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package pongo2
import (
"fmt"
)
// FilterFunction is the type filter functions must fulfil
type FilterFunction func(in *Value, param *Value) (out *Value, err *Error)
var filters map[string]FilterFunction
func init() {
filters = make(map[string]FilterFunction)
}
// FilterExists returns true if the given filter is already registered
func FilterExists(name string) bool {
_, existing := filters[name]
return existing
}
// RegisterFilter registers a new filter. If there's already a filter with the same
// name, RegisterFilter will panic. You usually want to call this
// function in the filter's init() function:
// http://golang.org/doc/effective_go.html#init
//
// See http://www.florian-schlachter.de/post/pongo2/ for more about
// writing filters and tags.
func RegisterFilter(name string, fn FilterFunction) error {
if FilterExists(name) {
return fmt.Errorf("filter with name '%s' is already registered", name)
}
filters[name] = fn
return nil
}
// ReplaceFilter replaces an already registered filter with a new implementation. Use this
// function with caution since it allows you to change existing filter behaviour.
func ReplaceFilter(name string, fn FilterFunction) error {
if !FilterExists(name) {
return fmt.Errorf("filter with name '%s' does not exist (therefore cannot be overridden)", name)
}
filters[name] = fn
return nil
}
// MustApplyFilter behaves like ApplyFilter, but panics on an error.
func MustApplyFilter(name string, value *Value, param *Value) *Value {
val, err := ApplyFilter(name, value, param)
if err != nil {
panic(err)
}
return val
}
// ApplyFilter applies a filter to a given value using the given parameters.
// Returns a *pongo2.Value or an error.
func ApplyFilter(name string, value *Value, param *Value) (*Value, *Error) {
fn, existing := filters[name]
if !existing {
return nil, &Error{
Sender: "applyfilter",
OrigError: fmt.Errorf("Filter with name '%s' not found.", name),
}
}
// Make sure param is a *Value
if param == nil {
param = AsValue(nil)
}
return fn(value, param)
}
type filterCall struct {
token *Token
name string
parameter IEvaluator
filterFunc FilterFunction
}
func (fc *filterCall) Execute(v *Value, ctx *ExecutionContext) (*Value, *Error) {
var param *Value
var err *Error
if fc.parameter != nil {
param, err = fc.parameter.Evaluate(ctx)
if err != nil {
return nil, err
}
} else {
param = AsValue(nil)
}
filteredValue, err := fc.filterFunc(v, param)
if err != nil {
return nil, err.updateFromTokenIfNeeded(ctx.template, fc.token)
}
return filteredValue, nil
}
// Filter = IDENT | IDENT ":" FilterArg | IDENT "|" Filter
func (p *Parser) parseFilter() (*filterCall, *Error) {
identToken := p.MatchType(TokenIdentifier)
// Check filter ident
if identToken == nil {
return nil, p.Error("Filter name must be an identifier.", nil)
}
filter := &filterCall{
token: identToken,
name: identToken.Val,
}
// Get the appropriate filter function and bind it
filterFn, exists := filters[identToken.Val]
if !exists {
return nil, p.Error(fmt.Sprintf("Filter '%s' does not exist.", identToken.Val), identToken)
}
filter.filterFunc = filterFn
// Check for filter-argument (2 tokens needed: ':' ARG)
if p.Match(TokenSymbol, ":") != nil {
if p.Peek(TokenSymbol, "}}") != nil {
return nil, p.Error("Filter parameter required after ':'.", nil)
}
// Get filter argument expression
v, err := p.parseVariableOrLiteral()
if err != nil {
return nil, err
}
filter.parameter = v
}
return filter, nil
}
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