From fd347fa1eb25861fecc3a0d26b0a23ebc196a663 Mon Sep 17 00:00:00 2001
From: Přemysl Janouch <p@janouch.name>
Date: Sat, 13 Apr 2019 05:16:16 +0200
Subject: sklad: initial commit for the web application
---
sklad/main.go | 186 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 186 insertions(+)
create mode 100644 sklad/main.go
diff --git a/sklad/main.go b/sklad/main.go
new file mode 100644
index 0000000..28fb258
--- /dev/null
+++ b/sklad/main.go
@@ -0,0 +1,186 @@
+package main
+
+import (
+ "encoding/json"
+ "errors"
+ "fmt"
+ "html/template"
+ "io"
+ "log"
+ "net/http"
+ "os"
+)
+
+type Series struct {
+ Prefix string // PK: prefix
+ Description string // what kind of containers this is for
+}
+
+type Container struct {
+ Series string // PK: what series does this belong to
+ Number uint // PK: order within the series
+ Parent ContainerId // the container we're in, if any, otherwise ""
+ Description string // description and/or contents of this container
+}
+
+type ContainerId string
+
+func (c *Container) Id() ContainerId {
+ return ContainerId(fmt.Sprintf("%s%s%d", db.Prefix, c.Series, c.Number))
+}
+
+type Database struct {
+ Password string // password for web users
+ Prefix string // prefix for all container IDs
+ Series []*Series // all known series
+ Containers []*Container // all known containers
+}
+
+var (
+ templates *template.Template
+ // TODO: Some kind of session storage, somewhere.
+
+ dbPath string
+ db Database
+ dbLast Database
+ dbLog io.Writer
+
+ indexSeries = map[string]*Series{}
+ indexContainer = map[ContainerId]*Container{}
+ indexChildren = map[ContainerId][]*Container{}
+)
+
+// TODO: Some functions to add, remove and change things in the database.
+// Indexes must be kept valid, just like any invariants.
+
+func dbCommit() error {
+ // Back up the current database contents.
+ e := json.NewEncoder(dbLog)
+ e.SetIndent("", " ")
+ if err := e.Encode(&dbLast); err != nil {
+ return err
+ }
+
+ // Atomically replace the current database file.
+ tempPath := dbPath + ".new"
+ temp, err := os.OpenFile(tempPath, os.O_WRONLY|os.O_CREATE, 0644)
+ if err != nil {
+ return err
+ }
+ defer temp.Close()
+
+ e = json.NewEncoder(temp)
+ e.SetIndent("", " ")
+ if err := e.Encode(&db); err != nil {
+ return err
+ }
+
+ if err := os.Rename(tempPath, dbPath); err != nil {
+ return err
+ }
+
+ dbLast = db
+ return nil
+}
+
+// loadDatabase loads the database from a simple JSON file. We do not use
+// any SQL stuff or even external KV storage because there is no real need
+// for our trivial use case, with our general amount of data.
+func loadDatabase() error {
+ dbFile, err := os.Open(dbPath)
+ if err != nil {
+ return err
+ }
+ if err := json.NewDecoder(dbFile).Decode(&db); err != nil {
+ return err
+ }
+
+ // Further validate the database.
+ if db.Prefix == "" {
+ return errors.New("misconfigured prefix")
+ }
+
+ // Construct indexes for primary keys, validate against duplicates.
+ for _, pv := range db.Series {
+ if _, ok := indexSeries[pv.Prefix]; ok {
+ return fmt.Errorf("duplicate series: %s", pv.Prefix)
+ }
+ indexSeries[pv.Prefix] = pv
+ }
+ for _, pv := range db.Containers {
+ id := pv.Id()
+ if _, ok := indexContainer[id]; ok {
+ return fmt.Errorf("duplicate container: %s", id)
+ }
+ indexContainer[id] = pv
+ }
+
+ // Construct an index that goes from parent containers to their children.
+ for _, pv := range db.Containers {
+ if pv.Parent == "" {
+ continue
+ }
+ if _, ok := indexContainer[pv.Parent]; !ok {
+ return fmt.Errorf("container %s has a nonexistent parent %s",
+ pv.Id(), pv.Parent)
+ }
+ indexChildren[pv.Parent] = append(indexChildren[pv.Parent], pv)
+ }
+
+ // Validate that no container is a parent of itself on any level.
+ for _, pv := range db.Containers {
+ parents := map[ContainerId]bool{pv.Id(): true}
+ for pv.Parent != "" {
+ if parents[pv.Parent] {
+ return fmt.Errorf("%s contains itself", pv.Parent)
+ }
+ parents[pv.Parent] = true
+ pv = indexContainer[pv.Parent]
+ }
+ }
+
+ // Open database log file for appending.
+ if dbLog, err = os.OpenFile(dbPath+".log",
+ os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644); err != nil {
+ return err
+ }
+
+ // Remember the current state of the database.
+ dbLast = db
+ return nil
+}
+
+func main() {
+ if len(os.Args) != 3 {
+ log.Fatalf("usage: %s ADDRESS DATABASE\n", os.Args[0])
+ }
+
+ var address string
+ address, dbPath = os.Args[1], os.Args[2]
+
+ // Load database.
+ if err := loadDatabase(); err != nil {
+ log.Fatalln(err)
+ }
+
+ // Load HTML templates from the current working directory.
+ var err error
+ templates, err = template.ParseGlob("*.tmpl")
+ if err != nil {
+ log.Fatalln(err)
+ }
+
+ // TODO: Some routing, don't forget about sessions.
+ // - https://stackoverflow.com/a/33880971/76313
+ //
+ // - GET /login
+ // - GET /container?id=UA1
+ // - GET /series?id=A
+ // - GET /search?q=bottle
+ //
+ // - POST /login?pass=hue
+ // - POST /logout
+ // - POST /label?id=UA1
+
+ log.Fatalln(http.ListenAndServe(address, nil))
+}
--
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