use crate::reduced_ir::{ReducedIR, Expression, Lookup, Function, FunctionDefinition, Statement, Literal};
use crate::symbol_table::{DefId};
use crate::util::ScopeStack;

use std::fmt::Write;
use std::convert::From;

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

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

//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)
}

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 RuntimeError {
    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
}

#[derive(Debug)]
enum RuntimeValue {
    Expression(Expression),
    Function(FunctionDefinition),
}

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

fn expr_to_repl(expr: &Expression) -> String {
    match expr {
        Expression::Unimplemented => format!("Expression {:?} not implemented", expr),
        Expression::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),
        }
        Expression::Tuple(terms) => paren_wrapped(terms.iter().map(|x| expr_to_repl(x))),
        Expression::Assign { lval, rval } => {
            "".to_string()
        },
        e => format!("Expression {:?} shouldn't be here", e),
    }
}

impl RuntimeValue {
    fn to_repl(&self) -> String {
        match self {
            RuntimeValue::Expression(ref expr) => expr_to_repl(expr),
            RuntimeValue::Function(ref expr) => "<function>".to_string(),
        }
    }
}

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, RuntimeValue::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.into()));
                    return acc;
                }
            }
        }
        acc
    }

    fn statement(&mut self, stmt: Statement) -> EvalResult<Option<RuntimeValue>> {
        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<Expression> {
      use Expression::Unimplemented;
      Ok(match expression {
          lit @ Expression::Literal(_) => lit,
          Expression::Tuple(items) => Expression::Tuple(items.into_iter().map(|expr| self.expression(expr)).collect::<EvalResult<Vec<Expression>>>()?),
          Expression::Lookup { ref id, kind } => {
              let mem = id.into();
              match kind {
                  Lookup::Function => {
                      if self.environments.lookup(&mem).is_some() {
                          Expression::Callable(Function::UserDefined(id.clone()))
                      } else {
                          return Err(format!("Function not found for id: {}", id));
                      }
                  },
                  kind @ Lookup::LocalVar | kind @ Lookup::GlobalVar | kind @ Lookup::Param => {
                      match self.environments.lookup(&mem) {
                          //Some(RuntimeValue::Expression(expr)) => (*expr).clone(),
                          Some(RuntimeValue::Expression(expr)) => Unimplemented,
                          _ => return Err(format!("Nothing found for variable lookup {} of kind {:?}", id, kind)),
                      }
                  },
              }
          },
          Expression::Assign { ref lval, box rval } => {
              let mem = lval.into();
              let mut env = self.environments.lookup(&mem);
              Unimplemented
          },
          Expression::Call { box f, args } => self.call_expression(f, args)?,
          Unimplemented => Unimplemented,
          Expression::ReductionError(e) => return Err(e.into()),
          e => return Err(format!("Can't yet handle {:?}", e)),
      })
  }

  fn call_expression(&mut self, f: Expression, args: Vec<Expression>) -> EvalResult<Expression> {
      Err("Call expression not implemented".to_string().into())
  }
}