├── .gitignore
├── composer.json
├── README.md
├── phpunit.xml
├── tests
    ├── data
    │   ├── data1.json
    │   ├── data2.json
    │   └── data3.json
    └── InvestorTest.php
├── calculate.php
└── app
    ├── CurlHelper.php
    └── Investor.php


/.gitignore:
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1 | .idea
2 | composer.lock
3 | vendor


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/composer.json:
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 1 | {
 2 |     "name": "pawlox/nbp-gold-investor",
 3 |     "type": "project",
 4 |     "license": "MIT",
 5 |     "authors": [
 6 |         {
 7 |             "name": "Paweł Marciniak",
 8 |             "email": "pawmarci@gmail.com"
 9 |         }
10 |     ],
11 |     "require": {},
12 |     "autoload": {
13 |         "psr-4": {
14 |             "App\\": "app/"
15 |         }
16 |     },
17 |     "require-dev": {
18 |         "phpunit/phpunit": "^8.1.4"
19 |     }
20 | }
21 | 


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/README.md:
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 1 | # nbp best investment
 2 | 
 3 | Simple application to calculate the best investment in gold during given time period.
 4 | 
 5 | It depends on NBP Web Api “http://api.nbp.pl” and returns the best moment to buy and sell gold to get the highest profit.
 6 | 
 7 | ##### Usage:
 8 | 
 9 | `php calculate.php [money] [startDate] [endDate]`
10 | 
11 | ##### Parameters:
12 | 
13 | `money` - amount of money to invest, float value,  
14 | `startDate` - time range start date in format Y-m-d,  
15 | `endDate` - time range end date in format Y-m-d.
16 | 
17 | ##### Example of usage:
18 | 
19 | `php calculate.php 600000 2013-01-02 2017-08-28`
20 | 


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/phpunit.xml:
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 1 | <?xml version="1.0" encoding="UTF-8"?>
 2 | 
 3 | <phpunit backupGlobals="false" backupStaticAttributes="false" colors="true" convertErrorsToExceptions="true" convertNoticesToExceptions="true" convertWarningsToExceptions="true" processIsolation="false" stopOnFailure="false" syntaxCheck="false" bootstrap="vendor/autoload.php">
 4 |     <testsuites>
 5 |         <testsuite name="Investor Test Suite">
 6 |             <directory>./tests/</directory>
 7 |         </testsuite>
 8 |     </testsuites>
 9 |     <filter>
10 |         <whitelist>
11 |             <directory>./app</directory>
12 |         </whitelist>
13 |     </filter>
14 | </phpunit>


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/tests/data/data1.json:
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 1 | [
 2 |   {
 3 |     "data": "2018-02-01",
 4 |     "cena": 160.23
 5 |   },
 6 |   {
 7 |     "data": "2018-02-02",
 8 |     "cena": 165.35
 9 |   },
10 |   {
11 |     "data": "2018-02-03",
12 |     "cena": 176.76
13 |   },
14 |   {
15 |     "data": "2018-02-04",
16 |     "cena": 171.90
17 |   },
18 |   {
19 |     "data": "2018-02-05",
20 |     "cena": 161.43
21 |   },
22 |   {
23 |     "data": "2018-02-06",
24 |     "cena": 167.77
25 |   },
26 |   {
27 |     "data": "2018-02-07",
28 |     "cena": 159.23
29 |   },
30 |   {
31 |     "data": "2018-02-08",
32 |     "cena": 169.99
33 |   },
34 |   {
35 |     "data": "2018-02-09",
36 |     "cena": 173.33
37 |   },
38 |   {
39 |     "data": "2018-02-10",
40 |     "cena": 172.22
41 |   }
42 | ]


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/tests/data/data2.json:
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 1 | [
 2 |   {
 3 |     "data": "2018-02-01",
 4 |     "cena": 167.23
 5 |   },
 6 |   {
 7 |     "data": "2018-02-02",
 8 |     "cena": 165.35
 9 |   },
10 |   {
11 |     "data": "2018-02-03",
12 |     "cena": 176.76
13 |   },
14 |   {
15 |     "data": "2018-02-04",
16 |     "cena": 171.90
17 |   },
18 |   {
19 |     "data": "2018-02-05",
20 |     "cena": 161.43
21 |   },
22 |   {
23 |     "data": "2018-02-06",
24 |     "cena": 167.77
25 |   },
26 |   {
27 |     "data": "2018-02-07",
28 |     "cena": 159.23
29 |   },
30 |   {
31 |     "data": "2018-02-08",
32 |     "cena": 169.99
33 |   },
34 |   {
35 |     "data": "2018-02-09",
36 |     "cena": 173.33
37 |   },
38 |   {
39 |     "data": "2018-02-10",
40 |     "cena": 172.22
41 |   }
42 | ]


