<?php

//添加了一个 _createSql 方法，负责创建所有sql

class Db{

    static private $ins;

    private $pdo;

    private $table;

    private $where;

    private $field = '*';

    private $joinWhere = 'where';

    private $order;

    private $limit;

    final private function __construct(){

        //从配置文件读入数据库信息

        $dsn  =  'mysql:dbname=wxguide;host=127.0.0.1' ;

        $user  =  'root';

        $password  =  '';

        try {

             $this->pdo  = new  PDO ( $dsn ,  $user ,  $password );

        } catch ( PDOException $e ) {

            die('Connection failed: '  .  $e -> getMessage ());

        }

    }

    final private function __clone(){}

    static public function table($table){

        if(!self::$ins instanceof self){

            self::$ins = new self();

        }

        self::$ins->table = $table;

        return self::$ins;

    }

    public function query($sql){

        return $this->pdo->query($sql);

    }

    public function exec($sql){

        return $this->pdo->exec($sql);

    }

    public function insert($data){

        $type = 'insert';

        $sql = $this->_createSql($type,$data);

        return $this->exec($sql);

    }

    public function delete(){

        $type = 'delete';

        $sql = $this->_createSql($type);

        return $this->exec($sql);

    }

    public function update($data){

        $type = 'update';

        $sql = $this->_createSql($type,$data);

        return $this->exec($sql);

    }

    public function find(){

        $type = 'select';

        $sql = $this->_createSql($type);

        return $this->query($sql)->fetch(PDO::FETCH_ASSOC);

    }

    public function select(){

        $type = 'select';

        $sql = $this->_createSql($type);

        return $this->query($sql)->fetchAll(PDO::FETCH_ASSOC);

    }

    //条件字符串的【条件的值】需要用 引号（值如果是数字可以不用，但是用也没影响，建议不用），如： $str = 'id = 1 and name = "王五" '

    public function where($str){

        $this->where = $str;

        return $this;

    }

    public function field($str){

        $this->field = $str;

        return $this;

    }

    public function limit($numstr){

        $this->limit = 'limit ' . $numstr;

        return $this;

    }

    public function order($str){

        $this->order = 'order by ' . $str;

        return $this;

    }

    public function group(){

    }

    public function having(){

    }

    //给表取别名

    public function alias($str){

        $this->table .= ' ' . $str;

        return $this;

    }

    //可以多表联查，join('tb1 b,tb2 c','a,id=b.id and a.id = c.id')

    //$join 可以取值 INNER，left或者right，默认值是 INNER

    public function join($alias,$where = null,$join = 'INNER'){

        $this->where .= $where;

        if($join != 'INNER'){

            $this->table .= ' '.$join . ' join ' . $alias;

            $this->joinWhere = 'ON';

        }else{

            $this->table .= ',' . $alias;

        }

        return $this;

    }

    //创建sql

    private function _createSql($type,$data=null){

        switch ($type) {

            case 'insert':

                $arr = $this->_cf($data);

                $sql = 'insert into ' . $this->table . ' (' . $arr['kstr'] . ') VALUES (' . $arr['vstr'] . ')';

                break;

            case 'delete':

                $sql = 'delete from ' . $this->table . ' '.$this->joinWhere.' ' . $this->where;

                break;

            case 'update':

                $arr = $this->_cf($data);

                $sql = 'update ' . $this->table . ' set '. $arr['ustr'] .' '.$this->joinWhere.' ' . $this->where;

                break;

            case 'select':

                $sql = 'select '. $this->field .' from ' . $this->table;

                if($this->where){

                    $sql = $sql . ' '.$this->joinWhere.' ' . $this->where;

                }

                $sql .= ' '.$this->order;

                $sql .= ' '. $this->limit;

                break;

            default:

                die('sql创建出现错误');

                break;

        }

        $this->_clear();

        return $sql;

    }

    //属性数据还原

    private function _clear(){

        $this->table = '';

        $this->where = '';

        $this->field = '*';

        $this->joinWhere = 'where';

        $this->order = '';

        $this->limit = '';

    }

    //拆分 数组，组装数据

    private function _cf($data){

        $arr = [];

        $str = '';

        foreach($data as $k=>$v){

            $arr['k'][] = $k;

            $arr['v'][] = '"'.$v.'"';

            $str .= $k . '="' . $v . '",';

        }

        $arr['kstr'] = implode(',',$arr['k']);

        $arr['vstr'] = implode(',',$arr['v']);

        $arr['ustr'] = rtrim($str, ",");

        return $arr;

    }

}

header('Content-type:text/html;charset=gbk');

$a = Db::table('model')->where('1')->select();

print_r($a);