const Url = require('url');
const errors = require('./Errors');
const utils = require('./utils');



class Transports {
    /*
    Handles multiple transports, API should be (almost) the same as for an individual transport)

    Fields:
    _transports         List of transports loaded (internal)
    namingcb            If set will be called cb(urls) => urls  to convert to urls from names.
    _transportclasses   All classes whose code is loaded e.g. {HTTP: TransportHTTP, IPFS: TransportIPFS}
    _optionspaused       Saves paused option for setup
    */

    constructor(options, verbose) {
        if (verbose) console.log("Transports(%o)",options);
    }

    static _connected() {
        /*
        Get an array of transports that are connected, i.e. currently usable
         */
        return this._transports.filter((t) => (!t.status));
    }
    static async p_connectedNames() {
        /*
        resolves to: an array of the names of connected transports
         */
        return this._connected().map(t => t.name);
    }
    static async p_connectedNamesParm() { // Doesnt strictly need to be async, but for consistency with Proxy it has to be.
        return (await this.p_connectedNames()).map(n => "transport="+n).join('&')
    }
    static async p_statuses() {
        /*
        resolves to: a dictionary of statuses of transports, e.g. { TransportHTTP: STATUS_CONNECTED }
         */
        return this._transports.map((t) => { return {"name": t.name, "status": t.status}})
    }
    static validFor(urls, func, options) {
        /*
        Finds an array or Transports that can support this URL.

        Excludes any transports whose status != 0 as they aren't connected

        urls:       Array of urls
        func:       Function to check support for: fetch, store, add, list, listmonitor, reverse - see supportFunctions on each Transport class
        options:    For future use
        returns:    Array of pairs of url & transport instance [ [ u1, t1], [u1, t2], [u2, t1]]
        throws:     CodingError if urls empty or [undefined...]
         */
        if (!((urls && urls[0]) || ["store", "newlisturls", "newdatabase", "newtable"].includes(func)))   {
            console.warn("Transports.validFor called with invalid arguments: urls=", urls, "func=", func); // FOr debugging old calling patterns with [ undefined ]
            return [];
        }
        if (!(urls && urls.length > 0)) {
            return this._connected().filter((t) => (t.supports(undefined, func)))
                .map((t) => [undefined, t]);
        } else {
            return [].concat(
                ...urls.map((url) => typeof url === 'string' ? Url.parse(url) : url) // parse URLs once
                    .map((url) =>
                        this._connected().filter((t) => (t.supports(url, func))) // [ t1, t2 ]
                            .map((t) => [url, t]))); // [[ u, t1], [u, t2]]
        }
    }
    static async p_urlsValidFor(urls, func, options) {
        // Need a async version of this for serviceworker and TransportsProxy
        return this.validFor(urls, func, options).map((ut) => ut[0]);
    }

    // SEE-OTHER-ADDTRANSPORT

    static http(verbose) {
        // Find an http transport if it exists, so for example YJS can use it.
        return Transports._connected().find((t) => t.name === "HTTP")
    }
    static ipfs(verbose) {
        // Find an ipfs transport if it exists, so for example YJS can use it.
        return Transports._connected().find((t) => t.name === "IPFS")
    }

    static webtorrent(verbose) {
        // Find an ipfs transport if it exists, so for example ServiceWorker.p_respondWebTorrent can use it.
        return Transports._connected().find((t) => t.name === "WEBTORRENT")
    }

    static gun(verbose) {
        // Find a GUN transport if it exists
        return Transports._connected().find((t) => t.name === "GUN")
    }


    static async p_resolveNames(urls) {
        /* If and only if TransportNAME was loaded (it might not be as it depends on higher level classes like Domain and SmartDict)
            then resolve urls that might be names, returning a modified array.
         */
        if (this.namingcb) {
            return await this.namingcb(urls);  // Array of resolved urls
        } else {
            return urls;
        }
    }
    static resolveNamesWith(cb) {
        // Set a callback for p_resolveNames
        this.namingcb = cb;
    }

    static async _p_rawstore(tt, data, {verbose}) {
        // Internal method to store at known transports
        let errs = [];
        let rr = await Promise.all(tt.map(async function(t) {
            try {
                return await t.p_rawstore(data, {verbose}); //url
            } catch(err) {
                console.log("Could not rawstore to", t.name, err.message);
                errs.push(err);
                return undefined;
            }
        }));
        rr = rr.filter((r) => !!r); // Trim any that had errors
        if (!rr.length) {
            throw new errors.TransportError(errs.map((err)=>err.message).join(', ')); // New error with concatenated messages
        }
        return rr;

