package toml

import (

	"unicode/utf8"

)

type utf8Err struct {

	Index int

	Size  int

}

func (u utf8Err) Zero() bool {

	return u.Size == 0

}

// Verified that a given string is only made of valid UTF-8 characters allowed

// by the TOML spec:

//

// Any Unicode character may be used except those that must be escaped:

// quotation mark, backslash, and the control characters other than tab (U+0000

// to U+0008, U+000A to U+001F, U+007F).

//

// It is a copy of the Go 1.17 utf8.Valid implementation, tweaked to exit early

// when a character is not allowed.

//

// The returned utf8Err is Zero() if the string is valid, or contains the byte

// index and size of the invalid character.

//

// quotation mark => already checked

// backslash => already checked

// 0-0x8 => invalid

// 0x9 => tab, ok

// 0xA - 0x1F => invalid

// 0x7F => invalid

func utf8TomlValidAlreadyEscaped(p []byte) (err utf8Err) {

	// Fast path. Check for and skip 8 bytes of ASCII characters per iteration.

	offset := 0

	for len(p) >= 8 {

		// Combining two 32 bit loads allows the same code to be used

		// for 32 and 64 bit platforms.

		// The compiler can generate a 32bit load for first32 and second32

		// on many platforms. See test/codegen/memcombine.go.

		first32 := uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24

		second32 := uint32(p[4]) | uint32(p[5])<<8 | uint32(p[6])<<16 | uint32(p[7])<<24

		if (first32|second32)&0x80808080 != 0 {

			// Found a non ASCII byte (>= RuneSelf).

			break

		}

		for i, b := range p[:8] {

			if invalidAscii(b) {

				err.Index = offset + i

				err.Size = 1

				return

			}

		}

		p = p[8:]

		offset += 8

	}

	n := len(p)

	for i := 0; i < n; {

		pi := p[i]

		if pi < utf8.RuneSelf {

			if invalidAscii(pi) {

				err.Index = offset + i

				err.Size = 1

				return

			}

			i++

			continue

		}

		x := first[pi]

		if x == xx {

			// Illegal starter byte.

			err.Index = offset + i

			err.Size = 1

			return

		}

		size := int(x & 7)

		if i+size > n {

			// Short or invalid.

			err.Index = offset + i

			err.Size = n - i

			return

		}

		accept := acceptRanges[x>>4]

		if c := p[i+1]; c < accept.lo || accept.hi < c {

			err.Index = offset + i

			err.Size = 2

			return

		} else if size == 2 {

		} else if c := p[i+2]; c < locb || hicb < c {

			err.Index = offset + i

			err.Size = 3

			return

		} else if size == 3 {

		} else if c := p[i+3]; c < locb || hicb < c {

			err.Index = offset + i

			err.Size = 4

			return

		}

		i += size

	}

	return

}

// Return the size of the next rune if valid, 0 otherwise.

func utf8ValidNext(p []byte) int {

	c := p[0]

	if c < utf8.RuneSelf {

		if invalidAscii(c) {

			return 0

		}

		return 1

	}

	x := first[c]

	if x == xx {

		// Illegal starter byte.

		return 0

	}

	size := int(x & 7)

	if size > len(p) {

		// Short or invalid.

		return 0

	}

	accept := acceptRanges[x>>4]

	if c := p[1]; c < accept.lo || accept.hi < c {

		return 0

	} else if size == 2 {

	} else if c := p[2]; c < locb || hicb < c {

		return 0

	} else if size == 3 {

	} else if c := p[3]; c < locb || hicb < c {

		return 0

	}

	return size

}

var invalidAsciiTable = [256]bool{

	0x00: true,

	0x01: true,

	0x02: true,

	0x03: true,

	0x04: true,

	0x05: true,

	0x06: true,

	0x07: true,

	0x08: true,

	// 0x09 TAB

	// 0x0A LF

	0x0B: true,

	0x0C: true,

	// 0x0D CR

	0x0E: true,

	0x0F: true,

	0x10: true,

	0x11: true,

	0x12: true,

	0x13: true,

	0x14: true,

	0x15: true,

	0x16: true,

	0x17: true,

	0x18: true,

	0x19: true,

	0x1A: true,

	0x1B: true,

	0x1C: true,

	0x1D: true,

	0x1E: true,

	0x1F: true,

	// 0x20 - 0x7E Printable ASCII characters

	0x7F: true,

}

func invalidAscii(b byte) bool {

	return invalidAsciiTable[b]

}

// acceptRange gives the range of valid values for the second byte in a UTF-8

// sequence.

type acceptRange struct {

	lo uint8 // lowest value for second byte.

	hi uint8 // highest value for second byte.

}

// acceptRanges has size 16 to avoid bounds checks in the code that uses it.

var acceptRanges = [16]acceptRange{

	0: {locb, hicb},

	1: {0xA0, hicb},

	2: {locb, 0x9F},

	3: {0x90, hicb},

	4: {locb, 0x8F},

}

// first is information about the first byte in a UTF-8 sequence.

var first = [256]uint8{

	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F

	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF

	xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF

	s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF

	s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF

	s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF

}

const (

	// The default lowest and highest continuation byte.

	locb = 0b10000000

	hicb = 0b10111111

	// These names of these constants are chosen to give nice alignment in the

	// table below. The first nibble is an index into acceptRanges or F for

	// special one-byte cases. The second nibble is the Rune length or the

	// Status for the special one-byte case.

	xx = 0xF1 // invalid: size 1

	as = 0xF0 // ASCII: size 1

	s1 = 0x02 // accept 0, size 2

	s2 = 0x13 // accept 1, size 3

	s3 = 0x03 // accept 0, size 3

	s4 = 0x23 // accept 2, size 3

	s5 = 0x34 // accept 3, size 4

	s6 = 0x04 // accept 0, size 4

	s7 = 0x44 // accept 4, size 4

)