use std::u32;
use std::fmt;
use std::rc::Rc;
use std::cell::RefCell;
use elements::{ResizableLimits, TableType};
use interpreter::Error;
use interpreter::module::check_limits;
use interpreter::func::FuncInstance;

/// Table instance.
pub struct TableInstance {
	/// Table limits.
	limits: ResizableLimits,
	/// Table memory buffer.
	buffer: RefCell<Vec<Option<Rc<FuncInstance>>>>,
}

impl fmt::Debug for TableInstance {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		f.debug_struct("TableInstance")
			.field("limits", &self.limits)
			.field("buffer.len", &self.buffer.borrow().len())
			.finish()
	}
}

impl TableInstance {
	/// New instance of the table
	pub fn new(table_type: &TableType) -> Result<Self, Error> {
		check_limits(table_type.limits())?;
		Ok(TableInstance {
			limits: table_type.limits().clone(),
			buffer: RefCell::new(vec![None; table_type.limits().initial() as usize]),
		})
	}

	/// Return table limits.
	pub fn limits(&self) -> &ResizableLimits {
		&self.limits
	}

	/// Get the specific value in the table
	pub fn get(&self, offset: u32) -> Result<Rc<FuncInstance>, Error> {
		let buffer = self.buffer.borrow();
		let buffer_len = buffer.len();
		let table_elem = buffer.get(offset as usize).cloned().ok_or(
			Error::Table(format!(
				"trying to read table item with index {} when there are only {} items",
				offset,
				buffer_len
			)),
		)?;
		Ok(table_elem.ok_or(Error::Table(format!(
			"trying to read uninitialized element on index {}",
			offset
		)))?)
	}

	/// Set the table element to the specified function.
	pub fn set(&self, offset: u32, value: Rc<FuncInstance>) -> Result<(), Error> {
		let mut buffer = self.buffer.borrow_mut();
		let buffer_len = buffer.len();
		let table_elem = buffer.get_mut(offset as usize).ok_or(Error::Table(format!(
			"trying to update table item with index {} when there are only {} items",
			offset,
			buffer_len
		)))?;
		*table_elem = Some(value);
		Ok(())
	}
}