//! Equivalence harness for the range-read migration
//! (`docs/design/range-reads.md`, milestones M1 and M2).
//!
//! Every 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.
//!
//! Nothing may answer [`FormatError::ContiguousStorageRequired`] any more:
//! since milestone M2 every read path works over `read_at` alone, the v2
//! B-tree structures (dense groups and attributes, a SOHM B-tree index,
//! huge fractal-heap objects) included.
//!
//! - `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, collect_btree_v2_records_in, find_btree_v2_records,
    find_btree_v2_records_in,
};
use clawhdf5_format::chunk_cache::ChunkCache;
use clawhdf5_format::chunked_read::{list_chunks, list_chunks_in};
use clawhdf5_format::data_layout::DataLayout;
use clawhdf5_format::data_read::{
    read_raw_data_cached, read_raw_data_cached_in, read_raw_data_full, read_raw_data_full_in,
    read_raw_data_indexed, read_raw_data_indexed_in, read_raw_data_selection,
    read_raw_data_selection_in,
};
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, read_full_with_fill,
    read_full_with_fill_in,
};
use clawhdf5_format::filter_pipeline::FilterPipeline;
use clawhdf5_format::fixed_array::{
    FixedArrayHeader, read_fixed_array_chunks, read_fixed_array_chunks_in,
};
use clawhdf5_format::fractal_heap::FractalHeapHeader;
use clawhdf5_format::group_v2;
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::selection::Selection;
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};
use clawhdf5_format::vds::{
    read_virtual_dataset, read_virtual_dataset_in, virtual_dataset_extent,
    virtual_dataset_extent_in,
};
use clawhdf5_format::vl_data::{VlResolver, read_vl_bytes, read_vl_bytes_in};

/// 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;
/// Datasets larger than this are not read (their chunk indexes still are).
const MAX_DATA_BYTES: u64 = 16 << 20;

#[derive(Default, Debug)]
struct Tally {
    files: usize,
    objects: usize,
    checks: 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,
    /// The file's directory, for external VDS sources.
    dir: Option<PathBuf>,
    tally: &'a mut Tally,
}

impl Walk<'_> {
    /// The storage result must equal the slice result; no parser may ask
    /// for the whole file.
    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 {
            panic!(
                "{}: {what} fell back to the whole file ({site}); every read path \
                 must work through read_at",
                self.name
            );
        }
        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);
            let children = group_v2::resolve_group_children(slice, &sb, addr);
            let got = group_v2::resolve_group_children_in(self.st(), &sb, addr);
            self.same("group listing", &children, &got);
            if let Ok(children) = children {
                for c in children.iter().take(MAX_HEAP_IDS) {
                    let want = group_v2::resolve_child(slice, &sb, addr, &c.name);
                    let got = group_v2::resolve_child_in(self.st(), &sb, addr, &c.name);
                    self.same("child lookup", &want, &got);
                }
                // A name no group has: the lookup's not-found path.
                let want = group_v2::resolve_child(slice, &sb, addr, "no such child");
                let got = group_v2::resolve_child_in(self.st(), &sb, addr, "no such child");
                self.same("child lookup (missing)", &want, &got);
                queue.extend(children.iter().map(|c| c.object_header_address));
            }
        }
        // Paths: every listed name from the root, and one that is missing.
        if let Ok(children) = group_v2::resolve_group_children(slice, &sb, sb.root_group_address) {
            for c in children.iter().take(MAX_HEAP_IDS) {
                let path = format!("/{}", c.name);
                let want = group_v2::resolve_path_any(slice, &sb, &path);
                let got = group_v2::resolve_path_any_in(self.st(), &sb, &path);
                self.same("path", &want, &got);
            }
        }
        let want = group_v2::resolve_path_any(slice, &sb, "/no/such/path");
        let got = group_v2::resolve_path_any_in(self.st(), &sb, "/no/such/path");
        self.same("path (missing)", &want, &got);
    }

