use std::fmt;
use std::str::FromStr;

use nom::{
    Finish, IResult,
    branch::alt,
    bytes::complete::{tag, take_till1, take_while1},
    character::complete::anychar,
    combinator::{all_consuming, map, opt, verify},
    multi::many1,
    sequence::{delimited, pair, preceded, separated_pair},
};

#[derive(PartialEq, Eq, Clone, Debug)]
pub struct TokenString(Vec<Token>);

impl TokenString {
    pub fn text(text: impl Into<String>) -> Self {
        Self(vec![Token::Text(text.into())])
    }

    pub fn tokens(&self) -> impl Iterator<Item=&Token> {
        self.0.iter()
    }

    pub fn first_token_mut(&mut self) -> &mut Token {
        &mut self.0[0]
    }

    pub fn split_once(&self, delimiter: char) -> Option<(TokenString, TokenString)> {
        let mut result0 = vec![];
        let mut iter = self.0.iter();
        while let Some(t) = iter.next() {
            match t {
                Token::Text(text) if text.contains(delimiter) => {
                    let split_text = text.splitn(2, delimiter);
                    let pieces = split_text.collect::<Vec<_>>();
                    assert_eq!(pieces.len(), 2, "wrong number of pieces!");
                    result0.push(Token::Text(pieces[0].into()));
                    let mut result1 = vec![Token::Text(pieces[1].into())];
                    result1.extend(iter.cloned());
                    return Some((TokenString(result0), TokenString(result1)));
                }
                _ => result0.push(t.clone()),
            }
        }
        None
    }

    pub fn ends_with(&self, pattern: &str) -> bool {
        match self.0.last() {
            Some(Token::Text(t)) => t.ends_with(pattern),
            _ => false
        }
    }

    pub fn strip_suffix(&mut self, suffix: &str) {
        if let Some(Token::Text(t)) = self.0.last_mut() {
            if let Some(x) = t.strip_suffix(suffix) {
                *t = x.into()
            }
        }
    }

    pub fn extend(&mut self, other: TokenString) {
        self.0.extend(other.0);
    }

    pub fn trim_start(&mut self) {
        if let Some(Token::Text(t)) = self.0.first_mut() {
            *t = t.trim_start().into();
        }
    }
}

impl fmt::Display for TokenString {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        for t in &self.0 {
            write!(f, "{}", t)?;
        }
        Ok(())
    }
}

#[derive(PartialEq, Eq, Clone, Debug)]
pub enum Token {
    Text(String),
    MacroExpansion {
        name: String,
        replacement: Option<(TokenString, TokenString)>,
    },
}

impl fmt::Display for Token {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Token::Text(t) => write!(f, "{}", t),
            Token::MacroExpansion { name, replacement: None } => write!(f, "$({})", name),
            Token::MacroExpansion { name, replacement: Some((r1, r2)) } => write!(f, "$({}:{}={})", name, r1, r2),
        }
    }
}

fn macro_name(input: &str) -> IResult<&str, &str> {
    // POSIX says "periods, underscores, digits, and alphabetics from the portable character set"
    take_while1(|c: char| {
        c == '.' || c == '_' || c.is_alphanumeric()
    })(input)
}

fn macro_expansion_body<'a>(end: char) -> impl FnMut(&'a str) -> IResult<&'a str, Token> {
    let subst = preceded(tag(":"), separated_pair(tokens_but_not('='), tag("="), tokens_but_not(end)));
    map(
        pair(macro_name, opt(subst)),
        |(name, replacement)| Token::MacroExpansion { name: name.into(), replacement },
    )
}

fn parens_macro_expansion(input: &str) -> IResult<&str, Token> {
    delimited(tag("$("), macro_expansion_body(')'), tag(")"))(input)
}

fn braces_macro_expansion(input: &str) -> IResult<&str, Token> {
    delimited(tag("${"), macro_expansion_body('}'), tag("}"))(input)
}

fn tiny_macro_expansion(input: &str) -> IResult<&str, Token> {
    let raw = preceded(tag("$"), verify(anychar, |&c| c != '(' && c != '{'));
    map(raw, |c| {
        if c == '$' {
            Token::Text("$".into())
        } else {
            Token::MacroExpansion {
                name: c.to_string(),
                replacement: None,
            }
        }
    })(input)
}

fn macro_expansion(input: &str) -> IResult<&str, Token> {
    alt((tiny_macro_expansion, parens_macro_expansion, braces_macro_expansion))(input)
}

fn text(input: &str) -> IResult<&str, Token> {
    map(take_till1(|c| c == '$'), |x: &str| Token::Text(x.into()))(input)
}

