use nom::branch::alt;
use nom::bytes::complete::{escaped, is_not, take, take_till, take_until, take_while};
use nom::bytes::complete::{tag, take_while1, take_while_m_n};
use nom::character::complete::{anychar, char, line_ending, newline, not_line_ending, one_of, multispace1};
use nom::character::complete::alphanumeric1 as alphanumeric;
use nom::character::is_alphabetic;
use nom::combinator::{cut, map, map_res, opt, value, verify, map_opt};
use nom::error::{ParseError, FromExternalError};
use nom::IResult;
use nom::multi::{many0, fold_many0};
use nom::number::complete::be_u16;
use nom::sequence::{delimited, preceded, terminated, tuple};

pub fn length_value(input: &[u8]) -> IResult<&[u8], &[u8]> {
    let (input, length) = be_u16(input)?;
    take(length)(input)
}

#[derive(Debug, PartialEq)]
pub struct Color {
    pub red: u8,
    pub green: u8,
    pub blue: u8,
}

pub enum ScriptMeta {
    Comment(String),
    Element(String),
    Meta(String),
}

pub fn from_hex(input: &str) -> Result<u8, std::num::ParseIntError> {
    u8::from_str_radix(input, 16)
}

pub fn is_hex_digit(c: char) -> bool {
    c.is_digit(16)
}

pub fn hex_primary(input: &str) -> IResult<&str, u8> {
    map_res(
        take_while_m_n(2, 2, is_hex_digit),
        from_hex,
    )(input)
}

pub fn hex_color(input: &str) -> IResult<&str, Color> {
    let (input, _) = tag("#")(input)?;
    let (input, (red, green, blue)) = tuple((hex_primary, hex_primary, hex_primary))(input)?;

    Ok((input, Color { red, green, blue }))
}

pub fn scope<'a, E: ParseError<&'a str>>(input: &'a str) -> IResult<&'a str, &'a str> {

    let (input, _) = delimited(opt(sp), delimited(char('{'), is_not("}"), char('}')), opt(sp))(input)?;
    //let (input, _) = delimited(char('{'), is_not("}"), char('}'))(input)?;

    Ok((input, input))
}

pub fn elem<'a, E: ParseError<&'a str>>(input: &'a str) -> IResult<&'a str, &'a str> {

    let (input, _) = delimited(opt(sp), tag("elem"), sp)(input)?;

    let (input, elem_name) = parse_token(input)?;

    let (input, _) = scope::<'a, E>(input)?;

    println!("elem , name : {:?} || scope : {:?}", elem_name, input);

    Ok((input, elem_name))

}

// Parse a single alphanumeric token delimited by spaces
fn parse_token<'a, E: ParseError<&'a str>>(i: &'a str) -> IResult<&'a str, &'a str, E> {
    let chars = "\n";
    escaped(alphanumeric, '\\', one_of(""))(i)
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum StringFragment<'a> {
    Literal(&'a str),
    EscapedChar(char),
    EscapedWS,
}

fn parse_unicode<'a, E: ParseError<&'a str> + FromExternalError<&'a str, std::num::ParseIntError>>(input: &'a str)
                                                                                                   -> IResult<&'a str, char, E> {
    // `take_while_m_n` parses between `m` and `n` bytes (inclusive) that match
    // a predicate. `parse_hex` here parses between 1 and 6 hexadecimal numerals.
    let parse_hex = take_while_m_n(1, 6, |c: char| c.is_ascii_hexdigit());

    // `preceeded` takes a prefix parser, and if it succeeds, returns the result
    // of the body parser. In this case, it parses u{XXXX}.
    let parse_delimited_hex = preceded(
        char('u'),
        // `delimited` is like `preceded`, but it parses both a prefix and a suffix.
        // It returns the result of the middle parser. In this case, it parses
        // {XXXX}, where XXXX is 1 to 6 hex numerals, and returns XXXX
        delimited(char('{'), parse_hex, char('}')),
    );

    // `map_res` takes the result of a parser and applies a function that returns
    // a Result. In this case we take the hex bytes from parse_hex and attempt to
    // convert them to a u32.
    let parse_u32 = map_res(parse_delimited_hex, move |hex| u32::from_str_radix(hex, 16));

    // map_opt is like map_res, but it takes an Option instead of a Result. If
    // the function returns None, map_opt returns an error. In this case, because
    // not all u32 values are valid unicode code points, we have to fallibly
    // convert to char with from_u32.
    map_opt(parse_u32, |value| std::char::from_u32(value))(input)
}

