src/obikmer/src/cmd/filter.rs

@@ -2,14 +2,14 @@ use std::path::PathBuf;
 
 use clap::Args;
 use obikindex::{KmerIndex, MergeMode};
-use obikpartitionner::filter::{MaxTotalCount, MinTotalCount};
+use obikpartitionner::filter::{MaxTotalCount, MinComplexity, MinTotalCount};
 use obisys::Reporter;
 use tracing::info;
 
 use super::predicate::FilterArgs as KmerFilterArgs;
 
 #[derive(Args)]
-pub struct FilterArgs {
+pub struct FilterCmdArgs {
     /// Source index directory
     pub source: PathBuf,
 
@@ -28,6 +28,18 @@ pub struct FilterArgs {
     #[arg(long)]
     pub max_total_count: Option<u32>,
 
+    /// Minimum normalized entropy (complexity) to keep a k-mer — same metric
+    /// as `obikmer index`'s --theta, applied here to k-mers already committed
+    /// to the source index (reconstructed from unitigs.bin). K-mers scoring
+    /// below this are removed.
+    #[arg(long)]
+    pub min_complexity: Option<f64>,
+
+    /// Maximum sub-word size for the complexity computation (see `obikmer
+    /// index`'s --level-max). Only used when --min-complexity is set.
+    #[arg(long, default_value_t = 6)]
+    pub complexity_level_max: usize,
+
     /// Output as presence/absence instead of counts
     #[arg(long)]
     pub presence: bool,
@@ -37,7 +49,7 @@ pub struct FilterArgs {
     pub force: bool,
 }
 
-pub fn run(args: FilterArgs) {
+pub fn run(args: FilterCmdArgs) {
     let src = KmerIndex::open(&args.source).unwrap_or_else(|e| {
         eprintln!("error opening source index: {e}");
         std::process::exit(1);
@@ -62,6 +74,9 @@ pub fn run(args: FilterArgs) {
     if let Some(v) = args.max_total_count {
         filters.push(Box::new(MaxTotalCount { total: v }));
     }
+    if let Some(theta) = args.min_complexity {
+        filters.push(Box::new(MinComplexity { level_max: args.complexity_level_max, theta }));
+    }
 
     let mut rep = Reporter::new();
     KmerIndex::rebuild(&args.output, &src, &filters, mode, args.force, &mut rep)

src/obikmer/src/main.rs

@@ -21,7 +21,7 @@ enum Commands {
     /// Merge multiple built indexes into one
     Merge(cmd::merge::MergeArgs),
     /// Apply row-level selection (σ) to an index: retain only k-mers matching the predicates
-    Filter(cmd::filter::FilterArgs),
+    Filter(cmd::filter::FilterCmdArgs),
     /// Project and/or aggregate genome columns into a new or in-place index
     Select(cmd::select::SelectArgs),
     /// Query an index with sequences and annotate matches

src/obikpartitionner/Cargo.toml

@@ -6,7 +6,6 @@ edition = "2024"
 [dev-dependencies]
 tempfile = "3"
 obikseq   = { path = "../obikseq",   features = ["test-utils"] }
-obiskbuilder = { path = "../obiskbuilder" }
 obiread   = { path = "../obiread" }
 obikrope  = { path = "../obikrope" }
 
@@ -14,6 +13,7 @@ obikrope  = { path = "../obikrope" }
 niffler = "3.0.0"
 remove_dir_all = "0.8"
 obikseq      = { path = "../obikseq" }
+obiskbuilder = { path = "../obiskbuilder" }
 obiskio      = { path = "../obiskio" }
 obidebruinj  = { path = "../obidebruinj" }
 obilayeredmap = { path = "../obilayeredmap" }