fn text_but_not<'a>(end: char) -> impl FnMut(&'a str) -> IResult<&'a str, Token> {
    map(take_till1(move |c| c == '$' || c == end), |x: &str| Token::Text(x.into()))
}

fn single_token(input: &str) -> IResult<&str, Token> {
    alt((text, macro_expansion))(input)
}

fn single_token_but_not<'a>(end: char) -> impl FnMut(&'a str) -> IResult<&'a str, Token> {
    alt((text_but_not(end), macro_expansion))
}

fn empty_tokens(input: &str) -> IResult<&str, TokenString> {
    map(tag(""), |_| TokenString(vec![Token::Text(String::new())]))(input)
}

fn tokens(input: &str) -> IResult<&str, TokenString> {
    alt((map(many1(single_token), TokenString), empty_tokens))(input)
}

fn tokens_but_not<'a>(end: char) -> impl FnMut(&'a str) -> IResult<&'a str, TokenString> {
    alt((map(many1(single_token_but_not(end)), TokenString), empty_tokens))
}

fn full_text_tokens(input: &str) -> IResult<&str, TokenString> {
    all_consuming(tokens)(input)
}

pub fn tokenize(input: &str) -> TokenString {
    // TODO handle errors gracefully
    let (_, result) = full_text_tokens(input).expect("couldn't parse");
    result
}

impl FromStr for TokenString {
    // TODO figure out how to get nom errors working (Error<&str> doesn't work because lifetimes)
    type Err = ();

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        full_text_tokens(s).finish()
            .map(|(_, x)| x)
            .map_err(|_| ())
    }
}

#[cfg(test)]
mod test {
    use super::{Token, TokenString, tokenize};

    impl From<Vec<Token>> for TokenString {
        fn from(x: Vec<Token>) -> Self {
            TokenString(x)
        }
    }

    fn token_text(text: impl Into<String>) -> Token {
        Token::Text(text.into())
    }

    fn token_macro_expansion(name: impl Into<String>) -> Token {
        Token::MacroExpansion { name: name.into(), replacement: None }
    }

    fn token_macro_expansion_replacement(name: impl Into<String>,
                                         subst1: impl Into<TokenString>,
                                         subst2: impl Into<TokenString>) -> Token {
        Token::MacroExpansion { name: name.into(), replacement: Some((subst1.into(), subst2.into())) }
    }

    #[test]
    fn no_macros() {
        let text = "This is an example sentence! There aren't macros in it at all!";
        let tokens = tokenize(text);
        assert_eq!(tokens, TokenString(vec![token_text(text)]));
    }

    #[test]
    fn no_replacement() {
        let text = "This is a $Q sentence! There are $(BORING) macros in it at ${YEET}!";
        let tokens = tokenize(text);
        assert_eq!(tokens, TokenString(vec![
            token_text("This is a "),
            token_macro_expansion("Q"),
            token_text(" sentence! There are "),
            token_macro_expansion("BORING"),
            token_text(" macros in it at "),
            token_macro_expansion("YEET"),
            token_text("!"),
        ]));
    }

    #[test]
    fn escaped() {
        let text = "This costs $$2 to run, which isn't ideal";
        let tokens = tokenize(text);
        assert_eq!(tokens, TokenString(vec![
            token_text("This costs "),
            token_text("$"),
            token_text("2 to run, which isn't ideal"),
        ]));
    }

    #[test]
    fn replacement() {
        let text = "Can I get a $(DATA:.c=.oof) in this ${SWAG:.yolo=}";
        let tokens = tokenize(text);
        assert_eq!(tokens, TokenString(vec![
            token_text("Can I get a "),
            token_macro_expansion_replacement("DATA", vec![token_text(".c")], vec![token_text(".oof")]),
            token_text(" in this "),
            token_macro_expansion_replacement("SWAG", vec![token_text(".yolo")], vec![token_text("")]),
        ]));
    }

    #[test]
    fn hell() {
        let text = "$(OOF:${ouch:hi=hey} there=$(owie:$(my)=${bones})), bro.";
        let tokens = tokenize(text);
        assert_eq!(tokens, TokenString(vec![
            token_macro_expansion_replacement(
                "OOF",
                vec![
                    token_macro_expansion_replacement("ouch", vec![token_text("hi")], vec![token_text("hey")]),
                    token_text(" there"),
                ],
                vec![
                    token_macro_expansion_replacement(
                        "owie",
                        vec![token_macro_expansion("my")],
                        vec![token_macro_expansion("bones")],
                    ),
                ],
            ),
            token_text(", bro."),
        ]));
    }
}