package number

import (
	"fmt"
	"math/big"
	"strconv"
	"strings"

	"gitea.zaclys.com/bvaudour/gob/option"
)

func undefinedString(sign int) string {
	switch sign {
	case -1:
		return "-∞"
	case +1:
		return "+∞"
	default:
		return "NaN"
	}
}

func integerString(n *big.Int, base uint, sign int) string {
	out := n.Text(int(base))

	if sign < 0 {
		out = fmt.Sprintf("-%s", out)
	}

	if base != 10 {
		out = fmt.Sprintf("(%d)%s", base, out)
	}

	return out
}

func fractionString(n, d *big.Int, base uint, sign int) string {
	out := fmt.Sprintf("%s/%s", n.Text(int(base)), d.Text(int(base)))

	if sign < 0 {
		out = fmt.Sprintf("-%s", out)
	}

	if base != 10 {
		out = fmt.Sprintf("(%d)%s", base, out)
	}

	return out
}

func decimalString(n Number) string {
	base := n.Base()
	num, denom := n.num(), n.denom()
	p := pow(base, FloatingPrecision)
	num = num.mul(p)
	q := num.quo(denom)

	out := "0"
	if num.cmp(denom) >= 0 {
		if qn, ok := q.get(); ok {
			out = qn.Num().Text(int(base))
		} else {
			return ""
		}
	}

	precision := int(FloatingPrecision)
	if len(out) < precision {
		out = fmt.Sprintf("%s%s", strings.Repeat("0", precision), out)
	}

	deltaPrecision := len(out) - precision
	out = fmt.Sprintf("%s.%s", out[:deltaPrecision], out[deltaPrecision:])

	if !FixedPrecision {
		l := len(out) - 1
		for out[l] == '0' {
			out, l = out[:l], l-1
		}
		if out == "." {
			out = "0."
		}
	}

	if n.IsNeg() {
		out = fmt.Sprintf("-%s", out)
	} else if q.IsZero() && !n.IsZero() {
		out = fmt.Sprintf("+%s", out)
	}

	if base != 10 {
		out = fmt.Sprintf("(%d)%s", base, out)
	}

	return out
}

func scientificStsring(n Number) string {
	base := n.Base()
	var exponent int
	tmp := n
	if n.IsZero() {
		num, denom := n.Abs().NumDenom()
		nl, dl := num.Len(), denom.Len()
		exponent := nl - dl
		if exponent > 0 {
			denom = denom.Mul(Number{
				base: base,
				tpe:  Integer,
				atom: pow(base, exponent),
			})
		} else if exponent < 0 {
			num = num.Mul(Number{
				base: base,
				tpe:  Integer,
				atom: pow(base, -exponent),
			})
		}

		if num.Lt(denom) {
			exponent--
			num.Mul(Int(base, base))
		}
		tmp = num.Div(denom)
	}

	out := decimalString(tmp)

	signExponent := ""
	if exponent > 0 {
		signExponent = "+"
	} else if exponent < 0 {
		signExponent = "-"
	}

	if base == 10 {
		return fmt.Sprintf("%sE%s%d", out, signExponent, exponent)
	}
	return fmt.Sprintf("%s×%d^%s%d", out, base, signExponent, exponent)
}

// String retourne la représentation du nombre sous forme de chaîne de caractères.
func (n Number) String() string {
	if nb, ok := n.get(); ok {
		switch n.Type() {
		case Integer:
			return integerString(nb.Num(), n.Base(), n.Sign())
		case Fraction:
			return fractionString(nb.Num(), nb.Denom(), n.base, n.Sign())
		case Scientific:
			return scientificStsring(n)
		default:
			return decimalString(n)
		}
	}

	return undefinedString(n.Sign())
}

func parseBase(str string) (next string, base option.Option[uint]) {
	begin := strings.Index(str, "(")
	end := strings.Index(str, ")")
	if begin > end || begin < 0 || end < 0 {
		return
	}

