usmobile_roaming_analyze.js

function convert(data) {
    const carriers = ["warp", "gsm", "dark_star"];
    const planKey = "annual_unlimited_premium";

    const offeringsByCarrier = {}; // carrier -> offering -> country[]

    for (const country of data) {
        const countryName = country.country;
        for (const carrier of carriers) {
            const offering = country[carrier][planKey];

            let offeringMap = (offeringsByCarrier[carrier] = offeringsByCarrier[carrier] || {});
            let countryList = (offeringMap[offering] = offeringMap[offering] || []);
            countryList.push(countryName);
        }
    }

    const countriesByCarrier = {}; // carrier -> Set<country>
    for (const [carrier, offerings] of Object.entries(offeringsByCarrier)) {
        let set = new Set();
        for (const [offering, countries] of Object.entries(offerings)) {
            if (offering == "Unavailable") continue;

            // Exclude Warp's eSIM-only (non-native) countries
            if (carrier == "warp" && offering.indexOf("mins") == -1) continue;

            set = set.union(new Set(countries));
        }
        countriesByCarrier[carrier] = set;
    }

    const exclusives = {}; // carrier -> Set<country>
    for (const [carrier, countries] of Object.entries(countriesByCarrier)) {
        const others = carriers.filter(c => c != carrier);
        const otherSet = others.reduce((accum, carrier) => accum.union(countriesByCarrier[carrier]), new Set());
        const exclusive = countries.difference(otherSet);
        exclusives[carrier] = exclusive;
    }

    const countryListString = coll => {
        const arr = Array.from(coll).sort();
        return `${arr.length} countries: ${arr.join(", ")}`;
    };
    const mapValues = (mapping, fn) => {
        let result = {};
        for (const [key, val] of Object.entries(mapping)) {
            result[key] = fn(val);
        }
        return result;
    };

    return {
        offeringsByCarrier,
        countriesByCarrier,
        exclusives,
        strings: {
            countriesByCarrier: mapValues(countriesByCarrier, countryListString),
            exclusives: mapValues(exclusives, countryListString),
            offeringsByCarrier: mapValues(offeringsByCarrier, (offerings) => mapValues(offerings, countryListString)),
        }
    };
}