# @name    Air Quality (CN)
# @desc    AQI for a Chinese city from the Tianapi air quality API
# @author  Golevka2001
# @version 1.0
# @config  api_key  text    "API Key"  help="tianapi.com console"
# @config  area     text    "City"     default="北京"  help="Chinese city name"
# @config  every    number  "Refresh"  default=60  min=1  unit=min

class AirQuality
  # AQI band thresholds with the matching icon and colour (China's standard)
  var levels, url, aqi, label, ic, color, tx, err
  # refresh countdown + failure backoff, see due()/failed()/ok()/now()
  var ticks, span, retry, busy

  def init()
    self.levels = [
      [50, "47651", 0x71D608],
      [100, "47652", 0xFAFF1B],
      [150, "47653", 0xF98718],
      [200, "47654", 0xF70017],
      [300, "47655", 0x8F00FF],
      [-1, "47656", 0x870089],
    ]
    # saving a setting restarts the app, so the URL built here never goes stale
    self.url = ""
    var key = store.get("api_key")
    if key != nil && key != ""
      self.url = "https://apis.tianapi.com/aqi/index?key=" + str(key) +
                 "&area=" + str(store.get("area"))
    end
    self.aqi = nil
    self.label = "--"
    self.ic = "47657"
    self.color = 0x666666
    self.tx = 9
    self.ticks = 0
    self.span = 60
    self.retry = 30
    self.busy = false
    self.err = false
  end

  # first fetch + fill display state before the first frame
  def setup()
    self.loop()
  end

  # select forces a refresh; left and right just rotate
  def on_button(btn)
    if btn == "select"
      self.now()
    end
  end

  def on_body(body, status)
    shared.set("f", 0)
    # non-200 or nil body: nothing usable this attempt
    if status != 200 || body == nil
      self.failed()
      return
    end
    var m = re.search("\"aqi\":\"?(\\d+)", body)
    if m == nil
      self.failed()
      return
    end
    var n = num(m[1])
    if n == nil
      self.failed()
      return
    end
    self.ok()
    self.aqi = n
  end

  def loop()
    # url checked first: due() raises busy as a side effect
    if self.url != "" && self.due(store.get("every"))
      shared.set("f", 1)
      # keep only the 24 bytes after the needle
      http.get(self.url, / b, st -> self.on_body(b, st),
               {'find': "\"aqi\":", 'keep': 24})
    end

    # pick the band, colour and label for the current reading
    if self.aqi != nil
      self.label = str(int(self.aqi))
      var i = 0
      while i < size(self.levels) - 1 && self.levels[i][0] >= 0 &&
            self.aqi > self.levels[i][0]
        i += 1
      end
      self.ic = self.levels[i][1]
      self.color = self.levels[i][2]
    else
      self.label = self.err ? "?" : "--"
      self.color = self.err ? 0xCC7722 : 0x666666
    end
    self.tx = 9 + int((width() - 9 - text_ink_width(self.label)) / 2)
  end

  # Fires at most once per interval, never while a request is out or another
  # app's TLS handshake is running (shared "f" flag, official convention).
  # Raises busy, so only call it when a request will actually be issued.
  def due(every)
    self.span = max(60, num(every, 1) * 60)
    if self.ticks > 0
      self.ticks = self.ticks - 1
      return false
    end
    if self.busy
      return false
    end
    for k : shared.keys()
      var n = size(k)
      if n > 2 && k[n - 2 .. n - 1] == ".f" && shared.get(k) == 1
        var a = shared.age(k)
        if a != nil && a < 20000
          return false
        end
      end
    end
    self.ticks = self.span
    self.busy = true
    return true
  end

  # failure backoff: retry at 30s, doubling, capped at the interval; raises
  # err so a fetch with no data yet can show "?" instead of "..."
  def failed()
    self.busy = false
    self.ticks = self.retry
    self.retry = min(self.retry * 2, self.span)
    self.err = true
  end

  def ok()
    self.busy = false
    self.retry = 30
    self.err = false
  end

  # manual refresh: clears the countdown but leaves busy alone, so a press
  # while a request is out can't fire a second one
  def now()
    self.ticks = 0
    self.retry = 30
  end

  def draw()
    clear()
    if !icon(self.ic, 0, 0)
      rect_fill(0, 0, 8, 8, 0x222222)
    end
    text(self.tx, 6, self.label, self.color)
  end
end

return AirQuality()