dcf77_pin=6
led_pin=4

min_ambient_light=25

last_valid_rise=0

valid_rise_min=990000
valid_rise_max=1010000
valid_timeout=5000000

valid_newmin_min=1990000
valid_newmin_max=2100000

valid_0_min=100000
valid_0_max=140000
valid_1_min=200000
valid_1_max=250000

dcfdata=""

valid_times=0
total_times=0

bcd={}
bcd[1]=1
bcd[2]=2
bcd[3]=4
bcd[4]=8
bcd[5]=10
bcd[6]=20
bcd[7]=40
bcd[8]=80

dow={}
dow[0]="Invalid"
dow[1]="Mon"
dow[2]="Tue"
dow[3]="Wed"
dow[4]="Thu"
dow[5]="Fri"
dow[6]="Sat"
dow[7]="Sun"

mon_days={}
mon_days[1]=31
mon_days[2]=28
mon_days[3]=31
mon_days[4]=30
mon_days[5]=31
mon_days[6]=30
mon_days[7]=31
mon_days[8]=31
mon_days[9]=30
mon_days[10]=31
mon_days[11]=30
mon_days[12]=31

function bcd2dec(data)
 local value=0
 for count=1,string.len(data),1
 do
  if string.sub(data,count,count)=="1" and bcd[count]~=nil then
   value=value+bcd[count]
  end
 end
 return value
end

function check_parity(data)
 local onecount=0
 for count=1,string.len(data),1
 do
  if string.sub(data,count,count)=="1" then
   onecount=onecount+1
  end
 end
 if onecount%2==0 then
  return true
 end
 return false
end

gps_sec=0
gps_valid=false
gps_part1=""
gps_part2=""
gps_part_checksum=0

hex={}
hex[0]="0"
hex[1]="1"
hex[2]="2"
hex[3]="3"
hex[4]="4"
hex[5]="5"
hex[6]="6"
hex[7]="7"
hex[8]="8"
hex[9]="9"
hex[10]="A"
hex[11]="B"
hex[12]="C"
hex[13]="D"
hex[14]="E"
hex[15]="F"

function send_gpsstring()
 local gps_data
 local gps_checksum=gps_part_checksum
 local part1len=string.len(gps_part1)

 if gps_sec<10 then
  gps_data=gps_part1.."0"..gps_sec..gps_part2
 else
  gps_data=gps_part1..gps_sec..gps_part2
 end

 gps_checksum=bit.bxor(gps_checksum,string.byte(string.sub(gps_data,part1len+1,part1len+1)))
 gps_checksum=bit.bxor(gps_checksum,string.byte(string.sub(gps_data,part1len+2,part1len+2)))

 local digit1=bit.rshift(gps_checksum,4)
 local digit2=bit.band(gps_checksum,15)

 print("$"..gps_data.."*"..hex[digit1]..hex[digit2].."\r")
end

function parse_data(data)
 total_times=total_times+1
 --print("-------------------------------------------------------------")
 --print(data)
 --print("Resrv: ",string.sub(data,1,15))
 --print("Info: ",string.sub(data,16,21))
 --print("Min: ",string.sub(data,22,29),bcd2dec(string.sub(data,22,28)),check_parity(string.sub(data,22,29)))
 --print("Hour: ",string.sub(data,30,36).." ",bcd2dec(string.sub(data,30,35)),check_parity(string.sub(data,30,36)))
 --print("Day: ",string.sub(data,37,42).."  ",bcd2dec(string.sub(data,37,42)))
 --print("DOW: ",string.sub(data,43,45).."     ",bcd2dec(string.sub(data,43,45)))
 --print("Month: ",string.sub(data,46,50).."    ",bcd2dec(string.sub(data,46,50)))
 --print("Year: ",string.sub(data,51,59),bcd2dec(string.sub(data,51,59)),check_parity(string.sub(data,37,59)))
 --print("Rest: ",string.sub(data,60))
 --if string.len(data)==59 then
 -- print("Time/date : "..bcd2dec(string.sub(data,30,35))..":"..bcd2dec(string.sub(data,22,28)).." "..dow[bcd2dec(string.sub(data,43,45))].." 20"..bcd2dec(string.sub(data,51,59)).."-"..bcd2dec(string.sub(data,46,50)).."-"..bcd2dec(string.sub(data,37,42)))
 --end

 gps_valid=false

 local min
 local hour
 local day
 local mon
 local year

 if data==nil then
  --print("No data received")
  return
 end

 if string.len(data)~=59 then
  --print("Data length invalid")
  return
 end
 --print("Data length valid")

 if string.sub(data,18,18)==string.sub(data,19,19) then
  --print("Timezone data is invalid")
  return
 end
 --print("Timezone data is valid")

 if string.sub(data,21,21)=="0" then
  --print("Start time bit is invalid")
  return
 end
 --print("Start time bit is valid")

 if not check_parity(string.sub(data,22,29)) then
  --print("Minute parity invalid")
  return
 end
 --print("Minute parity valid")
 min=bcd2dec(string.sub(data,22,28))
 if min>59 then
  --print("Minute value invalid")
  return
 end
 --print("Minute value valid")

 if not check_parity(string.sub(data,30,36)) then
  --print("Hour parity invalid")
  return
 end
 --print("Hour parity valid")
 hour=bcd2dec(string.sub(data,30,35))
 if hour>23 then
  --print("Hour valid invalid")
  return
 end
 --print("Hour valid valid")

