package strconv

using import "core:decimal"

Int_Flag :: enum {
	Prefix,
	Plus,
	Space,
}
Int_Flags :: bit_set[Int_Flag];


parse_bool :: proc(s: string) -> (result: bool = false, ok: bool) {
	switch s {
	case "1", "t", "T", "true", "TRUE", "True":
		return true, true;
	case "0", "f", "F", "false", "FALSE", "False":
		return false, true;
	}
	return;
}

_digit_value :: proc(r: rune) -> int {
	ri := int(r);
	v: int = 16;
	switch r {
	case '0'..'9': v = ri-'0';
	case 'a'..'z': v = ri-'a'+10;
	case 'A'..'Z': v = ri-'A'+10;
	}
	return v;
}

parse_i64 :: proc(s: string) -> i64 {
	neg := false;
	if len(s) > 1 {
		switch s[0] {
		case '-':
			neg = true;
			s = s[1:];
		case '+':
			s = s[1:];
		}
	}


	base: i64 = 10;
	if len(s) > 2 && s[0] == '0' {
		switch s[1] {
		case 'b': base =  2;  s = s[2:];
		case 'o': base =  8;  s = s[2:];
		case 'd': base = 10;  s = s[2:];
		case 'z': base = 12;  s = s[2:];
		case 'x': base = 16;  s = s[2:];
		}
	}


	value: i64;
	for r in s {
		if r == '_' {
			continue;
		}

		v := i64(_digit_value(r));
		if v >= base {
			break;
		}
		value *= base;
		value += v;
	}

	if neg do return -value;
	return value;
}

parse_u64 :: proc(s: string) -> u64 {
	neg := false;
	if len(s) > 1 && s[0] == '+' {
		s = s[1:];
	}


	base := u64(10);
	if len(s) > 2 && s[0] == '0' {
		switch s[1] {
		case 'b': base =  2;  s = s[2:];
		case 'o': base =  8;  s = s[2:];
		case 'd': base = 10;  s = s[2:];
		case 'z': base = 12;  s = s[2:];
		case 'x': base = 16;  s = s[2:];
		}
	}


	value: u64;
	for r in s {
		if r == '_' do continue;
		v := u64(_digit_value(r));
		if v >= base do break;
		value *= base;
		value += u64(v);
	}

	if neg do return -value;
	return value;
}


parse_int :: proc(s: string) -> int {
	return int(parse_i64(s));
}
parse_uint :: proc(s: string, base: int) -> uint {
	return uint(parse_u64(s));
}

parse_f32 :: proc(s: string) -> f32 {
	return f32(parse_f64(s));
}


parse_f64 :: proc(s: string) -> f64 {
	if s == "" {
		return 0;
	}
	i := 0;

	sign: f64 = 1;
	switch s[i] {
	case '-': i += 1; sign = -1;
	case '+': i += 1;
	}

	value: f64 = 0;
	for ; i < len(s); i += 1 {
		r := rune(s[i]);
		if r == '_' do continue;

		v := _digit_value(r);
		if v >= 10 do break;
		value *= 10;
		value += f64(v);
	}

	if i < len(s) && s[i] == '.' {
		pow10: f64 = 10;
		i += 1;

		for ; i < len(s); i += 1 {
			r := rune(s[i]);
			if r == '_' do continue;

			v := _digit_value(r);
			if v >= 10 do break;
			value += f64(v)/pow10;
			pow10 *= 10;
		}
	}

	frac := false;
	scale: f64 = 1;

	if i < len(s) && (s[i] == 'e' || s[i] == 'E') {
		i += 1;

		if i < len(s) {
			switch s[i] {
			case '-': i += 1; frac = true;
			case '+': i += 1;
			}

			exp: u32 = 0;
			for ; i < len(s); i += 1 {
				r := rune(s[i]);
				if r == '_' do continue;

				d := u32(_digit_value(r));
				if d >= 10 do break;
				exp = exp * 10 + d;
			}
			if exp > 308 { exp = 308; }

			for exp >= 50 { scale *= 1e50; exp -= 50; }
			for exp >=  8 { scale *=  1e8; exp -=  8; }
			for exp >   0 { scale *=   10; exp -=  1; }
		}
	}

	if frac do return sign * (value/scale);
	return sign * (value*scale);
}


append_bool :: proc(buf: []byte, b: bool) -> string {
	n := 0;
	if b do n = copy(buf, cast([]byte)"true");
	else do n = copy(buf, cast([]byte)"false");
	return string(buf[:n]);
}

