First working version

[nsscash/nsscash.git] / state.go

diff --git a/state.go b/state.go
new file mode 100644 (file)
index 0000000..b0dec1c
--- /dev/null
+++ b/state.go
@@ -0,0 +1,98 @@
+// Read and write the state file used to keep data over multiple runs
+
+// Copyright (C) 2019  Simon Ruderich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+import (
+       "encoding/json"
+       "io/ioutil"
+       "os"
+       "path/filepath"
+       "reflect"
+       "time"
+)
+
+type State struct {
+       LastModified map[string]time.Time
+
+       // Copy of LastModified to write the state file only on changes
+       origLastModified map[string]time.Time
+}
+
+func LoadState(path string) (*State, error) {
+       var state State
+
+       x, err := ioutil.ReadFile(path)
+       if err != nil {
+               // It's fine if the state file does not exist yet, we'll
+               // create it later when writing the state
+               if !os.IsNotExist(err) {
+                       return nil, err
+               }
+       } else {
+               err := json.Unmarshal(x, &state)
+               if err != nil {
+                       return nil, err
+               }
+       }
+
+       if state.LastModified == nil {
+               state.LastModified = make(map[string]time.Time)
+       }
+
+       state.origLastModified = make(map[string]time.Time)
+       for k, v := range state.LastModified {
+               state.origLastModified[k] = v
+       }
+
+       return &state, nil
+}
+
+func WriteStateIfChanged(path string, state *State) error {
+       // State hasn't changed, nothing to do
+       if reflect.DeepEqual(state.LastModified, state.origLastModified) {
+               return nil
+       }
+
+       x, err := json.Marshal(state)
+       if err != nil {
+               return err
+       }
+
+       // Write the file in an atomic fashion by creating a temporary file
+       // and renaming it over the target file
+
+       dir := filepath.Dir(path)
+       name := filepath.Base(path)
+
+       f, err := ioutil.TempFile(dir, "tmp-"+name+"-")
+       if err != nil {
+               return err
+       }
+       defer os.Remove(f.Name())
+       defer f.Close()
+
+       _, err = f.Write(x)
+       if err != nil {
+               return err
+       }
+       err = f.Sync()
+       if err != nil {
+               return err
+       }
+       return os.Rename(f.Name(), path)
+}