pi-plates/BASEplate.js

control Pi-Plates from node

const vasync = require('vasync');
const readline = require('readline');
const { spawn } = require('child_process');
const assert = require('assert');

let child = spawn(__dirname + '/env/bin/python3', ['-u', __dirname + '/plate_io.py']);

let child_status = 0;

child.on('error', (err) => {
    console.log('child error: ' + err);
});

child.on('exit', (code, signal) => {
    console.log(`code: ${code} signal: ${signal}`);
    child_status = code;
});

child.stderr.on('data', (data) => {
    console.log('stderr: ' + data);
});

const rl = readline.createInterface({
    input: child.stdout
});

function do_cmd(task, cb) {
    if (!child_status) {
        const cmd_str = JSON.stringify(task) + '\n';
        child.stdin.write(cmd_str);
        assert.equal(rl.listenerCount('line'), 0);
        rl.once('line', (line) => {
            try {
                const reply = JSON.parse(line);
                cb(reply);
            } catch (e) {
                console.log('invalid json received from python co-process: ' + line);
                // TODO: better error reporting/handling here
                cb();
            }
        });
    }
}

const queue = vasync.queue(do_cmd, 1);

class BASEplate {
    constructor (addr, plate_type) {
        this.addr = addr;
        this.plate_type = plate_type;
        this.queue = queue;

        /* plate_status stores information about whether or not this plate can currently
         * be used, or if there is an issue:
         * 0 = no error
         * 1 = plate not found
         * 2 = missing python dependencies
         * 3 = unknown python error
         * 4 = unknown state
         */
        this.plate_status = 4;

        this.update_status();
    }

    // Updates this.plate_status.
    update_status () {
        if (child_status) {
            this.plate_status = child_status;
        } else {
            const verifier = {cmd: "VERIFY", args: {}};

            this.send(verifier, (reply) => {
                // If the plate was invalid and now works, the piplates library
                // needs that update as well. So, we activate the piplate:

                if (this.plate_status == 1 && !reply.state) {
                    const update = {cmd: "ACTIVATE", args: {}};

                    this.send(update, (reply) => {});
                }

                this.plate_status = reply.state;
            });
        }
    }
    send (obj, receive_cb) {
        // send a request to this plate using the form:
        // {cmd: <pi-plate command>, args: {<command-specific args>}
        // e.g. {cmd: "relayTOGGLE", args: { relay: 4}}

        obj['plate_type'] = this.plate_type;
        obj['addr'] = this.addr;

        if (!child_status) {
            this.queue.push(obj, receive_cb);
        }
    }
    shutdown () {
        child.kill();
    }
}

module.exports = BASEplate;