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/tests/data/data3.json:
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 1 | [
 2 |   {
 3 |     "data": "2018-02-01",
 4 |     "cena": 177.23
 5 |   },
 6 |   {
 7 |     "data": "2018-02-02",
 8 |     "cena": 175.35
 9 |   },
10 |   {
11 |     "data": "2018-02-03",
12 |     "cena": 174.76
13 |   },
14 |   {
15 |     "data": "2018-02-04",
16 |     "cena": 173.90
17 |   },
18 |   {
19 |     "data": "2018-02-05",
20 |     "cena": 172.43
21 |   },
22 |   {
23 |     "data": "2018-02-06",
24 |     "cena": 171.77
25 |   },
26 |   {
27 |     "data": "2018-02-07",
28 |     "cena": 170.23
29 |   },
30 |   {
31 |     "data": "2018-02-08",
32 |     "cena": 169.99
33 |   },
34 |   {
35 |     "data": "2018-02-09",
36 |     "cena": 168.33
37 |   },
38 |   {
39 |     "data": "2018-02-10",
40 |     "cena": 167.22
41 |   }
42 | ]


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/calculate.php:
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 1 | <?php
 2 | 
 3 | require __DIR__ . '/vendor/autoload.php';
 4 | 
 5 | if (count($argv) < 4) {
 6 |     die('Error: Too few arguments for script!');
 7 | }
 8 | 
 9 | $investor = new \App\Investor('http://api.nbp.pl/api/cenyzlota/');
10 | 
11 | $money = $argv[1];
12 | $startDate = $argv[2];
13 | $endDate = $argv[3];
14 | 
15 | $goldInvest = $investor->bestGoldProfit($money, $startDate, $endDate);
16 | 
17 | if ($goldInvest['profit'] > 0) {
18 |     echo sprintf("Best buy price on:    %s (price %.2f zl) \n", $goldInvest['buyDate'], $goldInvest['buyPrice']);
19 |     echo sprintf("Best sell price on:   %s (price %.2f zl) \n", $goldInvest['saleDate'], $goldInvest['salePrice']);
20 |     echo sprintf("Best profit:          %.2f zl (percentage profit %.2f %%) \n", $goldInvest['profit'], $goldInvest['profitPercent']);
21 | } else {
22 |     echo 'In given range of time there was not possible to get any profit from gold buy/sell process.';
23 | }
24 | 


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/app/CurlHelper.php:
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 1 | <?php
 2 | 
 3 | namespace App;
 4 | 
 5 | /**
 6 |  * Helper class/wrapper for cURL
 7 |  *
 8 |  * Class CurlHelper
 9 |  * @package App
10 |  */
11 | class CurlHelper
12 | {
13 |     /**
14 |      * Send GET request to given url
15 |      *
16 |      * @param string $url
17 |      * @return mixed
18 |      * @throws \Exception
19 |      */
20 |     public static function get(string $url)
21 |     {
22 |         $curl = curl_init();
23 | 
24 |         curl_setopt_array($curl, [
25 |             CURLOPT_RETURNTRANSFER => 1,
26 |             CURLOPT_URL => $url,
27 |             CURLOPT_FAILONERROR => true,
28 |             CURLOPT_HTTPHEADER => [
29 |                 'Accept: application/json'
30 |             ]
31 |         ]);
32 | 
33 |         $result = curl_exec($curl);
34 | 
35 |         if (!$result) {
36 |             throw new \Exception('Error: "' . curl_error($curl) . '" - Code: ' . curl_errno($curl));
37 |         }
38 | 
39 |         curl_close($curl);
40 | 
41 |         return json_decode($result);
42 |     }
43 | }


