package global

import (
	"strconv"
	"unicode/utf8"
)

const (
	lowerhex = "0123456789abcdef"
	upperhex = "0123456789ABCDEF"
)

// Quote returns a double-quoted Go string literal representing s. The
// returned string uses Go escape sequences (\t, \n, \xFF, \u0100) for
// control characters and non-printable characters as defined by
// IsPrint.
func Quote(s string) string {
	return quoteWith(s, '"', false, false)
}

func quoteWith(s string, quote byte, asciiOnly, graphicOnly bool) string {
	return string(appendQuotedWith(make([]byte, 0, 3*len(s)/2), s, quote, asciiOnly, graphicOnly))
}

func appendQuotedWith(buf []byte, s string, quote byte, asciiOnly, graphicOnly bool) []byte {
	// Often called with big strings, so preallocate. If there's quoting,
	// this is conservative but still helps a lot.
	if cap(buf)-len(buf) < len(s) {
		nBuf := make([]byte, len(buf), len(buf)+1+len(s)+1)
		copy(nBuf, buf)
		buf = nBuf
	}
	buf = append(buf, quote)
	for width := 0; len(s) > 0; s = s[width:] {
		r := rune(s[0])
		width = 1
		if r >= utf8.RuneSelf {
			r, width = utf8.DecodeRuneInString(s)
		}
		if width == 1 && r == utf8.RuneError {
			buf = append(buf, `\x`...)
			buf = append(buf, lowerhex[s[0]>>4])
			buf = append(buf, lowerhex[s[0]&0xF])
			continue
		}
		buf = appendEscapedRune(buf, r, quote, asciiOnly, graphicOnly)
	}
	buf = append(buf, quote)
	return buf
}
func appendEscapedRune(buf []byte, r rune, quote byte, asciiOnly, graphicOnly bool) []byte {
	var runeTmp [utf8.UTFMax]byte
	if r == rune(quote) || r == '\\' { // always backslashed
		buf = append(buf, '\\')
		buf = append(buf, byte(r))
		return buf
	}
	if asciiOnly {
		if r < utf8.RuneSelf && strconv.IsPrint(r) {
			buf = append(buf, byte(r))
			return buf
		}
	} else if strconv.IsPrint(r) || graphicOnly && isInGraphicList(r) {
		n := utf8.EncodeRune(runeTmp[:], r)
		buf = append(buf, runeTmp[:n]...)
		return buf
	}
	switch r {
	case '\a':
		buf = append(buf, `\a`...)
	case '\b':
		buf = append(buf, `\b`...)
	case '\f':
		buf = append(buf, `\f`...)
	case '\n':
		buf = append(buf, `\n`...)
	case '\r':
		buf = append(buf, `\r`...)
	case '\t':
		buf = append(buf, `\t`...)
	case '\v':
		buf = append(buf, `\v`...)
	default:
		switch {
		case !utf8.ValidRune(r):
			r = 0xFFFD
			fallthrough
		case r < 0x10000:
			buf = append(buf, `\u`...)
			for s := 12; s >= 0; s -= 4 {
				buf = append(buf, lowerhex[r>>uint(s)&0xF])
			}
		default:
			buf = append(buf, `\U`...)
			for s := 28; s >= 0; s -= 4 {
				buf = append(buf, lowerhex[r>>uint(s)&0xF])
			}
		}
	}
	return buf
}

func isInGraphicList(r rune) bool {
	// We know r must fit in 16 bits - see makeisprint.go.
	if r > 0xFFFF {
		return false
	}
	rr := uint16(r)
	i := bsearch16(isGraphic, rr)
	return i < len(isGraphic) && rr == isGraphic[i]
}

// bsearch16 returns the smallest i such that a[i] >= x.
// If there is no such i, bsearch16 returns len(a).
func bsearch16(a []uint16, x uint16) int {
	i, j := 0, len(a)
	for i < j {
		h := i + (j-i)>>1
		if a[h] < x {
			i = h + 1
		} else {
			j = h
		}
	}
	return i
}

// isGraphic lists the graphic runes not matched by IsPrint.
var isGraphic = []uint16{
	0x00a0,
	0x1680,
	0x2000,
	0x2001,
	0x2002,
	0x2003,
	0x2004,
	0x2005,
	0x2006,
	0x2007,
	0x2008,
	0x2009,
	0x200a,
	0x202f,
	0x205f,
	0x3000,
}