function postgres6PatchFunction()

in src/diagnostic-channel-publishers/src/pg.pub.ts [33:153]
64 lines of code
10 McCabe index (conditional complexity)

function postgres6PatchFunction(originalPg, originalPgPath) {
    const originalClientQuery = originalPg.Client.prototype.query;
    const diagnosticOriginalFunc = "__diagnosticOriginalFunc";

    // wherever the callback is passed, find it, save it, and remove it from the call
    // to the the original .query() function
    originalPg.Client.prototype.query = function query(config, values, callback) {
        const data: IPostgresData = {
            query: {},
            database: {
                host: this.connectionParameters.host,
                port: this.connectionParameters.port,
            },
            result: null,
            error: null,
            duration: 0,
            time: new Date(),
        };
        const start = process.hrtime();
        let queryResult;

        function patchCallback(cb?: PostgresCallback): PostgresCallback {
            if (cb && cb[diagnosticOriginalFunc]) {
                cb = cb[diagnosticOriginalFunc];
            }

            const trackingCallback = channel.bindToContext(function(err: Error, res: IPostgresResult): any {
                const end = process.hrtime(start);
                data.result = res && { rowCount: res.rowCount, command: res.command };
                data.error = err;
                data.duration = Math.ceil((end[0] * 1e3) + (end[1] / 1e6));
                channel.publish("postgres", data);

                // emulate weird internal behavior in pg@6
                // on success, the callback is called *before* query events are emitted
                // on failure, the callback is called *instead of* the query emitting events
                // with no events, that means no promises (since the promise is resolved/rejected in an event handler)
                // since we are always inserting ourselves as a callback, we have to restore the original
                // behavior if the user didn't provide one themselves
                if (err) {
                    if (cb) {
                        return cb.apply(this, arguments);
                    } else if (queryResult && queryResult instanceof EventEmitter) {
                        queryResult.emit("error", err);
                    }
                } else if (cb) {
                    cb.apply(this, arguments);
                }
            });

            try {
                Object.defineProperty(trackingCallback, diagnosticOriginalFunc, { value: cb });
                return trackingCallback;
            } catch (e) {
                // this should never happen, but bailout in case it does
                return cb;
            }
        }

        // this function takes too many variations of arguments.
        // this patches any provided callback or creates a new callback if one wasn't provided.
        // since the callback is always called (if provided) in addition to always having a Promisified
        // EventEmitter returned (well, sometimes -- see above), its safe to insert a callback if none was given
        try {
            if (typeof config === "string") {
                if (values instanceof Array) {
                    data.query.preparable = {
                        text: config,
                        args: values,
                    };
                    callback = patchCallback(callback);
                } else {
                    data.query.text = config;

                    // pg v6 will, for some reason, accept both
                    // client.query("...", undefined, () => {...})
                    // **and**
                    // client.query("...", () => {...});
                    // Internally, precedence is given to the callback argument
                    if (callback) {
                        callback = patchCallback(callback);
                    } else {
                        values = patchCallback(values);
                    }
                }
            } else {
                if (typeof config.name === "string") {
                    data.query.plan = config.name;
                } else if (config.values instanceof Array) {
                    data.query.preparable = {
                        text: config.text,
                        args: config.values,
                    };
                } else {
                    data.query.text = config.text;
                }

                if (callback) {
                    callback = patchCallback(callback);
                } else if (values) {
                    values = patchCallback(values);
                } else {
                    config.callback = patchCallback(config.callback);
                }
            }
        } catch (e) {
            // if our logic here throws, bail out and just let pg do its thing
            return originalClientQuery.apply(this, arguments);
        }

        arguments[0] = config;
        arguments[1] = values;
        arguments[2] = callback;
        arguments.length = (arguments.length > 3) ? arguments.length : 3;

        queryResult = originalClientQuery.apply(this, arguments);
        return queryResult;
    };

    return originalPg;
}