// Cap'n Proto serialization and persistence
//
// capnp logs are the source of truth; redb provides indexed access.
// This module contains:
//   - Serialization macros (capnp_enum!, capnp_message!)
//   - Load/replay from capnp logs
//   - Append to capnp logs
//   - fsck (corruption repair)

use super::{index, types::*};
use redb::ReadableTableMetadata;

use crate::memory_capnp;
use super::Store;

use anyhow::{anyhow, Context, Result};
use capnp::message;
use capnp::serialize;

use std::collections::HashMap;
use std::fs;
use std::io::{BufReader, Seek};
use std::path::Path;

// ---------------------------------------------------------------------------
// Capnp serialization macros
//
// Declarative mapping between Rust types and capnp generated types.
// Adding a field to the schema means adding it in one place below;
// both read and write are generated from the same declaration.
// ---------------------------------------------------------------------------

/// Generate to_capnp/from_capnp conversion methods for an enum.
macro_rules! capnp_enum {
    ($rust_type:ident, $capnp_type:path, [$($variant:ident),+ $(,)?]) => {
        impl $rust_type {
            #[allow(clippy::wrong_self_convention, dead_code)]
            pub(crate) fn to_capnp(&self) -> $capnp_type {
                match self {
                    $(Self::$variant => <$capnp_type>::$variant,)+
                }
            }
            pub(crate) fn from_capnp(v: $capnp_type) -> Self {
                match v {
                    $(<$capnp_type>::$variant => Self::$variant,)+
                }
            }
        }
    };
}

/// Generate from_capnp/to_capnp methods for a struct with capnp serialization.
/// Fields are grouped by serialization kind:
///   text  - capnp Text fields (String in Rust)
///   uuid  - capnp Data fields ([u8; 16] in Rust)
///   prim  - copy types (u32, f32, f64, bool)
///   enm   - enums with to_capnp/from_capnp methods
///   skip  - Rust-only fields not in capnp (set to Default on read)
macro_rules! capnp_message {
    (
        $struct:ident,
        reader: $reader:ty,
        builder: $builder:ty,
        text: [$($tf:ident),* $(,)?],
        uuid: [$($uf:ident),* $(,)?],
        prim: [$($pf:ident),* $(,)?],
        enm: [$($ef:ident: $et:ident),* $(,)?],
        skip: [$($sf:ident),* $(,)?] $(,)?
    ) => {
        impl $struct {
            pub fn from_capnp(r: $reader) -> Result<Self> {
                paste::paste! {
                    Ok(Self {
                        $($tf: read_text(r.[<get_ $tf>]()),)*
                        $($uf: read_uuid(r.[<get_ $uf>]()),)*
                        $($pf: r.[<get_ $pf>](),)*
                        $($ef: $et::from_capnp(
                            r.[<get_ $ef>]().map_err(|_| anyhow!(concat!("bad ", stringify!($ef))))?
                        ),)*
                        $($sf: Default::default(),)*
                    })
                }
            }

            pub fn to_capnp(&self, mut b: $builder) {
                paste::paste! {
                    $(b.[<set_ $tf>](&self.$tf);)*
                    $(b.[<set_ $uf>](&self.$uf);)*
                    $(b.[<set_ $pf>](self.$pf);)*
                    $(b.[<set_ $ef>](self.$ef.to_capnp());)*
                }
            }
        }
    };
}

// ---------------------------------------------------------------------------
// Capnp helpers
// ---------------------------------------------------------------------------

/// Read a capnp text field, returning empty string on any error
fn read_text(result: capnp::Result<capnp::text::Reader>) -> String {
    result.ok()
        .and_then(|t| t.to_str().ok())
        .unwrap_or("")
        .to_string()
}

/// Read a capnp data field as [u8; 16], zero-padded
fn read_uuid(result: capnp::Result<&[u8]>) -> [u8; 16] {
    let mut out = [0u8; 16];
    if let Ok(data) = result
        && data.len() >= 16 {
            out.copy_from_slice(&data[..16]);
        }
    out
}

