qubit-codec 0.17.0

// =============================================================================
//    Copyright (c) 2026 Haixing Hu.
//
//    SPDX-License-Identifier: Apache-2.0
//
//    Licensed under the Apache License, Version 2.0.
// =============================================================================
//! Tests for the decoder trait contract.

use core::convert::Infallible;

use qubit_codec::ValueDecoder;

#[derive(Default)]
struct StringDecoder;

impl ValueDecoder<str> for StringDecoder {
    type Output = String;
    type Error = Infallible;

    fn decode(&mut self, input: &str) -> Result<Self::Output, Self::Error> {
        Ok(input.to_owned())
    }
}

#[test]
fn test_decoder_trait_dispatches_to_implementor() {
    let decoded = ValueDecoder::<str>::decode(&mut StringDecoder, "text").expect("decoding should be infallible");

    assert_eq!("text", decoded);
}

#[derive(Default)]
struct LowercaseCodec;

impl ValueDecoder<str> for LowercaseCodec {
    type Output = String;
    type Error = Infallible;

    fn decode(&mut self, input: &str) -> Result<Self::Output, Self::Error> {
        Ok(input.to_ascii_lowercase())
    }
}

#[test]
fn test_codec_types_can_be_used_through_decoder_trait() {
    let decoded =
        ValueDecoder::<str>::decode(&mut LowercaseCodec, "ABC").expect("lowercase decoding should be infallible");

    assert_eq!("abc", decoded);
}

struct RejectingDecoder;

impl ValueDecoder<str> for RejectingDecoder {
    type Output = String;
    type Error = &'static str;

    fn decode(&mut self, _input: &str) -> Result<Self::Output, Self::Error> {
        Err("unsupported input")
    }
}

#[test]
fn test_decoder_trait_propagates_implementor_error() {
    let error =
        ValueDecoder::<str>::decode(&mut RejectingDecoder, "text").expect_err("the rejecting decoder must fail");

    assert_eq!("unsupported input", error);
}