subms-merge-iterator 0.10.0

submillisecond.com cookbook recipe - storage: subms-merge-iterator. N-way merge of sorted streams via min-heap.
Documentation 
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use super::*;

fn e(k: &str, v: &str) -> DedupEntry<String, String> {
    DedupEntry::new(k.to_string(), v.to_string())
}

#[test]
fn distinct_keys_pass_through() {
    let s0 = vec![e("a", "1"), e("c", "3")];
    let s1 = vec![e("b", "2"), e("d", "4")];
    let merged: Vec<_> = DedupMergeIterator::new([s0.into_iter(), s1.into_iter()]).collect();
    assert_eq!(
        merged,
        vec![e("a", "1"), e("b", "2"), e("c", "3"), e("d", "4")]
    );
}

#[test]
fn duplicate_key_picks_latest_source() {
    let s0 = vec![e("k", "old")];
    let s1 = vec![e("k", "new")];
    let merged: Vec<_> = DedupMergeIterator::new([s0.into_iter(), s1.into_iter()]).collect();
    assert_eq!(merged, vec![e("k", "new")]);
}

#[test]
fn three_way_duplicate_picks_highest_source() {
    let s0 = vec![e("k", "v0")];
    let s1 = vec![e("k", "v1")];
    let s2 = vec![e("k", "v2")];
    let merged: Vec<_> =
        DedupMergeIterator::new([s0.into_iter(), s1.into_iter(), s2.into_iter()]).collect();
    assert_eq!(merged, vec![e("k", "v2")]);
}

#[test]
fn empty_sources_yield_empty() {
    let s0: Vec<DedupEntry<String, String>> = vec![];
    let s1: Vec<DedupEntry<String, String>> = vec![];
    let merged: Vec<_> = DedupMergeIterator::new([s0.into_iter(), s1.into_iter()]).collect();
    assert!(merged.is_empty());
}

#[test]
fn interleaved_with_some_duplicates() {
    let s0 = vec![e("a", "a0"), e("b", "b0"), e("c", "c0")];
    let s1 = vec![e("b", "b1"), e("d", "d1")];
    let merged: Vec<_> = DedupMergeIterator::new([s0.into_iter(), s1.into_iter()]).collect();
    assert_eq!(
        merged,
        vec![e("a", "a0"), e("b", "b1"), e("c", "c0"), e("d", "d1")]
    );
}

#[test]
fn dedup_preserves_count_with_unique_keys() {
    let s0: Vec<_> = (0..100i32).map(|i| DedupEntry::new(i * 2, i)).collect();
    let s1: Vec<_> = (0..100i32).map(|i| DedupEntry::new(i * 2 + 1, i)).collect();
    let merged: Vec<_> = DedupMergeIterator::new([s0.into_iter(), s1.into_iter()]).collect();
    assert_eq!(merged.len(), 200);
    for w in merged.windows(2) {
        assert!(w[0].key < w[1].key);
    }
}

#[test]
fn heap_item_eq_and_ord_direct() {
    let a = HeapItem {
        key: 5i32,
        source: 0,
        value: "a",
    };
    let b = HeapItem {
        key: 5i32,
        source: 0,
        value: "different-value",
    };
    let c = HeapItem {
        key: 5i32,
        source: 1,
        value: "a",
    };
    let d = HeapItem {
        key: 9i32,
        source: 0,
        value: "a",
    };
    // eq ignores value; keyed on (key, source).
    assert!(a == b);
    assert!(a != c);
    assert!(a != d);
    // Ord: key asc, then source DESC (latest source is "smaller").
    assert_eq!(a.cmp(&d), std::cmp::Ordering::Less);
    assert_eq!(a.cmp(&c), std::cmp::Ordering::Greater);
    assert_eq!(a.partial_cmp(&b), Some(std::cmp::Ordering::Equal));
}

// Multi-source, multi-element streams with duplicates. Repeatedly
// exercises the advance() re-push and the same-key drain (break arm)
// across many next() calls.
#[test]
fn long_interleaved_streams_with_repeated_advances() {
    let s0: Vec<_> = (0..30i32).map(|i| DedupEntry::new(i, i * 10)).collect();
    let s1: Vec<_> = (0..30i32).map(|i| DedupEntry::new(i, i * 100)).collect();
    let s2: Vec<_> = (10..40i32).map(|i| DedupEntry::new(i, i)).collect();
    let merged: Vec<_> =
        DedupMergeIterator::new([s0.into_iter(), s1.into_iter(), s2.into_iter()]).collect();
    // One entry per distinct key 0..40.
    assert_eq!(merged.len(), 40);
    for w in merged.windows(2) {
        assert!(w[0].key < w[1].key);
    }
    // Keys 10..30 have the highest source (2) winning; 0..10 source 1.
    assert_eq!(merged[0], DedupEntry::new(0, 0));
    assert_eq!(merged[20], DedupEntry::new(20, 20));
}

#[test]
fn all_duplicates_collapses_to_one_per_key() {
    // Three sources, each carrying the same five keys.
    let mk = |tag: &str| {
        (0..5i32)
            .map(move |k| DedupEntry::new(k, format!("{tag}-{k}")))
            .collect::<Vec<_>>()
    };
    let merged: Vec<_> = DedupMergeIterator::new([
        mk("a").into_iter(),
        mk("b").into_iter(),
        mk("c").into_iter(),
    ])
    .collect();
    // Latest source (c) wins for every key.
    assert_eq!(
        merged,
        (0..5i32)
            .map(|k| DedupEntry::new(k, format!("c-{k}")))
            .collect::<Vec<_>>()
    );
}