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use std::rc::Rc;
use std::fmt::{self, Debug};
use std::iter::empty;
use render_error::DataError;
use owning_ref::{OwningRef, Erased};
use {Var, Output, Number, Comparable};
pub type VarRef<'render> = OwningRef<Rc<Erased+'render>,
Variable<'render>+'render>;
pub struct RefVar<'render>(pub VarRef<'render>);
pub enum Val<'a, 'render: 'a>{
Ref(&'a (Variable<'render> + 'render)),
Rc(VarRef<'render>),
}
#[derive(Debug)]
pub struct Undefined;
#[derive(Debug)]
pub struct Empty;
pub const UNDEFINED: &'static Undefined = &Undefined;
pub const EMPTY: &'static Empty = &Empty;
pub const TRUE: &'static bool = &true;
pub const FALSE: &'static bool = &false;
/// A trait that you need to implement to put variable into the rendering
/// context
///
/// Note: by default all operations return unsupported error
pub trait Variable<'render>: Debug {
/// Evaluates `a.b` operation
///
/// Depending on your domain `a.x` may be equivalent of `a["x"]` or
/// maybe not. Integer arguments `a.0` are not supported.
fn attr<'x>(&'x self, _attr: &str)
-> Result<Var<'x, 'render>, DataError>
where 'render: 'x
{
Err(DataError::AttrUnsupported(self.typename()))
}
/// Evaluates `a[b]`
///
/// Depending on your domain `a["x"]` may be equivalent of `a.x` or
/// maybe not.
///
/// You may exract string value for a key with `key.as_str_key()`
/// and `key.as_int_key()`.
///
/// Note that actual key may have a (rust) type that is different from
/// type of self (i.e. may come from different library).
fn index<'x>(&'x self, _key: &(Variable<'render> + 'render))
-> Result<Var<'x, 'render>, DataError>
where 'render: 'x
{
Err(DataError::IndexUnsupported(self.typename()))
}
/// Evaluates `{{ x }}`
///
/// This operation may not be useful for array-, and mapping-like values
fn output(&self) -> Result<Output, DataError> {
Err(DataError::OutputUnsupported(self.typename()))
}
/// Returns type name to use in error messages
///
/// Note this must return actual type of value from user point of view
/// not just rust type. For example for `Json` type it should describe
/// `Json::Object` as a mapping and `Json::Array` as an array, not just
/// return `Json`
fn typename(&self) -> &'static str;
/// Return string value of the variable used as key in index
///
/// String keys are used for indexing dicts
///
/// It's okay not to implement this method for complex variables
fn as_str_key<'x>(&'x self) -> Result<&'x str, DataError> {
Err(DataError::StrKeyUnsupported(self.typename()))
}
/// Return intenger value of the variable used as key
///
/// Integer keys are used for indexing arrays
///
/// It's okay not to implement this method for complex variables
fn as_int_key(&self) -> Result<usize, DataError> {
Err(DataError::IntKeyUnsupported(self.typename()))
}
/// Return boolean value of this object
///
/// This is used in conditions `## if x`
fn as_bool(&self) -> Result<bool, DataError> {
Err(DataError::BoolUnsupported(self.typename()))
}
/// Return value as it could be treated in numeric context
///
/// Numeric context is where `+,-,*,/,%` operators are used. Use standard
/// `into()` conversion to convert built-in value into internal
/// representation.
fn as_number(&self) -> Result<Number, DataError> {
Err(DataError::NumberUnsupported(self.typename()))
}
/// Return value of the object that might be compared to another value
///
/// Note we can only compare numbers with number and strings with
/// strings. All other types of comparisons are unsupported. Use standard
/// `into()` conversion to convert built-in value into internal
/// representation.
