use std::{convert::From, fmt::Write, rc::Rc};

use crate::{
    builtin::Builtin,
    reduced_ir::{
        Alternative, Callable, Expression, FunctionDefinition, Literal, Lookup, Pattern, ReducedIR, Statement,
    },
    symbol_table::DefId,
    typechecking::TypeId,
    util::ScopeStack,
};

mod test;

type EvalResult<T> = Result<T, RuntimeError>;

#[derive(Debug)]
pub struct State<'a> {
    environments: ScopeStack<'a, Memory, MemoryValue>,
}

//TODO - eh, I dunno, maybe it doesn't matter exactly how memory works in the tree-walking
//evaluator
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
enum Memory {
    Index(u32),
}

// This is for function param lookups, and is a hack
impl From<u8> for Memory {
    fn from(n: u8) -> Self {
        Memory::Index(4_000_000 + (n as u32))
    }
}

impl From<&DefId> for Memory {
    fn from(id: &DefId) -> Self {
        Self::Index(id.as_u32())
    }
}

#[derive(Debug)]
struct RuntimeError {
    msg: String,
}

impl From<String> for RuntimeError {
    fn from(msg: String) -> Self {
        Self { msg }
    }
}

impl From<&str> for RuntimeError {
    fn from(msg: &str) -> Self {
        Self { msg: msg.to_string() }
    }
}

impl RuntimeError {
    #[allow(dead_code)]
    fn get_msg(&self) -> String {
        format!("Runtime error: {}", self.msg)
    }
}

fn paren_wrapped(terms: impl Iterator<Item = String>) -> String {
    let mut buf = String::new();
    write!(buf, "(").unwrap();
    for term in terms.map(Some).intersperse(None) {
        match term {
            Some(e) => write!(buf, "{}", e).unwrap(),
            None => write!(buf, ", ").unwrap(),
        };
    }
    write!(buf, ")").unwrap();
    buf
}

/// Anything that can be stored in memory; that is, a function definition, or a fully-evaluated
/// program value.
#[derive(Debug)]
enum MemoryValue {
    Function(FunctionDefinition),
    Primitive(Primitive),
}

impl From<Primitive> for MemoryValue {
    fn from(prim: Primitive) -> Self {
        Self::Primitive(prim)
    }
}

impl MemoryValue {
    fn to_repl(&self) -> String {
        match self {
            MemoryValue::Primitive(ref prim) => prim.to_repl(),
            MemoryValue::Function(..) => "<function>".to_string(),
        }
    }
}

#[derive(Debug)]
enum RuntimeValue {
    Expression(Expression),
    Evaluated(Primitive),
}

impl From<Expression> for RuntimeValue {
    fn from(expr: Expression) -> Self {
        Self::Expression(expr)
    }
}

impl From<Primitive> for RuntimeValue {
    fn from(prim: Primitive) -> Self {
        Self::Evaluated(prim)
    }
}

/// A fully-reduced value
#[derive(Debug, Clone)]
enum Primitive {
    Tuple(Vec<Primitive>),
    Literal(Literal),
    Callable(Callable),
    Object { type_id: TypeId, tag: u32, items: Vec<Primitive> },
}

impl Primitive {
    fn to_repl(&self) -> String {
        match self {
            Primitive::Object { type_id, items, .. } if items.is_empty() => type_id.local_name().to_string(),
            Primitive::Object { type_id, items, .. } => {
                format!("{}{}", type_id.local_name(), paren_wrapped(items.iter().map(|item| item.to_repl())))
            }
            Primitive::Literal(lit) => match lit {
                Literal::Nat(n) => format!("{}", n),
                Literal::Int(i) => format!("{}", i),
                Literal::Float(f) => format!("{}", f),
                Literal::Bool(b) => format!("{}", b),
                Literal::StringLit(s) => format!("\"{}\"", s),
            },
            Primitive::Tuple(terms) => paren_wrapped(terms.iter().map(|x| x.to_repl())),
            Primitive::Callable(..) => "<some-callable>".to_string(),
        }
    }

    fn unit() -> Self {
        Primitive::Tuple(vec![])
    }
}

impl From<Literal> for Primitive {
    fn from(lit: Literal) -> Self {
        Primitive::Literal(lit)
    }
}

impl<'a> State<'a> {
    pub fn new() -> Self {
        Self { environments: ScopeStack::new(Some("global".to_string())) }
    }

    pub fn evaluate(&mut self, reduced: ReducedIR, repl: bool) -> Vec<Result<String, String>> {
        let mut acc = vec![];

        for (def_id, function) in reduced.functions.into_iter() {
            let mem = (&def_id).into();
            self.environments.insert(mem, MemoryValue::Function(function));
        }

