use nom::{

    branch::alt,

    bytes::complete::{escaped_transform, is_not, tag, take_while, take_while1},

    character::{is_alphanumeric, is_digit, is_space},

    combinator::{map, map_res},

    multi::separated_list,

    sequence::{delimited, pair, preceded, separated_pair},

    IResult,

};

use std::collections::HashMap;

type HaskellResult<'a, T> = IResult<&'a [u8], T, ()>;

#[derive(Debug, PartialEq)]

pub enum HaskellValue {

    List(Vec<HaskellValue>),

    Tuple(Vec<HaskellValue>),

    String(String),

    Number(u8),

    Struct {

        name: String,

        fields: HashMap<String, HaskellValue>,

    },

    AnonStruct {

        name: String,

        fields: Vec<HaskellValue>,

    },

}

fn comma(input: &[u8]) -> HaskellResult<&[u8]> {

    delimited(take_while(is_space), tag(","), take_while(is_space))(input)

}

fn surrounded<'a, P, O>(

    prefix: &'static str,

    suffix: &'static str,

    parser: P,

) -> impl Fn(&'a [u8]) -> HaskellResult<'a, O>

where

    P: Fn(&'a [u8]) -> HaskellResult<'a, O>,

{

    move |input| {

        delimited(

            delimited(take_while(is_space), tag(prefix), take_while(is_space)),

            |i| parser(i),

            delimited(take_while(is_space), tag(suffix), take_while(is_space)),

        )(input)

    }

}

fn number_raw(input: &[u8]) -> HaskellResult<u8> {

    use std::str::FromStr;

    map_res(take_while(is_digit), |s| {

        std::str::from_utf8(s)

            .map_err(|_| ())

            .and_then(|s| u8::from_str(s).map_err(|_| ()))

    })(input)

}

fn number(input: &[u8]) -> HaskellResult<HaskellValue> {

    map(number_raw, HaskellValue::Number)(input)

}

const BYTES: &[u8] = b"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29\x2a\x2b\x2c\x2d\x2e\x2f\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39\x3a\x3b\x3c\x3d\x3e\x3f\x40\x41\x42\x43\x44\x45\x46\x47\x48\x49\x4a\x4b\x4c\x4d\x4e\x4f\x50\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a\x5b\x5c\x5d\x5e\x5f\x60\x61\x62\x63\x64\x65\x66\x67\x68\x69\x6a\x6b\x6c\x6d\x6e\x6f\x70\x71\x72\x73\x74\x75\x76\x77\x78\x79\x7a\x7b\x7c\x7d\x7e\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff";

