Geocoder plugin: support other built-in providers

[prusswan]

tested with Nominatim, Photon, Google:

from branca.element import MacroElement
from jinja2 import Template

from folium.elements import JSCSSMixin
from folium.utilities import parse_options

import folium

class EnhancedGeocoder(JSCSSMixin, MacroElement):
    """A simple geocoder for Leaflet that by default uses OSM/Nominatim.

    Please respect the Nominatim usage policy:
    https://operations.osmfoundation.org/policies/nominatim/
    Parameters
    ----------
    collapsed: bool, default False
        If True, collapses the search box unless hovered/clicked.
    position: str, default 'topright'
        Choose from 'topleft', 'topright', 'bottomleft' or 'bottomright'.
    add_marker: bool, default True
        If True, adds a marker on the found location.
    geocode_zoom: int, default 11
        Set zoom level used for displaying the geocode result, note that this only has an effect when add_marker is set to False. Set this to None to preserve the current map zoom level.
    geocode_provider: str, default 'nominatim'
        Defaults to "nominatim", see https://github.com/perliedman/leaflet-control-geocoder/tree/2.4.0/src/geocoders for other built-in providers.
    geocode_provider_options: dict, default {}
        For use with specific providers that may require api keys or other parameters.

    For all options see https://github.com/perliedman/leaflet-control-geocoder

    """

    _template = Template(
        """
        {% macro script(this, kwargs) %}

            var geocoderOpts_{{ this.get_name() }} = {{ this.options|tojson }};

            // note: geocoder name should start with lowercase
            var geocoderName_{{ this.get_name() }} = geocoderOpts_{{ this.get_name() }}["geocodeProvider"];

            var customGeocoder_{{ this.get_name() }} = L.Control.Geocoder[ geocoderName_{{ this.get_name() }} ](
                geocoderOpts_{{ this.get_name() }}['geocodeProviderOptions']
            );
            geocoderOpts_{{ this.get_name() }}["geocoder"] = customGeocoder_{{ this.get_name() }};

            L.Control.geocoder(
                geocoderOpts_{{ this.get_name() }}
            ).on('markgeocode', function(e) {
                var zoom = geocoderOpts_{{ this.get_name() }}['geocodeZoom'] || {{ this._parent.get_name() }}.getZoom();
                {{ this._parent.get_name() }}.setView(e.geocode.center, zoom);
            }).addTo({{ this._parent.get_name() }});

        {% endmacro %}
    """
    )

    default_js = [
        (
            "Control.Geocoder.js",
            "https://unpkg.com/leaflet-control-geocoder/dist/Control.Geocoder.js",
        )
    ]
    default_css = [
        (
            "Control.Geocoder.css",
            "https://unpkg.com/leaflet-control-geocoder/dist/Control.Geocoder.css",
        )
    ]

    def __init__(
        self,
        collapsed: bool = False,
        position: str = "topright",
        add_marker: bool = True,
        geocode_zoom: int | None = 11,
        geocode_provider: str = "nominatim",
        geocode_provider_options: dict = {},
        **kwargs
    ):
        super().__init__()
        self._name = "Geocoder"
        self.options = parse_options(
            collapsed=collapsed,
            position=position,
            default_mark_geocode=add_marker,
            geocode_zoom=geocode_zoom,
            geocode_provider=geocode_provider,
            geocode_provider_options=geocode_provider_options,
            **kwargs
        )

google_key = "placeholder"
gc2_default = EnhancedGeocoder() # nominatim
#gc2_photon = EnhancedGeocoder(geocode_provider="photon")
#gc2_google = EnhancedGeocoder(geocode_provider="google",
#                           geocode_provider_options={"apiKey": google_key})


m2 = folium.Map(location=[43.7798, 11.24148], zoom_start=13, tiles="cartodb positron")

gc2_default.add_to(m2)
#gc2_photon.add_to(m2)
#gc2_google.add_to(m2)

folium.LayerControl().add_to(m2)
m2

[Conengmo]

Looks good overall! Few small comments before we can merge this.

[Conengmo]

as the default zoom level of 11 is not suitable for close-up locations (and only works when add_marker is False)

Question: is 11 a good default? Or would None be a better default?

And another question: should we check or correct this value when add_marker is False?

[prusswan]

11 would preserve the current behavior so existing users would not be caught by surprise. The real gotcha would be the case when add_marker=True (when default handler in leaflet-control-geocoder will be using fit_bounds with no regard to current map zoom). What may not be obvious to normal folium users (with no knowledge of JS) is that both the default event handler for markgeocode as well as the one defined in _template would be triggered.

Not sure if there is a need to correct (beyond keeping the current default of 11). Can you explain more?

[Conengmo]

Not sure if there is a need to correct (beyond keeping the current default of 11).

That's good then. It was more a question for you. We can keep it like it is now then.

[Conengmo]

Thanks @prusswan! Nice addition!