    }
    static async p_rawstore(data, {verbose}) {
        /*
        data: Raw data to store - typically a string, but its passed on unmodified here
        returns:    Array of urls of where stored
        throws: TransportError with message being concatenated messages of transports if NONE of them succeed.
         */
        let tt = this.validFor(undefined, "store").map(([u, t]) => t); // Valid connected transports that support "store"
        if (verbose) console.log("Valid for transports:", tt.map(t => t.name));
        if (!tt.length) {
            throw new errors.TransportError('Transports.p_rawstore: Cant find transport for store');
        }
        return this._p_rawstore(tt, data, {verbose});
    }
    static async p_rawlist(urls, {verbose=false}={}) {
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        let tt = this.validFor(urls, "list"); // Valid connected transports that support "store"
        if (!tt.length) {
            throw new errors.TransportError('Transports.p_rawlist: Cant find transport to "list" urls:'+urls.join(','));
        }
        let errs = [];
        let ttlines = await Promise.all(tt.map(async function([url, t]) {
            try {
                return await t.p_rawlist(url, {verbose}); // [sig]
            } catch(err) {
                console.log("Could not rawlist ", url, "from", t.name, err.message);
                errs.push(err);
                return [];
            }
        })); // [[sig,sig],[sig,sig]]
        if (errs.length >= tt.length) {
            // All Transports failed (maybe only 1)
            throw new errors.TransportError(errs.map((err)=>err.message).join(', ')); // New error with concatenated messages
        }
        let uniques = {}; // Used to filter duplicates
        return [].concat(...ttlines)
            .filter((x) => (!uniques[x.signature] && (uniques[x.signature] = true)));
    }

    static async p_rawfetch(urls, opts) {
        /*
        Fetch the data for a url, transports act on the data, typically storing it.
        urls:	array of urls to retrieve (any are valid)
        opts {
            verbose,
            start,  integer - first byte wanted
            end     integer - last byte wanted (note this is inclusive start=0,end=1023 is 1024 bytes
            timeoutMS   integer - max time to wait on transports (IPFS) that support it
            }
        returns:	string - arbitrary bytes retrieved.
        throws:     TransportError with concatenated error messages if none succeed.
        throws:     CodingError if urls empty or [undefined ... ]
         */
        let verbose = opts.verbose;
        if (!urls.length)  throw new errors.TransportError("Transports.p_rawfetch given an empty list of urls");
        let resolvedurls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        if (!resolvedurls.length)  throw new errors.TransportError("Transports.p_rawfetch none of the urls resolved: " + urls);
        let tt = this.validFor(resolvedurls, "fetch"); //[ [Url,t],[Url,t]] throws CodingError on empty /undefined urls
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_rawfetch cant find any transport for urls: " + resolvedurls);
        }
        //With multiple transports, it should return when the first one returns something.
        let errs = [];
        let failedtransports = [];  // Will accumulate any transports fail on before the success
        for (const [url, t] of tt) {
            try {
                let data = await t.p_rawfetch(url, opts);   // throws errors if fails or timesout
                //TODO-MULTI-GATEWAY working here - it doesnt quite work yet as the "Add" on browser gets different url than on server
                if (opts.relay && failedtransports.length) {
                    console.log(`Relaying ${data.length} bytes from ${typeof url === "string" ? url : url.href} to ${failedtransports.map(t=>t.name)}`);
                    this._p_rawstore(failedtransports, data, {verbose})
                        .then(uu => console.log(`Relayed to ${uu}`)); // Happening async, not waiting and dont care if fails
                }
                //END TODO-MULTI-GATEWAY
                return data;
            } catch (err) {
                failedtransports.push(t);
                errs.push(err);
                console.log("Could not retrieve ", url && url.href, "from", t && t.name, err.message);
                // Don't throw anything here, loop round for next, only throw if drop out bottom
                //TODO-MULTI-GATEWAY potentially copy from success to failed URLs.
            }
        }
        throw new errors.TransportError(errs.map((err)=>err.message).join(', '));  //Throw err with combined messages if none succeed
    }