src/obikpartitionner/src/dump_layer.rs

@@ -62,7 +62,7 @@ impl KmerPartition {
                 for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
                     if let Some(slot) = mphf.find(kmer) {
                         let row = mat.row(slot);
-                        if passes_all(filters, &row, n_genomes) {
+                        if passes_all(filters, kmer, &row, n_genomes) {
                             cont = cb(kmer, row);
                             if !cont { break; }
                         }
@@ -75,7 +75,7 @@ impl KmerPartition {
                 for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
                     if let Some(slot) = mphf.find(kmer) {
                         let row: Box<[u32]> = mat.row(slot).iter().map(|&b| b as u32).collect();
-                        if passes_all(filters, &row, n_genomes) {
+                        if passes_all(filters, kmer, &row, n_genomes) {
                             cont = cb(kmer, row);
                             if !cont { break; }
                         }
@@ -83,18 +83,19 @@ impl KmerPartition {
                 }
                 cont
             } else {
-                // No data matrix: implicit presence — all values are 1.
-                // The filter result is identical for every kmer, so evaluate once.
+                // No data matrix: implicit presence — all values are 1. `row`
+                // is identical for every kmer, but a filter can still depend
+                // on the kmer's own sequence (e.g. MinComplexity), so this
+                // cannot be evaluated once for the whole layer — filters must
+                // still be tested per kmer.
                 let all_present: Box<[u32]> = vec![1u32; n_genomes].into();
                 let mut cont = true;
-                if passes_all(filters, &all_present, n_genomes) {
                 for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
-                        if mphf.find(kmer).is_some() {
+                    if mphf.find(kmer).is_some() && passes_all(filters, kmer, &all_present, n_genomes) {
                         cont = cb(kmer, all_present.clone());
                         if !cont { break; }
                     }
                 }
-                }
                 cont
             };
 
@@ -140,7 +141,7 @@ impl KmerPartition {
                 for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
                     if let Some(slot) = mphf.find(kmer) {
                         let row = mat.row(slot);
-                        if passes_all(filters, &row, n_genomes) {
+                        if passes_all(filters, kmer, &row, n_genomes) {
                             cont = cb(part, layer, kmer, row);
                             if !cont { break; }
                         }
@@ -153,7 +154,7 @@ impl KmerPartition {
                 for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
                     if let Some(slot) = mphf.find(kmer) {
                         let row: Box<[u32]> = mat.row(slot).iter().map(|&b| b as u32).collect();
-                        if passes_all(filters, &row, n_genomes) {
+                        if passes_all(filters, kmer, &row, n_genomes) {
                             cont = cb(part, layer, kmer, row);
                             if !cont { break; }
                         }
@@ -161,16 +162,17 @@ impl KmerPartition {
                 }
                 cont
             } else {
+                // Same as iter_partition_kmers: row is constant but a filter
+                // may still depend on the kmer's own sequence, so this must
+                // be tested per kmer, not once for the whole layer.
                 let all_present: Box<[u32]> = vec![1u32; n_genomes].into();
                 let mut cont = true;
-                if passes_all(filters, &all_present, n_genomes) {
                 for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
-                        if mphf.find(kmer).is_some() {
+                    if mphf.find(kmer).is_some() && passes_all(filters, kmer, &all_present, n_genomes) {
                         cont = cb(part, layer, kmer, all_present.clone());
                         if !cont { break; }
                     }
                 }
-                }
                 cont
             };
 

src/obikpartitionner/src/filter.rs

@@ -1,17 +1,24 @@
 use obicompactvec::FilterMask;
+use obikseq::CanonicalKmer;
 
-/// Trait for kmer row filters.
+/// Trait for kmer filters.
 ///
+/// `kmer` is the k-mer's own canonical sequence, reconstructed from the
+/// source index's `unitigs.bin` (always present — see `rebuild_layer.rs`);
 /// `row` contains raw per-genome counts (or 0/1 for presence/absence data).
-/// `n_genomes` equals `row.len()`.
+/// `n_genomes` equals `row.len()`. Most filters only need `row` — `kmer` is
+/// there for filters that reason about the k-mer's sequence itself (e.g.
+/// [`MinComplexity`]).
 pub trait KmerFilter: Send + Sync {
-    fn passes(&self, row: &[u32], n_genomes: usize) -> bool;
+    fn passes(&self, kmer: CanonicalKmer, row: &[u32], n_genomes: usize) -> bool;
 
