qubit-function 0.8.3

/*******************************************************************************
 *
 *    Copyright (c) 2025 - 2026.
 *    Haixing Hu, Qubit Co. Ltd.
 *
 *    All rights reserved.
 *
 ******************************************************************************/

use std::cell::Cell;

use qubit_function::{
    ArcPredicate,
    ArcStatefulTransformer,
    BoxPredicate,
    BoxStatefulTransformer,
    FnStatefulTransformerOps,
    Predicate,
    RcPredicate,
    RcStatefulTransformer,
    StatefulTransformer,
};

#[test]
fn test_stateful_transformer_default_conversions_allow_relaxed_generic_types() {
    #[derive(Clone, Debug, Eq, PartialEq)]
    struct BorrowedRc<'a> {
        value: &'a str,
    }

    #[derive(Debug)]
    struct BorrowedRcStatefulTransformer {
        count: Cell<usize>,
    }

    impl Clone for BorrowedRcStatefulTransformer {
        fn clone(&self) -> Self {
            Self {
                count: Cell::new(self.count.get()),
            }
        }
    }

    impl<'a> StatefulTransformer<BorrowedRc<'a>, BorrowedRc<'a>> for BorrowedRcStatefulTransformer {
        fn apply(&mut self, value: BorrowedRc<'a>) -> BorrowedRc<'a> {
            self.count.set(self.count.get() + 1);
            value
        }
    }

    fn assert_left(value: BorrowedRc<'_>) {
        assert_eq!(value.value, "left");
    }

    let text = String::from("left");
    let value = || BorrowedRc {
        value: text.as_str(),
    };
    let transformer = BorrowedRcStatefulTransformer {
        count: Cell::new(0),
    };

    assert_left(transformer.clone().into_box().apply(value()));
    assert_left(transformer.clone().into_rc().apply(value()));
    assert_left(transformer.clone().into_arc().apply(value()));
    assert_left(qubit_function::TransformerOnce::apply(
        transformer.clone().into_once(),
        value(),
    ));
    let mut into_fn = transformer.clone().into_fn();
    assert_left(into_fn(value()));

    assert_left(transformer.to_box().apply(value()));
    assert_left(transformer.to_rc().apply(value()));
    assert_left(transformer.to_arc().apply(value()));
    assert_left(qubit_function::TransformerOnce::apply(
        transformer.to_once(),
        value(),
    ));
    let mut to_fn = transformer.to_fn();
    assert_left(to_fn(value()));
}

// ============================================================================
// BoxStatefulTransformer Tests
// ============================================================================

#[test]
fn test_box_mapper_new() {
    let mut counter = 0;
    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    assert_eq!(mapper.apply(10), 11);
    assert_eq!(mapper.apply(10), 12);
    assert_eq!(mapper.apply(10), 13);
}

#[test]
fn test_box_mapper_identity() {
    let mut identity = BoxStatefulTransformer::<i32, i32>::identity();
    assert_eq!(identity.apply(42), 42);
    assert_eq!(identity.apply(100), 100);
}

#[test]
fn test_box_mapper_constant() {
    let mut constant = BoxStatefulTransformer::constant("hello");
    assert_eq!(constant.apply(1), "hello");
    assert_eq!(constant.apply(2), "hello");
    assert_eq!(constant.apply(3), "hello");
}

#[test]
fn test_box_mapper_and_then() {
    let mut counter1 = 0;
    let mapper1 = BoxStatefulTransformer::new(move |x: i32| {
        counter1 += 1;
        x + counter1
    });

    let mut counter2 = 0;
    let mapper2 = BoxStatefulTransformer::new(move |x: i32| {
        counter2 += 1;
        x * counter2
    });

    let mut composed = mapper1.and_then(mapper2);
    assert_eq!(composed.apply(10), 11); // (10 + 1) * 1
    assert_eq!(composed.apply(10), 24); // (10 + 2) * 2
    assert_eq!(composed.apply(10), 39); // (10 + 3) * 3
}

#[test]
fn test_box_mapper_and_then_with_closure() {
    let mut counter = 0;
    let mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });

    let mut composed = mapper.and_then(|x: i32| x + 1);
    assert_eq!(composed.apply(10), 11); // 10 * 1 + 1
    assert_eq!(composed.apply(10), 21); // 10 * 2 + 1
    assert_eq!(composed.apply(10), 31); // 10 * 3 + 1
}

#[test]
fn test_box_mapper_when_or_else() {
    let mut high_count = 0;
    let mut low_count = 0;

    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        high_count += 1;
        format!("High[{}]: {}", high_count, x * 2)
    })
    .when(|x: &i32| *x >= 10)
    .or_else(move |x| {
        low_count += 1;
        format!("Low[{}]: {}", low_count, x + 1)
    });

    assert_eq!(mapper.apply(15), "High[1]: 30");
    assert_eq!(mapper.apply(5), "Low[1]: 6");
    assert_eq!(mapper.apply(20), "High[2]: 40");
    assert_eq!(mapper.apply(3), "Low[2]: 4");
}

#[test]
fn test_box_mapper_into_box() {
    let mut counter = 0;
    let mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut boxed = StatefulTransformer::into_box(mapper);
    assert_eq!(boxed.apply(10), 11);
    assert_eq!(boxed.apply(10), 12);
}

#[test]
fn test_mapper_to_box_rc_arc_fn_non_consuming() {
    // Test non-consuming adapters `to_box`, `to_rc`, `to_arc`, `to_fn`
    // using a Cloneable custom mapper.
    #[derive(Clone)]
    struct CloneStatefulTransformer {
        counter: i32,
    }

    impl StatefulTransformer<i32, i32> for CloneStatefulTransformer {
        fn apply(&mut self, input: i32) -> i32 {
            self.counter += 1;
            input + self.counter
        }
    }

    let mapper = CloneStatefulTransformer { counter: 0 };

    let mut b = StatefulTransformer::to_box(&mapper);
    assert_eq!(b.apply(10), 11);
    assert_eq!(b.apply(10), 12);

    let rc = mapper.to_rc();
    let mut r1 = rc.clone();
    let mut r2 = rc.clone();
    assert_eq!(r1.apply(10), 11);
    assert_eq!(r2.apply(10), 12);

    // to_arc requires Send+Sync. Make a trivially Send+Sync cloneable
    #[derive(Clone)]
    struct SCloneStatefulTransformer {
        counter: i32,
    }

    impl StatefulTransformer<i32, i32> for SCloneStatefulTransformer {
        fn apply(&mut self, input: i32) -> i32 {
            self.counter += 1;
            input * self.counter
        }
    }

    unsafe impl Send for SCloneStatefulTransformer {}
    unsafe impl Sync for SCloneStatefulTransformer {}

    let sm = SCloneStatefulTransformer { counter: 0 };
    let mut a = sm.to_arc();
    assert_eq!(a.apply(3), 3);
    assert_eq!(a.apply(3), 6);

    let mut f = StatefulTransformer::to_fn(&mapper);
    assert_eq!(f(5), 6);
    assert_eq!(f(5), 7);
}

