// Copyright 2020 The Libc Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package libc // import "modernc.org/libc"

import (
	"bytes"
	"fmt"
	"strconv"
	"strings"
	"unsafe"
)

const (
	modNone = iota
	modHH
	modH
	modL
	modLL
	modQ
	modCapitalL
	modJ
	modZ
	modCapitalZ
	modT
	mod32
	mod64
)

// Format of the format string
//
// The format string is a character string, beginning and ending in its initial
// shift state, if any.  The format string is composed of zero or more
// directives: ordinary  characters  (not  %), which  are  copied unchanged to
// the output stream; and conversion specifications, each of which results in
// fetching zero or more subsequent arguments.
func printf(format, args uintptr) []byte {
	format0 := format
	args0 := args
	buf := bytes.NewBuffer(nil)
	for {
		switch c := *(*byte)(unsafe.Pointer(format)); c {
		case '%':
			format = printfConversion(buf, format, &args)
		case 0:
			if dmesgs {
				dmesg("%v: %q, %#x -> %q", origin(1), GoString(format0), args0, buf.Bytes())
			}
			return buf.Bytes()
		default:
			format++
			buf.WriteByte(c)
		}
	}
}

// Each conversion specification is introduced by the character %, and ends
// with a conversion specifier.  In between there may be (in this order) zero
// or more flags, an optional minimum field width, an optional  precision  and
// an optional length modifier.
func printfConversion(buf *bytes.Buffer, format uintptr, args *uintptr) uintptr {
	format++ // '%'
	spec := "%"

	// Flags characters
	//
	// The character % is followed by zero or more of the following flags:
flags:
	for {
		switch c := *(*byte)(unsafe.Pointer(format)); c {
		case '#':
			// The value should be converted to an "alternate form".  For o conversions,
			// the first character of the output string is made zero (by prefixing a 0 if
			// it was not zero already).  For x and  X  conversions,  a nonzero result has
			// the string "0x" (or "0X" for X conversions) prepended to it.  For a, A, e,
			// E, f, F, g, and G conversions, the result will always contain a decimal
			// point, even if no digits follow it (normally, a decimal point appears in the
			// results of those conversions only if a digit follows).  For g and G
			// conversions, trailing  zeros are not removed from the result as they would
			// otherwise be.  For other conversions, the result is undefined.
			format++
			spec += "#"
		case '0':
			// The  value  should  be zero padded.  For d, i, o, u, x, X, a, A, e, E, f, F,
			// g, and G conversions, the converted value is padded on the left with zeros
			// rather than blanks.  If the 0 and - flags both appear, the 0 flag is
			// ignored.  If a precision is given with a numeric conversion (d, i, o, u, x,
			// and X), the 0 flag is ignored.  For other conversions, the  behav‐ ior is
			// undefined.
			format++
			spec += "0"
		case '-':
			// The  converted value is to be left adjusted on the field boundary.  (The
			// default is right justification.)  The converted value is padded on the right
			// with blanks, rather than on the left with blanks or zeros.  A - overrides a
			// 0 if both are given.
			format++
			spec += "-"
		case ' ':
			// A blank should be left before a positive number (or empty string) produced
			// by a signed conversion.
			format++
			spec += " "
		case '+':
			// A sign (+ or -) should always be placed before a number produced by a signed
			// conversion.  By default, a sign is used only for negative numbers.  A +
			// overrides a space  if  both  are used.
			format++
			spec += "+"
		default:
			break flags
		}
	}
	format, width, hasWidth := parseFieldWidth(format)
	if hasWidth {
		spec += strconv.Itoa(width)
	}
	format, prec, hasPrecision := parsePrecision(format, args)
	format, mod := parseLengthModifier(format)

	var str string

more:
	// Conversion specifiers
	//
	// A character that specifies the type of conversion to be applied.  The
	// conversion specifiers and their meanings are:
	switch c := *(*byte)(unsafe.Pointer(format)); c {
	case 'd', 'i':
		// The  int argument is converted to signed decimal notation.  The precision,
		// if any, gives the minimum number of digits that must appear; if the
		// converted value requires fewer digits, it is padded on the left with zeros.
		// The default precision is 1.  When 0 is printed with an explicit precision 0,
		// the output is empty.
		format++
		var arg int64
		switch mod {
		case modNone, modL, modLL, mod64:
			arg = VaInt64(args)
		case modH:
			arg = int64(int16(VaInt32(args)))
		case modHH:
			arg = int64(int8(VaInt32(args)))
		case mod32:
			arg = int64(VaInt32(args))
		default:
			panic(todo("", mod))
		}