     /// Express this filter as a [`FilterMask`] column-operation expression.
     ///
     /// Returns `Some(expr)` if the filter can be evaluated solely from matrix
     /// column aggregates (no per-kmer row scan needed).  Returns `None` if the
-    /// filter requires row-level inspection.
+    /// filter requires row-level inspection — always the case for a filter
+    /// that needs the k-mer's sequence, since a `FilterMask` only expresses
+    /// per-genome column aggregates, never per-slot sequence data.
     ///
     /// `threshold` semantics in the returned mask use `>= threshold`, matching
     /// [`obicompactvec::MatrixGroupOps`].  Implementations must add 1 to any
@@ -23,8 +30,13 @@ pub trait KmerFilter: Send + Sync {
 
 /// True when `row` passes every filter in `filters`.
 /// Returns `true` if `filters` is empty.
-pub fn passes_all(filters: &[Box<dyn KmerFilter>], row: &[u32], n_genomes: usize) -> bool {
-    filters.iter().all(|f| f.passes(row, n_genomes))
+pub fn passes_all(
+    filters: &[Box<dyn KmerFilter>],
+    kmer: CanonicalKmer,
+    row: &[u32],
+    n_genomes: usize,
+) -> bool {
+    filters.iter().all(|f| f.passes(kmer, row, n_genomes))
 }
 
 // ── Quorum filters ─────────────────────────────────────────────────────────────
@@ -40,7 +52,7 @@ pub struct MinGenomeFraction {
 }
 
 impl KmerFilter for MinGenomeFraction {
-    fn passes(&self, row: &[u32], n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], n_genomes: usize) -> bool {
         let p = present_count(row, self.threshold);
         p as f64 / n_genomes as f64 >= self.frac
     }
@@ -63,7 +75,7 @@ pub struct MaxGenomeFraction {
 }
 
 impl KmerFilter for MaxGenomeFraction {
-    fn passes(&self, row: &[u32], n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], n_genomes: usize) -> bool {
         let p = present_count(row, self.threshold);
         p as f64 / n_genomes as f64 <= self.frac
     }
@@ -86,7 +98,7 @@ pub struct MinGenomeCount {
 }
 
 impl KmerFilter for MinGenomeCount {
-    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], _n_genomes: usize) -> bool {
         present_count(row, self.threshold) >= self.count
     }
 
@@ -107,7 +119,7 @@ pub struct MaxGenomeCount {
 }
 
 impl KmerFilter for MaxGenomeCount {
-    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], _n_genomes: usize) -> bool {
         present_count(row, self.threshold) <= self.count
     }
 
@@ -129,7 +141,7 @@ pub struct MinTotalCount {
 }
 
 impl KmerFilter for MinTotalCount {
-    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], _n_genomes: usize) -> bool {
         row.iter().sum::<u32>() >= self.total
     }
 
@@ -147,7 +159,7 @@ pub struct MaxTotalCount {
 }
 
 impl KmerFilter for MaxTotalCount {
-    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], _n_genomes: usize) -> bool {
         row.iter().sum::<u32>() <= self.total
     }
 