#[test]
fn test_box_mapper_into_rc() {
    let mut counter = 0;
    let mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut rc_mapper = StatefulTransformer::into_rc(mapper);
    assert_eq!(rc_mapper.apply(10), 11);
    assert_eq!(rc_mapper.apply(10), 12);
}

// ============================================================================
// ArcStatefulTransformer Tests
// ============================================================================

#[test]
fn test_arc_mapper_new() {
    let mut counter = 0;
    let mut mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    assert_eq!(mapper.apply(10), 11);
    assert_eq!(mapper.apply(10), 12);
    assert_eq!(mapper.apply(10), 13);
}

#[test]
fn test_arc_mapper_identity() {
    let mut identity = ArcStatefulTransformer::<i32, i32>::identity();
    assert_eq!(identity.apply(42), 42);
    assert_eq!(identity.apply(100), 100);
}

#[test]
fn test_arc_mapper_constant() {
    let mut constant = ArcStatefulTransformer::constant("hello");
    assert_eq!(constant.apply(1), "hello");
    assert_eq!(constant.apply(2), "hello");
    assert_eq!(constant.apply(3), "hello");
}

#[test]
fn test_arc_mapper_clone() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut mapper1 = mapper.clone();
    let mut mapper2 = mapper.clone();

    assert_eq!(mapper1.apply(10), 11);
    assert_eq!(mapper2.apply(10), 12);
    assert_eq!(mapper1.apply(10), 13);
}

#[test]
fn test_arc_mapper_and_then() {
    let mut counter1 = 0;
    let mapper1 = ArcStatefulTransformer::new(move |x: i32| {
        counter1 += 1;
        x + counter1
    });

    let mut counter2 = 0;
    let mapper2 = ArcStatefulTransformer::new(move |x: i32| {
        counter2 += 1;
        x * counter2
    });

    let mut composed = mapper1.and_then(mapper2);
    assert_eq!(composed.apply(10), 11); // (10 + 1) * 1
    assert_eq!(composed.apply(10), 24); // (10 + 2) * 2
    assert_eq!(composed.apply(10), 39); // (10 + 3) * 3
}

#[test]
fn test_arc_mapper_and_then_with_closure() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });

    let mut composed = mapper.and_then(|x: i32| x + 1);
    assert_eq!(composed.apply(10), 11); // 10 * 1 + 1
    assert_eq!(composed.apply(10), 21); // 10 * 2 + 1
    assert_eq!(composed.apply(10), 31); // 10 * 3 + 1
}

#[test]
fn test_arc_mapper_when_or_else() {
    let mut high_count = 0;
    let mut low_count = 0;

    let mut mapper = ArcStatefulTransformer::new(move |x: i32| {
        high_count += 1;
        format!("High[{}]: {}", high_count, x * 2)
    })
    .when(|x: &i32| *x >= 10)
    .or_else(move |x| {
        low_count += 1;
        format!("Low[{}]: {}", low_count, x + 1)
    });

    assert_eq!(mapper.apply(15), "High[1]: 30");
    assert_eq!(mapper.apply(5), "Low[1]: 6");
    assert_eq!(mapper.apply(20), "High[2]: 40");
    assert_eq!(mapper.apply(3), "Low[2]: 4");
}

#[test]
fn test_arc_mapper_into_box() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut boxed = StatefulTransformer::into_box(mapper);
    assert_eq!(boxed.apply(10), 11);
    assert_eq!(boxed.apply(10), 12);
}

#[test]
fn test_arc_mapper_into_arc() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut arc_mapper = StatefulTransformer::into_arc(mapper);
    assert_eq!(arc_mapper.apply(10), 11);
    assert_eq!(arc_mapper.apply(10), 12);
}

#[test]
fn test_arc_mapper_into_rc() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut rc_mapper = StatefulTransformer::into_rc(mapper);
    assert_eq!(rc_mapper.apply(10), 11);
    assert_eq!(rc_mapper.apply(10), 12);
}

#[test]
fn test_arc_mapper_to_box() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    // Non-consuming conversion: the original mapper is still usable
    let mut boxed1 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed1.apply(10), 11); // 10 + 1
    assert_eq!(boxed1.apply(10), 12); // 10 + 2

    // Can call to_box() multiple times, each sharing the same underlying state
    let mut boxed2 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed2.apply(10), 13); // 10 + 3 (shared state)

    // Original mapper also shares state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(10), 14); // 10 + 4
}

#[test]
fn test_arc_mapper_to_rc() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });

    // Non-consuming conversion
    let rc_mapper = StatefulTransformer::to_rc(&mapper);
    let mut rc1 = rc_mapper.clone();
    let mut rc2 = rc_mapper.clone();

    // Shared state
    assert_eq!(rc1.apply(10), 10); // 10 * 1
    assert_eq!(rc2.apply(10), 20); // 10 * 2
    assert_eq!(rc1.apply(10), 30); // 10 * 3

    // Original mapper also shares the same state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(10), 40); // 10 * 4
}

#[test]
fn test_arc_mapper_to_arc() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x - counter
    });

    // Non-consuming conversion
    let arc_mapper = StatefulTransformer::to_arc(&mapper);
    let mut arc1 = arc_mapper.clone();
    let mut arc2 = arc_mapper.clone();

    // Shared state
    assert_eq!(arc1.apply(10), 9); // 10 - 1
    assert_eq!(arc2.apply(10), 8); // 10 - 2
    assert_eq!(arc1.apply(10), 7); // 10 - 3

    // Original mapper also shares the same state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(10), 6); // 10 - 4
}

#[test]
fn test_arc_mapper_to_fn() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter * 10
    });

    // Non-consuming conversion
    let mut closure1 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(closure1(5), 15); // 5 + 1 * 10
    assert_eq!(closure1(5), 25); // 5 + 2 * 10

    // Can call to_fn() multiple times, each sharing the same underlying state
    let mut closure2 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(closure2(5), 35); // 5 + 3 * 10 (shared state)

    // Original mapper also shares state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(5), 45); // 5 + 4 * 10
}

#[test]
fn test_arc_mapper_to_box_with_string() {
    let mut count = 0;
    let mapper = ArcStatefulTransformer::new(move |x: String| {
        count += 1;
        format!("[{}] {}", count, x)
    });

    let mut boxed1 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed1.apply("hello".to_string()), "[1] hello");
    assert_eq!(boxed1.apply("world".to_string()), "[2] world");

    let mut boxed2 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed2.apply("rust".to_string()), "[3] rust"); // shared state
}

#[test]
fn test_arc_mapper_to_rc_shared_state() {
    let mut sum = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        sum += x;
        sum
    });

    let rc_mapper = StatefulTransformer::to_rc(&mapper);
    let mut rc1 = rc_mapper.clone();
    let mut rc2 = rc_mapper.clone();

    // Verify shared state
    assert_eq!(rc1.apply(10), 10);
    assert_eq!(rc2.apply(20), 30); // sharing the same sum
    assert_eq!(rc1.apply(30), 60); // continue accumulating