		if arg == 0 && hasPrecision && prec == 0 {
			break
		}

		if hasPrecision {
			panic(todo("", prec))
		}

		f := spec + "d"
		str = fmt.Sprintf(f, arg)
	case 'u':
		// The unsigned int argument is converted to unsigned decimal notation. The
		// precision, if any, gives the minimum number of digits that must appear; if
		// the converted value requires fewer digits, it is padded on the left with
		// zeros.  The default precision is 1.  When 0 is printed with an explicit
		// precision 0, the output is empty.
		format++
		var arg uint64
		switch mod {
		case modNone:
			arg = uint64(VaUint32(args))
		case modL, modLL, mod64:
			arg = VaUint64(args)
		case modH:
			arg = uint64(uint16(VaInt32(args)))
		case modHH:
			arg = uint64(uint8(VaInt32(args)))
		case mod32:
			arg = uint64(VaInt32(args))
		default:
			panic(todo("", mod))
		}

		if arg == 0 && hasPrecision && prec == 0 {
			break
		}

		if hasPrecision {
			panic(todo("", prec))
		}

		f := spec + "d"
		str = fmt.Sprintf(f, arg)
	case 'o':
		// The unsigned int argument is converted to unsigned octal notation. The
		// precision, if any, gives the minimum number of digits that must appear; if
		// the converted value requires fewer digits, it is padded on the left with
		// zeros.  The default precision is 1.  When 0 is printed with an explicit
		// precision 0, the output is empty.
		format++
		var arg uint64
		switch mod {
		case modNone:
			arg = uint64(VaUint32(args))
		case modL, modLL, mod64:
			arg = VaUint64(args)
		case modH:
			arg = uint64(uint16(VaInt32(args)))
		case modHH:
			arg = uint64(uint8(VaInt32(args)))
		case mod32:
			arg = uint64(VaInt32(args))
		default:
			panic(todo("", mod))
		}

		if arg == 0 && hasPrecision && prec == 0 {
			break
		}

		if hasPrecision {
			panic(todo("", prec))
		}

		f := spec + "o"
		str = fmt.Sprintf(f, arg)
	case 'I':
		if !isWindows {
			panic(todo("%#U", c))
		}

		format++
		switch c = *(*byte)(unsafe.Pointer(format)); c {
		case 'x', 'X':
			// https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-wsprintfa
			//
			// Ix, IX
			//
			// 64-bit unsigned hexadecimal integer in lowercase or uppercase on 64-bit
			// platforms, 32-bit unsigned hexadecimal integer in lowercase or uppercase on
			// 32-bit platforms.
			if unsafe.Sizeof(int(0)) == 4 {
				mod = mod32
			}
		case '3':
			// https://en.wikipedia.org/wiki/Printf_format_string#Length_field
			//
			// I32	For integer types, causes printf to expect a 32-bit (double word) integer argument.
			format++
			switch c = *(*byte)(unsafe.Pointer(format)); c {
			case '2':
				format++
				mod = mod32
				goto more
			default:
				panic(todo("%#U", c))
			}
		case '6':
			// https://en.wikipedia.org/wiki/Printf_format_string#Length_field
			//
			// I64	For integer types, causes printf to expect a 64-bit (quad word) integer argument.
			format++
			switch c = *(*byte)(unsafe.Pointer(format)); c {
			case '4':
				format++
				mod = mod64
				goto more
			default:
				panic(todo("%#U", c))
			}
		default:
			panic(todo("%#U", c))
		}
		fallthrough
	case 'X':
		fallthrough
	case 'x':
		// The unsigned int argument is converted to unsigned hexadecimal notation.
		// The letters abcdef are used for x  conversions;  the letters ABCDEF are used
		// for X conversions.  The precision, if any, gives the minimum number of
		// digits that must appear; if the converted value requires fewer digits, it is
		// padded on the left with zeros.  The default precision is 1.  When 0 is
		// printed with an explicit precision 0, the output is empty.
		format++
		var arg uint64
		switch mod {
		case modNone:
			arg = uint64(VaUint32(args))
		case modL, modLL, mod64:
			arg = VaUint64(args)
		case modH:
			arg = uint64(uint16(VaInt32(args)))
		case modHH:
			arg = uint64(uint8(VaInt32(args)))
		case mod32:
			arg = uint64(VaInt32(args))
		default:
			panic(todo("", mod))
		}

