// redb index tables
//
// capnp logs are source of truth; redb provides indexed access.
//
// Node tables:
//   KEY_TO_UUID: key → (uuid, node_type, timestamp, deleted)
//                Keeps entries for deleted nodes to enable index-based restore.
//   UUID_OFFSETS: [uuid:16][offset:8 BE] → () composite key for O(log n) max-offset lookup
//   NODES_BY_PROVENANCE: provenance → (timestamp, uuid) (multimap)
//
// Relation tables:
//   RELS: node_uuid → (other_uuid, strength, rel_type, is_outgoing) packed (multimap)
//         Each relation stored twice — once per endpoint with direction bit.
//
// To get current offset: KEY_TO_UUID[key] → uuid → max(UUID_OFFSETS[uuid][*])
// To get key from uuid: read_node_at_offset(max_offset) → node.key

use anyhow::{Context, Result};
use redb::{Database, MultimapTableDefinition, ReadableDatabase, ReadableTable, ReadableTableMetadata, TableDefinition, WriteTransaction};
use std::collections::HashMap;
use std::path::Path;

use super::types::Node;
use super::capnp::read_node_at_offset;

// Node tables
// KEY_TO_UUID: key → [uuid:16][node_type:1][timestamp:8][deleted:1][weight:4] = 30 bytes
pub const KEY_TO_UUID: TableDefinition<&str, &[u8]> = TableDefinition::new("key_to_uuid");
// UUID_OFFSETS: [uuid:16][offset:8 BE] → () — offset in key for range scans
pub const UUID_OFFSETS: TableDefinition<&[u8], ()> = TableDefinition::new("uuid_offsets");
// NODES_BY_PROVENANCE: provenance → [negated_timestamp:8][uuid:16] = 24 bytes (sorted by timestamp desc)
pub const NODES_BY_PROVENANCE: MultimapTableDefinition<&str, &[u8]> = MultimapTableDefinition::new("nodes_by_provenance");
// NODES_BY_TYPE: [type:1][neg_timestamp:8] → uuid (for type+date range queries, newest first)
pub const NODES_BY_TYPE: TableDefinition<&[u8], &[u8]> = TableDefinition::new("nodes_by_type");

// Relations table - each relation stored twice (once per endpoint)
// Value: (other_uuid: [u8;16], strength: f32, rel_type: u8, is_outgoing: bool)
// Packed as 22 bytes: [other_uuid:16][strength:4][rel_type:1][is_outgoing:1]
pub const RELS: MultimapTableDefinition<&[u8], &[u8]> = MultimapTableDefinition::new("rels");

/// Open or create the redb database, ensuring all tables exist.
pub fn open_db(path: &Path) -> Result<Database> {
    let db = Database::create(path)
        .with_context(|| format!("create redb {}", path.display()))?;

    // Ensure tables exist by opening a write transaction
    let txn = db.begin_write()?;
    {
        // Node tables
        let _ = txn.open_table(KEY_TO_UUID)?;
        let _ = txn.open_table(UUID_OFFSETS)?;
        let _ = txn.open_multimap_table(NODES_BY_PROVENANCE)?;
        let _ = txn.open_table(NODES_BY_TYPE)?;
        // Relations
        let _ = txn.open_multimap_table(RELS)?;
    }
    txn.commit()?;

    Ok(db)
}

/// Pack node metadata: [uuid:16][node_type:1][timestamp:8][deleted:1][weight:4] = 30 bytes
fn pack_node_meta(uuid: &[u8; 16], node_type: u8, timestamp: i64, deleted: bool, weight: f32) -> [u8; 30] {
    let mut buf = [0u8; 30];
    buf[0..16].copy_from_slice(uuid);
    buf[16] = node_type;
    buf[17..25].copy_from_slice(&timestamp.to_be_bytes());
    buf[25] = if deleted { 1 } else { 0 };
    buf[26..30].copy_from_slice(&weight.to_be_bytes());
    buf
}

