#!/usr/bin/python
#
# Read sensors and store them in individual files
#
# author: Vasilis.Vlachoudis@cern.ch
# version: 0.0
# date: Sep 2012

import os
import sys
import time
import math
import serial
import struct

recordFmt = "=dBHHff"
recordLength = struct.calcsize(recordFmt)

recordSeekStep = 20		# Seeking record block

port     = "/dev/ttyAMA0"
baudrate = 4800
#parity  = "N"

tempR = R10 = 10000.0	# Ohm
tempB = 3988.0		# K
tempA = tempR / math.exp(tempB / (273.0+25.0))

# -----------------------------------------------------------------------------
# Convert adc reading to temperature 
# Rt = A*exp(B/T(K))
#
# V1 = V / (R10 + Rt) * R10
# adc = V1/V * 255(max)
# Rt = (255/adc - 1.0)*R10
# T(C) = B/log(Rt/A) - 273.0
# -----------------------------------------------------------------------------
def temp(adc):
	Rt = (255.0/float(adc) - 1.0) * R10
	t = tempB / math.log(Rt/tempA) - 273.0
	return max(-30.0,min(t,45.0))	# Limit to -30 .. 45

# -----------------------------------------------------------------------------
def humidity(adc, temp):
	return 0.0

# -----------------------------------------------------------------------------
# Read a sensors record to database
# -----------------------------------------------------------------------------
def writeRecord(f, timestamp, record):
	if len(record) != 6: return False
	if record[0] != "DATA": return False
	try:
		sid    = int(record[1])
		switch = int(record[2])
		adc1   = int(record[3])
		adc2   = int(record[4])
		chk    = int(record[5])
	except:
		return False

	# Verify checksum
	sum  = 2*switch + sid
	sum += 3*adc1
	sum += 4*adc2
	sum %= 256
	if chk != sum: return False

	t = temp(adc1)
	h = humidity(adc2,t)

	f.write(struct.pack(recordFmt, timestamp, switch, adc1, adc2, t, h))
	f.flush()
	#sys.stdout.write('insert into Sensors values (%d,%f,%d,%d,%d,%f)\n' % \
	#	(sid, timestamp, switch, adc1, adc2, t))
	return True

# -----------------------------------------------------------------------------
def readRecord(f):
	try:
		return f.read(recordLength)
	except:
		return None

# -----------------------------------------------------------------------------
def seekTime(f, tstart):
	# Seek to the end
	try: f.seek(-recordSeekStep*recordLength,2)
	except: pass
	while True:
		record = readRecord(f)
		if record is None: break
		rec = unpack(record)
		if rec is None: break

		if rec[0] > tstart:
			# roll back another block
			try:
				f.seek(-recordSeekStep*recordLength,1)
				continue
			except:
				break

		# We are getting close
		# read one by one the records and stop when >
		for i in range(recordSeekStep-1):
			record = readRecord(f)
			if record is None: break
			rec = unpack(record)
			if rec is None: break
			if rec[0] > tstart:
				# seek one back
				f.seek(-recordLength,1)
				break
		break
	return f.tell()

# -----------------------------------------------------------------------------
def unpack(record):
	if len(record)!=recordLength: return None
	return struct.unpack(recordFmt, record)

# -----------------------------------------------------------------------------
# Open communication port with PICAXE
# -----------------------------------------------------------------------------
def openComm():
	return serial.Serial(port, baudrate)
		#, parity=parity) #, rtscts=rtscts, xonxoff=xonxoff, timeout=1)