import time
import struct

# dictionary to map device names to numeric values 
# (<255 means we can fit it into a 1-byte categorical variable)
device_map = { "iphone":0, "android":1, "windows":2 }

# write header
output_file = open("example.dmp","w")
output_file.write("name: example\n")
output_file.write("encoding: binary\n")
output_file.write("field: latitude,float\n")
output_file.write("field: longitude,float\n")
output_file.write("field: checkin_time,uint64\n")
output_file.write("field: checkin_device,uint8\n")
for (k,v) in device_map.iteritems():
    output_file.write("valname: checkin_device," + str(v) + "," + str(k) +"\n")
output_file.write("\n")

# write records based on the csv lines
input_file = open("example.csv","r")
line_no = 0
while True:
    line_no += 1
    line = input_file.readline().strip()
    if not line:
        break
    if line_no == 1:
        continue
    tokens = line.split(",")
    latitude       = float(tokens[0])
    longitude      = float(tokens[1])
    checkin_time   = int(time.mktime(time.strptime(tokens[2],"%Y-%m-%dT%H:%M")))
    checkin_device = int(device_map[tokens[3]])
    # print latitude, longitude, checkin_time, checkin_device
    # little endian: 4 bytes float, 4 bytes float, 8 bytes unix time, 1 byte device
    data = struct.pack("<ffQB", latitude, longitude, checkin_time, checkin_device)
    output_file.write(data)

input_file.close()
output_file.close()