#[macro_use]
extern crate pest;
#[macro_use]
extern crate pest_derive;
extern crate rand;

use std::cell::RefCell;
use std::rc::Rc;
use std::fs::File;
use std::io::prelude::*;
use std::fmt;
use std::fmt::Write;
use std::collections::HashMap;
use pest::Parser;
use pest::error::{Error, ErrorVariant};
use pest::iterators::Pair;
use rand::prelude::*;

#[derive(Parser)]
#[grammar = "grammar.pest"]
pub struct PseudocodeParser;

pub struct Program {
    instructions: Vec<Instruction>
}

impl Program {
    fn new(insts: Vec<Instruction>) -> Self {
        Program{
            instructions: insts,
        }
    }
}

#[derive(Clone, Debug)]
pub enum Op {
    NEQ,
    EQ,
    GT,
    LT,
    GTE,
    LTE,
    MULT,
    DIV,
    PLUS,
    MINUS,
    MOD
}

#[derive(Clone, Debug)]
pub enum Expr {
    ProcedureCall(String, Vec<Expr>),
    Number(f64),
    String(String),
    Boolean(bool),
    Identifier(String),
    BinaryExpr(Box<Expr>, Op, Box<Expr>),
    Negate(Box<Expr>),
    Not(Box<Expr>),
    List(Vec<Expr>),
    Index(String, Box<Expr>)
}

#[derive(Clone, Debug)]
pub enum Instruction {
    ProcedureDef(String, Vec<String>, Vec<Instruction>),
    RepeatUntilBlock(Expr, Vec<Instruction>),
    RepeatTimes(Expr, Vec<Instruction>),
    ForEach(String, String, Vec<Instruction>),
    IfSelection(Expr, Vec<Instruction>),
    IfElseSelection(Expr, Vec<Instruction>, Vec<Instruction>),
    ReturnStmt(Expr),
    DisplayStmt(Expr),
    ProcedureCall(String, Vec<Expr>),
    IdentAssignment(String, Expr),
    IndexAssignment(String, Expr, Expr) // list ident, index expr, value expr
}

#[derive(Clone, Debug)]
pub enum Value {
    Number(f64),
    String(String),
    Boolean(bool),
    List(Rc<RefCell<Vec<Rc<RefCell<Value>>>>>)
}

impl fmt::Display for Value {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self  {
            Value::Number(val) => write!(f, "{}", val),
            Value::String(val) => write!(f, "{}", val),
            Value::Boolean(val) => write!(f, "{}", val),
            Value::List(list) => {
                write!(f, "[")?;
                let numvals = list.borrow().len();
                for (idx, val) in list.borrow().iter().enumerate() {
                    if idx < numvals-1 {
                        write!(f, "{}, ", *val.borrow())?;
                    } else {
                        write!(f, "{}", *val.borrow())?;
                    }
                }
                write!(f, "]")
            }
        }
    }
}

pub struct Procedure {
    arglist: Vec<String>,
    body: Vec<Instruction>,
    native: Option<Box<dyn Fn(Rc<RefCell<Scope>>) -> Result<Vec<Instruction>, String>>>
}

impl Procedure {
    fn new(arglist: Vec<String>, body: Vec<Instruction>, native: Option<Box<dyn Fn(Rc<RefCell<Scope>>) -> Result<Vec<Instruction>, String>>>) -> Self {
        Procedure { arglist: arglist, body: body, native: native}
    }
}

fn call_proc(scope: Rc<RefCell<Scope>>, name: String, args: Vec<Expr>, output: Rc<RefCell<String>>) -> Result<Option<Rc<RefCell<Value>>>, String> {
    if let Some(_proc) = scope.clone().borrow().get_proc(&name) {
        let proc = _proc.clone();
        let func_scope = Rc::new(RefCell::new(Scope::new(scope.clone())));
        for (idx, varname) in proc.borrow().arglist.iter().enumerate() {
            let expr = &args[idx];
            let evaluated = expr.eval(scope.clone(), output.clone())?;
            func_scope.borrow_mut().variables.insert(varname.to_string(), evaluated);
        }
        if let Some(native_impl) = &proc.borrow().native {
            // get instructions from native impl
            let instructions = native_impl(func_scope.clone())?;
            return run_instructions(instructions, func_scope, output.clone());
        }
        return run_instructions(proc.borrow().body.clone(), func_scope, output.clone());
    } else {
        return Err(format!("No procedure named {}", name));
    }
}