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/tests/InvestorTest.php:
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 1 | <?php
 2 | 
 3 | use App\Investor;
 4 | use PHPUnit\Framework\TestCase;
 5 | 
 6 | class InvestorTest extends TestCase
 7 | {
 8 |     private $investor;
 9 | 
10 |     public function setUp() {
11 |         $this->investor = new Investor('http://api.nbp.pl/api/cenyzlota/');
12 |     }
13 | 
14 |     public function testBasicGettingTheBestProfit()
15 |     {
16 |         $mockData = json_decode(file_get_contents(__DIR__ . '/data/data1.json'));
17 | 
18 |         $goldInvest = $this->investor->getBestProfit($mockData);
19 | 
20 |         $this->assertEquals("2018-02-01", $goldInvest['buyDate']);
21 |         $this->assertEquals("2018-02-03", $goldInvest['saleDate']);
22 |         $this->assertEquals(160.23, $goldInvest['buyPrice']);
23 |         $this->assertEquals(176.76, $goldInvest['salePrice']);
24 |     }
25 | 
26 |     public function testOtherGettingTheBestProfit()
27 |     {
28 |         $mockData = json_decode(file_get_contents(__DIR__ . '/data/data2.json'));
29 | 
30 |         $goldInvest = $this->investor->getBestProfit($mockData);
31 | 
32 |         $this->assertEquals("2018-02-07", $goldInvest['buyDate']);
33 |         $this->assertEquals("2018-02-09", $goldInvest['saleDate']);
34 |         $this->assertEquals(159.23, $goldInvest['buyPrice']);
35 |         $this->assertEquals(173.33, $goldInvest['salePrice']);
36 |     }
37 | 
38 |     public function testNoProfit()
39 |     {
40 |         $mockData = json_decode(file_get_contents(__DIR__ . '/data/data3.json'));
41 | 
42 |         $goldInvest = $this->investor->getBestProfit($mockData);
43 | 
44 |         $this->assertEquals(null, $goldInvest['buyDate']);
45 |         $this->assertEquals(null, $goldInvest['saleDate']);
46 |         $this->assertEquals(null, $goldInvest['buyPrice']);
47 |         $this->assertEquals(null, $goldInvest['salePrice']);
48 |         $this->assertEquals(0, $goldInvest['finalProfit']);
49 |     }
50 | }
51 | 


