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use crate::queryable::{Queryable, Decoder, DescriptorContext};
use crate::queryable::{DescriptorMismatch};
use crate::errors::DecodeError;
use crate::descriptors::{Descriptor, TypePos};
use crate::serialization::decode::DecodeArrayLike;
use std::iter::FromIterator;


impl<T:Queryable> Queryable for Option<T> {
    fn decode(decoder: &Decoder, buf: &[u8]) -> Result<Self, DecodeError> {
        Ok(Some(T::decode(decoder, buf)?))
    }

    fn decode_optional(decoder: &Decoder, buf: Option<&[u8]>)
        -> Result<Self, DecodeError>
    {
        buf.map(|buf|T::decode(decoder, buf)).transpose()
    }

    fn check_descriptor(ctx: &DescriptorContext, type_pos: TypePos)
        -> Result<(), DescriptorMismatch>
    {
        T::check_descriptor(ctx, type_pos)
    }
}

struct Collection<T>(T);

impl<T:IntoIterator + FromIterator<<T as IntoIterator>::Item>> Collection<T>
    where <T as IntoIterator>::Item : Queryable
{
    fn decode(decoder: &Decoder, buf: &[u8]) -> Result<T, DecodeError> {
        let elements = DecodeArrayLike::new_collection(buf)?;
        let elements = elements.map(|e| {
            <T as IntoIterator>::Item::decode(decoder, e?)
        });
        elements.collect::<Result<T, DecodeError>>()
    }

    fn decode_optional(decoder: &Decoder, buf: Option<&[u8]>)
        -> Result<T, DecodeError>
    {
        match buf {
            Some(buf) => Self::decode(decoder, buf),
            None => Ok(T::from_iter(std::iter::empty())),
        }
    }

    fn check_descriptor(ctx: &DescriptorContext, type_pos: TypePos)
        -> Result<(), DescriptorMismatch>
    {
        let desc = ctx.get(type_pos)?;
        let element_type_pos = match desc {
            Descriptor::Set(desc) => desc.type_pos,
            Descriptor::Array(desc) => desc.type_pos,
            _ => return Err(ctx.wrong_type(desc, "array or set"))
        };
        <T as IntoIterator>::Item::check_descriptor(ctx, element_type_pos)
    }
}

impl<T:Queryable> Queryable for Vec<T> {
    fn decode(decoder: &Decoder, buf: &[u8]) -> Result<Self, DecodeError> {
        Collection::<Vec<T>>::decode(decoder, buf)
    }

    fn decode_optional(decoder: &Decoder, buf: Option<&[u8]>)
        -> Result<Self, DecodeError>
    {
        Collection::<Vec<T>>::decode_optional(decoder, buf)
    }

    fn check_descriptor(ctx: &DescriptorContext, type_pos: TypePos)
        -> Result<(), DescriptorMismatch>
    {
        Collection::<Vec<T>>::check_descriptor(ctx, type_pos)
    }
}