pub struct Scope<'a> {
    variables: HashMap<String, Rc<RefCell<Value>>>,
    procedures: HashMap<String, Rc<RefCell<Procedure>>>,
    parent: Option<Rc<RefCell<Scope<'a>>>>,
}

impl<'a> Scope<'a> {
    fn new(parent: Rc<RefCell<Scope<'a>>>) -> Self {
        Scope {
            variables: HashMap::new(),
            procedures: HashMap::new(),
            parent: Some(parent),
        }
    }

    fn new_base_scope() -> Self {
        let mut s = Scope {
            variables: HashMap::new(),
            procedures: HashMap::new(),
            parent: None,
        };

        // populate pre-defined functions
        let random_func = Procedure::new(vec!["a".to_string(), "b".to_string()], vec![], Some(Box::new(|scope| {
            let mut rng = rand::thread_rng();
            let a = scope.borrow().resolve("a".to_string()).ok_or("a is undefined")?;
            let b = scope.borrow().resolve("b".to_string()).ok_or("a is undefined")?;
            let val = match (a.borrow().clone(), b.borrow().clone()) {
                (Value::Number(a), Value::Number(b)) => {
                    rng.gen_range(a as i64, (b as i64)+1)
                },
                _ => {
                    return Err("a and b most both be integers".to_string())
                }
            };
            Ok(vec![
                Instruction::ReturnStmt(Expr::Number(val as f64)),
            ])
        })));
        s.procedures.insert("RANDOM".to_string(), Rc::new(RefCell::new(random_func)));

        let concat_func = Procedure::new(vec!["a".to_string(), "b".to_string()], vec![], Some(Box::new(|scope| {
            let a = scope.borrow().resolve("a".to_string()).ok_or("a is undefined")?;
            let b = scope.borrow().resolve("b".to_string()).ok_or("a is undefined")?;
            let val = match (a.borrow().clone(), b.borrow().clone()) {
                (Value::String(a), Value::String(b)) => {
                    format!("{}{}", a, b)
                },
                _ => {
                    return Err("a and b most both be strings".to_string())
                }
            };
            Ok(vec![
                Instruction::ReturnStmt(Expr::String(val)),
            ])
        })));
        s.procedures.insert("CONCAT".to_string(), Rc::new(RefCell::new(concat_func)));

        let length_func = Procedure::new(vec!["l".to_string()], vec![], Some(Box::new(|scope| {
            let list_val = scope.borrow().resolve("l".to_string()).ok_or("list is undefined")?;
            let val = match list_val.borrow().clone() {
                Value::List(list) => list.borrow().len() as f64,
                _ => return Err("Argument to LENGTH must be a list".to_string())
            };
            Ok(vec![Instruction::ReturnStmt(Expr::Number(val))])
        })));
        s.procedures.insert("LENGTH".to_string(), Rc::new(RefCell::new(length_func)));

        let insert_func = Procedure::new(vec!["list".to_string(), "i".to_string(), "value".to_string()], vec![], Some(Box::new(|scope| {
            let list_val = scope.borrow().resolve("list".to_string()).ok_or("list is undefined")?;
            let list = match list_val.borrow().clone() {
                Value::List(list) => list,
                _ => return Err("First argument to INSERT must be a list".to_string())
            };
            let idx_val = scope.borrow().resolve("i".to_string()).ok_or("i is undefined")?;
            let idx = match *idx_val.borrow() {
                Value::Number(idx) => if idx.fract() != 0.0 {
                                          return Err("Second argument to INSERT must be an integer".to_string())
                                      } else if idx < 1.0 || idx > list.borrow().len() as f64 {
                                          return Err("Second argument to INSERT must be between 1 and the length of the list".to_string())
                                      } else {
                                          idx as usize
                                      },
                _ => return Err("First argument to INDEX must be a list".to_string())
            };
            let value = scope.borrow().resolve("value".to_string()).ok_or("value is undefined")?;
            list.borrow_mut().insert(idx - 1, value);
            Ok(vec![])
        })));
        s.procedures.insert("INSERT".to_string(), Rc::new(RefCell::new(insert_func)));

