#![allow(non_upper_case_globals)]

use crate::{
    convalue::ConValue,
    env::Environment,
    error::{Error, IResult},
};
use std::{
    io::{stdout, Write},
    slice,
};

/// A function built into the interpreter.
#[derive(Clone, Copy)]
pub struct Builtin {
    /// An identifier to be used during registration
    pub name: &'static str,
    /// The signature, displayed when the builtin is printed
    pub desc: &'static str,
    /// The function to be run when called
    pub func: &'static dyn Fn(&mut Environment, &[ConValue]) -> IResult<ConValue>,
}

impl Builtin {
    /// Constructs a new Builtin
    pub const fn new(
        name: &'static str,
        desc: &'static str,
        func: &'static impl Fn(&mut Environment, &[ConValue]) -> IResult<ConValue>,
    ) -> Builtin {
        Builtin { name, desc, func }
    }

    pub const fn description(&self) -> &'static str {
        self.desc
    }
}

impl std::fmt::Debug for Builtin {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Builtin")
            .field("description", &self.desc)
            .finish_non_exhaustive()
    }
}

impl super::Callable for Builtin {
    fn call(&self, interpreter: &mut Environment, args: &[ConValue]) -> IResult<ConValue> {
        (self.func)(interpreter, args)
    }

    fn name(&self) -> cl_ast::Sym {
        self.name.into()
    }
}

/// Turns a function definition into a [Builtin].
///
/// ```rust
/// # use cl_interpret::{builtin2::builtin, convalue::ConValue};
/// let my_builtin = builtin! {
///     /// Use the `@env` suffix to bind the environment!
///     /// (needed for recursive calls)
///     fn my_builtin(ConValue::Bool(b), rest @ ..) @env {
///         // This is all Rust code!
///         eprintln!("my_builtin({b}, ..)");
///         match rest {
///             [] => Ok(ConValue::Empty),
///             _ => my_builtin(env, rest), // Can be called as a normal function!
///         }
///     }
/// };
/// ```
pub macro builtin(
    $(#[$($meta:tt)*])*
    fn $name:ident ($($arg:pat),*$(,)?) $(@$env:tt)? $body:block
) {{
    $(#[$($meta)*])*
    fn $name(_env: &mut Environment, _args: &[ConValue]) -> IResult<ConValue> {
        // Set up the builtin! environment
        $(let $env = _env;)?
        // Allow for single argument `fn foo(args @ ..)` pattern
        #[allow(clippy::redundant_at_rest_pattern, irrefutable_let_patterns)]
        let [$($arg),*] = _args else {
            Err($crate::error::Error::TypeError)?
        };
        $body.map(Into::into)
    }
    Builtin {
        name: stringify!($name),
        desc: stringify![builtin fn $name($($arg),*)],
        func: &$name,
    }
}}

/// Constructs an array of [Builtin]s from pseudo-function definitions
pub macro builtins($(
    $(#[$($meta:tt)*])*
    fn $name:ident ($($args:tt)*) $(@$env:tt)? $body:block
)*) {
    [$(builtin!($(#[$($meta)*])* fn $name ($($args)*) $(@$env)? $body)),*]
}

/// Creates an [Error::BuiltinDebug] using interpolation of runtime expressions.
/// See [std::format].
pub macro error_format ($($t:tt)*) {
    $crate::error::Error::BuiltinDebug(format!($($t)*))
}

pub const Builtins: &[Builtin] = &builtins![
    /// Unstable variadic format function
    fn fmt(args @ ..) {
        use std::fmt::Write;
        let mut out = String::new();
        if let Err(e) = args.iter().try_for_each(|arg| write!(out, "{arg}")) {
            eprintln!("{e}");
        }
        Ok(out)
    }

    /// Prints the arguments in-order, with no separators
    fn print(args @ ..) {
        let mut out = stdout().lock();
        args.iter().try_for_each(|arg| write!(out, "{arg}") ).ok();
        Ok(())
    }

    /// Prints the arguments in-order, followed by a newline
    fn println(args @ ..) {
        let mut out = stdout().lock();
        args.iter().try_for_each(|arg| write!(out, "{arg}") ).ok();
        writeln!(out).ok();
        Ok(())
    }

    /// Debug-prints the argument, returning a copy
    fn dbg(arg) {
        println!("{arg:?}");
        Ok(arg.clone())
    }

    /// Debug-prints the argument
    fn dbgp(args @ ..) {
        let mut out = stdout().lock();
        args.iter().try_for_each(|arg| writeln!(out, "{arg:#?}") ).ok();
        Ok(())
    }

