From 9cd7e0596d0c4b822f2ec26291285c4bfd149764 Mon Sep 17 00:00:00 2001
From: Chris Raastad <craastad@gmail.com>
Date: Sat, 24 Aug 2019 08:28:08 -0400
Subject: [PATCH] Add getNeighbors function to compute 8 neighbor hashes of a
 hash. Upgrade PHP version. Update README. (#4)

---
 README.md             | 16 ++++++++
 composer.json         |  9 +++-
 src/Geohash.php       | 95 +++++++++++++++++++++++++++++++++++++++++++
 tests/GeohashTest.php | 23 ++++++++++-
 4 files changed, 139 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index c145027..c8c9760 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,22 @@ The result is
 latitude : 17.38,  longitude : 78.42
 ~~~
 
+Get geohashes of 8 neighbors of a geohash
+~~~
+use Sk\Geohash\Geohash;
+
+$g = new Geohash();
+$hash = $g->encode(25.813646, -80.133761, 7);
+$neighbors = $g->getNeighbors($hash);
+echo "Hash: $hash\n";
+echo "Neighbors: " . json_encode($neighors) . "\n";
+~~~
+The result is
+~~~
+Hash: 
+Neighbors: {"North":"dhx4be2","East":"dhx4be1","South":"dhx4bdb","West":"dhx4b7p","NorthEast":"dhx4be3","SouthEast":"dhx4bdc","SouthWest":"dhx4b6z","NorthWest":"dhx4b7r"}
+~~~
+
 Running the unit tests
 -------
 Go to this directory from your project folder
diff --git a/composer.json b/composer.json
index 16eb233..72b2b43 100644
--- a/composer.json
+++ b/composer.json
@@ -8,11 +8,16 @@
         {
             "name": "Saikiran Ch",
             "email": "saikiranchavan@gmail.com"
+        },{
+            "name": "Chris Raastad",
+            "email": "craastad@gmail.com"
         }
     ],
-    "require": {},
+    "require": {
+        "php": ">=7.0.0"
+    },
     "require-dev": {
-        "phpunit/phpunit": "4.0.*"
+        "phpunit/phpunit": "~6.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Geohash.php b/src/Geohash.php
index b142b0d..19dc08f 100644
--- a/src/Geohash.php
+++ b/src/Geohash.php
@@ -9,11 +9,53 @@
  */
 class Geohash
 {
+    const NORTH = 0;
+    const EAST = 1;
+    const SOUTH = 2;
+    const WEST = 3;
+
+    const EVEN = 0;
+    const ODD = 1;
+
     /**
      * Used for decoding the hash from base32
      */
     protected $base32Mapping = "0123456789bcdefghjkmnpqrstuvwxyz";
 
+    private $borderChars = [
+        self::EVEN => [
+            self::NORTH => 'bcfguvyz',
+            self::EAST => 'prxz',
+            self::SOUTH => '0145hjnp',
+            self::WEST => '028b',
+        ]
+    ];
+
+    private $neighborChars = [
+        self::EVEN => [
+            self::NORTH => '238967debc01fg45kmstqrwxuvhjyznp',
+            self::EAST => '14365h7k9dcfesgujnmqp0r2twvyx8zb',
+            self::SOUTH => 'bc01fg45238967deuvhjyznpkmstqrwx',
+            self::WEST => 'p0r21436x8zb9dcf5h7kjnmqesgutwvy',
+        ],
+    ];
+
+    public function __construct() {
+        $this->neighborChars[self::ODD] = array(
+            self::NORTH => $this->neighborChars[self::EVEN][self::EAST],
+            self::EAST => $this->neighborChars[self::EVEN][self::NORTH],
+            self::SOUTH => $this->neighborChars[self::EVEN][self::WEST],
+            self::WEST => $this->neighborChars[self::EVEN][self::SOUTH],
+        );
+
+        $this->borderChars[self::ODD] = array(
+            self::NORTH => $this->borderChars[self::EVEN][self::EAST],
+            self::EAST => $this->borderChars[self::EVEN][self::NORTH],
+            self::SOUTH => $this->borderChars[self::EVEN][self::WEST],
+            self::WEST => $this->borderChars[self::EVEN][self::SOUTH],
+        );
+    }
+
     /**
      * Encode the latitude and longitude into a hashed string
      * @param  float   Latitude
@@ -145,4 +187,57 @@ public function getBits($coordinate, $min, $max, $bitsLength)
         }
         return $binaryString;
     }
+
+    /**
+     * Computes neighboring geohash values for given geohash.
