//! Equivalence harness for the range-read migration
//! (`docs/design/range-reads.md`, milestone M1).
//!
//! Every metadata parser converted to [`Storage`] must give exactly what its
//! `&[u8]` form gives. This walks real files — the fixtures, files h5py
//! writes to exercise the less common structures, and optionally the
//! conformance corpus — and, for every object, runs each converted parser
//! twice: over the file as a slice, and over a [`CountingStorage`] that
//! serves the same bytes through `read_at` only (`as_contiguous()` is
//! `None`, so no parser can fall back to the whole slice). The results must
//! be identical, value for value and error for error.
//!
//! The one allowed difference is [`FormatError::ContiguousStorageRequired`]
//! from the storage path, and only from the structures still indexed by a v2
//! B-tree (dense attributes, a SOHM B-tree index, huge fractal-heap objects;
//! see `CONTIGUOUS_REQUIRED`), which fail cleanly instead of reading the
//! whole file. Those are counted; the error from any other site or check
//! fails the harness.
//!
//! Milestones M2/M3 extend `check_object` with the raw-data and group
//! parsers as they are converted.
//!
//! - `CLAWHDF5_STORAGE_CORPUS=dir[:dir...]` adds every `.h5`/`.hdf5`/`.he5`/
//!   `.nc`/`.h5ad` file under those directories (the conformance corpus is
//!   `conformance/.cache/corpus`); `CLAWHDF5_STORAGE_REPORT=1` prints the
//!   per-file read counts.
//! - The h5py-written files honour `CLAWHDF5_PYTHON` and
//!   `CLAWHDF5_REQUIRE_INTEROP` like the facade's interop tests.

use std::collections::{HashSet, VecDeque};
use std::fmt::Debug;
use std::path::{Path, PathBuf};
use std::process::Command;

use clawhdf5_format::attribute::{
    extract_attributes_full, extract_attributes_full_in, extract_attributes_tolerant,
    extract_attributes_tolerant_in,
};
use clawhdf5_format::attribute_info::AttributeInfoMessage;
use clawhdf5_format::btree_v1::{collect_symbol_table_nodes, collect_symbol_table_nodes_in};
use clawhdf5_format::btree_v2::{BTreeV2Header, collect_btree_v2_records};
use clawhdf5_format::data_layout::DataLayout;
use clawhdf5_format::dataspace::Dataspace;
use clawhdf5_format::datatype::Datatype;
use clawhdf5_format::error::FormatError;
use clawhdf5_format::extensible_array::{
    ExtensibleArrayHeader, read_extensible_array_chunks, read_extensible_array_chunks_in,
};
use clawhdf5_format::fill_value::{dataset_fill_value_from_storage, dataset_fill_value_in};
use clawhdf5_format::fixed_array::{
    FixedArrayHeader, read_fixed_array_chunks, read_fixed_array_chunks_in,
};
use clawhdf5_format::fractal_heap::FractalHeapHeader;
use clawhdf5_format::link_info::LinkInfoMessage;
use clawhdf5_format::local_heap::LocalHeap;
use clawhdf5_format::message_type::MessageType;
use clawhdf5_format::object_header::ObjectHeader;
use clawhdf5_format::shared_message::{
    self, load_sohm_table, load_sohm_table_in, message_data_with_sohm, message_data_with_sohm_in,
    parse_sohm_btree_entries, parse_sohm_btree_entries_in, parse_sohm_list, parse_sohm_list_in,
};
use clawhdf5_format::signature::split_user_block;
use clawhdf5_format::storage::{CountingStorage, Storage};
use clawhdf5_format::superblock::Superblock;
use clawhdf5_format::superblock_ext::{
    cache_image_state, cache_image_state_in, read_superblock_extension,
    read_superblock_extension_in,
};
use clawhdf5_format::symbol_table::{SymbolTableMessage, SymbolTableNode};

/// Objects visited per file, heap objects read per heap: enough to cover
/// every structure kind while keeping a 35 000-group file fast.
const MAX_OBJECTS: usize = 1500;
const MAX_HEAP_IDS: usize = 200;

