/// Defines whitespace characters including space and tab.
WHITESPACE = { " " | "\t" }
/// A sequence of one or more whitespace characters.
SPACE = { WHITESPACE+ }
/// Represents a newline character.
NEWLINE = { "\n" }
/// Defines the format for the title of a book, which starts with "Book", followed by a number,
/// an optional space, quoted text for the title, and ends with a newline.
book_title = { "Book " ~ book_num ~ ":" ~ SPACE? ~ quoted_text ~ NEWLINE }
/// Defines the format for the publication year of a book, which starts with "Publication Year:",
/// followed by an optional space, a year, and ends with a newline.
publication_year = { "Publication Year:" ~ SPACE? ~ year ~ NEWLINE }
/// Specifies the format for a book's price, which starts with "Price:", followed by an optional space,
/// a number, an optional space, a currency code, and ends with a newline.
price = { "Price:" ~ SPACE? ~ number ~ SPACE? ~ currency ~ NEWLINE }
/// Represents the format for a book's rating, which starts with "Rating:", followed by an optional space,
/// a rating value, and ends with a newline.
rating = { "Rating:" ~ SPACE? ~ rating_value ~ NEWLINE }
/// Matches a sequence of alphabetic characters representing a currency code.
currency = @{ ASCII_ALPHA+ }
/// Matches a sequence of digits representing a year.
year = @{ ASCII_DIGIT+ }
/// Matches a sequence of digits representing a book number.
book_num = @{ ASCII_DIGIT+ }
/// Matches a number, which can optionally include a negative sign and a decimal part.
number = @{ ("-"? ~ ASCII_DIGIT+) ~ (("." ~ ASCII_DIGIT+)?) }
/// Matches quoted text, which starts and ends with double quotes and can include any characters
/// except another double quote.
quoted_text = { "\"" ~ (!"\"" ~ ANY)* ~ "\"" }
/// Matches a numeric rating value from 0 to 10, optionally with a decimal part.
rating_value = @{ ("0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | "10") ~ ("." ~ ASCII_DIGIT+)? }
/// Defines a list of authors, which starts with "Authors:", followed by an optional space,
/// square brackets containing one or more authors separated by commas, and ends with a newline.
list_of_authors = { "Authors:" ~ SPACE? ~ "[" ~ SPACE? ~ (author ~ ("," ~ SPACE? ~ author)*)? ~ SPACE? ~ "]" ~ NEWLINE }
/// Matches a single author's name, which can include any characters except a comma or square brackets.
author = @{ (!"," ~ !"[" ~ !"]" ~ ANY)+ }
/// Defines a list of genres, which starts with "Genres:", followed by an optional space,
/// square brackets containing one or more genres separated by commas, and ends with a newline.
list_of_genres = { "Genres:" ~ SPACE? ~ "[" ~ SPACE? ~ (genre_item ~ ("," ~ SPACE? ~ genre_item)*)? ~ SPACE? ~ "]" ~ NEWLINE }
/// Matches a single genre item, which can include any characters except a comma or square brackets.
genre_item = { (!"," ~ !"[" ~ !"]" ~ ANY)+ }
/// Defines the structure of a single book entry, which includes a title, a list of authors,
/// a list of genres, a publication year, a rating, and a price.
book = { book_title ~ list_of_authors ~ list_of_genres ~ publication_year ~ rating ~ price }
/// Represents a collection of books, each separated by one or more newlines, with a final book entry at the end.
books = { (book ~ NEWLINE+)* ~ book }