Link previous trip shapes for GPS positioning on circular routes (#111)

Co-authored-by: Ariel Costas Guerrero <ariel@costas.dev>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: arielcostas <94913521+arielcostas@users.noreply.github.com>

1 files changed, 135 insertions, 3 deletions

diff --git a/src/gtfs_vigo_stops/stop_report.py b/src/gtfs_vigo_stops/stop_report.py
index a827eaa..cee11ea 100644
--- a/src/gtfs_vigo_stops/stop_report.py
+++ b/src/gtfs_vigo_stops/stop_report.py
@@ -4,7 +4,7 @@ import shutil
 import sys
 import time
 import traceback
-from typing import Any, Dict, List
+from typing import Any, Dict, List, Optional, Tuple
 
 from src.shapes import process_shapes
 from src.common import get_all_feed_dates
@@ -13,10 +13,10 @@ from src.logger import get_logger
 from src.report_writer import write_stop_json, write_stop_protobuf
 from src.routes import load_routes
 from src.services import get_active_services
-from src.stop_times import get_stops_for_trips
+from src.stop_times import get_stops_for_trips, StopTime
 from src.stops import get_all_stops, get_all_stops_by_code, get_numeric_code
 from src.street_name import get_street_name, normalise_stop_name
-from src.trips import get_trips_for_services
+from src.trips import get_trips_for_services, TripLine
 
 logger = get_logger("stop_report")
 
@@ -143,6 +143,130 @@ def is_next_day_service(time_str: str) -> bool:
         return False
 
