//! The basic AST types.

mod args;
mod expr;
mod header;

use std::fmt::{Debug, Formatter, Result as FmtResult};

use gc::Gc;

pub use ast::args::{Args, ArgsBindingError, ArgsConvertError};
pub use ast::expr::Expr;
pub use ast::header::{ModuleHeaderError, parse_module_header};
use context::Context;
use symbol::Symbol;
use util::{as_list, as_shl};
use value::Value;

/// An error converting a value to an AST node.
pub enum ConvertError<C: 'static + Context> {
    /// An error parsing the arguments of a `defn` or `fn`.
    ArgsConvertError(ArgsConvertError<C>),

    /// A builtin was used in an invalid way.
    InvalidBuiltin(&'static str, Gc<Value<C>>),

    /// An invalid value was found in a position where a decl should have
    /// appeared.
    InvalidDecl(Gc<Value<C>>),

    /// A `def` decl was invalid.
    InvalidDef(Gc<Value<C>>),

    /// A `defn` decl was invalid.
    InvalidDefn(Gc<Value<C>>),

    /// A value of an invalid type was encountered where an expr was expected.
    InvalidExpr(Gc<Value<C>>),
}

impl<C: 'static + Context> Debug for ConvertError<C> {
    fn fmt(&self, fmt: &mut Formatter) -> FmtResult {
        match *self {
            ConvertError::ArgsConvertError(ref err) => {
                fmt.debug_tuple("ArgsConvertError").field(err).finish()
            }
            ConvertError::InvalidBuiltin(ref name, ref val) => {
                fmt.debug_tuple("InvalidBuiltin")
                    .field(name)
                    .field(val)
                    .finish()
            }
            ConvertError::InvalidDecl(ref val) => {
                fmt.debug_tuple("InvalidDecl").field(val).finish()
            }
            ConvertError::InvalidDef(ref val) => fmt.debug_tuple("InvalidDef").field(val).finish(),
            ConvertError::InvalidDefn(ref val) => {
                fmt.debug_tuple("InvalidDefn").field(val).finish()
            }
            ConvertError::InvalidExpr(ref val) => {
                fmt.debug_tuple("InvalidExpr").field(val).finish()
            }
        }
    }
}

impl<C: 'static + Context> From<ArgsConvertError<C>> for ConvertError<C> {
    fn from(err: ArgsConvertError<C>) -> ConvertError<C> {
        ConvertError::ArgsConvertError(err)
    }
}

/// Converts the body values of a module to an AST.
pub fn convert_body<C: 'static + Context>(
    body: Vec<Gc<Value<C>>>,
) -> Result<Vec<(Symbol, Gc<Expr<C>>)>, ConvertError<C>> {
    body.into_iter().map(convert_decl).collect()
}

/// Converts a declaration to its AST node.
pub fn convert_decl<C: 'static + Context>(
    value: Gc<Value<C>>,
) -> Result<(Symbol, Gc<Expr<C>>), ConvertError<C>> {
    let (head, mut rest) = as_shl(value.clone()).ok_or_else(|| {
        ConvertError::InvalidDecl(value.clone())
    })?;
    match head.as_str() {
        "def" => {
            if rest.len() == 2 {
                let value = rest.pop().unwrap();
                let name = rest.pop().unwrap();
                assert_eq!(rest.len(), 0);
                if let Value::Symbol(name, _) = *name {
                    convert_expr(value).map(|expr| (name, expr))
                } else {
                    Err(ConvertError::InvalidDef(value))
                }
            } else {
                Err(ConvertError::InvalidDef(value))
            }
        }
        "defn" => {
            if rest.len() > 2 {
                let name = if let Value::Symbol(sym, _) = *rest.remove(0) {
                    sym
                } else {
                    return Err(ConvertError::InvalidDefn(value));
                };
                let args = rest.remove(0);
                let expr = convert_fn(Some(name), args, rest)?;
                Ok((name, expr))
            } else {
                Err(ConvertError::InvalidDefn(value))
            }
        }
        _ => Err(ConvertError::InvalidDecl(value)),
    }
}

