package unstable

import "github.com/pelletier/go-toml/v2/internal/characters"

func scanFollows(b []byte, pattern string) bool {

	n := len(pattern)

	return len(b) >= n && string(b[:n]) == pattern

}

func scanFollowsMultilineBasicStringDelimiter(b []byte) bool {

	return scanFollows(b, `"""`)

}

func scanFollowsMultilineLiteralStringDelimiter(b []byte) bool {

	return scanFollows(b, `'''`)

}

func scanFollowsTrue(b []byte) bool {

	return scanFollows(b, `true`)

}

func scanFollowsFalse(b []byte) bool {

	return scanFollows(b, `false`)

}

func scanFollowsInf(b []byte) bool {

	return scanFollows(b, `inf`)

}

func scanFollowsNan(b []byte) bool {

	return scanFollows(b, `nan`)

}

func scanUnquotedKey(b []byte) ([]byte, []byte) {

	// unquoted-key = 1*( ALPHA / DIGIT / %x2D / %x5F ) ; A-Z / a-z / 0-9 / - / _

	for i := 0; i < len(b); i++ {

		if !isUnquotedKeyChar(b[i]) {

			return b[:i], b[i:]

		}

	}

	return b, b[len(b):]

}

func isUnquotedKeyChar(r byte) bool {

	return (r >= 'A' && r <= 'Z') || (r >= 'a' && r <= 'z') || (r >= '0' && r <= '9') || r == '-' || r == '_'

}

func scanLiteralString(b []byte) ([]byte, []byte, error) {

	// literal-string = apostrophe *literal-char apostrophe

	// apostrophe = %x27 ; ' apostrophe

	// literal-char = %x09 / %x20-26 / %x28-7E / non-ascii

	for i := 1; i < len(b); {

		switch b[i] {

		case '\'':

			return b[:i+1], b[i+1:], nil

		case '\n', '\r':

			return nil, nil, NewParserError(b[i:i+1], "literal strings cannot have new lines")

		}

		size := characters.Utf8ValidNext(b[i:])

		if size == 0 {

			return nil, nil, NewParserError(b[i:i+1], "invalid character")

		}

		i += size

	}

	return nil, nil, NewParserError(b[len(b):], "unterminated literal string")

}

func scanMultilineLiteralString(b []byte) ([]byte, []byte, error) {

	// ml-literal-string = ml-literal-string-delim [ newline ] ml-literal-body

	// ml-literal-string-delim

	// ml-literal-string-delim = 3apostrophe

	// ml-literal-body = *mll-content *( mll-quotes 1*mll-content ) [ mll-quotes ]

	//

	// mll-content = mll-char / newline

	// mll-char = %x09 / %x20-26 / %x28-7E / non-ascii

	// mll-quotes = 1*2apostrophe

	for i := 3; i < len(b); {

		switch b[i] {

		case '\'':

			if scanFollowsMultilineLiteralStringDelimiter(b[i:]) {

				i += 3

				// At that point we found 3 apostrophe, and i is the

				// index of the byte after the third one. The scanner

				// needs to be eager, because there can be an extra 2

				// apostrophe that can be accepted at the end of the

				// string.

				if i >= len(b) || b[i] != '\'' {

					return b[:i], b[i:], nil

				}

				i++

				if i >= len(b) || b[i] != '\'' {

					return b[:i], b[i:], nil

				}

				i++

				if i < len(b) && b[i] == '\'' {

					return nil, nil, NewParserError(b[i-3:i+1], "''' not allowed in multiline literal string")

				}

				return b[:i], b[i:], nil

			}

		case '\r':

			if len(b) < i+2 {

				return nil, nil, NewParserError(b[len(b):], `need a \n after \r`)

			}

			if b[i+1] != '\n' {

				return nil, nil, NewParserError(b[i:i+2], `need a \n after \r`)

			}

			i += 2 // skip the \n

			continue

		}

		size := characters.Utf8ValidNext(b[i:])

		if size == 0 {

			return nil, nil, NewParserError(b[i:i+1], "invalid character")

		}

		i += size

	}

	return nil, nil, NewParserError(b[len(b):], `multiline literal string not terminated by '''`)

}

func scanWindowsNewline(b []byte) ([]byte, []byte, error) {

	const lenCRLF = 2

	if len(b) < lenCRLF {

		return nil, nil, NewParserError(b, "windows new line expected")