    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);
        self.check_data(&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 bt = BTreeV2Header::parse(slice, index as usize, os, ls);
        self.same(
            "v2 B-tree header",
            &bt,
            &BTreeV2Header::parse_in(self.st(), index, os, ls),
        );
        let Ok(bt) = bt else { return };
        let records = collect_btree_v2_records(slice, &bt, os, ls);
        let got = collect_btree_v2_records_in(self.st(), &bt, os, ls);
        self.same("v2 B-tree records", &records, &got);
        let Ok(records) = records else { return };
        // Descents to single records (by their bytes), as name lookups do.
        for rec in records.iter().take(8) {
            let key = rec.data.clone();
            let want = find_btree_v2_records(slice, &bt, os, &mut |r| r.cmp(&key[..]));
            let got = find_btree_v2_records_in(self.st(), &bt, os, &mut |r| r.cmp(&key[..]));
            self.same("v2 B-tree descent", &want, &got);
        }
        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 values through every raw-data path: whole reads (plain,
    /// cached, indexed, fill-aware, virtual), chunk listings, selections
    /// (a box, a strided hyperslab, points), VL strings and sequences.
    fn check_data(&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(dt), Some(ds), Some(dl)) = (
            find(MessageType::Datatype),
            find(MessageType::Dataspace),
            find(MessageType::DataLayout),
        ) else {
            return;
        };
        let (Ok((dt, _)), Ok(ds), Ok(dl)) = (
            Datatype::parse(&dt),
            Dataspace::parse(&ds, ls),
            DataLayout::parse(&dl, os, ls),
        ) else {
            return;
        };
        let pipeline = match find(MessageType::FilterPipeline).map(|p| FilterPipeline::parse(&p)) {
            Some(Ok(p)) => Some(p),
            Some(Err(_)) => return,
            None => None,
        };
        let pl = pipeline.as_ref();
        let elem = dt.type_size() as u64;
        let bytes = ds
            .dimensions
            .iter()
            .try_fold(elem, |a, &d| a.checked_mul(d));
        if bytes.is_none_or(|b| b > MAX_DATA_BYTES) {
            return;
        }

        if matches!(dl, DataLayout::Virtual { .. }) {
            let resolver = self.resolver();
            let r: &clawhdf5_format::vds::VdsFileResolver = &resolver;
            let want = virtual_dataset_extent(slice, &dl, &ds, os, ls, Some(r));
            let got = virtual_dataset_extent_in(self.st(), &dl, &ds, os, ls, Some(r));
            self.same("VDS extent", &want, &got);
            let want = read_virtual_dataset(slice, &dl, &ds, &dt, None, os, ls, Some(r));
            let got = read_virtual_dataset_in(self.st(), &dl, &ds, &dt, None, os, ls, Some(r));
            self.same("VDS read", &want, &got);
            return;
        }

        let want = read_raw_data_full(slice, &dl, &ds, &dt, pl, os, ls);
        let got = read_raw_data_full_in(self.st(), &dl, &ds, &dt, pl, os, ls);
        self.same("raw data", &want, &got);
        let want_fill = read_full_with_fill(
            &header.messages,
            slice,
            &dl,
            &ds,
            elem as usize,
            os,
            ls,
            || read_raw_data_full(slice, &dl, &ds, &dt, pl, os, ls),
        );
        let got_fill = read_full_with_fill_in(
            &header.messages,
            self.st(),
            &dl,
            &ds,
            elem as usize,
            os,
            ls,
            || read_raw_data_full_in(self.st(), &dl, &ds, &dt, pl, os, ls),
        );
        self.same("raw data with fill", &want_fill, &got_fill);

