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

use anyhow::Context;
use nom::{
    branch::alt,
    bytes::complete::{tag, take_till1, take_while1},
    character::complete::{anychar, space1},
    combinator::{all_consuming, map, opt, verify},
    multi::{many1, separated_list1},
    sequence::{delimited, pair, preceded, separated_pair},
    Finish, IResult,
};

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

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

    pub(crate) fn r#macro(name: impl Into<String>) -> Self {
        Self(vec![Token::MacroExpansion {
            name: name.into(),
            replacement: None,
        }])
    }

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

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

    pub(crate) fn split_once(&self, delimiter: char) -> Option<(Self, Self)> {
        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((Self(result0), Self(result1)));
                }
                _ => result0.push(t.clone()),
            }
        }
        None
    }

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

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

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

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

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

    pub(crate) fn trim_end(&mut self) {
        if let Some(Token::Text(t)) = self.0.last_mut() {
            *t = t.trim_end().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(crate) enum Token {
    Text(String),
    MacroExpansion {
        name: String,
        replacement: Option<(TokenString, TokenString)>,
    },
    FunctionCall {
        name: String,
        args: Vec<TokenString>,
    },
}

impl fmt::Display for Token {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Self::Text(t) => write!(f, "{}", t),
            Self::MacroExpansion {
                name,
                replacement: None,
            } => write!(f, "$({})", name),
            Self::MacroExpansion {
                name,
                replacement: Some((r1, r2)),
            } => write!(f, "$({}:{}={})", name, r1, r2),
            Self::FunctionCall { name, args } => write!(
                f,
                "$({} {})",
                name,
                args.iter()
                    .map(|x| format!("{}", x))
                    .collect::<Vec<_>>()
                    .join(", ")
            ),
        }
    }
}

fn macro_function_name(input: &str) -> IResult<&str, &str> {
    // POSIX says "periods, underscores, digits, and alphabetics from the portable character set"
    // one GNUism is a function with a - in the name
    take_while1(|c: char| c == '.' || c == '_' || c.is_alphanumeric() || c == '-')(input)
}

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

fn function_call_body<'a>(end: char) -> impl FnMut(&'a str) -> IResult<&'a str, Token> {
    map(
        separated_pair(
            macro_function_name,
            space1,
            separated_list1(tag(","), tokens_but_not(vec![',', end])),
        ),
        |(name, args)| Token::FunctionCall {
            name: name.into(),
            args,
        },
    )
}

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

fn braces_macro_expansion(input: &str) -> IResult<&str, Token> {
    delimited(
        tag("${"),
        alt((macro_expansion_body('}'), function_call_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_but_not<'a>(ends: Vec<char>) -> impl FnMut(&'a str) -> IResult<&'a str, Token> {
    map(
        take_till1(move |c| c == '$' || ends.contains(&c)),
        |x: &str| Token::Text(x.into()),
    )
}

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

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

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

fn full_text_tokens(input: &str) -> IResult<&str, TokenString> {
    all_consuming(tokens_but_not(vec![]))(input)
}

pub(crate) fn tokenize(input: &str) -> anyhow::Result<TokenString> {
    let (_, result) = full_text_tokens(input)
        .finish()
        .map_err(|err| anyhow::anyhow!(err.to_string()))
        .with_context(|| format!("couldn't parse {:?}", input))?;
    Ok(result)
}

impl FromStr for TokenString {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        tokenize(s)
    }
}

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

    type R = anyhow::Result<()>;

    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() -> R {
        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)]));
        Ok(())
    }

    #[test]
    fn no_replacement() -> R {
        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("!"),
            ])
        );
        Ok(())
    }

    #[test]
    fn escaped() -> R {
        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"),
            ])
        );
        Ok(())
    }

    #[test]
    fn replacement() -> R {
        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("")]
                ),
            ])
        );
        Ok(())
    }

    #[test]
    fn hell() -> R {
        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."),
            ])
        );
        Ok(())
    }
}