append_uint :: proc(buf: []byte, u: u64, base: int) -> string {
	return append_bits(buf, u64(u), base, false, 8*size_of(uint), digits, nil);
}
append_int :: proc(buf: []byte, i: i64, base: int) -> string {
	return append_bits(buf, u64(i), base, true, 8*size_of(int), digits, nil);
}
itoa :: proc(buf: []byte, i: int) -> string do return append_int(buf, i64(i), 10);

append_float :: proc(buf: []byte, f: f64, fmt: byte, prec, bit_size: int) -> string {
	return string(generic_ftoa(buf, f, fmt, prec, bit_size));
}




DecimalSlice :: struct {
	digits:        []byte,
	count:         int,
	decimal_point: int,
	neg:           bool,
}

FloatInfo :: struct {
	mantbits: uint,
	expbits:  uint,
	bias:     int,
}


_f16_info := FloatInfo{10, 5,   -15};
_f32_info := FloatInfo{23, 8,  -127};
_f64_info := FloatInfo{52, 11, -1023};


generic_ftoa :: proc(buf: []byte, val: f64, fmt: byte, prec, bit_size: int) -> []byte {
	bits: u64;
	flt: ^FloatInfo;
	switch bit_size {
	case 32:
		bits = u64(transmute(u32)f32(val));
		flt = &_f32_info;
	case 64:
		bits = transmute(u64)val;
		flt = &_f64_info;
	case:
		panic("strconv: invalid bit_size");
	}

	neg  := bits>>(flt.expbits+flt.mantbits) != 0;
	exp  := int(bits>>flt.mantbits) & (1<<flt.expbits - 1);
	mant := bits & (u64(1) << flt.mantbits - 1);

	switch exp {
	case 1<<flt.expbits - 1:
		s: string;
		if mant != 0 {
			s = "NaN";
		} else if neg {
			s = "-Inf";
		} else {
			s = "+Inf";
		}
		n := copy(buf, cast([]byte)s);
		return buf[:n];

	case 0: // denormalized
		exp += 1;

	case:
		mant |= u64(1) << flt.mantbits;
	}

	exp += flt.bias;

	d_: Decimal;
	d := &d_;
	assign(d, mant);
	shift(d, exp - int(flt.mantbits));
	digs: DecimalSlice;
	shortest := prec < 0;
	if shortest {
		round_shortest(d, mant, exp, flt);
		digs = DecimalSlice{digits = d.digits[:], count = d.count, decimal_point = d.decimal_point};
		switch fmt {
		case 'e', 'E': prec = digs.count-1;
		case 'f', 'F': prec = max(digs.count-digs.decimal_point, 0);
		case 'g', 'G': prec = digs.count;
		}
	} else {
		switch fmt {
		case 'e', 'E': round(d, prec+1);
		case 'f', 'F': round(d, d.decimal_point+prec);
		case 'g', 'G':
			if prec == 0 {
				prec = 1;
			}
			round(d, prec);
		}

		digs = DecimalSlice{digits = d.digits[:], count = d.count, decimal_point = d.decimal_point};
	}
	return format_digits(buf, shortest, neg, digs, prec, fmt);
}



format_digits :: proc(buf: []byte, shortest: bool, neg: bool, digs: DecimalSlice, prec: int, fmt: byte) -> []byte {
	Buffer :: struct {
		b: []byte,
		n: int,
	}

	to_bytes :: proc(b: Buffer) -> []byte do return b.b[:b.n];
	add_bytes :: proc(buf: ^Buffer, bytes: ..byte) {
		buf.n += copy(buf.b[buf.n:], bytes);
	}

	b := Buffer{b = buf};

	switch fmt {
	case 'f', 'F':
		add_bytes(&b, neg ? '-' : '+');

		// integer, padded with zeros when needed
		if digs.decimal_point > 0 {
			m := min(digs.count, digs.decimal_point);
			add_bytes(&b, ..digs.digits[0:m]);
			for ; m < digs.decimal_point; m += 1 {
				add_bytes(&b, '0');
			}
		} else {
			add_bytes(&b, '0');
		}


