--[[
  altlog.lua 
  Verson: 1.2

  A Lua script for EdgeTX. When activated, logs the instantaneous value of "Alt+" to a CSV file.

  USAGE
  -----
    EdgeTX Special Function, type='Lua Script', value = 'altlog.lua', repeat = '1x'

  WHAT IT DOES
  ============
  On activation of special function: 
  1. Builds a log filename from the model name and today's date:
    /LOGS/modelname_ALT_yyyy-mm-dd.csv
  2. Creates the file (with a header row) if it doesn't already exist.
  3. Reads the "Alt+" telemetry sensor (max altitude).
  4. Appends one line: either
      2026-08-12 15:23:26, 45 m
    or, if no telemetry is available:
      2026-08-12 15:23:26, no ALT+ telemetry

  INSTALLATION
  ============
  Install the script on your EdgeTX radio as follows:
  1. Rename the file to altlog.lua (if different)
  2. Copy the file to /SCRIPTS/FUNCTIONS/ on the SD card or flash memory.
  3. In MODEL -> Special Functions, add a special function with these settings:
      Trigger: <whatever switch you want to trigger the log, e.g. a momentary SA>
      Function: 'Lua Script'
      Value: altlog.lua
      Repeat: 1x (important to avoid repeated logging while the switch is held)
      Enable: checked

  To record launch heights with an RC-Soar DLG template, identify the existing special function 
  which calls out launch height, and use the same trigger in the new special function.

  HISTORY
  =======
  2026-08-27: v1.2 - More robust checking for telemetry stream
  2026-08-26: v1.1 - Mild refactoring
  2026-08-25: v1.0 - Initial release
  
  LICENSE
  =======
  Copyright (c) Mike Shellim
  This script is provided under the GNU General Public License v3.
  https://www.gnu.org/licenses/gpl-3.0.en.html
]]

local LOG_DIR    = "/LOGS/"
local ALT_SENSOR = "Alt+" -- '+' so that maximum height is logged, not current height

local function sanitise(name)
  return (string.gsub(name, "[^%w%-]", "_"))
end

local function buildTimestamps()
  local dt = getDateTime()
  local dateStr = string.format("%04d-%02d-%02d", dt.year, dt.mon, dt.day)
  local timeStr = string.format("%02d:%02d:%02d", dt.hour, dt.min, dt.sec)
  return dateStr, dateStr .. " " .. timeStr
end

local function logFilePath(dateStr)
  local modelName = sanitise(model.getInfo().name or "model")
  return LOG_DIR .. modelName .. "_ALT_" .. dateStr .. ".csv"
end

local function fileExists(path)
  local f = io.open(path, "r")
  if f then
    io.close(f)
    return true
  end
  return false
end

local function writeRecord()
  local dateStr, timestamp = buildTimestamps()
  local path = logFilePath(dateStr)
  local isNew = not fileExists(path)

  local f = io.open(path, "a")
  if not f then
    -- Couldn't open (e.g. /LOGS missing on the SD card) - nothing more
    -- we can do from here.
    return
  end

  if isNew then
    io.write(f, "time, altitude\n")
  end

  local alt = getSourceValue(ALT_SENSOR)
  local line
  if alt ~= nil then
    line = string.format("%s, %.2f", timestamp, alt)
  else
    line = string.format("%s, no %s telemetry", timestamp, ALT_SENSOR)
  end

  io.write(f, line .. "\n")
  io.close(f)
end

local function init()
end

local function run(event)
  writeRecord()
  return 0
end

return { init = init, run = run }