@@ -212,7 +224,7 @@ impl GroupQuorumFilter {
 }
 
 impl KmerFilter for GroupQuorumFilter {
-    fn passes(&self, row: &[u32], _n_genomes: usize) -> bool {
+    fn passes(&self, _kmer: CanonicalKmer, row: &[u32], _n_genomes: usize) -> bool {
         if !self.ingroup_idx.is_empty() {
             let n = self.ingroup_idx.iter()
                 .filter(|&&i| row.get(i).copied().unwrap_or(0) > self.threshold)
@@ -260,3 +272,27 @@ impl KmerFilter for GroupQuorumFilter {
         Some(FilterMask::And(parts))
     }
 }
+
+// ── Complexity filter (post-hoc, sequence-based) ──────────────────────────────
+
+/// Reject k-mers with normalized entropy below `theta` — the same complexity
+/// metric `obikmer index`'s `--theta`/`--level-max` apply *during* superkmer
+/// construction (see [`obiskbuilder::KmerEntropy`]), applied here after the
+/// fact, to k-mers already committed to a built index.
+///
+/// Unlike every other filter in this module, this one needs the k-mer's own
+/// sequence, not its per-genome row — `column_mask_expr` is never overridden
+/// (stays `None`), so this filter always forces the row-level scan path in
+/// `rebuild_layer.rs` (which reconstructs the sequence from `unitigs.bin`
+/// regardless, so no extra I/O beyond what filtering already requires).
+pub struct MinComplexity {
+    pub level_max: usize,
+    pub theta: f64,
+}
+
+impl KmerFilter for MinComplexity {
+    fn passes(&self, kmer: CanonicalKmer, _row: &[u32], _n_genomes: usize) -> bool {
+        use obiskbuilder::KmerEntropy;
+        kmer.entropy(self.level_max) >= self.theta
+    }
+}

src/obikpartitionner/src/rebuild_layer.rs

@@ -126,7 +126,7 @@ fn iter_src_kmers_masked(
                 Some(m) => m.get(slot),
                 None => {
                     let row = src_data.fill_row_by_slot(slot, n_genomes);
-                    filters.iter().all(|f| f.passes(&row, n_genomes))
+                    filters.iter().all(|f| f.passes(kmer, &row, n_genomes))
                 }
             };
             if passes { cb(kmer); }
@@ -165,7 +165,7 @@ fn iter_src_layers(
                 cb(kmer, row.into_boxed_slice());
             } else {
                 let row = src_data.fill_row_by_slot(slot, n_genomes);
-                if filters.iter().all(|f| f.passes(&row, n_genomes)) {
+                if filters.iter().all(|f| f.passes(kmer, &row, n_genomes)) {
                     cb(kmer, row.into_boxed_slice());
                 }
             }

src/obiskbuilder/src/iter.rs

@@ -149,157 +149,5 @@ impl Iterator for SuperKmerIter<'_> {
 // ── tests ─────────────────────────────────────────────────────────────────────
 
