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

use crate::string_interner::{
	Interner,
	InternedString,
};

#[derive (Debug, Eq, PartialEq)]
pub struct BogusClosure {
	// I'm pretty sure this should be absolute?
	pub idx: usize,
	pub upvalues: Vec <Value>,
}

#[derive (Clone, PartialEq)]
#[repr (u8)]
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),
	RsFunc (fn (&mut crate::state::State, usize) -> usize),
	String (InternedString),
	Table (usize),
	
	// These are all bogus, I haven't figured out how to implement
	// closures yet
	
	BogusClosure (Rc <RefCell <BogusClosure>>),
}

const NIL: Value = Value::Nil;

impl fmt::Debug 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::RsFunc (x) => write! (f, "function: {:?}", x),
			Value::String (s) => write! (f, "unimplemented Debug",),
			Value::Table (t) => write! (f, "table"),
			
			Value::BogusClosure (x) => write! (f, "{:?}", x.borrow ()),
		}
	}
}

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::RsFunc (x) => write! (f, "function: {:?}", x),
			Value::String (s) => write! (f, "unimplemented Display"),
			Value::Table (t) => write! (f, "table"),
			
			Value::BogusClosure (x) => write! (f, "BogusClosure: {:?}", std::rc::Rc::as_ptr (x)),
		}
	}
}

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

impl From <bool> for Value {
	fn from (x: bool) -> Self {
		Self::Boolean (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 <usize> for Value {
	fn from (x: usize) -> Self {
		Self::Integer (i64::try_from (x).unwrap ())
	}
}

impl From <InternedString> for Value {
	fn from (x: InternedString) -> Self {
		Self::String (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) => {
				[0x01].hash (state);
				x.hash (state)
			},
			Self::Float (x) => {
				[0x02].hash (state);
				x.to_ne_bytes ().hash (state)
			},
			Self::Integer (x) => {
				[0x03].hash (state);
				x.hash (state)
			},
			Self::RsFunc (x) => {
				[0x04].hash (state);
				x.hash (state)
			},
			// TODO: Implement string interning so we don't hash the whole string here
			Self::String (x) => {
				[0x05].hash (state);
				x.hash (state)
			},
			Self::Table (x) => {
				[0x06].hash (state);
				x.hash (state)
			},
			
			Self::BogusClosure (_) => 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_closure (&self) -> Option <&Rc <RefCell <BogusClosure>>> {
		match self {
			Self::BogusClosure (x) => Some (x),
			_ => None,
		}
	}
	
	/// Coerces ints to float
	
	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,
		}
	}
	
	/// Does not coerce floats
	
	pub fn as_int (&self) -> Option <i64> {
		match self {
			Self::Integer (x) => Some (*x),
			_ => None,
		}
	}
	
	pub fn as_str (&self) -> Option <InternedString> {
		match self {
			Self::String (x) => Some (*x),
			_ => None,
		}
	}
	
	pub fn as_table (&self) -> Option <usize> {
		match self {
			Self::Table (t) => Some (*t),
			_ => None,
		}
	}
	
	pub fn from_str (si: &mut Interner, s: &str) -> Value {
		Value::String (si.intern (s))
	}
	
	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 (Default, Eq, PartialEq)]
pub struct Table {
	array: Vec <Value>,
	hash: HashMap <Value, Value>,
	strings: Vec <(InternedString, Value)>,
	map: BTreeMap <InternedString, Value>,
}

impl fmt::Debug for Table {
	fn fmt (&self, f: &mut fmt::Formatter) -> fmt::Result {
		write! (f, "Table {:#?}", self.map)?;
		
		Ok (())
	}
}

impl Table {
	fn get_inner (&self, key: &Value) -> &Value {
		match key {
			Value::Nil => &NIL,
			Value::String (x) => self.get_str (*x),
			Value::Integer (x) => self.array.get (usize::try_from (*x).unwrap ()).unwrap_or (&NIL),
			x => self.hash.get (x).unwrap_or (&NIL),
		}
	}
	
	pub fn get <A: Into <Value>> (&self, key: A) -> &Value {
		self.get_inner (&(key.into ()))
	}
	
	pub fn get_int (&self, key: i64) -> &Value {
		self.array.get (usize::try_from (key).unwrap ()).unwrap_or (&NIL)
	}
	
	pub fn get_str (&self, key: InternedString) -> &Value {
		self.strings.iter ().find (|(hay, _)| hay == &key).map (|(_, v)| v).unwrap_or (&NIL)
	}
	
	/// Insert value at arbitrary key
	
	pub fn insert <A: Into <Value>, B: Into <Value>> (
		&mut self,
		a: A,
		b: B,
	) {
		match a.into () {
			Value::Integer (x) => self.insert_int (x, b),
			Value::Nil => (),
			Value::String (x) => self.insert_str (x, b.into ()),
			x => {
				self.hash.insert (x, b.into ());
			},
		}
	}
	
	/// Insert value at integer key
	
	pub fn insert_int <A: Into <Value>> (&mut self, k: i64, v: A) 
	{
		let k = usize::try_from (k).unwrap ();
		self.array.resize (k + 1, NIL);
		self.array [k] = v.into ();
	}
	
	pub fn insert_str (&mut self, key: InternedString, v: Value) {
		match self.strings.iter_mut ().find (|(hay, _)| hay == &key).map (|(_, v)| v)
		{
			None => self.strings.push ((key, v)),
			Some (x) => *x = v,
		}
	}
	
	pub fn length (&self) -> i64 {
		for i in 1..i64::MAX {
			if self.get (i) == &NIL {
				return i - 1;
			}
		}
		0
	}
}

impl FromIterator <(Value, Value)> for Table {
	fn from_iter<I: IntoIterator<Item = (Value, Value)>> (i: I) -> Self 
	{
		let mut that = Self::default ();
		for (k, v) in i.into_iter () {
			that.insert (k, v);
		}
		that
	}
}

#[cfg (test)]
mod tests {
	use std::collections::HashMap;
	use super::*;
	
	#[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;
		let mut si = Interner::default ();
		
		assert_ne! (Value::from (18.0), Value::from (19.0));
		
		let mut t = HashMap::new ();
		t.insert (Value::from_str (&mut si, "x"), Value::from (19.0));
		assert_eq! (t.get (&Value::from_str (&mut si, "x")), Some (&Value::from (19.0)));
		
		let mut t = Table::default ();
		
		assert_eq! (t.get (si.intern ("a")), &nil);
		assert_eq! (t.get (si.intern ("b")), &nil);
		
		t.insert (si.to_value ("a"), 1993);
		t.insert (si.to_value ("b"), 2007);
		
		assert_eq! (t.get (si.intern ("a")), &Value::from (1993));
		assert_eq! (t.get (si.intern ("b")), &Value::from (2007));
		
		t.insert (19, 93);
		assert_eq! (t.get (19), &Value::from (93));
	}
}