refactor: restructure partitioner with shared utilities and pipeline

This commit restructures the partitioner crate by extracting shared utilities and the `ColBuilder` enum into a new `common` module. It introduces a multi-phase `graph_pipeline` for constructing and materializing De Bruijn graphs, replacing manual graph construction in `index_layer`, `merge_layer`, and `rebuild_layer`. All layer workflows now use centralized `build_graph` and `materialize_layer` abstractions, with standardized error context strings for improved diagnostics.

src/obikpartitionner/src/common.rs

@@ -0,0 +1,84 @@
+use std::fs;
+use std::io;
+use std::path::{Path, PathBuf};
+
+use obicompactvec::{PersistentBitVecBuilder, PersistentCompactIntVecBuilder};
+use obilayeredmap::meta::PartitionMeta;
+use obilayeredmap::{IndexMode, OLMError};
+use obiskio::{SKError, SKResult};
+
+// ── olm_to_sk ────────────────────────────────────────────────────────────────
+
+pub(crate) fn olm_to_sk(e: OLMError, context: &'static str) -> SKError {
+    match e {
+        OLMError::Io(e) => SKError::Io(e),
+        other => SKError::InvalidData {
+            context,
+            detail: other.to_string(),
+        },
+    }
+}
+
+// ── load_meta ────────────────────────────────────────────────────────────────
+
+/// Load PartitionMeta, or recover it by probing layer directories.
+/// Indexes built before meta.json was introduced lack the file.
+pub(crate) fn load_meta(dir: &Path, context: &'static str) -> SKResult<PartitionMeta> {
+    match PartitionMeta::load(dir) {
+        Ok(m) => Ok(m),
+        Err(e) if matches!(e, OLMError::Io(ref io_e) if io_e.kind() == std::io::ErrorKind::NotFound) =>
+        {
+            let mut n = 0usize;
+            while dir.join(format!("layer_{n}")).exists() {
+                n += 1;
+            }
+            let m = PartitionMeta {
+                n_layers: n,
+                mode: IndexMode::default(),
+            };
+            m.save(dir).map_err(|e| olm_to_sk(e, context))?;
+            Ok(m)
+        }
+        Err(e) => Err(olm_to_sk(e, context)),
+    }
+}
+
+// ── path helpers ──────────────────────────────────────────────────────────────
+
+pub(crate) fn col_path_bit(dir: &Path, col: usize) -> PathBuf {
+    dir.join(format!("col_{col:06}.pbiv"))
+}
+
+pub(crate) fn col_path_int(dir: &Path, col: usize) -> PathBuf {
+    dir.join(format!("col_{col:06}.pciv"))
+}
+
+pub(crate) fn write_matrix_meta(dir: &Path, n: usize, n_cols: usize) -> io::Result<()> {
+    fs::write(
+        dir.join("meta.json"),
+        format!("{{\"n\":{n},\"n_cols\":{n_cols}}}\n"),
+    )
+}
+
+// ── ColBuilder ────────────────────────────────────────────────────────────────
+
+pub(crate) enum ColBuilder {
+    Bit(PersistentBitVecBuilder),
+    Int(PersistentCompactIntVecBuilder),
+}
+
+impl ColBuilder {
+    pub(crate) fn set_val(&mut self, slot: usize, value: u32) {
+        match self {
+            ColBuilder::Bit(b) => b.set(slot, value > 0),
+            ColBuilder::Int(b) => b.set(slot, value),
+        }
+    }
+
+    pub(crate) fn close(self) -> SKResult<()> {
+        match self {
+            ColBuilder::Bit(b) => b.close().map_err(SKError::Io),
+            ColBuilder::Int(b) => b.close().map_err(SKError::Io),
+        }
+    }
+}