/// Converts an expression to its AST node.
pub fn convert_expr<C: 'static + Context>(
    value: Gc<Value<C>>,
) -> Result<Gc<Expr<C>>, ConvertError<C>> {
    match *value.clone() {
        Value::Cons(..) => {
            if let Some(mut l) = as_list(value.clone()) {
                let func = l.remove(0);
                match *func {
                    Value::Symbol(s, _) if s.as_str() == "def" || s.as_str() == "defn" => {
                        let (n, e) = convert_decl(value)?;
                        Ok(Gc::new(Expr::Def(n, e)))
                    }
                    Value::Symbol(s, _) if s.as_str() == "fn" => {
                        if l.len() > 1 {
                            let args = l.remove(0);
                            convert_fn(None, args, l)
                        } else {
                            unimplemented!("invalid lambda: {:?}", l);
                        }
                    }
                    Value::Symbol(s, _) if s.as_str() == "if" => {
                        if l.len() == 2 {
                            let t = convert_expr(l.pop().unwrap())?;
                            let c = convert_expr(l.pop().unwrap())?;
                            let nil = Gc::new(Value::Nil(Default::default()));
                            let nil = Gc::new(Expr::Literal(nil));
                            Ok(Gc::new(Expr::If(c, t, nil)))
                        } else if l.len() == 3 {
                            let e = convert_expr(l.pop().unwrap())?;
                            let t = convert_expr(l.pop().unwrap())?;
                            let c = convert_expr(l.pop().unwrap())?;
                            Ok(Gc::new(Expr::If(c, t, e)))
                        } else {
                            Err(ConvertError::InvalidBuiltin("if".into(), value))
                        }
                    }
                    Value::Symbol(s, _) if s.as_str() == "macro-progn" || s.as_str() == "progn" => {
                        let exprs = l.into_iter().map(convert_expr).collect::<Result<_, _>>()?;
                        Ok(Gc::new(Expr::Progn(exprs)))
                    }
                    Value::Symbol(s, _) if s.as_str() == "quote" => {
                        if l.len() == 1 {
                            let value = l.pop().unwrap();
                            Ok(Gc::new(Expr::Literal(value)))
                        } else {
                            Err(ConvertError::InvalidBuiltin("quote".into(), value))
                        }
                    }
                    _ => {
                        let args = l.into_iter()
                            .map(convert_expr)
                            .collect::<Result<Vec<_>, _>>()?;
                        convert_expr(func).map(|func| Gc::new(Expr::Call(func, args)))
                    }
                }
            } else {
                Err(ConvertError::InvalidExpr(value))
            }
        }
        Value::Bytes(..) |
        Value::Fixnum(..) |
        Value::String(..) => Ok(Gc::new(Expr::Literal(value))),
        Value::Symbol(sym, _) => Ok(Gc::new(Expr::Variable(sym))),
        Value::Vector(ref v, _) => {
            let v = v.iter()
                .cloned()
                .map(|v| convert_expr(v))
                .collect::<Result<_, _>>()?;
            Ok(Gc::new(Expr::Vector(v)))
        }
        _ => Err(ConvertError::InvalidExpr(value)),
    }
}

pub(crate) fn convert_fn<C: 'static + Context>(
    name: Option<Symbol>,
    args: Gc<Value<C>>,
    body: Vec<Gc<Value<C>>>,
) -> Result<Gc<Expr<C>>, ConvertError<C>> {
    let mut body = body.into_iter()
        .map(convert_expr)
        .collect::<Result<Vec<_>, _>>()?;
    let tail = body.pop().unwrap();
    let args = Args::from_value(args)?;
    Ok(Gc::new(Expr::Lambda(name, Gc::new(args), body, tail)))
}