    // Original mapper also shares state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(40), 100); // 60 + 40
}

#[test]
fn test_arc_mapper_to_arc_multiple_clones() {
    let mut product = 1;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        product *= x;
        product
    });

    let arc_mapper = StatefulTransformer::to_arc(&mapper);
    let mut arc1 = arc_mapper.clone();
    let mut arc2 = arc_mapper.clone();

    // Verify shared state
    assert_eq!(arc1.apply(2), 2); // 1 * 2
    assert_eq!(arc2.apply(3), 6); // 2 * 3
    assert_eq!(arc1.apply(4), 24); // 6 * 4

    // Original mapper also shares state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(5), 120); // 24 * 5
}

#[test]
fn test_arc_mapper_to_fn_complex_type() {
    let mut history = Vec::new();
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        history.push(x);
        (x, history.len())
    });

    let mut fn1 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(fn1(10), (10, 1));
    assert_eq!(fn1(20), (20, 2));

    let mut fn2 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(fn2(30), (30, 3)); // shared state

    // Original mapper also shares state
    let mut mapper_clone = mapper.clone();
    assert_eq!(mapper_clone.apply(40), (40, 4));
}

// ============================================================================
// RcStatefulTransformer Tests
// ============================================================================

#[test]
fn test_rc_mapper_new() {
    let mut counter = 0;
    let mut mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    assert_eq!(mapper.apply(10), 11);
    assert_eq!(mapper.apply(10), 12);
    assert_eq!(mapper.apply(10), 13);
}

#[test]
fn test_rc_mapper_identity() {
    let mut identity = RcStatefulTransformer::<i32, i32>::identity();
    assert_eq!(identity.apply(42), 42);
    assert_eq!(identity.apply(100), 100);
}

#[test]
fn test_rc_mapper_constant() {
    let mut constant = RcStatefulTransformer::constant("hello");
    assert_eq!(constant.apply(1), "hello");
    assert_eq!(constant.apply(2), "hello");
    assert_eq!(constant.apply(3), "hello");
}

#[test]
fn test_rc_mapper_clone() {
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut mapper1 = mapper.clone();
    let mut mapper2 = mapper.clone();

    assert_eq!(mapper1.apply(10), 11);
    assert_eq!(mapper2.apply(10), 12);
    assert_eq!(mapper1.apply(10), 13);
}

#[test]
fn test_rc_mapper_and_then() {
    let mut counter1 = 0;
    let mapper1 = RcStatefulTransformer::new(move |x: i32| {
        counter1 += 1;
        x + counter1
    });

    let mut counter2 = 0;
    let mapper2 = RcStatefulTransformer::new(move |x: i32| {
        counter2 += 1;
        x * counter2
    });

    let mut composed = mapper1.and_then(mapper2);
    assert_eq!(composed.apply(10), 11); // (10 + 1) * 1
    assert_eq!(composed.apply(10), 24); // (10 + 2) * 2
    assert_eq!(composed.apply(10), 39); // (10 + 3) * 3
}

#[test]
fn test_rc_mapper_and_then_with_closure() {
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });

    let mut composed = mapper.and_then(|x: i32| x + 1);
    assert_eq!(composed.apply(10), 11); // 10 * 1 + 1
    assert_eq!(composed.apply(10), 21); // 10 * 2 + 1
    assert_eq!(composed.apply(10), 31); // 10 * 3 + 1
}

#[test]
fn test_rc_mapper_when_or_else() {
    let mut high_count = 0;
    let mut low_count = 0;

    let mut mapper = RcStatefulTransformer::new(move |x: i32| {
        high_count += 1;
        format!("High[{}]: {}", high_count, x * 2)
    })
    .when(|x: &i32| *x >= 10)
    .or_else(move |x| {
        low_count += 1;
        format!("Low[{}]: {}", low_count, x + 1)
    });

    assert_eq!(mapper.apply(15), "High[1]: 30");
    assert_eq!(mapper.apply(5), "Low[1]: 6");
    assert_eq!(mapper.apply(20), "High[2]: 40");
    assert_eq!(mapper.apply(3), "Low[2]: 4");
}

#[test]
fn test_rc_mapper_into_box() {
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut boxed = StatefulTransformer::into_box(mapper);
    assert_eq!(boxed.apply(10), 11);
    assert_eq!(boxed.apply(10), 12);
}

#[test]
fn test_rc_mapper_into_rc() {
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut rc_mapper = StatefulTransformer::into_rc(mapper);
    assert_eq!(rc_mapper.apply(10), 11);
    assert_eq!(rc_mapper.apply(10), 12);
}

#[test]
fn test_rc_mapper_to_rc() {
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });

    // Non-consuming conversion
    let rc_mapper = StatefulTransformer::to_rc(&mapper);
    let mut rc1 = rc_mapper.clone();
    let mut rc2 = rc_mapper.clone();

    // Both share the same state
    assert_eq!(rc1.apply(10), 10); // 10 * 1
    assert_eq!(rc2.apply(10), 20); // 10 * 2
    assert_eq!(rc1.apply(10), 30); // 10 * 3

    // Original mapper is still available
    let mut original = mapper;
    assert_eq!(original.apply(10), 40); // 10 * 4 (shared state)
}

#[test]
fn test_rc_mapper_to_rc_preserves_original() {
    let mut sum = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        sum += x;
        sum
    });

    // to_rc() doesn't consume the original
    let rc_mapper = StatefulTransformer::to_rc(&mapper);
    let mut rc1 = rc_mapper.clone();
    assert_eq!(rc1.apply(5), 5);
    assert_eq!(rc1.apply(10), 15);

    // Original mapper shares the same state
    let mut original = mapper;
    assert_eq!(original.apply(3), 18);
}

// ============================================================================
// Closure StatefulTransformer Tests
// ============================================================================

#[test]
fn test_closure_as_mapper() {
    let mut counter = 0;
    let mut mapper = |x: i32| {
        counter += 1;
        x + counter
    };

    assert_eq!(mapper.apply(10), 11);
}

#[test]
fn test_closure_into_box() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x + counter
    };

    let mut boxed = StatefulTransformer::into_box(mapper);
    assert_eq!(boxed.apply(10), 11);
    assert_eq!(boxed.apply(10), 12);
}

#[test]
fn test_closure_into_rc() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x + counter
    };

    let mut rc_mapper = StatefulTransformer::into_rc(mapper);
    assert_eq!(rc_mapper.apply(10), 11);
    assert_eq!(rc_mapper.apply(10), 12);
}

#[test]
fn test_closure_into_arc() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x + counter
    };

    let mut arc_mapper = StatefulTransformer::into_arc(mapper);
    assert_eq!(arc_mapper.apply(10), 11);
    assert_eq!(arc_mapper.apply(10), 12);
}

// ============================================================================
// FnStatefulTransformerOps Tests
// ============================================================================