        for statement in reduced.entrypoint.into_iter() {
            match self.statement(statement) {
                Ok(Some(output)) if repl => acc.push(Ok(output.to_repl())),
                Ok(_) => (),
                Err(error) => {
                    acc.push(Err(error.msg));
                    return acc;
                }
            }
        }
        acc
    }

    fn block(&mut self, statements: Vec<Statement>) -> EvalResult<Primitive> {
        //TODO need to handle breaks, returns, etc.
        let mut ret = None;
        for stmt in statements.into_iter() {
            if let Some(MemoryValue::Primitive(prim)) = self.statement(stmt)? {
                ret = Some(prim);
            }
        }
        Ok(if let Some(ret) = ret { ret } else { self.expression(Expression::unit())? })
    }

    fn statement(&mut self, stmt: Statement) -> EvalResult<Option<MemoryValue>> {
        match stmt {
            Statement::Binding { ref id, expr, constant: _ } => {
                println!("eval() binding id: {}", id);
                let evaluated = self.expression(expr)?;
                self.environments.insert(id.into(), evaluated.into());
                Ok(None)
            }
            Statement::Expression(expr) => {
                let evaluated = self.expression(expr)?;
                Ok(Some(evaluated.into()))
            }
        }
    }

    fn expression(&mut self, expression: Expression) -> EvalResult<Primitive> {
        Ok(match expression {
            Expression::Literal(lit) => Primitive::Literal(lit),
            Expression::Tuple(items) => Primitive::Tuple(
                items
                    .into_iter()
                    .map(|expr| self.expression(expr))
                    .collect::<EvalResult<Vec<Primitive>>>()?,
            ),
            Expression::Lookup(kind) => match kind {
                Lookup::Function(ref id) => {
                    let mem = id.into();
                    match self.environments.lookup(&mem) {
                        // This just checks that the function exists in "memory" by ID, we don't
                        // actually retrieve it until `apply_function()`
                        Some(MemoryValue::Function(_)) => {
                            Primitive::Callable(Callable::UserDefined(id.clone()))
                        }
                        x => return Err(format!("Function not found for id: {} : {:?}", id, x).into()),
                    }
                }
                Lookup::Param(n) => {
                    let mem = n.into();
                    match self.environments.lookup(&mem) {
                        Some(MemoryValue::Primitive(prim)) => prim.clone(),
                        e => return Err(format!("Param lookup error, got {:?}", e).into()),
                    }
                }
                Lookup::LocalVar(ref id) | Lookup::GlobalVar(ref id) => {
                    let mem = id.into();
                    match self.environments.lookup(&mem) {
                        Some(MemoryValue::Primitive(expr)) => expr.clone(),
                        _ => {
                            return Err(
                                format!("Nothing found for local/gloval variable lookup {}", id).into()
                            )
                        }
                    }
                }
            },
            Expression::Assign { ref lval, box rval } => {
                let mem = lval.into();
                let evaluated = self.expression(rval)?;
                self.environments.insert(mem, MemoryValue::Primitive(evaluated));
                Primitive::unit()
            }
            Expression::Call { box f, args } => self.call_expression(f, args)?,
            Expression::Callable(Callable::DataConstructor { type_id, arity, tag }) if arity == 0 => {
                Primitive::Object { type_id, tag, items: vec![] }
            }
            Expression::Callable(func) => Primitive::Callable(func),
            Expression::Conditional { box cond, then_clause, else_clause } => {
                let cond = self.expression(cond)?;
                match cond {
                    Primitive::Literal(Literal::Bool(true)) => self.block(then_clause)?,
                    Primitive::Literal(Literal::Bool(false)) => self.block(else_clause)?,
                    v => return Err(format!("Non-boolean value {:?} in if-statement", v).into()),
                }
            }
            Expression::CaseMatch { box cond, alternatives } => {
                self.case_match_expression(cond, alternatives)?
            }
            Expression::ReductionError(e) => return Err(e.into()),
        })
    }