src/obikpartitionner/src/graph_pipeline.rs

@@ -0,0 +1,152 @@
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex};
+
+use tracing::debug;
+use obipipeline::{
+    Pipeline, PipelineError, PipelineSender, SharedFlatFn, Stage, WorkerPool,
+    make_sink, make_source, make_transform,
+    throttle,
+};
+
+use obidebruinj::GraphDeBruijn;
+use obikseq::CanonicalKmer;
+use obilayeredmap::{IndexMode, Layer};
+use obiskio::{SKError, SKResult};
+
+use crate::common::olm_to_sk;
+
+// ── KmerGraphData ─────────────────────────────────────────────────────────────
+
+enum KmerGraphData {
+    File(obipipeline::Throttled<PathBuf>),
+    RawBatch(Vec<CanonicalKmer>),
+    FilteredBatch(Vec<CanonicalKmer>),
+}
+
+// ── build_graph ───────────────────────────────────────────────────────────────
+
+/// Phase 1: pipeline that reads files, filters kmers, pushes into a GraphDeBruijn.
+///
+/// `flat_fn(path, emit)`: opens path, iterates kmers, calls `emit(batch)` for each batch.
+/// `filter(kmer) -> bool`: secondary filter applied in the Transform stage.
+pub(crate) fn build_graph<I, F, G>(
+    file_source: I,
+    flat_fn: F,
+    filter: G,
+    n_workers: usize,
+    max_open: usize,
+) -> SKResult<GraphDeBruijn>
+where
+    I: Iterator<Item = PathBuf> + Send + 'static,
+    F: Fn(PathBuf, &mut dyn FnMut(Vec<CanonicalKmer>)) -> SKResult<()> + Send + Sync + 'static,
+    G: Fn(CanonicalKmer) -> bool + Send + Sync + 'static,
+{
+    let capacity = 2;
+
+    let flat_fn = Arc::new(flat_fn);
+    let filter = Arc::new(filter);
+    let g_shared = Arc::new(Mutex::new(GraphDeBruijn::new()));
+    let g_sink = Arc::clone(&g_shared);
+    let err_cap: Arc<Mutex<Option<SKError>>> = Arc::new(Mutex::new(None));
+    let err_flat = Arc::clone(&err_cap);
+
+    let throttled = throttle(file_source, max_open);
+
+    let pipeline = Pipeline::new(
+        make_source!(KmerGraphData, throttled, File),
+        vec![
+            Stage::Flat(Arc::new(
+                move |data: KmerGraphData,
+                      push: &PipelineSender<Result<KmerGraphData, PipelineError>>,
+                      delta: &PipelineSender<isize>|
+                {
+                    if let KmerGraphData::File(t) = data {
+                        let path = t.item;
+                        let _guard = t.guard; // released at end of block
+                        let mut count: isize = 0;
+                        let push_clone = push.clone();
+                        let result = flat_fn(path, &mut |batch: Vec<CanonicalKmer>| {
+                            push_clone.send(Ok(KmerGraphData::RawBatch(batch))).ok();
+                            count += 1;
+                        });
+                        match result {
+                            Ok(()) => {
+                                delta.send(count - 1).ok();
+                            }
+                            Err(e) => {
+                                *err_flat.lock().unwrap() = Some(e);
+                                delta.send(-1).ok();
+                            }
+                        }
+                    }
+                },
+            ) as SharedFlatFn<KmerGraphData>),
+            make_transform!(KmerGraphData, {
+                let filter = Arc::clone(&filter);
+                move |batch: Vec<CanonicalKmer>| -> Vec<CanonicalKmer> {
+                    batch.into_iter().filter(|k| filter(*k)).collect()
+                }
+            }, RawBatch, FilteredBatch),
+        ],
+        make_sink!(KmerGraphData, {
+            move |batch: Vec<CanonicalKmer>| {
+                let mut g = g_sink.lock().unwrap();
+                for kmer in batch {
+                    g.push(kmer);
+                }
+            }
+        }, FilteredBatch),
+    );
+
+    WorkerPool::new(pipeline, n_workers, capacity).run();
+
+    if let Some(e) = Arc::try_unwrap(err_cap)
+        .unwrap_or_else(|_| panic!("build_graph: err_cap not uniquely owned after pipeline"))
+        .into_inner()
+        .unwrap_or_else(|e| e.into_inner())
+    {
+        return Err(e);
+    }
+
+    let g = Arc::try_unwrap(g_shared)
+        .unwrap_or_else(|_| panic!("build_graph: g_shared not uniquely owned after pipeline"))
+        .into_inner()
+        .unwrap_or_else(|e| e.into_inner());
+
+    Ok(g)
+}
+
+// ── write_graph_as_unitigs ────────────────────────────────────────────────────
+
+/// Phase 2 (write unitigs only): compute degrees, write unitigs to `layer_dir`, drop graph.
+///
+/// Returns n_kmers. Does NOT build the MPHF — caller does it.
+pub(crate) fn write_graph_as_unitigs(g: GraphDeBruijn, layer_dir: &Path) -> SKResult<usize> {
+    let n_kmers = g.len();
+    g.compute_degrees_and_mark_starts();
+    std::fs::create_dir_all(layer_dir)?;
+    let mut uw = Layer::<()>::unitig_writer(layer_dir).map_err(|e| olm_to_sk(e, "graph pipeline"))?;
+    g.try_for_each_unitig(|unitig| uw.write(unitig))?;
+    uw.close()?;
+    drop(g);
+    Ok(n_kmers)
+}
+
+// ── materialize_layer ─────────────────────────────────────────────────────────
+
+/// Phase 2 (full): write_graph_as_unitigs + `Layer::<()>::build`.
+///
+/// Returns n_kmers.
+pub(crate) fn materialize_layer(
+    g: GraphDeBruijn,
+    layer_dir: &Path,
+    block_bits: u8,
+    evidence: &IndexMode,
+) -> SKResult<usize> {
+    let n = write_graph_as_unitigs(g, layer_dir)?;
+    debug!("materialize_layer: unitigs written ({n} kmers), building MPHF");
+    Layer::<()>::build(layer_dir, block_bits, evidence)
+        .map_err(|e| olm_to_sk(e, "graph pipeline"))?;
+    debug!("materialize_layer: MPHF build done");
+    Ok(n)
+}

