X-Git-Url: https://ruderich.org/simon/gitweb/?p=nsscash%2Fnsscash.git;a=blobdiff_plain;f=state.go;fp=state.go;h=b0dec1c2d47673fffa5eb81ee8e3d3113fce689f;hp=0000000000000000000000000000000000000000;hb=92afde4e875a96e1ab865e29b9f0d11b08d7db1c;hpb=748846b9a65726fd19d43b45a4db68ef4c2e77f4

diff --git a/state.go b/state.go
new file mode 100644
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)
+}