use std::{
	cell::RefCell,
	cmp::{
		Eq,
		PartialEq,
	},
	collections::HashMap,
	fmt,
	rc::Rc,
};

#[derive (Debug, Eq, PartialEq)]
pub struct BogusClosure {
	pub idx: usize,
	pub upvalues: Vec <Value>,
}

#[derive (Clone, Debug, PartialEq)]
pub enum Value {
	Nil,
	Boolean (bool),
	
	// Rust is very strict about float equality, so some of my code
	// here is probably wrong in subtle ways.
	Float (f64),
	
	Integer (i64),
	String (Rc <String>),
	Table (Rc <RefCell <Table>>),
	
	// These are all bogus, I haven't figured out how to implement
	// tables and function pointers yet
	
	BogusArg (Rc <Vec <String>>),
	BogusClosure (Rc <BogusClosure>),
	BogusEnv (Rc <HashMap <String, Value>>),
	BogusPrint,
}

impl Default for Value {
	fn default () -> Self {
		Self::Nil
	}
}

impl fmt::Display for Value {
	fn fmt (&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			Value::Nil => write! (f, "nil"),
			Value::Boolean (false) => write! (f, "false"),
			Value::Boolean (true) => write! (f, "true"),
			Value::Float (x) => write! (f, "{:?}", x),
			Value::Integer (x) => write! (f, "{}", x),
			Value::String (s) => write! (f, "{}", s),
			Value::Table (t) => write! (f, "table: {:?}", std::rc::Rc::as_ptr (t)),
			
			Value::BogusArg (_) => write! (f, "BogusArg"),
			Value::BogusClosure (_) => write! (f, "BogusClosure"),
			Value::BogusEnv (_) => write! (f, "BogusEnv"),
			Value::BogusPrint => write! (f, "BogusPrint"),
		}
	}
}

impl From <bool> for Value {
	fn from (x: bool) -> Self {
		Self::Boolean (x)
	}
}

impl From <String> for Value {
	fn from (x: String) -> Self {
		Self::String (x.into ())
	}
}

impl From <&str> for Value {
	fn from (x: &str) -> Self {
		Self::from (String::from (x))
	}
}

impl From <i32> for Value {
	fn from (x: i32) -> Self {
		Self::Integer (i64::from (x))
	}
}

impl From <i64> for Value {
	fn from (x: i64) -> Self {
		Self::Integer (x)
	}
}

impl From <f64> for Value {
	fn from (x: f64) -> Self {
		Self::Float (x)
	}
}

impl From <Table> for Value {
	fn from (x: Table) -> Self {
		Self::Table (Rc::new (RefCell::new (x)))
	}
}

impl Eq for Value {}

impl std::hash::Hash for Value {
	fn hash <H: std::hash::Hasher> (&self, state: &mut H) {
		// Per https://doc.rust-lang.org/std/hash/trait.Hash.html#prefix-collisions
		[0xff].hash (state);
		
		match self {
			// TODO: Weaken to a Lua error
			Self::Nil => panic! ("can't hash a nil value"),
			Self::Boolean (x) => x.hash (state),
			Self::Float (x) => x.to_ne_bytes ().hash (state),
			Self::Integer (x) => x.hash (state),
			
			// TODO: Implement string interning so we don't hash the whole string here
			Self::String (x) => x.hash (state),
			Self::Table (x) => Rc::as_ptr (&x).hash (state),
			
			Self::BogusArg (_) => panic! ("can't hash Bogus values"),
			Self::BogusClosure (_) => panic! ("can't hash Bogus values"),
			Self::BogusEnv (_) => panic! ("can't hash Bogus values"),
			Self::BogusPrint => panic! ("can't hash Bogus values"),
		}
	}
}

impl PartialEq <i64> for Value {
	fn eq (&self, rhs: &i64) -> bool {
		*self == Value::from (*rhs)
	}
}

impl Value {
	pub fn as_float (&self) -> Option <f64> {
		match self {
			Self::Float (x) => Some (*x),
			// FloatToInt isn't stable yet, so only ints in i32 space can practically be used for now
			Self::Integer (x) => f64::try_from (i32::try_from (*x).ok ()?).ok (),
			_ => None,
		}
	}
	
	pub fn as_table (&self) -> Option <&Rc <RefCell <Table>>> {
		match self {
			Self::Table (t) => Some (t),
			_ => None,
		}
	}
	
	pub fn is_truthy (&self) -> bool {
		// And this is something Lua does better than JS and Python.
		
		match self {
			Value::Nil => false,
			Value::Boolean (false) => false,
			_ => true,
		}
	}
	
	pub fn take (&mut self) -> Self {
		let mut x = Value::Nil;
		std::mem::swap (self, &mut x);
		x
	}
}

#[derive (Debug, Default, Eq, PartialEq)]
pub struct Table {
	array: Vec <Value>,
	hash: HashMap <Value, Value>,
}

impl Table {
	fn get_inner (&self, key: &Value) -> Value {
		self.hash.get (key).cloned ().unwrap_or_default ()
	}
	
	pub fn get <A: Into <Value>> (&self, key: A) -> Value {
		self.get_inner (&(key.into ()))
	}
	
	fn insert_inner (&mut self, a: Value, b: Value) {
		self.hash.insert (a, b);
	}
	
	pub fn insert <A: Into <Value>, B: Into <Value>> (
		&mut self,
		a: A,
		b: B,
	) {
		self.insert_inner (a.into (), b.into ())
	}
}

#[cfg (test)]
mod tests {
	use std::collections::HashMap;
	use super::{
		Table,
		Value,
	};
	
	#[test]
	fn smoke () {
		let v_a = Value::from (5.0);
		let v_b = Value::from (5);
		
		assert_eq! (v_a.as_float (), Some (5.0));
		assert_eq! (v_b.as_float (), Some (5.0));
	}
	
	#[test]
	fn tables () {
		let nil = Value::Nil;
		
		assert_ne! (Value::from (18.0), Value::from (19.0));
		
		let mut t = HashMap::new ();
		t.insert (Value::from ("x"), Value::from (19.0));
		assert_eq! (t.get (&Value::from ("x")), Some (&Value::from (19.0)));
		
		let mut t = Table::default ();
		
		assert_eq! (t.get ("a"), nil);
		assert_eq! (t.get ("b"), nil);
		
		t.insert ("a", 1993);
		t.insert ("b", 2007);
		
		assert_eq! (t.get ("a"), 1993);
		assert_eq! (t.get ("b"), 2007);
		
		t.insert (19, 93);
		assert_eq! (t.get (19), 93);
	}
}