func replaceLeadingIndentation()

in internal/pkgdoc/funcs.go [289:369]
72 lines of code
19 McCabe index (conditional complexity)

func replaceLeadingIndentation(body, oldIndent, newIndent string) string {
	// Handle indent at the beginning of the first line. After this, we handle
	// indentation only after a newline.
	var buf bytes.Buffer
	if strings.HasPrefix(body, oldIndent) {
		buf.WriteString(newIndent)
		body = body[len(oldIndent):]
	}

	// Use a state machine to keep track of whether we're in a string or
	// rune literal while we process the rest of the code.
	const (
		codeState = iota
		runeState
		interpretedStringState
		rawStringState
	)
	searchChars := []string{
		"'\"`\n", // codeState
		`\'`,     // runeState
		`\"`,     // interpretedStringState
		"`\n",    // rawStringState
		// newlineState does not need to search
	}
	state := codeState
	for {
		i := strings.IndexAny(body, searchChars[state])
		if i < 0 {
			buf.WriteString(body)
			break
		}
		c := body[i]
		buf.WriteString(body[:i+1])
		body = body[i+1:]
		switch state {
		case codeState:
			switch c {
			case '\'':
				state = runeState
			case '"':
				state = interpretedStringState
			case '`':
				state = rawStringState
			case '\n':
				if strings.HasPrefix(body, oldIndent) {
					buf.WriteString(newIndent)
					body = body[len(oldIndent):]
				}
			}

		case runeState:
			switch c {
			case '\\':
				r, size := utf8.DecodeRuneInString(body)
				buf.WriteRune(r)
				body = body[size:]
			case '\'':
				state = codeState
			}

		case interpretedStringState:
			switch c {
			case '\\':
				r, size := utf8.DecodeRuneInString(body)
				buf.WriteRune(r)
				body = body[size:]
			case '"':
				state = codeState
			}

		case rawStringState:
			switch c {
			case '`':
				state = codeState
			case '\n':
				buf.WriteString(newIndent)
			}
		}
	}
	return buf.String()
}