/// The structures that still need the whole file in memory, because they
/// are found through a version-2 B-tree (not converted yet), and the checks
/// that can reach each of them. Anything else answering
/// [`FormatError::ContiguousStorageRequired`] is a converted parser falling
/// back to the whole file, and fails the harness.
const CONTIGUOUS_REQUIRED: &[(&str, &[&str])] = &[
    (
        "dense attribute storage (a v2 B-tree)",
        &["attributes", "attributes (tolerant)"],
    ),
    (
        "a shared-message B-tree index",
        &[
            "SOHM B-tree",
            "shared message",
            "fill value",
            "attributes",
            "attributes (tolerant)",
        ],
    ),
    (
        "a huge fractal-heap object's B-tree",
        &["heap object", "attributes", "attributes (tolerant)"],
    ),
];

fn may_require_contiguous(check: &str, site: &str) -> bool {
    CONTIGUOUS_REQUIRED
        .iter()
        .any(|(s, checks)| *s == site && checks.contains(&check))
}

#[derive(Default, Debug)]
struct Tally {
    files: usize,
    objects: usize,
    checks: usize,
    contiguous_required: usize,
    reads: u64,
    bytes: u64,
    /// Chunk indexes (fixed and extensible arrays) read, and the most bytes
    /// one of them took through the storage.
    chunk_indexes: usize,
    max_chunk_index_bytes: u64,
}

struct Walk<'a> {
    slice: &'a [u8],
    storage: &'a CountingStorage,
    name: String,
    tally: &'a mut Tally,
}

impl Walk<'_> {
    /// The storage result must equal the slice result, or be the clean
    /// "needs the whole file" error.
    fn same<T: Debug>(
        &mut self,
        what: &str,
        want: &Result<T, FormatError>,
        got: &Result<T, FormatError>,
    ) {
        self.tally.checks += 1;
        if let Err(FormatError::ContiguousStorageRequired(site)) = got {
            assert!(
                may_require_contiguous(what, site),
                "{}: {what} fell back to the whole file ({site}), which only the \
                 v2-B-tree-indexed structures may do",
                self.name
            );
            self.tally.contiguous_required += 1;
            return;
        }
        let (w, g) = (format!("{want:?}"), format!("{got:?}"));
        assert!(
            w == g,
            "{}: {what} differs\n slice:   {}\n storage: {}",
            self.name,
            &w[..w.len().min(600)],
            &g[..g.len().min(600)]
        );
    }

    fn index_read(&mut self, bytes_before: u64) {
        self.tally.chunk_indexes += 1;
        let bytes = self.storage.bytes_read() - bytes_before;
        self.tally.max_chunk_index_bytes = self.tally.max_chunk_index_bytes.max(bytes);
    }

    fn st(&self) -> &dyn Storage {
        self.storage
    }

    fn run(&mut self) {
        let slice = self.slice;
        let sb = Superblock::parse(slice, 0);
        self.same("superblock", &sb, &Superblock::parse_in(self.st(), 0));
        let Ok(sb) = sb else { return };
        let (os, ls) = (sb.offset_size, sb.length_size);

        let want = read_superblock_extension(slice, &sb);
        self.same(
            "superblock extension",
            &want,
            &read_superblock_extension_in(self.st(), &sb),
        );
        let want = cache_image_state(slice, &sb);
        self.same("cache image", &want, &cache_image_state_in(self.st(), &sb));
        let table = load_sohm_table(slice, os, ls);
        self.same("SOHM table", &table, &load_sohm_table_in(self.st(), os, ls));
        if let Ok(Some(table)) = &table {
            for idx in &table.indexes {
                if idx.index_type == 0 {
                    let want =
                        parse_sohm_list(slice, idx.index_addr as usize, idx.num_messages, os);
                    let got = parse_sohm_list_in(self.st(), idx.index_addr, idx.num_messages, os);
                    self.same("SOHM list", &want, &got);
                } else {
                    let want = parse_sohm_btree_entries(slice, idx.index_addr as usize, os, ls);
                    let got = parse_sohm_btree_entries_in(self.st(), idx.index_addr, os, ls);
                    self.same("SOHM B-tree", &want, &got);
                }
            }
        }

