From fd347fa1eb25861fecc3a0d26b0a23ebc196a663 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C5=99emysl=20Janouch?= <p@janouch.name>
Date: Sat, 13 Apr 2019 05:16:16 +0200
Subject: [PATCH] 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))
+}