#! /usr/bin/env python3
# encoding: utf-8

"""
Fan control service.

Measures temperatures and sets fan PWM according to a configured curve.

See /etc/fand/config.json.example for more.
"""

import dec8
import os
import sys
import time

class Sensor:
	def __init__(self, source, weight=0.2):
		self.f = open(source, "rb")
		self.weight = weight
		self.value = None
	
	def measure(self):
		self.f.seek(0)
		raw = int(self.f.read())
		
		if self.value is None:
			self.value = raw
		else:
			self.value = int(self.weight * raw + (1-self.weight) * self.value)
		
		return self.value

class PWM:
	def __init__(self, chip, ch, period):
		self.chip_base = "/sys/class/pwm/pwmchip%d/" %(chip)
		self.ch_base = "/sys/class/pwm/pwmchip%d/pwm%d/" %(chip, ch)
		self.period = period
		self.duty_cycle = 0
		
		# export the channel to sysfs if necessary
		if not os.path.isdir(self.ch_base):
			with open(self.chip_base + "export", "w") as f:
				f.write(str(ch))
		
		# disable channel
		self.set_enabled(False)
		
		# acquire a duty cycle file descriptor
		self.f_dc = open(self.ch_base + "duty_cycle", "w")
		
		# Set 0 duty cycle so period can be freely set even if the channel was used before.
		# This may fail: ignore.
		try:
			self.set_duty_cycle(0)
		except OSError:
			pass
		
		# set period & polarity
		with open(self.ch_base + "period", "w") as f:
			f.write(str(period))
			
		with open(self.ch_base + "polarity", "w") as f:
			f.write("normal")
		
		# re-enable channel
		self.set_enabled(True)
	
	def set_enabled(self, enabled):
		with open(self.ch_base + "enable", "r+") as f:
			current = f.read().strip()
			requested = "1" if enabled else "0"
			
			if current != requested:
				f.seek(0)
				f.write(requested)
	
	def set_percent(self, pc):
		self.set_duty_cycle(self.period * pc/100)
	
	def set_duty_cycle(self, dc):
		self.duty_cycle = int(dc)
		self.f_dc.seek(0)
		self.f_dc.write(str(self.duty_cycle))
		self.f_dc.flush()

def linlut(a, seq):
	"""
	Given a value `a` and a sorted list of tuples `seq`,
	finds a pair in `seq` whose first elements are closest
	to ... well you know what I mean. Read the code. It's
	shorter than this paragraph.
	"""
	
	smaller = None
	larger = None
	
	for d in seq:
		if d[0] <= a:
			smaller = d
		
		elif d[0] > a:
			larger = d
			break
	
	if not smaller:
		return seq[0][1]
	
	if not larger:
		return seq[-1][1]
	
	ratio = (a - smaller[0]) / (larger[0] - smaller[0])
	dy = larger[1] - smaller[1]
	
	return smaller[1] + ratio * dy

def printf(fmt, *args, stream=sys.stderr):
	print(fmt % args, file=stream, flush=True)

if __name__ == "__main__":
	try:
		cfg = dec8.cfg.Config.from_file("/etc/fand/config.json")
	except FileNotFoundError:
		printf("!!! missing /etc/fand/config.json")
	
	s = Sensor(cfg.sensor.source, cfg.sensor.weight)
	p = PWM(cfg.pwm.chip, cfg.pwm.channel, cfg.pwm.period)
	
	if len(sys.argv) == 3 and sys.argv[1] == "--set":
		try:
			percentage = int(sys.argv[2])
		except:
			print("--set must be followed by a number")
			sys.exit(1)
		
		p.set_percent(percentage)
		sys.exit(0)
	
	while True:
		temperature = s.measure()
		percentage = linlut(temperature, cfg.map)
		p.set_percent(percentage)
		
		if cfg.control.verbose:
			printf("%.01f °C -> %d %% (%d/%d µs)",
				temperature / 1000,
				percentage,
				p.duty_cycle // 1000,
				p.period // 1000
			)
		
		time.sleep(cfg.control.interval)