From 59516714d1f4cb601af4f2f345eed87fc2ddae4c Mon Sep 17 00:00:00 2001
From: George Bartolomey <george@bh4.ru>
Date: Sun, 15 Sep 2024 12:00:30 +0300
Subject: [PATCH] [#14] Use quadtree to find continent

Signed-off-by: George Bartolomey <george@bh4.ru>
---
 pkg/locode/db/continents/geojson/calls.go | 64 ++++++++++++++++++-----
 pkg/locode/db/continents/geojson/db.go    |  3 ++
 2 files changed, 53 insertions(+), 14 deletions(-)

diff --git a/pkg/locode/db/continents/geojson/calls.go b/pkg/locode/db/continents/geojson/calls.go
index b5a58d1..a766cbd 100644
--- a/pkg/locode/db/continents/geojson/calls.go
+++ b/pkg/locode/db/continents/geojson/calls.go
@@ -8,6 +8,7 @@ import (
 	"github.com/paulmach/orb"
 	"github.com/paulmach/orb/geojson"
 	"github.com/paulmach/orb/planar"
+	"github.com/paulmach/orb/quadtree"
 )
 
 const continentProperty = "Continent"
@@ -36,22 +37,24 @@ func (db *DB) PointContinent(point *locodedb.Point) (*locodedb.Continent, error)
 		minDst    float64
 	)
 
-	for _, feature := range db.features {
-		if multiPolygon, ok := feature.Geometry.(orb.MultiPolygon); ok {
-			if planar.MultiPolygonContains(multiPolygon, planarPoint) {
+	pointer := db.tree.Matching(planarPoint, func(p orb.Pointer) bool {
+		return planar.PolygonContains(
+			p.(*geojson.Feature).Geometry.(orb.Polygon),
+			planarPoint,
+		)
+	})
+
+	if pointer != nil {
+		continent = pointer.(*geojson.Feature).Properties.MustString(continentProperty)
+	}
+
+	if continent == "" {
+		for _, feature := range db.features {
+			distance := planar.DistanceFrom(feature.Geometry, planarPoint)
+			if minDst == 0 || minDst > distance {
+				minDst = distance
 				continent = feature.Properties.MustString(continentProperty)
-				break
 			}
-		} else if polygon, ok := feature.Geometry.(orb.Polygon); ok {
-			if planar.PolygonContains(polygon, planarPoint) {
-				continent = feature.Properties.MustString(continentProperty)
-				break
-			}
-		}
-		distance := planar.DistanceFrom(feature.Geometry, planarPoint)
-		if minDst == 0 || minDst > distance {
-			minDst = distance
-			continent = feature.Properties.MustString(continentProperty)
 		}
 	}
 
@@ -73,6 +76,39 @@ func (db *DB) init() error {
 
 	db.features = features.Features
 
+	err = db.buildQuadtree()
+	if err != nil {
+		return fmt.Errorf("could not build quadtree: %w", err)
+	}
+
+	return nil
+}
+
+func (db *DB) buildQuadtree() error {
+	db.tree = quadtree.New(orb.Bound{
+		Min: orb.Point{-180, -180},
+		Max: orb.Point{180, 180},
+	})
+
+	for _, feature := range db.features {
+		var multiPolygon orb.MultiPolygon
+
+		if polygon, ok := feature.Geometry.(orb.Polygon); ok {
+			multiPolygon = append(multiPolygon, polygon)
+		} else {
+			multiPolygon = feature.Geometry.(orb.MultiPolygon)
+		}
+
+		for _, polygon := range multiPolygon {
+			newFeature := geojson.NewFeature(polygon)
+			newFeature.Properties = feature.Properties.Clone()
+			err := db.tree.Add(newFeature)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
 	return nil
 }
 
diff --git a/pkg/locode/db/continents/geojson/db.go b/pkg/locode/db/continents/geojson/db.go
index ee43bd8..244da02 100644
--- a/pkg/locode/db/continents/geojson/db.go
+++ b/pkg/locode/db/continents/geojson/db.go
@@ -5,6 +5,7 @@ import (
 	"sync"
 
 	"github.com/paulmach/orb/geojson"
+	"github.com/paulmach/orb/quadtree"
 )
 
 // Prm groups the required parameters of the DB's constructor.
@@ -31,6 +32,8 @@ type DB struct {
 	once sync.Once
 
 	features []*geojson.Feature
+
+	tree *quadtree.Quadtree
 }
 
 const invalidPrmValFmt = "invalid parameter %s (%T):%v"