Create agent/ package for backend agnostic logic (#338)

* Refactor: Move agent stats structs to agent/

Based in part on changes by laszlocph (kube branch):
7f4a0c8c12 Factor into Runner
f7fe9edd0b Using Runner in server

* Refactor: Add Runner constructor with counter field

Based in part on changes by laszlocph (kube branch):
7f4a0c8c12 Factor into Runner
f7fe9edd0b Using Runner in server

* Refactor: Move Runner to agent/ package

Based in part on changes by laszlocph (kube branch):
7f4a0c8c12 Factor into Runner
f7fe9edd0b Using Runner in server

* Refactor: pass pipeline.backend.Engine into agent.Runner

Based in part on changes by laszlocph (kube branch):
7f4a0c8 Factor into Runner
f7fe9ed Using Runner in server

* Use well-known function signature for WriteTo

* Rename stats.go -> state.go

Co-authored-by: Anbraten <anton@ju60.de>

agent/state.go

@@ -0,0 +1,80 @@
+// Copyright 2018 Drone.IO Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package agent
+
+import (
+	"encoding/json"
+	"io"
+	"sync"
+	"time"
+)
+
+type State struct {
+	sync.Mutex `json:"-"`
+	Polling    int             `json:"polling_count"`
+	Running    int             `json:"running_count"`
+	Metadata   map[string]Info `json:"running"`
+}
+
+type Info struct {
+	ID      string        `json:"id"`
+	Repo    string        `json:"repository"`
+	Build   string        `json:"build_number"`
+	Started time.Time     `json:"build_started"`
+	Timeout time.Duration `json:"build_timeout"`
+}
+
+func (s *State) Add(id string, timeout time.Duration, repo, build string) {
+	s.Lock()
+	s.Polling--
+	s.Running++
+	s.Metadata[id] = Info{
+		ID:      id,
+		Repo:    repo,
+		Build:   build,
+		Timeout: timeout,
+		Started: time.Now().UTC(),
+	}
+	s.Unlock()
+}
+
+func (s *State) Done(id string) {
+	s.Lock()
+	s.Polling++
+	s.Running--
+	delete(s.Metadata, id)
+	s.Unlock()
+}
+
+func (s *State) Healthy() bool {
+	s.Lock()
+	defer s.Unlock()
+	now := time.Now()
+	buf := time.Hour // 1 hour buffer
+	for _, item := range s.Metadata {
+		if now.After(item.Started.Add(item.Timeout).Add(buf)) {
+			return false
+		}
+	}
+	return true
+}
+
+func (s *State) WriteTo(w io.Writer) (int64, error) {
+	s.Lock()
+	out, _ := json.Marshal(s)
+	s.Unlock()
+	ret, err := w.Write(out)
+	return int64(ret), err
+}