/// Unpack node metadata. Returns (uuid, node_type, timestamp, deleted, weight).
/// Handles old formats (16-byte, 25-byte, 26-byte) and new (30-byte).
pub fn unpack_node_meta(data: &[u8]) -> ([u8; 16], u8, i64, bool, f32) {
    let mut uuid = [0u8; 16];
    uuid.copy_from_slice(&data[0..16]);
    if data.len() >= 30 {
        let node_type = data[16];
        let timestamp = i64::from_be_bytes([
            data[17], data[18], data[19], data[20],
            data[21], data[22], data[23], data[24],
        ]);
        let deleted = data[25] != 0;
        let weight = f32::from_be_bytes([data[26], data[27], data[28], data[29]]);
        (uuid, node_type, timestamp, deleted, weight)
    } else if data.len() >= 26 {
        let node_type = data[16];
        let timestamp = i64::from_be_bytes([
            data[17], data[18], data[19], data[20],
            data[21], data[22], data[23], data[24],
        ]);
        let deleted = data[25] != 0;
        (uuid, node_type, timestamp, deleted, 0.5) // default weight
    } else if data.len() >= 25 {
        let node_type = data[16];
        let timestamp = i64::from_be_bytes([
            data[17], data[18], data[19], data[20],
            data[21], data[22], data[23], data[24],
        ]);
        (uuid, node_type, timestamp, false, 0.5)
    } else {
        // Old format: just uuid, default metadata
        (uuid, 0, 0, false, 0.5)
    }
}

/// Pack provenance value: [negated_timestamp:8][uuid:16] = 24 bytes for descending sort
fn pack_provenance_value(timestamp: i64, uuid: &[u8; 16]) -> [u8; 24] {
    let mut buf = [0u8; 24];
    let neg_ts = (!timestamp).to_be_bytes(); // negate for descending order
    buf[0..8].copy_from_slice(&neg_ts);
    buf[8..24].copy_from_slice(uuid);
    buf
}

/// Unpack provenance value: returns (timestamp, uuid)
pub fn unpack_provenance_value(data: &[u8]) -> (i64, [u8; 16]) {
    let neg_ts = i64::from_be_bytes([data[0], data[1], data[2], data[3], data[4], data[5], data[6], data[7]]);
    let timestamp = !neg_ts;
    let mut uuid = [0u8; 16];
    uuid.copy_from_slice(&data[8..24]);
    (timestamp, uuid)
}

/// Pack UUID_OFFSETS key: [uuid:16][offset:8 BE] = 24 bytes
fn pack_uuid_offset(uuid: &[u8; 16], offset: u64) -> [u8; 24] {
    let mut buf = [0u8; 24];
    buf[0..16].copy_from_slice(uuid);
    buf[16..24].copy_from_slice(&offset.to_be_bytes());
    buf
}

/// Pack NODES_BY_TYPE key: [type:1][neg_timestamp:8] = 9 bytes (newest first within type)
fn pack_type_key(node_type: u8, timestamp: i64) -> [u8; 9] {
    let mut buf = [0u8; 9];
    buf[0] = node_type;
    buf[1..9].copy_from_slice(&(!timestamp).to_be_bytes());
    buf
}

/// Unpack offset from UUID_OFFSETS key
fn unpack_uuid_offset_key(key: &[u8]) -> ([u8; 16], u64) {
    let mut uuid = [0u8; 16];
    uuid.copy_from_slice(&key[0..16]);
    let offset = u64::from_be_bytes([key[16], key[17], key[18], key[19], key[20], key[21], key[22], key[23]]);
    (uuid, offset)
}

/// Record a node's location in the index (for live nodes).
pub fn index_node(txn: &WriteTransaction, key: &str, offset: u64, uuid: &[u8; 16], node_type: u8, timestamp: i64, provenance: &str, weight: f32) -> Result<()> {
    let mut key_uuid_table = txn.open_table(KEY_TO_UUID)?;
    let mut uuid_offsets = txn.open_table(UUID_OFFSETS)?;
    let mut by_provenance = txn.open_multimap_table(NODES_BY_PROVENANCE)?;
    let mut by_type = txn.open_table(NODES_BY_TYPE)?;

    let packed = pack_node_meta(uuid, node_type, timestamp, false, weight);
    key_uuid_table.insert(key, packed.as_slice())?;
    let uuid_offset_key = pack_uuid_offset(uuid, offset);
    uuid_offsets.insert(uuid_offset_key.as_slice(), ())?;
    let prov_val = pack_provenance_value(timestamp, uuid);
    by_provenance.insert(provenance, prov_val.as_slice())?;
    let type_key = pack_type_key(node_type, timestamp);
    by_type.insert(type_key.as_slice(), uuid.as_slice())?;
    Ok(())
}

