-- ============================================================================
-- X-Plane Glass Cockpit  —  Terrain awareness probe  (FlyWithLua companion)
-- ============================================================================
-- The web MFD can't read X-Plane's scenery elevation over the Web API. This
-- script samples a grid of terrain heights around the aircraft with X-Plane's
-- terrain probe and writes them to terrain.json in the sync folder; the bridge
-- streams it to the tablets, which colour it red/yellow vs aircraft altitude
-- (G1000 TAWS). See terrain-sync in server/fmssync.js.
--
-- INSTALL: copy to <X-Plane>/Resources/plugins/FlyWithLua/Scripts/ (alongside
-- fms-sync.lua). Needs FlyWithLua NG+ (XPLM scenery-probe bindings).
-- ============================================================================

local SYNC = SYSTEM_DIRECTORY .. "Output/fms-sync/"
local OUT  = SYNC .. "terrain.json"
os.execute('mkdir -p "' .. SYNC .. '" 2>/dev/null || mkdir "' .. SYNC .. '" 2>nul')

local M_FT  = 3.28084
local ROWS, COLS = 24, 24
local DLAT, DLON = 0.35, 0.5          -- half-box (deg) around the aircraft
local probe = XPLMCreateProbe(0)      -- xplm_ProbeY

-- terrain elevation (ft MSL) at a lat/lon, via the vertical scenery probe
local function elev_ft(lat, lon)
  local x, y, z = XPLMWorldToLocal(lat, lon, 0)
  local res, _px, py = XPLMProbeTerrainXYZ(probe, x, y, z)
  if res ~= 0 then return 0 end                 -- 0 = xplm_ProbeHitTerrain
  local _plat, _plon, palt = XPLMLocalToWorld(x, py, z)
  return math.max(0, math.floor(palt * M_FT))
end

function gc_terrain_tick()
  local lat = get("sim/flightmodel/position/latitude")
  local lon = get("sim/flightmodel/position/longitude")
  local alt = math.floor(get("sim/flightmodel/position/elevation") * M_FT)  -- true MSL
  local n, s = lat + DLAT, lat - DLAT
  local w, e = lon - DLON, lon + DLON
  local cells = {}
  for r = 0, ROWS - 1 do                          -- r = 0 → north (top)
    local glat = n - (r / (ROWS - 1)) * (n - s)
    for c = 0, COLS - 1 do                         -- c = 0 → west
      local glon = w + (c / (COLS - 1)) * (e - w)
      cells[#cells + 1] = elev_ft(glat, glon)
    end
  end
  local f = io.open(OUT, "w")
  if not f then return end
  f:write(string.format(
    '{"lat":%.5f,"lon":%.5f,"alt":%d,"n":%.5f,"s":%.5f,"w":%.5f,"e":%.5f,"rows":%d,"cols":%d,"elev":[%s]}',
    lat, lon, alt, n, s, w, e, ROWS, COLS, table.concat(cells, ",")))
  f:close()
end

do_often("gc_terrain_tick()")     -- ~1×/sec
logMsg("[glass-cockpit] terrain probe active -> " .. OUT)