src/obikpartitionner/src/index_layer.rs

@@ -6,24 +6,16 @@ use epserde::prelude::*;
 use obicompactvec::{PersistentCompactIntMatrix, PersistentCompactIntVec};
 use obidebruinj::GraphDeBruijn;
 use obilayeredmap::meta::PartitionMeta;
-use obilayeredmap::{IndexMode, OLMError, layer::Layer};
+use obilayeredmap::{IndexMode, layer::Layer};
 use obiskio::{SKError, SKFileMeta, SKFileReader};
 use ptr_hash::{PtrHash, bucket_fn::CubicEps, hash::Xx64};
 
+use crate::common::olm_to_sk;
+use crate::graph_pipeline::{materialize_layer, write_graph_as_unitigs};
 use crate::partition::KmerPartition;
 
 type Mphf = PtrHash<u64, CubicEps, CachelineEfVec<Vec<CachelineEf>>, Xx64, Vec<u8>>;
 
-fn olm_to_sk(e: OLMError) -> SKError {
-    match e {
-        OLMError::Io(io_err) => SKError::Io(io_err),
-        other => SKError::InvalidData {
-            context: "layer build",
-            detail: other.to_string(),
-        },
-    }
-}
-
 fn remove_if_exists(path: &std::path::Path) {
     if let Err(e) = fs::remove_file(path) {
         if e.kind() != io::ErrorKind::NotFound {
@@ -101,18 +93,8 @@ impl KmerPartition {
             }
         }
 
-        let n_kmers = g.len();
-        g.compute_degrees_and_mark_starts();
-
-        fs::create_dir_all(&layer_dir)?;
-
-        let mut uw = Layer::<()>::unitig_writer(&layer_dir).map_err(olm_to_sk)?;
-        g.try_for_each_unitig(|unitig| {
-            uw.write(unitig)
-        })?;
-        uw.close()?;
-
-        if with_counts {
+        let n_kmers = if with_counts {
+            let n = write_graph_as_unitigs(g, &layer_dir)?;
             Layer::<PersistentCompactIntMatrix>::build(
                 &layer_dir,
                 block_bits,
@@ -122,10 +104,11 @@ impl KmerPartition {
                     _ => 1,
                 },
             )
-            .map_err(olm_to_sk)?;
+            .map_err(|e| olm_to_sk(e, "layer build"))?;
+            n
         } else {
-            Layer::<()>::build(&layer_dir, block_bits, mode).map_err(olm_to_sk)?;
-        }
+            materialize_layer(g, &layer_dir, block_bits, mode)?
+        };
 
         let index_dir = layer_dir.parent().expect("layer_dir has a parent");
         PartitionMeta {
@@ -133,7 +116,7 @@ impl KmerPartition {
             mode: mode.clone(),
         }
         .save(index_dir)
-        .map_err(olm_to_sk)?;
+        .map_err(|e| olm_to_sk(e, "layer build"))?;
 
         Ok(n_kmers)
     }

src/obikpartitionner/src/lib.rs

@@ -1,6 +1,8 @@
 pub mod filter;
+mod common;
 mod distance;
 mod dump_layer;
+mod graph_pipeline;
 mod index_layer;
 mod kmer_sort;
 mod merge_layer;

src/obikpartitionner/src/merge_layer.rs

@@ -1,5 +1,4 @@
 use std::fs;
-use std::io;
 use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
 
