#!/usr/bin/env python
  
  # Copyright 2017 Yiwen Shao
  # Apache 2.0
  import sys
  import struct
  
  """ Provide an function to write bmp image to stdout with the input two dimensional
      list.
      usage: bmp_encoder(data, width, height)
      For instance:
      data = [[0, 255, 0, 0, 0, 255], [255, 0, 0, 0, 255, 255]]
      bmp_encoder(data, 2, 2) will write a 2*2 rgb bmp image to the stdout. 
      image :[ green    blue
               red      yellow ]
  """
  
  def bmp_encoder(data, width, height):
      bmp_header = [0] * 16
      header_size = 54 # the bmp header is 54 bytes long
      bmp_header[0] = struct.pack('<B', 0x42) # 1 byte, B
      bmp_header[1] = struct.pack('<B', 0x4D) # 1 byte, D
      bmp_header[2] = struct.pack('<I',0) # 4 bytes, fullsize of file, fill in later
      bmp_header[3] = struct.pack('<I',0) # 4 bytes, This data is reserved but can just be set to 0
      bmp_header[4] = struct.pack('<I',header_size) # 4 bytes, Pixel offset, 54 bytes here
      bmp_header[5] = struct.pack('<I',40) # 4 bytes, BITMAPINFOHEADER
      bmp_header[6] = struct.pack('<I',width) # 4 bytes, width
      bmp_header[7] = struct.pack('<I',height) # 4 bytes, width
      bmp_header[8] = struct.pack('<H',1) # 2 bytes, The number of color planes, must be set to 1
      bmp_header[9] = struct.pack('<H',24) # 2 bytes, The number of bits per pixel. 
      bmp_header[10] = struct.pack('<I',0) # 4 bytes, Disable Compression
      bmp_header[11] = struct.pack('<I',0) # 4 bytes, Size of raw pixel data, fill in later
      bmp_header[12] = struct.pack('<I',2835) # 4 bytes, horizontal resolution. Just leave it at 2835
      bmp_header[13] = struct.pack('<I',2835) # 4 bytes, vertical resolution. Just leave it at 2835.
      bmp_header[14] = struct.pack('<I',0) # 4 bytes, The number of colors, leave at 0 to default to all colors
      bmp_header[15] = struct.pack('<I',0) # 4 bytes, The important colors, leave at 0 to default to all colors
      
      bmp_body = []
      for i in range(height):
          for j in range(width):
              # bmp is in GBR and from bottom to top
              bmp_body.append(struct.pack('<B', data[height -1 - i][j * 3 + 2]))
              bmp_body.append(struct.pack('<B', data[height -1 - i][j * 3 + 1]))
              bmp_body.append(struct.pack('<B', data[height -1 - i][j * 3 + 0]))
          while len(bmp_body) % 4 != 0:
              bmp_body.append(struct.pack('<B',0)) # pad each row with bytes at the end till its length is a multiple of 4
      
      rawpixel_size = len(bmp_body)        
      file_size = rawpixel_size + header_size
      bmp_header[2] = struct.pack('<I',file_size)
      bmp_header[11] = struct.pack('<I',rawpixel_size)
      
      output = bmp_header + bmp_body
      for i in range(len(output)):
          sys.stdout.write(output[i])