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fragments.go
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fragments.go
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/*
Package fragments provides a simple way to cache pieces of web text. A
fragment is an object which can be rendered and can inform about
children (has interface Fragment). The package provides two types of
simple fragments: Text and Templates.
Here is an example usage of the package:
fragments.Register("salute", func(C *Cache, args []string) fragments.Fragment {
return fragments.Text("hello, " + args[1] + "\n")
})
fragments.Register("pair-salute", func(C *Cache, a []string) fragments.Fragment {
s := fmt.Sprintf("salute 1: {salute %s}salute 2: {salute %s}", a[1], a[2])
f, _ := fragments.Parser{"{", "}"}.Parse(s)
return f
})
...
fragments.Render(os.Stdout, "salute pauek")
fragments.Render(os.Stdout, "pair-salute pauek other")
*/
package fragments
import (
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
_ "log"
"strings"
"sync"
"time"
)
type Mode int
const (
Recursive = Mode(0)
NonRecursive = Mode(1)
)
type Fragment interface {
Render(w io.Writer, C *Cache, mode Mode)
EachChild(fn func(id string))
}
// Text
type Text string
func (t Text) Render(w io.Writer, C *Cache, mode Mode) {
w.Write([]byte(t))
}
func (t Text) EachChild(fn func(id string)) {}
type tmplItem struct {
text string
isAction bool
}
// Template
type Template []tmplItem
type Parser struct {
Ldelim, Rdelim string
}
var ParseError = errors.New("Unmatched delimiters")
func (p Parser) Parse(s string) (Template, error) {
t := []tmplItem{}
lsz, rsz := len(p.Ldelim), len(p.Rdelim)
for {
i := strings.Index(s, p.Ldelim)
if i == -1 {
break
}
t = append(t, tmplItem{s[:i], false})
s = s[i+lsz:]
j := strings.Index(s, p.Rdelim)
if j == -1 {
return nil, ParseError
}
t = append(t, tmplItem{s[:j], true})
s = s[j+rsz:]
}
if len(s) > 0 {
t = append(t, tmplItem{s, false})
}
return Template(t), nil
}
func (t Template) Exec(w io.Writer, fn func(action string)) {
for _, item := range t {
if item.isAction {
fn(item.text)
} else {
w.Write([]byte(item.text))
}
}
}
func (t Template) Render(w io.Writer, C *Cache, mode Mode) {
t.Exec(w, func(id string) {
if mode == Recursive {
C.Render(w, id)
} else {
inDiv(w, id, nil)
}
})
}
func (t Template) EachChild(fn func(id string)) {
for _, item := range t {
if item.isAction {
fn(item.text)
}
}
}
func (t Template) RenderFn(fn func(_w io.Writer, _id string)) RenderFn {
return RenderFn(func(w io.Writer, C *Cache, mode Mode) {
t.Exec(w, func(id string) {
if mode == Recursive {
fn(w, id)
}
})
})
}
// RenderFn
type RenderFn func(w io.Writer, C *Cache, mode Mode)
func (f RenderFn) Render(w io.Writer, C *Cache, m Mode) { f(w, C, m) }
func (f RenderFn) EachChild(fn func(id string)) {}
// Cache
type cacheItem struct {
frag Fragment
stamp time.Time
}
type Cache struct {
mutex sync.Mutex
cache map[string]*cacheItem
valid map[string]bool
registry map[string]Generator
depends map[string]map[string]bool
}
type Generator func(C *Cache, args []string) Fragment
func NewCache() *Cache {
C := new(Cache)
C.cache = make(map[string]*cacheItem)
C.valid = make(map[string]bool)
C.registry = make(map[string]Generator)
C.depends = make(map[string]map[string]bool)
return C
}
func (C *Cache) get(id string) *cacheItem {
f, ok := C.cache[id]
if !ok || !C.valid[id] {
C.mutex.Lock()
C.valid[id] = true
C.mutex.Unlock()
f = &cacheItem{
frag: C.generate(id),
stamp: time.Now(),
}
C.mutex.Lock()
C.cache[id] = f
C.mutex.Unlock()
} else {
// log.Printf("Hit: %q", id)
}
return f
}
func (C *Cache) Get(id string) Fragment {
return C.get(id).frag
}
func (C *Cache) generate(id string) Fragment {
args := strings.Split(id, " ")
gen, ok := C.registry[args[0]]
if !ok {
return Text(fmt.Sprintf(`No generator "%s"`, args[0]))
}
return gen(C, args)
}
func (C *Cache) Register(gen Generator, ids ...string) {
C.mutex.Lock()
for _, id := range ids {
C.registry[id] = gen
}
C.mutex.Unlock()
}
func Static(f Fragment) Generator {
return func(C *Cache, args []string) Fragment {
return f
}
}
func StaticText(text string) Generator {
return Static(Text(text))
}
func inDiv(w io.Writer, id string, fn func()) {
fmt.Fprintf(w, `<div fragment="%s">`, id)
if fn != nil {
fn()
}
fmt.Fprintf(w, `</div>`)
}
func (C *Cache) Render(w io.Writer, id string) {
inDiv(w, id, func() {
C.get(id).frag.Render(w, C, Recursive)
})
}
func (C *Cache) RenderToString(id string) string {
var b bytes.Buffer
C.Render(&b, id)
return b.String()
}
type ListItem struct {
Id, Html string
Stamp time.Time
}
func (C *Cache) Diff(id string, since time.Time) (list []ListItem) {
item := C.get(id)
list = []ListItem{{Id: id, Stamp: item.stamp}}
if item.stamp.After(since) {
var b bytes.Buffer
inDiv(&b, id, func() {
item.frag.Render(&b, C, NonRecursive)
})
list[0].Html = b.String()
}
item.frag.EachChild(func(id string) {
sublist := C.Diff(id, since)
list = append(list, sublist...)
})
return
}
// Declare dependencies: fragment fid depends on all objects in the
// oids list
//
func (C *Cache) Depends(fid string, oids ...string) {
C.mutex.Lock()
for _, oid := range oids {
if C.depends[oid] == nil {
C.depends[oid] = make(map[string]bool)
}
C.depends[oid][fid] = true
}
C.mutex.Unlock()
}
// Invalidate fragment with ID fid (if it exists)
//
func (C *Cache) Invalidate(fid string) {
C.mutex.Lock()
if _, found := C.valid[fid]; found {
fmt.Printf("Invalidate: '%s'\n", fid)
C.valid[fid] = false
}
C.mutex.Unlock()
// notify observers
}
// Invalidate all fragments associated with object oid
//
func (C *Cache) Touch(oid string) {
for fid := range C.depends[oid] {
C.Invalidate(fid)
}
}
// Default Parser
var DefaultParser = Parser{"{% ", " %}"}
func Parse(s string) (Template, error) {
return DefaultParser.Parse(s)
}
func MustParse(s string) (t Template) {
if t, err := Parse(s); err == nil {
return t
}
panic(fmt.Sprintf("Cannot Parse"))
}
func MustParseFile(filename string) (t Template) {
if data, err := ioutil.ReadFile(filename); err == nil {
return MustParse(string(data))
}
panic(fmt.Sprintf("Cannot Read File '%s'", filename))
}