        let remove_func = Procedure::new(vec!["list".to_string(), "i".to_string()], vec![], Some(Box::new(|scope| {
            let list_val = scope.borrow().resolve("list".to_string()).ok_or("list is undefined")?;
            let list = match list_val.borrow().clone() {
                Value::List(list) => list,
                _ => return Err("First argument to REMOVE must be a list".to_string())
            };
            let idx_val = scope.borrow().resolve("i".to_string()).ok_or("i is undefined")?;
            let idx = match *idx_val.borrow() {
                Value::Number(idx) => if idx.fract() != 0.0 {
                    return Err("Second argument to REMOVE must be an integer".to_string())
                } else {
                    idx as usize
                },
                _ => return Err("First argument to REMOVE must be a list".to_string())
            };
            list.borrow_mut().remove(idx);
            Ok(vec![])
        })));
        s.procedures.insert("REMOVE".to_string(), Rc::new(RefCell::new(remove_func)));

        let append_func = Procedure::new(vec!["list".to_string(), "value".to_string()], vec![], Some(Box::new(|scope| {
            let list_val = scope.borrow().resolve("list".to_string()).ok_or("list is undefined")?;
            let list = match list_val.borrow().clone() {
                Value::List(list) => list,
                _ => return Err("First argument to APPEND must be a list".to_string())
            };
            let value = scope.borrow().resolve("value".to_string()).ok_or("value is undefined")?;
            list.borrow_mut().push(value);
            Ok(vec![])
        })));
        s.procedures.insert("APPEND".to_string(), Rc::new(RefCell::new(append_func)));

        return s
    }

    fn define_proc(&mut self, name: String, arglist: Vec<String>, body: Vec<Instruction>) {
        self.procedures.insert(name,
            Rc::new(RefCell::new(Procedure::new(arglist, body, None))));
    }

    fn defined_in_parent(&self, ident: &String) -> bool {
        if let Some(parent_scope) = &self.parent {
            if parent_scope.borrow().variables.contains_key(ident) {
                return true
            } else {
                parent_scope.borrow().defined_in_parent(ident)
            }
        } else {
            false
        }
    }

    fn assign(&mut self, ident: String, value: Rc<RefCell<Value>>) {
        if self.variables.contains_key(&ident) {
            self.variables.insert(ident, value);
        } else if self.defined_in_parent(&ident) {
            if let Some(parent_scope) = &self.parent {
                parent_scope.borrow_mut().assign(ident, value);
            }
        } else {
            self.variables.insert(ident, value);
        }
    }


    fn resolve(&self, ident: String) -> Option<Rc<RefCell<Value>>> {
        match self.variables.get(&ident) {
            Some(val) => Some(val.clone()),
            None => match &self.parent {
                Some(parent_scope) => parent_scope.borrow().resolve(ident),
                None => None
            }
        }
    }

    fn get_proc(&self, ident: &String) -> Option<Rc<RefCell<Procedure>>> {
        match self.procedures.get(ident) {
            Some(val) => Some(val.clone()),
            None => match &self.parent {
                Some(parent_scope) => parent_scope.borrow().get_proc(ident),
                None => None
            }
        }
    }

    fn dump(&self) {
        println!("### DUMPING SCOPE ###");
        for (var, val) in self.variables.iter() {
            println!("{} => {:?}", var, val);
        }
    }
}

