controller.js

import configureMeasurements from 'convert-units';
import allMeasures from 'convert-units/definitions/all';

export const
    convertUnits = configureMeasurements(allMeasures),
    knownUnits = convertUnits().possibilities();


export var activeController;  // hack to provide current context for gauges to register with


function maybeConvert(v, fromUnit, toUnit) {
    var u = v;
    if (fromUnit && toUnit) {
        try {
            u = convertUnits(v).from(fromUnit).to(toUnit);
        } catch(err) {
            console.log('Unit conversion error: ' + err.message);
        }
    } else if (typeof v === 'string' && v.match(/^\d{4}-[01]\d-[0-3]\dT[0-2]\d:[0-5]\d:[0-5]\d/)) {
        // convert string-serialized date metrics back to JS objects
        u = new Date(v);
    }
    return u;
}


export function gaugeController() {
    /*
    create a gauge controller that we'll use to update values

    `callbacks` is keyed by the panel indicator names,
    which can be more precise than the actual metric name, e.g. fuel.copilot;
    `updaters` is populated after the first call with best match to actual metrics
    */

    var callbacks = {},     // nested dict of metric => (unit || '') => list of update fns
        fakes = {},         // dict of metric => generator
        updaters = null;    // dict of metric keys => {metric: {unit: updaters: {unit: fns}}}
        /*
        After initial set up we build an updaters structure like this which lets us route
        incoming metrics to clients in appropriate units:
        {
            altitude: {                         // incoming metric name
                unit: meters,                   // incoming unit
                updaters: {
                    feet: [ f1, f2, ... ],      // clients segmented by desired unit
                    meters: [ f3, f4, ... ],
                    ...
                }
            },
            ...
        }
        */

    // call the controller to display current metric values
    function gaugeController(data, transition) {
        /*
        data is a dictionary {latest: 1234, metrics: {}, [units: {}]}
        where metrics is a dictionary
        with keys like: "metric.some.qualification"
        and corresponding values
        */
        if (!updaters) {
            // First call, we establish the mapping from metric keys => callbacks
            updaters = {};
            Object.keys(data.metrics).forEach(m => {
                updaters[m] = {unit: (data.units || {})[m] || '', updaters: null};
            })

            Object.entries(callbacks).forEach(([m, ufs]) => {
                /*
                for each callback, find best qualified metric from the input values,
                which we'll convert to appropriate units
                e.g. a gauge requesting fuel.copilot.rear will match
                a metric called fuel.copilot.rear,
                or else fuel.copilot or else simply fuel but never fuel.pilot
                */
                var ks = m.split('.'),
                    matched = false;
                while (ks.length && !matched) {
                    let k = ks.join('.');
                    if (k in updaters) {
                        updaters[k].updaters = ufs
                        matched = true;
                    }
                    ks.pop();
                }
                if (!matched) console.log('Warning: no source metric matching', m);
            });
            Object.entries(updaters).forEach(([m, d]) => {
                if (!d.updaters) {
                    console.log('Warning: unmapped source metric', m)
                    delete updaters[m];
                }
            });
        }

        // Trigger updates for each source metric
        Object.entries(updaters).forEach(([m, d]) => {
            if (m in data.metrics) {
                Object.entries(d.updaters).forEach(([unit, fs]) => {
                    let v = maybeConvert(data.metrics[m], d.unit, unit);
                    if (typeof v == 'undefined') {
                        console.log(`Warning: failed to convert ${data.metrics[m]} from ${d.unit} to ${unit}`);
                    } else {
                        fs.forEach(f => f(v, transition));
                    }
                });
            }
        });
    }
    gaugeController.register = function(updater, metric, unit) {
        if (!metric) return;
        unit = unit || '';
        if (!(metric in callbacks)) callbacks[metric] = {};
        if (!(unit in callbacks[metric])) callbacks[metric][unit] = [];
        callbacks[metric][unit].push(updater);
    }
    gaugeController.fake = function(metric, generator) {
        fakes[metric] = generator;
    }
    gaugeController.fakeMetrics = function() {
        return {
            latest: 0,
            units: {},
            metrics: Object.fromEntries(
                Object.entries(fakes).map(([m, g]) => [m, g()])
            )
        }
    }
    gaugeController.indicators = function() {
        // return panel indicator keys, available at startup but possibly more specific than actual metrics
        return Object.keys(callbacks);
    }
    gaugeController.mappedMetrics = function() {
        // return matched metrics, available after first data update
        return updaters && Object.keys(updaters);
    }
    activeController = gaugeController;
    return gaugeController;
}