 #[cfg(test)]
-mod tests {
-    use super::*;
-    use obikrope::Rope;
-
-    fn setup() {
-        obikseq::params::set_k(K);
-        obikseq::params::set_m(5);
-    }
-
-    fn make_rope(data: &[u8]) -> Rope {
-        let mut r = Rope::new(None);
-        r.push(data.to_vec());
-        r
-    }
-
-    fn run_nofilter(data: &[u8], k: usize) -> Vec<Vec<u8>> {
-        let rope = make_rope(data);
-        SuperKmerIter::new(&rope, k, 1, 0.0)
-            .map(|rsk| rsk.superkmer().to_ascii())
-            .collect()
-    }
-
-    // k=11, m=5 — valeurs minimales du projet (k ∈ [11,31])
-    const K: usize = 11;
-
-    /// Collect the set of canonical k-mers from a raw ASCII sequence (no NUL).
-    fn direct_canonical_kmers(seq: &[u8]) -> std::collections::HashSet<Vec<u8>> {
-        (0..seq.len().saturating_sub(K - 1))
-            .map(|i| obikseq::SuperKmer::from_ascii(&seq[i..i + K]).to_ascii())
-            .collect()
-    }
-
-    /// Collect the set of canonical k-mers emitted by SuperKmerIter over a rope.
-    fn iter_canonical_kmers(rope: &Rope) -> std::collections::HashSet<Vec<u8>> {
-        SuperKmerIter::new(rope, K, 1, 0.0)
-            .flat_map(|rsk| {
-                rsk.superkmer()
-                    .iter_canonical_kmers()
-                    .map(|km| km.to_ascii())
-                    .collect::<Vec<_>>()
-            })
-            .collect()
-    }
-
-    #[test]
-    fn coverage_single_segment() {
-        setup();
-        let seq = b"ACGTACGTACGTACGTACGT";
-        let rope = make_rope(&[seq.as_ref(), b"\x00"].concat());
-        let direct = direct_canonical_kmers(seq);
-        let from_iter = iter_canonical_kmers(&rope);
-        let missing: Vec<_> = direct.difference(&from_iter).collect();
-        assert!(
-            missing.is_empty(),
-            "k-mers perdus dans segment unique : {missing:?}"
-        );
-    }
-
-    #[test]
-    fn coverage_two_segments() {
-        setup();
-        let seg1 = b"ACGTACGTACGTACGTACGT";
-        let seg2 = b"TGCATGCATGCATGCATGCA";
-        let rope = make_rope(&[seg1.as_ref(), b"\x00", seg2.as_ref(), b"\x00"].concat());
-        let mut direct = direct_canonical_kmers(seg1);
-        direct.extend(direct_canonical_kmers(seg2));
-        let from_iter = iter_canonical_kmers(&rope);
-        let missing: Vec<_> = direct.difference(&from_iter).collect();
-        assert!(
-            missing.is_empty(),
-            "k-mers perdus dans deux segments : {missing:?}"
-        );
-    }
-
-    #[test]
-    fn coverage_minimizer_boundary() {
-        setup();
-        // sequence assez longue pour forcer plusieurs changements de minimiseur
-        let seq: Vec<u8> = (0..80).map(|i| b"ACGT"[i % 4]).collect();
-        let rope = make_rope(&[seq.as_slice(), b"\x00"].concat());
-        let direct = direct_canonical_kmers(&seq);
-        let from_iter = iter_canonical_kmers(&rope);
-        let missing: Vec<_> = direct.difference(&from_iter).collect();
-        assert!(
-            missing.is_empty(),
-            "k-mers perdus à la frontière de minimiseur : {missing:?}"
-        );
-    }
-
-    #[test]
-    fn single_segment_one_superkmer() {
-        setup();
-        let out = run_nofilter(b"ACGTACGTACGTACGTACGT\x00", K);
-        assert!(!out.is_empty());
-        let total: Vec<u8> = out.into_iter().flatten().collect();
-        assert!(total.len() >= K);
-    }
-
-    #[test]
-    fn segment_shorter_than_k_emits_nothing() {
-        setup();
-        let out = run_nofilter(b"ACGTACGT\x00", K);
-        assert_eq!(out, Vec::<Vec<u8>>::new());
-    }
-
-    #[test]
-    fn empty_input_emits_nothing() {
-        setup();
-        let out = run_nofilter(b"", K);
-        assert_eq!(out, Vec::<Vec<u8>>::new());
-    }
-
-    #[test]
-    fn two_segments_both_emitted() {
-        setup();
-        let out = run_nofilter(b"ACGTACGTACGTACGT\x00TGCATGCATGCATGCA\x00", K);
-        assert!(!out.is_empty());
-    }
-
-    #[test]
-    fn low_complexity_kmer_is_rejected() {
-        setup();
-        let out_pass = run_nofilter(b"AAAAAAAAAAAACGTACGTACGT\x00", K);
-        assert!(!out_pass.is_empty());
-
-        let rope = make_rope(b"AAAAAAAAAAAAAAAAAAAA\x00");
-        let out_reject: Vec<Vec<u8>> = SuperKmerIter::new(&rope, K, 6, 0.9)
-            .map(|rsk| rsk.superkmer().to_ascii())
-            .collect();
-        assert!(out_reject.is_empty());
-    }
-
-    #[test]
-    fn multi_slice_rope() {
-        setup();
-        let data = b"ACGTACGTACGTACGTACGT\x00";
-        let mid = data.len() / 2;
-        let mut rope = Rope::new(None);
-        rope.push(data[..mid].to_vec());
-        rope.push(data[mid..].to_vec());
-        let out: Vec<Vec<u8>> = SuperKmerIter::new(&rope, K, 1, 0.0)
-            .map(|rsk| rsk.superkmer().to_ascii())
-            .collect();
-        assert!(!out.is_empty());
-    }
-
-    #[test]
-    fn yields_minimizer_value() {
-        setup();
-        let rope = make_rope(b"ACGTACGTACGTACGTACGT\x00");
-        let results: Vec<RoutableSuperKmer> = SuperKmerIter::new(&rope, K, 1, 0.0).collect();
-        assert!(!results.is_empty());
-    }
-}
+#[path = "tests/iter.rs"]
+mod tests;

