// written by Daniel Oaks <daniel@danieloaks.net>
// released under the ISC license

package ircfmt

import (
	"regexp"
	"strings"
)

const (
	// raw bytes and strings to do replacing with
	bold          string = "\x02"
	colour        string = "\x03"
	monospace     string = "\x11"
	reverseColour string = "\x16"
	italic        string = "\x1d"
	strikethrough string = "\x1e"
	underline     string = "\x1f"
	reset         string = "\x0f"

	runecolour        rune = '\x03'
	runebold          rune = '\x02'
	runemonospace     rune = '\x11'
	runereverseColour rune = '\x16'
	runeitalic        rune = '\x1d'
	runestrikethrough rune = '\x1e'
	runereset         rune = '\x0f'
	runeunderline     rune = '\x1f'

	// valid characters in a colour code character, for speed
	colours1 string = "0123456789"
)

var (
	// valtoescape replaces most of IRC characters with our escapes.
	valtoescape = strings.NewReplacer("$", "$$", colour, "$c", reverseColour, "$v", bold, "$b", italic, "$i", strikethrough, "$s", underline, "$u", monospace, "$m", reset, "$r")
	// valToStrip replaces most of the IRC characters with nothing
	valToStrip = strings.NewReplacer(colour, "$c", reverseColour, "", bold, "", italic, "", strikethrough, "", underline, "", monospace, "", reset, "")

	// escapetoval contains most of our escapes and how they map to real IRC characters.
	// intentionally skips colour, since that's handled elsewhere.
	escapetoval = map[rune]string{
		'$': "$",
		'b': bold,
		'i': italic,
		'v': reverseColour,
		's': strikethrough,
		'u': underline,
		'm': monospace,
		'r': reset,
	}

	// valid colour codes
	numtocolour = map[string]string{
		"99": "default",
		"15": "light grey",
		"14": "grey",
		"13": "pink",
		"12": "light blue",
		"11": "light cyan",
		"10": "cyan",
		"09": "light green",
		"08": "yellow",
		"07": "orange",
		"06": "magenta",
		"05": "brown",
		"04": "red",
		"03": "green",
		"02": "blue",
		"01": "black",
		"00": "white",
		"9":  "light green",
		"8":  "yellow",
		"7":  "orange",
		"6":  "magenta",
		"5":  "brown",
		"4":  "red",
		"3":  "green",
		"2":  "blue",
		"1":  "black",
		"0":  "white",
	}

	colourcodesTruncated = map[string]string{
		"white":       "0",
		"black":       "1",
		"blue":        "2",
		"green":       "3",
		"red":         "4",
		"brown":       "5",
		"magenta":     "6",
		"orange":      "7",
		"yellow":      "8",
		"light green": "9",
		"cyan":        "10",
		"light cyan":  "11",
		"light blue":  "12",
		"pink":        "13",
		"grey":        "14",
		"light grey":  "15",
		"default":     "99",
	}

	bracketedExpr = regexp.MustCompile(`^\[.*?\]`)
	colourDigits  = regexp.MustCompile(`^[0-9]{1,2}$`)
)

// Escape takes a raw IRC string and returns it with our escapes.
//
// IE, it turns this: "This is a \x02cool\x02, \x034red\x0f message!"
// into: "This is a $bcool$b, $c[red]red$r message!"
func Escape(in string) string {
	// replace all our usual escapes
	in = valtoescape.Replace(in)

	inRunes := []rune(in)
	//var out string
	out := strings.Builder{}
	for 0 < len(inRunes) {
		if 1 < len(inRunes) && inRunes[0] == '$' && inRunes[1] == 'c' {
			// handle colours
			out.WriteString("$c")
			inRunes = inRunes[2:] // strip colour code chars

			if len(inRunes) < 1 || !strings.Contains(colours1, string(inRunes[0])) {
				out.WriteString("[]")
				continue
			}

			var foreBuffer, backBuffer string
			foreBuffer += string(inRunes[0])
			inRunes = inRunes[1:]
			if 0 < len(inRunes) && strings.Contains(colours1, string(inRunes[0])) {
				foreBuffer += string(inRunes[0])
				inRunes = inRunes[1:]
			}
			if 1 < len(inRunes) && inRunes[0] == ',' && strings.Contains(colours1, string(inRunes[1])) {
				backBuffer += string(inRunes[1])
				inRunes = inRunes[2:]
				if 0 < len(inRunes) && strings.Contains(colours1, string(inRunes[0])) {
					backBuffer += string(inRunes[0])
					inRunes = inRunes[1:]
				}
			}

			foreName, exists := numtocolour[foreBuffer]
			if !exists {
				foreName = foreBuffer
			}
			backName, exists := numtocolour[backBuffer]
			if !exists {
				backName = backBuffer
			}

			out.WriteRune('[')
			out.WriteString(foreName)
			if backName != "" {
				out.WriteRune(',')
				out.WriteString(backName)
			}
			out.WriteRune(']')

