAME = "history.txt",
   vals = {},
 }
 
+-- Index of the first history entry shown; scrolls in steps of History.PAGE
+local histOffset = 0
+
 function History.add(s)
   if s == nil or s == "" then
     return
@@ -65,6 +69,9 @@ function History.add(s)
     table.remove(History.vals)
   end
 
+  -- a new entry goes to the top of the list, make sure it is on screen
+  histOffset = 0
+
   History.save()
 end
 
@@ -276,18 +283,45 @@ local function sendBindRx()
 end
 
 local rebuildUi
+
+-- Keep the scroll window inside the bounds of the current history
+local function history_clampOffset()
+  local maxOffset = #History.vals - History.PAGE
+  if maxOffset < 0 then
+    maxOffset = 0
+  end
+  if histOffset > maxOffset then
+    histOffset = maxOffset
+  end
+  if histOffset < 0 then
+    histOffset = 0
+  end
+end
+
 local function history_text(id)
-  return History.vals[id]
+  return History.vals[id + histOffset]
 end
 local function history_visible(id)
   return history_text(id) ~= nil
 end
 local function history_press(id)
-  bindPhrase = History.vals[id]
+  bindPhrase = History.vals[id + histOffset]
   rebuildUi()
 end
 local function history_remove(id)
-  History.remove(id)
+  History.remove(id + histOffset)
+  history_clampOffset()
+end
+local function history_scroll(delta)
+  histOffset = histOffset + delta
+  history_clampOffset()
+end
+local function history_position()
+  local last = histOffset + History.PAGE
+  if last > #History.vals then
+    last = #History.vals
+  end
+  return string.format("%d-%d / %d", histOffset + 1, last, #History.vals)
 end
 
 rebuildUi = function()
@@ -425,7 +459,7 @@ rebuildUi = function()
     w = lvgl.PERCENT_SIZE + 100,
     align = CENTER,
   })
-  for i = 1, History.MAX do
+  for i = 1, History.PAGE do
     local row = histSection:box({
       w = lvgl.PERCENT_SIZE + 100,
       flexFlow = lvgl.FLOW_ROW,
@@ -453,6 +487,39 @@ rebuildUi = function()
       end,
     })
   end
+
+  -- Scroll controls, only shown when the history is longer than one page
+  local navRow = histSection:box({
+    w = lvgl.PERCENT_SIZE + 100,
+    flexFlow = lvgl.FLOW_ROW,
+    flexPad = lvgl.PAD_SMALL,
+    visible = function()
+      return #History.vals > History.PAGE
+    end,
+  })
+  navRow:button({
+    text = "Up",
+    press = function()
+      return history_scroll(-History.PAGE)
+    end,
+    active = function()
+      return histOffset > 0
+    end,
+  })
+  navRow:button({
+    text = "Down",
+    press = function()
+      return history_scroll(History.PAGE)
+    end,
+    active = function()
+      return histOffset + History.PAGE < #History.vals
+    end,
+  })
+  navRow:label({
+    text = function()
+      return history_position()
+    end,
+  })
 end
 
 local function init()