src/obiskbuilder/src/kmer_entropy.rs

@@ -0,0 +1,49 @@
+//! Normalized entropy of an isolated, already-built k-mer.
+//!
+//! [`SuperKmerIter`](crate::SuperKmerIter) uses [`RollingStat`] to reject
+//! low-complexity k-mers *during* superkmer construction, incrementally, over
+//! a streaming window. [`KmerEntropy`] exposes the same metric for a single
+//! k-mer taken in isolation (e.g. one already reconstructed from an index's
+//! `unitigs.bin`, with no surrounding sequence) — built on the identical
+//! `RollingStat` code path, not a re-derived formula, so a `theta` threshold
+//! chosen for index-build-time filtering means the same thing when applied
+//! after the fact (e.g. `obikmer filter`).
+
+use obikseq::CanonicalKmer;
+
+use crate::rolling_stat::RollingStat;
+
+/// Extension trait: compute the normalized entropy of a single canonical
+/// k-mer, independent of any surrounding sequence.
+pub trait KmerEntropy {
+    /// Normalized entropy across sub-word orders `1..=level_max` (the
+    /// minimum is taken across orders, same as
+    /// [`RollingStat::normalized_entropy`]). Lower means less complex;
+    /// `theta` in `index`/`filter` rejects k-mers with a score `< theta`.
+    ///
+    /// # Panics
+    ///
+    /// Requires both `obikseq::params::k()` *and* `params::m()` to already be
+    /// set (via `set_k`/`set_m`), even though the minimizer length plays no
+    /// conceptual role in an entropy score: `RollingStat` is a shared,
+    /// general-purpose struct (also used for minimizer selection during
+    /// superkmer decomposition) and unconditionally sizes an `m`-dependent
+    /// mask in its constructor. Callers must call `set_m` with a valid value
+    /// (e.g. the index's own stored `minimizer_size`) even when only the
+    /// entropy score is needed.
+    fn entropy(&self, level_max: usize) -> f64;
+}
+
+impl KmerEntropy for CanonicalKmer {
+    fn entropy(&self, level_max: usize) -> f64 {
+        let mut stat = RollingStat::new(level_max);
+        for &base in self.to_ascii().iter() {
+            stat.push(base);
+        }
+        stat.normalized_entropy().unwrap_or(1.0)
+    }
+}
+
+#[cfg(test)]
+#[path = "tests/kmer_entropy.rs"]
+mod tests;

src/obiskbuilder/src/lib.rs

@@ -6,6 +6,7 @@
 #![deny(missing_docs)]
 
 pub mod iter;
+pub mod kmer_entropy;
 pub mod stream_iter;
 mod scratch;
 
@@ -14,6 +15,7 @@ pub(crate) mod entropy_table;
 pub(crate) mod rolling_stat;
 
 pub use iter::SuperKmerIter;
+pub use kmer_entropy::KmerEntropy;
 pub use scratch::SuperKmerScratch;
 pub use stream_iter::SuperKmerStreamIter;
 

