From aa9334d37281faec3d2723a8cbec95ea3c4ff536 Mon Sep 17 00:00:00 2001
From: Oliver Gaskell <olivergaskell700@gmail.com>
Date: Sun, 2 Nov 2025 12:40:31 +0000
Subject: [PATCH] engine: refactoring, caching

---
 engine.py | 114 ++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 72 insertions(+), 42 deletions(-)

diff --git a/engine.py b/engine.py
index d843e26..4dea71a 100755
--- a/engine.py
+++ b/engine.py
@@ -25,6 +25,9 @@ FIRST_SEP = ':'
 OTHER_SEP = ','
 LOC_SEP = ';'
 
+cached_dists = {}
+cached_series = {}
+
 EncodedLocation = list[tuple[float, list[float]]]
 
 
@@ -85,6 +88,37 @@ def spherical_dist(pos1, pos2, r=6378137):
     return r * np.arccos(cos_lat_d - cos_lat1 * cos_lat2 * (1 - cos_lon_d))
 
 
+def get_dist_matrix(brand: str):
+    try:
+        return cached_dists[brand]
+    except KeyError:
+        greggs = np.array(fetch_data(brand))
+
+        repeat_rows = np.tile(greggs, (len(greggs), 1, 1))
+        repeat_cols = np.transpose(repeat_rows, (1, 0, 2))
+        dist_matrix = spherical_dist(repeat_rows, repeat_cols)
+
+        cached_dists[brand] = dist_matrix
+
+        return dist_matrix
+
+
+def get_dist_series_list(brand: str, n_locs: int):
+    if brand in cached_series and cached_series[brand][0] == n_locs:
+        return cached_series[brand][1]
+
+    dist_matrix = get_dist_matrix("greggs")
+
+    # split the distances matrix into a list of series, which allows us to sort each row
+    dist_series_list = []
+    for i in dist_matrix:
+        dist_series_list.append(pd.Series(i).sort_values().head(n_locs+1)[1:])
+
+    cached_series[brand] = (n_locs, dist_series_list)
+
+    return dist_series_list
+
+
 # (lat, lon), dist
 StationT = tuple[tuple[float, float], float]
 
@@ -102,7 +136,39 @@ def trilaterate(stations: list[StationT], disp: bool = False) -> tuple[float, fl
     Each station is of the format ((lat, lon), distance).
     """
 
-    return scipy.optimize.fmin(lambda pos: trilat_error(stations, pos), (0., 0.), disp=disp)
+    res = scipy.optimize.minimize(
+        lambda pos: trilat_error(stations, pos),
+        stations[0][0],
+        method='Nelder-Mead',
+    )
+
+    if res.success:
+        return res.x
+    else:
+        raise ValueError("Optimisation failed.")
+
+
+def encode_greggs(loc: int) -> list[float]:
+    """Given the id of a greggs, encode as a list of distances."""
+
+    dist_matrix = get_dist_matrix("greggs")
+    greggs_distances = np.sort(dist_matrix[loc])[1:DISTS_COUNT+1]
+
+    return list(map(float, greggs_distances))
+
+
+def decode_greggs(distances: list[float]) -> int:
+    """Get the id of a greggs given a list of distances."""
+
+    dist_series_list = get_dist_series_list("greggs", len(distances))
+
+    errors = [sum((pd.Series(j) - distances) ** 2) for j in dist_series_list]
+
+    minerr = min(errors)
+    if minerr > 1:
+        print(f"warning: high error value of {minerr}")
+
+    return errors.index(min(errors))
 
 
 def encode(location: tuple[float, float]) -> EncodedLocation:
@@ -110,57 +176,21 @@ def encode(location: tuple[float, float]) -> EncodedLocation:
 
     greggs = np.array(fetch_data("greggs"))
 
-    repeat_rows = np.tile(greggs, (len(greggs), 1, 1))
-    repeat_cols = np.transpose(repeat_rows, (1, 0, 2))
-    dist_matrix = spherical_dist(repeat_rows, repeat_cols)
-
     repeated = np.tile(location, (len(greggs), 1))
-    distances = spherical_dist(repeated, greggs)
-    distances = pd.Series(distances)
-    distances = distances.sort_values()
-
+    distances = pd.Series(spherical_dist(repeated, greggs)).sort_values()
     closest = distances.head(LOCS_COUNT)
 
-    result: EncodedLocation = []
-    for v, i in zip(closest.values, closest.index):
-        greggs_distances = np.sort(dist_matrix[i])[1:DISTS_COUNT+1]
-
-        result.append((v, list(map(float, greggs_distances))))
-
-    # Stub
-    return result
+    return [(v, encode_greggs(i)) for v, i in zip(closest.values, closest.index)]
 
 
 def decode(location: EncodedLocation, disp: bool = False) -> tuple[float, float]:
     """Decode into a location."""
-
-    # form the distances matrix
-    greggs_raw = fetch_data("greggs")
-    greggs = np.array(greggs_raw)
-    repeat_rows = np.tile(greggs, (len(greggs), 1, 1))
-    repeat_cols = np.transpose(repeat_rows, (1, 0, 2))
-    dist_matrix = spherical_dist(repeat_rows, repeat_cols)
-
-    # split the distances matrix into a list of series, which allows us to sort each row
-    dist_series_list = []
-    for i in dist_matrix:
-        dist_series_list.append(pd.Series(i).sort_values().head(len(location[0][1])+1)[1:])
-
     # part 1: find the ID of each gregg's
-    closest_greggs = []
-    for loc in location:
-        dists = loc[1]
-
-        errors = [sum((j - dists) ** 2) for j in dist_series_list]
-
-        minerr = min(errors)
-        if minerr > 1:
-            print(f"warning: high error value of {minerr}")
-
-        closest_greggs.append(errors.index(min(errors)))
+    closest_greggs = [decode_greggs(dists) for _, dists in location]
 
     # part 2: trilaterate
-    stations: list[StationT] = [(greggs_raw[g], location[i][0]) for i, g in enumerate(closest_greggs)]
+    greggs = fetch_data("greggs")
+    stations: list[StationT] = [(greggs[g], location[i][0]) for i, g in enumerate(closest_greggs)]
     return trilaterate(stations, disp=disp)