use quote::{quote, ToTokens};
use syn::{
    braced, bracketed,
    parse::{discouraged::Speculative, Parse},
    punctuated::Punctuated,
    token, Token,
};

pub struct Command {
    cd: CurrentDir,
    env_vars: EnvVars,
    program: Value,
    args: Option<Punctuated<LogicArg, Token![,]>>,
}

impl Parse for Command {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let cd = input.parse()?;
        let env_vars = input.parse()?;
        let program = input.parse()?;

        if input.is_empty() {
            Ok(Self {
                cd,
                env_vars,
                program,
                args: None,
            })
        } else {
            _ = input.parse::<Token![,]>()?;
            Ok(Self {
                cd,
                env_vars,
                program,
                args: Some(Punctuated::parse_terminated(input)?),
            })
        }
    }
}

impl ToTokens for Command {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self {
            cd,
            env_vars,
            program,
            args,
        } = self;
        let program = quote! { ::std::process::Command::new(#program) };
        let args = args
            .as_ref()
            .map(Punctuated::iter)
            .map_or_else(Vec::new, Iterator::collect);

        tokens.extend(quote! {
            {
                let mut _c = #program;
                #cd
                #env_vars
                #(#args)*
                _c
            }
        });
    }
}

enum LogicArg {
    Expr(SingleArg),
    ForIter(ForIter),
    ForIn(ForIn),
    IfLet(IfLet),
    If(If),
    Match(Match),
    Closure(Closure),
}

impl Parse for LogicArg {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        if input.peek(Token![for]) {
            let pat_fork = input.fork();
            _ = pat_fork.parse::<Token![for]>()?;

            if pat_fork.call(syn::Pat::parse_single).is_ok() && pat_fork.peek(Token![in]) {
                input.parse().map(Self::ForIn)
            } else {
                input.parse().map(Self::ForIter)
            }
        } else if input.peek(Token![if]) {
            if input.peek2(Token![let]) {
                input.parse().map(Self::IfLet)
            } else {
                input.parse().map(Self::If)
            }
        } else if input.peek(Token![match]) {
            input.parse().map(Self::Match)
        } else if input.peek(Token![||]) {
            input.parse().map(Self::Closure)
        } else {
            input.parse().map(Self::Expr)
        }
    }
}

impl ToTokens for LogicArg {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        tokens.extend(match self {
            Self::Expr(expr) => quote! { #expr },
            Self::ForIter(for_iter) => quote! { #for_iter },
            Self::ForIn(for_in) => quote! { #for_in },
            Self::IfLet(if_let) => quote! { #if_let },
            Self::If(if_) => quote! { #if_ },
            Self::Match(match_) => quote! { #match_ },
            Self::Closure(closure) => quote! { #closure },
        });
    }
}

struct ForIter {
    expr: Value,
}

impl Parse for ForIter {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        _ = input.parse::<Token![for]>()?;
        let expr = input.parse()?;

        Ok(Self { expr })
    }
}

impl ToTokens for ForIter {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let expr = &self.expr;

        tokens.extend(quote! {
            for _a in #expr {
                _c.arg(_a);
            }
        });
    }
}

struct ForIn {
    pattern: syn::Pat,
    iter: Value,
    args: Arguments,
}

impl Parse for ForIn {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        _ = input.parse::<Token![for]>()?;
        let pattern = input.call(syn::Pat::parse_single)?;
        _ = input.parse::<Token![in]>()?;
        let iter = input.parse()?;
        _ = input.parse::<Token![=>]>()?;
        let args = input.parse()?;

        Ok(Self {
            pattern,
            iter,
            args,
        })
    }
}

impl ToTokens for ForIn {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self {
            pattern,
            iter,
            args,
        } = self;

        tokens.extend(quote! {
            for #pattern in #iter {
                #args
            }
        });
    }
}

struct IfLet {
    pattern: syn::Pat,
    expr: Value,
    args: Arguments,
}

impl Parse for IfLet {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        _ = input.parse::<Token![if]>()?;
        _ = input.parse::<Token![let]>()?;
        let pattern = input.call(syn::Pat::parse_single)?;
        _ = input.parse::<Token![=]>()?;
        let expr = input.parse()?;
        _ = input.parse::<Token![=>]>()?;
        let args = input.parse()?;

        Ok(Self {
            pattern,
            expr,
            args,
        })
    }
}

impl ToTokens for IfLet {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self {
            pattern,
            expr,
            args,
        } = &self;

        tokens.extend(quote! {
            if let #pattern = #expr {
                #args
            }
        });
    }
}

struct If {
    expr: Value,
    args: Arguments,
}

impl Parse for If {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        _ = input.parse::<Token![if]>()?;
        let expr = input.parse()?;
        _ = input.parse::<Token![=>]>()?;
        let args = input.parse()?;

        Ok(Self { expr, args })
    }
}

impl ToTokens for If {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self { expr, args } = self;

        tokens.extend(quote! {
            if #expr {
                #args
            }
        });
    }
}

struct Match {
    expr: Value,
    match_arms: Punctuated<MatchArm, Token![,]>,
}

impl Parse for Match {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        _ = input.parse::<Token![match]>()?;
        let expr = input.parse()?;
        let arms;
        braced!(arms in input);
        let match_arms = Punctuated::parse_terminated(&arms)?;