src/obiskbuilder/src/tests/iter.rs

@@ -0,0 +1,152 @@
+use super::*;
+use obikrope::Rope;
+
+fn setup() {
+    obikseq::params::set_k(K);
+    obikseq::params::set_m(5);
+}
+
+fn make_rope(data: &[u8]) -> Rope {
+    let mut r = Rope::new(None);
+    r.push(data.to_vec());
+    r
+}
+
+fn run_nofilter(data: &[u8], k: usize) -> Vec<Vec<u8>> {
+    let rope = make_rope(data);
+    SuperKmerIter::new(&rope, k, 1, 0.0)
+        .map(|rsk| rsk.superkmer().to_ascii())
+        .collect()
+}
+
+// k=11, m=5 — valeurs minimales du projet (k ∈ [11,31])
+const K: usize = 11;
+
+/// Collect the set of canonical k-mers from a raw ASCII sequence (no NUL).
+fn direct_canonical_kmers(seq: &[u8]) -> std::collections::HashSet<Vec<u8>> {
+    (0..seq.len().saturating_sub(K - 1))
+        .map(|i| obikseq::SuperKmer::from_ascii(&seq[i..i + K]).to_ascii())
+        .collect()
+}
+
+/// Collect the set of canonical k-mers emitted by SuperKmerIter over a rope.
+fn iter_canonical_kmers(rope: &Rope) -> std::collections::HashSet<Vec<u8>> {
+    SuperKmerIter::new(rope, K, 1, 0.0)
+        .flat_map(|rsk| {
+            rsk.superkmer()
+                .iter_canonical_kmers()
+                .map(|km| km.to_ascii())
+                .collect::<Vec<_>>()
+        })
+        .collect()
+}
+
+#[test]
+fn coverage_single_segment() {
+    setup();
+    let seq = b"ACGTACGTACGTACGTACGT";
+    let rope = make_rope(&[seq.as_ref(), b"\x00"].concat());
+    let direct = direct_canonical_kmers(seq);
+    let from_iter = iter_canonical_kmers(&rope);
+    let missing: Vec<_> = direct.difference(&from_iter).collect();
+    assert!(
+        missing.is_empty(),
+        "k-mers perdus dans segment unique : {missing:?}"
+    );
+}
+
+#[test]
+fn coverage_two_segments() {
+    setup();
+    let seg1 = b"ACGTACGTACGTACGTACGT";
+    let seg2 = b"TGCATGCATGCATGCATGCA";
+    let rope = make_rope(&[seg1.as_ref(), b"\x00", seg2.as_ref(), b"\x00"].concat());
+    let mut direct = direct_canonical_kmers(seg1);
+    direct.extend(direct_canonical_kmers(seg2));
+    let from_iter = iter_canonical_kmers(&rope);
+    let missing: Vec<_> = direct.difference(&from_iter).collect();
+    assert!(
+        missing.is_empty(),
+        "k-mers perdus dans deux segments : {missing:?}"
+    );
+}
+
+#[test]
+fn coverage_minimizer_boundary() {
+    setup();
+    // sequence assez longue pour forcer plusieurs changements de minimiseur
+    let seq: Vec<u8> = (0..80).map(|i| b"ACGT"[i % 4]).collect();
+    let rope = make_rope(&[seq.as_slice(), b"\x00"].concat());
+    let direct = direct_canonical_kmers(&seq);
+    let from_iter = iter_canonical_kmers(&rope);
+    let missing: Vec<_> = direct.difference(&from_iter).collect();
+    assert!(
+        missing.is_empty(),
+        "k-mers perdus à la frontière de minimiseur : {missing:?}"
+    );
+}
+
+#[test]
+fn single_segment_one_superkmer() {
+    setup();
+    let out = run_nofilter(b"ACGTACGTACGTACGTACGT\x00", K);
+    assert!(!out.is_empty());
+    let total: Vec<u8> = out.into_iter().flatten().collect();
+    assert!(total.len() >= K);
+}
+
+#[test]
+fn segment_shorter_than_k_emits_nothing() {
+    setup();
+    let out = run_nofilter(b"ACGTACGT\x00", K);
+    assert_eq!(out, Vec::<Vec<u8>>::new());
+}
+
+#[test]
+fn empty_input_emits_nothing() {
+    setup();
+    let out = run_nofilter(b"", K);
+    assert_eq!(out, Vec::<Vec<u8>>::new());
+}
+
+#[test]
+fn two_segments_both_emitted() {
+    setup();
+    let out = run_nofilter(b"ACGTACGTACGTACGT\x00TGCATGCATGCATGCA\x00", K);
+    assert!(!out.is_empty());
+}
+
+#[test]
+fn low_complexity_kmer_is_rejected() {
+    setup();
+    let out_pass = run_nofilter(b"AAAAAAAAAAAACGTACGTACGT\x00", K);
+    assert!(!out_pass.is_empty());
+
+    let rope = make_rope(b"AAAAAAAAAAAAAAAAAAAA\x00");
+    let out_reject: Vec<Vec<u8>> = SuperKmerIter::new(&rope, K, 6, 0.9)
+        .map(|rsk| rsk.superkmer().to_ascii())
+        .collect();
+    assert!(out_reject.is_empty());
+}
+
+#[test]
+fn multi_slice_rope() {
+    setup();
+    let data = b"ACGTACGTACGTACGTACGT\x00";
+    let mid = data.len() / 2;
+    let mut rope = Rope::new(None);
+    rope.push(data[..mid].to_vec());
+    rope.push(data[mid..].to_vec());
+    let out: Vec<Vec<u8>> = SuperKmerIter::new(&rope, K, 1, 0.0)
+        .map(|rsk| rsk.superkmer().to_ascii())
+        .collect();
+    assert!(!out.is_empty());
+}
+
+#[test]
+fn yields_minimizer_value() {
+    setup();
+    let rope = make_rope(b"ACGTACGTACGTACGTACGT\x00");
+    let results: Vec<RoutableSuperKmer> = SuperKmerIter::new(&rope, K, 1, 0.0).collect();
+    assert!(!results.is_empty());
+}

