import csv
import math
import os
import re
from collections import deque


class Vector(complex):
	def __getitem__(self, index):
		if index == 0:
			return self.real
		elif index == 1:
			return self.imag
		else:
			raise IndexError


def load(directory):
	def _read(iterable):
		for x, y in iterable:
			yield Vector(float(x), float(y))

	def _load(filename):
		with open(filename) as fd:
			reader = csv.reader(fd)
			return list(_read(reader))

	def _files(directory):
		for file in os.listdir(directory):
			match = re.match(r"SWI_(-?\d+)\.csv", file)
			if match:
				yield int(match.group(1)), os.path.join(directory, file)

	return [(x, _load(y)) for x, y in sorted(_files(directory), key=lambda x: x[0])]


def look_downwards(data, x, start):
	for i in range(start, 0, -1):
		if data[i - 1][0] < x:
			break
	else:
		raise IndexError
	return i - 1


def look_upwards(data, x, start):
	for i in range(start, len(data)):
		if data[i + 1][0] > x:
			break
	else:
		raise IndexError
	return i


def find_segment(data, x):
	width = data[-1][0] - data[0][0]
	relative = x - data[0][0]
	candidate = math.floor(relative / width * len(data))
	look = look_downwards if data[candidate][0] > x else look_upwards  # May raise IndexError
	candidate = look(data, x, candidate)
	return candidate, candidate + 1


def find_boundary_curves(swis, x, y):
	segments = deque()
	for index, data in swis:
		i, j = find_segment(data, x)
		if data[i][1] > y and data[j][1] > y:
			segments.append((index, data, i, j))
			break
		if data[i][1] < y and data[j][1] < y:
			if segments:
				segments.popleft()
		segments.append((index, data, i, j))
	if len(segments) == 3:
		middle = segments[1][1]
		run = middle[j][0] - middle[i][0]
		if run == 0:
			raise RuntimeError  # tidy up dataset
		slope = (middle[j][1] - middle[i][1]) / run
		intercept = middle[j][1] - slope * middle[j][0]
		value = slope * x + intercept
		if value == y:
			raise RuntimeError  # Exactly on point; SWI == index
		if value < y:
			segments.popleft()
		else:
			segments.pop()
	if len(segments) == 1:
		raise RuntimeError  # SWI == -10
	return segments


def calculate_swi(segments, x, y):
	vec = Vector(x, y)
	low = segments[0]
	high = segments[1]
	dist_to_low = min(abs(vec - p) for p in (low[1][low[2]], low[1][low[2]]))
	dist_to_high = min(abs(vec - p) for p in (high[1][high[2]], high[1][high[2]]))
	return dist_to_low / (dist_to_low + dist_to_high) * (high[0] - low[0]) + low[0]