use std::fmt::{Debug, Formatter, Error};
use std::collections::{HashMap, HashSet};

#[derive(PartialEq)]
pub struct ModelicaModel {
    pub name: String,
    pub components: Vec<Component>,
    pub equations: Vec<SimpleEquation>,
    pub connections: Vec<Connection>,
    pub extends: Vec<String>,
}

#[derive(Copy, Clone, PartialEq)]
pub enum ComponentPrefix {
    // incomplete: eg, can be parameter and input
    Flow,
    Stream,
    Input,
    Output,
    Discrete,
    Parameter,
    Constant,
}

#[derive(PartialEq)]
pub struct Component {
    pub prefix: Option<ComponentPrefix>,
    pub specifier: String,
    pub name: String,
    pub value: Option<Expr>,
    pub units: Option<String>,
    pub description: Option<String>,
}

#[derive(Clone, PartialEq)]
pub struct Connection {
    pub a: String,
    pub b: String,
}

#[derive(PartialEq)]
pub struct SimpleEquation {
    pub lhs: Expr,
    pub rhs: Expr,
}

#[derive(PartialEq)]
pub enum Expr {
    Integer(i64),
    Float(f64),
    Ident(String),
    Der(Box<Expr>),
    Abs(Box<Expr>),
    BinExpr(BinOperator, Box<Expr>, Box<Expr>),
}

#[derive(Copy, Clone, PartialEq)]
pub enum BinOperator {
    Multiply,
    Divide,
    Add,
    Subtract,
}

//// Helpers

impl ModelicaModel {

    pub fn get_constant_vars(&self) -> HashMap<String,Expr> {
        let mut binds = HashMap::new();
        for c in &self.components {
            match c.prefix {
                Some(ComponentPrefix::Constant) => { binds.insert(c.name.clone(), Expr::Integer(123)); },
                Some(ComponentPrefix::Parameter) => { binds.insert(c.name.clone(), Expr::Float(4.56)); },
                _ => (),
            }
        }
        binds
    }

    // This crude function finds "unbound" variables: those which are not constants, parameters, or
    // the sole element on the LHS of an equation.
    // Bugs:
    //   if a var is on LHS and RHS of same equation
    pub fn get_free_vars(&self) -> Vec<String> {
        // Start with components, and remove constants and parameters
        let vars = self.components.iter().filter(|v| match v.prefix {
                Some(ComponentPrefix::Constant) | Some(ComponentPrefix::Parameter) => false,
                _ => true,
            });

        // Remove LHS (bound) vars
        let mut outputs = vec![];
        for eq in self.equations.iter() {
            // TODO:
            if let Expr::Ident(ref symb) = eq.lhs {
                outputs.push(symb.to_string());
            }
        }
        let vars = vars.filter(|v| !outputs.contains(&v.name));

        vars.map(|c| c.name.clone()).collect()
    }

fn union_vecs(a: &Vec<String>, b: &Vec<String>) -> Vec<String> {
    let mut u = a.clone();
    for e in b {
        if !(u.contains(&e)) {
            u.push(e.clone());
        }
    }
    u
}

impl Expr {

    // Order is undefined
    pub fn identifiers(&self) -> Vec<String> {
        use self::Expr::*;
        match *self {
            Integer(_) | Float(_) => vec![],
            Ident(ref s) => vec![s.clone()],
            Der(ref e) | Abs(ref e) => e.identifiers(),
            BinExpr(_, ref e1, ref e2) => {
                union_vecs(&e1.identifiers(), &e2.identifiers())
            },
        }
    }
}

#[cfg(test)]
fn set_eq(a: Vec<String>, b: Vec<String>) -> bool {
    let set_a: HashSet<String> = HashSet::from_iter(a);
    let set_b: HashSet<String> = HashSet::from_iter(b);
    return set_a == set_b;
}

#[test]
fn test_expr_identifiers() {
    use self::Expr::*;

    assert!(set_eq(
        vec![],
        Integer(0).identifiers()));
    assert!(set_eq(
        vec!["x".to_string()],
        Ident("x".to_string()).identifiers()));
    assert!(set_eq(
        vec!["x".to_string(), "y".to_string(), "z".to_string()],
        BinExpr(BinOperator::Add,
            Box::new(Abs(Box::new(Ident("z".to_string())))),
            Box::new(BinExpr(BinOperator::Add,
                Box::new(Abs(Box::new(Ident("x".to_string())))),
                Box::new(Abs(Box::new(Ident("y".to_string()))))))).identifiers()));
    assert!(set_eq(
        vec!["z".to_string()],
        BinExpr(BinOperator::Add,
            Box::new(Ident("z".to_string())),
            Box::new(Ident("z".to_string()))).identifiers()));
}

impl SimpleEquation {

    // Order is undefined
    pub fn identifiers(&self) -> Vec<String> {
        union_vecs(&self.lhs.identifiers(), &self.rhs.identifiers())
    }
}

#[test]
fn test_eqn_identifiers() {
    use self::Expr::*;

    assert!(set_eq(
        vec![],
        SimpleEquation{
            lhs: Integer(0),
            rhs: Integer(0),
        }.identifiers()));
    assert!(set_eq(
        vec!["z".to_string()],
        SimpleEquation{
            lhs: Ident("z".to_string()),
            rhs: BinExpr(BinOperator::Add,
                Box::new(Ident("z".to_string())),
                Box::new(Ident("z".to_string()))),
        }.identifiers()));
}

//// Debug Implementations

impl Debug for ModelicaModel {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        try!(write!(fmt, "model {}\n", self.name));
        for e in self.extends.iter() {
            try!(write!(fmt, "  extends {};\n", e));
        }
        for v in self.components.iter() {
            try!(write!(fmt, "  {:?};\n", v));
        }
        try!(write!(fmt, "equation\n"));
        for c in self.connections.iter() {
            try!(write!(fmt, "  {:?};\n", c));
        }
        for e in self.equations.iter() {
            try!(write!(fmt, "  {:?};\n", e));
        }
        write!(fmt, "end {};\n", self.name)
    }
}

impl Debug for ComponentPrefix {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        use self::ComponentPrefix::*;
        write!(fmt, "{}", 
            match *self {
                Flow => "flow",
                Stream => "stream",
                Input => "input",
                Output => "output",
                Discrete => "discrete",
                Parameter => "parameter",
                Constant => "constant",
            })
    }
}

impl Debug for Component {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        write!(fmt, "{}{} {}",
            match self.prefix {
                Some(p) => format!("{:?} ", p),
                None => "".to_string(),
            },
            self.specifier,
            self.name,
        )
    }
}

impl Debug for Connection {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        write!(fmt, "connect({}, {})", self.a, self.b)
    }
}

impl Debug for SimpleEquation {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        write!(fmt, "{:?} = {:?}", self.lhs, self.rhs)
    }
}

impl Debug for Expr {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        use self::Expr::*;
        match *self {
            Integer(e) => write!(fmt, "{}", e),
            Float(e) => write!(fmt, "{}", e),
            Ident(ref e) => write!(fmt, "{}", e),
            Der(ref e) => write!(fmt, "der({:?})", e),
            Abs(ref e) => write!(fmt, "abs({:?})", e),
            BinExpr(op, ref l, ref r) => write!(fmt, "({:?} {:?} {:?})", l, op, r),
        }
    }
}

impl Debug for BinOperator {
    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
        use self::BinOperator::*;
        match *self {
            Multiply => write!(fmt, "*"),
            Divide => write!(fmt, "/"),
            Add => write!(fmt, "+"),
            Subtract => write!(fmt, "-"),
        }
    }
}