/* jshint esversion: 6 */
/* global process */

const HK = require("./hk-util");
const Store = require("./storage/file");
const Util = require("./common-util");
const nThen = require("nthen");

const Env = {};

var ready = false;
var store;
const init = function (config, cb) {
    if (!config) {
        return void cb('E_INVALID_CONFIG');
    }

    Store.create(config, function (_store) {
        store = _store;
        cb();
    });
};

const tryParse = function (Env, str) {
    try {
        return JSON.parse(str);
    } catch (err) {
        // XXX
    }
};

/*  computeIndex
    can call back with an error or a computed index which includes:
        * cpIndex:
            * array including any checkpoints pushed within the last 100 messages
            * processed by 'sliceCpIndex(cpIndex, line)'
        * offsetByHash:
            * a map containing message offsets by their hash
            * this is for every message in history, so it could be very large...
                * except we remove offsets from the map if they occur before the oldest relevant checkpoint
        * size: in bytes
        * metadata:
            * validationKey
            * expiration time
            * owners
            * ??? (anything else we might add in the future)
        * line
            * the number of messages in history
            * including the initial metadata line, if it exists

*/
const computeIndex = function (channelName, cb) {
    const cpIndex = [];
    let messageBuf = [];
    let i = 0;

    const CB = Util.once(cb);

    const offsetByHash = {};
    let size = 0;
    nThen(function (w) {
        // iterate over all messages in the channel log
        // old channels can contain metadata as the first message of the log
        // skip over metadata as that is handled elsewhere
        // otherwise index important messages in the log
        store.readMessagesBin(channelName, 0, (msgObj, readMore) => {
            let msg;
            // keep an eye out for the metadata line if you haven't already seen it
            // but only check for metadata on the first line
            if (!i && msgObj.buff.indexOf('{') === 0) {
                i++; // always increment the message counter
                msg = tryParse(Env, msgObj.buff.toString('utf8'));
                if (typeof msg === "undefined") { return readMore(); }

                // validate that the current line really is metadata before storing it as such
                // skip this, as you already have metadata...
                if (HK.isMetadataMessage(msg)) { return readMore(); }
            }
            i++;
            if (msgObj.buff.indexOf('cp|') > -1) {
                msg = msg || tryParse(Env, msgObj.buff.toString('utf8'));
                if (typeof msg === "undefined") { return readMore(); }
                // cache the offsets of checkpoints if they can be parsed
                if (msg[2] === 'MSG' && msg[4].indexOf('cp|') === 0) {
                    cpIndex.push({
                        offset: msgObj.offset,
                        line: i
                    });
                    // we only want to store messages since the latest checkpoint
                    // so clear the buffer every time you see a new one
                    messageBuf = [];
                }
            }
            // if it's not metadata or a checkpoint then it should be a regular message
            // store it in the buffer
            messageBuf.push(msgObj);
            return readMore();
        }, w((err) => {
            if (err && err.code !== 'ENOENT') {
                w.abort();
                return void CB(err);
            }

            // once indexing is complete you should have a buffer of messages since the latest checkpoint
            // map the 'hash' of each message to its byte offset in the log, to be used for reconnecting clients
            messageBuf.forEach((msgObj) => {
                const msg = tryParse(Env, msgObj.buff.toString('utf8'));
                if (typeof msg === "undefined") { return; }
                if (msg[0] === 0 && msg[2] === 'MSG' && typeof(msg[4]) === 'string') {
                    // msgObj.offset is API guaranteed by our storage module
                    // it should always be a valid positive integer
                    offsetByHash[HK.getHash(msg[4])] = msgObj.offset;
                }
                // There is a trailing \n at the end of the file
                size = msgObj.offset + msgObj.buff.length + 1;
            });
        }));
    }).nThen(function () {
        // return the computed index
        CB(null, {
            // Only keep the checkpoints included in the last 100 messages
            cpIndex: HK.sliceCpIndex(cpIndex, i),
            offsetByHash: offsetByHash,
            size: size,
            //metadata: metadata,
            line: i
        });
    });
};

process.on('message', function (data) {
    if (!data || !data.txid) {
        return void process.send({
            error:'E_INVAL'
        });
    }
    const txid = data.txid;

    if (!ready) {
        return void init(data.config, function (err) {
            if (err) {
                return void process.send({
                    txid: txid,
                    error: err,
                });
            }
            ready = true;
            process.send({txid: txid,});
        });
    }

    const channel = data.args;
    if (!channel) {
        return void process.send({
            error: 'E_NO_CHANNEL',
        });
    }

    // computeIndex
    computeIndex(channel, function (err, index) {
        if (err) {
            return void process.send({
                txid: txid,
                error: err,
            });
        }
        return void process.send({
            txid: txid,
            value: index,
        });
    });
});