const { MonitorType } = require("./monitor-type");
const { UP, log } = require("../../src/util");
const exec = require("child_process").exec;

/**
 * A TailscalePing class extends the MonitorType.
 * It runs Tailscale ping to monitor the status of a specific node.
 */
class TailscalePing extends MonitorType {

    name = "tailscale-ping";

    /**
     * Checks the ping status of the URL associated with the monitor.
     * It then parses the Tailscale ping command output to update the heatrbeat.
     *
     * @param {Object} monitor - The monitor object associated with the check.
     * @param {Object} heartbeat - The heartbeat object to update.
     * @throws Will throw an error if checking Tailscale ping encounters any error
     */
    async check(monitor, heartbeat) {
        try {
            let tailscaleOutput = await this.runTailscalePing(monitor.hostname, monitor.interval);
            this.parseTailscaleOutput(tailscaleOutput, heartbeat);
        } catch (err) {
            log.debug("Tailscale", err);
            // trigger log function somewhere to display a notification or alert to the user (but how?)
            throw new Error(`Error checking Tailscale ping: ${err}`);
        }
    }

    /**
     * Runs the Tailscale ping command to the given URL.
     *
     * @param {string} hostname - The hostname to ping.
     * @returns {Promise<string>} - A Promise that resolves to the output of the Tailscale ping command
     * @throws Will throw an error if the command execution encounters any error.
     */
    async runTailscalePing(hostname, interval) {
        let cmd = `tailscale ping ${hostname}`;

        log.debug("Tailscale", cmd);

        return new Promise((resolve, reject) => {
            let timeout = interval * 1000 * 0.8;
            exec(cmd, { timeout: timeout }, (error, stdout, stderr) => {
                // we may need to handle more cases if tailscale reports an error that isn't necessarily an error (such as not-logged in or DERP health-related issues)
                if (error) {
                    reject(`Execution error: ${error.message}`);
                    return;
                }
                if (stderr) {
                    reject(`Error in output: ${stderr}`);
                    return;
                }

                resolve(stdout);
            });
        });
    }

    /**
     * Parses the output of the Tailscale ping command to update the heartbeat.
     *
     * @param {string} tailscaleOutput - The output of the Tailscale ping command.
     * @param {Object} heartbeat - The heartbeat object to update.
     * @throws Will throw an eror if the output contains any unexpected string.
     */
    parseTailscaleOutput(tailscaleOutput, heartbeat) {
        let lines = tailscaleOutput.split("\n");

        for (let line of lines) {
            if (line.includes("pong from")) {
                heartbeat.status = UP;
                let time = line.split(" in ")[1].split(" ")[0];
                heartbeat.ping = parseInt(time);
                heartbeat.msg = line;
                break;
            } else if (line.includes("timed out")) {
                throw new Error(`Ping timed out: "${line}"`);
                // Immediately throws upon "timed out" message, the server is expected to re-call the check function
            } else if (line.includes("no matching peer")) {
                throw new Error(`Nonexistant or inaccessible due to ACLs: "${line}"`);
            } else if (line.includes("is local Tailscale IP")) {
                throw new Error(`Tailscale only works if used on other machines: "${line}"`);
            } else if (line !== "") {
                throw new Error(`Unexpected output: "${line}"`);
            }
        }
    }
}

module.exports = {
    TailscalePing,
};