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use quote::{quote_spanned, ToTokens};

use super::{
    OperatorCategory, OperatorConstraints, OperatorWriteOutput,
    WriteContextArgs, RANGE_0, RANGE_1, RANGE_ANY,
};

/// > *n* input streams of the same type, 1 output stream of the same type
///
/// Unions an arbitrary number of input streams into a single stream. Each input sequence is a subsequence of the output, but no guarantee is given on how the inputs are interleaved.
///
/// Since `union` has multiple input streams, it needs to be assigned to
/// a variable to reference its multiple input ports across statements.
///
/// ```dfir
/// source_iter(vec!["hello", "world"]) -> my_union;
/// source_iter(vec!["stay", "gold"]) -> my_union;
/// source_iter(vec!["don't", "give", "up"]) -> my_union;
/// my_union = union()
///     -> map(|x| x.to_uppercase())
///     -> assert_eq(["HELLO", "WORLD", "STAY", "GOLD", "DON'T", "GIVE", "UP"]);
/// ```
pub const UNION: OperatorConstraints = OperatorConstraints {
    name: "union",
    categories: &[OperatorCategory::MultiIn],
    hard_range_inn: RANGE_ANY,
    soft_range_inn: &(2..),
    hard_range_out: RANGE_1,
    soft_range_out: RANGE_1,
    num_args: 0,
    persistence_args: RANGE_0,
    type_args: RANGE_0,
    is_external_input: false,
    has_singleton_output: false,
    flo_type: None,
    ports_inn: None,
    ports_out: None,
    input_delaytype_fn: |_| None,
    write_fn: |&WriteContextArgs {
                   op_span,
                   ident,
                   inputs,
                   outputs,
                   is_pull,
                   ..
               },
               _| {
        let write_iterator = if is_pull {
            let chains = inputs
                .iter()
                .map(|i| i.to_token_stream())
                .reduce(|a, b| quote_spanned! {op_span=> check_inputs(#a, #b) })
                .unwrap_or_else(|| quote_spanned! {op_span=> std::iter::empty() });
            quote_spanned! {op_span=>
                let #ident = {
                    #[allow(unused)]
                    #[inline(always)]
                    fn check_inputs<A: ::std::iter::Iterator<Item = Item>, B: ::std::iter::Iterator<Item = Item>, Item>(a: A, b: B) -> impl ::std::iter::Iterator<Item = Item> {
                        a.chain(b)
                    }
                    #chains
                };
            }
        } else {
            assert_eq!(1, outputs.len());
            let output = &outputs[0];
            quote_spanned! {op_span=>
                let #ident = #output;
            }
        };
        Ok(OperatorWriteOutput {
            write_iterator,
            ..Default::default()
        })
    },
};