 if not check_parity(string.sub(data,37,59)) then
  --print("Date parity invalid")
  return
 end
 --print("Date parity valid")

 day=bcd2dec(string.sub(data,37,42))
 if day<1 or day>31 then
  --print("Day value invalid")
  return
 end
 --print("Day valud valid")

 mon=bcd2dec(string.sub(data,46,50))
 if mon<1 or mon>12 then
  --print("Month value invalid")
  return
 end
 --print("Month value valid")

 year=bcd2dec(string.sub(data,51,59))
 if year<22 or year>30 then
  --print("Year value invalid")
  return
 end
 --print("Year value valid")

 valid_times=valid_times+1
 --print("Total "..valid_times.." valid times and "..total_times-valid_times.." invalid times")

 if string.sub(data,18,18)==1 then
  --print("Subtracting 1 hour for CET timezone")
  hour=hour-1
 else
  --print("Subtracting 2 hours for CEST timezone")
  hour=hour-2
 end
 if hour<0 then
  hour=hour+24
  day=day-1
  if day<1 then
   mon=mon-1
   if mon<1 then
    mon=12
    year=year-1
   end
   if mon==2 and year%4==0 then
    day=day+1
   end
   day=mon_days[mon]
  end
 end
 gps_part1=string.format("GPZDA,%02d%02d",hour,min)
 gps_part2=string.format(".000,%02d,%02d,20%02d,,",day,mon,year)

 local gps_data=gps_part1..gps_part2
 gps_part_checksum=0

 for count=1,string.len(gps_data)
 do
  gps_part_checksum=bit.bxor(gps_part_checksum,string.byte(string.sub(gps_data,count,count)))
 end

 gps_sec=0
 gps_valid=true
 send_gpsstring()
end

function irq_handler(level,when,count)
 if count>10 then
  --print("Waiting for stable signal, changing to polling")
  start_poll()
  return
 end
 if when<last_valid_rise then
  delta=(2147483647-last_valid_rise)+when
 else
  delta=when-last_valid_rise
 end
 if level==1 then
  --print("Rise delta: "..delta)
  if last_valid_rise==0 then
   last_valid_rise=when
   return
  end
  if delta>valid_newmin_min and delta<valid_newmin_max then
   parse_data(dcfdata)
   dcfdata=""
   last_valid_rise=when
   return
  end
  if delta>valid_rise_min and delta<valid_rise_max then
   --print("valid")
   last_valid_rise=when
   if gps_valid==true then
    gps_sec=gps_sec+1
    if gps_sec<60 then
     send_gpsstring()
     if adc.read(0)>min_ambient_light then
      gpio.write(led_pin,gpio.LOW)
     end
    else
     gps_valid=false
     gpio.write(led_pin,gpio.HIGH)
    end
   end
   return
  end
  if delta>valid_timeout then
   --print("Valid timeout")
   last_valid_rise=0
   return
  end
 end
 if level==0 then
  --print("Pulse length: "..delta)
  if delta>valid_0_min and delta<valid_0_max then
   --print("0")
   dcfdata=dcfdata.."0"
   gpio.write(led_pin,gpio.HIGH)
  end
  if delta>valid_1_min and delta<valid_1_max then
   --print("1")
   dcfdata=dcfdata.."1"
   gpio.write(led_pin,gpio.HIGH)
  end
  if string.len(dcfdata)>59 then
   dcfdata=string.sub(dcfdata,2)
  end
 end
end

function irq_dummy(level,when,count)
 --print("Dummy IRQ handler")
 return
end

poll_prev_value=0
poll_value_count={}
poll_value_count[0]=0
poll_value_count[1]=0
poll_clean=0

function poll_handler()
 local value
 value=gpio.read(dcf77_pin)
 if value==nil then
  poll_timer:start()
 end
 if value==1 and poll_prev_value==0 then
  --print(poll_value_count[0],poll_value_count[1])
  if poll_value_count[0]>70 and poll_value_count[0]<100 and poll_value_count[1]>6 and poll_value_count[1]<30 then
   poll_clean=poll_clean+1
   --print(poll_clean.." clean pulses")
   if poll_clean>10 then
    poll_clean=0
    --print("Clean signal, swithcing to IRQ handling")
    start_irq()
    return
   end
  else
   poll_clean=0
  end
  poll_value_count[0]=0
  poll_value_count[1]=0
 end
 poll_prev_value=value
 poll_value_count[value]=poll_value_count[value]+1
 poll_timer:start()
end

poll_timer=tmr.create()
poll_timer:register(10, tmr.ALARM_SEMI,poll_handler)

function start_poll()
 gpio.write(led_pin,gpio.HIGH)
 gpio.trig(dcf77_pin,"none",irq_dummy)
 gpio.mode(dcf77_pin,gpio.INPUT)
 poll_timer:start()
end

function start_irq()
 gpio.mode(led_pin,gpio.OUTPUT)
 gpio.write(led_pin,gpio.HIGH)
 gps_valid=false
 gpio.trig(dcf77_pin,"both",irq_handler)
 gpio.mode(dcf77_pin,gpio.INT)
end

function start_dcf77()
 start_irq()
end

function stop_dcf77()
 gpio.mode(dcf77_pin,gpio.INPUT)
 poll_timer:stop()
 gpio.write(led_pin,gpio.HIGH)
end