add examples

examples/queue.js

@@ -0,0 +1,66 @@
+var shasum = require('shasum')
+
+//if a job starts, and another is queued before the current job ends,
+//delay it, so that the job is only triggered once.
+
+
+module.exports = function (input, jobs, map, work) {
+  if(!work) work = map, map = function (data) { return data.key }
+  //create a subsection for the jobs,
+  //if you don't pass in a separate db,
+  //create a section inside the input
+  var pending = {}, running = {}
+
+  if('string' === typeof jobs)
+    jobs = input.sublevel(jobs)
+
+  var retry = []
+
+  function doJob (data) {
+    //don't process deletes!
+    if(!data.value) return
+    var hash = shasum(data.value)
+
+    if(!running[hash])
+      running[hash] = true
+    else return
+
+    var done = false
+
+    work(data.value, function (err) {
+      if(done) return
+      done = true
+      if(err) {
+        running[hash]
+        return setTimeout(function () {
+          doJob(data)
+        }, 500)
+      }
+
+      jobs.del(data.key, function (err) {
+        if(err) return retry.push(data)
+        delete running[hash]
+        if(pending[hash]) {
+          delete pending[hash]
+          doJob(data)
+        }
+      })
+    })
+  }
+
+  input.pre(function (ch, add) {
+    var key = map(ch)
+    var hash = shasum(key)
+    console.log('KEY', key)
+    if(!pending[hash])
+      add({key: Date.now(), value: key, type: 'put'}, jobs)
+    else
+      pending[hash] = (0 || pending[hash]) + 1
+  })
+
+  jobs.createReadStream().on('data', doJob)
+  jobs.post(doJob)
+
+  return jobs
+}
+

examples/trigger.js

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+
+var db   = require('../')(require('levelup')('/tmp/whatever'))
+var copy = require('../')(require('levelup')('/tmp/whatever2'))
+
+var makeQueue = require('./queue')
+
+makeQueue(db, 'jobs', function (key, done) {
+  console.log("JOB KEY", key)
+  db.get(key, function (err, value) {
+    console.log(key, value, err)
+    value && copy.put(key, value, done) || done()
+  })
+})
+
+db.put('hello' + Date.now(), 'value_' + new Date(), function () {
+
+  setTimeout(function () {
+
+    copy
+      .createReadStream()
+      .on('data', console.log)
+
+  }, 1000)
+
+})
+