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use std::convert::TryInto;

use anyhow::Result;
use geo::{Area, Contains};
use geojson::GeoJson;

use abstutil::Timer;
use geom::LonLat;

/// Given the path to an Osmosis boundary polygon, return the URL of a Geofabrik osm.pbf file that
/// best covers the boundary.
///
/// If the boundary splits multiple Geofabrik files, the result may be any of the overlapping
/// files.
pub async fn pick_geofabrik(input: String) -> Result<String> {
    let boundary_pts = LonLat::read_osmosis_polygon(&input)?;
    // For now, just use the boundary's center. Some boundaries might cross multiple geofabrik
    // regions; don't handle that yet.
    let center = LonLat::center(&boundary_pts);

    let geofabrik_idx = load_remote_geojson(
        abstio::path_shared_input("geofabrik-index.json"),
        "https://download.geofabrik.de/index-v1.json",
    )
    .await?;
    let matches = find_matching_regions(geofabrik_idx, center);
    info!(
        "{} regions contain boundary center {}",
        matches.len(),
        center
    );
    // Find the smallest matching region. Just round to the nearest square meter for comparison.
    let (_, url) = matches
        .into_iter()
        .min_by_key(|(mp, _)| mp.unsigned_area() as usize)
        .unwrap();
    Ok(url)
}

async fn load_remote_geojson(path: String, url: &str) -> Result<GeoJson> {
    if !abstio::file_exists(&path) {
        info!("Downloading {}", url);
        abstio::download_to_file(url, None, &path).await?;
    }
    abstio::maybe_read_json(path, &mut Timer::throwaway())
}

fn find_matching_regions(geojson: GeoJson, center: LonLat) -> Vec<(geo::MultiPolygon, String)> {
    let center: geo::Point = center.into();

    let mut matches = Vec::new();

    // We're assuming some things about the geofabrik_idx index format -- it's a feature
    // collection, every feature has a multipolygon geometry, the properties have a particular
    // form.
    if let GeoJson::FeatureCollection(fc) = geojson {
        info!("Searching {} regions", fc.features.len());
        for mut feature in fc.features {
            let mp: geo::MultiPolygon = feature.geometry.take().unwrap().value.try_into().unwrap();
            if mp.contains(&center) {
                matches.push((
                    mp,
                    feature
                        .property("urls")
                        .unwrap()
                        .get("pbf")
                        .unwrap()
                        .as_str()
                        .unwrap()
                        .to_string(),
                ));
            }
        }
    }

    matches
}