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filter.go
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filter.go
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// Copyright 2022 Twitter, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package main
import (
"errors"
"fmt"
"regexp"
)
type filter interface {
match(string) bool
additive() bool
}
type exact string
func (e exact) match(in string) bool { return in == string(e) }
func (exact) additive() bool { return true }
type pattern struct{ *regexp.Regexp }
func (p pattern) match(in string) bool { return p.MatchString(in) }
func (pattern) additive() bool { return true }
type exclude struct{ filter }
func (e exclude) match(s string) bool { return e.filter.match(s) }
func (exclude) additive() bool { return false }
// parseFilter parses a command-line syntax of a matcher.
func parseFilter(in string) (filter, error) {
if in == "" {
return nil, errors.New("empty string cannot be used as a filter")
}
var exclusion bool
if in[0] == '^' {
in = in[1:]
exclusion = true
}
var f filter
// pattern /re/
if len(in) > 1 && in[0] == '/' && in[len(in)-1] == '/' {
r, err := regexp.Compile(in[1 : len(in)-1])
if err != nil {
return nil, fmt.Errorf("invalid pattern '%s': %w", in, err)
}
f = pattern{r}
} else {
// exact match
f = exact(in)
}
if exclusion {
return exclude{f}, nil
}
return f, nil
}