    static async p_rawadd(urls, sig, {verbose=false}={}) {
        /*
        urls: of lists to add to
        sig: Sig to add
        returns:    undefined
        throws: TransportError with message being concatenated messages of transports if NONE of them succeed.
         */
        //TODO-REFACTOR remove dependecy on the object having a .preflight, this should be handled one layer up.
        //TODO-REFACTOR requires changes in: dweb-transports: TransportXyz, Transport, API.md; dweb-objects: CommonList.js, test.js; dweb-serviceworker/TransportsProxy.js;
        //TODO-MULTI-GATEWAY might be smarter about not waiting but Promise.race is inappropriate as returns after a failure as well.
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        let tt = this.validFor(urls, "add"); // Valid connected transports that support "store"
        if (!tt.length) {
            throw new errors.TransportError('Transports.p_rawstore: Cant find transport for urls:'+urls.join(','));
        }
        let errs = [];
        await Promise.all(tt.map(async function([u, t]) {
            try {
                await t.p_rawadd(u, sig, {verbose}); //undefined
                return undefined;
            } catch(err) {
                console.log("Could not rawlist ", u, "from", t.name, err.message);
                errs.push(err);
                return undefined;
            }
        }));
        if (errs.length >= tt.length) {
            // All Transports failed (maybe only 1)
            throw new errors.TransportError(errs.map((err)=>err.message).join(', ')); // New error with concatenated messages
        }
        return undefined;

    }

    static listmonitor(urls, cb, opts={}) {
        /*
        Add a listmonitor for each transport - note this means if multiple transports support it, then will get duplicate events back if everyone else is notifying all of them.
         */
        // Note cant do p_resolveNames since sync but should know real urls of resource by here.
        this.validFor(urls, "listmonitor")
            .map(([u, t]) => t.listmonitor(u, cb, opts));
    }

    static async p_newlisturls(cl, {verbose=false}={}) {
        // Create a new list in any transport layer that supports lists.
        // cl is a CommonList or subclass and can be used by the Transport to get info for choosing the list URL (normally it won't use it)
        // Note that normally the CL will not have been stored yet, so you can't use its urls.
        let uuu = await Promise.all(this.validFor(undefined, "newlisturls")
            .map(([u, t]) => t.p_newlisturls(cl, {verbose})) );   // [ [ priv, pub] [ priv, pub] [priv pub] ]
        return [uuu.map(uu=>uu[0]), uuu.map(uu=>uu[1])];    // [[ priv priv priv ] [ pub pub pub ] ]
    }

    // Stream handling ===========================================
    //myArray[Math.floor(Math.random() * myArray.length)];
    
    static async p_f_createReadStream(urls, {verbose=false, wanturl=false}={}) { // Note options is options for selecting a stream, not the start/end in a createReadStream call
        /*
        urls:   Urls of the stream
        returns:    f(opts) => stream returning bytes from opts.start || start of file to opts.end-1 || end of file
         */
        let tt = this.validFor(urls, "createReadStream", {}); //[ [Url,t],[Url,t]]  // Can pass options TODO-STREAM support options in validFor
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_createReadStream cant find any transport for urls: " + urls);
        }
        //With multiple transports, it should return when the first one returns something.
        let errs = [];
        // Until we have transport ordering, try randomly
        let z;
        while ((z = tt.splice(Math.floor(Math.random() * tt.length),1)).length) {
            let url = z[0][0];
            let t = z[0][1];
            try {
                return await t.p_f_createReadStream(url, {verbose, wanturl} );
            } catch (err) {
                errs.push(err);
                console.log("Could not retrieve ", url.href, "from", t.name, err.message);
                // Don't throw anything here, loop round for next, only throw if drop out bottom
                //TODO-MULTI-GATEWAY potentially copy from success to failed URLs.
            }
        }
        throw new errors.TransportError(errs.map((err)=>err.message).join(', '));  //Throw err with combined messages if none succeed
}


