// 日志命令操作类

const fs = require("fs");
const HISTORY_SIZE_LINE = 1024;
const FILE_CODE = "utf8";

// 默认目录 RecordTmp
class RecordCommand {

    constructor(path = "") {
        this.path = path;
        this.timerlock = false;
    }

    // 获取当前这一刻的 log 文本文件大小
    // 可以定位当前日志起始位置
    recordLength() {
        try {
            let fsstat = fs.statSync(this.path);
            return fsstat.size;
        } catch (err) {
            return 0;
        }
    }

    // 向最后追加一行或一堆数据
    writeRecord(data = "") {
        if (fs.existsSync(this.path))
            fs.appendFile(this.path, data, FILE_CODE, function (err) {});
        else
            fs.writeFileSync(this.path, new Buffer(HISTORY_SIZE_LINE * 2).toString() + data);
    }

    readRecord(pstart = 0, length = 32, callback = (logStr) => {}) {
        if (!fs.existsSync(this.path)) return;

        const fsstat = fs.statSync(this.path);
        const filesize = fsstat.size;

        let buffer = new Buffer(length);

        // Start Read from file
        fs.open(this.path, 'r', function (err, fd) {
            if (err) return;

            if (pstart >= filesize || pstart <= 0)
                return

            // 读取文件
            fs.read(fd, buffer, 0, length, pstart, function (err, bytesRead, buffer) {
                if (err) return;

                // 打印出buffer中存入的数据
                let resStr = buffer.slice(0, bytesRead).toString();
                callback(resStr);

                // 关闭文件
                fs.close(fd, () => {});
            });

        });
    }
}


module.exports.RecordCommand = RecordCommand;