/// Record a uuid→offset mapping only (for deleted nodes - preserves version history).
pub fn record_uuid_offset(txn: &WriteTransaction, uuid: &[u8; 16], offset: u64) -> Result<()> {
    let mut uuid_offsets = txn.open_table(UUID_OFFSETS)?;
    let uuid_offset_key = pack_uuid_offset(uuid, offset);
    uuid_offsets.insert(uuid_offset_key.as_slice(), ())?;
    Ok(())
}

/// Get max offset for a UUID from an already-opened table.
/// Uses reverse range scan to find the highest offset (last key in range).
fn max_offset_for_uuid_in_table(
    table: &redb::ReadOnlyTable<&[u8], ()>,
    uuid: &[u8; 16],
) -> Result<Option<u64>> {
    let start = pack_uuid_offset(uuid, 0);
    let end = pack_uuid_offset(uuid, u64::MAX);

    // Get last entry in range (highest offset)
    if let Some(entry) = table.range(start.as_slice()..=end.as_slice())?.next_back() {
        let (key, _) = entry?;
        let (_, offset) = unpack_uuid_offset_key(key.value());
        Ok(Some(offset))
    } else {
        Ok(None)
    }
}

/// Get recent keys for a given provenance, sorted by timestamp descending.
/// Resolves UUID → current key by reading node at latest offset.
/// Single transaction for all index lookups.
pub fn recent_by_provenance(db: &Database, provenance: &str, limit: usize) -> Result<Vec<(String, i64)>> {
    let txn = db.begin_read()?;
    let prov_table = txn.open_multimap_table(NODES_BY_PROVENANCE)?;
    let uuid_offsets = txn.open_table(UUID_OFFSETS)?;

    let mut results = Vec::new();
    for entry in prov_table.get(provenance)? {
        if results.len() >= limit { break; }
        let (timestamp, uuid) = unpack_provenance_value(entry?.value());

        if let Some(offset) = max_offset_for_uuid_in_table(&uuid_offsets, &uuid)? {
            if let Ok(node) = read_node_at_offset(offset) {
                results.push((node.key, timestamp));
            }
        }
    }
    Ok(results)
}

/// Get UUIDs for nodes of a given type, sorted by timestamp descending (newest first).
/// Optionally filter to timestamps >= after_ts.
/// Returns up to `limit` UUIDs.
pub fn nodes_by_type(db: &Database, node_type: u8, limit: usize, after_ts: Option<i64>) -> Result<Vec<[u8; 16]>> {
    let txn = db.begin_read()?;
    let by_type = txn.open_table(NODES_BY_TYPE)?;

    // Range: [type][0x80..] to [type][0xFF..] for positive timestamps (newest first)
    // !i64::MAX = 0x8000... (far future, smallest), !0 = 0xFFFF... (epoch, largest)
    let start = pack_type_key(node_type, i64::MAX); // !MAX = 0x8000... = smallest
    let end = pack_type_key(node_type, 0);          // !0 = 0xFFFF... = largest

    let mut results = Vec::new();
    for entry in by_type.range(start.as_slice()..=end.as_slice())? {
        if results.len() >= limit { break; }
        let (key_bytes, uuid_bytes) = entry?;

        // Decode timestamp from key to check after_ts filter
        let key = key_bytes.value();
        let neg_ts = i64::from_be_bytes([key[1], key[2], key[3], key[4], key[5], key[6], key[7], key[8]]);
        let timestamp = !neg_ts;

        if let Some(after) = after_ts {
            if timestamp < after { continue; }
        }

        let mut uuid = [0u8; 16];
        uuid.copy_from_slice(uuid_bytes.value());
        results.push(uuid);
    }
    Ok(results)
}

