var nest = require('depnest') var pull = require('pull-stream') var MutantPullReduce = require('mutant-pull-reduce') exports.needs = nest({ 'sbot.pull.backlinks': 'first' }) exports.gives = nest('backlinks.obs.filter', true) /** * sbot.obs.filter returns an observable list of messages that link * back to the message with the given message ID (@id). Only messages that * pass the filter are added to the list. * * When a message arrives, if a filter function is given in the options (opts.filter) * and passing it to the filter function does not result in it returning * 'true' the message is not added to the observable list. * * A 'sync' observable property is also added to the returned observable * which is 'true' when all previously seen messages are caught up with. * * Note: Unlike backlinks.obs.for this does not cache the observable for * callers that supply the same arguments. */ exports.create = function (api) { function pullFilterReduceObs (id, opts) { if (!id || typeof (id) !== 'string') { throw new Error('id must be a string.') } var sbotFilter = { $filter: { dest: id } } var msgBacklinks = api.sbot.pull.backlinks({ query: [sbotFilter], sync: true }) // If a filter function is supplied in the options, we use it to filter // the links stream, otherwise we use all the messages from the stream var filterFunction = opts && opts.filter ? opts.filter : () => true var filteredBacklinks = pull( msgBacklinks, pull.filter(filterFunction) ) var backlinksObs = MutantPullReduce(filteredBacklinks, (state, msg) => { state.push(msg) return state }, { startValue: [], nextTick: true, sync: true }) return backlinksObs } return nest({ 'backlinks.obs.filter': (id, opts) => pullFilterReduceObs(id, opts) }) }