#[test]
fn test_fn_mapper_ops_and_then() {
    let mut counter1 = 0;
    let mapper1 = move |x: i32| {
        counter1 += 1;
        x + counter1
    };

    let mut counter2 = 0;
    let mapper2 = move |x: i32| {
        counter2 += 1;
        x * counter2
    };

    let mut composed = FnStatefulTransformerOps::and_then(mapper1, mapper2);
    assert_eq!(composed.apply(10), 11); // (10 + 1) * 1
    assert_eq!(composed.apply(10), 24); // (10 + 2) * 2
}

#[test]
fn test_fn_mapper_ops_when() {
    let mut mapper =
        FnStatefulTransformerOps::when(|x: i32| x * 2, |x: &i32| *x > 0).or_else(|x: i32| -x);

    assert_eq!(mapper.apply(5), 10);
    assert_eq!(mapper.apply(-5), 5);
}

// ============================================================================
// Conditional StatefulTransformer Tests
// ============================================================================

#[test]
fn test_box_conditional_mapper_with_predicate() {
    let predicate = BoxPredicate::new(|x: &i32| *x >= 10);

    let mut mapper = BoxStatefulTransformer::new(|x: i32| x * 2)
        .when(predicate)
        .or_else(|x| x + 1);

    assert_eq!(mapper.apply(15), 30);
    assert_eq!(mapper.apply(5), 6);
}

#[test]
fn test_arc_conditional_mapper_clone() {
    let conditional = ArcStatefulTransformer::new(|x: i32| x * 2).when(|x: &i32| *x > 0);

    // Clone the ArcConditionalStatefulTransformer before calling or_else
    let conditional_clone = conditional.clone();

    let mut mapper1 = conditional.or_else(|x: i32| -x);
    let mut mapper2 = conditional_clone.or_else(|x: i32| x + 100);

    // Both cloned conditional mappers work correctly
    assert_eq!(mapper1.apply(5), 10); // Condition satisfied: 5 * 2
    assert_eq!(mapper1.apply(-5), 5); // Condition not satisfied: -(-5)
    assert_eq!(mapper2.apply(5), 10); // Condition satisfied: 5 * 2
    assert_eq!(mapper2.apply(-5), 95); // Condition not satisfied: -5 + 100
}

#[test]
fn test_rc_conditional_mapper_clone() {
    let conditional = RcStatefulTransformer::new(|x: i32| x * 2).when(|x: &i32| *x > 0);

    // Clone the RcConditionalStatefulTransformer before calling or_else
    let conditional_clone = conditional.clone();

    let mut mapper1 = conditional.or_else(|x: i32| -x);
    let mut mapper2 = conditional_clone.or_else(|x: i32| x + 100);

    // Both cloned conditional mappers work correctly
    assert_eq!(mapper1.apply(5), 10); // Condition satisfied: 5 * 2
    assert_eq!(mapper1.apply(-5), 5); // Condition not satisfied: -(-5)
    assert_eq!(mapper2.apply(5), 10); // Condition satisfied: 5 * 2
    assert_eq!(mapper2.apply(-5), 95); // Condition not satisfied: -5 + 100
}

// ============================================================================
// Complex Composition Tests
// ============================================================================

#[test]
fn test_complex_pipeline() {
    let mut counter1 = 0;
    let step1 = BoxStatefulTransformer::new(move |x: i32| {
        counter1 += 1;
        format!("Step1[{}]: {}", counter1, x)
    });

    let mut counter2 = 0;
    let step2 = BoxStatefulTransformer::new(move |s: String| {
        counter2 += 1;
        format!("{} -> Step2[{}]", s, counter2)
    });

    let mut counter3 = 0;
    let step3 = BoxStatefulTransformer::new(move |s: String| {
        counter3 += 1;
        format!("{} -> Step3[{}]", s, counter3)
    });

    let mut pipeline = step1.and_then(step2).and_then(step3);

    assert_eq!(pipeline.apply(10), "Step1[1]: 10 -> Step2[1] -> Step3[1]");
    assert_eq!(pipeline.apply(20), "Step1[2]: 20 -> Step2[2] -> Step3[2]");
}

#[test]
fn test_nested_conditional() {
    let mut valid_count = 0;
    let mut invalid_count = 0;
    let mut error_count = 0;

    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        valid_count += 1;
        format!("Valid[{}]: {}", valid_count, x * 2)
    })
    .when(|x: &i32| *x > 0)
    .or_else(move |x: i32| {
        let mut sub_mapper = BoxStatefulTransformer::new(move |x: i32| {
            invalid_count += 1;
            format!("Invalid[{}]: {}", invalid_count, x + 100)
        })
        .when(move |x: &i32| *x < 0)
        .or_else(move |x: i32| {
            error_count += 1;
            format!("Error[{}]: {}", error_count, x)
        });
        sub_mapper.apply(x)
    });

    assert_eq!(mapper.apply(5), "Valid[1]: 10");
    assert_eq!(mapper.apply(-5), "Invalid[1]: 95");
    assert_eq!(mapper.apply(0), "Error[1]: 0");
    assert_eq!(mapper.apply(10), "Valid[2]: 20");
}

// ============================================================================
// State Modification Tests
// ============================================================================

#[test]
fn test_stateful_counting() {
    let mut count = 0;
    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        count += 1;
        (x, count)
    });

    assert_eq!(mapper.apply(100), (100, 1));
    assert_eq!(mapper.apply(200), (200, 2));
    assert_eq!(mapper.apply(300), (300, 3));
}

#[test]
fn test_stateful_accumulation() {
    let mut sum = 0;
    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        sum += x;
        sum
    });

    assert_eq!(mapper.apply(10), 10);
    assert_eq!(mapper.apply(20), 30);
    assert_eq!(mapper.apply(30), 60);
}

// ============================================================================
// Type Conversion Tests
// ============================================================================

#[test]
fn test_different_types() {
    let mut counter = 0;
    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        format!("Item #{}: {}", counter, x)
    });

    assert_eq!(mapper.apply(100), "Item #1: 100");
    assert_eq!(mapper.apply(200), "Item #2: 200");
}

#[test]
fn test_string_to_length() {
    let mut total_length = 0;
    let mut mapper = BoxStatefulTransformer::new(move |s: String| {
        total_length += s.len();
        total_length
    });

    assert_eq!(mapper.apply("hello".to_string()), 5);
    assert_eq!(mapper.apply("world".to_string()), 10);
    assert_eq!(mapper.apply("!".to_string()), 11);
}

// ============================================================================
// Predicate Integration Tests
// ============================================================================

#[test]
fn test_with_arc_predicate() {
    let predicate = ArcPredicate::new(|x: &i32| *x > 0);

    let mut mapper = ArcStatefulTransformer::new(|x: i32| x * 2)
        .when(predicate.clone())
        .or_else(|x: i32| -x);

    assert_eq!(mapper.apply(5), 10);
    assert_eq!(mapper.apply(-5), 5);

    // Predicate still usable
    assert!(predicate.test(&10));
    assert!(!predicate.test(&-10));
}