/// Parse an escaped character: \n, \t, \r, \u{00AC}, etc.
fn parse_escaped_char<'a, E: ParseError<&'a str>+ FromExternalError<&'a str, std::num::ParseIntError>>(input: &'a str)
                                                                                                       -> IResult<&'a str, char, E> {
    preceded(
        char('\\'),
        // `alt` tries each parser in sequence, returning the result of
        // the first successful match
        alt((
            parse_unicode,
            // The `value` parser returns a fixed value (the first argument) if its
            // parser (the second argument) succeeds. In these cases, it looks for
            // the marker characters (n, r, t, etc) and returns the matching
            // character (\n, \r, \t, etc).
            value('\n', char('n')),
            value('\r', char('r')),
            value('\t', char('t')),
            value('\u{08}', char('b')),
            value('\u{0C}', char('f')),
            value('\\', char('\\')),
            value('/', char('/')),
            value('"', char('"')),
        )),
    )(input)
}

/// Parse a backslash, followed by any amount of whitespace. This is used later
/// to discard any escaped whitespace.
fn parse_escaped_whitespace<'a, E: ParseError<&'a str>>(
    input: &'a str,
) -> IResult<&'a str, &'a str, E> {
    preceded(char('\\'), multispace1)(input)
}

/// Parse a non-empty block of text that doesn't include \ or "
fn parse_literal<'a, E: ParseError<&'a str>>(input: &'a str) -> IResult<&'a str, &'a str, E> {
    // `is_not` parses a string of 0 or more characters that aren't one of the
    // given characters.
    let not_quote_slash = is_not("\"\\");

    // `verify` runs a parser, then runs a verification function on the output of
    // the parser. The verification function accepts out output only if it
    // returns true. In this case, we want to ensure that the output of is_not
    // is non-empty.
    verify(not_quote_slash, |s: &str| !s.is_empty())(input)
}

/// Combine parse_literal, parse_escaped_whitespace, and parse_escaped_char
/// into a StringFragment.
fn parse_fragment<'a, E: ParseError<&'a str>+ FromExternalError<&'a str, std::num::ParseIntError>>(
    input: &'a str,
) -> IResult<&'a str, StringFragment<'a>, E> {
    alt((
        // The `map` combinator runs a parser, then applies a function to the output
        // of that parser.
        map(parse_literal, StringFragment::Literal),
        map(parse_escaped_char, StringFragment::EscapedChar),
        value(StringFragment::EscapedWS, parse_escaped_whitespace),
    ))(input)
}

/// Parse a string. Use a loop of parse_fragment and push all of the fragments
/// into an output string.
fn parse_string<'a, E: ParseError<&'a str> + FromExternalError<&'a str, std::num::ParseIntError>>(input: &'a str) -> IResult<&'a str, String, E> {
    // fold_many0 is the equivalent of iterator::fold. It runs a parser in a loop,
    // and for each output value, calls a folding function on each output value.
    let build_string = fold_many0(
        // Our parser function– parses a single string fragment
        parse_fragment,
        // Our init value, an empty string
        String::new(),
        // Our folding function. For each fragment, append the fragment to the
        // string.
        |mut string, fragment| {
            match fragment {
                StringFragment::Literal(s) => string.push_str(s),
                StringFragment::EscapedChar(c) => string.push(c),
                StringFragment::EscapedWS => {}
            }
            string
        },
    );

    delimited(char('"'), build_string, char('"'))(input)
}

// Parse from a # to a newline character
pub fn comment<'a, E: ParseError<&'a str>>(input: &'a str) -> IResult<&'a str, &'a str, E> {

    let v = preceded(char('#'),
                     cut(terminated(
                         is_not("\n"),
                         newline,
                     )),
    )(input)?;

    println!("comment : # {:?}", v.1);

    Ok((v.0, v.0))
}


// Eat up whitespace characters
fn sp<'a>(i: &'a str) -> IResult<&'a str, &'a str> {
    let chars = " \t\r\n";
    take_while(move |c| chars.contains(c))(i)
}

pub fn parse_script<'a, E: ParseError<&'a str>>(input: &'a str) -> IResult<&'a str, ScriptMeta, E> {

    println!("Full input string : {:?}\n", input);

    let mut remaining_str = input;
    while remaining_str.len() > 0 {
        println!("Remaining Length : {:?}", remaining_str.len());
        println!("Remaining String: {:?}", remaining_str);
        let x = delimited(
            sp,
            alt((map(comment, |s| ScriptMeta::Comment(String::from(s))),
                 map(elem::<'a, E>, |s| ScriptMeta::Element(String::from(s)))
            )),
            opt(sp),
        )(remaining_str);
        remaining_str = x.unwrap().0;
    }

    return Ok((remaining_str, ScriptMeta::Comment(String::default())));
}


/*
// ( and any amount of bytes ). Returns the bytes between the ()
fn parens(input: &str) -> IResult<&str, &str> {
  delimited(char('('), is_not(")"), char(')'))(input)
}

// `take_while_m_n` parses between `m` and `n` bytes (inclusive) that match
// a predicate. `parse_hex` here parses between 1 and 6 hexadecimal numerals.
let parse_hex = take_while_m_n(1, 6, |c: char| c.is_ascii_hexdigit());
*/