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package pongo2
import (
"bytes"
)
type tagIfchangedNode struct {
watchedExpr []IEvaluator
lastValues []*Value
lastContent []byte
thenWrapper *NodeWrapper
elseWrapper *NodeWrapper
}
func (node *tagIfchangedNode) Execute(ctx *ExecutionContext, writer TemplateWriter) *Error {
if len(node.watchedExpr) == 0 {
// Check against own rendered body
buf := bytes.NewBuffer(make([]byte, 0, 1024)) // 1 KiB
err := node.thenWrapper.Execute(ctx, buf)
if err != nil {
return err
}
bufBytes := buf.Bytes()
if !bytes.Equal(node.lastContent, bufBytes) {
// Rendered content changed, output it
writer.Write(bufBytes)
node.lastContent = bufBytes
}
} else {
nowValues := make([]*Value, 0, len(node.watchedExpr))
for _, expr := range node.watchedExpr {
val, err := expr.Evaluate(ctx)
if err != nil {
return err
}
nowValues = append(nowValues, val)
}
// Compare old to new values now
changed := len(node.lastValues) == 0
for idx, oldVal := range node.lastValues {
if !oldVal.EqualValueTo(nowValues[idx]) {
changed = true
break // we can stop here because ONE value changed
}
}
node.lastValues = nowValues
if changed {
// Render thenWrapper
err := node.thenWrapper.Execute(ctx, writer)
if err != nil {
return err
}
} else {
// Render elseWrapper
err := node.elseWrapper.Execute(ctx, writer)
if err != nil {
return err
}
}
}
return nil
}
func tagIfchangedParser(doc *Parser, start *Token, arguments *Parser) (INodeTag, *Error) {
ifchangedNode := &tagIfchangedNode{}
for arguments.Remaining() > 0 {
// Parse condition
expr, err := arguments.ParseExpression()
if err != nil {
return nil, err
}
ifchangedNode.watchedExpr = append(ifchangedNode.watchedExpr, expr)
}
if arguments.Remaining() > 0 {
return nil, arguments.Error("Ifchanged-arguments are malformed.", nil)
}
// Wrap then/else-blocks
wrapper, endargs, err := doc.WrapUntilTag("else", "endifchanged")
if err != nil {
return nil, err
}
ifchangedNode.thenWrapper = wrapper
if endargs.Count() > 0 {
return nil, endargs.Error("Arguments not allowed here.", nil)
}
if wrapper.Endtag == "else" {
// if there's an else in the if-statement, we need the else-Block as well
wrapper, endargs, err = doc.WrapUntilTag("endifchanged")
if err != nil {
return nil, err
}
ifchangedNode.elseWrapper = wrapper
if endargs.Count() > 0 {
return nil, endargs.Error("Arguments not allowed here.", nil)
}
}
return ifchangedNode, nil
}
func init() {
RegisterTag("ifchanged", tagIfchangedParser)
}
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