-- ============================================================================
-- X-Plane Glass Cockpit  —  FMS two-way sync  (FlyWithLua companion)
-- ============================================================================
-- The web cockpit's bridge can't write the FMS via X-Plane's Web API. This
-- script runs INSIDE X-Plane (FlyWithLua) and has the FMS SDK, so it bridges
-- the shared plan <-> the in-sim FMS through two text files:
--
--   <X-Plane>/Output/fms-sync/to_sim.txt    written by the bridge (our plan)
--   <X-Plane>/Output/fms-sync/from_sim.txt  written here (the sim's plan)
--
-- A 3-decimal lat/lon signature de-dupes both sides so they never loop.
--
-- INSTALL: copy this file to  <X-Plane>/Resources/plugins/FlyWithLua/Scripts/
--          (install FlyWithLua NG+ first), then restart X-Plane or run
--          "FlyWithLua > Reload all Lua script files".
-- ============================================================================

local SYNC   = SYSTEM_DIRECTORY .. "Output/fms-sync/"
local TO_SIM   = SYNC .. "to_sim.txt"
local FROM_SIM = SYNC .. "from_sim.txt"
local last_sig = nil

-- make sure the folder exists (bridge also creates it)
os.execute('mkdir -p "' .. SYNC .. '" 2>/dev/null || mkdir "' .. SYNC .. '" 2>nul')

-- 3-decimal lat/lon signature of a waypoint list ---------------------------
local function sig_of(wps)
  local parts = {}
  for i = 1, #wps do
    parts[i] = string.format("%.3f,%.3f", wps[i].lat, wps[i].lon)
  end
  return table.concat(parts, ";")
end

local function read_file(p)
  local f = io.open(p, "r"); if not f then return nil end
  local s = f:read("*a"); f:close(); return s
end

local function write_file(p, s)
  local f = io.open(p, "w"); if not f then return end
  f:write(s); f:close()
end

-- parse the bridge file: skip "# sig" lines, take "lat lon alt id type" ------
local function parse(txt)
  local wps = {}
  if not txt then return wps end
  for line in txt:gmatch("[^\r\n]+") do
    if line:sub(1, 1) ~= "#" then
      local lat, lon, alt, id = line:match("^%s*(-?%d+%.?%d*)%s+(-?%d+%.?%d*)%s+(-?%d+)%s+(%S+)")
      if lat and lon then
        wps[#wps + 1] = { lat = tonumber(lat), lon = tonumber(lon), alt = tonumber(alt) or 0, id = id or "WPT" }
      end
    end
  end
  return wps
end

-- read the current in-sim FMS plan ------------------------------------------
local function read_fms()
  local wps = {}
  local n = XPLMCountFMSEntries()
  for i = 0, n - 1 do
    -- FlyWithLua: type, id, ref, altitude, lat, lon
    local _t, id, _ref, alt, lat, lon = XPLMGetFMSEntryInfo(i)
    if lat and lon and (math.abs(lat) > 0.0001 or math.abs(lon) > 0.0001) then
      wps[#wps + 1] = { lat = lat, lon = lon, alt = alt or 0, id = (id ~= "" and id) or "WPT" }
    end
  end
  return wps
end

-- write our plan into the in-sim FMS ----------------------------------------
local function apply_to_fms(wps)
  local old = XPLMCountFMSEntries()
  for i = 1, #wps do
    -- lat/lon entries keep our exact coords -> stable round-trip (no drift)
    XPLMSetFMSEntryLatLon(i - 1, wps[i].lat, wps[i].lon, math.floor(wps[i].alt or 0))
  end
  for i = old - 1, #wps, -1 do XPLMClearFMSEntry(i) end  -- trim leftovers
  if #wps >= 1 then
    XPLMSetDisplayedFMSEntry(0)
    XPLMSetDestinationFMSEntry(#wps - 1)
  end
end

local function serialize(wps)
  local lines = { "# " .. sig_of(wps) }
  for i = 1, #wps do
    lines[#lines + 1] = string.format("%.6f %.6f %d %s WPT", wps[i].lat, wps[i].lon, math.floor(wps[i].alt or 0), wps[i].id)
  end
  return table.concat(lines, "\n") .. "\n"
end

-- main loop (~1×/sec): whichever side differs from the agreed plan wins ------
function fms_sync_tick()
  local to_wps = parse(read_file(TO_SIM))
  local tsig   = sig_of(to_wps)
  local fm_wps = read_fms()
  local fsig   = sig_of(fm_wps)

  if tsig ~= "" and tsig ~= last_sig then
    apply_to_fms(to_wps)            -- App -> Sim
    last_sig = tsig
  elseif fsig ~= last_sig then
    write_file(FROM_SIM, serialize(fm_wps))  -- Sim -> App
    last_sig = fsig
  end
end

do_often("fms_sync_tick()")
logMsg("[glass-cockpit] FMS sync active -> " .. SYNC)