--[[
  ac-power.lua - displays Home Assistant AC power usage in the mpv HUD.

  Features:
    * Polls `/api/states/<sensor_id>` via curl with a long-lived token and trims the base URL to avoid duplicate slashes.
    * Debounces HUD spam by only re-rendering when watt deltas exceed `min_delta_watts` (or `min_delta_percent`) or when `force_refresh_interval` elapses.
    * Survives flaky networks with capped exponential backoff, optional HUD error messages, and redraws of the last known value after OSD clears.

  Configuration:
    Edit the CONFIG table below to match your Home Assistant deployment; the script ignores script-opts files.
]]

local CONFIG = {
  sensor_id = "sensor.ac_power", -- Home Assistant entity id
  ha_base_url = "http://homeassistant.local:8123",
  ha_token = "REPLACE_WITH_LONG_LIVED_TOKEN",
  poll_interval = 3, -- seconds between successful polls
  min_delta_watts = 5, -- only show when change ≥ delta
  min_delta_percent = 0, -- optional % change relative to last reading
  force_refresh_interval = 30, -- seconds, even if delta small
  force_refresh_obeys_threshold = true, -- skip force refresh when thresholds active
  display_label = "AC Power",
  units_label = "W",
  use_sensor_unit = true, -- prefer HA provided unit if any
  display_timeout = 3, -- seconds OSD message stays up
  decimal_places = 0, -- number formatting precision
  http_timeout = 2, -- curl timeout in seconds
  curl_binary = "curl", -- binary used for HTTP calls
  insecure_ssl = false, -- set true to allow self-signed
  max_backoff = 30, -- cap between retries when failing
  show_errors = true, -- display API errors via HUD
  initial_message = "Fetching AC power…", -- shown until first reading
  initial_message_duration = 0, -- 0 keeps OSD up until refreshed
}

-- No edits are required below unless you want to change script behavior.

local mp = require("mp")
local utils = require("mp.utils")
local msg = require("mp.msg")

local last_watts
local last_display_ts = 0
local last_unit
local request_inflight = false
local backoff_failures = 0
local poll_timer

local function log(level, text)
  msg[level]("ac-power: " .. text)
end

local function trim_trailing_slash(url)
  if url:sub(-1) == "/" then
    return url:sub(1, -2)
  end
  return url
end

local function build_url()
  return string.format(
    "%s/api/states/%s",
    trim_trailing_slash(CONFIG.ha_base_url),
    CONFIG.sensor_id
  )
end

local function build_request()
  local args = { CONFIG.curl_binary, "-sS", "-m", tostring(CONFIG.http_timeout) }
  if CONFIG.insecure_ssl then
    table.insert(args, "-k")
  end
  table.insert(args, "-H")
  table.insert(args, "Authorization: Bearer " .. CONFIG.ha_token)
  table.insert(args, build_url())
  return {
    name = "subprocess",
    playback_only = false,
    capture_stdout = true,
    args = args,
  }
end

local function format_value(value)
  local fmt = "%0." .. tostring(CONFIG.decimal_places) .. "f"
  return string.format(fmt, value)
end

local function sensor_units(payload)
  if CONFIG.use_sensor_unit and payload and payload.attributes then
    local unit = payload.attributes.unit_of_measurement
    if unit and unit ~= "" then
      return unit
    end
  end
  return CONFIG.units_label
end

local function show_message(text, duration)
  local timeout = duration
  if timeout == nil then
    timeout = CONFIG.display_timeout
  end
  mp.osd_message(text, timeout)
  last_display_ts = mp.get_time()
end

local function show_value(value_text, unit)
  show_message(string.format("%s: %s %s", CONFIG.display_label, value_text, unit or ""))
end

local function show_error(err)
  if CONFIG.show_errors then
    show_message(string.format("%s: -- (%s)", CONFIG.display_label, err))
  end
end

local function ensure_poll_timer(delay, fn)
  if poll_timer then
    poll_timer:kill()
  end
  poll_timer = mp.add_timeout(delay, function()
    poll_timer = nil
    fn()
  end)
end

local function meets_delta_threshold(value)
  if not value then
    return false
  end
  if not last_watts then
    return true
  end

  local delta = math.abs(value - last_watts)
  if delta >= CONFIG.min_delta_watts then
    return true
  end

  if CONFIG.min_delta_percent > 0 then
    local baseline = math.abs(last_watts)
    if baseline < 1e-6 then
      baseline = math.abs(value)
    end
    if baseline < 1e-6 then
      baseline = 1
    end
    local percent_delta = (delta / baseline) * 100
    if percent_delta >= CONFIG.min_delta_percent then
      return true
    end
  end