#[test]
fn test_with_rc_predicate() {
    let predicate = RcPredicate::new(|x: &i32| *x > 0);

    let mut mapper = RcStatefulTransformer::new(|x: i32| x * 2)
        .when(predicate.clone())
        .or_else(|x: i32| -x);

    assert_eq!(mapper.apply(5), 10);
    assert_eq!(mapper.apply(-5), 5);

    // Predicate still usable
    assert!(predicate.test(&10));
    assert!(!predicate.test(&-10));
}

// ============================================================================
// Custom StatefulTransformer Default Implementation Tests
// ============================================================================

/// Custom StatefulTransformer struct for testing default into_xxx() methods
#[derive(Clone)]
struct CustomStatefulTransformer {
    multiplier: i32,
}

impl StatefulTransformer<i32, i32> for CustomStatefulTransformer {
    fn apply(&mut self, input: i32) -> i32 {
        self.multiplier += 1;
        input * self.multiplier
    }
}

/// Custom thread-safe StatefulTransformer struct
#[derive(Clone)]
struct CustomSendStatefulTransformer {
    multiplier: i32,
}

impl StatefulTransformer<i32, i32> for CustomSendStatefulTransformer {
    fn apply(&mut self, input: i32) -> i32 {
        self.multiplier += 1;
        input * self.multiplier
    }
}

// Implement Send for CustomSendStatefulTransformer to allow conversion to ArcStatefulTransformer
unsafe impl Send for CustomSendStatefulTransformer {}
unsafe impl Sync for CustomSendStatefulTransformer {}

#[test]
fn test_custom_mapper_into_box() {
    let mapper = CustomStatefulTransformer { multiplier: 0 };
    let mut boxed = StatefulTransformer::into_box(mapper);

    assert_eq!(boxed.apply(10), 10); // 10 * 1
    assert_eq!(boxed.apply(10), 20); // 10 * 2
    assert_eq!(boxed.apply(10), 30); // 10 * 3
}

#[test]
fn test_custom_mapper_into_rc() {
    let mapper = CustomStatefulTransformer { multiplier: 0 };
    let mut rc_mapper = StatefulTransformer::into_rc(mapper);

    assert_eq!(rc_mapper.apply(10), 10); // 10 * 1
    assert_eq!(rc_mapper.apply(10), 20); // 10 * 2
    assert_eq!(rc_mapper.apply(10), 30); // 10 * 3
}

#[test]
fn test_custom_mapper_into_rc_clone() {
    let mapper = CustomStatefulTransformer { multiplier: 0 };
    let rc_mapper = mapper.into_rc();

    let mut mapper1 = rc_mapper.clone();
    let mut mapper2 = rc_mapper.clone();

    // Sharing the same state
    assert_eq!(mapper1.apply(10), 10); // 10 * 1
    assert_eq!(mapper2.apply(10), 20); // 10 * 2
    assert_eq!(mapper1.apply(10), 30); // 10 * 3
}

#[test]
fn test_custom_send_mapper_into_arc() {
    let mapper = CustomSendStatefulTransformer { multiplier: 0 };
    let mut arc_mapper = StatefulTransformer::into_arc(mapper);

    assert_eq!(arc_mapper.apply(10), 10); // 10 * 1
    assert_eq!(arc_mapper.apply(10), 20); // 10 * 2
    assert_eq!(arc_mapper.apply(10), 30); // 10 * 3
}

#[test]
fn test_custom_send_mapper_into_arc_clone() {
    let mapper = CustomSendStatefulTransformer { multiplier: 0 };
    let arc_mapper = mapper.into_arc();

    let mut mapper1 = arc_mapper.clone();
    let mut mapper2 = arc_mapper.clone();

    // Sharing the same state
    assert_eq!(mapper1.apply(10), 10); // 10 * 1
    assert_eq!(mapper2.apply(10), 20); // 10 * 2
    assert_eq!(mapper1.apply(10), 30); // 10 * 3
}

#[test]
fn test_custom_mapper_composition() {
    let mapper1 = CustomStatefulTransformer { multiplier: 0 };
    let boxed1 = mapper1.into_box();

    let mapper2 = CustomStatefulTransformer { multiplier: 10 };
    let boxed2 = mapper2.into_box();

    let mut composed = boxed1.and_then(boxed2);

    // (10 * 1) = 10, then 10 * 11 = 110
    assert_eq!(composed.apply(10), 110);
    // (10 * 2) = 20, then 20 * 12 = 240
    assert_eq!(composed.apply(10), 240);
}

#[test]
fn test_custom_mapper_conditional() {
    let mapper1 = CustomStatefulTransformer { multiplier: 1 };
    let boxed1 = mapper1.into_box();

    let mapper2 = CustomStatefulTransformer { multiplier: 100 };
    let boxed2 = mapper2.into_box();

    let mut conditional = boxed1.when(|x: &i32| *x > 10).or_else(boxed2);

    // 15 > 10, use mapper1: 15 * 2 = 30
    assert_eq!(conditional.apply(15), 30);
    // 5 <= 10, use mapper2: 5 * 101 = 505
    assert_eq!(conditional.apply(5), 505);
    // 20 > 10, use mapper1: 20 * 3 = 60
    assert_eq!(conditional.apply(20), 60);
}

/// Test custom StatefulTransformer with string types
#[derive(Clone)]
struct StringLengthStatefulTransformer {
    total_length: usize,
}

impl StatefulTransformer<String, String> for StringLengthStatefulTransformer {
    fn apply(&mut self, input: String) -> String {
        self.total_length += input.len();
        format!("[{}] {}", self.total_length, input)
    }
}

#[test]
fn test_custom_string_mapper_into_box() {
    let mapper = StringLengthStatefulTransformer { total_length: 0 };
    let mut boxed = StatefulTransformer::into_box(mapper);

    assert_eq!(boxed.apply("hello".to_string()), "[5] hello");
    assert_eq!(boxed.apply("world".to_string()), "[10] world");
    assert_eq!(boxed.apply("!".to_string()), "[11] !");
}

#[test]
fn test_custom_string_mapper_into_rc() {
    let mapper = StringLengthStatefulTransformer { total_length: 0 };
    let mut rc_mapper = StatefulTransformer::into_rc(mapper);

    assert_eq!(rc_mapper.apply("hello".to_string()), "[5] hello");
    assert_eq!(rc_mapper.apply("world".to_string()), "[10] world");
    assert_eq!(rc_mapper.apply("!".to_string()), "[11] !");
}

/// Test custom StatefulTransformer with complex state
struct StatefulStatefulTransformer {
    count: i32,
    sum: i32,
    history: Vec<i32>,
}

impl StatefulTransformer<i32, (i32, i32, usize)> for StatefulStatefulTransformer {
    fn apply(&mut self, input: i32) -> (i32, i32, usize) {
        self.count += 1;
        self.sum += input;
        self.history.push(input);
        (self.count, self.sum, self.history.len())
    }
}