        if matches!(dl, DataLayout::Chunked { .. }) {
            let want = list_chunks(slice, &dl, &ds, elem as usize, os, ls);
            let got = list_chunks_in(self.st(), &dl, &ds, elem as usize, os, ls);
            self.same("chunk list", &want, &got);
            // Through a chunk cache, twice (the second read is served from
            // it), and through the indexed path.
            let (c1, c2) = (ChunkCache::new(), ChunkCache::new());
            for _ in 0..2 {
                let want = read_raw_data_cached(slice, &dl, &ds, &dt, pl, os, ls, &c1);
                let got = read_raw_data_cached_in(self.st(), &dl, &ds, &dt, pl, os, ls, &c2);
                // A cache lists the chunks in hash-map order (see below).
                if want.is_err() && got.is_err() {
                    self.tally.checks += 1;
                } else {
                    self.same("raw data (cached)", &want, &got);
                }
            }
            let (c1, c2) = (ChunkCache::new(), ChunkCache::new());
            let want = read_raw_data_indexed(slice, &dl, &ds, &dt, pl, os, ls, &c1);
            let got = read_raw_data_indexed_in(self.st(), &dl, &ds, &dt, pl, os, ls, &c2);
            // The indexed path decodes chunks in hash-map order, so which
            // failing chunk it reports varies between two caches (with the
            // slice alone, too): only whether it fails must agree.
            if want.is_err() && got.is_err() {
                self.tally.checks += 1;
            } else {
                self.same("raw data (indexed)", &want, &got);
            }
        }

        let dims = &ds.dimensions;
        if !dims.is_empty() && dims.iter().all(|&d| d > 0) {
            let rank = dims.len();
            let ones = vec![1u64; rank];
            let quarter = Selection::Hyperslab {
                start: dims.iter().map(|&d| d / 4).collect(),
                stride: ones.clone(),
                count: dims.iter().map(|&d| (d / 3).max(1)).collect(),
                block: ones.clone(),
            };
            let mut stride = ones.clone();
            stride[rank - 1] = 2;
            let mut count = dims.clone();
            count[rank - 1] = dims[rank - 1].div_ceil(2);
            let strided = Selection::Hyperslab {
                start: vec![0; rank],
                stride,
                count,
                block: ones.clone(),
            };
            let points = Selection::Points(vec![
                dims.iter().map(|&d| d - 1).collect(),
                vec![0; rank],
                dims.iter().map(|&d| d / 2).collect(),
            ]);
            for (what, sel) in [
                ("selection (box)", &quarter),
                ("selection (strided)", &strided),
                ("selection (points)", &points),
            ] {
                let want = read_raw_data_selection(slice, &dl, &ds, &dt, pl, os, ls, sel);
                let got = read_raw_data_selection_in(self.st(), &dl, &ds, &dt, pl, os, ls, sel);
                self.same(what, &want, &got);
            }
        }

        // Variable-length strings and sequences, resolved in the global heap.
        if let (Datatype::VariableLength { base_type, .. }, Ok(raw)) = (&dt, &want) {
            let n = raw.len() / clawhdf5_format::vl_data::element_size(os).max(1);
            let raw = &raw[..n * clawhdf5_format::vl_data::element_size(os)];
            let want = VlResolver::new(slice, os, ls).string_bytes(raw);
            let got = VlResolver::new_in(self.st(), os, ls).string_bytes(raw);
            self.same("VL strings", &want, &got);
            let base = base_type.type_size() as usize;
            let want = VlResolver::new(slice, os, ls).sequences(raw, base);
            let got = VlResolver::new_in(self.st(), os, ls).sequences(raw, base);
            self.same("VL sequences", &want, &got);
            let want = read_vl_bytes(slice, raw, n as u64, os, ls);
            let got = read_vl_bytes_in(self.st(), raw, n as u64, os, ls);
            self.same("VL bytes", &want, &got);
        }
    }

    /// External VDS source files: siblings of the file being walked.
    fn resolver(&self) -> impl Fn(&str) -> Result<Option<Vec<u8>>, FormatError> + use<> {
        let dir = self.dir.clone();
        move |name: &str| {
            let (Some(dir), false) = (dir.as_ref(), name.contains("..") || name.starts_with('/'))
            else {
                return Ok(None);
            };
            Ok(std::fs::read(dir.join(name)).ok())
        }
    }