	}

	if b[1] != '\n' {

		return nil, nil, NewParserError(b, `windows new line should be \r\n`)

	}

	return b[:lenCRLF], b[lenCRLF:], nil

}

func scanWhitespace(b []byte) ([]byte, []byte) {

	for i := 0; i < len(b); i++ {

		switch b[i] {

		case ' ', '\t':

			continue

		default:

			return b[:i], b[i:]

		}

	}

	return b, b[len(b):]

}

//nolint:unparam

func scanComment(b []byte) ([]byte, []byte, error) {

	// comment-start-symbol = %x23 ; #

	// non-ascii = %x80-D7FF / %xE000-10FFFF

	// non-eol = %x09 / %x20-7F / non-ascii

	//

	// comment = comment-start-symbol *non-eol

	for i := 1; i < len(b); {

		if b[i] == '\n' {

			return b[:i], b[i:], nil

		}

		if b[i] == '\r' {

			if i+1 < len(b) && b[i+1] == '\n' {

				return b[:i+1], b[i+1:], nil

			}

			return nil, nil, NewParserError(b[i:i+1], "invalid character in comment")

		}

		size := characters.Utf8ValidNext(b[i:])

		if size == 0 {

			return nil, nil, NewParserError(b[i:i+1], "invalid character in comment")

		}

		i += size

	}

	return b, b[len(b):], nil

}

func scanBasicString(b []byte) ([]byte, bool, []byte, error) {

	// basic-string = quotation-mark *basic-char quotation-mark

	// quotation-mark = %x22            ; "

	// basic-char = basic-unescaped / escaped

	// basic-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii

	// escaped = escape escape-seq-char

	escaped := false

	i := 1

	for ; i < len(b); i++ {

		switch b[i] {

		case '"':

			return b[:i+1], escaped, b[i+1:], nil

		case '\n', '\r':

			return nil, escaped, nil, NewParserError(b[i:i+1], "basic strings cannot have new lines")

		case '\\':

			if len(b) < i+2 {

				return nil, escaped, nil, NewParserError(b[i:i+1], "need a character after \\")

			}

			escaped = true

			i++ // skip the next character

		}

	}

	return nil, escaped, nil, NewParserError(b[len(b):], `basic string not terminated by "`)

}

func scanMultilineBasicString(b []byte) ([]byte, bool, []byte, error) {

	// ml-basic-string = ml-basic-string-delim [ newline ] ml-basic-body

	// ml-basic-string-delim

	// ml-basic-string-delim = 3quotation-mark

	// ml-basic-body = *mlb-content *( mlb-quotes 1*mlb-content ) [ mlb-quotes ]

	//

	// mlb-content = mlb-char / newline / mlb-escaped-nl

	// mlb-char = mlb-unescaped / escaped

	// mlb-quotes = 1*2quotation-mark

	// mlb-unescaped = wschar / %x21 / %x23-5B / %x5D-7E / non-ascii

	// mlb-escaped-nl = escape ws newline *( wschar / newline )

	escaped := false

	i := 3

	for ; i < len(b); i++ {

		switch b[i] {

		case '"':

			if scanFollowsMultilineBasicStringDelimiter(b[i:]) {

				i += 3

				// At that point we found 3 apostrophe, and i is the

				// index of the byte after the third one. The scanner

				// needs to be eager, because there can be an extra 2

				// apostrophe that can be accepted at the end of the

				// string.

				if i >= len(b) || b[i] != '"' {

					return b[:i], escaped, b[i:], nil

				}

				i++

				if i >= len(b) || b[i] != '"' {

					return b[:i], escaped, b[i:], nil

				}

				i++

				if i < len(b) && b[i] == '"' {

					return nil, escaped, nil, NewParserError(b[i-3:i+1], `""" not allowed in multiline basic string`)

				}

				return b[:i], escaped, b[i:], nil

			}

		case '\\':

			if len(b) < i+2 {

				return nil, escaped, nil, NewParserError(b[len(b):], "need a character after \\")

			}

			escaped = true

			i++ // skip the next character

		case '\r':

			if len(b) < i+2 {

				return nil, escaped, nil, NewParserError(b[len(b):], `need a \n after \r`)

			}

			if b[i+1] != '\n' {

				return nil, escaped, nil, NewParserError(b[i:i+2], `need a \n after \r`)

			}

			i++ // skip the \n

		}

	}

	return nil, escaped, nil, NewParserError(b[len(b):], `multiline basic string not terminated by """`)

}