#[test]
fn test_stateful_mapper_into_box() {
    let mapper = StatefulStatefulTransformer {
        count: 0,
        sum: 0,
        history: Vec::new(),
    };
    let mut boxed = StatefulTransformer::into_box(mapper);

    assert_eq!(boxed.apply(10), (1, 10, 1));
    assert_eq!(boxed.apply(20), (2, 30, 2));
    assert_eq!(boxed.apply(30), (3, 60, 3));
}

#[test]
fn test_stateful_mapper_into_rc() {
    let mapper = StatefulStatefulTransformer {
        count: 0,
        sum: 0,
        history: Vec::new(),
    };
    let rc_mapper = mapper.into_rc();

    let mut mapper1 = rc_mapper.clone();
    let mut mapper2 = rc_mapper;

    // Sharing the same state
    assert_eq!(mapper1.apply(10), (1, 10, 1));
    assert_eq!(mapper2.apply(20), (2, 30, 2));
    assert_eq!(mapper1.apply(30), (3, 60, 3));
}

// ============================================================================
// into_fn Tests
// ============================================================================

#[test]
fn test_box_mapper_into_fn() {
    let mut counter = 0;
    let mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    let mut closure = StatefulTransformer::into_fn(mapper);
    assert_eq!(closure(10), 11); // 10 + 1
    assert_eq!(closure(10), 12); // 10 + 2
    assert_eq!(closure(10), 13); // 10 + 3
}

#[test]
fn test_box_mapper_into_fn_identity() {
    let mapper = BoxStatefulTransformer::<i32, i32>::identity();
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(42), 42);
    assert_eq!(closure(100), 100);
}

#[test]
fn test_box_mapper_into_fn_constant() {
    let mapper = BoxStatefulTransformer::constant("hello");
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(1), "hello");
    assert_eq!(closure(2), "hello");
    assert_eq!(closure(3), "hello");
}

#[test]
fn test_arc_mapper_into_fn() {
    let mut counter = 0;
    let mapper = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x * counter
    });

    let mut closure = StatefulTransformer::into_fn(mapper);
    assert_eq!(closure(10), 10); // 10 * 1
    assert_eq!(closure(10), 20); // 10 * 2
    assert_eq!(closure(10), 30); // 10 * 3
}

#[test]
fn test_arc_mapper_into_fn_identity() {
    let mapper = ArcStatefulTransformer::<i32, i32>::identity();
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(42), 42);
    assert_eq!(closure(100), 100);
}

#[test]
fn test_arc_mapper_into_fn_constant() {
    let mapper = ArcStatefulTransformer::constant("world");
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(1), "world");
    assert_eq!(closure(2), "world");
}

#[test]
fn test_rc_mapper_into_fn() {
    let mut counter = 0;
    let mapper = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x - counter
    });

    let mut closure = StatefulTransformer::into_fn(mapper);
    assert_eq!(closure(10), 9); // 10 - 1
    assert_eq!(closure(10), 8); // 10 - 2
    assert_eq!(closure(10), 7); // 10 - 3
}

#[test]
fn test_rc_mapper_into_fn_identity() {
    let mapper = RcStatefulTransformer::<i32, i32>::identity();
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(42), 42);
    assert_eq!(closure(100), 100);
}

#[test]
fn test_rc_mapper_into_fn_constant() {
    let mapper = RcStatefulTransformer::constant("rust");
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(1), "rust");
    assert_eq!(closure(2), "rust");
}

#[test]
fn test_closure_into_fn() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x + counter * 10
    };

    let mut closure = StatefulTransformer::into_fn(mapper);
    assert_eq!(closure(5), 15); // 5 + 1 * 10
    assert_eq!(closure(5), 25); // 5 + 2 * 10
    assert_eq!(closure(5), 35); // 5 + 3 * 10
}

#[test]
fn test_closure_into_fn_direct() {
    let mut counter = 0;
    let mut closure = StatefulTransformer::into_fn(move |x: i32| {
        counter += 1;
        x * counter
    });

    assert_eq!(closure(10), 10); // 10 * 1
    assert_eq!(closure(10), 20); // 10 * 2
}

#[test]
fn test_custom_mapper_into_fn() {
    let mapper = CustomStatefulTransformer { multiplier: 0 };
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(10), 10); // 10 * 1
    assert_eq!(closure(10), 20); // 10 * 2
    assert_eq!(closure(10), 30); // 10 * 3
}

#[test]
fn test_custom_string_mapper_into_fn() {
    let mapper = StringLengthStatefulTransformer { total_length: 0 };
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure("hello".to_string()), "[5] hello");
    assert_eq!(closure("world".to_string()), "[10] world");
    assert_eq!(closure("!".to_string()), "[11] !");
}

#[test]
fn test_stateful_mapper_into_fn() {
    let mapper = StatefulStatefulTransformer {
        count: 0,
        sum: 0,
        history: Vec::new(),
    };
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(10), (1, 10, 1));
    assert_eq!(closure(20), (2, 30, 2));
    assert_eq!(closure(30), (3, 60, 3));
}

#[test]
fn test_into_fn_composition() {
    let mut counter1 = 0;
    let mapper1 = BoxStatefulTransformer::new(move |x: i32| {
        counter1 += 1;
        x + counter1
    });

    let mapper2 = RcStatefulTransformer::new(|x: i32| x * 2);

    let composed = mapper1.and_then(mapper2);
    let mut closure = composed.into_fn();

    assert_eq!(closure(10), 22); // (10 + 1) * 2
    assert_eq!(closure(10), 24); // (10 + 2) * 2
}

#[test]
fn test_into_fn_after_conversion() {
    let mut counter = 0;
    let original_closure = move |x: i32| {
        counter += 1;
        x + counter
    };

    // First convert to BoxStatefulTransformer, then back to closure
    let boxed = StatefulTransformer::into_box(original_closure);
    let mut final_closure = boxed.into_fn();

    assert_eq!(final_closure(10), 11);
    assert_eq!(final_closure(10), 12);
}

#[test]
fn test_into_fn_with_string_return() {
    let mapper = BoxStatefulTransformer::new(|x: i32| format!("Value: {}", x * 2));
    let mut closure = StatefulTransformer::into_fn(mapper);

    assert_eq!(closure(5), "Value: 10");
    assert_eq!(closure(10), "Value: 20");
}

#[test]
fn test_into_fn_chained_usage() {
    // Test chained calls: StatefulTransformer -> into_box -> and_then -> into_fn
    let mut counter = 0;
    let mapper1 = move |x: i32| {
        counter += 1;
        x + counter
    };

    let boxed = StatefulTransformer::into_box(mapper1);
    let composed = boxed.and_then(|x: i32| x * 2);
    let mut closure = composed.into_fn();

    assert_eq!(closure(10), 22); // (10 + 1) * 2
    assert_eq!(closure(10), 24); // (10 + 2) * 2
}

// ============================================================================
// Closure to_xxx Non-Consuming Conversion Tests
// ============================================================================

#[test]
fn test_closure_to_box() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x + counter
    };

    // Non-consuming conversion: original closure still usable
    let mut boxed = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed.apply(10), 11); // 10 + 1
    assert_eq!(boxed.apply(10), 12); // 10 + 2