// KeyValue support ===========================================

    static async p_get(urls, keys, {verbose=false}={}) {
        /*
        Fetch the values for a url and one or more keys, transports act on the data, typically storing it.
        urls:	array of urls to retrieve (any are valid)
        keys:   array of keys wanted or single key
        returns:	string - arbitrary bytes retrieved or dict of key: value
        throws:     TransportError with concatenated error messages if none succeed.
         */
        let tt = this.validFor(urls, "get"); //[ [Url,t],[Url,t]]
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_get cant find any transport for urls: " + urls);
        }
        //With multiple transports, it should return when the first one returns something.
        let errs = [];
        for (const [url, t] of tt) {
            try {
                return await t.p_get(url, keys, {verbose}); //TODO-MULTI-GATEWAY potentially copy from success to failed URLs.
            } catch (err) {
                errs.push(err);
                console.log("Could not retrieve ", url.href, "from", t.name, err.message);
                // Don't throw anything here, loop round for next, only throw if drop out bottom
            }
        }
        throw new errors.TransportError(errs.map((err)=>err.message).join(', '));  //Throw err with combined messages if none succeed
    }
    static async p_set(urls, keyvalues, value, {verbose=false}={}) {
        /* Set a series of key/values or a single value
         keyvalues:    Either dict or a string
         value: if kv is a string, this is the value to set
        throws: TransportError with message being concatenated messages of transports if NONE of them succeed.
        */
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        let tt = this.validFor(urls, "set"); //[ [Url,t],[Url,t]]
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_set cant find any transport for urls: " + urls);
        }
        let errs = [];
        let success = false;
        await Promise.all(tt.map(async function([url, t]) {
            try {
                await t.p_set(url, keyvalues, value, {verbose});
                success = true; // Any one success will return true
            } catch(err) {
                console.log("Could not rawstore to", t.name, err.message);
                errs.push(err);
            }
        }));
        if (!success) {
            throw new errors.TransportError(errs.map((err)=>err.message).join(', ')); // New error with concatenated messages
        }
    }

    static async p_delete(urls, keys, {verbose=false}={}) {
        /* Delete a key or a list of keys
         kv:    Either dict or a string
         value: if kv is a string, this is the value to set
        throws: TransportError with message being concatenated messages of transports if NONE of them succeed.
        */
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        let tt = this.validFor(urls, "set"); //[ [Url,t],[Url,t]]
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_set cant find any transport for urls: " + urls);
        }
        let errs = [];
        let success = false;
        await Promise.all(tt.map(async function([url, t]) {
            try {
                await t.p_delete(url, keys, {verbose});
                success = true; // Any one success will return true
            } catch(err) {
                console.log("Could not rawstore to", t.name, err.message);
                errs.push(err);
            }
        }));
        if (!success) {
            throw new errors.TransportError(errs.map((err)=>err.message).join(', ')); // New error with concatenated messages
        }
    }
    static async p_keys(urls, {verbose=false}={}) {
        /*
        Fetch the values for a url and one or more keys, transports act on the data, typically storing it.
        urls:	array of urls to retrieve (any are valid)
        keys:   array of keys wanted
        returns:	string - arbitrary bytes retrieved or dict of key: value
        throws:     TransportError with concatenated error messages if none succeed.
         */
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        let tt = this.validFor(urls, "keys"); //[ [Url,t],[Url,t]]
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_keys cant find any transport for urls: " + urls);
        }
        //With multiple transports, it should return when the first one returns something.
        let errs = [];
        for (const [url, t] of tt) {
            try {
                return await t.p_keys(url, {verbose}); //TODO-MULTI-GATEWAY potentially copy from success to failed URLs.
            } catch (err) {
                errs.push(err);
                console.log("Could not retrieve keys for", url.href, "from", t.name, err.message);
                // Don't throw anything here, loop round for next, only throw if drop out bottom
            }
        }
        throw new errors.TransportError(errs.map((err)=>err.message).join(', '));  //Throw err with combined messages if none succeed
    }