impl Expr {
    fn eval(&self, scope: Rc<RefCell<Scope>>, output: Rc<RefCell<String>>) -> Result<Rc<RefCell<Value>>, String> {
        match self {
            Expr::Number(val) => Ok(Rc::new(RefCell::new(Value::Number(*val)))),
            Expr::String(val) => Ok(Rc::new(RefCell::new(Value::String(val.clone())))),
            Expr::Boolean(val) => Ok(Rc::new(RefCell::new(Value::Boolean(val.clone())))),
            Expr::Identifier(ident) => match scope.borrow().resolve(ident.to_string()) {
                Some(val) => Ok(val),
                None => Err(format!("Variable {} is not defined", ident))
            },
            Expr::Negate(expr) => {
                let val = expr.eval(scope.clone(), output.clone())?.borrow().clone();
                match val {
                    Value::Number(n) => Ok(Rc::new(RefCell::new(Value::Number(-n)))),
                    _ => Err(format!("Value {} must be a number", val))
                }
            },
            Expr::Not(expr) => {
                let val = expr.eval(scope.clone(), output.clone())?.borrow().clone();
                match val {
                    Value::Boolean(n) => Ok(Rc::new(RefCell::new(Value::Boolean(!n)))),
                    _ => Err(format!("Value {} must be a boolean value but was a {:?}", val, val)),
                }
            },
            Expr::BinaryExpr(lhs, op, rhs) => {
                let lhsval = lhs.eval(scope.clone(), output.clone())?;
                let rhsval = rhs.eval(scope.clone(), output.clone())?;
                match op {
                    Op::PLUS => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Number(f1 + f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must both be numbers", lhsval, rhsval))
                            }
                        }
                    },
                    Op::MINUS => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Number(f1 - f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must both be numbers", lhsval, rhsval))
                            }
                        }
                    },
                    Op::MULT => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Number(f1 * f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must both be numbers", lhsval, rhsval))
                            }
                        }
                    },
                    Op::DIV => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Number(f1 / f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must both be numbers", lhsval, rhsval))
                            }
                        }
                    },
                    Op::MOD => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Number(f1 % f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must both be numbers", lhsval, rhsval))
                            }
                        }
                    },
                    Op::EQ => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 == f2))))
                            },
                            (Value::String(f1), Value::String(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 == f2))))
                            },
                            (Value::Boolean(f1), Value::Boolean(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 == f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must be same type", lhsval, rhsval))
                            }
                        }
                    },
                    Op::NEQ => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 != f2))))
                            },
                            (Value::String(f1), Value::String(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 != f2))))
                            },
                            (Value::Boolean(f1), Value::Boolean(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 != f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must be same type", lhsval, rhsval))
                            }
                        }
                    },
                    Op::GT => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 > f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must be same type", lhsval, rhsval))
                            }
                        }
                    },
                    Op::LT => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 < f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must be same type", lhsval, rhsval))
                            }
                        }
                    },
                    Op::GTE => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 >= f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must be same type", lhsval, rhsval))
                            }
                        }
                    },
                    Op::LTE => {
                        match (lhsval.borrow().clone(), rhsval.borrow().clone()) {
                            (Value::Number(f1), Value::Number(f2)) => {
                                Ok(Rc::new(RefCell::new(Value::Boolean(f1 <= f2))))
                            },
                            (_, _) => {
                                Err(format!("{:?} and {:?} must be same type", lhsval, rhsval))
                            }
                        }
                    },
                }
            },
            Expr::ProcedureCall(procname, arglist) =>  {
                let value = call_proc(scope.clone(), procname.to_string(), arglist.clone(), output.clone())?;
                if let Some(value) = value {
                    Ok(value)
                } else {
                    Ok(Rc::new(RefCell::new(Value::Number(-1.0))))
                }
            },
            Expr::List(list) => {
                let mut list_val: Vec<Rc<RefCell<Value>>> = Vec::new();
                for vexpr in list.iter() {
                    // 'vexpr' is the Expr at the list value
                    let val = vexpr.eval(scope.clone(), output.clone())?;
                    list_val.push(val)
                }
                let l = Rc::new(RefCell::new(list_val));
                Ok(Rc::new(RefCell::new(Value::List(l))))
            },
            Expr::Index(list_ident, index_expr) => {
                let list_val = scope.borrow().resolve(list_ident.to_string())
                                    .expect(&format!("List variable {} is not defined", list_ident)).borrow().clone();
                if let Value::List(list) = list_val {
                    let index_val = index_expr.eval(scope.clone(), output.clone())?;
                    if let Value::Number(index) = *index_val.borrow() {
                        if index.fract() != 0.0 {
                            return Err(format!("Index {} must be an integer", *index_val.borrow()))
                        }
                        match list.borrow().get(index as usize-1) {
                            Some(val) => return Ok(val.clone()),
                            None => return Err(format!("List index {} is out of range", index))
                        };
                    } else {
                        return Err(format!("Index {} must be an integer", *index_val.borrow()));
                    };
                } else {
                    return Err(format!("Variable {} must be a list", list_ident))
                }
            }
        }
    }
}