	next = str[end+1:]
	if b, err := strconv.ParseUint(str[begin+1:end], 10, 64); err == nil && isBaseValid(b) {
		base = option.Some(uint(b))
	}
	return
}

func parseBaseN(str string) (next string, base uint) {
	next = str[1:]
	switch str[0] {
	case 'B', 'b':
		base = 2
	case 'O', 'o':
		base = 8
	default:
		base = 16
	}

	return
}

func parseSign(str string) (next string, sign int) {
	switch str[0] {
	case '-':
		next, sign = str[1:], -1
	case '+':
		next, sign = str[1:], 1
	default:
		next, sign = str, 1
	}

	return
}

func parseSignN(str string) (next string, sign int) {
	next, sign = str[1:], 1
	if str[0] == '1' {
		sign = -1
	}

	return
}

func parseNumber(str string, base uint) (n option.Option[*big.Int]) {
	if e, ok := new(big.Int).SetString(str, int(base)); ok {
		n = option.Some(e)
	}

	return
}

func setInt(str string, base uint, sign int) (n option.Option[Number]) {
	if nb, ok := parseNumber(str, base).Get(); ok {
		nn := Number{
			base: base,
			tpe:  Integer,
			atom: entire0(nb, sign),
		}
		n = option.Some(nn.format())
	}

	return
}

func parseInt(str string) (n option.Option[Number]) {
	next, base := parseBase(str)

	if b, ok := base.Get(); ok {
		next, sign := parseSign(next)
		n = setInt(next, b, sign)
	}

	return
}

func parseInt10(str string) (n option.Option[Number]) {
	next, sign := parseSign(str)

	return setInt(next, 10, sign)
}

func parseIntN(str string) (n option.Option[Number]) {
	next, sign := parseSignN(str)
	next, base := parseBaseN(next)

	return setInt(next, base, sign)
}

func setFrac(str string, base uint, sign int) (n option.Option[Number]) {
	i := strings.Index(str, "/")
	if i < 0 {
		return
	}

	sNum, sDenom := str[:i], str[i:]
	if num, ok := parseNumber(sNum, base).Get(); ok {
		if denom, ok := parseNumber(sDenom, base).Get(); ok {
			nn := Number{
				base: base,
				tpe:  Fraction,
				atom: frac0(num, denom, sign),
			}
			n = option.Some(nn.format())
		}
	}

	return
}

func parseFrac(str string) (n option.Option[Number]) {
	next, base := parseBase(str)

	if b, ok := base.Get(); ok {
		next, sign := parseSign(next)
		n = setFrac(next, b, sign)
	}

	return
}

func parseFrac10(str string) (n option.Option[Number]) {
	next, sign := parseSign(str)

	return setFrac(next, 10, sign)
}

func parseDot(str string) (next string, dot int) {
	i := strings.Index(str, ".")
	if i >= 0 {
		next = str[:i] + str[:i]
		dot = len(next) - i
	}

	return
}

func setDec(str string, base uint, sign int) (n option.Option[Number]) {
	next, dot := parseDot(str)

	if num, ok := parseNumber(next, base).Get(); ok {
		denom := pow(base, dot)
		nn := Number{
			base: base,
			tpe:  Decimal,
			atom: entire0(num, sign).div(denom),
		}
		n = option.Some(nn.format())
	}

	return
}

func parseDec(str string) (n option.Option[Number]) {
	next, base := parseBase(str)

	if b, ok := base.Get(); ok {
		next, sign := parseSign(next)
		n = setDec(next, b, sign)
	}

	return
}

func parseDec10(str string) (n option.Option[Number]) {
	next, sign := parseSign(str)

	return setDec(next, 10, sign)
}

func parseDecN(str string) (n option.Option[Number]) {
	next, sign := parseSignN(str)
	next, base := parseBaseN(next)