		if arg == 0 && hasPrecision && prec == 0 {
			break
		}

		if strings.Contains(spec, "#") && arg == 0 {
			spec = strings.ReplaceAll(spec, "#", "")
		}
		var f string
		switch {
		case hasPrecision:
			f = fmt.Sprintf("%s.%d%c", spec, prec, c)
		default:
			f = spec + string(c)
		}
		str = fmt.Sprintf(f, arg)
	case 'e', 'E':
		// The double argument is rounded and converted in the style [-]d.ddde±dd where
		// there is one digit before the decimal-point character and the number of
		// digits after it is equal to  the precision;  if the precision is missing, it
		// is taken as 6; if the precision is zero, no decimal-point character appears.
		// An E conversion uses the letter E (rather than e) to intro‐ duce the
		// exponent.  The exponent always contains at least two digits; if the value is
		// zero, the exponent is 00.
		format++
		arg := VaFloat64(args)
		if !hasPrecision {
			prec = 6
		}
		f := fmt.Sprintf("%s.%d%c", spec, prec, c)
		str = fmt.Sprintf(f, arg)
	case 'f', 'F':
		// The double argument is rounded and converted to decimal notation in the
		// style [-]ddd.ddd, where the number of digits after the decimal-point
		// character  is  equal  to  the  precision specification.   If  the  precision
		// is missing, it is taken as 6; if the precision is explicitly zero, no
		// decimal-point character appears.  If a decimal point appears, at least one
		// digit appears before it.
		format++
		arg := VaFloat64(args)
		if !hasPrecision {
			prec = 6
		}
		f := fmt.Sprintf("%s.%d%c", spec, prec, c)
		str = fmt.Sprintf(f, arg)
	case 'G':
		fallthrough
	case 'g':
		// The double argument is converted in style f or e (or F or E for G
		// conversions).  The precision specifies the number of significant digits.  If
		// the precision is missing, 6 digits are given;  if the precision is zero, it
		// is treated as 1.  Style e is used if the exponent from its conversion is
		// less than -4 or greater than or equal to the precision.  Trailing zeros are
		// removed from the fractional part of the result; a decimal point appears only
		// if it is followed by at least one digit.
		format++
		arg := VaFloat64(args)
		if !hasPrecision {
			prec = 6
		}
		if prec == 0 {
			prec = 1
		}

		f := fmt.Sprintf("%s.%d%c", spec, prec, c)
		str = fmt.Sprintf(f, arg)
	case 's':
		// If  no l modifier is present: the const char * argument is expected to be a
		// pointer to an array of character type (pointer to a string).  Characters
		// from the array are written up to (but not including) a terminating null byte
		// ('\0'); if a precision is specified, no more than the number specified are
		// written.  If a precision  is  given,  no  null  byte  need  be present; if
		// the precision is not specified, or is greater than the size of the array,
		// the array must contain a terminating null byte.
		//
		// If  an  l  modifier  is  present: the const wchar_t * argument is expected
		// to be a pointer to an array of wide characters.  Wide characters from the
		// array are converted to multibyte characters (each by a call to the
		// wcrtomb(3) function, with a conversion state starting in the initial state
		// before the first wide character), up to and including a terminating null
		// wide  character.   The  resulting  multibyte  characters are written up to
		// (but not including) the terminating null byte.  If a precision is specified,
		// no more bytes than the number specified are written, but no partial
		// multibyte characters are written.  Note that the precision determines the
		// number of bytes written, not the number of wide characters or  screen
		// positions.   The  array  must contain a terminating null wide character,
		// unless a precision is given and it is so small that the number of bytes
		// written exceeds it before the end of the array is reached.
		format++
		arg := VaUintptr(args)
		switch mod {
		case modNone:
			var f string
			switch {
			case hasPrecision:
				f = fmt.Sprintf("%s.%ds", spec, prec)
				str = fmt.Sprintf(f, GoString(arg))
			default:
				f = spec + "s"
				str = fmt.Sprintf(f, GoString(arg))
			}
		default:
			panic(todo(""))
		}
	case 'p':
		// The void * pointer argument is printed in hexadecimal (as if by %#x or
		// %#lx).
		format++
		arg := VaUintptr(args)
		buf.WriteString("0x")
		buf.WriteString(strconv.FormatInt(int64(arg), 16))
	case 'c':
		// If no l modifier is present, the int argument is converted to an unsigned
		// char, and the resulting character is written.  If an l modifier is present,
		// the wint_t (wide character) ar‐ gument is converted to a multibyte sequence
		// by a call to the wcrtomb(3) function, with a conversion state starting in
		// the initial state, and the resulting multibyte string is  writ‐ ten.
		format++
		switch mod {
		case modNone:
			arg := VaInt32(args)
			buf.WriteByte(byte(arg))
		default:
			panic(todo(""))
		}
	case '%':
		// A '%' is written.  No argument is converted.  The complete conversion
		// specification is '%%'.
		format++
		buf.WriteByte('%')
	default:
		panic(todo("%#U", c))
	}