/// Get offset for a node by key (via KEY_TO_UUID → UUID_OFFSETS).
/// Single transaction, returns the newest offset.
pub fn get_offset(db: &Database, key: &str) -> Result<Option<u64>> {
    let txn = db.begin_read()?;
    let key_uuid = txn.open_table(KEY_TO_UUID)?;
    let uuid_offsets = txn.open_table(UUID_OFFSETS)?;

    let uuid = match key_uuid.get(key)? {
        Some(data) => {
            let (uuid, _, _, deleted, _) = unpack_node_meta(data.value());
            if deleted { return Ok(None); }
            uuid
        }
        None => return Ok(None),
    };

    max_offset_for_uuid_in_table(&uuid_offsets, &uuid)
}

/// Check if a key exists in the index (and is not deleted).
pub fn contains_key(db: &Database, key: &str) -> Result<bool> {
    let txn = db.begin_read()?;
    let table = txn.open_table(KEY_TO_UUID)?;
    match table.get(key)? {
        Some(data) => {
            let (_, _, _, deleted, _) = unpack_node_meta(data.value());
            Ok(!deleted)
        }
        None => Ok(false),
    }
}

/// Get a node's UUID from its key (returns UUID even for deleted nodes).
pub fn get_uuid_for_key(db: &Database, key: &str) -> Result<Option<[u8; 16]>> {
    let txn = db.begin_read()?;
    let table = txn.open_table(KEY_TO_UUID)?;
    match table.get(key)? {
        Some(data) => {
            let (uuid, _, _, _, _) = unpack_node_meta(data.value());
            Ok(Some(uuid))
        }
        None => Ok(None),
    }
}

/// Get all offsets for a UUID (all versions). Returns newest (highest) first.
pub fn get_offsets_for_uuid(db: &Database, uuid: &[u8; 16]) -> Result<Vec<u64>> {
    let txn = db.begin_read()?;
    let table = txn.open_table(UUID_OFFSETS)?;

    // Range scan: [uuid][0x00..] to [uuid][0xFF..]
    let start = pack_uuid_offset(uuid, 0);
    let end = pack_uuid_offset(uuid, u64::MAX);

    let mut offsets = Vec::new();
    for entry in table.range(start.as_slice()..=end.as_slice())? {
        let (key, _) = entry?;
        let (_, offset) = unpack_uuid_offset_key(key.value());
        offsets.push(offset);
    }
    // Already sorted ascending by key; reverse for newest first
    offsets.reverse();
    Ok(offsets)
}

/// Mark a node as deleted in the index (key stays for history; UUID_OFFSETS preserved).
pub fn remove_node(txn: &WriteTransaction, key: &str) -> Result<()> {
    let mut key_uuid_table = txn.open_table(KEY_TO_UUID)?;
    // Copy out data to avoid borrow conflict
    let meta = key_uuid_table.get(key)?.map(|data| {
        unpack_node_meta(data.value())
    });
    if let Some((uuid, node_type, timestamp, _, weight)) = meta {
        let packed = pack_node_meta(&uuid, node_type, timestamp, true, weight);
        key_uuid_table.insert(key, packed.as_slice())?;
    }
    Ok(())
}

/// Collect all keys from the index (excludes deleted nodes).
pub fn all_keys(db: &Database) -> Result<Vec<String>> {
    let txn = db.begin_read()?;
    let table = txn.open_table(KEY_TO_UUID)?;
    let mut keys = Vec::new();
    for entry in table.iter()? {
        let (key, data) = entry?;
        let (_, _, _, deleted, _) = unpack_node_meta(data.value());
        if !deleted {
            keys.push(key.value().to_string());
        }
    }
    Ok(keys)
}

/// Collect all (key, uuid, node_type, timestamp, deleted, weight) in a single table scan.
pub fn all_key_uuid_pairs(db: &Database) -> Result<Vec<(String, [u8; 16], u8, i64, bool, f32)>> {
    let txn = db.begin_read()?;
    let table = txn.open_table(KEY_TO_UUID)?;
    let mut pairs = Vec::new();
    for entry in table.iter()? {
        let (key, data) = entry?;
        let (uuid, node_type, timestamp, deleted, weight) = unpack_node_meta(data.value());
        pairs.push((key.value().to_string(), uuid, node_type, timestamp, deleted, weight));
    }
    Ok(pairs)
}