pub fn parse_op(pair: Pair<Rule>) -> Op {
    let op = pair.into_inner().next().unwrap();
    match op.as_rule() {
        Rule::neq => Op::NEQ,
        Rule::eq => Op::EQ,
        Rule::gt => Op::GT,
        Rule::lt => Op::LT,
        Rule::gte => Op::GTE,
        Rule::lte => Op::LTE,
        Rule::mult => Op::MULT,
        Rule::div => Op::DIV,
        Rule::plus => Op::PLUS,
        Rule::minus => Op::MINUS,
        Rule::modop => Op::MOD,
        _ => { panic!("{:#?} is unknown", op); }
    }
}

fn parse_value_inner(val: Pair<Rule>) -> Expr {
    match val.as_rule() {
        Rule::procedure_call => {
            let mut block = val.into_inner();
            let ident = block.next().unwrap().as_str().to_string();
            let arg_list: Vec<Expr> = block.next().unwrap().into_inner().map(parse_expr).collect();
            Expr::ProcedureCall(ident, arg_list)
        },
        Rule::number => {
            let val: f64 = val.as_str().parse().unwrap();
            Expr::Number(val)
        },
        Rule::string => {
            // get 'inner' value
            Expr::String(val.into_inner().next().unwrap().as_str().to_string())
        },
        Rule::boolean => {
            Expr::Boolean(val.as_str() == "true")
        },
        Rule::identifier => {
            Expr::Identifier(val.as_str().trim().to_string())
        },
        Rule::expression => {
            parse_expr(val)
        },
        Rule::list => {
            let x: Vec<Expr> = val.into_inner().map(|v| {
                parse_expr(v)
            }).collect();
            Expr::List(x)
        },
        Rule::index => {
            let mut block = val.into_inner();
            let ident = block.next().unwrap().as_str().to_string();
            let index = parse_expr(block.next().unwrap());
            Expr::Index(ident, Box::new(index))
        },
        _ => {
            panic!("UNEXPECTED VALUE parse_value_inner {:?}", val);
        }
    }
}

pub fn parse_value(pair: Pair<Rule>) -> Expr {
    let mut block = pair.into_inner();
    let val = block.next().unwrap();
    match val.as_rule() {
        Rule::prefix_op => {
            let inner_val = parse_value_inner(block.next().unwrap());
            match val.into_inner().next().unwrap().as_rule() {
                Rule::minus => Expr::Negate(Box::new(inner_val)),
                Rule::not => Expr::Not(Box::new(inner_val)),
                _ => unreachable!()
            }
        }
        _ => parse_value_inner(val)
    }
}

pub fn parse_expr(pair: Pair<Rule>) -> Expr {
    match pair.as_rule() {
        Rule::value => parse_value(pair),
        Rule::expression => {
            let mut parts = pair.into_inner();
            let mut lhs = parse_expr(parts.next().unwrap());
            while let Some(_) = parts.peek() {
                let op = parse_op(parts.next().unwrap());
                let rhs = parse_expr(parts.next().unwrap());
                lhs = Expr::BinaryExpr(Box::new(lhs), op, Box::new(rhs));
            }
            return lhs;
        },
        _ => {
            panic!("other {:?}", pair);
        }
    }
}

pub fn parse_block(block: Pair<Rule>) -> Vec<Instruction> {
    let mut instructions: Vec<Instruction> = Vec::new();
    // block -> block_instruction -> match
    for inst in block.into_inner() {
        let bi = inst.into_inner().next().unwrap();
        match bi.as_rule() {
            Rule::selection_block => {
                if let Some(sel_block) = parse_selection(bi) {
                    instructions.push(sel_block);
                }
            },
            Rule::assignment => {
                let mut block = bi.into_inner();
                let symbol = block.next().unwrap();
                block.next(); // consume assign symbol
                match symbol.as_rule() {
                    Rule::identifier => {
                        let ident = symbol.as_str().trim().to_string();
                        let expr = block.next().unwrap();
                        instructions.push(Instruction::IdentAssignment(ident, parse_expr(expr)));
                    },
                    _ => {
                        panic!("UNEXPECTED parse_block {:?}", symbol);
                    }
                }
                // .as_str().trim().to_string();
            },
            Rule::return_statement => {
                let expr = parse_expr(bi.into_inner().next().unwrap());
                instructions.push(Instruction::ReturnStmt(expr));
            }
            Rule::display => {
                let expr = parse_expr(bi.into_inner().next().unwrap());
                instructions.push(Instruction::DisplayStmt(expr));
            }
            _ => {
                panic!("other {:?}", bi);
            }
        }
    }
    return instructions;
}

