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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2018 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package strutil
import (
"bytes"
"regexp"
)
// A MatchCounter is a discarding io.Writer that retains up to N
// matches to its Regexp before just counting matches.
//
// It does not work with regexps that cross newlines; in fact it will
// probably not work if the data written isn't line-orineted.
//
// If Regexp is not set (or nil), it matches whole non-empty lines.
type MatchCounter struct {
// Regexp to use to find matches in the stream
Regexp *regexp.Regexp
// Maximum number of matches to keep; if < 0, keep all matches
N int
// LastN when true indicates that only N last matches shall be kept.
LastN bool
count int
matches []string
partial bytes.Buffer
}
func (w *MatchCounter) Write(p []byte) (int, error) {
n := len(p)
if w.partial.Len() > 0 {
idx := bytes.IndexByte(p, '\n')
if idx < 0 {
// no newline yet, carry on accumulating
w.partial.Write(p)
return n, nil
}
idx++
w.partial.Write(p[:idx])
w.check(w.partial.Bytes())
p = p[idx:]
}
w.partial.Reset()
idx := bytes.LastIndexByte(p, '\n')
if idx < 0 {
w.partial.Write(p)
return n, nil
}
idx++
w.partial.Write(p[idx:])
w.check(p[:idx])
return n, nil
}
func (w *MatchCounter) check(p []byte) {
addMatch := func(m string) {
switch {
case w.N == 0:
// keep none
return
case w.N < 0:
// keep all
fallthrough
case !w.LastN && len(w.matches) < w.N:
w.matches = append(w.matches, m)
case w.LastN:
// keep only last N matches
keep := w.matches
if len(w.matches)+1 > w.N {
keep = w.matches[1:]
}
w.matches = append(keep, m)
}
}
if w.Regexp == nil {
for {
idx := bytes.IndexByte(p, '\n')
if idx < 0 {
return
}
if idx == 0 {
// empty line
p = p[1:]
continue
}
addMatch(string(p[:idx]))
w.count++
p = p[idx+1:]
}
}
matches := w.Regexp.FindAll(p, -1)
for _, match := range matches {
addMatch(string(match))
}
w.count += len(matches)
}
// Matches returns the first few matches, and the total number of matches seen.
func (w *MatchCounter) Matches() ([]string, int) {
return w.matches, w.count
}
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