from collections import namedtuple

class Pixel(namedtuple('Pixel', ['r', 'g', 'b'])):
	def _verify(self):
		if max(self.r, self.g, self.b) > 255:
			raise ValueError('Some component too bright.')
		if min(self.r, self.g, self.b) < 0:
			raise ValueError('Some component negative.')
	def __add__(self, other):
		return Pixel(
			self.r + other.r,
			self.g + other.g,
			self.b + other.b,
			)
	def __mul__(self, other):
		if not isinstance(other, int) or not isinstance(other, float):
			raise ValueError('Can only multiply by number')
		return Pixel(
			other*pixel.r,
			other*pixel.g,
			other*pixel.b,
			)

def weighted_average(p1, w1, p2, w2):
	too_big = w1*p1 + w2*p2
	coef = 1/(w1+w2)
	return coef * too_big

class Picture:
	def __init__(self, data):
		self.pixels = data
		self.w = len(data[0])
		self.h = len(data)

	@classmethod
	def load(cls, filename):
		from PIL import Image
		im = Image.open(filename)
		im = im.convert('RGB')
		ht = im.height
		wt = im.width
		data = []
		access = im.getdata().pixel_access()
		for y in range(ht):
			line = []
			for x in range(wt):
				line.append(Pixel(*(access[x, y])))
			data.append(line)
		
		result = cls(data)
		assert result.w == wt
		assert result.h == ht
		return result

	def _to_pil(self):
		# Create int iterable
		# TODO: If this is slow, we should use a generator.
		seq = []
		for line in self.pixels:
			for pix in line:
				seq.extend(pix)
		
		# bytes…
		b = bytes(seq)

		# PIL image
		from PIL import Image
		img = Image.frombytes('RGB', (self.w, self.h), b)
		return img
	
	def show(self):
		img = self._to_pil()
		img.show()

	def save(self, filename):
		img = self._to_pil()
		img.save(filename)

class Interpolator:
	def interpolate(self, picture, new_h, new_w):
		quantum_x = picture.w / new_w
		quantum_y = picture.h / new_h
		result = [[None for _ in range(new_w)] for _ in range(new_h)]
		for x in range(new_w):
			for y in range(new_h):
				result[y][x] = self.get_pixel(picture, x*quantum_x, y*quantum_y, result, quantum_x, quantum_y)
		return Picture(result)


	def get_pixel(self, picture, x, y, result, quantum_x, quantum_y):
		raise NotImplementedError('You write this :-)')