		} else {
			// special case for $$c
			if len(inRunes) > 2 && inRunes[0] == '$' && inRunes[1] == '$' && inRunes[2] == 'c' {
				out.WriteRune(inRunes[0])
				out.WriteRune(inRunes[1])
				out.WriteRune(inRunes[2])
				inRunes = inRunes[3:]
			} else {
				out.WriteRune(inRunes[0])
				inRunes = inRunes[1:]
			}
		}
	}

	return out.String()
}

// Strip takes a raw IRC string and removes it with all formatting codes removed
// IE, it turns this: "This is a \x02cool\x02, \x034red\x0f message!"
// into: "This is a cool, red message!"
func Strip(in string) string {
	out := strings.Builder{}
	runes := []rune(in)
	if out.Len() < len(runes) { // Reduce allocations where needed
		out.Grow(len(in) - out.Len())
	}
	for len(runes) > 0 {
		switch runes[0] {
		case runebold, runemonospace, runereverseColour, runeitalic, runestrikethrough, runeunderline, runereset:
			runes = runes[1:]
		case runecolour:
			runes = removeColour(runes)
		default:
			out.WriteRune(runes[0])
			runes = runes[1:]
		}
	}
	return out.String()
}

func removeNumber(runes []rune) []rune {
	if len(runes) > 0 && runes[0] >= '0' && runes[0] <= '9' {
		runes = runes[1:]
	}
	return runes
}

func removeColour(runes []rune) []rune {
	if runes[0] != runecolour {
		return runes
	}

	runes = runes[1:]
	runes = removeNumber(runes)
	runes = removeNumber(runes)

	if len(runes) > 1 && runes[0] == ',' && runes[1] >= '0' && runes[1] <= '9' {
		runes = runes[2:]
	} else {
		return runes // Nothing else because we dont have a comma
	}
	runes = removeNumber(runes)
	return runes
}

// resolve "light blue" to "12", "12" to "12", "asdf" to "", etc.
func resolveToColourCode(str string) (result string) {
	str = strings.ToLower(strings.TrimSpace(str))
	if colourDigits.MatchString(str) {
		return str
	}
	return colourcodesTruncated[str]
}

// resolve "[light blue, black]" to ("13, "1")
func resolveToColourCodes(namedColors string) (foreground, background string) {
	// cut off the brackets
	namedColors = strings.TrimPrefix(namedColors, "[")
	namedColors = strings.TrimSuffix(namedColors, "]")

	var foregroundStr, backgroundStr string
	commaIdx := strings.IndexByte(namedColors, ',')
	if commaIdx != -1 {
		foregroundStr = namedColors[:commaIdx]
		backgroundStr = namedColors[commaIdx+1:]
	} else {
		foregroundStr = namedColors
	}

	return resolveToColourCode(foregroundStr), resolveToColourCode(backgroundStr)
}

// Unescape takes our escaped string and returns a raw IRC string.
//
// IE, it turns this: "This is a $bcool$b, $c[red]red$r message!"
// into this: "This is a \x02cool\x02, \x034red\x0f message!"
func Unescape(in string) string {
	var out strings.Builder

	remaining := in
	for len(remaining) != 0 {
		char := remaining[0]
		remaining = remaining[1:]

		if char != '$' || len(remaining) == 0 {
			// not an escape
			out.WriteByte(char)
			continue
		}

		// ingest the next character of the escape
		char = remaining[0]
		remaining = remaining[1:]

		if char == 'c' {
			out.WriteString(colour)

			namedColors := bracketedExpr.FindString(remaining)
			if namedColors == "" {
				// for a non-bracketed color code, output the following characters directly,
				// e.g., `$c1,8` will become `\x031,8`
				continue
			}
			// process bracketed color codes:
			remaining = remaining[len(namedColors):]
			followedByDigit := len(remaining) != 0 && ('0' <= remaining[0] && remaining[0] <= '9')

			foreground, background := resolveToColourCodes(namedColors)
			if foreground != "" {
				if len(foreground) == 1 && background == "" && followedByDigit {
					out.WriteByte('0')
				}
				out.WriteString(foreground)
				if background != "" {
					out.WriteByte(',')
					if len(background) == 1 && followedByDigit {
						out.WriteByte('0')
					}
					out.WriteString(background)
				}
			}
		} else {
			val, exists := escapetoval[rune(char)]
			if exists {
				out.WriteString(val)
			} else {
				// invalid escape, use the raw char
				out.WriteByte(char)
			}
		}
	}

	return out.String()
}