@@ -14,12 +13,13 @@ use obicompactvec::{
     PersistentBitMatrix, PersistentBitMatrixBuilder, PersistentBitVecBuilder,
     PersistentCompactIntMatrix, PersistentCompactIntMatrixBuilder, PersistentCompactIntVecBuilder,
 };
-use obidebruinj::GraphDeBruijn;
 use obikseq::CanonicalKmer;
 use obilayeredmap::meta::PartitionMeta;
-use obilayeredmap::{IndexMode, Layer, LayeredMap, MphfOnly, OLMError};
+use obilayeredmap::{IndexMode, Layer, LayeredMap, MphfOnly};
 use obiskio::{SKError, SKResult, UnitigFileReader};
 
+use crate::common::{ColBuilder, col_path_bit, col_path_int, load_meta, olm_to_sk, write_matrix_meta};
+use crate::graph_pipeline::{build_graph, materialize_layer};
 use crate::partition::KmerPartition;
 
 // ── MergeMode ─────────────────────────────────────────────────────────────────
@@ -30,29 +30,6 @@ pub enum MergeMode {
     Count,
 }
 
-// ── ColBuilder — enum dispatch to avoid trait-object boxing issues ─────────────
-
-enum ColBuilder {
-    Bit(PersistentBitVecBuilder),
-    Int(PersistentCompactIntVecBuilder),
-}
-
-impl ColBuilder {
-    fn set_val(&mut self, slot: usize, value: u32) {
-        match self {
-            ColBuilder::Bit(b) => b.set(slot, value > 0),
-            ColBuilder::Int(b) => b.set(slot, value),
-        }
-    }
-
-    fn close(self) -> SKResult<()> {
-        match self {
-            ColBuilder::Bit(b) => b.close().map_err(SKError::Io),
-            ColBuilder::Int(b) => b.close().map_err(SKError::Io),
-        }
-    }
-}
-
 // ── SrcLayerData — opened source matrix for pass-2 lookup ─────────────────────
 
 pub(crate) enum SrcLayerData {
@@ -66,18 +43,18 @@ impl SrcLayerData {
         match merge_mode {
             MergeMode::Presence => {
                 if counts_dir.exists() && !layer_dir.join("presence").exists() {
-                    let mphf = MphfOnly::open(layer_dir).map_err(olm_to_sk)?;
+                    let mphf = MphfOnly::open(layer_dir).map_err(|e| olm_to_sk(e, "merge"))?;
                     let mat = PersistentCompactIntMatrix::open(layer_dir).map_err(SKError::Io)?;
                     Ok(SrcLayerData::Count(mphf, mat))
                 } else {
                     // presence dir exists, or neither exists → Implicit handled by open()
-                    let mphf = MphfOnly::open(layer_dir).map_err(olm_to_sk)?;
+                    let mphf = MphfOnly::open(layer_dir).map_err(|e| olm_to_sk(e, "merge"))?;
                     let mat = PersistentBitMatrix::open(layer_dir).map_err(SKError::Io)?;
                     Ok(SrcLayerData::Presence(mphf, mat))
                 }
             }
             MergeMode::Count => {
-                let mphf = MphfOnly::open(layer_dir).map_err(olm_to_sk)?;
+                let mphf = MphfOnly::open(layer_dir).map_err(|e| olm_to_sk(e, "merge"))?;
                 if counts_dir.exists() {
                     let mat = PersistentCompactIntMatrix::open(layer_dir).map_err(SKError::Io)?;
                     Ok(SrcLayerData::Count(mphf, mat))
@@ -107,53 +84,6 @@ impl SrcLayerData {
 
 const INDEX_SUBDIR: &str = "index";
 