    /// 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_in(
        &path.display().to_string(),
        &bytes,
        path.parent().map(Path::to_path_buf),
        tally,
    );
}

fn check_bytes(name: &str, bytes: &[u8], tally: &mut Tally) {
    check_bytes_in(name, bytes, None, tally);
}

fn check_bytes_in(name: &str, bytes: &[u8], dir: Option<PathBuf>, 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(),
        dir,
        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);
}

/// A storage that misbehaves: fails its `fail_at`-th read (1-based, `0`
/// never), and, with `short`, serves one byte less than asked for inside
/// the file (a truncated response).
struct Adversary {
    data: Vec<u8>,
    reads: std::sync::atomic::AtomicUsize,
    fail_at: usize,
    short: bool,
}

impl Storage for Adversary {
    fn read_at(&self, offset: u64, len: usize) -> Result<std::borrow::Cow<'_, [u8]>, FormatError> {
        let n = self
            .reads
            .fetch_add(1, std::sync::atomic::Ordering::Relaxed)
            + 1;
        if n == self.fail_at {
            return Err(FormatError::Storage(format!(
                "injected failure of read {n}"
            )));
        }
        let got = self.data.as_slice().read_at(offset, len)?;
        let mut v = got.into_owned();
        if self.short && v.len() > 1 {
            v.pop();
        }
        Ok(std::borrow::Cow::Owned(v))
    }