// ── Relation index operations ──────────────────────────────────────
//
// RELS value format: [other_uuid:16][strength:4][rel_type:1][is_outgoing:1] = 22 bytes

/// Pack relation data into bytes for RELS table.
fn pack_rel(other_uuid: &[u8; 16], strength: f32, rel_type: u8, is_outgoing: bool) -> [u8; 22] {
    let mut buf = [0u8; 22];
    buf[0..16].copy_from_slice(other_uuid);
    buf[16..20].copy_from_slice(&strength.to_be_bytes());
    buf[20] = rel_type;
    buf[21] = if is_outgoing { 1 } else { 0 };
    buf
}

/// Unpack relation data from RELS table.
pub fn unpack_rel(data: &[u8]) -> ([u8; 16], f32, u8, bool) {
    let mut other_uuid = [0u8; 16];
    other_uuid.copy_from_slice(&data[0..16]);
    let strength = f32::from_be_bytes([data[16], data[17], data[18], data[19]]);
    let rel_type = data[20];
    let is_outgoing = data[21] != 0;
    (other_uuid, strength, rel_type, is_outgoing)
}

/// Index a relation: store twice (once per endpoint).
pub fn index_relation(
    txn: &WriteTransaction,
    source_uuid: &[u8; 16],
    target_uuid: &[u8; 16],
    strength: f32,
    rel_type: u8,
) -> Result<()> {
    let mut rels = txn.open_multimap_table(RELS)?;

    // Store outgoing: source → (target, strength, type, true)
    let outgoing = pack_rel(target_uuid, strength, rel_type, true);
    rels.insert(source_uuid.as_slice(), outgoing.as_slice())?;

    // Store incoming: target → (source, strength, type, false)
    let incoming = pack_rel(source_uuid, strength, rel_type, false);
    rels.insert(target_uuid.as_slice(), incoming.as_slice())?;
    Ok(())
}

/// Remove a relation from the index.
pub fn remove_relation(
    txn: &WriteTransaction,
    source_uuid: &[u8; 16],
    target_uuid: &[u8; 16],
    strength: f32,
    rel_type: u8,
) -> Result<()> {
    let mut rels = txn.open_multimap_table(RELS)?;

    let outgoing = pack_rel(target_uuid, strength, rel_type, true);
    rels.remove(source_uuid.as_slice(), outgoing.as_slice())?;

    let incoming = pack_rel(source_uuid, strength, rel_type, false);
    rels.remove(target_uuid.as_slice(), incoming.as_slice())?;
    Ok(())
}

/// Get all edges for a node. Returns (other_uuid, strength, rel_type, is_outgoing).
pub fn edges_for_node(db: &Database, node_uuid: &[u8; 16]) -> Result<Vec<([u8; 16], f32, u8, bool)>> {
    let txn = db.begin_read()?;
    let rels = txn.open_multimap_table(RELS)?;

    let mut edges = Vec::new();
    for entry in rels.get(node_uuid.as_slice())? {
        let guard = entry?;
        let slice = guard.value();
        let mut data = [0u8; 22];
        data.copy_from_slice(slice);
        edges.push(unpack_rel(&data));
    }
    Ok(edges)
}

// ── Index rebuild ──────────────────────────────────────────────────────

/// Rebuild the index from a sequence of (offset, Node) pairs.
/// Records ALL uuid→offset mappings (for history), but only the latest version per key in KEY_TO_UUID.
pub fn rebuild(db: &Database, nodes: Vec<(u64, Node)>) -> Result<()> {
    // Track latest (offset, node) per key - newest timestamp wins
    let mut latest: HashMap<String, (u64, Node)> = HashMap::new();
    // Track ALL uuid→offset mappings for history
    let mut all_offsets: Vec<([u8; 16], u64)> = Vec::new();

    for (offset, node) in nodes {
        // Record every offset for history
        all_offsets.push((node.uuid, offset));

        let dominated = latest.get(&node.key)
            .map(|(_, existing)| node.timestamp >= existing.timestamp)
            .unwrap_or(true);
        if dominated {
            latest.insert(node.key.clone(), (offset, node));
        }
    }

