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migrate_headings.go
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/
migrate_headings.go
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package tools
import (
"regexp"
"strings"
)
var headingMatcher *regexp.Regexp
func init() {
var headingM, err = regexp.Compile(`^\s*#{1,6} `)
if err != nil {
panic("disaster")
}
headingMatcher = headingM
}
// MigrateHeadings replaces all instances of the old heading syntax with the new one it can find in the given document and returns the modified version.
func MigrateHeadings(old string) string {
var result strings.Builder
for i, line := range strings.Split(old, "\n") {
if i > 0 {
result.WriteRune('\n')
}
if headingMatcher.MatchString(line) {
result.WriteString(oldHeadingToNew(line))
} else {
result.WriteString(line)
}
}
return result.String()
}
type headingReplacer int
const (
eatingSpace headingReplacer = iota
replacingOctothorps
writingRest
)
// this function enforces some style
func oldHeadingToNew(heading string) string {
var (
result strings.Builder
state = eatingSpace
octothorpCount = 0
)
for _, r := range heading {
runeCaster:
switch state {
case eatingSpace:
switch r {
case ' ', '\t':
result.WriteRune(r)
case '#':
state = replacingOctothorps
goto runeCaster
default:
panic("bad input")
}
case replacingOctothorps:
switch r {
case '#':
octothorpCount++
case ' ':
switch octothorpCount {
case 1, 2:
result.WriteRune('=')
case 3:
result.WriteString("==")
case 4:
result.WriteString("===")
case 5, 6:
result.WriteString("====")
}
result.WriteRune(' ')
state = writingRest
default:
panic("bad input")
}
case writingRest:
result.WriteRune(r)
}
}
return result.String()
}