	return setDec(next, base, sign)
}

func parseExp(str string) (next string, baseExponent option.Option[int], exponent option.Option[int]) {
	begin := strings.Index(str, "x")
	end := strings.Index(str, "^")
	if begin > end || begin < 0 || end < 0 {
		return
	}

	sBase, sExponent := str[begin+1:end], str[end+1:]

	if b, err := strconv.Atoi(sBase); err == nil && isBaseValid(b) {
		if e, err := strconv.Atoi(sExponent); err == nil {
			next, baseExponent, exponent = str[:begin], option.Some(b), option.Some(e)
		}
	}

	return
}

func parseExp10(str string) (next string, exponent option.Option[int]) {
	i := strings.Index(strings.ToLower(str), "e")
	if i < 0 {
		return
	}

	sExponent := str[i+1:]

	if e, err := strconv.Atoi(sExponent); err == nil {
		next, exponent = str[:i], option.Some(e)
	}

	return
}

func setSci(str string, base uint, sign, baseExponent, exponent int) (n option.Option[Number]) {
	next, dot := parseDot(str)

	if num, ok := parseNumber(next, base).Get(); ok {
		denom := pow(base, dot)
		nn := Number{
			base: base,
			tpe:  Scientific,
			atom: entire0(num, sign).div(denom),
		}
		if exponent > 0 {
			nn.atom = nn.atom.mul(pow(baseExponent, exponent))
		} else if exponent < 0 {
			nn.atom = nn.atom.div(pow(baseExponent, -exponent))
		}

		n = option.Some(nn.format())
	}

	return
}

func parseSci(str string) (n option.Option[Number]) {
	next, base := parseBase(str)

	if b, ok := base.Get(); ok {
		next, sign := parseSign(next)
		next, be, e := parseExp(next)
		if baseExponent, ok := be.Get(); ok {
			if exponent, ok := e.Get(); ok {
				n = setSci(next, b, sign, baseExponent, exponent)
			}
		}
	}

	return
}

func parseSci10(str string) (n option.Option[Number]) {
	next, sign := parseSign(str)
	next, be, e := parseExp(next)

	if baseExponent, ok := be.Get(); ok {
		if exponent, ok := e.Get(); ok {
			n = setSci(next, 10, sign, baseExponent, exponent)
		}
	}

	return
}

func parseSci10Simple(str string) (n option.Option[Number]) {
	next, sign := parseSign(str)
	next, e := parseExp10(next)

	if exponent, ok := e.Get(); ok {
		n = setSci(next, 10, sign, 10, exponent)
	}

	return
}

// Parse retourne un nombre à partir d’une chaîne de caractères.
func Parse(str string) option.Option[Number] {
	switch str {
	case "+∞", "<inf>", "<+inf>":
		return option.Some(Inf())
	case "-∞", "<-inf>":
		return option.Some(NegInf())
	case "NaN", "<NaN>":
		return option.Some(Nan())
	}

	switch {
	case regInt.MatchString(str):
		return parseInt(str)
	case regInt10.MatchString(str):
		return parseInt10(str)
	case regInt2.MatchString(str), regInt8.MatchString(str), regInt16.MatchString(str):
		return parseIntN(str)
	case regFrac.MatchString(str):
		return parseFrac(str)
	case regFrac10.MatchString(str):
		return parseFrac10(str)
	case regDec.MatchString(str):
		return parseInt(str)
	case regDec10.MatchString(str):
		return parseInt10(str)
	case regDec2.MatchString(str), regDec8.MatchString(str), regDec16.MatchString(str):
		return parseIntN(str)
	case regSci.MatchString(str):
		return parseSci(str)
	case regSci10.MatchString(str):
		return parseSci10(str)
	case regSci10Simple.MatchString(str):
		return parseSci10Simple(str)
	}

	return option.None[Number]()
}

func ParseBool(b bool) Number {
	if b {
		return One()
	}
	return Zero()
}

func ToBool(n Number) bool {
	return !n.IsZero() && !n.IsNan()
}