package reporttemplate

import (
	"strings"
	"unicode"
)

var inlineMarkdownReplacer = strings.NewReplacer(
	`\`, `\\`,
	"`", "\\`",
	"*", "\\*",
	"_", "\\_",
	"[", "\\[",
	"]", "\\]",
	"(", "\\(",
	")", "\\)",
	"<", "\\<",
	">", "\\>",
	"!", "\\!",
	"~", "\\~",
	"|", "\\|",
	"&", "\\&",
)

// plainText preserves prose and paragraph breaks while preventing dynamic
// values from creating Markdown structure owned by repository templates.
func plainText(value string) string {
	value = strings.ReplaceAll(value, "\r\n", "\n")
	value = strings.ReplaceAll(value, "\r", "\n")
	lines := strings.Split(value, "\n")
	for index, line := range lines {
		lines[index] = escapeMarkdownLine(line)
	}
	return strings.Join(lines, "\n")
}

func escapeMarkdownLine(line string) string {
	indentEnd := 0
	spaces := 0
	hasTab := false
	for indentEnd < len(line) {
		switch line[indentEnd] {
		case ' ':
			spaces++
			indentEnd++
		case '\t':
			hasTab = true
			indentEnd++
		default:
			goto escaped
		}
	}

escaped:
	indent := line[:indentEnd]
	if hasTab || spaces >= 4 {
		indent = ""
	}
	return indent + escapeMarkdownBlockPrefix(escapeMarkdownInline(line[indentEnd:]))
}

func escapeMarkdownInline(value string) string {
	value = inlineMarkdownReplacer.Replace(value)
	return strings.Map(func(r rune) rune {
		if unicode.IsControl(r) {
			return ' '
		}
		return r
	}, value)
}

func escapeMarkdownBlockPrefix(value string) string {
	if value == "" {
		return value
	}
	switch value[0] {
	case '#', '+', '-', '>', '=':
		return "\\" + value
	}

	index := 0
	for index < len(value) && value[index] >= '0' && value[index] <= '9' {
		index++
	}
	if index > 0 && index < len(value) && value[index] == '.' {
		return value[:index] + "\\" + value[index:]
	}
	return value
}