    /// Dumps the environment
    fn dump() @env {
        println!("{env}");
        Ok(())
    }

    fn builtins() @env {
        for builtin in env.builtins().values().flatten() {
            println!("{builtin}");
        }
        Ok(())
    }

    /// Returns the length of the input list as a [ConValue::Int]
    fn len(list) @env {
        Ok(match list {
            ConValue::Empty => 0,
            ConValue::String(s) => s.chars().count() as _,
            ConValue::Ref(r) => return len(env, slice::from_ref(r.as_ref())),
            ConValue::Array(t) => t.len() as _,
            ConValue::Tuple(t) => t.len() as _,
            ConValue::RangeExc(start, end) => (end - start) as _,
            ConValue::RangeInc(start, end) => (end - start + 1) as _,
            _ => Err(Error::TypeError)?,
        })
    }

    fn dump_symbols() {
        println!("{}", cl_structures::intern::string_interner::StringInterner::global());
        Ok(ConValue::Empty)
    }

    /// Returns a shark
    fn shark() {
        Ok('\u{1f988}')
    }
];

pub const Math: &[Builtin] = &builtins![
    /// Multiplication `a * b`
    fn mul(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a * b),
            _ => Err(Error::TypeError)?
        })
    }

    /// Division `a / b`
    fn div(lhs, rhs) {
        Ok(match (lhs, rhs){
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a / b),
            _ => Err(Error::TypeError)?
        })
    }

    /// Remainder `a % b`
    fn rem(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a % b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Addition `a + b`
    fn add(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a + b),
            (ConValue::String(a), ConValue::String(b)) => (a.to_string() + &b.to_string()).into(),
            _ => Err(Error::TypeError)?
        })
    }

    /// Subtraction `a - b`
    fn sub(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a - b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Shift Left `a << b`
    fn shl(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a << b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Shift Right `a >> b`
    fn shr(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a >> b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Bitwise And `a & b`
    fn and(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a & b),
            (ConValue::Bool(a), ConValue::Bool(b)) => ConValue::Bool(a & b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Bitwise Or `a | b`
    fn or(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a | b),
            (ConValue::Bool(a), ConValue::Bool(b)) => ConValue::Bool(a | b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Bitwise Exclusive Or `a ^ b`
    fn xor(lhs, rhs) {
        Ok(match (lhs, rhs) {
            (ConValue::Empty, ConValue::Empty) => ConValue::Empty,
            (ConValue::Int(a), ConValue::Int(b)) => ConValue::Int(a ^ b),
            (ConValue::Bool(a), ConValue::Bool(b)) => ConValue::Bool(a ^ b),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Exclusive Range `a..b`
    fn range_exc(from, to) {
        let (&ConValue::Int(from), &ConValue::Int(to)) = (from, to) else {
            Err(Error::TypeError)?
        };
        Ok(ConValue::RangeExc(from, to))
    }

    /// Inclusive Range `a..=b`
    fn range_inc(from, to) {
        let (&ConValue::Int(from), &ConValue::Int(to)) = (from, to) else {
            Err(Error::TypeError)?
        };
        Ok(ConValue::RangeInc(from, to))
    }

    /// Negates the ConValue
    fn neg(tail) {
        Ok(match tail {
            ConValue::Empty => ConValue::Empty,
            ConValue::Int(v) => ConValue::Int(v.wrapping_neg()),
            ConValue::Float(v) => ConValue::Float(-v),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Inverts the ConValue
    fn not(tail) {
        Ok(match tail {
            ConValue::Empty => ConValue::Empty,
            ConValue::Int(v) => ConValue::Int(!v),
            ConValue::Bool(v) => ConValue::Bool(!v),
            _ => Err(Error::TypeError)?,
        })
    }

    /// Compares two values
    fn cmp(head, tail) {
        Ok(ConValue::Int(match (head, tail) {
            (ConValue::Int(a), ConValue::Int(b)) => a.cmp(b) as _,
            (ConValue::Bool(a), ConValue::Bool(b)) => a.cmp(b) as _,
            (ConValue::Char(a), ConValue::Char(b)) => a.cmp(b) as _,
            (ConValue::String(a), ConValue::String(b)) => a.cmp(b) as _,
            _ => Err(error_format!("Incomparable values: {head}, {tail}"))?
        }))
    }

    /// Does the opposite of `&`
    fn deref(tail) {
        use std::rc::Rc;
        Ok(match tail {
            ConValue::Ref(v) => Rc::as_ref(v).clone(),
            _ => tail.clone(),
        })
    }
];