sklad: proper validations on container update

Since the browser's back button cannot be used because of our
fascist caching policy.

cmd/sklad/container.tmpl

@@ -36,18 +36,19 @@
 		</form>
 	</header>
 	<form method=post action="container?id={{ .Container.Id }}">
-		<textarea name=description
+		{{- $description := or .NewDescription .Container.Description }}
-			rows="{{ max 5 (lines .Container.Description) }}"
+		<textarea name=description rows="{{ max 5 (lines $description) }}"
 			placeholder="Popis obalu nebo jeho obsahu">
-			{{- .Container.Description -}}
+			{{- $description -}}
 		</textarea>
 		<footer>
 			<div>
 				<label for=series>Řada:</label>
 				<select name=series id=series>
+				{{- $preselect := or .NewSeries .Container.Series }}
 				{{- range $prefix, $desc := .AllSeries }}
 					<option value="{{ $prefix }}"
-						{{ if eq $prefix $.Container.Series }}selected{{ end -}}
+						{{ if eq $prefix $preselect }}selected{{ end -}}
 						>{{ $prefix }} &mdash; {{ $desc }}</option>
 				{{- end }}
 				</select>
@@ -55,7 +56,7 @@
 			<div>
 				<label for=parent>Nadobal:</label>
 				<input type=text name=parent id=parent
-					value="{{ .Container.Parent }}">
+					value="{{ or .NewParent .Container.Parent }}">
 			</div>
 			<input type=submit value="Uložit">
 		</footer>
@@ -69,21 +70,27 @@
 		<h2>Nový obal</h2>
 	</header>
 	<form method=post action="container">
-		<textarea name=description rows=5
+		{{- $description := or .NewDescription "" }}
-			placeholder="Popis obalu nebo jeho obsahu"></textarea>
+		<textarea name=description rows="{{ max 5 (lines $description) }}"
+			placeholder="Popis obalu nebo jeho obsahu">
+			{{- $description -}}
+		</textarea>
 		<footer>
 			<div>
 				<label for=series>Řada:</label>
 				<select name=series id=series>
+				{{- $preselect := or .NewSeries "" }}
 				{{- range $prefix, $desc := .AllSeries }}
 					<option value="{{ $prefix }}"
+						{{ if eq $prefix $preselect }}selected{{ end -}}
 						>{{ $prefix }} &mdash; {{ $desc }}</option>
 				{{- end }}
 				</select>
 			</div>
 			<div>
 				<label for=parent>Nadobal:</label>
-				<input type=text name=parent id=parent value="">
+				<input type=text name=parent id=parent
+					value="{{ or .NewParent "" }}">
 			</div>
 			<input type=submit value="Uložit">
 		</footer>

cmd/sklad/db.go

@@ -205,6 +205,13 @@ func dbContainerCreate(c *Container) error {
 }
 
 func dbContainerUpdate(c *Container, updated Container) error {
+	if _, ok := indexSeries[updated.Series]; !ok {
+		return errNoSuchSeries
+	}
+	if updated.Parent != "" && indexContainer[updated.Parent] == nil {
+		return errNoSuchContainer
+	}
+
 	newID := updated.Id()
 	if updated.Series != c.Series && len(c.Children()) > 0 {
 		return errCannotChangeSeriesNotEmpty

cmd/sklad/main.go

@@ -116,14 +116,13 @@ func handleContainer(w http.ResponseWriter, r *http.Request) {
 	var err error
 	if r.Method == http.MethodPost {
 		if err = handleContainerPost(r); err == nil {
-			redirect := "container"
+			redirect := r.URL.EscapedPath()
 			if shownId != "" {
 				redirect += "?id=" + url.QueryEscape(shownId)
 			}
 			http.Redirect(w, r, redirect, http.StatusSeeOther)
 			return
 		}
-		// TODO: Use the last data as a prefill.
 	} else if r.Method != http.MethodGet {
 		w.WriteHeader(http.StatusMethodNotAllowed)
 		return
@@ -134,14 +133,6 @@ func handleContainer(w http.ResponseWriter, r *http.Request) {
 		allSeries[s.Prefix] = s.Description
 	}
 
-	var container *Container
-	children := indexChildren[""]
-
-	if c, ok := indexContainer[ContainerId(shownId)]; ok {
-		children = c.Children()
-		container = c
-	}
-
 	params := struct {
 		Error                           error
 		ErrorNoSuchSeries               bool
@@ -152,6 +143,9 @@ func handleContainer(w http.ResponseWriter, r *http.Request) {
 		ErrorWouldContainItself         bool
 		ErrorContainerInUse             bool
 		Container                       *Container
+		NewDescription                  *string
+		NewSeries                       string
+		NewParent                       *string
 		Children                        []*Container
 		AllSeries                       map[string]string
 	}{
@@ -163,10 +157,24 @@ func handleContainer(w http.ResponseWriter, r *http.Request) {
 		ErrorCannotChangeNumber:         err == errCannotChangeNumber,
 		ErrorWouldContainItself:         err == errWouldContainItself,
 		ErrorContainerInUse:             err == errContainerInUse,
-		Container:                       container,
+		Children:                        indexChildren[""],
-		Children:                        children,
 		AllSeries:                       allSeries,
 	}
+	if c, ok := indexContainer[ContainerId(shownId)]; ok {
+		params.Children = c.Children()
+		params.Container = c
+	}
+	if description, ok := r.Form["description"]; ok {
+		params.NewDescription = &description[0]
+	}
+	if series, ok := r.Form["series"]; ok {
+		// It seems impossible to dereference strings in text/template so that
+		// `eq` can be used, and we don't actually need a null value here.
+		params.NewSeries = series[0]
+	}
+	if parent, ok := r.Form["parent"]; ok {
+		params.NewParent = &parent[0]
+	}
 
 	executeTemplate("container.tmpl", w, &params)
 }
@@ -198,7 +206,7 @@ func handleSeries(w http.ResponseWriter, r *http.Request) {
 	var err error
 	if r.Method == http.MethodPost {
 		if err = handleSeriesPost(r); err == nil {
-			http.Redirect(w, r, "series", http.StatusSeeOther)
+			http.Redirect(w, r, r.URL.EscapedPath(), http.StatusSeeOther)
 			return
 		}
 		// XXX: This is rather ugly.