class Diff

class Diff {
    
    /**
     * The list of differences as an array of diff operations.
     *
     * @var \Drupal\Component\Diff\Engine\DiffOp[]
     */
    protected $edits;
    
    /**
     * Constructor.
     * Computes diff between sequences of strings.
     *
     * @param array $from_lines
     *   An array of strings.
     *   (Typically these are lines from a file.)
     * @param array $to_lines
     *   An array of strings.
     */
    public function __construct($from_lines, $to_lines) {
        $eng = new DiffEngine();
        $this->edits = $eng->diff($from_lines, $to_lines);
        
        //$this->_check($from_lines, $to_lines);
    }
    
    /**
     * Compute reversed Diff.
     *
     * SYNOPSIS:
     *
     *  $diff = new Diff($lines1, $lines2);
     *  $rev = $diff->reverse();
     * @return object
     *   A Diff object representing the inverse of the original diff.
     */
    public function reverse() {
        $rev = $this;
        $rev->edits = [];
        foreach ($this->edits as $edit) {
            $rev->edits[] = $edit->reverse();
        }
        return $rev;
    }
    
    /**
     * Check for empty diff.
     *
     * @return bool True iff two sequences were identical.
     */
    public function isEmpty() {
        foreach ($this->edits as $edit) {
            if ($edit->type != 'copy') {
                return FALSE;
            }
        }
        return TRUE;
    }
    
    /**
     * Compute the length of the Longest Common Subsequence (LCS).
     *
     * This is mostly for diagnostic purposed.
     *
     * @return int The length of the LCS.
     */
    public function lcs() {
        $lcs = 0;
        foreach ($this->edits as $edit) {
            if ($edit->type == 'copy') {
                $lcs += sizeof($edit->orig);
            }
        }
        return $lcs;
    }
    
    /**
     * Gets the original set of lines.
     *
     * This reconstructs the $from_lines parameter passed to the
     * constructor.
     *
     * @return array The original sequence of strings.
     */
    public function orig() {
        $lines = [];
        foreach ($this->edits as $edit) {
            if ($edit->orig) {
                array_splice($lines, sizeof($lines), 0, $edit->orig);
            }
        }
        return $lines;
    }
    
    /**
     * Gets the closing set of lines.
     *
     * This reconstructs the $to_lines parameter passed to the
     * constructor.
     *
     * @return array The sequence of strings.
     */
    public function closing() {
        $lines = [];
        foreach ($this->edits as $edit) {
            if ($edit->closing) {
                array_splice($lines, sizeof($lines), 0, $edit->closing);
            }
        }
        return $lines;
    }
    
    /**
     * Check a Diff for validity.
     *
     * This is here only for debugging purposes.
     */
    public function check($from_lines, $to_lines) {
        if (serialize($from_lines) != serialize($this->orig())) {
            trigger_error("Reconstructed original doesn't match", E_USER_ERROR);
        }
        if (serialize($to_lines) != serialize($this->closing())) {
            trigger_error("Reconstructed closing doesn't match", E_USER_ERROR);
        }
        $rev = $this->reverse();
        if (serialize($to_lines) != serialize($rev->orig())) {
            trigger_error("Reversed original doesn't match", E_USER_ERROR);
        }
        if (serialize($from_lines) != serialize($rev->closing())) {
            trigger_error("Reversed closing doesn't match", E_USER_ERROR);
        }
        $prevtype = 'none';
        foreach ($this->edits as $edit) {
            if ($prevtype == $edit->type) {
                trigger_error("Edit sequence is non-optimal", E_USER_ERROR);
            }
            $prevtype = $edit->type;
        }
        $lcs = $this->lcs();
        trigger_error('Diff okay: LCS = ' . $lcs, E_USER_NOTICE);
    }
    
    /**
     * Gets the list of differences as an array of diff operations.
     *
     * @return \Drupal\Component\Diff\Engine\DiffOp[]
     *   The list of differences as an array of diff operations.
     */
    public function getEdits() {
        return $this->edits;
    }

}