 
+def parse_trip_id_components(trip_id: str) -> Optional[Tuple[str, str, int]]:
+    """
+    Parse a trip ID in format XXXYYY-Z or XXXYYY_Z where:
+    - XXX = line number (e.g., 003)
+    - YYY = shift/internal ID (e.g., 001)
+    - Z = trip number (e.g., 12)
+    
+    Supported formats:
+    1. ..._XXXYYY_Z (e.g. "C1 01SNA00_001001_18")
+    2. ..._XXXYYY-Z (e.g. "VIGO_20241122_003001-12")
+    
+    Returns tuple of (line, shift_id, trip_number) or None if parsing fails.
+    """
+    try:
+        parts = trip_id.split("_")
+        if len(parts) < 2:
+            return None
+
+        # Try format 1: ..._XXXYYY_Z
+        # Check if second to last part is 6 digits (XXXYYY) and last part is numeric
+        if len(parts) >= 2:
+            shift_part = parts[-2]
+            trip_num_str = parts[-1]
+            
+            if len(shift_part) == 6 and shift_part.isdigit() and trip_num_str.isdigit():
+                line = shift_part[:3]
+                shift_id = shift_part[3:6]
+                trip_number = int(trip_num_str)
+                return (line, shift_id, trip_number)
+
+        # Try format 2: ..._XXXYYY-Z
+        # The trip ID is the last part in format XXXYYY-Z
+        trip_part = parts[-1]
+        
+        if "-" in trip_part:
+            shift_part, trip_num_str = trip_part.split("-", 1)
+            
+            # shift_part should be 6 digits: XXXYYY
+            if len(shift_part) == 6 and shift_part.isdigit():
+                line = shift_part[:3]  # First 3 digits
+                shift_id = shift_part[3:6]  # Next 3 digits
+                trip_number = int(trip_num_str)
+                return (line, shift_id, trip_number)
+                
+        return None
+    except (ValueError, IndexError):
+        return None
+
+
+def build_trip_previous_shape_map(
+    trips: Dict[str, List[TripLine]],
+    stops_for_all_trips: Dict[str, List[StopTime]],
+) -> Dict[str, Optional[str]]:
+    """
+    Build a mapping from trip_id to previous_trip_shape_id.
+    
+    Links trips based on trip ID structure (XXXYYY-Z) where trips with the same
+    XXX (line) and YYY (shift) and sequential Z (trip numbers) are connected
+    if the terminus of trip N matches the start of trip N+1.
+    
+    Args:
+        trips: Dictionary of service_id -> list of trips
+        stops_for_all_trips: Dictionary of trip_id -> list of stop times
+        
+    Returns:
+        Dictionary mapping trip_id to previous_trip_shape_id (or None)
+    """
+    trip_previous_shape: Dict[str, Optional[str]] = {}
+    
+    # Collect all trips across all services
+    all_trips_list: List[TripLine] = []
+    for trip_list in trips.values():
+        all_trips_list.extend(trip_list)
+    
+    # Group trips by shift ID (line + shift combination)
+    trips_by_shift: Dict[str, List[Tuple[TripLine, int, str, str]]] = {}
+    
+    for trip in all_trips_list:
+        parsed = parse_trip_id_components(trip.trip_id)
+        if not parsed:
+            continue
+        
+        line, shift_id, trip_number = parsed
+        shift_key = f"{line}{shift_id}"
+        
+        trip_stops = stops_for_all_trips.get(trip.trip_id)
+        if not trip_stops or len(trip_stops) < 2:
+            continue
+        
+        first_stop = trip_stops[0]
+        last_stop = trip_stops[-1]
+        
+        if shift_key not in trips_by_shift:
+            trips_by_shift[shift_key] = []
+        
+        trips_by_shift[shift_key].append((
+            trip,
+            trip_number,
+            first_stop.stop_id,
+            last_stop.stop_id
+        ))
+    
+    # For each shift, sort trips by trip number and link consecutive trips
+    for shift_key, shift_trips in trips_by_shift.items():
+        # Sort by trip number
+        shift_trips.sort(key=lambda x: x[1])
+        
+        # Link consecutive trips if their stops match
+        for i in range(1, len(shift_trips)):
+            current_trip, current_num, current_start_stop, _ = shift_trips[i]
+            prev_trip, prev_num, _, prev_end_stop = shift_trips[i - 1]
+            
+            # Check if trips are consecutive (trip numbers differ by 1),
+            # if previous trip's terminus matches current trip's start,
+            # and if both trips have valid shape IDs
+            if (current_num == prev_num + 1 and 
+                prev_end_stop == current_start_stop and 
+                prev_trip.shape_id and
+                current_trip.shape_id):
+                trip_previous_shape[current_trip.trip_id] = prev_trip.shape_id
+    
+    return trip_previous_shape
+
+
 def get_stop_arrivals(feed_dir: str, date: str) -> Dict[str, List[Dict[str, Any]]]:
     """
     Process trips for the given date and organize stop arrivals.
@@ -192,6 +316,10 @@ def get_stop_arrivals(feed_dir: str, date: str) -> Dict[str, List[Dict[str, Any]
     stops_for_all_trips = get_stops_for_trips(feed_dir, all_trip_ids)
     logger.info(f"Precomputed stops for {len(stops_for_all_trips)} trips.")
 
+    # Build mapping from trip_id to previous trip's shape_id
+    trip_previous_shape_map = build_trip_previous_shape_map(trips, stops_for_all_trips)
+    logger.info(f"Built previous trip shape mapping for {len(trip_previous_shape_map)} trips.")
+
     # Load routes information
     routes = load_routes(feed_dir)
     logger.info(f"Loaded {len(routes)} routes from feed.")
@@ -335,6 +463,9 @@ def get_stop_arrivals(feed_dir: str, date: str) -> Dict[str, List[Dict[str, Any]
                         next_streets = []
 
                     trip_id_fmt = "_".join(trip_id.split("_")[1:3])
+                    
+                    # Get previous trip shape_id if available
+                    previous_trip_shape_id = trip_previous_shape_map.get(trip_id, "")
 
                     stop_arrivals[stop_code].append(
                         {
@@ -356,6 +487,7 @@ def get_stop_arrivals(feed_dir: str, date: str) -> Dict[str, List[Dict[str, Any]
                             "terminus_code": terminus_code,
                             "terminus_name": terminus_name,
                             "terminus_time": final_terminus_time,
+                            "previous_trip_shape_id": previous_trip_shape_id,
                         }
                     )