    static async p_getall(urls, {verbose=false}={}) {
        /*
        Fetch the values for a url and one or more keys, transports act on the data, typically storing it.
        urls:	array of urls to retrieve (any are valid)
        keys:   array of keys wanted
        returns:	array of strings returned for the keys. //TODO consider issues around return a data type rather than array of strings
        throws:     TransportError with concatenated error messages if none succeed.
         */
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        let tt = this.validFor(urls, "getall"); //[ [Url,t],[Url,t]]
        if (!tt.length) {
            throw new errors.TransportError("Transports.p_getall cant find any transport for urls: " + urls);
        }
        //With multiple transports, it should return when the first one returns something.
        let errs = [];
        for (const [url, t] of tt) {
            try {
                return await t.p_getall(url, {verbose}); //TODO-MULTI-GATEWAY potentially copy from success to failed URLs.
            } catch (err) {
                errs.push(err);
                console.log("Could not retrieve all keys for", url.href, "from", t.name, err.message);
                // Don't throw anything here, loop round for next, only throw if drop out bottom
            }
        }
        throw new errors.TransportError(errs.map((err)=>err.message).join(', '));  //Throw err with combined messages if none succeed
    }

    static async p_newdatabase(pubkey, {verbose=false}={}) {
        /*
            Create a new database in any transport layer that supports databases (key value pairs).
            pubkey: CommonList, KeyPair, or exported public key
            resolves to: [ privateurl, publicurl]
         */
        let uuu = await Promise.all(this.validFor(undefined, "newdatabase")
            .map(([u, t]) => t.p_newdatabase(pubkey, {verbose})) );   // [ { privateurl, publicurl} { privateurl, publicurl} { privateurl, publicurl} ]
        return { privateurls: uuu.map(uu=>uu.privateurl), publicurls: uuu.map(uu=>uu.publicurl) };    // { privateurls: [], publicurls: [] }
    }

    static async p_newtable(pubkey, table, {verbose=false}={}) {
        /*
            Create a new table in any transport layer that supports the function (key value pairs).
            pubkey: CommonList, KeyPair, or exported public key
            resolves to: [ privateurl, publicurl]
         */
        let uuu = await Promise.all(this.validFor(undefined, "newtable")
            .map(([u, t]) => t.p_newtable(pubkey, table, {verbose})) );   // [ [ priv, pub] [ priv, pub] [priv pub] ]
        return { privateurls: uuu.map(uu=>uu.privateurl), publicurls: uuu.map(uu=>uu.publicurl)};    // {privateurls: [ priv priv priv ], publicurls: [ pub pub pub ] }
    }

    static async p_connection(urls, verbose) {
        /*
        Do any asynchronous connection opening work prior to potentially synchronous methods (like monitor)
         */
        urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        await Promise.all(
            this.validFor(urls, "connection")
            .map(([u, t]) => t.p_connection(u, verbose)));
    }

    static monitor(urls, cb, {verbose=false, current=false}={}) {
        /*
        Add a listmonitor for each transport - note this means if multiple transports support it, then will get duplicate events back if everyone else is notifying all of them.
        Stack: KVT()|KVT.p_new => KVT.monitor => (a: Transports.monitor => YJS.monitor)(b: dispatchEvent)
        cb:         function({type, key, value})
        current:    If true then then send all current entries as well
         */
        //Cant' its async. urls = await this.p_resolveNames(urls); // If naming is loaded then convert to a name
        this.validFor(urls, "monitor")
            .map(([u, t]) => t.monitor(u, cb, {verbose, current}));
    }

    // Setup and connection

    static addtransport(t) {
        /*
        Add a transport to _transports,
         */
        Transports._transports.push(t);
    }

    // Setup Transports - setup0 is called once, and should return quickly, p_setup1 and p_setup2 are asynchronous and p_setup2 relies on p_setup1 having resolved.