        let mut seen = HashSet::new();
        let mut queue = VecDeque::from([sb.root_group_address]);
        while let Some(addr) = queue.pop_front() {
            if seen.len() >= MAX_OBJECTS || !seen.insert(addr) {
                continue;
            }
            self.tally.objects += 1;
            self.check_object(&sb, addr);
            // Traversal only (group lookups are milestone M0/M3 work).
            if let Ok(children) =
                clawhdf5_format::group_v2::resolve_group_children(slice, &sb, addr)
            {
                queue.extend(children.iter().map(|c| c.object_header_address));
            }
        }
    }

    fn check_object(&mut self, sb: &Superblock, addr: u64) {
        let slice = self.slice;
        let (os, ls) = (sb.offset_size, sb.length_size);
        let header = ObjectHeader::parse(slice, addr as usize, os, ls);
        self.same(
            "object header",
            &header,
            &ObjectHeader::parse_in(self.st(), addr, os, ls),
        );
        let Ok(header) = header else { return };

        let want = extract_attributes_full(slice, &header, os, ls);
        self.same(
            "attributes",
            &want,
            &extract_attributes_full_in(self.st(), &header, os, ls),
        );
        let want = extract_attributes_tolerant(slice, &header, os, ls);
        let got = extract_attributes_tolerant_in(self.st(), &header, os, ls);
        self.same("attributes (tolerant)", &want, &got);
        let want = dataset_fill_value_in(slice, &header.messages, os, ls);
        self.same(
            "fill value",
            &want,
            &dataset_fill_value_from_storage(self.st(), &header.messages, os, ls),
        );

        for msg in &header.messages {
            if shared_message::is_shared(msg.flags) {
                let want = message_data_with_sohm(slice, msg, os, ls);
                let got = message_data_with_sohm_in(self.st(), msg, os, ls);
                self.same("shared message", &want, &got);
            }
            match msg.msg_type {
                MessageType::SymbolTable => {
                    if let Ok(stm) = SymbolTableMessage::parse(&msg.data, os) {
                        self.check_v1_group(&stm, os, ls);
                    }
                }
                MessageType::LinkInfo => {
                    if let Ok(li) = LinkInfoMessage::parse(&msg.data, os) {
                        self.check_heap(
                            li.fractal_heap_address,
                            li.btree_name_index_address,
                            4,
                            os,
                            ls,
                        );
                    }
                }
                MessageType::AttributeInfo => {
                    if let Ok(ai) = AttributeInfoMessage::parse(&msg.data, os) {
                        self.check_heap(
                            ai.fractal_heap_address,
                            ai.btree_name_index_address,
                            0,
                            os,
                            ls,
                        );
                    }
                }
                _ => {}
            }
        }
        self.check_layout(&header, os, ls);
    }

    /// A symbol-table group: its local heap, B-tree, nodes and names.
    fn check_v1_group(&mut self, stm: &SymbolTableMessage, os: u8, ls: u8) {
        let slice = self.slice;
        let heap = LocalHeap::parse(slice, stm.local_heap_address as usize, os, ls);
        self.same(
            "local heap",
            &heap,
            &LocalHeap::parse_in(self.st(), stm.local_heap_address, os, ls),
        );
        let nodes = collect_symbol_table_nodes(slice, stm.btree_address, os, ls);
        let got = collect_symbol_table_nodes_in(self.st(), stm.btree_address, os, ls);
        self.same("group B-tree", &nodes, &got);
        let Ok(heap) = heap else { return };
        let want = heap.validate_free_list(slice, ls);
        self.same(
            "local heap free list",
            &want,
            &heap.validate_free_list_in(self.st(), ls),
        );
        let Ok(nodes) = nodes else { return };
        for &node in nodes.iter().take(MAX_HEAP_IDS) {
            let snod = SymbolTableNode::parse(slice, node as usize, os);
            self.same(
                "symbol table node",
                &snod,
                &SymbolTableNode::parse_in(self.st(), node, os),
            );
            let Ok(snod) = snod else { continue };
            for e in &snod.entries {
                let want = heap.read_string(slice, e.link_name_offset);
                self.same(
                    "link name",
                    &want,
                    &heap.read_string_in(self.st(), e.link_name_offset),
                );
            }
        }
    }

