from pygeoif.geometry import mapping
from shapely.geometry import shape


def merge_features(geojson, condition, aggregate={}):
    """Merge the geometries using shapely's union for all the geojson's features that
    meet the condition, condition get's passed an item of feature. Then aggregate the properties
    in the aggregate dict using a function that get as input the list of property values off alle
    matched features. Operates inplace."""
    indices = [index for index, feature in enumerate(geojson['features']) if condition(feature)]
    if len(indices) == 0: # also if there is one index, we
        return geojson
    properties = {
        prop: agg([
            properties_[prop]
            for index in indices
            for properties_ in [geojson['features'][index]['properties']]
            if prop in properties_
        ])
        for prop, agg in aggregate.items()
    }
    properties.update({
        key: value
        for index in indices
        for key, value in geojson['features'][index]['properties'].items()
        if key not in aggregate
    })
    if len(indices) == 1:
        geojson['features'][indices[0]]['properties'] = properties
        return geojson

    union = shape(geojson['features'][indices[0]]['geometry'])
    for index in indices[1:]:
        union = union.union(shape(geojson['features'][index]['geometry']))

    for index in indices[::-1]: # reverse, such that the 'todo' indices willnot change.
        del geojson['features'][index]

    geojson['features'].append({
        'geometry': mapping(union),
        'properties': properties
    })
    return geojson