use std::collections::{HashMap, HashSet};

use abstutil::MultiMap;
use geom::{Duration, Polygon};
use map_gui::tools::Grid;
use map_model::{
    connectivity, AmenityType, BuildingID, BuildingType, LaneType, Map, Path, PathConstraints,
    PathRequest,
};
use widgetry::{Color, Drawable, EventCtx, GeomBatch};

use crate::App;

/// Represents the area reachable from a single building.
pub struct Isochrone {
    /// The center of the isochrone
    pub start: BuildingID,
    /// The options used to generate this isochrone
    pub options: Options,
    /// Colored polygon contours, uploaded to the GPU and ready for drawing
    pub draw: Drawable,
    /// How far away is each building from the start?
    pub time_to_reach_building: HashMap<BuildingID, Duration>,
    /// Per category of amenity, what buildings have that?
    pub amenities_reachable: MultiMap<AmenityType, BuildingID>,
    /// How many people live in the returned area, according to estimates included in the map (from
    /// city-specific parcel data, guesses from census, or a guess based on OSM tags)
    pub population: usize,
    /// How many sreet parking spots are on the same road as any buildings returned.
    pub onstreet_parking_spots: usize,
}

/// The constraints on how we're moving.
#[derive(Clone)]
pub enum Options {
    Walking(connectivity::WalkingOptions),
    Biking,
}

impl Options {
    pub fn time_to_reach_building(
        self,
        map: &Map,
        start: BuildingID,
    ) -> HashMap<BuildingID, Duration> {
        match self {
            Options::Walking(opts) => {
                connectivity::all_walking_costs_from(map, start, Duration::minutes(15), opts)
            }
            Options::Biking => connectivity::all_vehicle_costs_from(
                map,
                start,
                Duration::minutes(15),
                PathConstraints::Bike,
            ),
        }
    }
}

impl Isochrone {
    pub fn new(ctx: &mut EventCtx, app: &App, start: BuildingID, options: Options) -> Isochrone {
        let time_to_reach_building = options.clone().time_to_reach_building(&app.map, start);

        let mut amenities_reachable = MultiMap::new();
        let mut population = 0;
        let mut all_roads = HashSet::new();
        for b in time_to_reach_building.keys() {
            let bldg = app.map.get_b(*b);
            for amenity in &bldg.amenities {
                if let Some(category) = AmenityType::categorize(&amenity.amenity_type) {
                    amenities_reachable.insert(category, bldg.id);
                }
            }
            match bldg.bldg_type {
                BuildingType::Residential { num_residents, .. }
                | BuildingType::ResidentialCommercial(num_residents, _) => {
                    population += num_residents;
                }
                _ => {}
            }
            all_roads.insert(app.map.get_l(bldg.sidewalk_pos.lane()).parent);
        }

        let mut onstreet_parking_spots = 0;
        for r in all_roads {
            let r = app.map.get_r(r);
            for (l, _, lt) in r.lanes_ltr() {
                if lt == LaneType::Parking {
                    onstreet_parking_spots +=
                        app.map.get_l(l).number_parking_spots(app.map.get_config());
                }
            }
        }

        let mut i = Isochrone {
            start,
            options,
            draw: Drawable::empty(ctx),
            time_to_reach_building,
            amenities_reachable,
            population,
            onstreet_parking_spots,
        };
        i.draw = i.draw_isochrone(app).upload(ctx);
        i
    }

    pub fn path_to(&self, map: &Map, to: BuildingID) -> Option<Path> {
        // Don't draw paths to places far away
        if !self.time_to_reach_building.contains_key(&to) {
            return None;
        }

        let req = PathRequest::between_buildings(
            map,
            self.start,
            to,
            match self.options {
                Options::Walking(_) => PathConstraints::Pedestrian,
                Options::Biking => PathConstraints::Bike,
            },
        )?;
        map.pathfind(req).ok()
    }

    pub fn draw_isochrone(&self, app: &App) -> GeomBatch {
        // To generate the polygons covering areas between 0-5 mins, 5-10 mins, etc, we have to feed
        // in a 2D grid of costs. Use a 100x100 meter resolution.
        let bounds = app.map.get_bounds();
        let resolution_m = 100.0;
        // The costs we're storing are currenly durations, but the contour crate needs f64, so
        // just store the number of seconds.
        let mut grid: Grid<f64> = Grid::new(
            (bounds.width() / resolution_m).ceil() as usize,
            (bounds.height() / resolution_m).ceil() as usize,
            0.0,
        );

        // Calculate the cost from the start building to every other building in the map
        for (b, cost) in &self.time_to_reach_building {
            // What grid cell does the building belong to?
            let pt = app.map.get_b(*b).polygon.center();
            let idx = grid.idx(
                ((pt.x() - bounds.min_x) / resolution_m) as usize,
                ((pt.y() - bounds.min_y) / resolution_m) as usize,
            );
            // Don't add! If two buildings map to the same cell, we should pick a finer resolution.
            grid.data[idx] = cost.inner_seconds();
        }

        // Generate polygons covering the contour line where the cost in the grid crosses these
        // threshold values.
        let thresholds = vec![
            0.1,
            Duration::minutes(5).inner_seconds(),
            Duration::minutes(10).inner_seconds(),
            Duration::minutes(15).inner_seconds(),
        ];
        // And color the polygon for each threshold
        let colors = vec![
            Color::GREEN.alpha(0.5),
            Color::ORANGE.alpha(0.5),
            Color::RED.alpha(0.5),
        ];
        let smooth = false;
        let c = contour::ContourBuilder::new(grid.width as u32, grid.height as u32, smooth);
        let mut batch = GeomBatch::new();
        // The last feature returned will be larger than the last threshold value. We don't want to
        // display that at all. zip() will omit this last pair, since colors.len() ==
        // thresholds.len() - 1.
        //
        // TODO Actually, this still isn't working. I think each polygon is everything > the
        // threshold, not everything between two thresholds?
        for (feature, color) in c
            .contours(&grid.data, &thresholds)
            .unwrap()
            .into_iter()
            .zip(colors)
        {
            match feature.geometry.unwrap().value {
                geojson::Value::MultiPolygon(polygons) => {
                    for p in polygons {
                        if let Ok(poly) = Polygon::from_geojson(&p) {
                            batch.push(color, poly.scale(resolution_m));
                        }
                    }
                }
                _ => unreachable!(),
            }
        }

        batch
    }
}