    static setup0(tabbrevs, options, verbose, cb) {
        /*
        Setup Transports for a range of classes
        tabbrevs is abbreviation HTTP, IPFS, LOCAL or list of them e.g. "HTTP,IPFS"
        Handles "LOCAL" specially, turning into a HTTP to a local server (for debugging)

        returns array of transport instances
         */
        // "IPFS" or "IPFS,LOCAL,HTTP"
        let localoptions = {http: {urlbase: "http://localhost:4244"}};
        return tabbrevs.map((tabbrev) => {
            let transportclass;
            if (tabbrev === "LOCAL") {
                transportclass = this._transportclasses["HTTP"];
            } else {
                transportclass = this._transportclasses[tabbrev];
            }
            if (!transportclass) {
                let tt = Object.keys(this._transportclasses);
                console.error(`Requested ${tabbrev} but ${tt.length ? tt : "No"} transports have been loaded`);
                return undefined;
            } else {
                return transportclass.setup0(tabbrev === "LOCAL" ? localoptions : options, verbose);
            }
        }).filter(f => !!f); // Trim out any undefined
    }
    static async p_setup1(verbose, cb) {
        /* Second stage of setup, connect if possible */
        // Does all setup1a before setup1b since 1b can rely on ones with 1a, e.g. YJS relies on IPFS
        await Promise.all(this._transports
            .filter((t) => (! this._optionspaused.includes(t.name)))
            .map((t) => t.p_setup1(verbose, cb)))
    }
    static async p_setup2(verbose, cb) {
        /* Second stage of setup, connect if possible */
        // Does all setup1a before setup1b since 1b can rely on ones with 1a, e.g. YJS relies on IPFS
        await Promise.all(this._transports
            .filter((t) => (! this._optionspaused.includes(t.name)))
            .map((t) => t.p_setup2(verbose, cb)))
    }

    static async refreshstatus(t) {
        //Note "this' undefined as called as callback
        let statusclasses = ["transportstatus0","transportstatus1","transportstatus2","transportstatus3","transportstatus4"];
        let el = t.statuselement;
        if (el) {
            el.classList.remove(...statusclasses);
            el.classList.add(statusclasses[t.status]);
        }
        if (Transports.statuscb) {
            Transports.statuscb(t);
        }
    }

    static async p_connect(options, verbose) {
        /*
            This is a standardish starting process, feel free to subclass or replace !
            It will connect to a set of standard transports and is intended to work inside a browser.
            options = { defaulttransports: ["IPFS"], statuselement: el, http: {}, ipfs: {}; paused: ["IPFS"] }
         */
        if (verbose) console.group("p_connect ---");
        try {
            options = options || {};
            let setupoptions = {};
            let tabbrevs = options.transports;    // Array of transport abbreviations
            this._optionspaused = (options.paused || []).map(n => n.toUpperCase());       // Array of transports paused - defaults to none, upper cased
            if (!(tabbrevs && tabbrevs.length)) { tabbrevs = options.defaulttransports || [] }
            if (! tabbrevs.length) { tabbrevs = ["HTTP", "YJS", "IPFS", "WEBTORRENT", "GUN"]; } // SEE-OTHER-ADDTRANSPORT
            tabbrevs = tabbrevs.map(n => n.toUpperCase());
            let transports = this.setup0(tabbrevs, options, verbose);
            if (options.statuscb) {
                this.statuscb = options.statuscb;
            }
            if (!!options.statuselement) {
                while (statuselement.lastChild) {statuselement.removeChild(statuselement.lastChild); }   // Remove any exist status
                statuselement.appendChild(
                    utils.createElement("UL", {}, transports.map(t => {
                            let el = utils.createElement("LI",
                                {onclick: "this.source.togglePaused(DwebTransports.refreshstatus);", source: t, name: t.name}, //TODO-SW figure out how t osend this back
                                t.name);
                            t.statuselement = el;   // Save status element on transport
                            return el;
                        }
                    )));
            }
            await this.p_setup1(verbose, this.refreshstatus);
            await this.p_setup2(verbose, this.refreshstatus);
        } catch(err) {
            console.error("ERROR in p_connect:",err.message);
            throw(err);
        }
        if (verbose) console.groupEnd("p_connect ---");
    }

