B4J Code Snippet [PyBridge] Using folium (OpenStreetMap) in a webview

import folium
from folium.plugins import MarkerCluster, Draw, MousePosition
import json
import os

# File paths for persistence
MARKERS_FILE = "markers.json"
POLYGONS_FILE = "polygons.json"
MAP_FILE = "map.html"

# Global variable to store the map instance
#map_EWS = None
global map_EWS


# Load markers and polygons
def load_markers():
    if os.path.exists(MARKERS_FILE):
        with open(MARKERS_FILE, "r") as f:
            try:
                return json.load(f)
            except json.JSONDecodeError:
                return {}
    return {}


def save_markers():
    with open(MARKERS_FILE, "w") as f:
        json.dump(markers, f, indent=4)


def load_polygons():
    if os.path.exists(POLYGONS_FILE):
        with open(POLYGONS_FILE, "r") as f:
            try:
                return json.load(f)
            except json.JSONDecodeError:
                return {}
    return {}


def save_polygons():
    with open(POLYGONS_FILE, "w") as f:
        json.dump(polygons, f, indent=4)

markers = load_markers()
polygons = load_polygons()


# Start map (Called once at entry point)
def start_map(lat, lon, zoom):
    global map_EWS
    global current_lat, current_lon, current_zoom
    current_lat, current_lon, current_zoom = lat, lon, zoom
    print(f"📍 Starting new map at: lat={current_lat}, lon={current_lon}, zoom={current_zoom}")
    regenerate_map()


# Regenerate map
def regenerate_map():
    global map_EWS
  
    map_EWS = folium.Map(location=[current_lat,current_lon], zoom_start=current_zoom,tiles="OpenStreetMap")
    marker_cluster = MarkerCluster().add_to(map_EWS)

    formatter = "function(num) {return L.Util.formatNum(num, 4) + ' ° ';};"
    MousePosition(
        position="bottomleft", separator=" | ", empty_string="NaN",
        lng_first=False, num_digits=22, prefix="Coordinates:",
        lat_formatter=formatter, lng_formatter=formatter
    ).add_to(map_EWS)

    for marker_id, data in markers.items():
        lat, lon, popup_text = data["lat"], data["lon"], data["popup_text"]
        folium.Marker(
            location=[lat, lon],
            popup=f"{popup_text} (ID: {marker_id})",
            tooltip=f"Marker {marker_id}"
        ).add_to(marker_cluster)

    for polygon_id, data in polygons.items():
        coordinates, label, color = data["coordinates"], data["label"], data["color"]
        folium.Polygon(
            locations=coordinates,
            color=color,
            weight=3,
            fill=True,
            fill_opacity=0.3,
            fill_color=color,
            popup=f"{label} (ID: {polygon_id})",
            tooltip=f"Polygon {polygon_id}"
        ).add_to(map_EWS)

    draw_options = {
        "polyline": False,
        "polygon": {
            "shapeOptions": {
                "color": "red",
                "weight": 3,
                "fillColor": "blue",
                "fillOpacity": 0.3
            }
        },
        "rectangle": False,
        "circle": False,
        "marker": False,
        "circlemarker": False
    }

    Draw(export=True, position='topleft', filename='data.geojson', draw_options=draw_options, edit_options={'poly': {'allowIntersection': False}}).add_to(map_EWS) 
    save_map()


# Save map
def save_map():
    global map_EWS, current_lat, current_lon, current_zoom
    if map_EWS:
        map_EWS.save(MAP_FILE)
        print(f"✅ Map saved as {MAP_FILE}")
    else:
        print("❌ Error: map_EWS is not initialized.")
    return MAP_FILE


# Marker functions
def add_marker(marker_id, lat, lon, popup_text):
    if marker_id in markers:
        print("Error: Marker ID already exists. Marker not added.")
        return
    markers[marker_id] = {"lat": lat, "lon": lon, "popup_text": popup_text}
    save_markers()
    regenerate_map()
    return save_map()


def update_marker(marker_id, new_lat, new_lon, new_popup_text):
    if marker_id not in markers:
        print("Error: Marker not found. Position not updated.")
        return
    markers[marker_id] = {"lat": new_lat, "lon": new_lon, "popup_text": new_popup_text}
    save_markers()
    regenerate_map()
    return save_map()


def remove_marker(marker_id):
    if marker_id not in markers:
        print("Error: Marker not found. Marker not removed.")
        return
    del markers[marker_id]
    save_markers()
    regenerate_map()
    return save_map()

# Polygon functions
def add_polygon(polygon_id, coordinates, label="Polygon", border_color="red"):
    valid_colors = {"blue", "red", "black", "green"}
    if polygon_id in polygons:
        print("Error: Polygon ID already exists. Polygon not added.")
        return
    if border_color not in valid_colors:
        border_color = "red"
    polygons[polygon_id] = {"coordinates": coordinates, "label": label, "color": border_color}
    save_polygons()
    regenerate_map()
    return save_map()


def update_polygon(polygon_id, new_coordinates, new_label="Polygon", new_border_color="red"):
    valid_colors = {"blue", "red", "black", "green"}
    if polygon_id not in polygons:
        print("Error: Polygon not found. Polygon not updated.")
        return
    polygons[polygon_id]= {"coordinates": new_coordinates, "label": new_label, "color": new_border_color}
    save_polygons()
    regenerate_map()
    return save_map()


def remove_polygon(polygon_id):
    if polygon_id not in polygons:
        print("Error: Polygon not found. Polygon not removed.")
        return
    del polygons[polygon_id]
    save_polygons()
    regenerate_map()
    return save_map()