use std::ops;
use rbson::Document;
use crate::ops::{OpsIndex, OpsIndexMut, Value};

pub trait Index: private::Sealed {
    /// Return None if the key is not already in the array or object.
    #[doc(hidden)]
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value>;

    /// Return None if the key is not already in the array or object.
    #[doc(hidden)]
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value>;

    /// Panic if array index out of bounds. If key is not already in the object,
    /// insert it with a value of null. Panic if Value is a type that cannot be
    /// indexed into, except if Value is null then it can be treated as an empty
    /// object.
    #[doc(hidden)]
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value;
}

impl Index for usize {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        match *v {
            Value::Array(ref vec) => vec.get(*self),
            _ => None,
        }
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        match *v {
            Value::Array(ref mut vec) => vec.get_mut(*self),
            _ => None,
        }
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        match *v {
            Value::Array(ref mut vec) => {
                let len = vec.len();
                vec.get_mut(*self).unwrap_or_else(|| {
                    panic!(
                        "cannot access index {} of JSON array of length {}",
                        self, len
                    )
                })
            }
            _ => panic!("cannot access index {} of JSON {}", self, Type(v)),
        }
    }
}

impl Index for str {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        match *v {
            Value::Document(ref map) => map.get(self),
            _ => None,
        }
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        match *v {
            Value::Document(ref mut map) => map.get_mut(self),
            _ => None,
        }
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        if let Value::Null = *v {
            *v = Value::Document(Document::new());
        }
        match *v {
            Value::Document(ref mut map) => map.entry(self.to_owned()).or_insert(Value::Null),
            _ => panic!("cannot access key {:?} in JSON {}", self, Type(v)),
        }
    }
}

impl Index for String {
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        self[..].index_into(v)
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        self[..].index_into_mut(v)
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        self[..].index_or_insert(v)
    }
}

impl<'a, T> Index for &'a T
where
    T: ?Sized + Index,
{
    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
        (**self).index_into(v)
    }
    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
        (**self).index_into_mut(v)
    }
    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
        (**self).index_or_insert(v)
    }
}

// Prevent users from implementing the Index trait.
mod private {
    pub trait Sealed {}
    impl Sealed for usize {}
    impl Sealed for str {}
    impl Sealed for String {}
    impl<'a, T> Sealed for &'a T where T: ?Sized + Sealed {}
}

/// Used in panic messages.
struct Type<'a>(&'a Value);

impl<'a> std::fmt::Display for Type<'a> {
    fn fmt(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
        match *self.0 {
            Value::Null => formatter.write_str("Null"),
            Value::Boolean(_) => formatter.write_str("Boolean"),
            Value::Int32(_) => formatter.write_str("Int32"),
            Value::Int64(_) => formatter.write_str("Int64"),
            Value::Double(_) => formatter.write_str("Double"),
            Value::String(_) => formatter.write_str("String"),
            Value::Array(_) => formatter.write_str("Array"),
            Value::Document(_) => formatter.write_str("Document"),
            _ => {
                formatter.write_str("Other")
            }
        }
    }
}



// The usual semantics of Index is to panic on invalid indexing.
//
// That said, the usual semantics are for things like Vec and BTreeMap which
// have different use cases than Value. If you are working with a Vec, you know
// that you are working with a Vec and you can get the len of the Vec and make
// sure your indices are within bounds. The Value use cases are more
// loosey-goosey. You got some JSON from an endpoint and you want to pull values
// out of it. Outside of this Index impl, you already have the option of using
// value.as_array() and working with the Vec directly, or matching on
// Value::Array and getting the Vec directly. The Index impl means you can skip
// that and index directly into the thing using a concise syntax. You don't have
// to check the type, you don't have to check the len, it is all about what you
// expect the Value to look like.
//
// Basically the use cases that would be well served by panicking here are
// better served by using one of the other approaches: get and get_mut,
// as_array, or match. The value of this impl is that it adds a way of working
// with Value that is not well served by the existing approaches: concise and
// careless and sometimes that is exactly what you want.
impl<I> OpsIndex<I> for Value
where
    I: Index,
{
    type Output = Value;


    fn index(&self, index: I) -> &Value {
        static NULL: Value = Value::Null;
        index.index_into(self).unwrap_or(&NULL)
    }
}



impl<I> OpsIndexMut<I> for Value
where
    I: Index,
{
    
    fn index_mut(&mut self, index: I) -> &mut Value {
        index.index_or_insert(self)
    }
}