<?php

class streamDownload
{
    public $flg = false;
    public $fileName = '';
    public $to_encoding = 'sjis';
    public $from_encoding = 'UTF-8';

    public function __construct($fileName,$to_encoding = 'sjis',$from_encoding = 'UTF-8')
    {
        $this->fileName = $fileName;
        return $this;
    }

    public function checkSplFileInfo()
    {
        if((new SplFileInfo($this->fileName))->getExtension() === 'csv'){
            $this->flg = true;
        }
        return $this;
    }

    public function download($data)
    {
        if(!$this->flg){
            return $this->flg;
        }

        header('Content-Type: application/octet-stream');
        header('Content-Disposition: attachment; filename='.$this->fileName);        
        $stream = fopen('php://output', 'w');
            foreach ($data as $row) {
                $row = mb_convert_encoding($row,$this->to_encoding,$this->from_encoding);
                fputcsv($stream, $row);
            }
        fclose($stream);
        exit;
    }
}

$data = [
    ['テスト1', '高知太郎', 'abc@example.com'],
    ['テスト2', '高知花子', 'def@example.com'],
    ['テスト3', '高知喜多郎', 'dev@example.com'],
];

(new streamDownload('test.csv'))->checkSplFileInfo()->download($data);