		// fractional part
		if prec > 0 {
			add_bytes(&b, '.');
			for i in 0..prec-1 {
				c: byte = '0';
				if j := digs.decimal_point + i; 0 <= j && j < digs.count {
					c = digs.digits[j];
				}
				add_bytes(&b, c);
			}
		}
		return to_bytes(b);

	case 'e', 'E':
		panic("strconv: e/E float printing is not yet supported");
		return to_bytes(b); // TODO

	case 'g', 'G':
		panic("strconv: g/G float printing is not yet supported");
		return to_bytes(b); // TODO

	case:
		add_bytes(&b, '%', fmt);
		return to_bytes(b);
	}


}

round_shortest :: proc(d: ^Decimal, mant: u64, exp: int, flt: ^FloatInfo) {
	if mant == 0 { // If mantissa is zero, the number is zero
		d.count = 0;
		return;
	}

	/*
		10^(dp-nd) > 2^(exp-mantbits)
		log2(10) * (dp-nd) > exp-mantbits
		log(2) >~ 0.332
		332*(dp-nd) >= 100*(exp-mantbits)
	 */
	minexp := flt.bias+1;
	if exp > minexp && 332*(d.decimal_point-d.count) >= 100*(exp - int(flt.mantbits)) {
		// Number is already its shortest
		return;
	}

	upper_: Decimal; upper := &upper_;
	assign(upper, 2*mant - 1);
	shift(upper, exp - int(flt.mantbits) - 1);

	mantlo: u64;
	explo:  int;
	if mant > 1<<flt.mantbits || exp == minexp {
		mantlo = mant-1;
		explo = exp;
	} else {
		mantlo = 2*mant - 1;
		explo = exp-1;
	}
	lower_: Decimal; lower := &lower_;
	assign(lower, 2*mantlo + 1);
	shift(lower, explo - int(flt.mantbits) - 1);

	inclusive := mant%2 == 0;

	for i in 0..d.count-1 {
		l: byte = '0'; // lower digit
		if i < lower.count {
			l = lower.digits[i];
		}
		m := d.digits[i];   // middle digit
		u: byte = '0'; // upper digit
		if i < upper.count {
			u = upper.digits[i];
		}

		ok_round_down := l != m || inclusive && i+1 == lower.count;
		ok_round_up   := m != u && (inclusive || m+1 < u || i+1 < upper.count);

		if ok_round_down && ok_round_up {
			round(d, i+1);
			return;
		}
		if ok_round_down {
			round_down(d, i+1);
			return;
		}
		if ok_round_up {
			round_up(d, i+1);
			return;
		}
	}

}

MAX_BASE :: 32;
digits := "0123456789abcdefghijklmnopqrstuvwxyz";


is_integer_negative :: proc(u: u64, is_signed: bool, bit_size: int) -> (unsigned: u64, neg: bool) {
	if is_signed {
		switch bit_size {
		case 8:
			i := i8(u);
			neg = i < 0;
			u = u64(abs(i));
		case 16:
			i := i16(u);
			neg = i < 0;
			u = u64(abs(i));
		case 32:
			i := i32(u);
			neg = i < 0;
			u = u64(abs(i));
		case 64:
			i := i64(u);
			neg = i < 0;
			u = u64(abs(i));
		case:
			panic("is_integer_negative: Unknown integer size");
		}
	}
	return u, neg;
}

append_bits :: proc(buf: []byte, u: u64, base: int, is_signed: bool, bit_size: int, digits: string, flags: Int_Flags) -> string {
	if base < 2 || base > MAX_BASE {
		panic("strconv: illegal base passed to append_bits");
	}

	neg: bool;
	a: [129]byte;
	i := len(a);
	u, neg = is_integer_negative(u, is_signed, bit_size);
	b := u64(base);
	for u >= b {
		i-=1; a[i] = digits[u % b];
		u /= b;
	}
	i-=1; a[i] = digits[u % b];

	if Int_Flag.Prefix in flags {
		ok := true;
		switch base {
		case  2: i-=1; a[i] = 'b';
		case  8: i-=1; a[i] = 'o';
		case 10: i-=1; a[i] = 'd';
		case 12: i-=1; a[i] = 'z';
		case 16: i-=1; a[i] = 'x';
		case: ok = false;
		}
		if ok {
			i-=1; a[i] = '0';
		}
	}

	switch {
	case neg:
		i-=1; a[i] = '-';
	case Int_Flag.Plus in flags:
		i-=1; a[i] = '+';
	case Int_Flag.Space in flags:
		i-=1; a[i] = ' ';
	}

	out := a[i:];
	copy(buf, out);
	return string(buf[0:len(out)]);
}