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package gui
import (
"bytes"
"encoding/json"
"fmt"
"log"
"net/http"
"sync"
"text/template"
)
var Debug = false
// Page holds the state to serve a single GUI page to the browser
type Page struct {
elems map[string]*E
htmlCache []byte // static html content, rendered only once
haveJS bool // have called JS()?
data interface{} // any additional data to be passed to template
onUpdate func()
onAnyEvent func()
httpLock sync.Mutex
lastPageID string
}
// NewPage constructs a Page based on an HTML template containing
// element tags like {{.Button}}, {{.Textbox}}, etc. data is fed
// to the template as additional arbitrary data, available as {{.Data}}.
func NewPage(htmlTemplate string, data interface{}) *Page {
d := &Page{elems: make(map[string]*E), data: data}
// exec template (once)
t := template.Must(template.New("").Parse(htmlTemplate))
cache := bytes.NewBuffer(nil)
check(t.Execute(cache, d))
d.htmlCache = cache.Bytes()
// check if template contains {{.JS}}
if !d.haveJS {
log.Panic("template should call {{.JS}}")
}
return d
}
// Value returns the value of the HTML element with given id.
// E.g.: the text in a textbox, the checked value of a checkbox, etc.
func (d *Page) Value(id string) interface{} {
return d.elem(id).value()
}
// StringValue is like Value but returns the value as string,
// converting if necessary.
func (d *Page) StringValue(id string) string {
v := d.Value(id)
if s, ok := v.(string); ok {
return s
} else {
return fmt.Sprint(v)
}
}
func (d *Page) Set(id string, v interface{}) {
d.elem(id).set(v)
}
func (d *Page) Attr(id string, k string, v interface{}) {
d.elem(id).attr(k, v)
}
// OnEvent sets a handler to be called when an event happens
// to the HTML element with given id. The event depends on the
// element type: click for Button, change for TextBox, etc...
func (d *Page) OnEvent(id string, handler func()) {
d.elem(id).onevent = handler
}
// OnEvent sets a handler to be called when an event happens
// to any of the page's HTML elements.
func (d *Page) OnAnyEvent(handler func()) {
d.onAnyEvent = handler
}
// Set func to be executed each time javascript polls for updates
func (d *Page) OnUpdate(f func()) {
d.onUpdate = f
}
// {{.JS}} should always be embedded in the template <head>.
// Expands to needed JavaScript code.
func (d *Page) JS() string {
d.haveJS = true
return JS
}
// {{.ErrorBox}} should be embedded in the template where errors are to be shown.
// CSS rules for class ErrorBox may be set, e.g., to render errors in red.
func (t *Page) ErrorBox() string {
return `<span id=ErrorBox class=ErrorBox></span> <span id=MsgBox class=ErrorBox></span>`
}
// {{.UpdateButton}} adds a page Update button
func (t *Page) UpdateButton(text string) string {
if text == "" {
text = `↻`
}
return `<button onclick="update();"> ` + text + ` </button>`
}
// {{.UpdateBox}} adds an auto update checkbox
func (t *Page) UpdateBox(text string) string {
if text == "" {
text = "auto update"
}
return `<input type=checkbox id=UpdateBox class=CheckBox checked=true onchange="autoUpdate=elementById('UpdateBox').checked").checked">` + text + `</input>`
}
// {{.Data}} returns the extra data that was passed to NewPage
func (t *Page) Data() interface{} {
return t.data
}
// return elem[id], panic if non-existent
func (d *Page) elem(id string) *E {
if e, ok := d.elems[id]; ok {
return e
} else {
panic("no element with id: " + id)
}
}
// elem[id] = e, panic if already defined
func (d *Page) addElem(id string, e El) {
if _, ok := d.elems[id]; ok {
panic("addElem: already defined: " + id)
} else {
d.elems[id] = newE(e)
}
}
// ServeHTTP implements http.Handler.
func (d *Page) ServeHTTP(w http.ResponseWriter, r *http.Request) {
d.httpLock.Lock()
defer d.httpLock.Unlock()
switch r.Method {
default:
http.Error(w, "not allowed: "+r.Method+" "+r.URL.Path, http.StatusForbidden)
case "GET":
d.serveContent(w, r)
case "POST":
d.serveUpdate(w, r)
case "PUT":
d.serveEvent(w, r)
}
}
// serves the html content.
func (d *Page) serveContent(w http.ResponseWriter, r *http.Request) {
w.Write(d.htmlCache)
}
// HTTP handler for event notifications by button clicks etc
func (d *Page) serveEvent(w http.ResponseWriter, r *http.Request) {
var ev event
check(json.NewDecoder(r.Body).Decode(&ev))
if Debug {
fmt.Println(ev)
}
if d.onAnyEvent != nil {
d.onAnyEvent()
}
el := d.elem(ev.ID)
el.set(ev.Arg)
if el.onevent != nil {
el.onevent()
}
}
type event struct {
ID string
Arg interface{}
}
// HTTP handler for updating the dynamic elements
func (d *Page) serveUpdate(w http.ResponseWriter, r *http.Request) {
if d.onUpdate != nil {
d.onUpdate()
}
// read page ID from body
buf := make([]byte, 100)
r.Body.Read(buf)
pageID := string(buf)
if pageID != d.lastPageID {
for _, e := range d.elems {
e.setDirty()
}
d.lastPageID = pageID
}
calls := make([]jsCall, 0, len(d.elems))
for id, e := range d.elems {
calls = append(calls, e.update(id)...) // update atomically checks dirty and clears it
}
if Debug && len(calls) != 0 {
fmt.Println(calls) // debug
}
check(json.NewEncoder(w).Encode(calls))
}
// javascript call
type jsCall struct {
F string // function to call
Args []interface{} // function arguments
}
func check(err error) {
if err != nil {
log.Panic(err)
}
}
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