-/// Load PartitionMeta, or recover it by probing layer directories.
-/// Indexes built before meta.json was introduced lack the file.
-fn load_meta(dir: &Path) -> SKResult<PartitionMeta> {
-    match PartitionMeta::load(dir) {
-        Ok(m) => Ok(m),
-        Err(e) if matches!(e, OLMError::Io(ref io_e) if io_e.kind() == std::io::ErrorKind::NotFound) =>
-        {
-            let mut n = 0usize;
-            while dir.join(format!("layer_{n}")).exists() {
-                n += 1;
-            }
-            let m = PartitionMeta {
-                n_layers: n,
-                mode: IndexMode::default(),
-            };
-            m.save(dir).map_err(olm_to_sk)?;
-            Ok(m)
-        }
-        Err(e) => Err(olm_to_sk(e)),
-    }
-}
-
-fn olm_to_sk(e: OLMError) -> SKError {
-    match e {
-        OLMError::Io(e) => SKError::Io(e),
-        other => SKError::InvalidData {
-            context: "merge",
-            detail: other.to_string(),
-        },
-    }
-}
-
-fn col_path_bit(dir: &Path, col: usize) -> PathBuf {
-    dir.join(format!("col_{col:06}.pbiv"))
-}
-
-fn col_path_int(dir: &Path, col: usize) -> PathBuf {
-    dir.join(format!("col_{col:06}.pciv"))
-}
-
-fn write_matrix_meta(dir: &Path, n: usize, n_cols: usize) -> io::Result<()> {
-    fs::write(
-        dir.join("meta.json"),
-        format!("{{\"n\":{n},\"n_cols\":{n_cols}}}\n"),
-    )
-}
-
 // ── KmerPartition::merge_partition ────────────────────────────────────────────
 
 impl KmerPartition {
@@ -180,8 +110,8 @@ impl KmerPartition {
             return Ok(0);
         }
 
-        load_meta(&dst_index_dir)?; // ensure meta.json exists before LayeredMap::open
-        let dst_map = Arc::new(LayeredMap::<()>::open(&dst_index_dir).map_err(olm_to_sk)?);
+        load_meta(&dst_index_dir, "merge")?; // ensure meta.json exists before LayeredMap::open
+        let dst_map = Arc::new(LayeredMap::<()>::open(&dst_index_dir).map_err(|e| olm_to_sk(e, "merge"))?);
         let n_dst_layers = dst_map.n_layers();
         let n_src_total: usize = sources.iter().map(|(_, n)| *n).sum();
 
@@ -191,7 +121,7 @@ impl KmerPartition {
             for l in 0..n_dst_layers {
                 let layer_dir = dst_index_dir.join(format!("layer_{l}"));
                 Layer::<()>::init_presence_matrix(&layer_dir, dst_map.layer(l).n())
-                    .map_err(olm_to_sk)?;
+                    .map_err(|e| olm_to_sk(e, "merge"))?;
             }
         }
 
@@ -209,7 +139,7 @@ impl KmerPartition {
             if !src_index_dir.exists() {
                 continue;
             }
-            let src_meta = load_meta(&src_index_dir)?;
+            let src_meta = load_meta(&src_index_dir, "merge")?;
             for l in 0..src_meta.n_layers {
                 let p = src_index_dir.join(format!("layer_{l}")).join("unitigs.bin");
                 if p.exists() {
@@ -221,92 +151,36 @@ impl KmerPartition {
         let n_src_layers = unitig_paths.len();
         debug!("partition {i}: de Bruijn graph build start — {n_src_layers} source layer(s)");
 
-        enum Pass1Data {
-            File((PathBuf, ThrottleGuard)),
-            Batch(Vec<CanonicalKmer>),
-            NewKmers(Vec<CanonicalKmer>),
-        }
-
         const BATCH: usize = 4096;
         let n_workers = rayon::current_num_threads().min(16).max(4);
-        let capacity  = 2;
         // At most 2 files open simultaneously: keeps n_workers-2 workers free
         // for the Transform stage. Each open file monopolises one worker for the
         // full duration of its read, so this must stay well below n_workers.
-        let max_open  = 2;
+        let max_open = 2;
 
         let dst_filter = Arc::clone(&dst_map);
-        let g_shared   = Arc::new(Mutex::new(GraphDeBruijn::new()));
-        let g_sink     = Arc::clone(&g_shared);
-        let pass1_err: Arc<Mutex<Option<String>>> = Arc::new(Mutex::new(None));
-        let err_cap    = Arc::clone(&pass1_err);
 