    // Can call to_box() multiple times
    let mut boxed2 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed2.apply(20), 21); // 20 + 1 (new state)
    assert_eq!(boxed2.apply(20), 22); // 20 + 2

    // Original boxed still maintains its state
    assert_eq!(boxed.apply(10), 13); // 10 + 3
}

#[test]
fn test_closure_to_rc() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x * counter
    };

    // Non-consuming conversion
    let rc_mapper = StatefulTransformer::to_rc(&mapper);
    let mut rc1 = rc_mapper.clone();
    let mut rc2 = rc_mapper.clone();

    // Shared state
    assert_eq!(rc1.apply(10), 10); // 10 * 1
    assert_eq!(rc2.apply(10), 20); // 10 * 2
    assert_eq!(rc1.apply(10), 30); // 10 * 3

    // Can call to_rc() again, creating a new independent state
    let rc_mapper2 = StatefulTransformer::to_rc(&mapper);
    let mut rc3 = rc_mapper2.clone();
    assert_eq!(rc3.apply(10), 10); // 10 * 1 (new state)
}

#[test]
fn test_closure_to_arc() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x - counter
    };

    // Non-consuming conversion (requires Clone + Send + Sync)
    let arc_mapper = StatefulTransformer::to_arc(&mapper);
    let mut arc1 = arc_mapper.clone();
    let mut arc2 = arc_mapper.clone();

    // Shared state
    assert_eq!(arc1.apply(10), 9); // 10 - 1
    assert_eq!(arc2.apply(10), 8); // 10 - 2
    assert_eq!(arc1.apply(10), 7); // 10 - 3

    // Can call to_arc() again, creating a new independent state
    let arc_mapper2 = StatefulTransformer::to_arc(&mapper);
    let mut arc3 = arc_mapper2.clone();
    assert_eq!(arc3.apply(10), 9); // 10 - 1 (new state)
}

#[test]
fn test_closure_to_fn() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        x + counter * 10
    };

    // Non-consuming conversion
    let mut closure = StatefulTransformer::to_fn(&mapper);
    assert_eq!(closure(5), 15); // 5 + 1 * 10
    assert_eq!(closure(5), 25); // 5 + 2 * 10

    // Can call to_fn() again, creating a new independent state
    let mut closure2 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(closure2(5), 15); // 5 + 1 * 10 (new state)
    assert_eq!(closure2(5), 25); // 5 + 2 * 10

    // Original closure still maintains its state
    assert_eq!(closure(5), 35); // 5 + 3 * 10
}

#[test]
fn test_closure_to_box_with_string() {
    let mut count = 0;
    let mapper = move |x: String| {
        count += 1;
        format!("[{}] {}", count, x)
    };

    let mut boxed1 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed1.apply("hello".to_string()), "[1] hello");
    assert_eq!(boxed1.apply("world".to_string()), "[2] world");

    let mut boxed2 = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed2.apply("rust".to_string()), "[1] rust"); // new state
}

#[test]
fn test_closure_to_rc_shared_state() {
    let mut sum = 0;
    let mapper = move |x: i32| {
        sum += x;
        sum
    };

    let rc_mapper = StatefulTransformer::to_rc(&mapper);
    let mut rc1 = rc_mapper.clone();
    let mut rc2 = rc_mapper.clone();

    // Verify shared state
    assert_eq!(rc1.apply(10), 10);
    assert_eq!(rc2.apply(20), 30); // sharing the same sum
    assert_eq!(rc1.apply(30), 60); // continue accumulating
}

#[test]
fn test_closure_to_arc_thread_safe() {
    let mut product = 1;
    let mapper = move |x: i32| {
        product *= x;
        product
    };

    let arc_mapper = StatefulTransformer::to_arc(&mapper);
    let mut arc1 = arc_mapper.clone();
    let mut arc2 = arc_mapper.clone();

    // Verify shared state (thread-safe)
    assert_eq!(arc1.apply(2), 2); // 1 * 2
    assert_eq!(arc2.apply(3), 6); // 2 * 3
    assert_eq!(arc1.apply(4), 24); // 6 * 4
}

#[test]
fn test_closure_to_box_complex_type() {
    let mut history = Vec::new();
    let mapper = move |x: i32| {
        history.push(x);
        (x, history.len())
    };

    let mut boxed = StatefulTransformer::to_box(&mapper);
    assert_eq!(boxed.apply(10), (10, 1));
    assert_eq!(boxed.apply(20), (20, 2));
    assert_eq!(boxed.apply(30), (30, 3));
}

#[test]
fn test_closure_to_fn_multiple_calls() {
    let mut counter = 0;
    let mapper = move |x: i32| {
        counter += 1;
        (x, counter)
    };

    // First call to to_fn()
    let mut fn1 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(fn1(100), (100, 1));
    assert_eq!(fn1(200), (200, 2));

    // Second call to to_fn(), creating independent state
    let mut fn2 = StatefulTransformer::to_fn(&mapper);
    assert_eq!(fn2(300), (300, 1)); // new counter starts from 1

    // First closure's state unaffected
    assert_eq!(fn1(400), (400, 3));
}

#[test]
fn test_closure_to_rc_multiple_conversions() {
    let mut value = 0;
    let mapper = move |x: i32| {
        value += x;
        value
    };

    // First RcStatefulTransformer
    let rc1 = StatefulTransformer::to_rc(&mapper);
    let mut rc1_ref = rc1.clone();
    assert_eq!(rc1_ref.apply(10), 10);

    // Second RcStatefulTransformer (independent state)
    let rc2 = StatefulTransformer::to_rc(&mapper);
    let mut rc2_ref = rc2.clone();
    assert_eq!(rc2_ref.apply(20), 20); // independent state, starts from 0

    // First RcStatefulTransformer's state unaffected
    assert_eq!(rc1_ref.apply(30), 40); // 10 + 30
}

#[test]
fn test_closure_to_arc_multiple_conversions() {
    let mut count = 0;
    let mapper = move |x: i32| {
        count += 1;
        x * count
    };

    // First ArcStatefulTransformer
    let arc1 = StatefulTransformer::to_arc(&mapper);
    let mut arc1_ref = arc1.clone();
    assert_eq!(arc1_ref.apply(10), 10); // 10 * 1

    // Second ArcStatefulTransformer (independent state)
    let arc2 = StatefulTransformer::to_arc(&mapper);
    let mut arc2_ref = arc2.clone();
    assert_eq!(arc2_ref.apply(10), 10); // 10 * 1 (new count)

    // First ArcStatefulTransformer's state unaffected
    assert_eq!(arc1_ref.apply(10), 20); // 10 * 2
}

// ============================================================================
// TransformerOnce Implementation Tests
// ============================================================================

/// Test BoxStatefulTransformer implements TransformerOnce trait
#[test]
fn test_box_mapper_apply() {
    let mut counter = 0;
    let mut mapper = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });

    // BoxStatefulTransformer can be consumed as TransformerOnce
    assert_eq!(StatefulTransformer::apply(&mut mapper, 10), 11); // 10 + 1
}