pub fn parse_selection(sel: Pair<Rule>) -> Option<Instruction> {
    let inst = sel.into_inner().next().unwrap();
    match inst.as_rule() {
        Rule::if_expr => {
            let mut block = inst.into_inner();
            let cond_expr = parse_expr(block.next().unwrap());
            let cond_inst = parse_block(block.next().unwrap());
            Some(Instruction::IfSelection(cond_expr, cond_inst))
        },
        Rule::if_else_expr => {
            let mut block = inst.into_inner();
            let cond_expr = parse_expr(block.next().unwrap());
            let cond_inst = parse_block(block.next().unwrap());
            let else_inst = parse_block(block.next().unwrap());
            Some(Instruction::IfElseSelection(cond_expr, cond_inst, else_inst))
        },
        _ => { None }
    }
}

pub fn parse_prog(prog: &str) -> Result<Program, Error<Rule>> {
    if let Err(a) = PseudocodeParser::parse(Rule::program, prog) {
        println!("syntax error at {:?}", a.location);
        println!("syntax error at line col: {:?}", a.line_col);
        match a.variant {
            ErrorVariant::ParsingError{positives, negatives: _} => {
                println!("positive? {:?}", positives.get(0).unwrap());
            },
            ErrorVariant::CustomError{message: _} => {},
        }
    };

    let parsed = PseudocodeParser::parse(Rule::program, prog)?;
    let mut instructions: Vec<Instruction> = Vec::new();
    for inst in parsed {
        match inst.as_rule() {
            Rule::selection_block => {
                if let Some(sel_block) = parse_selection(inst) {
                    instructions.push(sel_block);
                }
            },
            Rule::iteration_block => {
                let block = inst.into_inner().next().unwrap();
                match block.as_rule() {
                    Rule::repeat_until => {
                        let mut ib = block.into_inner();
                        let expr = parse_expr(ib.next().unwrap());
                        let inst = parse_block(ib.next().unwrap());
                        instructions.push(Instruction::RepeatUntilBlock(expr, inst));
                    },
                    Rule::repeat_times => {
                        let mut ib = block.into_inner();
                        let times = parse_expr(ib.next().unwrap());
                        let inst = parse_block(ib.next().unwrap());
                        instructions.push(Instruction::RepeatTimes(times, inst));
                    },
                    Rule::for_each => {
                        let mut ib = block.into_inner();
                        let ident = ib.next().unwrap().as_str().trim().to_string();
                        let loopvar = ib.next().unwrap().as_str().trim().to_string(); //parse_expr(ib.next().unwrap());
                        let inst = parse_block(ib.next().unwrap());
                        instructions.push(Instruction::ForEach(loopvar, ident, inst));
                    },
                    _ => {
                        panic!("other {:?}", block);
                    }
                }
            },
            Rule::procedure_def => {
                let mut block = inst.into_inner();
                let proc_name = block.next().unwrap().as_str().to_string();
                let arg_list: Vec<String> = block.next().unwrap().into_inner().map(|pair|
                    pair.as_str().to_string()
                ).collect();
                let proc_list = parse_block(block.next().unwrap());
                instructions.push(Instruction::ProcedureDef(proc_name, arg_list, proc_list));
            },
            Rule::assignment => {
                let mut block = inst.into_inner();
                let symbol = block.next().unwrap();
                block.next(); // consume assign symbol
                match symbol.as_rule() {
                    Rule::identifier => {
                        let ident = symbol.as_str().trim().to_string();
                        let expr = block.next().unwrap();
                        instructions.push(Instruction::IdentAssignment(ident, parse_expr(expr)));
                    },
                    Rule::index => {
                        let mut index_sym = symbol.into_inner();
                        let list_ident = index_sym.next().unwrap().as_str().trim().to_string();
                        let list_index = index_sym.next().unwrap();
                        let list_value = block.next().unwrap();
                        instructions.push(Instruction::IndexAssignment(list_ident, parse_expr(list_index), parse_expr(list_value)));
                    },
                    _ => {
                        panic!("UNEXPECTED parse_block {:?}", symbol);
                    }
                }
            },
            Rule::display => {
                let inner = inst.into_inner().next().unwrap();
                let expr = parse_expr(inner);
                instructions.push(Instruction::DisplayStmt(expr));
            }
            Rule::expression => {
                let inner = inst.into_inner().next().unwrap().into_inner().next().unwrap();
                match inner.as_rule() {
                    Rule::procedure_call => {
                        let mut call = inner.into_inner();
                        let ident = call.next().unwrap().as_str().trim().to_string();
                        let arg_list: Vec<Expr> = call.next().unwrap().into_inner().map(parse_expr).collect();
                        instructions.push(Instruction::ProcedureCall(ident, arg_list));
                    },
                    _ => {}
                }
            },
            _ => {}
        }
    }
    Ok(Program::new(instructions))
}