src/obiskbuilder/src/tests/kmer_entropy.rs

@@ -0,0 +1,54 @@
+use super::*;
+use obikseq::Sequence;
+use obikseq::kmer::Kmer;
+
+const K: usize = 21;
+const M: usize = 9; // RollingStat also tracks the minimizer window internally
+const LEVEL_MAX: usize = 6;
+
+fn kmer_from_ascii(seq: &[u8]) -> CanonicalKmer {
+    obikseq::set_k(K);
+    obikseq::set_m(M);
+    Kmer::from_ascii(seq).expect("valid k-mer sequence").canonical()
+}
+
+#[test]
+fn homopolymer_scores_lower_than_diverse_sequence() {
+    let homopolymer = kmer_from_ascii(b"AAAAAAAAAAAAAAAAAAAAA"); // 21 bases
+    let diverse = kmer_from_ascii(b"CATTAGCGTACCTGATCAGGT"); // 21 bases, same as used elsewhere in this workspace's tests
+
+    let e_homopolymer = homopolymer.entropy(LEVEL_MAX);
+    let e_diverse = diverse.entropy(LEVEL_MAX);
+
+    assert!(
+        e_homopolymer < e_diverse,
+        "homopolymer ({e_homopolymer}) should score lower than a diverse sequence ({e_diverse})"
+    );
+    // A pure homopolymer is the most degenerate case representable — its
+    // score should sit near the bottom of the range, not just "somewhat lower".
+    assert!(e_homopolymer < 0.3, "homopolymer entropy unexpectedly high: {e_homopolymer}");
+}
+
+#[test]
+fn entropy_is_deterministic_for_the_same_kmer() {
+    let a = kmer_from_ascii(b"CATTAGCGTACCTGATCAGGT");
+    let b = kmer_from_ascii(b"CATTAGCGTACCTGATCAGGT");
+    assert_eq!(a.entropy(LEVEL_MAX), b.entropy(LEVEL_MAX));
+}
+
+#[test]
+fn entropy_is_within_zero_one_range() {
+    let mut repeat = "AT".repeat(K / 2 + 1);
+    repeat.truncate(K);
+
+    for seq in [
+        "AAAAAAAAAAAAAAAAAAAAA".to_string(),
+        repeat,
+        "CATTAGCGTACCTGATCAGGT".to_string(),
+    ] {
+        assert_eq!(seq.len(), K, "test sequence must be exactly K bases: {seq:?}");
+        let kmer = kmer_from_ascii(seq.as_bytes());
+        let e = kmer.entropy(LEVEL_MAX);
+        assert!((0.0..=1.0).contains(&e), "entropy {e} out of [0,1] for {seq:?}");
+    }
+}