    fn len(&self) -> u64 {
        self.data.len() as u64
    }
}

/// Every group listing and every dataset's values (whole, fill-aware and
/// through a selection) read through a storage that fails or serves short
/// reads: each result is an error or exactly the in-memory result, never
/// other data; and a failing read is reported as that failure.
#[test]
fn misbehaving_storage_never_returns_wrong_data() {
    let dir = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures");
    let mut files = Vec::new();
    hdf5_files(&dir, &mut files);
    files.sort();
    let (mut compared, mut failures_seen) = (0usize, 0usize);
    for path in &files {
        let Ok(bytes) = std::fs::read(path) else {
            continue;
        };
        let Ok((_, hdf5)) = split_user_block(&bytes) else {
            continue;
        };
        let Ok(sb) = Superblock::parse(hdf5, 0) else {
            continue;
        };
        // The whole read of every object, as one result to compare.
        let everything = |file: &dyn Storage| -> Result<String, FormatError> {
            let (os, ls) = (sb.offset_size, sb.length_size);
            let mut out = String::new();
            let mut queue = VecDeque::from([sb.root_group_address]);
            let mut seen = HashSet::new();
            while let Some(addr) = queue.pop_front() {
                if seen.len() > 200 || !seen.insert(addr) {
                    continue;
                }
                let header = ObjectHeader::parse_in(file, addr, os, ls)?;
                let find = |t: MessageType| {
                    header
                        .messages
                        .iter()
                        .find(|m| m.msg_type == t)
                        .map(|m| message_data_with_sohm_in(file, m, os, ls))
                        .transpose()
                };
                if let (Some(dt), Some(ds), Some(dl)) = (
                    find(MessageType::Datatype)?,
                    find(MessageType::Dataspace)?,
                    find(MessageType::DataLayout)?,
                ) {
                    let dt = Datatype::parse(&dt)?.0;
                    let ds = Dataspace::parse(&ds, ls)?;
                    let dl = DataLayout::parse(&dl, os, ls)?;
                    let pl = find(MessageType::FilterPipeline)?
                        .map(|p| FilterPipeline::parse(&p))
                        .transpose()?;
                    let data = read_full_with_fill_in(
                        &header.messages,
                        file,
                        &dl,
                        &ds,
                        dt.type_size() as usize,
                        os,
                        ls,
                        || read_raw_data_full_in(file, &dl, &ds, &dt, pl.as_ref(), os, ls),
                    );
                    out.push_str(&format!("{addr}: {data:?}\n"));
                    if let Some(&d0) = ds.dimensions.first() {
                        let rank = ds.dimensions.len();
                        let sel = Selection::Hyperslab {
                            start: vec![0; rank],
                            stride: vec![1; rank],
                            count: std::iter::once(d0.div_ceil(2))
                                .chain(ds.dimensions[1..].iter().copied())
                                .collect(),
                            block: vec![1; rank],
                        };
                        let part = read_raw_data_selection_in(
                            file,
                            &dl,
                            &ds,
                            &dt,
                            pl.as_ref(),
                            os,
                            ls,
                            &sel,
                        );
                        out.push_str(&format!("{addr} half: {part:?}\n"));
                    }
                }
                let children = group_v2::resolve_group_children_in(file, &sb, addr);
                out.push_str(&format!("{addr} children: {children:?}\n"));
                if let Ok(c) = children {
                    queue.extend(c.iter().map(|c| c.object_header_address));
                }
            }
            Ok(out)
        };
        let want = everything(&hdf5);
        let counting = CountingStorage::new(hdf5.to_vec());
        assert_eq!(
            format!("{:?}", everything(&counting)),
            format!("{want:?}"),
            "{}",
            path.display()
        );
        let total = counting.reads() as usize;
        let step = (total / 25).max(1);
        for fail_at in (1..=total).step_by(step) {
            for short in [false, true] {
                if short && fail_at != 1 {
                    continue;
                }
                let adv = Adversary {
                    data: hdf5.to_vec(),
                    reads: Default::default(),
                    fail_at: if short { 0 } else { fail_at },
                    short,
                };
                let got = everything(&adv);
                compared += 1;
                match (&got, &want) {
                    (Ok(g), Ok(w)) => {
                        // Per-object results inside may be errors; values
                        // that were read must be the right ones.
                        for (gl, wl) in g.lines().zip(w.lines()) {
                            if gl != wl {
                                assert!(
                                    gl.contains("Err("),
                                    "{}: fail_at {fail_at} short {short}:\n got  {gl}\n want {wl}",
                                    path.display()
                                );
                                failures_seen += 1;
                                // A listing that failed ends the walk
                                // differently from here on.
                                if gl.contains("children: Err(") {
                                    break;
                                }
                            }
                        }
                    }
                    (Err(FormatError::Storage(_)), _) => failures_seen += 1,
                    (Err(e), Ok(_)) => panic!(
                        "{}: fail_at {fail_at} short {short}: {e:?} instead of a storage error",
                        path.display()
                    ),
                    (Err(_), Err(_)) => {}
                    // A listing failed, so the walk never reached the
                    // object that fails in memory.
                    (Ok(g), Err(e)) => assert!(
                        g.contains("children: Err(Storage"),
                        "{}: fail_at {fail_at} short {short}: read where memory fails ({e:?})",
                        path.display()
                    ),
                }
            }
        }
    }
    eprintln!("misbehaving storage: {compared} runs, {failures_seen} failures reported");
    assert!(
        compared > 500 && failures_seen > 100,
        "{compared} {failures_seen}"
    );
}

/// A read_at-only storage that also counts `read_ranges` calls and ranges.
struct BatchCounting {
    inner: CountingStorage,
    batches: std::sync::atomic::AtomicUsize,
    ranges: std::sync::atomic::AtomicUsize,
}

impl Storage for BatchCounting {
    fn read_at(&self, offset: u64, len: usize) -> Result<std::borrow::Cow<'_, [u8]>, FormatError> {
        self.inner.read_at(offset, len)
    }

    fn len(&self) -> u64 {
        self.inner.len()
    }

    fn read_ranges(
        &self,
        ranges: &[std::ops::Range<u64>],
    ) -> Result<Vec<std::borrow::Cow<'_, [u8]>>, FormatError> {
        use std::sync::atomic::Ordering::Relaxed;
        self.batches.fetch_add(1, Relaxed);
        self.ranges.fetch_add(ranges.len(), Relaxed);
        ranges
            .iter()
            .map(|r| self.inner.read_at(r.start, (r.end - r.start) as usize))
            .collect()
    }
}