//TODO: return value
fn run_instructions(instructions: Vec<Instruction>, scope: Rc<RefCell<Scope>>, output: Rc<RefCell<String>>) -> Result<Option<Rc<RefCell<Value>>>, String> {
    let mut return_value: Option<Rc<RefCell<Value>>> = None;
    for instruction in instructions.iter() {
        match instruction {
            Instruction::ProcedureDef(name, arglist, block) => {
                scope.borrow_mut().define_proc(name.to_string(), arglist.to_vec(), block.to_vec());
            },
            Instruction::RepeatUntilBlock(expr, block) => {
                loop {
                    if let Value::Boolean(doloop) = *expr.eval(scope.clone(), output.clone())?.borrow() {
                        if !doloop {
                            run_instructions(block.to_vec(), scope.clone(), output.clone())?;
                        } else {
                            break
                        }
                    }
                }
            },
            Instruction::RepeatTimes(expr, block) => {
                if let Value::Number(ntimes) = *expr.eval(scope.clone(), output.clone())?.borrow() {
                    for _ in 0..(ntimes as u64) {
                        run_instructions(block.to_vec(), scope.clone(), output.clone())?;
                    }
                }
            },
            // TODO: ForEach
            Instruction::ForEach(list_ident, loopvar, block) => {
                if let Value::List(list) = scope.borrow().resolve(list_ident.to_string())
                                    .expect(&format!("List variable {} is not defined", list_ident)).borrow().clone() {

                    for item in list.borrow().iter() {
                        let loop_scope = Rc::new(RefCell::new(Scope::new(scope.clone())));
                        loop_scope.borrow_mut().variables.insert(loopvar.to_string(), item.clone());
                        run_instructions(block.to_vec(), loop_scope, output.clone())?;
                    }
                }

            },
            Instruction::IfSelection(cond, block) => {
                if let Value::Boolean(expr) = *cond.eval(scope.clone(), output.clone())?.borrow() {
                    // if boolean expression is true
                    if expr {
                        return_value = run_instructions(block.to_vec(), scope.clone(), output.clone())?;
                    }
                }
            },
            Instruction::IfElseSelection(cond, block, elseblock) => {
                if let Value::Boolean(expr) = *cond.eval(scope.clone(), output.clone())?.borrow() {
                    // if boolean expression is true
                    if expr {
                        return_value = run_instructions(block.to_vec(), scope.clone(), output.clone())?;
                    } else {
                        return_value = run_instructions(elseblock.to_vec(), scope.clone(), output.clone())?;
                    }
                }
            },
            Instruction::ProcedureCall(procname, arglist) => {
                return_value = call_proc(scope.clone(), procname.to_string(), arglist.clone(), output.clone())?;
            }
            Instruction::DisplayStmt(expr) => {
                let value = expr.eval(scope.clone(), output.clone())?;
                match write!(&mut output.borrow_mut(), "{} ", *value.borrow()) {
                    Err(e) => panic!("Could not print to output: {}", e),
                    _ => {}
                };
            },
            Instruction::IdentAssignment(ident, expr) => {
                let value = expr.eval(scope.clone(), output.clone())?;
                scope.borrow_mut().assign(ident.to_string(), value);
            },
            Instruction::IndexAssignment(list_ident, list_index, list_value) => {
                let list_val = scope.borrow().resolve(list_ident.to_string())
                                    .expect(&format!("List variable {} is not defined", list_ident));
                //let mut val = list_val.borrow_mut();
                if let Value::List(list) = list_val.borrow().clone() {
                    let index_val = list_index.eval(scope.clone(), output.clone())?;
                    if let Value::Number(index) = *index_val.borrow() {
                        if index.fract() != 0.0 {
                            return Err(format!("Index {} must be an integer", index))
                        }
                        if (index) < 1.0 || (index as usize) > list.borrow().len() {
                            return Err(format!("Index {} is out of range", index))
                        }
                        let value = list_value.eval(scope.clone(), output.clone())?;
                        list.borrow_mut()[index as usize - 1] = value;
                        // assign the new list to the original identifier
                        let l = Rc::new(RefCell::new(Value::List(list)));
                        scope.borrow_mut().assign(list_ident.to_string(), l);
                    };
                };
            },
            Instruction::ReturnStmt(expr) => {
                let value = expr.eval(scope.clone(), output.clone())?;
                return_value = Some(value);
            }
        }
    }
    Ok(return_value)
}