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/app/Investor.php:
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  1 | <?php
  2 | 
  3 | namespace App;
  4 | 
  5 | 
  6 | use DateTime;
  7 | use Exception;
  8 | 
  9 | /**
 10 |  * Class for calculating gains from investments
 11 |  *
 12 |  * Class Investor
 13 |  * @package App
 14 |  */
 15 | class Investor
 16 | {
 17 |     /**
 18 |      * Limit of days that we can get data for at once
 19 |      */
 20 |     protected const DAYS_LIMIT = 367;
 21 | 
 22 |     /**
 23 |      * API url
 24 |      *
 25 |      * @var string
 26 |      */
 27 |     protected $url;
 28 | 
 29 |     /**
 30 |      * Investor constructor
 31 |      *
 32 |      * @param string $url
 33 |      */
 34 |     public function __construct(string $url)
 35 |     {
 36 |         $this->url = $url;
 37 |     }
 38 | 
 39 |     /**
 40 |      * Calculate optimal buy and sell prices of gold in given time period
 41 |      * for get the best profit
 42 |      *
 43 |      * @param float $money      Invested amount of money
 44 |      * @param string $startDate Period start date
 45 |      * @param string $endDate   Period end date
 46 |      * @return array|null
 47 |      */
 48 |     public function bestGoldProfit(float $money, string $startDate, string $endDate)
 49 |     {
 50 |         $goldCosts = $this->getGoldCostData($startDate, $endDate);
 51 | 
 52 |         $bestProfit = $this->getBestProfit($goldCosts);
 53 | 
 54 |         return [
 55 |             'buyDate' => $bestProfit['buyDate'],
 56 |             'buyPrice' => $bestProfit['buyPrice'],
 57 |             'saleDate' => $bestProfit['saleDate'],
 58 |             'salePrice' => $bestProfit['salePrice'],
 59 |             'profitPercent' => $bestProfit['finalProfit'] * 100,
 60 |             'profit' => ($money * $bestProfit['finalProfit']) - $money
 61 |         ];
 62 |     }
 63 | 
 64 |     /**
 65 |      * Helper method to get gold cost data from given time range
 66 |      *
 67 |      * NBP gold cost API is limited to certain number of days per one request
 68 |      * so we need multimple requests to get data for period longer than that
 69 |      * limit.
 70 |      *
 71 |      * @param string $startDate Start date
 72 |      * @param string $endDate   End date
 73 |      * @return array
 74 |      */
 75 |     public function getGoldCostData(string $startDate, string $endDate): array
 76 |     {
 77 |         $dStart = new DateTime($startDate);
 78 |         $dEnd  = new DateTime($endDate);
 79 | 
 80 |         $dDiff = $dStart->diff($dEnd);
 81 |         $data = [];
 82 | 
 83 |         try {
 84 |             if ($dDiff->days < self::DAYS_LIMIT) {
 85 |                 // If requested time range is lower that the API limit
 86 |                 $data = CurlHelper::get($this->url . $startDate . '/' . $endDate);
 87 |             } else {
 88 |                 // If requested time period is larger than the API limit we must divide the given
 89 |                 // range to smaller parts, get data for them separately and merge them in one data set
 90 |                 $start = $end = new DateTime($startDate);
 91 | 
 92 |                 while ($start->diff($dEnd)->days > 0) {
 93 |                     $partial = CurlHelper::get($this->url . $start->format('Y-m-d') . '/' . $end->format('Y-m-d'));
 94 |                     $data = array_merge($data, $partial);
 95 | 
 96 |                     $start = clone $end;
 97 | 
 98 |                     if (($start->diff($dEnd))->days > self::DAYS_LIMIT) {
 99 |                         $end->modify('+' . self::DAYS_LIMIT . ' day');
100 |                     } else {
101 |                         $end = new DateTime($endDate);
102 |                     }
103 |                 }
104 |             }
105 |         } catch (Exception $e) {
106 |             echo $e->getMessage() . "\n";
107 |         }
108 | 
109 |         return $data;
110 |     }
111 | 
112 |     /**
113 |      * Recursive method implementing divide and conquer strategy to find the best
114 |      * buy and sell points in prices dataset
115 |      *
116 |      * @param array $prices Dataset/array containing gold prices
117 |      * @return array|mixed
118 |      */
119 |     public function getBestProfit(array $prices)
120 |     {
121 |         $length = count($prices);
122 | 
123 |         // If dataset contains one or zero elements then the profit is zero
124 |         if ($length <= 1) {
125 |             return [
126 |                 'buyDate' => null,
127 |                 'buyPrice' => null,
128 |                 'saleDate' => null,
129 |                 'salePrice' => null,
130 |                 'finalProfit' => 0
131 |             ];
132 |         }
133 | 
134 |         // Divide dataset to two parts
135 |         $leftHalf = array_slice($prices, 0, $length / 2);
136 |         $rightHalf = array_slice($prices, $length / 2);
137 | 
138 |         // Calculate the best profit separately for "left" and "right" part
139 |         $leftBest = $this->getBestProfit($leftHalf);
140 |         $rightBest = $this->getBestProfit($rightHalf);
141 | 
142 |         // Get the lowest price from left part and highest from right part and calculate best profit for them
143 |         $leftMin = array_reduce($leftHalf, function ($prev, $next) {
144 |             return ($prev === null || $next->cena < $prev->cena) ? $next : $prev;
145 |         });
146 | 
147 |         $rightMax = array_reduce($rightHalf, function ($prev, $next) {
148 |             return ($prev === null || $next->cena > $prev->cena) ? $next : $prev;
149 |         });
150 | 
151 |         if ($rightMax->cena > $leftMin->cena) {
152 |             $bothBest = [
153 |                 'buyDate' => $leftMin->data,
154 |                 'buyPrice' => $leftMin->cena,
155 |                 'saleDate' => $rightMax->data,
156 |                 'salePrice' => $rightMax->cena,
157 |                 'finalProfit' => $rightMax->cena / $leftMin->cena
158 |             ];
159 |         } else {
160 |             $bothBest = [
161 |                 'buyDate' => null,
162 |                 'buyPrice' => null,
163 |                 'saleDate' => null,
164 |                 'salePrice' => null,
165 |                 'finalProfit' => 0
166 |             ];
167 |         }
168 | 
169 |         // Choose the best profit from three results and return it
170 |         $bestProfit = array_reduce([$leftBest, $rightBest, $bothBest], function ($first, $second) {
171 |             return ($first === null || $second['finalProfit'] > $first['finalProfit']) ? $second : $first;
172 |         });
173 | 
174 |         return $bestProfit;
175 |     }
176 | }
177 | 


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