import utime
import gc

from lcd_api import LcdApi
from machine import I2C

# PCF8574 pin definitions
MASK_RS = 0x01       # P0
MASK_RW = 0x02       # P1
MASK_E  = 0x04       # P2

SHIFT_BACKLIGHT = 3  # P3
SHIFT_DATA      = 4  # P4-P7

class I2cLcd(LcdApi):
	
	#Implements a HD44780 character LCD connected via PCF8574 on I2C

	def __init__(self, i2c, i2c_addr, num_lines, num_columns):
		self.i2c = i2c
		self.i2c_addr = i2c_addr
		self.i2c.writeto(self.i2c_addr, bytes([0]))
		utime.sleep_ms(20)   # Allow LCD time to powerup
		# Send reset 3 times
		self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
		utime.sleep_ms(5)    # Need to delay at least 4.1 msec
		self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
		utime.sleep_ms(1)
		self.hal_write_init_nibble(self.LCD_FUNCTION_RESET)
		utime.sleep_ms(1)
		# Put LCD into 4-bit mode
		self.hal_write_init_nibble(self.LCD_FUNCTION)
		utime.sleep_ms(1)
		LcdApi.__init__(self, num_lines, num_columns)
		cmd = self.LCD_FUNCTION
		if num_lines > 1:
			cmd |= self.LCD_FUNCTION_2LINES
		self.hal_write_command(cmd)
		gc.collect()

	def hal_write_init_nibble(self, nibble):
		# Writes an initialization nibble to the LCD.
		# This particular function is only used during initialization.
		byte = ((nibble >> 4) & 0x0f) << SHIFT_DATA
		self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
		self.i2c.writeto(self.i2c_addr, bytes([byte]))
		gc.collect()
		
	def hal_backlight_on(self):
		# Allows the hal layer to turn the backlight on
		self.i2c.writeto(self.i2c_addr, bytes([1 << SHIFT_BACKLIGHT]))
		gc.collect()
		
	def hal_backlight_off(self):
		#Allows the hal layer to turn the backlight off
		self.i2c.writeto(self.i2c_addr, bytes([0]))
		gc.collect()
		
	def hal_write_command(self, cmd):
		# Write a command to the LCD. Data is latched on the falling edge of E.
		byte = ((self.backlight << SHIFT_BACKLIGHT) |
				(((cmd >> 4) & 0x0f) << SHIFT_DATA))
		self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
		self.i2c.writeto(self.i2c_addr, bytes([byte]))
		byte = ((self.backlight << SHIFT_BACKLIGHT) |
				((cmd & 0x0f) << SHIFT_DATA))
		self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
		self.i2c.writeto(self.i2c_addr, bytes([byte]))
		if cmd <= 3:
			# The home and clear commands require a worst case delay of 4.1 msec
			utime.sleep_ms(5)
		gc.collect()

	def hal_write_data(self, data):
		# Write data to the LCD. Data is latched on the falling edge of E.
		byte = (MASK_RS |
				(self.backlight << SHIFT_BACKLIGHT) |
				(((data >> 4) & 0x0f) << SHIFT_DATA))
		self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
		self.i2c.writeto(self.i2c_addr, bytes([byte]))
		byte = (MASK_RS |
				(self.backlight << SHIFT_BACKLIGHT) |
				((data & 0x0f) << SHIFT_DATA))      
		self.i2c.writeto(self.i2c_addr, bytes([byte | MASK_E]))
		self.i2c.writeto(self.i2c_addr, bytes([byte]))
		gc.collect()