// ---------------------------------------------------------------------------
// Type-to-capnp mappings
// ---------------------------------------------------------------------------

capnp_enum!(NodeType, memory_capnp::NodeType,
    [EpisodicSession, EpisodicDaily, EpisodicWeekly, Semantic, EpisodicMonthly]);

capnp_enum!(RelationType, memory_capnp::RelationType,
    [Link, Causal, Auto]);

capnp_message!(Node,
    reader: memory_capnp::content_node::Reader<'_>,
    builder: memory_capnp::content_node::Builder<'_>,
    text: [key, content, source_ref, provenance],
    uuid: [uuid],
    prim: [version, timestamp, weight, emotion, deleted,
           retrievals, uses, wrongs, last_replayed,
           spaced_repetition_interval, created_at, last_scored],
    enm:  [node_type: NodeType],
    skip: [community_id, clustering_coefficient, degree],
);

capnp_message!(Relation,
    reader: memory_capnp::relation::Reader<'_>,
    builder: memory_capnp::relation::Builder<'_>,
    text: [source_key, target_key, provenance],
    uuid: [uuid, source, target],
    prim: [version, timestamp, strength, deleted],
    enm:  [rel_type: RelationType],
    skip: [],
);

// ---------------------------------------------------------------------------
// Migration helpers (legacy provenance enum → string)
// ---------------------------------------------------------------------------

/// Convert legacy capnp provenance enum to string label.
fn legacy_provenance_label(p: memory_capnp::Provenance) -> &'static str {
    use memory_capnp::Provenance::*;
    match p {
        Manual => "manual",
        Journal => "journal",
        Agent => "agent",
        Dream => "dream",
        Derived => "derived",
        AgentExperienceMine => "agent:experience-mine",
        AgentKnowledgeObservation => "agent:knowledge-observation",
        AgentKnowledgePattern => "agent:knowledge-pattern",
        AgentKnowledgeConnector => "agent:knowledge-connector",
        AgentKnowledgeChallenger => "agent:knowledge-challenger",
        AgentConsolidate => "agent:consolidate",
        AgentDigest => "agent:digest",
        AgentFactMine => "agent:fact-mine",
        AgentDecay => "agent:decay",
    }
}

impl Node {
    /// Read from capnp with migration: if the new provenance text field
    /// is empty (old record), fall back to the deprecated provenanceOld enum.
    pub fn from_capnp_migrate(r: memory_capnp::content_node::Reader<'_>) -> Result<Self> {
        let mut node = Self::from_capnp(r)?;
        if node.provenance.is_empty()
            && let Ok(old) = r.get_provenance_old() {
                node.provenance = legacy_provenance_label(old).to_string();
            }
        // Sanitize timestamps: old capnp records have raw offsets instead
        // of unix epoch. Anything past year 2100 (~4102444800) is bogus.
        const MAX_SANE_EPOCH: i64 = 4_102_444_800;
        if node.timestamp > MAX_SANE_EPOCH || node.timestamp < 0 {
            node.timestamp = node.created_at;
        }
        if node.created_at > MAX_SANE_EPOCH || node.created_at < 0 {
            node.created_at = node.timestamp.min(MAX_SANE_EPOCH);
        }
        Ok(node)
    }
}

impl Relation {
    pub fn from_capnp_migrate(r: memory_capnp::relation::Reader<'_>) -> Result<Self> {
        let mut rel = Self::from_capnp(r)?;
        if rel.provenance.is_empty()
            && let Ok(old) = r.get_provenance_old() {
                rel.provenance = legacy_provenance_label(old).to_string();
            }
        Ok(rel)
    }
}

// ---------------------------------------------------------------------------
// Direct node access
// ---------------------------------------------------------------------------

/// Read a single node at the given offset in the capnp log.
/// The offset must point to a valid message containing the node.
pub fn read_node_at_offset(offset: u64) -> Result<Node> {
    let path = nodes_path();
    let mut file = fs::File::open(&path)
        .with_context(|| format!("open {}", path.display()))?;

    use std::io::{Seek, SeekFrom};
    file.seek(SeekFrom::Start(offset))?;

    let mut reader = BufReader::new(file);
    let msg = serialize::read_message(&mut reader, message::ReaderOptions::new())
        .with_context(|| format!("read message at offset {}", offset))?;

    let log = msg.get_root::<memory_capnp::node_log::Reader>()
        .with_context(|| "read node log")?;
    let nodes = log.get_nodes()
        .with_context(|| "get nodes")?;

    // A message at this offset should have exactly one node (from upsert),
    // or we take the last one if there are multiple (from batch operations like rename)
    if nodes.is_empty() {
        anyhow::bail!("no nodes in message at offset {}", offset);
    }

    // Return the first non-deleted node, or the first one if all are deleted
    for node_reader in nodes.iter() {
        let node = Node::from_capnp_migrate(node_reader)?;
        if !node.deleted {
            return Ok(node);
        }
    }

    // All nodes in this message are deleted - shouldn't happen if index is correct
    Node::from_capnp_migrate(nodes.get(0))
}