pub fn eval(prog: &str) -> Result<String, String> {
    let output = Rc::new(RefCell::new(String::new()));
    match parse_prog(prog) {
        Ok(program) => {
            let scope = Rc::new(RefCell::new(Scope::new_base_scope()));
            run_instructions(program.instructions, scope.clone(), output.clone())?;
            //(*scope.borrow()).dump();
            Ok(output.borrow().to_string())
        },
        Err(err) => Err(format!("Parse Error: {}", err.to_string()))
    }
}

pub fn eval_file(filename: &str) -> Result<String, String> {
    let mut file = File::open(filename).expect("Problem opening file");
    let mut prog = String::new();
    file.read_to_string(&mut prog).expect("Problem reading file");
    eval(&prog)
}

#[cfg(test)]
mod tests {
    use super::*;
    use pest::parses_to;

    macro_rules! map(
        { $($key:expr => $value:expr),+ } => {
            {
                let mut m = ::std::collections::HashMap::new();
                $(
                    m.insert($key, $value);
                )+
                m
            }
         };
    );

    #[test]
    fn test_parse() {
        let success = PseudocodeParser::parse(Rule::program, "abc ← 3.0").unwrap();
        println!("{:?}", success);
    }

    #[test]
    fn test_parse_binary_expr() {
        let success = PseudocodeParser::parse(Rule::expression, "(3 * 2) < (4 * 10.3)").unwrap();
        println!("{:?}", success);
    }

    #[test]
    fn test_parse_assignment_expr() {
        let success = PseudocodeParser::parse(Rule::expression, "a ← 1 + 2").unwrap();
        println!("{:#?}", success);
    }

    #[test]
    fn test_file_output() -> Result<(), String> {
        let file_output = map!(
            "test_programs/assignment.ap" => "a is 3 b is 10.5 string_val is hello",
            "test_programs/expr.ap" => "1 2 3 4 5 6 7 8 9 10",
            "test_programs/loops.ap" => "1 2 3 x is even 2 x is odd 3 x is even 4 x is odd 5",
            "test_programs/procedure.ap" => "inside did func work? true",
            "test_programs/negate.ap" => "-1 -3 -6 -6 false true false true",
            "test_programs/ops.ap" => "true false true",
            "test_programs/list.ap" => "[] [1, 2, 3] [abc, def] [[1, 2, 3], [4, 5, 6]] [2, 7, 17.5]",
            "test_programs/list2.ap" => "[1, 2, 3] [a, 1, 2, 3] [a, 1, b, 2, 3]",
            "test_programs/recursion.ap" => "1 720"
        );
        for (file, expected_output) in file_output.iter() {
            let output = eval_file(file).unwrap().trim().to_string();
            assert!(output.eq(expected_output))
        }
        Ok(())
    }

    #[test]
    fn test_parses_to() {
        parses_to! {
            parser: PseudocodeParser,
            input: "my_variable",
            rule: Rule::identifier,
            tokens: [identifier(0, 11)]
        }

        parses_to! {
            parser: PseudocodeParser,
            input: "\"hello world\"",
            rule: Rule::string,
            tokens: [string(0, 13, [inner(1, 12)])]
        }
    }
}