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import math
from collections import deque
from . import _dataset
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(x, y):
low, high = find_boundary_curves(_dataset.INDICES, x, y)
vec = _dataset.Vector(x, y)
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]
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