# 07_light_meter.py
# From the code for the Electronics Starter Kit for the Raspberry Pi by MonkMakes.com

#from Tkinter import *
from tkinter import *
import json
import RPi.GPIO as GPIO
import time, math
import requests # for pushing the readings to roaming-light-api
from datetime import datetime

# Configure the Pi to use the BCM (Broadcom) pin names, rather than the pin positions
GPIO.setmode(GPIO.BCM)

# This project uses a photoresistor, a component whose resistance varies with the light falling on it.
# To measure its resistance, the code records the time it takes for a capacitor to fill  
# when supplied by a current passing through the resistor. The lower the resistance the faster 
# it fills up. 
#
# You can think of a capacitor as a tank of electricity, and as it fills with charge, the voltage
# across it increases. We cannot measure that voltage directly, because the Raspberry Pi
# does not have an analog to digital convertor (ADC or analog input). However, we can time how long it
# takes for the capacitor to fill with charge to the extent that it gets above the 1.65V or so
# that counts as being a high digital input. 
# 
# For more information on this technique take a look at: 
# learn.adafruit.com/basic-resistor-sensor-reading-on-raspberry-pi
# The code here is based on that in the Raspberry Pi Cookbook (Recipes 12.1 to 12.3)


# Pin a charges the capacitor through a fixed 1k resistor and the thermistor in series
# pin b discharges the capacitor through a fixed 1k resistor 
a_pin = 18
b_pin = 23

# empty the capacitor ready to start filling it up
def discharge():
    GPIO.setup(a_pin, GPIO.IN)
    GPIO.setup(b_pin, GPIO.OUT)
    GPIO.output(b_pin, False)
    time.sleep(0.01) # 0.01 -- initial value

# return the time taken for the voltage on the capacitor to count as a digital input HIGH
# than means around 1.65V
def charge_time():
    GPIO.setup(b_pin, GPIO.IN)
    GPIO.setup(a_pin, GPIO.OUT)
    GPIO.output(a_pin, True)
    t1 = time.time()
    while not GPIO.input(b_pin):
        pass
    t2 = time.time()
    return (t2 - t1) * 1000000

# Take an analog readin as the time taken to charge after first discharging the capacitor
def analog_read():
    discharge()
    return charge_time()

# Convert the time taken to charge the cpacitor into a value of resistance
# To reduce errors, do it 100 times and take the average.
def read_resistance():
    n = 20
    total = 0;
    for i in range(1, n):
        total = total + analog_read()
    reading = total / float(n)
    resistance = reading * 6.05 - 939
    return resistance

def light_from_r(R):
    # Log the reading to compress the range
    return math.log(1000000.0/R) * 10.0

# Gets the time and date (at the time of the reading)
def get_timestamp():
    return datetime.now().strftime(("%Y-%m-%d %H:%M:%S"))

# Pushes the reading to roaming-light-api
def push_reading(lvalue):
    act = False
    if lvalue > 20:
        act = True
    time = get_timestamp()
    headers = {"content-type": "application/json"}
#    payload = { "active": act, "light-reading": int(lvalue), "timestamp": time }
    payload = { "reading": int(lvalue), "time": time}
#    res = requests.post("http://192.168.1.228:5000/api/readings/add/1", data=json.dumps(payload), headers=headers)
    res = requests.post("http://ritherdon.abbether.net/api/readings/add/1", data=json.dumps(payload), headers=headers)
#    print(int(lvalue))
#    print(res.status_code)
    print(payload)

# group together all of the GUI code into a class called App
class App:

    # this function gets called when the app is created
    def __init__(self, master):
        self.master = master
        frame = Frame(master, bg="black")
        frame.pack(expand=1)
        label = Label(frame, text='Light', fg="white", bg="black", font=("Helvetica", 32))
        label.grid(row=0)
        self.reading_label = Label(frame, text='12.34', bg="black", fg="white", font=("Helvetica", 110))
        self.reading_label.grid(row=1)
        self.update_reading()

    # Update the reading
    def update_reading(self):
        light = light_from_r(read_resistance())
        reading_str = "{:.0f}".format(light)
        self.reading_label.configure(text=reading_str)
        self.master.after(200, self.update_reading)
        push_reading(light)

# Set the GUI running, give the window a title, size and position
root = Tk()
# Uncomment when app. is ready for deployment
#root.attributes("-fullscreen", True)
root.attributes("-zoomed", True)
root.configure(background="black")
root.wm_title('Light Meter')
app = App(root)
root.geometry("400x300+0+0")
try:
    root.mainloop()
finally:
    print("Cleaning up")
    GPIO.cleanup()