-        let throttled_paths = throttle(unitig_paths.into_iter(), max_open);
-
-        let pipeline = Pipeline::new(
-            make_source!(Pass1Data, throttled_paths.map(|t| (t.item, t.guard)), File),
-            vec![
-                Stage::Flat(Arc::new(
-                    move |data: Pass1Data,
-                          push:  &PipelineSender<Result<Pass1Data, PipelineError>>,
-                          delta: &PipelineSender<isize>|
-                    {
-                        if let Pass1Data::File((path, _guard)) = data {
-                            // _guard is dropped at end of this block, releasing the slot.
-                            let reader = match UnitigFileReader::open_sequential(&path) {
-                                Ok(r)  => r,
-                                Err(e) => {
-                                    *err_cap.lock().unwrap() = Some(e.to_string());
-                                    delta.send(-1).ok();
-                                    return;
-                                }
-                            };
-                            let mut batch: Vec<CanonicalKmer> = Vec::with_capacity(BATCH);
-                            let mut count: isize = 0;
-                            for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
-                                batch.push(kmer);
-                                if batch.len() == BATCH {
-                                    let b = std::mem::replace(&mut batch, Vec::with_capacity(BATCH));
-                                    push.send(Ok(Pass1Data::Batch(b))).ok();
-                                    count += 1;
-                                }
-                            }
-                            if !batch.is_empty() {
-                                push.send(Ok(Pass1Data::Batch(batch))).ok();
-                                count += 1;
-                            }
-                            delta.send(count - 1).ok();
-                        }
-                    }
-                ) as SharedFlatFn<Pass1Data>),
-                make_transform!(Pass1Data, {
-                    move |batch: Vec<CanonicalKmer>| -> Vec<CanonicalKmer> {
-                        batch.into_iter()
-                            .filter(|&k| dst_filter.query(k).is_none())
-                            .collect()
-                    }
-                }, Batch, NewKmers),
-            ],
-            make_sink!(Pass1Data, {
-                move |batch: Vec<CanonicalKmer>| {
-                    let mut g = g_sink.lock().unwrap();
-                    for kmer in batch {
-                        g.push(kmer);
+        let g = build_graph(
+            unitig_paths.into_iter(),
+            move |path: PathBuf, emit: &mut dyn FnMut(Vec<CanonicalKmer>)| -> SKResult<()> {
+                let reader = UnitigFileReader::open_sequential(&path)?;
+                let mut batch: Vec<CanonicalKmer> = Vec::with_capacity(BATCH);
+                for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
+                    batch.push(kmer);
+                    if batch.len() == BATCH {
+                        emit(std::mem::replace(&mut batch, Vec::with_capacity(BATCH)));
                     }
                 }
-            }, NewKmers),
-        );
+                if !batch.is_empty() {
+                    emit(batch);
+                }
+                Ok(())
+            },
+            move |kmer| dst_filter.query(kmer).is_none(),
+            n_workers,
+            max_open,
+        )?;
 
-        WorkerPool::new(pipeline, n_workers, capacity).run();
-
-        if let Some(msg) = Arc::try_unwrap(pass1_err).unwrap().into_inner().unwrap() {
-            return Err(SKError::InvalidData { context: "merge pass1", detail: msg });
-        }
-
-        let g = Arc::try_unwrap(g_shared)
-            .unwrap_or_else(|_| panic!("pass1: g_shared not uniquely owned after pipeline"))
-            .into_inner()
-            .unwrap_or_else(|e| e.into_inner());
         let any_new = g.len() > 0;
         debug!("partition {i}: de Bruijn graph done — {} new kmers", g.len());
 
@@ -315,25 +189,8 @@ impl KmerPartition {
         let new_layer_dir = dst_index_dir.join(format!("layer_{new_layer_idx}"));
 
         let n_new = if any_new {
-            let t_deg = std::time::Instant::now();
-            g.compute_degrees_and_mark_starts();
-            debug!("partition {i}: compute_degrees in {:.3}s — {} nodes",
-                t_deg.elapsed().as_secs_f64(), g.len());
-            fs::create_dir_all(&new_layer_dir)?;
-            let mut uw = Layer::<()>::unitig_writer(&new_layer_dir).map_err(olm_to_sk)?;
             debug!("partition {i}: unitig traversal start — {} nodes", g.len());
-            let mut n_unitigs = 0usize;
-            g.try_for_each_unitig(|unitig| {
-                n_unitigs += 1;
-                uw.write(unitig)
-            })?;
-            debug!("partition {i}: unitig writer closing");
-            uw.close()?;
-            let n_nodes = g.len();
-            debug!("partition {i}: unitig writer closed — dropping graph ({n_nodes} nodes)");
-            drop(g);
-            debug!("partition {i}: graph dropped — starting MPHF build ({n_unitigs} unitigs)");
-            Layer::<()>::build(&new_layer_dir, block_bits, evidence).map_err(olm_to_sk)?;
+            let n_nodes = materialize_layer(g, &new_layer_dir, block_bits, evidence)?;
             debug!("partition {i}: MPHF build done");
             n_nodes
         } else {
@@ -343,7 +200,7 @@ impl KmerPartition {
 