fn string_escape(input: &[u8]) -> HaskellResult<&[u8]> {

    alt((

        map(number_raw, |n| &BYTES[n as usize..(n + 1) as usize]),

        alt((

            map(tag("\\"), |_| &b"\\"[..]),

            map(tag("\""), |_| &b"\""[..]),

            map(tag("'"), |_| &b"'"[..]),

            map(tag("n"), |_| &b"\n"[..]),

            map(tag("r"), |_| &b"\r"[..]),

            map(tag("t"), |_| &b"\t"[..]),

            map(tag("a"), |_| &b"\x07"[..]),

            map(tag("b"), |_| &b"\x08"[..]),

            map(tag("v"), |_| &b"\x0B"[..]),

            map(tag("f"), |_| &b"\x0C"[..]),

            map(tag("NUL"), |_| &b"\x00"[..]),

            map(tag("SOH"), |_| &b"\x01"[..]),

            map(tag("STX"), |_| &b"\x02"[..]),

            map(tag("ETX"), |_| &b"\x03"[..]),

            map(tag("EOT"), |_| &b"\x04"[..]),

            map(tag("ENQ"), |_| &b"\x05"[..]),

            map(tag("ACK"), |_| &b"\x06"[..]),

        )),

        alt((

            map(tag("SO"), |_| &b"\x0E"[..]),

            map(tag("SI"), |_| &b"\x0F"[..]),

            map(tag("DLE"), |_| &b"\x10"[..]),

            map(tag("DC1"), |_| &b"\x11"[..]),

            map(tag("DC2"), |_| &b"\x12"[..]),

            map(tag("DC3"), |_| &b"\x13"[..]),

            map(tag("DC4"), |_| &b"\x14"[..]),

            map(tag("NAK"), |_| &b"\x15"[..]),

            map(tag("SYN"), |_| &b"\x16"[..]),

            map(tag("ETB"), |_| &b"\x17"[..]),

            map(tag("CAN"), |_| &b"\x18"[..]),

            map(tag("EM"), |_| &b"\x19"[..]),

            map(tag("SUB"), |_| &b"\x1A"[..]),

            map(tag("ESC"), |_| &b"\x1B"[..]),

            map(tag("FS"), |_| &b"\x1C"[..]),

            map(tag("GS"), |_| &b"\x1D"[..]),

            map(tag("RS"), |_| &b"\x1E"[..]),

            map(tag("US"), |_| &b"\x1F"[..]),

            map(tag("SP"), |_| &b"\x20"[..]),

            map(tag("DEL"), |_| &b"\x7F"[..]),

        )),

    ))(input)

}

fn string_content(mut input: &[u8]) -> HaskellResult<String> {

    map_res(

        escaped_transform(is_not("\"\\"), '\\', string_escape),

        |bytes| String::from_utf8(bytes).map_err(|_| ()),

    )(input)

}

fn string(input: &[u8]) -> HaskellResult<HaskellValue> {

    map(surrounded("\"", "\"", string_content), HaskellValue::String)(input)

}

fn tuple(input: &[u8]) -> HaskellResult<HaskellValue> {

    map(

        surrounded("(", ")", separated_list(comma, value)),

        HaskellValue::Tuple,

    )(input)

}

fn list(input: &[u8]) -> HaskellResult<HaskellValue> {

    map(

        surrounded("[", "]", separated_list(comma, value)),

        HaskellValue::List,

    )(input)

}

fn identifier(input: &[u8]) -> HaskellResult<String> {

    map_res(take_while1(is_alphanumeric), |s| {

        std::str::from_utf8(s).map_err(|_| ()).map(String::from)

    })(input)

}

fn named_field(input: &[u8]) -> HaskellResult<(String, HaskellValue)> {

    separated_pair(

        identifier,

        delimited(take_while(is_space), tag("="), take_while(is_space)),

        value,

    )(input)

}

fn structure(input: &[u8]) -> HaskellResult<HaskellValue> {

    alt((

        map(

            pair(

                identifier,

                surrounded("{", "}", separated_list(comma, named_field)),

            ),

            |(name, mut fields)| HaskellValue::Struct {

                name,

                fields: fields.drain(..).collect(),

            },

        ),

        map(

            pair(

                identifier,

                preceded(take_while1(is_space), separated_list(comma, value)),

            ),

            |(name, mut fields)| HaskellValue::AnonStruct {

                name: name.clone(),

                fields,

            },

        ),

    ))(input)

}

fn value(input: &[u8]) -> HaskellResult<HaskellValue> {

    alt((number, string, tuple, list, structure))(input)

}

#[inline]

pub fn parse(input: &[u8]) -> HaskellResult<HaskellValue> {

    delimited(take_while(is_space), value, take_while(is_space))(input)

}

mod test {

    use super::*;

    #[test]

    fn terminals() {

        use HaskellValue::*;

        matches!(number(b"127"), Ok((_, Number(127))));

        matches!(number(b"adas"), Err(nom::Err::Error(())));

        assert_eq!(

            string(b"\"Hail \\240\\159\\166\\148!\""),

            Ok((&b""[..], String("Hail \u{1f994}!".to_string())))

        );

    }

    #[test]

    fn sequences() {

        use HaskellValue::*;

        let value = Tuple(vec![

            Number(64),

            String("text".to_string()),

            List(vec![Number(1), Number(2), Number(3)]),

        ]);

        assert_eq!(tuple(b"(64, \"text\", [1 , 2, 3])"), Ok((&b""[..], value)));

    }

    #[test]

    fn structures() {

        use HaskellValue::*;

        let value = Struct {

            name: "Hog".to_string(),

            fields: vec![

                ("name".to_string(), String("\u{1f994}".to_string())),

                ("health".to_string(), Number(100)),

            ]

            .drain(..)

            .collect(),

        };

        assert_eq!(

            structure(b"Hog {name = \"\\240\\159\\166\\148\", health = 100}"),

            Ok((&b""[..], value))

        );

        let value = AnonStruct {

            name: "Hog".to_string(),

            fields: vec![Number(100), String("\u{1f994}".to_string())],

        };

        assert_eq!(

            structure(b"Hog 100, \"\\240\\159\\166\\148\""),

            Ok((&b""[..], value))

        );

    }

}