/// A chunked read lists its chunks, then fetches all their bytes with one
/// `read_ranges` call (a remote backend coalesces and parallelises it), and
/// a selection fetches only the chunks it overlaps, in one call too.
#[test]
fn chunked_reads_fetch_their_chunks_in_one_batch() {
    use std::sync::atomic::Ordering::Relaxed;
    let dir = Path::new(env!("CARGO_MANIFEST_DIR")).join("tests/fixtures");
    let mut datasets = 0;
    for name in [
        "chunked_large.h5",
        "chunked_deflate.h5",
        "chunked_2d.h5",
        "v4_fixed_array.h5",
    ] {
        let bytes = std::fs::read(dir.join(name)).unwrap();
        let sb = Superblock::parse(&bytes, 0).unwrap();
        let (os, ls) = (sb.offset_size, sb.length_size);
        let st = BatchCounting {
            inner: CountingStorage::new(bytes.clone()),
            batches: Default::default(),
            ranges: Default::default(),
        };
        for child in group_v2::resolve_group_children(&bytes, &sb, sb.root_group_address).unwrap() {
            let header =
                ObjectHeader::parse(&bytes, child.object_header_address as usize, os, ls).unwrap();
            let msg = |t: MessageType| {
                header
                    .messages
                    .iter()
                    .find(|m| m.msg_type == t)
                    .map(|m| m.data.clone())
            };
            let Some(dl) = msg(MessageType::DataLayout) else {
                continue;
            };
            let dl = DataLayout::parse(&dl, os, ls).unwrap();
            if !matches!(dl, DataLayout::Chunked { .. }) {
                continue;
            }
            let dt = Datatype::parse(&msg(MessageType::Datatype).unwrap())
                .unwrap()
                .0;
            let ds = Dataspace::parse(&msg(MessageType::Dataspace).unwrap(), ls).unwrap();
            let pl = msg(MessageType::FilterPipeline).map(|p| FilterPipeline::parse(&p).unwrap());
            let es = dt.type_size() as usize;
            let (chunks, _) = list_chunks(&bytes, &dl, &ds, es, os, ls).unwrap();
            let want = read_raw_data_full(&bytes, &dl, &ds, &dt, pl.as_ref(), os, ls).unwrap();
            st.batches.store(0, Relaxed);
            st.ranges.store(0, Relaxed);
            let got = read_raw_data_full_in(&st, &dl, &ds, &dt, pl.as_ref(), os, ls).unwrap();
            assert_eq!(got, want, "{name} {}", child.name);
            assert_eq!(st.batches.load(Relaxed), 1, "{name} {}", child.name);
            assert_eq!(
                st.ranges.load(Relaxed),
                chunks.len(),
                "{name} {}",
                child.name
            );
            // The first chunk only.
            let rank = ds.dimensions.len();
            let sel = Selection::Hyperslab {
                start: vec![0; rank],
                stride: vec![1; rank],
                count: vec![1; rank],
                block: vec![1; rank],
            };
            let want = read_raw_data_selection(&bytes, &dl, &ds, &dt, pl.as_ref(), os, ls, &sel);
            st.batches.store(0, Relaxed);
            st.ranges.store(0, Relaxed);
            let got = read_raw_data_selection_in(&st, &dl, &ds, &dt, pl.as_ref(), os, ls, &sel);
            assert_eq!(got, want, "{name} {}", child.name);
            if chunks.len() > 2 {
                assert_eq!(st.batches.load(Relaxed), 1, "{name} {}", child.name);
                assert_eq!(st.ranges.load(Relaxed), 1, "{name} {}", child.name);
            }
            datasets += 1;
        }
    }
    assert!(datasets >= 4, "{datasets}");
}

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:?}");
}