         let t_open = std::time::Instant::now();
         let new_mphf: Option<Arc<MphfOnly>> = if any_new {
-            Some(Arc::new(MphfOnly::open(&new_layer_dir).map_err(olm_to_sk)?))
+            Some(Arc::new(MphfOnly::open(&new_layer_dir).map_err(|e| olm_to_sk(e, "merge"))?))
         } else {
             None
         };
@@ -449,7 +306,7 @@ impl KmerPartition {
                     col_offset += src_n;
                     continue;
                 }
-                let src_meta = load_meta(&src_index_dir)?;
+                let src_meta = load_meta(&src_index_dir, "merge")?;
                 for l in 0..src_meta.n_layers {
                     let src_layer_dir = src_index_dir.join(format!("layer_{l}"));
                     if src_layer_dir.join("unitigs.bin").exists() {
@@ -483,6 +340,7 @@ impl KmerPartition {
         let pass2_err: Arc<Mutex<Option<String>>> = Arc::new(Mutex::new(None));
         let err_cap2       = Arc::clone(&pass2_err);
 
+        let capacity = 2;
         let throttled_pass2 = throttle(pass2_items.into_iter(), max_open);
 
         let pipeline2 = Pipeline::new(
@@ -516,6 +374,7 @@ impl KmerPartition {
                                     return;
                                 }
                             };
+                            const BATCH: usize = 4096;
                             let mut batch: Vec<CanonicalKmer> = Vec::with_capacity(BATCH);
                             let mut count: isize = 0;
                             for (kmer, _, _) in reader.iter_indexed_canonical_kmers() {
@@ -617,9 +476,9 @@ impl KmerPartition {
             write_matrix_meta(&data_dir, n_new, n_dst_genomes + n_src_total)
                 .map_err(SKError::Io)?;
 
-            let mut part_meta = PartitionMeta::load(&dst_index_dir).map_err(olm_to_sk)?;
+            let mut part_meta = PartitionMeta::load(&dst_index_dir).map_err(|e| olm_to_sk(e, "merge"))?;
             part_meta.n_layers = new_layer_idx + 1;
-            part_meta.save(&dst_index_dir).map_err(olm_to_sk)?;
+            part_meta.save(&dst_index_dir).map_err(|e| olm_to_sk(e, "merge"))?;
         }
 
         debug!("partition {i}: builders closed in {:.3}s", t_close.elapsed().as_secs_f64());

src/obikpartitionner/src/rebuild_layer.rs

@@ -1,6 +1,4 @@
-use std::fs;
-use std::io;
-use std::path::{Path, PathBuf};
+use std::path::Path;
 
 use obicompactvec::{
     PersistentBitMatrixBuilder, PersistentBitVecBuilder, PersistentCompactIntMatrixBuilder,
@@ -9,85 +7,17 @@ use obicompactvec::{
 use obidebruinj::GraphDeBruijn;
 use obikseq::CanonicalKmer;
 use obilayeredmap::meta::PartitionMeta;
-use obilayeredmap::{IndexMode, Layer, MphfLayer, OLMError};
+use obilayeredmap::{IndexMode, MphfLayer};
 use obiskio::{SKError, SKResult, UnitigFileReader};
 
+use crate::common::{ColBuilder, col_path_bit, col_path_int, load_meta, olm_to_sk, write_matrix_meta};
 use crate::filter::{KmerFilter, passes_all};
+use crate::graph_pipeline::materialize_layer;
 use crate::merge_layer::{MergeMode, SrcLayerData};
 use crate::partition::KmerPartition;
 
 const INDEX_SUBDIR: &str = "index";
 