fn as_comparable(&self) -> Result<Comparable, DataError> {
Err(DataError::ComparisonUnsupported(self.typename()))
}
/// Return iterator over the value if appropriate
fn iterate<'x>(&'x self)
-> Result<Box<Iterator<Item=Var<'x, 'render>>+'x>, DataError>
where 'render: 'x
{
Err(DataError::IterationUnsupported(self.typename()))
}
/// Return iterator over pairs if appropriate
fn iterate_pairs<'x>(&'x self)
-> Result<Box<Iterator<Item=(Var<'x, 'render>, Var<'x, 'render>)>+'x>,
DataError>
where 'render: 'x
{
Err(DataError::PairIterationUnsupported(self.typename()))
}
}
impl<'a> Variable<'a> for Undefined {
fn attr<'x>(&'x self, _attr: &str)
-> Result<Var<'x, 'a>, DataError>
where 'a: 'x
{
Ok(Var::undefined())
}
fn index<'x>(&'x self, _key: &Variable)
-> Result<Var<'x, 'a>, DataError>
where 'a: 'x
{
Ok(Var::undefined())
}
fn output(&self) -> Result<Output, DataError> {
Ok(Output::empty())
}
fn typename(&self) -> &'static str {
"undefined"
}
fn as_bool(&self) -> Result<bool, DataError> {
Ok(false)
}
fn iterate<'x>(&'x self)
-> Result<Box<Iterator<Item=Var<'x, 'a>>+'x>, DataError>
where 'a: 'x
{
Ok(Box::new(empty()))
}
fn iterate_pairs<'x>(&'x self)
-> Result<Box<Iterator<Item=(Var<'x, 'a>, Var<'x, 'a>)>+'x>,
DataError>
where 'a: 'x
{
Ok(Box::new(empty()))
}
}
impl<'a> Variable<'a> for Empty {
fn output(&self) -> Result<Output, DataError> {
Ok(Output::empty())
}
fn typename(&self) -> &'static str {
"str"
}
fn as_bool(&self) -> Result<bool, DataError> {
Ok(false)
}
}
impl<'a, 'render> Var<'a, 'render> {
/// Embed and owned reference to a value
pub fn owned<'x, 'y: 'x, T: Variable<'y>+'y>(x: T) -> Var<'x, 'y>
where 'y: 'x, T: 'y
{
Var(Val::Rc(OwningRef::new(Rc::new(x))
.map(|x| x as &Variable).erase_owner()))
}
/// Embed a static string as a variable
///
/// Currently this uses reference counted object that contains pointer,
/// but we want to figure out better way to reference static strings
pub fn str(x: &'static str) -> Var<'a, 'render> {
// This is a limitation of a rust type system
Var(Val::Rc(OwningRef::new(Rc::new(x))
.map(|x| x as &Variable)
.erase_owner()))
}
/// Create a borrowed reference to the variable
pub fn borrow<'x, T: Variable<'render>+'render>(x: &'x T)
-> Var<'x, 'render>
where 'render: 'x
{
Var(Val::Ref(x))
}
/// Create an undefined variable reference
pub fn undefined<'x, 'y: 'x>() -> Var<'x, 'y> {
Var(Val::Ref(UNDEFINED))
}
/// Create a variable that contains an empty string
pub fn empty<'x, 'y: 'x>() -> Var<'x, 'y> {
Var(Val::Ref(EMPTY))
}
/// Create a variable that boolean true
pub fn bool_true<'x, 'y: 'x>() -> Var<'x, 'y> {
Var(Val::Ref(EMPTY))
}
/// Create a variable that boolean false
pub fn bool_false<'x, 'y: 'x>() -> Var<'x, 'y> {
Var(Val::Ref(EMPTY))
}
}
impl<'r> fmt::Debug for RefVar<'r> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
(*self.0).fmt(f)
}
}
impl<'render> Variable<'render> for RefVar<'render>
{
fn attr<'x>(&'x self, attr: &str)
-> Result<Var<'x, 'render>, DataError>
where 'render: 'x
{
self.0.attr(attr)
}
fn index<'x>(&'x self,
key: &(Variable<'render> + 'render))
-> Result<Var<'x, 'render>, DataError>
where 'render: 'x
{
self.0.index(key)
}
fn output(&self) -> Result<Output, DataError> {
self.0.output()
}
fn typename(&self) -> &'static str {
return stringify!(#name);
}
fn as_str_key<'x>(&'x self)
-> Result<&'x str, DataError>
{
self.0.as_str_key()
}
fn as_int_key(&self) -> Result<usize, DataError> {
self.0.as_int_key()
}
fn as_bool(&self) -> Result<bool, DataError> {
self.0.as_bool()
}
fn as_number(&self) -> Result<Number, DataError> {
self.0.as_number()
}
fn as_comparable(&self) -> Result<Comparable, DataError> {
self.0.as_comparable()
}
fn iterate<'x>(&'x self)
-> Result<Box<Iterator<Item=
Var<'x, 'render>>+'x>,
DataError>
where 'render: 'x
{
self.0.iterate()
}
fn iterate_pairs<'x>(&'x self)
-> Result<Box<Iterator<Item=(Var<'x, 'render>, Var<'x, 'render>)>+'x>,
DataError>
where 'render: 'x
{
self.0.iterate_pairs()
}
}