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// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package present
import (
"errors"
"regexp"
"strconv"
"unicode/utf8"
)
// This file is stolen from go/src/cmd/godoc/codewalk.go.
// It's an evaluator for the file address syntax implemented by acme and sam,
// but using Go-native regular expressions.
// To keep things reasonably close, this version uses (?m:re) for all user-provided
// regular expressions. That is the only change to the code from codewalk.go.
// See http://plan9.bell-labs.com/sys/doc/sam/sam.html Table II
// for details on the syntax.
// addrToByte evaluates the given address starting at offset start in data.
// It returns the lo and hi byte offset of the matched region within data.
func addrToByteRange(addr string, start int, data []byte) (lo, hi int, err error) {
if addr == "" {
lo, hi = start, len(data)
return
}
var (
dir byte
prevc byte
charOffset bool
)
lo = start
hi = start
for addr != "" && err == nil {
c := addr[0]
switch c {
default:
err = errors.New("invalid address syntax near " + string(c))
case ',':
if len(addr) == 1 {
hi = len(data)
} else {
_, hi, err = addrToByteRange(addr[1:], hi, data)
}
return
case '+', '-':
if prevc == '+' || prevc == '-' {
lo, hi, err = addrNumber(data, lo, hi, prevc, 1, charOffset)
}
dir = c
case '$':
lo = len(data)
hi = len(data)
if len(addr) > 1 {
dir = '+'
}
case '#':
charOffset = true
case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
var i int
for i = 1; i < len(addr); i++ {
if addr[i] < '0' || addr[i] > '9' {
break
}
}
var n int
n, err = strconv.Atoi(addr[0:i])
if err != nil {
break
}
lo, hi, err = addrNumber(data, lo, hi, dir, n, charOffset)
dir = 0
charOffset = false
prevc = c
addr = addr[i:]
continue
case '/':
var i, j int
Regexp:
for i = 1; i < len(addr); i++ {
switch addr[i] {
case '\\':
i++
case '/':
j = i + 1
break Regexp
}
}
if j == 0 {
j = i
}
pattern := addr[1:i]
lo, hi, err = addrRegexp(data, lo, hi, dir, pattern)
prevc = c
addr = addr[j:]
continue
}
prevc = c
addr = addr[1:]
}
if err == nil && dir != 0 {
lo, hi, err = addrNumber(data, lo, hi, dir, 1, charOffset)
}
if err != nil {
return 0, 0, err
}
return lo, hi, nil
}
// addrNumber applies the given dir, n, and charOffset to the address lo, hi.
// dir is '+' or '-', n is the count, and charOffset is true if the syntax
// used was #n. Applying +n (or +#n) means to advance n lines
// (or characters) after hi. Applying -n (or -#n) means to back up n lines
// (or characters) before lo.
// The return value is the new lo, hi.
func addrNumber(data []byte, lo, hi int, dir byte, n int, charOffset bool) (int, int, error) {
switch dir {
case 0:
lo = 0
hi = 0
fallthrough
case '+':
if charOffset {
pos := hi
for ; n > 0 && pos < len(data); n-- {
_, size := utf8.DecodeRune(data[pos:])
pos += size
}
if n == 0 {
return pos, pos, nil
}
break
}
// find next beginning of line
if hi > 0 {
for hi < len(data) && data[hi-1] != '\n' {
hi++
}
}
lo = hi
if n == 0 {
return lo, hi, nil
}
for ; hi < len(data); hi++ {
if data[hi] != '\n' {
continue
}
switch n--; n {
case 1:
lo = hi + 1
case 0:
return lo, hi + 1, nil
}
}
case '-':
if charOffset {
// Scan backward for bytes that are not UTF-8 continuation bytes.
pos := lo
for ; pos > 0 && n > 0; pos-- {
if data[pos]&0xc0 != 0x80 {
n--
}
}
if n == 0 {
return pos, pos, nil
}
break
}
// find earlier beginning of line
for lo > 0 && data[lo-1] != '\n' {
lo--
}
hi = lo
if n == 0 {
return lo, hi, nil
}
for ; lo >= 0; lo-- {
if lo > 0 && data[lo-1] != '\n' {
continue
}
switch n--; n {
case 1:
hi = lo
case 0:
return lo, hi, nil
}
}
}
return 0, 0, errors.New("address out of range")
}
// addrRegexp searches for pattern in the given direction starting at lo, hi.
// The direction dir is '+' (search forward from hi) or '-' (search backward from lo).
// Backward searches are unimplemented.
func addrRegexp(data []byte, lo, hi int, dir byte, pattern string) (int, int, error) {
// We want ^ and $ to work as in sam/acme, so use ?m.
re, err := regexp.Compile("(?m:" + pattern + ")")
if err != nil {
return 0, 0, err
}
if dir == '-' {
// Could implement reverse search using binary search
// through file, but that seems like overkill.
return 0, 0, errors.New("reverse search not implemented")
}
m := re.FindIndex(data[hi:])
if len(m) > 0 {
m[0] += hi
m[1] += hi
} else if hi > 0 {
// No match. Wrap to beginning of data.
m = re.FindIndex(data)
}
if len(m) == 0 {
return 0, 0, errors.New("no match for " + pattern)
}
return m[0], m[1], nil
}