#!/usr/bin/python3
#
import time
import threading
import json
import gzip
#
PROC_STAT_HEADERS = ('user', 'nice', 'system', 'idle', 'iowait', 'irq', 'softirq', 'steal', 'guest', 'guest_nice')
#
def get_cpu_stats(path='/proc/stat'):
	"""
	Get CPU statistics from /proc/stat. Output is returned for the system and each CPU.

	Ex:

	{'system': {'user': 8696397, 'nice': 22431, ...},
	 'cpus': {
	     0: {'user': 4199206, 'nice': 11615, ...},
	     1: {'user': 4199308, 'nice': 10642, ...}
	 }
	}
	"""
	#
	with open(path, 'r') as f:
		lines = f.readlines()
	#
	cpu_lines = [l for l in lines if l.startswith('cpu')]
	stats = {'system':None, 'cpus':{}}
	#
	for l in cpu_lines:
		l_split = l.split()
		cpu_index = l_split[0][3:]
		cpu_stats = {x[0]: int(x[1]) for x in zip(PROC_STAT_HEADERS, l_split[1:])}
		#
		if cpu_index == '':
			stats['system'] = cpu_stats
		else:
			stats['cpus'][int(cpu_index)] = cpu_stats
		#
	#
	return stats
#
def calculate_cpu_usage(initial, current):
	"""
	Calculation adapted from: https://stackoverflow.com/questions/23367857/accurate-calculation-of-cpu-usage-given-in-percentage-in-linux/
	"""
	#
	initial_idle = initial['idle'] + initial['iowait']
	current_idle = current['idle'] + current['iowait']
	#
	initial_non_idle = initial['user'] + initial['nice'] + initial['system'] + initial['irq'] + initial['softirq'] + initial['steal']
	current_non_idle = current['user'] + current['nice'] + current['system'] + current['irq'] + current['softirq'] + current['steal']
	#
	initial_total = initial_idle + initial_non_idle
	current_total = current_idle + current_non_idle
	#
	return (current_non_idle-initial_non_idle)/(current_total-initial_total)
#
def log_cpu_stats(path, interval, stop_event):
	"""
	Log the cpu stats to a gz compressed JSON file. Storing JSON
	seems to only use about 10% more disk space than storing
	bytes directly (4 bytes per value), so JSON is used for
	simplicity.

	path: file to save to
	interval: how many seconds to wait before getting more data
	stop_event: a threading.Event which stops the function
	"""
	#
	stats = {'timestamps':[], 'stats':{'system':[], 'cpus':{}}}
	while not stop_event.is_set():
		stats['timestamps'].append(time.time())
		#stats['stats'].append(get_cpu_stats())
		current_stats = get_cpu_stats()
		stats['stats']['system'].append(current_stats['system'])
		for cpu in current_stats['cpus']:
			if cpu not in stats['stats']['cpus']:
				stats['stats']['cpus'][cpu] = []
			#
			stats['stats']['cpus'][cpu].append(current_stats['cpus'][cpu])
		#
		stop_event.wait(interval)
	#
	with gzip.GzipFile(path, 'w') as f:
		# json.dump writes a string, but a gzip.GzipFile can only write bytes, so monkey-patch it
		old_write = f.write
		f.write = lambda s: old_write(s.encode('utf-8'))
		json.dump(stats, f)
	#
#
def load_cpu_stats(path):
	with gzip.GzipFile(path, 'r') as f:
		return json.load(f)
	#
#
'''
def log_cpu_stats(path, interval, stop_event):
	path: file to save to
	interval: how many seconds to wait before getting more data
	stop_event: a threading.Event which stops the function
	#
	with gzip.GzipFile(path+'.2.gz', 'w') as f:
		f.write(' '.join(PROC_STAT_HEADERS).encode('utf-8'))
		f.write('\n\n'.encode('utf-8'))
		#
		while not stop_event.is_set():
			f.write(str(time.time()).encode('utf-8'))
			f.write('\n'.encode('utf-8'))
			stats = get_cpu_stats()
			f.write('cpu '.encode('utf-8'))
			#f.write(' '.join([str(stats['system'][x]) for x in PROC_STAT_HEADERS]).encode('utf-8'))
			f.write(b''.join([stats['system'][x].to_bytes(4, byteorder='big') for x in PROC_STAT_HEADERS]))
			f.write('\n'.encode('utf-8'))
			for cpu in stats['cpus']:
				f.write('cpu{} '.format(cpu).encode('utf-8'))
				#f.write(' '.join([str(stats['cpus'][cpu][x]) for x in PROC_STAT_HEADERS]).encode('utf-8'))
				f.write(b''.join([stats['cpus'][cpu][x].to_bytes(4, byteorder='big') for x in PROC_STAT_HEADERS]))
				f.write('\n'.encode('utf-8'))
			#
			f.write('\n'.encode('utf-8'))
			time.sleep(interval)
		#
	#
#
'''
if __name__ == '__main__':
	stop_event = threading.Event()
	t = threading.Thread(target=log_cpu_stats, args=('/tmp/cpu_stats.json.gz', 0.5, stop_event))
	t.start()
	#
	try:
		while True:
			time.sleep(100)
		#
	except KeyboardInterrupt:
		stop_event.set()
		print()
	#
	t.join()
#