    /// A dense group's or dense attributes' fractal heap: the header, and
    /// the objects its name index points at. `id_at` is where the heap ID
    /// starts in a name-index record (after the hash for links).
    fn check_heap(&mut self, heap: Option<u64>, index: Option<u64>, id_at: usize, os: u8, ls: u8) {
        let slice = self.slice;
        let Some(heap_addr) = heap else { return };
        let fh = FractalHeapHeader::parse(slice, heap_addr as usize, os, ls);
        self.same(
            "fractal heap",
            &fh,
            &FractalHeapHeader::parse_in(self.st(), heap_addr, os, ls),
        );
        let (Ok(fh), Some(index)) = (fh, index) else {
            return;
        };
        let Ok(bt) = BTreeV2Header::parse(slice, index as usize, os, ls) else {
            return;
        };
        let Ok(records) = collect_btree_v2_records(slice, &bt, os, ls) else {
            return;
        };
        let id_len = fh.heap_id_length as usize;
        for rec in records.iter().take(MAX_HEAP_IDS) {
            let Some(id) = rec.data.get(id_at..id_at + id_len) else {
                continue;
            };
            let want = fh.read_managed_object(slice, id, os);
            self.same(
                "heap object",
                &want,
                &fh.read_managed_object_in(self.st(), id, os),
            );
        }
    }

    /// A dataset's layout: VDS mappings, and fixed/extensible array chunk
    /// indexes.
    fn check_layout(&mut self, header: &ObjectHeader, os: u8, ls: u8) {
        let slice = self.slice;
        let find = |t: MessageType| {
            header
                .messages
                .iter()
                .find(|m| m.msg_type == t)
                .and_then(|m| shared_message::message_data_with_sohm(slice, m, os, ls).ok())
        };
        let Some(layout) = find(MessageType::DataLayout) else {
            return;
        };
        let Ok(layout) = DataLayout::parse(&layout, os, ls) else {
            return;
        };
        match &layout {
            DataLayout::Virtual { .. } => {
                let (mut want, mut got) = (layout.clone(), layout.clone());
                let w = want.resolve_vds_mappings(slice, ls).map(|()| want);
                let g = got.resolve_vds_mappings_in(self.st(), ls).map(|()| got);
                self.same("VDS mappings", &w, &g);
            }
            DataLayout::Chunked {
                chunk_dimensions,
                btree_address: Some(addr),
                version: 4,
                chunk_index_type: Some(kind @ (3 | 4)),
                ..
            } => {
                let (Some(ds), Some(dt)) =
                    (find(MessageType::Dataspace), find(MessageType::Datatype))
                else {
                    return;
                };
                let (Ok(ds), Ok((dt, _))) = (Dataspace::parse(&ds, ls), Datatype::parse(&dt))
                else {
                    return;
                };
                let rank = ds.dimensions.len();
                if chunk_dimensions.len() < rank {
                    return;
                }
                let dims = &chunk_dimensions[..rank];
                let max = ds.max_dimensions.as_deref();
                let es = dt.type_size();
                if *kind == 3 {
                    let h = FixedArrayHeader::parse(slice, *addr as usize, os, ls);
                    self.same(
                        "fixed array header",
                        &h,
                        &FixedArrayHeader::parse_in(self.st(), *addr, os, ls),
                    );
                    let Ok(h) = h else { return };
                    let want =
                        read_fixed_array_chunks(slice, &h, &ds.dimensions, max, dims, es, os, ls);
                    let before = self.storage.bytes_read();
                    let got = read_fixed_array_chunks_in(
                        self.st(),
                        &h,
                        &ds.dimensions,
                        max,
                        dims,
                        es,
                        os,
                        ls,
                    );
                    self.index_read(before);
                    self.same("fixed array chunks", &want, &got);
                } else {
                    let h = ExtensibleArrayHeader::parse(slice, *addr as usize, os, ls);
                    let got = ExtensibleArrayHeader::parse_in(self.st(), *addr, os, ls);
                    self.same("extensible array header", &h, &got);
                    let Ok(h) = h else { return };
                    let want = read_extensible_array_chunks(
                        slice,
                        &h,
                        &ds.dimensions,
                        max,
                        dims,
                        es,
                        os,
                        ls,
                    );
                    let before = self.storage.bytes_read();
                    let got = read_extensible_array_chunks_in(
                        self.st(),
                        &h,
                        &ds.dimensions,
                        max,
                        dims,
                        es,
                        os,
                        ls,
                    );
                    self.index_read(before);
                    self.same("extensible array chunks", &want, &got);
                }
            }
            _ => {}
        }
    }
}