  return false
end

local function thresholds_enabled()
  return (CONFIG.min_delta_watts or 0) > 0 or (CONFIG.min_delta_percent or 0) > 0
end

local function handle_success(value, payload)
  backoff_failures = 0
  local now = mp.get_time()
  local printable = value and format_value(value) or "--"
  local unit = sensor_units(payload)
  local force_due = CONFIG.force_refresh_interval > 0
    and (now - last_display_ts) >= CONFIG.force_refresh_interval
  local significant_change = meets_delta_threshold(value)

  local should_render = significant_change or last_watts == nil
  if not should_render and force_due then
    local allow_force = true
    if thresholds_enabled() and CONFIG.force_refresh_obeys_threshold then
      allow_force = false
    end
    if allow_force then
      should_render = true
    end
  end

  if should_render then
    show_value(printable, unit)
    last_unit = unit
    last_watts = value
  end
end

local function redraw_last_value()
  if last_watts then
    show_value(format_value(last_watts), last_unit)
    return
  end
  if CONFIG.initial_message and CONFIG.initial_message ~= "" then
    show_message(
      string.format("%s: %s", CONFIG.display_label, CONFIG.initial_message),
      CONFIG.initial_message_duration
    )
  end
end

local function poll_sensor()
  if request_inflight then
    return
  end
  request_inflight = true

  mp.command_native_async(build_request(), function(success, result, err)
    request_inflight = false

    if not success or not result then
      backoff_failures = backoff_failures + 1
      local message = err or "request failed"
      log("error", message)
      show_error(message)
      local next_delay = math.min(CONFIG.max_backoff, CONFIG.poll_interval * (2 ^ backoff_failures))
      ensure_poll_timer(next_delay, poll_sensor)
      return
    end

    if result.status ~= 0 then
      backoff_failures = backoff_failures + 1
      local stderr = (result.stderr and result.stderr ~= "" and result.stderr)
        or ("curl exit " .. tostring(result.status))
      log("error", stderr)
      show_error(stderr)
      local next_delay = math.min(CONFIG.max_backoff, CONFIG.poll_interval * (2 ^ backoff_failures))
      ensure_poll_timer(next_delay, poll_sensor)
      return
    end

    if not result.stdout or result.stdout == "" then
      backoff_failures = backoff_failures + 1
      log("error", "empty response from Home Assistant")
      show_error("empty response")
      local next_delay = math.min(CONFIG.max_backoff, CONFIG.poll_interval * (2 ^ backoff_failures))
      ensure_poll_timer(next_delay, poll_sensor)
      return
    end

    local payload = utils.parse_json(result.stdout)
    if not payload then
      backoff_failures = backoff_failures + 1
      log("error", "invalid JSON payload")
      show_error("invalid JSON")
      local next_delay = math.min(CONFIG.max_backoff, CONFIG.poll_interval * (2 ^ backoff_failures))
      ensure_poll_timer(next_delay, poll_sensor)
      return
    end

    local numeric_value = tonumber(payload.state)
    if not numeric_value then
      log("warn", "sensor state not numeric: " .. tostring(payload.state))
      show_error("state unknown")
    else
      handle_success(numeric_value, payload)
    end

    backoff_failures = 0
    ensure_poll_timer(CONFIG.poll_interval, poll_sensor)
  end)
end

local function validate_config()
  if CONFIG.ha_base_url == "" then
    log("error", "ha_base_url is required")
    show_error("missing base url")
    return false
  end
  if CONFIG.sensor_id == "" then
    log("error", "sensor_id is required")
    show_error("missing sensor id")
    return false
  end
  if CONFIG.ha_token == "" or CONFIG.ha_token == "REPLACE_WITH_LONG_LIVED_TOKEN" then
    log("error", "ha_token must be set to a Home Assistant long-lived token")
    show_error("missing HA token")
    return false
  end
  return true
end

local function start()
  if not validate_config() then
    return
  end
  if CONFIG.initial_message and CONFIG.initial_message ~= "" then
    show_message(
      string.format("%s: %s", CONFIG.display_label, CONFIG.initial_message),
      CONFIG.initial_message_duration
    )
  end
  ensure_poll_timer(0.1, poll_sensor)
end

mp.register_script_message("ac-power-refresh", function()
  log("info", "manual refresh requested")
  ensure_poll_timer(0.01, poll_sensor)
end)

mp.register_event("shutdown", function()
  if poll_timer then
    poll_timer:kill()
    poll_timer = nil
  end
end)

mp.register_event("file-loaded", redraw_last_value)
mp.register_event("playback-restart", redraw_last_value)

start()