datatable.directory codebase
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53 lines
1.4 KiB
53 lines
1.4 KiB
6 years ago
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<?php
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namespace App\Tables;
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use App\Models\Row;
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use MightyPork\Utils\Utils;
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/**
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* Generates a sequence of string codes for internal naming of columns
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*
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* Produces database-unique lowercase identifiers for created or proposed columns.
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* Column identifiers are used in row objects to uniquely identify data even if the
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* revision header (columns object) is modified, such as reordering, changing name,
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* adding new column in concurrent proposals, etc.
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*
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* Thanks to this uniqueness, it could even be possible to compare or merge forks
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* of the same table.
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*/
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class ColumnNumerator
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{
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const ALPHABET = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
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'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];
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/** @var int */
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private $next;
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/** @var int */
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private $last;
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/**
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* Create numerator for the given number of columns
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*/
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public function __construct($capacity)
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{
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list($this->next, $this->last) = Row::allocateColIDs($capacity);
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}
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/**
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* Get next column name, incrementing the internal state
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*
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* @return string
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*/
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public function next()
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{
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if ($this->next > $this->last)
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throw new \OutOfBoundsException("Column numerator has run out of allocated GCID slots");
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$key = Utils::alphabetEncode($this->next, self::ALPHABET);
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$this->next++;
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return $key;
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}
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}
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