    // Write to index
    let txn = db.begin_write()?;
    {
        // Record all uuid→offset mappings
        let mut uuid_offsets = txn.open_table(UUID_OFFSETS)?;
        for (uuid, offset) in &all_offsets {
            let key = pack_uuid_offset(uuid, *offset);
            uuid_offsets.insert(key.as_slice(), ())?;
        }
        drop(uuid_offsets);

        // Record KEY_TO_UUID and NODES_BY_PROVENANCE for latest version of each key
        for (key, (_offset, node)) in &latest {
            if !node.deleted {
                index_node_no_offset(&txn, key, &node.uuid, node.node_type as u8, node.timestamp, &node.provenance, node.weight)?;
            } else {
                // For deleted nodes, just mark KEY_TO_UUID as deleted
                let mut key_uuid_table = txn.open_table(KEY_TO_UUID)?;
                let packed = pack_node_meta(&node.uuid, node.node_type as u8, node.timestamp, true, node.weight);
                key_uuid_table.insert(key.as_str(), packed.as_slice())?;
            }
        }
    }
    txn.commit()?;

    Ok(())
}

/// Record a node in KEY_TO_UUID, NODES_BY_PROVENANCE, and NODES_BY_TYPE (but not UUID_OFFSETS - for rebuild use).
fn index_node_no_offset(txn: &WriteTransaction, key: &str, uuid: &[u8; 16], node_type: u8, timestamp: i64, provenance: &str, weight: f32) -> Result<()> {
    let mut key_uuid_table = txn.open_table(KEY_TO_UUID)?;
    let mut by_provenance = txn.open_multimap_table(NODES_BY_PROVENANCE)?;
    let mut by_type = txn.open_table(NODES_BY_TYPE)?;

    let packed = pack_node_meta(uuid, node_type, timestamp, false, weight);
    key_uuid_table.insert(key, packed.as_slice())?;
    let prov_val = pack_provenance_value(timestamp, uuid);
    by_provenance.insert(provenance, prov_val.as_slice())?;
    let type_key = pack_type_key(node_type, timestamp);
    by_type.insert(type_key.as_slice(), uuid.as_slice())?;
    Ok(())
}

/// Fsck report — discrepancies found between capnp logs and redb index.
#[derive(Debug, Default)]
pub struct FsckReport {
    /// Keys in current index but not in rebuilt (zombie entries)
    pub zombies: Vec<String>,
    /// Keys in rebuilt but not in current index (missing from index)
    pub missing: Vec<String>,
    /// Was capnp log repaired?
    pub capnp_repaired: bool,
}

impl FsckReport {
    pub fn is_clean(&self) -> bool {
        self.zombies.is_empty() && self.missing.is_empty() && !self.capnp_repaired
    }
}

/// Full fsck: verify capnp logs, rebuild index to temp, compare with current.
/// Returns a report of discrepancies found.
pub fn fsck_full() -> Result<FsckReport> {
    use std::collections::HashSet;
    use tempfile::TempDir;
    use super::capnp::{fsck, iter_nodes};
    use super::types::{nodes_path, db_path};

    let mut report = FsckReport::default();

    // Step 1: Run capnp log fsck (may truncate corrupt messages)
    let nodes_size_before = nodes_path().metadata().map(|m| m.len()).unwrap_or(0);
    fsck()?;
    let nodes_size_after = nodes_path().metadata().map(|m| m.len()).unwrap_or(0);
    report.capnp_repaired = nodes_size_after != nodes_size_before;

    // Step 2: Rebuild index to temp file
    let temp_dir = TempDir::new().context("create temp dir")?;
    let temp_db_path = temp_dir.path().join("rebuilt.redb");
    let rebuilt_db = open_db(&temp_db_path)?;
    rebuild(&rebuilt_db, iter_nodes()?)?;