fn check_file(path: &Path, tally: &mut Tally) {
    let Ok(bytes) = std::fs::read(path) else {
        return;
    };
    check_bytes(&path.display().to_string(), &bytes, tally);
}

fn check_bytes(name: &str, bytes: &[u8], tally: &mut Tally) {
    let Ok((_, hdf5)) = split_user_block(bytes) else {
        return;
    };
    let storage = CountingStorage::new(hdf5.to_vec());
    let before = (tally.checks, tally.objects);
    let mut walk = Walk {
        slice: hdf5,
        storage: &storage,
        name: name.to_string(),
        tally,
    };
    walk.run();
    tally.files += 1;
    tally.reads += storage.reads();
    tally.bytes += storage.bytes_read();
    if std::env::var("CLAWHDF5_STORAGE_REPORT").is_ok_and(|v| v == "1") {
        eprintln!(
            "{:>6} objects {:>7} checks {:>8} reads {:>12} bytes  {}",
            tally.objects - before.1,
            tally.checks - before.0,
            storage.reads(),
            storage.bytes_read(),
            name
        );
    }
}

fn hdf5_files(dir: &Path, out: &mut Vec<PathBuf>) {
    let Ok(entries) = std::fs::read_dir(dir) else {
        return;
    };
    for e in entries.flatten() {
        let p = e.path();
        if p.is_dir() {
            hdf5_files(&p, out);
        } else if p
            .extension()
            .and_then(|x| x.to_str())
            .is_some_and(|x| matches!(x, "h5" | "hdf5" | "he5" | "nc" | "h5ad" | "hdf"))
        {
            out.push(p);
        }
    }
}

#[test]
fn fixtures_parse_identically_through_storage() {
    let mut files = Vec::new();
    hdf5_files(
        &Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures"),
        &mut files,
    );
    files.sort();
    assert!(files.len() >= 40, "{} fixtures", files.len());
    let mut tally = Tally::default();
    for f in &files {
        check_file(f, &mut tally);
    }
    eprintln!("fixtures: {tally:?}");
    assert!(tally.objects >= 150 && tally.checks >= 1000, "{tally:?}");
    // Reads really went through read_at.
    assert!(tally.reads > tally.objects as u64);
}

#[test]
fn corpus_parses_identically_through_storage() {
    let Ok(dirs) = std::env::var("CLAWHDF5_STORAGE_CORPUS") else {
        eprintln!("CLAWHDF5_STORAGE_CORPUS not set; skipping the corpus");
        return;
    };
    let mut files = Vec::new();
    for d in std::env::split_paths(&dirs) {
        hdf5_files(&d, &mut files);
    }
    files.sort();
    let mut tally = Tally::default();
    for f in &files {
        check_file(f, &mut tally);
    }
    eprintln!("corpus: {tally:?}");
    assert!(tally.files > 0);
}

fn python() -> String {
    std::env::var("CLAWHDF5_PYTHON").unwrap_or_else(|_| "python3".to_string())
}

fn interop_required() -> bool {
    std::env::var("CLAWHDF5_REQUIRE_INTEROP").is_ok_and(|v| v == "1")
}