-fn olm_to_sk(e: OLMError) -> SKError {
-    match e {
-        OLMError::Io(e) => SKError::Io(e),
-        other => SKError::InvalidData {
-            context: "rebuild",
-            detail: other.to_string(),
-        },
-    }
-}
-
-fn col_path_bit(dir: &Path, col: usize) -> PathBuf {
-    dir.join(format!("col_{col:06}.pbiv"))
-}
-
-fn col_path_int(dir: &Path, col: usize) -> PathBuf {
-    dir.join(format!("col_{col:06}.pciv"))
-}
-
-fn write_matrix_meta(dir: &Path, n: usize, n_cols: usize) -> io::Result<()> {
-    fs::write(
-        dir.join("meta.json"),
-        format!("{{\"n\":{n},\"n_cols\":{n_cols}}}\n"),
-    )
-}
-
-// ── ColBuilder ────────────────────────────────────────────────────────────────
-
-enum ColBuilder {
-    Bit(PersistentBitVecBuilder),
-    Int(PersistentCompactIntVecBuilder),
-}
-
-impl ColBuilder {
-    fn set_val(&mut self, slot: usize, value: u32) {
-        match self {
-            ColBuilder::Bit(b) => b.set(slot, value > 0),
-            ColBuilder::Int(b) => b.set(slot, value),
-        }
-    }
-
-    fn close(self) -> SKResult<()> {
-        match self {
-            ColBuilder::Bit(b) => b.close().map_err(SKError::Io),
-            ColBuilder::Int(b) => b.close().map_err(SKError::Io),
-        }
-    }
-}
-
-// ── Helpers ───────────────────────────────────────────────────────────────────
-
-fn load_meta(dir: &Path) -> SKResult<PartitionMeta> {
-    match PartitionMeta::load(dir) {
-        Ok(m) => Ok(m),
-        Err(e) if matches!(e, OLMError::Io(ref io_e) if io_e.kind() == std::io::ErrorKind::NotFound) =>
-        {
-            let mut n = 0usize;
-            while dir.join(format!("layer_{n}")).exists() {
-                n += 1;
-            }
-            let m = PartitionMeta {
-                n_layers: n,
-                mode: IndexMode::default(),
-            };
-            m.save(dir).map_err(olm_to_sk)?;
-            Ok(m)
-        }
-        Err(e) => Err(olm_to_sk(e)),
-    }
-}
-
 /// Iterate all kmers in `src_index_dir` that pass `filters`, yielding `(kmer, row)`.
 ///
 /// Uses [`SrcLayerData`] semantics: counts take priority over presence when
@@ -99,7 +29,7 @@ fn iter_src_layers(
     filters: &[Box<dyn KmerFilter>],
     mut cb: impl FnMut(CanonicalKmer, Box<[u32]>),
 ) -> SKResult<()> {
-    let src_meta = load_meta(src_index_dir)?;
+    let src_meta = load_meta(src_index_dir, "rebuild")?;
     for l in 0..src_meta.n_layers {
         let src_layer_dir = src_index_dir.join(format!("layer_{l}"));
         let unitigs_path = src_layer_dir.join("unitigs.bin");
@@ -144,7 +74,7 @@ impl KmerPartition {
             return Ok(());
         }
 
-        let src_meta = load_meta(&src_index_dir)?;
+        let src_meta = load_meta(&src_index_dir, "rebuild")?;
         if src_meta.n_layers == 0 {
             return Ok(());
         }
@@ -159,30 +89,20 @@ impl KmerPartition {
             return Ok(());
         }
 
-        let n_new = g.len();
-        g.compute_degrees_and_mark_starts();
-
         // ── Build MPHF in dst layer_0 ─────────────────────────────────────────
         let dst_index_dir = self.part_dir(i).join(INDEX_SUBDIR);
         let dst_layer_dir = dst_index_dir.join("layer_0");
-        fs::create_dir_all(&dst_layer_dir)?;
 
-        let mut uw = Layer::<()>::unitig_writer(&dst_layer_dir).map_err(olm_to_sk)?;
-        g.try_for_each_unitig(|unitig| {
-            uw.write(unitig)
-        })?;
-        uw.close()?;
-        drop(g);
-
-        Layer::<()>::build(&dst_layer_dir, block_bits, &IndexMode::Exact).map_err(olm_to_sk)?;
-        let dst_mphf = MphfLayer::open(&dst_layer_dir, &IndexMode::Exact).map_err(olm_to_sk)?;
+        let n_new = materialize_layer(g, &dst_layer_dir, block_bits, &IndexMode::Exact)?;
+        let dst_mphf = MphfLayer::open(&dst_layer_dir, &IndexMode::Exact)
+            .map_err(|e| olm_to_sk(e, "rebuild"))?;
 
         // ── Prepare matrix builders (one column per genome) ───────────────────
         let data_dir = match mode {
             MergeMode::Presence => dst_layer_dir.join("presence"),
             MergeMode::Count => dst_layer_dir.join("counts"),
         };
-        fs::create_dir_all(&data_dir)?;
+        std::fs::create_dir_all(&data_dir)?;
 
         let mut builders: Vec<ColBuilder> = match mode {
             MergeMode::Presence => {
@@ -234,7 +154,7 @@ impl KmerPartition {
             mode: IndexMode::Exact,
         }
         .save(&dst_index_dir)
-        .map_err(olm_to_sk)?;
+        .map_err(|e| olm_to_sk(e, "rebuild"))?;
 
         Ok(())
     }