class Ajax {

    xhr = new XMLHttpRequest()

    get(option) {
        return new Promise((success, error) => {
            var params = ""
            for (const key in option.data) {
                params += `&${key}=${option.data[key]}`
            }
            params = params.replace("&", "?")

            // option.url == /home/hot?id=1
            this.xhr.open("GET", `${config.checkUrl()}${option.url}${params}`)

            this.xhr.send()
            this.stateChange(success, error)
        })
    }

    post(option) {
        return new Promise((success, error) => {
            this.xhr.open("POST", option.url)
            this.xhr.setRequestHeader("Content-Type", "application/json")
            // post 参数在请求体(body)中发送
            this.xhr.send(JSON.stringify(option.data))
            this.stateChange(success, error)
        })
    }

    stateChange(suc, err) {
        this.xhr.onreadystatechange = () => {
            if (this.xhr.readyState == 4) {
                if (this.xhr.status == 200) {
                    let res = JSON.parse(this.xhr.response)
                    switch (res.status) {
                        case 200:
                            suc(res.data)
                            break;

                        case 404:
                            alert(res.message)
                            err(this.xhr)
                            break;

                        default:
                            break;
                    }
                    suc()
                } else {
                    err(this.xhr)
                }
            }
        }
    }

}