	buf.WriteString(str)
	return format
}

// Field width
//
// An optional decimal digit string (with nonzero first digit) specifying a
// minimum field width.  If the converted value has fewer characters than the
// field width, it will be padded with spa‐ ces on the left (or right, if the
// left-adjustment flag has been given).  Instead of a decimal digit string one
// may write "*" or "*m$" (for some decimal integer m) to specify that the
// field width  is  given  in the next argument, or in the m-th argument,
// respectively, which must be of type int.  A negative field width is taken as
// a '-' flag followed by a positive field width.  In no case does a
// nonexistent or small field width cause truncation of a field; if the result
// of a conversion is wider than the field width, the field is expanded to
// contain the conversion result.
func parseFieldWidth(format uintptr) (_ uintptr, n int, ok bool) {
	first := true
	for {
		var digit int
		switch c := *(*byte)(unsafe.Pointer(format)); {
		case first && c == '0':
			return format, n, ok
		case first && c == '*':
			panic(todo(""))
		case c >= '0' && c <= '9':
			format++
			ok = true
			first = false
			digit = int(c) - '0'
		default:
			return format, n, ok
		}

		n0 := n
		n = 10*n + digit
		if n < n0 {
			panic(todo(""))
		}
	}
}

// Precision
//
// An  optional precision, in the form of a period ('.')  followed by an
// optional decimal digit string.  Instead of a decimal digit string one may
// write "*" or "*m$" (for some decimal integer m) to specify that the
// precision is given in the next argument, or in the m-th argument,
// respectively, which must be of type int.  If the precision is given as just
// '.', the  precision  is taken  to  be  zero.  A negative precision is taken
// as if the precision were omitted.  This gives the minimum number of digits
// to appear for d, i, o, u, x, and X conversions, the number of digits to
// appear after the radix character for a, A, e, E, f, and F conversions, the
// maximum number of significant digits for g and G conversions, or the maximum
// number of characters to be printed from a string for s and S conversions.
func parsePrecision(format uintptr, args *uintptr) (_ uintptr, n int, ok bool) {
	for {
		switch c := *(*byte)(unsafe.Pointer(format)); c {
		case '.':
			format++
			first := true
			for {
				switch c := *(*byte)(unsafe.Pointer(format)); {
				case first && c == '*':
					format++
					n = int(VaInt32(args))
					return format, n, true
				case c >= '0' && c <= '9':
					format++
					first = false
					n0 := n
					n = 10*n + (int(c) - '0')
					if n < n0 {
						panic(todo(""))
					}
				default:
					return format, n, true
				}
			}
		default:
			return format, 0, false
		}
	}
}

// Length modifier
//
// Here, "integer conversion" stands for d, i, o, u, x, or X conversion.
//
// hh     A following integer conversion corresponds to a signed char or
// unsigned char argument, or a following n conversion corresponds to a pointer
// to a signed char argument.
//
// h      A following integer conversion corresponds to a short int or unsigned
// short int argument, or a following n conversion corresponds to a pointer to
// a short int argument.
//
// l      (ell)  A following integer conversion corresponds to a long int or
// unsigned long int argument, or a following n conversion corresponds to a
// pointer to a long int argument, or a fol‐ lowing c conversion corresponds to
// a wint_t argument, or a following s conversion corresponds to a pointer to
// wchar_t argument.
//
// ll     (ell-ell).  A following integer conversion corresponds to a long long
// int or unsigned long long int argument, or a following n conversion
// corresponds to a pointer to a long long int argument.
//
// q      A synonym for ll.  This is a nonstandard extension, derived from BSD;
// avoid its use in new code.
//
// L      A following a, A, e, E, f, F, g, or G conversion corresponds to a
// long double argument.  (C99 allows %LF, but SUSv2 does not.)
//
// j      A following integer conversion corresponds to an intmax_t or
// uintmax_t argument, or a following n conversion corresponds to a pointer to
// an intmax_t argument.
//
// z      A following integer conversion corresponds to a size_t or ssize_t
// argument, or a following n conversion corresponds to a pointer to a size_t
// argument.
//
// Z      A nonstandard synonym for z that predates the appearance of z.  Do
// not use in new code.
//
// t      A following integer conversion corresponds to a ptrdiff_t argument,
// or a following n conversion corresponds to a pointer to a ptrdiff_t
// argument.

func parseLengthModifier(format uintptr) (_ uintptr, n int) {
	switch c := *(*byte)(unsafe.Pointer(format)); c {
	case 'h':
		format++
		n = modH
		switch c := *(*byte)(unsafe.Pointer(format)); c {
		case 'h':
			format++
			n = modHH
		}
		return format, n
	case 'l':
		format++
		n = modL
		switch c := *(*byte)(unsafe.Pointer(format)); c {
		case 'l':
			format++
			n = modLL
		}
		return format, n
	case 'q':
		panic(todo(""))
	case 'L':
		panic(todo(""))
	case 'j':
		panic(todo(""))
	case 'z':
		panic(todo(""))
	case 'Z':
		panic(todo(""))
	case 't':
		panic(todo(""))
	default:
		return format, 0
	}
}