+     *
+     * @param string $hash
+     * @return array
+     */
+    public function getNeighbors($hash) {
+        $hashNorth = $this->calculateNeighbor($hash, self::NORTH);
+        $hashEast = $this->calculateNeighbor($hash, self::EAST);
+        $hashSouth = $this->calculateNeighbor($hash, self::SOUTH);
+        $hashWest = $this->calculateNeighbor($hash, self::WEST);
+
+        $hashNorthEast = $this->calculateNeighbor($hashNorth, self::EAST);
+        $hashSouthEast = $this->calculateNeighbor($hashSouth, self::EAST);
+        $hashSouthWest = $this->calculateNeighbor($hashSouth, self::WEST);
+        $hashNorthWest = $this->calculateNeighbor($hashNorth, self::WEST);
+        return [
+            'North'     => $hashNorth,
+            'East'      => $hashEast,
+            'South'     => $hashSouth,
+            'West'      => $hashWest,
+            'NorthEast' => $hashNorthEast,
+            'SouthEast' => $hashSouthEast,
+            'SouthWest' => $hashSouthWest,
+            'NorthWest' => $hashNorthWest,
+        ];
+    }
+
+    /**
+     * Calculates neighbor geohash for given geohash and direction
+     *
+     * @param string $hash
+     * @param string $direction
+     * @return string $neighborHash
+     */
+    private function calculateNeighbor($hash, $direction) {
+        $length = strlen($hash);
+        if ($length == 0) {
+            return '';
+        }
+        $lastChar = $hash{$length - 1};
+        $evenOrOdd = ($length - 1) % 2;
+        $baseHash = substr($hash, 0, -1);
+        if (strpos($this->borderChars[$evenOrOdd][$direction], $lastChar) !== false) {
+            $baseHash = $this->calculateNeighbor($baseHash, $direction);
+        }
+        if (isset($baseHash{0})) {
+            return $baseHash . $this->neighborChars[$evenOrOdd][$direction]{strpos($this->base32Mapping, $lastChar)};
+        } else {
+            return '';
+        }
+    }
 }
\ No newline at end of file
diff --git a/tests/GeohashTest.php b/tests/GeohashTest.php
index 5313f34..15c00c1 100644
--- a/tests/GeohashTest.php
+++ b/tests/GeohashTest.php
@@ -1,8 +1,9 @@
 <?php
- 
+
+use PHPUnit\Framework\TestCase;
 use Sk\Geohash\Geohash;
  
-class GeohashTest extends PHPUnit_Framework_TestCase
+class GeohashTest extends TestCase
 {
     /**
      * @dataProvider encodeProvider
@@ -56,4 +57,22 @@ public function decodeProvider()
             array(17.3850320186, 78.48672056569, "tepffhb71hue")
         );
     }
+
+    public function testGetNeighbors() {
+        $geohash = new Geohash();
+        list($lat1, $lon1) = [25.813646, -80.133761];
+        $hash = $geohash->encode($lat1, $lon1, 7);
+        $neighbors = $geohash->getNeighbors($hash);
+        $this->assertEquals('dhx4be0', $hash);
+        $this->assertEquals([
+            'North' => 'dhx4be2',
+            'East'=> 'dhx4be1',
+            'South' => 'dhx4bdb',
+            'West' => 'dhx4b7p',
+            'NorthEast' => 'dhx4be3',
+            'SouthEast' => 'dhx4bdc',
+            'SouthWest' => 'dhx4b6z',
+            'NorthWest' => 'dhx4b7r',
+        ], $neighbors);
+    }
 }
\ No newline at end of file