// ============================================================================
// Conditional StatefulTransformer Display/Debug Tests
// ============================================================================

#[cfg(test)]
mod conditional_stateful_transformer_display_debug_tests {
    use super::*;

    #[test]
    fn test_box_conditional_stateful_transformer_display() {
        let mut counter = 0;
        let add = BoxStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let display_str = format!("{}", conditional);
        assert!(display_str.contains("BoxConditionalStatefulTransformer"));
    }

    #[test]
    fn test_box_conditional_stateful_transformer_display_no_name() {
        let mut counter = 0;
        let add = BoxStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let display_str = format!("{}", conditional);
        assert_eq!(
            display_str,
            "BoxConditionalStatefulTransformer(BoxStatefulTransformer, BoxPredicate(unnamed))"
        );
    }

    #[test]
    fn test_box_conditional_stateful_transformer_debug() {
        let mut counter = 0;
        let add = BoxStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let debug_str = format!("{:?}", conditional);
        assert!(debug_str.contains("BoxConditionalStatefulTransformer"));
    }

    #[test]
    fn test_rc_conditional_stateful_transformer_display() {
        let mut counter = 0;
        let add = RcStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let display_str = format!("{}", conditional);
        assert!(display_str.contains("RcConditionalStatefulTransformer"));
    }

    #[test]
    fn test_rc_conditional_stateful_transformer_display_no_name() {
        let mut counter = 0;
        let add = RcStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let display_str = format!("{}", conditional);
        assert_eq!(
            display_str,
            "RcConditionalStatefulTransformer(RcStatefulTransformer, RcPredicate(unnamed))"
        );
    }

    #[test]
    fn test_rc_conditional_stateful_transformer_debug() {
        let mut counter = 0;
        let add = RcStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let debug_str = format!("{:?}", conditional);
        assert!(debug_str.contains("RcConditionalStatefulTransformer"));
    }

    #[test]
    fn test_arc_conditional_stateful_transformer_display() {
        let mut counter = 0;
        let add = ArcStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let display_str = format!("{}", conditional);
        assert!(display_str.contains("ArcConditionalStatefulTransformer"));
    }

    #[test]
    fn test_arc_conditional_stateful_transformer_display_no_name() {
        let mut counter = 0;
        let add = ArcStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let display_str = format!("{}", conditional);
        assert_eq!(
            display_str,
            "ArcConditionalStatefulTransformer(ArcStatefulTransformer, ArcPredicate(unnamed))"
        );
    }

    #[test]
    fn test_arc_conditional_stateful_transformer_debug() {
        let mut counter = 0;
        let add = ArcStatefulTransformer::new(move |x: i32| {
            counter += 1;
            x + counter
        });
        let conditional = add.when(|x: &i32| *x > 0);
        let debug_str = format!("{:?}", conditional);
        assert!(debug_str.contains("ArcConditionalStatefulTransformer"));
    }
}

// ============================================================================
// Basic StatefulTransformer Display Tests
// ============================================================================

#[test]
fn test_box_stateful_transformer_display_with_name() {
    let mut counter = 0;
    let transformer = BoxStatefulTransformer::new_with_name("counter", move |x: i32| {
        counter += 1;
        x + counter
    });
    let display_str = format!("{}", transformer);
    assert_eq!(display_str, "BoxStatefulTransformer(counter)");
}

#[test]
fn test_box_stateful_transformer_display_without_name() {
    let mut counter = 0;
    let transformer = BoxStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });
    let display_str = format!("{}", transformer);
    assert_eq!(display_str, "BoxStatefulTransformer");
}

#[test]
fn test_rc_stateful_transformer_display_with_name() {
    let mut counter = 0;
    let transformer = RcStatefulTransformer::new_with_name("counter", move |x: i32| {
        counter += 1;
        x + counter
    });
    let display_str = format!("{}", transformer);
    assert_eq!(display_str, "RcStatefulTransformer(counter)");
}

#[test]
fn test_rc_stateful_transformer_display_without_name() {
    let mut counter = 0;
    let transformer = RcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });
    let display_str = format!("{}", transformer);
    assert_eq!(display_str, "RcStatefulTransformer");
}

#[test]
fn test_arc_stateful_transformer_display_with_name() {
    let mut counter = 0;
    let transformer = ArcStatefulTransformer::new_with_name("counter", move |x: i32| {
        counter += 1;
        x + counter
    });
    let display_str = format!("{}", transformer);
    assert_eq!(display_str, "ArcStatefulTransformer(counter)");
}

#[test]
fn test_arc_stateful_transformer_display_without_name() {
    let mut counter = 0;
    let transformer = ArcStatefulTransformer::new(move |x: i32| {
        counter += 1;
        x + counter
    });
    let display_str = format!("{}", transformer);
    assert_eq!(display_str, "ArcStatefulTransformer");
}

// ============================================================================
// StatefulTransformer Trait Default Methods Tests - into_once, to_once
// ============================================================================

#[cfg(test)]
mod test_stateful_transformer_trait_default_methods {
    use super::*;
    use qubit_function::TransformerOnce;
    use std::sync::{
        atomic::{
            AtomicUsize,
            Ordering,
        },
        Arc,
    };

    #[test]
    fn test_custom_stateful_transformer_into_once() {
        let counter = Arc::new(AtomicUsize::new(0));

        struct MyStatefulTransformer {
            counter: Arc<AtomicUsize>,
        }

        impl StatefulTransformer<i32, i32> for MyStatefulTransformer {
            fn apply(&mut self, value: i32) -> i32 {
                self.counter.fetch_add(1, Ordering::SeqCst);
                value * 2
            }
        }

        let my_transformer = MyStatefulTransformer {
            counter: counter.clone(),
        };

        // Test into_once() - should consume the transformer
        let once_transformer = my_transformer.into_once();
        let result = once_transformer.apply(5);
        assert_eq!(result, 10);
        assert_eq!(counter.load(Ordering::SeqCst), 1);
    }

    #[test]
    fn test_custom_stateful_transformer_to_once() {
        let counter = Arc::new(AtomicUsize::new(0));

        #[derive(Clone)]
        struct MyStatefulTransformer {
            counter: Arc<AtomicUsize>,
        }

        impl StatefulTransformer<i32, i32> for MyStatefulTransformer {
            fn apply(&mut self, value: i32) -> i32 {
                self.counter.fetch_add(1, Ordering::SeqCst);
                value * 2
            }
        }

        let mut my_transformer = MyStatefulTransformer {
            counter: counter.clone(),
        };

        // Test to_once() - should not consume the original
        let once_transformer = my_transformer.to_once();
        let result = once_transformer.apply(5);
        assert_eq!(result, 10);
        assert_eq!(counter.load(Ordering::SeqCst), 1);

        // Original transformer should still be usable
        let result2 = my_transformer.apply(3);
        assert_eq!(result2, 6);
        assert_eq!(counter.load(Ordering::SeqCst), 2);
    }
}