    static async p_urlsFrom(url) {
        /* Utility to convert to urls form wanted for Transports functions, e.g. from user input
        url:    Array of urls, or string representing url or representing array of urls
        return: Array of strings representing url
         */
        if (typeof(url) === "string") {
            if (url[0] === '[')
                url = JSON.parse(url);
            else if (url.includes(','))
                url = url.split(',');
            else
                url = [ url ];
        }
        if (!Array.isArray(url)) throw new Error(`Unparsable url: ${url}`);
        return url;
    }

    static async p_httpfetchurl(urls) {
        /*
        Utility to take a array of Transport urls, convert back to a single url that can be used for a fetch, typically
        this is done when cant handle a stream, so want to give the url to the <VIDEO> tag.
         */
        return Transports.http()._url(urls.find(u => (u.startsWith("contenthash") || u.startsWith("http") )), "content/rawfetch");
    }

    static async test(verbose) {
        if (verbose) {console.log("Transports.test")}
        try {
            /* Could convert this - copied fom YJS to do a test at the "Transports" level
            let testurl = "yjs:/yjs/THISATEST";  // Just a predictable number can work with
            let res = await transport.p_rawlist(testurl, verbose);
            let listlen = res.length;   // Holds length of list run intermediate
            if (verbose) console.log("rawlist returned ", ...utils.consolearr(res));
            transport.listmonitor(testurl, (obj) => console.log("Monitored", obj), verbose);
            let sig = new Dweb.Signature({urls: ["123"], date: new Date(Date.now()), signature: "Joe Smith", signedby: [testurl]}, verbose);
            await transport.p_rawadd(testurl, sig, {verbose});
            if (verbose) console.log("TransportIPFS.p_rawadd returned ");
            res = await transport.p_rawlist(testurl, verbose);
            if (verbose) console.log("rawlist returned ", ...utils.consolearr(res)); // Note not showing return
            await delay(500);
            res = await transport.p_rawlist(testurl, verbose);
            console.assert(res.length === listlen + 1, "Should have added one item");
            */
            //console.log("TransportYJS test complete");
            /* TODO-KEYVALUE reenable these tests,s but catch http examples
            let db = await this.p_newdatabase("TESTNOTREALLYAKEY", {verbose});    // { privateurls, publicurls }
            console.assert(db.privateurls[0] === "yjs:/yjs/TESTNOTREALLYAKEY");
            let table = await this.p_newtable("TESTNOTREALLYAKEY","TESTTABLE", {verbose});         // { privateurls, publicurls }
            let mapurls = table.publicurls;
            console.assert(mapurls[0] === "yjs:/yjs/TESTNOTREALLYAKEY/TESTTABLE");
            await this.p_set(mapurls, "testkey", "testvalue", {verbose});
            let res = await this.p_get(mapurls, "testkey", {verbose});
            console.assert(res === "testvalue");
            await this.p_set(mapurls, "testkey2", {foo: "bar"}, {verbose});
            res = await this.p_get(mapurls, "testkey2", {verbose});
            console.assert(res.foo === "bar");
            await this.p_set(mapurls, "testkey3", [1,2,3], {verbose});
            res = await this.p_get(mapurls, "testkey3", {verbose});
            console.assert(res[1] === 2);
            res = await this.p_keys(mapurls);
            console.assert(res.length === 3 && res.includes("testkey3"));
            res = await this.p_getall(mapurls, {verbose});
            console.assert(res.testkey2.foo === "bar");
            */

        } catch(err) {
            console.log("Exception thrown in Transports.test:", err.message);
            throw err;
        }
    }

}
Transports._transports = [];    // Array of transport instances connected
Transports.namingcb = undefined;    // Will be defined by the naming component (turns URLs for names into URLs for transport)
Transports._transportclasses = {};  // Pointers to classes whose code is loaded.

exports = module.exports = Transports;