""" OLED_SSD1306 via I2C
    This program communicates with the OLED_SSD1306 via I2C.
    It uses a class SSD1306 that inherits from FrameBuffer.
    Connection: SCL - GP17, SDA - GP16
"""

import time
import framebuf
from machine import I2C, Pin

class SSD1306(framebuf.FrameBuffer):
    """Class for SSD1306 Graphic LCD controller
          which inherits class FrameBuffer from module framebuf.
    """

    DEV_ADDR = 0x3C
    SCREEN_WIDTH = 128
    SCREEN_HEIGHT = 64
    SCREEN_PAGE_NUM = 8
    WHITE = 1
    BLACK = 0

    def __init__(self):
        # Instantiate i2c with SCL - GP17, SDA - GP16
        self.i2c = I2C(0, scl = Pin(17), sda = Pin(16), freq = 100_000)
        self.ssd1306_init()     # send initialization commands

        # Instantiate a frame buffer
        self.buffer = bytearray(self.SCREEN_WIDTH * self.SCREEN_HEIGHT // 8)
        super().__init__(self.buffer, self.SCREEN_WIDTH, self.SCREEN_HEIGHT,
                         framebuf.MONO_VLSB)

    def send_data(self, data):
        """Write a byte of data to SSD1306"""
        self.i2c.writeto(self.DEV_ADDR, bytearray([0xC0, data]))

    def send_command(self, cmd):
        """Write a byte of command to SSD1306"""
        self.i2c.writeto(self.DEV_ADDR, bytearray([0x80, cmd]))

    def ssd1306_init(self):
        """Initialize SSD1306"""
        INIT_SEQ = (
            0xae,       # turn off oled panel
            0x00,       # set low column address
            0x10,       # set high column address
            0x40,       # set start line address
            0x20, 0x02, # page addressing mode
            0xc8,       # top-down segment (4th quadrant)
            0x81,       # set contrast control register
            0xcf, 0xa1, # set segment re-map 95 to 0
            0xa6,       # set normal display
            0xa8,       # set multiplex ratio(1 to 64)
            0x3f,       # 1/64 duty
            0xd3,       # set display offset
            0x00,       # not offset
            0xd5,       # set display clock divide ratio/oscillator frequency
            0x80,       # set divide ratio
            0xd9,       # set pre-charge period
            0xf1, 0xda, # set com pins hardware configuration
            0x12, 0xdb, # set vcomh
            0x40, 0x8d, # set Charge Pump enable/disable
            0x14,       # set(0x10) disable
            0xaf        # turn on oled panel
            )

        time.sleep_ms(100)

        for command in INIT_SEQ:
            self.send_command(command)

    def setRegion(self, x0, x1, y):
        """Set active region to x0, x1, y, y.
           The maximum region can be set is a page."""
        self.send_command(0x21)       # set column
        self.send_command(x0)         # starting column
        self.send_command(x1)         # end column
        self.send_command(0x22)       # set page
        self.send_command(y)          # starting page
        self.send_command(y)          # end page

    def flush(self):
        """Write the buffer to the display one page at a time"""
        for page in range(self.SCREEN_PAGE_NUM):
            self.setRegion(0, self.SCREEN_WIDTH - 1, page)
            for column in range(self.SCREEN_WIDTH):
                self.send_data(self.buffer[page * self.SCREEN_WIDTH + column])

"""The rest of the code will only be executed
   when program execution starts from this file.
"""
if __name__ == '__main__':
    # Initialize the SSD1306 controller
    ssd1306 = SSD1306()            

    # Write a message
    ssd1306.fill(ssd1306.BLACK)
    ssd1306.text('Hello from', 0, 5, ssd1306.WHITE)
    ssd1306.text('MicroPython!', 20, 16, ssd1306.WHITE)

    # Draw nested rectangles
    x = 10
    y = 30
    w = ssd1306.SCREEN_WIDTH - 20
    h = ssd1306.SCREEN_HEIGHT - 30
    c = ssd1306.WHITE

    while h > 0:
        ssd1306.fill_rect(x, y, w, h, c)
        x += 2
        y += 2
        w -= 4
        h -= 4
        c = ssd1306.WHITE if c == ssd1306.BLACK else ssd1306.BLACK

    # Write the frame buffer out to the display
    ssd1306.flush()