    fn case_match_expression(
        &mut self,
        cond: Expression,
        alternatives: Vec<Alternative>,
    ) -> EvalResult<Primitive> {
        fn matches(scrut: &Primitive, pat: &Pattern, scope: &mut ScopeStack<Memory, MemoryValue>) -> bool {
            match pat {
                Pattern::Ignored => true,
                Pattern::Binding(ref def_id) => {
                    let mem = def_id.into();
                    scope.insert(mem, MemoryValue::Primitive(scrut.clone())); //TODO make sure this doesn't cause problems with nesting
                    true
                }
                Pattern::Literal(pat_literal) => {
                    if let Primitive::Literal(scrut_literal) = scrut {
                        pat_literal == scrut_literal
                    } else {
                        false
                    }
                }
                Pattern::Tuple { subpatterns, tag } => match tag {
                    None => match scrut {
                        Primitive::Tuple(items) if items.len() == subpatterns.len() => items
                            .iter()
                            .zip(subpatterns.iter())
                            .all(|(item, subpat)| matches(item, subpat, scope)),
                        _ => false, //TODO should be a type error
                    },
                    Some(pattern_tag) => match scrut {
                        //TODO should test type_ids for runtime type checking, once those work
                        Primitive::Object { tag, items, .. }
                            if tag == pattern_tag && items.len() == subpatterns.len() =>
                        {
                            items
                                .iter()
                                .zip(subpatterns.iter())
                                .all(|(item, subpat)| matches(item, subpat, scope))
                        }
                        _ => false,
                    },
                },
            }
        }
        let cond = self.expression(cond)?;

        for alt in alternatives.into_iter() {
            let mut new_scope = self.environments.new_scope(None);
            if matches(&cond, &alt.pattern, &mut new_scope) {
                let mut new_state = State { environments: new_scope };

                return new_state.block(alt.item);
            }
        }
        Err("No valid match in match expression".into())
    }

    fn call_expression(&mut self, f: Expression, args: Vec<Expression>) -> EvalResult<Primitive> {
        let func = match self.expression(f)? {
            Primitive::Callable(func) => func,
            other => return Err(format!("Trying to call non-function value: {:?}", other).into()),
        };
        match func {
            Callable::Builtin(builtin) => self.apply_builtin(builtin, args),
            Callable::UserDefined(def_id) => {
                let mem = (&def_id).into();
                match self.environments.lookup(&mem) {
                    Some(MemoryValue::Function(FunctionDefinition { body })) => {
                        let body = body.clone(); //TODO ideally this clone would not happen
                        self.apply_function(body, args)
                    }
                    e => Err(format!("Error looking up function with id {}: {:?}", def_id, e).into()),
                }
            }
            Callable::Lambda { arity, body } => {
                if arity as usize != args.len() {
                    return Err(format!(
                        "Lambda expression requries {} arguments, only {} provided",
                        arity,
                        args.len()
                    )
                    .into());
                }
                self.apply_function(body, args)
            }
            Callable::DataConstructor { type_id, arity, tag } => {
                if arity as usize != args.len() {
                    return Err(format!(
                        "Constructor expression requries {} arguments, only {} provided",
                        arity,
                        args.len()
                    )
                    .into());
                }

                let mut evaluated_args: Vec<Primitive> = vec![];
                for arg in args.into_iter() {
                    evaluated_args.push(self.expression(arg)?);
                }
                Ok(Primitive::Object { type_id, tag, items: evaluated_args })
            }
            Callable::RecordConstructor { type_id: _, tag: _ } => {
                unimplemented!()
            }
        }
    }

    fn apply_builtin(&mut self, builtin: Builtin, args: Vec<Expression>) -> EvalResult<Primitive> {
        use Builtin::*;
        use Literal::*;
        use Primitive::Literal as Lit;

        let evaled_args: EvalResult<Vec<Primitive>> =
            args.into_iter().map(|arg| self.expression(arg)).collect();
        let evaled_args = evaled_args?;

        Ok(match (builtin, evaled_args.as_slice()) {
            (FieldAccess, /*&[Node::PrimObject { .. }]*/ _) => {
                return Err("Field access unimplemented".into());
            }
            /* builtin functions */
            (IOPrint, &[ref anything]) => {
                print!("{}", anything.to_repl());
                Primitive::Tuple(vec![])
            }
            (IOPrintLn, &[ref anything]) => {
                print!("{}", anything.to_repl());
                Primitive::Tuple(vec![])
            }
            (IOGetLine, &[]) => {
                let mut buf = String::new();
                std::io::stdin().read_line(&mut buf).expect("Error readling line in 'getline'");
                StringLit(Rc::new(buf.trim().to_string())).into()
            }
            /* Binops */
            (binop, &[ref lhs, ref rhs]) => match (binop, lhs, rhs) {
                // TODO need a better way of handling these literals
                (Add, Lit(Nat(l)), Lit(Nat(r))) => Nat(l + r).into(),
                (Add, Lit(Int(l)), Lit(Int(r))) => Int(l + r).into(),
                (Add, Lit(Nat(l)), Lit(Int(r))) => Int((*l as i64) + (*r as i64)).into(),
                (Add, Lit(Int(l)), Lit(Nat(r))) => Int((*l as i64) + (*r as i64)).into(),
                (Concatenate, Lit(StringLit(ref s1)), Lit(StringLit(ref s2))) => {
                    StringLit(Rc::new(format!("{}{}", s1, s2))).into()
                }
                (Subtract, Lit(Nat(l)), Lit(Nat(r))) => Nat(l - r).into(),
                (Multiply, Lit(Nat(l)), Lit(Nat(r))) => Nat(l * r).into(),
                (Divide, Lit(Nat(l)), Lit(Nat(r))) => Float((*l as f64) / (*r as f64)).into(),
                (Quotient, Lit(Nat(l)), Lit(Nat(r))) => {
                    if *r == 0 {
                        return Err("Divide-by-zero error".into());
                    } else {
                        Nat(l / r).into()
                    }
                }
                (Modulo, Lit(Nat(l)), Lit(Nat(r))) => Nat(l % r).into(),
                (Exponentiation, Lit(Nat(l)), Lit(Nat(r))) => Nat(l ^ r).into(),
                (BitwiseAnd, Lit(Nat(l)), Lit(Nat(r))) => Nat(l & r).into(),
                (BitwiseOr, Lit(Nat(l)), Lit(Nat(r))) => Nat(l | r).into(),