/// Files h5py writes to cover what the fixtures do not: extensible arrays
/// deep enough for super blocks and paged data blocks, paged fixed arrays,
/// big symbol-table and dense groups, dense and shared attributes, a SOHM
/// list and a SOHM B-tree, committed datatypes, and a user block.
const GENERATE: &str = r#"
import ctypes, glob, os, sys, h5py, numpy as np
out = sys.argv[1]
def p(n): return os.path.join(out, n)

with h5py.File(p('ea.h5'), 'w', libver='latest') as f:
    # One unlimited dimension: extensible array. 3000 chunks reach super
    # blocks; 2-element chunks of int8 keep data small.
    d = f.create_dataset('ea', shape=(6000,), maxshape=(None,), chunks=(2,), dtype='i1')
    d[:] = np.arange(6000) % 100
    d2 = f.create_dataset('ea_deflate', shape=(4000, 3), maxshape=(None, 3), chunks=(2, 3),
                          dtype='f4', compression='gzip')
    d2[:] = np.random.default_rng(1).random((4000, 3))
    d3 = f.create_dataset('ea_sparse', shape=(100000,), maxshape=(None,), chunks=(4,), dtype='i2')
    d3[0:8] = 1; d3[50000:50004] = 2; d3[99996:] = 3
    fa = f.create_dataset('fa_paged', shape=(5000,), chunks=(1,), dtype='u1')
    fa[::3] = 7
    fa2 = f.create_dataset('fa', shape=(40, 40), chunks=(8, 8), dtype='f8', compression='gzip')
    fa2[:] = 1.5
    for i in range(30):
        f.attrs[f'a{i}'] = np.arange(i + 1)
    g = f.create_group('dense')
    for i in range(300):
        g.create_group(f'child{i:04d}').attrs['i'] = i
    f['committed'] = np.dtype([('x', 'i4'), ('y', 'f8')])
    f.create_dataset('uses_committed', shape=(3,), dtype=f['committed'])
    f['uses_committed'].attrs.create('ta', data=np.zeros(2, dtype=f['committed'].dtype), dtype=f['committed'])
    f.attrs['vl'] = ['alpha', 'beta', 'gamma']

with h5py.File(p('v1_groups.h5'), 'w', libver='earliest', userblock_size=512) as f:
    for i in range(400):
        g = f.create_group(f'g{i:04d}')
        g.attrs['n'] = i
    f.create_dataset('x', data=np.arange(10))

# Paged chunk indexes whose data blocks are bigger than the storage reads
# in one piece (1 MiB), with two chunks written: a fixed array of 300 000
# chunks (a 2.4 MB data block) and an extensible array grown to 1.2e9 (its
# last data block holds 131 072 chunks: over 1 MiB).
with h5py.File(p('big_paged.h5'), 'w', libver='latest') as f:
    d = f.create_dataset('fa', shape=(300000,), chunks=(1,), dtype='u1')
    d[5] = 1; d[250000] = 2
    e = f.create_dataset('ea', shape=(1,), maxshape=(None,), chunks=(1,), dtype='u1')
    e.resize((1200000000,)); e[10] = 1; e[1100000000] = 3