    // Step 3: Copy current index to temp and open (avoids write lock contention)
    let current_db_path = db_path();
    if !current_db_path.exists() {
        // No current index — all rebuilt keys are "missing"
        let txn = rebuilt_db.begin_read()?;
        let table = txn.open_table(KEY_TO_UUID)?;
        for entry in table.iter()? {
            let (key, _) = entry?;
            report.missing.push(key.value().to_string());
        }
        return Ok(report);
    }

    // Copy to temp to avoid lock contention with running daemon
    let current_copy_path = temp_dir.path().join("current.redb");
    std::fs::copy(&current_db_path, &current_copy_path)
        .with_context(|| format!("copy {} to temp", current_db_path.display()))?;

    let current_db = Database::open(&current_copy_path)
        .with_context(|| "open current db copy")?;

    // Step 4: Compare KEY_TO_UUID tables
    let rebuilt_keys: HashSet<String> = {
        let txn = rebuilt_db.begin_read()?;
        let table = txn.open_table(KEY_TO_UUID)?;
        table.iter()?.map(|e| e.map(|(k, _)| k.value().to_string())).collect::<Result<_, _>>()?
    };

    let current_keys: HashSet<String> = {
        let txn = current_db.begin_read()?;
        let table = txn.open_table(KEY_TO_UUID)?;
        table.iter()?.map(|e| e.map(|(k, _)| k.value().to_string())).collect::<Result<_, _>>()?
    };

    // Keys in current but not rebuilt = zombies (shouldn't exist)
    for key in current_keys.difference(&rebuilt_keys) {
        report.zombies.push(key.clone());
    }
    report.zombies.sort();

    // Keys in rebuilt but not current = missing (should exist but don't)
    for key in rebuilt_keys.difference(&current_keys) {
        report.missing.push(key.clone());
    }
    report.missing.sort();

    Ok(report)
}

/// Repair the index by rebuilding from capnp logs.
pub fn repair_index() -> Result<()> {
    use super::capnp::iter_nodes;
    use super::types::db_path;
    use std::fs;

    let db_p = db_path();
    if db_p.exists() {
        fs::remove_file(&db_p).context("remove old index")?;
    }
    let db = open_db(&db_p)?;
    rebuild(&db, iter_nodes()?)?;
    eprintln!("index rebuilt from capnp log");
    Ok(())
}

/// Check if redb index is healthy by verifying some offsets are valid.
pub fn is_healthy(db: &Database) -> Result<bool> {
    use super::types::nodes_path;
    use std::fs;

    let txn = db.begin_read()?;
    let key_uuid_table = txn.open_table(KEY_TO_UUID)?;

    // Check that we can read the table and it has entries
    if key_uuid_table.len()? == 0 {
        let capnp_size = fs::metadata(nodes_path()).map(|m| m.len()).unwrap_or(0);
        return Ok(capnp_size == 0); // healthy only if capnp is also empty
    }

    // Spot check: verify a few offsets point to valid messages
    let uuid_offsets = txn.open_table(UUID_OFFSETS)?;
    let mut checked = 0;
    for entry in key_uuid_table.iter()? {
        if checked >= 5 { break; }
        let (_key, data) = entry?;
        let (uuid, _, _, _, _) = unpack_node_meta(data.value());

        if let Some(offset) = max_offset_for_uuid_in_table(&uuid_offsets, &uuid)? {
            if read_node_at_offset(offset).is_err() {
                return Ok(false);
            }
        }
        checked += 1;
    }

    Ok(true)
}

/// Open redb database, rebuilding if unhealthy.
pub fn open_or_rebuild(path: &Path) -> Result<Database> {
    use super::capnp::iter_nodes;
    use std::fs;

    // Try opening existing database
    if path.exists() {
        match open_db(path) {
            Ok(database) => {
                if is_healthy(&database)? {
                    return Ok(database);
                }
                eprintln!("redb index stale, rebuilding...");
            }
            Err(e) => {
                eprintln!("redb open failed ({}), rebuilding...", e);
            }
        }
    }

    // Rebuild index from capnp log
    if path.exists() {
        fs::remove_file(path).with_context(|| format!("remove old db {}", path.display()))?;
    }
    let database = open_db(path)?;
    rebuild(&database, iter_nodes()?)?;
    Ok(database)
}