                /* comparisons */
                (Equality, Lit(Nat(l)), Lit(Nat(r))) => Bool(l == r).into(),
                (Equality, Lit(Int(l)), Lit(Int(r))) => Bool(l == r).into(),
                (Equality, Lit(Float(l)), Lit(Float(r))) => Bool(l == r).into(),
                (Equality, Lit(Bool(l)), Lit(Bool(r))) => Bool(l == r).into(),
                (Equality, Lit(StringLit(ref l)), Lit(StringLit(ref r))) => Bool(l == r).into(),

                (LessThan, Lit(Nat(l)), Lit(Nat(r))) => Bool(l < r).into(),
                (LessThan, Lit(Int(l)), Lit(Int(r))) => Bool(l < r).into(),
                (LessThan, Lit(Float(l)), Lit(Float(r))) => Bool(l < r).into(),

                (LessThanOrEqual, Lit(Nat(l)), Lit(Nat(r))) => Bool(l <= r).into(),
                (LessThanOrEqual, Lit(Int(l)), Lit(Int(r))) => Bool(l <= r).into(),
                (LessThanOrEqual, Lit(Float(l)), Lit(Float(r))) => Bool(l <= r).into(),

                (GreaterThan, Lit(Nat(l)), Lit(Nat(r))) => Bool(l > r).into(),
                (GreaterThan, Lit(Int(l)), Lit(Int(r))) => Bool(l > r).into(),
                (GreaterThan, Lit(Float(l)), Lit(Float(r))) => Bool(l > r).into(),

                (GreaterThanOrEqual, Lit(Nat(l)), Lit(Nat(r))) => Bool(l >= r).into(),
                (GreaterThanOrEqual, Lit(Int(l)), Lit(Int(r))) => Bool(l >= r).into(),
                (GreaterThanOrEqual, Lit(Float(l)), Lit(Float(r))) => Bool(l >= r).into(),

                (binop, lhs, rhs) => {
                    return Err(format!("Invalid binop expression {:?} {:?} {:?}", lhs, binop, rhs).into())
                }
            },
            (prefix, &[ref arg]) => match (prefix, arg) {
                (BooleanNot, Lit(Bool(true))) => Bool(false),
                (BooleanNot, Lit(Bool(false))) => Bool(true),
                (Negate, Lit(Nat(n))) => Int(-(*n as i64)),
                (Negate, Lit(Int(n))) => Int(-(*n as i64)),
                (Negate, Lit(Float(f))) => Float(-(*f as f64)),
                (Increment, Lit(Int(n))) => Int(*n),
                (Increment, Lit(Nat(n))) => Nat(*n),
                _ => return Err("No valid prefix op".into()),
            }
            .into(),
            (x, args) => return Err(format!("bad or unimplemented builtin {:?} | {:?}", x, args).into()),
        })
    }

    fn apply_function(&mut self, body: Vec<Statement>, args: Vec<Expression>) -> EvalResult<Primitive> {
        let mut evaluated_args: Vec<Primitive> = vec![];
        for arg in args.into_iter() {
            evaluated_args.push(self.expression(arg)?);
        }

        let mut frame_state = State { environments: self.environments.new_scope(None) };

        for (n, evaled) in evaluated_args.into_iter().enumerate() {
            let n = n as u8;
            let mem = n.into();
            frame_state.environments.insert(mem, MemoryValue::Primitive(evaled));
        }

        frame_state.block(body)
    }
}