libs = glob.glob(os.path.join(os.path.dirname(h5py.__file__), '..', 'h5py.libs', 'libhdf5-*.so*'))
if libs:
    lib = ctypes.CDLL(libs[0])
    lib.H5Pset_shared_mesg_nindexes.argtypes = [ctypes.c_int64, ctypes.c_uint]
    lib.H5Pset_shared_mesg_index.argtypes = [ctypes.c_int64, ctypes.c_uint, ctypes.c_uint, ctypes.c_uint]
    lib.H5Pset_shared_mesg_phase_change.argtypes = [ctypes.c_int64, ctypes.c_uint, ctypes.c_uint]
    for name, list_max in [('sohm_list.h5', 50), ('sohm_btree.h5', 0)]:
        fcpl = h5py.h5p.create(h5py.h5p.FILE_CREATE)
        assert lib.H5Pset_shared_mesg_nindexes(fcpl.id, 1) >= 0
        # datatype, dataspace, fill value, filter pipeline, attribute
        assert lib.H5Pset_shared_mesg_index(fcpl.id, 0, 0x02 | 0x04 | 0x08 | 0x10 | 0x20, 1) >= 0
        assert lib.H5Pset_shared_mesg_phase_change(fcpl.id, list_max, 0) >= 0
        fapl = h5py.h5p.create(h5py.h5p.FILE_ACCESS)
        fapl.set_libver_bounds(h5py.h5f.LIBVER_LATEST, h5py.h5f.LIBVER_LATEST)
        fid = h5py.h5f.create(p(name).encode(), h5py.h5f.ACC_TRUNC, fcpl=fcpl, fapl=fapl)
        with h5py.File(fid) as f:
            for i in range(20):
                d = f.create_dataset(f'd{i}', shape=(10, i + 1), dtype='f4', fillvalue=-1.0,
                                     chunks=(5, 1), compression='gzip')
                d.attrs['units'] = 'metres per second, a long enough string to share'
                d.attrs['scale'] = np.arange(20, dtype='f8')
print('ok')
"#;

#[test]
fn h5py_files_parse_identically_through_storage() {
    let dir = Path::new(env!("CARGO_TARGET_TMPDIR")).join("storage_equivalence");
    let _ = std::fs::remove_dir_all(&dir);
    std::fs::create_dir_all(&dir).unwrap();
    let out = Command::new(python())
        .args(["-c", GENERATE, dir.to_str().unwrap()])
        .output();
    match out {
        Ok(o) if o.status.success() => {}
        Ok(o) if interop_required() => panic!(
            "h5py generation failed:\n{}\n{}",
            String::from_utf8_lossy(&o.stdout),
            String::from_utf8_lossy(&o.stderr)
        ),
        Err(e) if interop_required() => panic!("python not available: {e}"),
        _ => {
            eprintln!("python3 with h5py unavailable; skipping");
            return;
        }
    }
    let mut files = Vec::new();
    hdf5_files(&dir, &mut files);
    files.sort();
    let names: Vec<_> = files
        .iter()
        .map(|f| f.file_name().unwrap().to_string_lossy().into_owned())
        .collect();
    for want in ["ea.h5", "v1_groups.h5", "big_paged.h5"] {
        assert!(names.iter().any(|n| n == want), "{names:?}");
    }
    if interop_required() {
        assert!(names.iter().any(|n| n == "sohm_btree.h5"), "{names:?}");
    }
    let mut tally = Tally::default();
    for f in &files {
        if f.ends_with("big_paged.h5") {
            // Only the pages in use are read, not the whole data blocks:
            // read in one piece, the fixed array took 2.4 MB and the
            // extensible array 1.2 MB (its super block's page bitmap and
            // block addresses are most of what remains).
            let mut big = Tally::default();
            check_file(f, &mut big);
            eprintln!("big paged blocks: {big:?}");
            assert_eq!(big.chunk_indexes, 2, "{big:?}");
            assert!(big.max_chunk_index_bytes < 256 << 10, "{big:?}");
            // Truncated anywhere, the page-by-page reads still agree with
            // the slice reads (errors included).
            let bytes = std::fs::read(f).unwrap();
            for cut in (0..bytes.len()).step_by(bytes.len() / 97) {
                check_bytes(
                    &format!("big_paged.h5 cut at {cut}"),
                    &bytes[..cut],
                    &mut big,
                );
            }
            eprintln!("big paged blocks, truncated: {big:?}");
            assert!(big.chunk_indexes > 100, "{big:?}");
        }
        check_file(f, &mut tally);
    }
    eprintln!("h5py files: {tally:?}");
    assert!(tally.objects >= 700, "{tally:?}");
    // Dense attributes and the SOHM B-tree are the known clean errors.
    assert!(tally.contiguous_required > 0, "{tally:?}");
}