func skipComment(f fancy.Reader) {
	for {
		c, err := f.ReadByte()
		if err != nil || c == 13 || c == 10 {
			break
		}
	}
}

// xrefStart() queries the start of the xref-table in a PDF file.
func xrefStart(f fancy.Reader) int {
	s := int(f.Size())
	pdf := make([]byte, min(s, 1024))
	f.ReadAt(pdf, int64(max(0, s-1024)))
	ps := xref.AllMatches(pdf, 0)
	if ps == nil {
		return -1
	}
	return num(xref.MatchSlices(ps[len(ps)-1])[2])
}

func skipSpaces(f fancy.Reader) byte {
	for {
		c, err := f.ReadByte()
		if err != nil {
			break
		}
		if c > 32 {
			return c
		}
	}
	return 0
}

func skipString(f fancy.Reader) {
	for depth := 1; depth > 0; {
		c, err := f.ReadByte()
		if err != nil {
			break
		}
		switch c {
		case '(':
			depth++
		case ')':
			depth--
		case '\\':
			f.ReadByte()
		}
	}
}

func skipToDelim(f fancy.Reader) byte {
	for {
		c, err := f.ReadByte()
		if err != nil {
			break
		}
		if c < 33 {
			return c
		}
		switch c {
		case '<', '>', '(', ')', '[', ']', '/', '%', '{', '}':
			return c
		}
	}
	return 255
}

// xrefSkip() queries the start of the trailer for a (partial) xref-table.
func xrefSkip(f fancy.Reader, xref int) int {
	f.Seek(int64(xref), 0)
	t, p := ps.Token(f)
	if string(t) != "xref" {
		return -1
	}
	for {
		t, p = ps.Token(f)
		if t[0] < '0' || t[0] > '9' {
			f.Seek(p, 0)
			break
		}
		t, _ = ps.Token(f)
		ps.SkipLE(f)
		f.Seek(int64(num(t)*20), 1)
	}
	r, _ := f.Seek(0, 1)
	return int(r)
}

func refToken(f fancy.Reader) ([]byte, int64) {
	tok, p := ps.Token(f)
	if len(tok) > 0 && tok[0] >= '0' && tok[0] <= '9' {
		ps.Token(f)
		r, q := ps.Token(f)
		if string(r) == "R" {
			f.Seek(p, 0)
			tok = f.Slice(int(1 + q - p))
		} else {
			f.Seek(p+int64(len(tok)), 0)
		}
	}
	return tok, p
}

func SkipLE(f fancy.Reader) {
	for {
		c, err := f.ReadByte()
		if err != nil {
			return
		}
		if c > 32 {
			f.UnreadByte()
			return
		}
		if c == 13 {
			c, err = f.ReadByte()
			if err == nil && c != 10 {
				f.UnreadByte()
			}
			return
		}
		if c == 10 {
			return
		}
	}
}

// xrefRead() reads the xref table(s) of a PDF file. This is not recursive
// in favour of not to have to keep track of already used starting points
// for xrefs.
func xrefRead(f fancy.Reader, p int) map[int]int {
	var back [MAX_PDF_UPDATES]int
	b := 0
	s := _Bytes
	for ok := true; ok; {
		back[b] = p
		b++
		p = xrefSkip(f, p)
		f.Seek(int64(p), 0)
		s, _ = ps.Token(f)
		if string(s) != "trailer" {
			return nil
		}
		s, _ = ps.Token(f)
		s, ok = Dictionary(s)["/Prev"]
		p = num(s)
	}
	r := make(map[int]int)
	for b != 0 {
		b--
		f.Seek(int64(back[b]), 0)
		ps.Token(f) // skip "xref"
		for {
			m := tupel(f, 2)
			if string(m[0]) == "trailer" {
				break
			}
			ps.SkipLE(f)
			o := num(m[0])
			dat := f.Slice(num(m[1]) * 20)
			for i := 0; i < len(dat); i += 20 {
				if dat[i+17] != 'n' {
					r[o] = 0, false
				} else {
					r[o] = num(dat[i : i+10])
				}
				o++
			}
		}
	}
	return r
}

func Token(f fancy.Reader) ([]byte, int64) {
again:
	c := skipSpaces(f)
	if c == 0 {
		return []byte{}, -1
	}
	p := fpos(f) - 1
	switch c {
	case '%':
		skipComment(f)
		goto again
	case '<', '[', '{':
		skipComposite(f)
	case '(':
		skipString(f)
	default:
		if skipToDelim(f) != 255 {
			f.UnreadByte()
		}
	}
	n := int(fpos(f) - p)
	f.Seek(p, 0)
	return f.Slice(n), p
}

func fpos(f fancy.Reader) int64 {
	r, _ := f.Seek(0, 1)
	return r
}