        Ok(Self { expr, match_arms })
    }
}

impl ToTokens for Match {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self { expr, match_arms } = self;
        let match_arms = match_arms.iter();

        tokens.extend(quote! {
            match #expr {
                #(#match_arms)*
            }
        });
    }
}

struct MatchArm {
    pattern: syn::Pat,
    if_expr: Option<Value>,
    args: Arguments,
}

impl Parse for MatchArm {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let pattern = input.call(syn::Pat::parse_multi)?;
        let if_expr = if input.peek(Token![if]) {
            _ = input.parse::<Token![if]>()?;
            Some(input.parse()?)
        } else {
            None
        };
        _ = input.parse::<Token![=>]>()?;
        let args = input.parse()?;

        Ok(Self {
            pattern,
            if_expr,
            args,
        })
    }
}

impl ToTokens for MatchArm {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self {
            pattern,
            if_expr,
            args,
        } = self;

        tokens.extend(if_expr.as_ref().map_or_else(
            || {
                quote! {
                    #pattern => {
                        #args
                    }
                }
            },
            |if_expr| {
                quote! {
                    #pattern if #if_expr => {
                        #args
                    }
                }
            },
        ));
    }
}

struct Closure(syn::Expr);

impl Parse for Closure {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        _ = input.parse::<Token![||]>()?;

        input.parse().map(Self)
    }
}

impl ToTokens for Closure {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self(block) = self;

        tokens.extend(quote! {
            let _fn = || #block;
            for _a in _fn() {
                _c.arg(_a);
            }
        });
    }
}

enum Arguments {
    Single(SingleArg),
    Multi(MultiArg),
}

impl Parse for Arguments {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        if input.peek(token::Bracket) {
            input.parse().map(Self::Multi)
        } else {
            input.parse().map(Self::Single)
        }
    }
}

impl ToTokens for Arguments {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        tokens.extend(match self {
            Self::Single(arg) => quote! { #arg },
            Self::Multi(args) => quote! { #args },
        });
    }
}

struct MultiArg(Punctuated<SingleArg, Token![,]>);

impl Parse for MultiArg {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let args;
        bracketed!(args in input);

        Punctuated::parse_terminated(&args).map(Self)
    }
}

impl ToTokens for MultiArg {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let args = self.0.iter().collect::<Vec<_>>();

        tokens.extend(quote! { #(#args)* });
    }
}

struct SingleArg(Value);

impl Parse for SingleArg {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        input.parse().map(Self)
    }
}

impl ToTokens for SingleArg {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let arg = &self.0;
        tokens.extend(quote! {
            _c.arg(#arg);
        });
    }
}

struct EnvVars(Option<Punctuated<EnvVar, Token![,]>>);

impl Parse for EnvVars {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let fork = input.fork();
        let ident = fork.cursor().ident();

        match ident {
            Some((ident, _)) if ident == "env" => {
                _ = fork.parse::<syn::Ident>()?;
                let envs;
                braced!(envs in fork);
                Punctuated::parse_terminated(&envs)
                    .and_then(|envs| {
                        _ = fork.parse::<Token![;]>()?;
                        input.advance_to(&fork);
                        Ok(Self(Some(envs)))
                    })
                    .or_else(|_| Ok(Self(None)))
            }
            _ => Ok(Self(None)),
        }
    }
}

impl ToTokens for EnvVars {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self(envs) = self;
        let envs = envs
            .as_ref()
            .map_or_else(Vec::new, |envs| envs.iter().collect());

        tokens.extend(quote! {
            #(#envs)*
        });
    }
}

struct EnvVar {
    key: Value,
    value: Value,
}

impl Parse for EnvVar {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let key = input.parse()?;
        _ = input.parse::<Token![:]>()?;
        let value = input.parse()?;

        Ok(Self { key, value })
    }
}

impl ToTokens for EnvVar {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self { key, value } = self;

        tokens.extend(quote! { _c.env(#key, #value); });
    }
}

struct CurrentDir(Option<Value>);

impl Parse for CurrentDir {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let fork = input.fork();
        let ident = fork.cursor().ident();

        match ident {
            Some((ident, _)) if ident == "cd" => {
                _ = fork.parse::<syn::Ident>();
                fork.parse()
                    .and_then(|value| {
                        _ = fork.parse::<Token![;]>()?;
                        input.advance_to(&fork);
                        Ok(Self(Some(value)))
                    })
                    .or_else(|_| Ok(Self(None)))
            }
            _ => Ok(Self(None)),
        }
    }
}

impl ToTokens for CurrentDir {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let Self(cd) = self;
        let cd = cd.iter();

        tokens.extend(quote! { #(_c.current_dir(#cd);)* });
    }
}

enum Value {
    Lit(syn::Lit),
    Ident(syn::Ident),
    Expr(syn::Expr),
}

impl Parse for Value {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let expr_fork = input.fork();
        expr_fork
            .parse()
            .map(|expr| {
                input.advance_to(&expr_fork);
                Self::Expr(expr)
            })
            .or_else(|_| {
                if input.peek(syn::Ident) {
                    input.parse().map(Self::Ident)
                } else if input.peek(syn::Lit) {
                    input.parse().map(Self::Lit)
                } else {
                    Err(syn::Error::new(
                        input.span(),
                        "Expected an expression, ident, or literal",
                    ))
                }
            })
    }
}

impl ToTokens for Value {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        tokens.extend(match self {
            Self::Lit(lit) => quote! { #lit },
            Self::Ident(ident) => quote! { #ident },
            Self::Expr(expr) => quote! { #expr },
        });
    }
}