// ---------------------------------------------------------------------------
// Store persistence methods
// ---------------------------------------------------------------------------

impl Store {
    /// Load store by opening redb index and replaying relations.
    pub fn load() -> Result<Store> {
        let nodes_p = nodes_path();
        let rels_p = relations_path();

        let mut store = Store::default();

        // Open redb index first (rebuilds from capnp if needed)
        let db_p = db_path();
        store.db = Some(store.open_or_rebuild_db(&db_p)?);

        // Replay relations
        if rels_p.exists() {
            store.replay_relations(&rels_p)?;
        }

        // Record log sizes
        store.loaded_nodes_size = fs::metadata(&nodes_p).map(|m| m.len()).unwrap_or(0);
        store.loaded_rels_size = fs::metadata(&rels_p).map(|m| m.len()).unwrap_or(0);

        // Drop edges referencing deleted/missing nodes
        let db = store.db.as_ref().unwrap();
        store.relations.retain(|r|
            index::contains_key(db, &r.source_key).unwrap_or(false) &&
            index::contains_key(db, &r.target_key).unwrap_or(false)
        );

        Ok(store)
    }

    /// Open redb database, rebuilding if unhealthy.
    fn open_or_rebuild_db(&self, path: &Path) -> Result<redb::Database> {
        // Try opening existing database
        if path.exists() {
            match index::open_db(path) {
                Ok(database) => {
                    if self.db_is_healthy(&database)? {
                        return Ok(database);
                    }
                    eprintln!("redb index stale, rebuilding...");
                }
                Err(e) => {
                    eprintln!("redb open failed ({}), rebuilding...", e);
                }
            }
        }

        // Rebuild index from capnp log
        rebuild_index(path, &nodes_path())
    }

    /// Check if redb index is healthy by verifying some offsets are valid.
    fn db_is_healthy(&self, database: &redb::Database) -> Result<bool> {
        use redb::{ReadableDatabase, ReadableTable};

        let txn = database.begin_read()?;
        let nodes_table = txn.open_table(index::NODES)?;

        // Check that we can read the table and it has entries
        if nodes_table.len()? == 0 {
            // Empty database - might be stale or new
            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 mut checked = 0;
        for entry in nodes_table.iter()? {
            if checked >= 5 { break; }
            let (key, offset) = entry?;
            let offset = offset.value();

            // Try to read the node at this offset
            if read_node_at_offset(offset).is_err() {
                return Ok(false);
            }
            checked += 1;
            let _ = key; // silence unused warning
        }

        Ok(true)
    }

    /// Replay relation log, keeping latest version per UUID
    fn replay_relations(&mut self, path: &Path) -> Result<()> {
        let file = fs::File::open(path)
            .with_context(|| format!("open {}", path.display()))?;
        let mut reader = BufReader::new(file);

        // Collect all, then deduplicate by UUID keeping latest version
        let mut by_uuid: HashMap<[u8; 16], Relation> = HashMap::new();

        while let Ok(msg) = serialize::read_message(&mut reader, message::ReaderOptions::new()) {
            let log = msg.get_root::<memory_capnp::relation_log::Reader>()
                .with_context(|| format!("read relation log"))?;
            for rel_reader in log.get_relations()
                .with_context(|| format!("get relations"))? {
                let rel = Relation::from_capnp_migrate(rel_reader)?;
                let existing_version = by_uuid.get(&rel.uuid)
                    .map(|r| r.version)
                    .unwrap_or(0);
                if rel.version >= existing_version {
                    by_uuid.insert(rel.uuid, rel);
                }
            }
        }

        self.relations = by_uuid.into_values()
            .filter(|r| !r.deleted)
            .collect();
        Ok(())
    }

    /// Find all duplicate keys: keys with multiple live UUIDs in the log.
    /// Returns a map from key → vec of all live Node versions (one per UUID).
    /// The "winner" in self.nodes is always one of them.
    pub fn find_duplicates(&self) -> Result<HashMap<String, Vec<Node>>> {
        let path = nodes_path();
        if !path.exists() { return Ok(HashMap::new()); }

        let file = fs::File::open(&path)
            .with_context(|| format!("open {}", path.display()))?;
        let mut reader = BufReader::new(file);

        // Track latest version of each UUID
        let mut by_uuid: HashMap<[u8; 16], Node> = HashMap::new();

        while let Ok(msg) = serialize::read_message(&mut reader, message::ReaderOptions::new()) {
            let log = msg.get_root::<memory_capnp::node_log::Reader>()
                .with_context(|| format!("read node log"))?;
            for node_reader in log.get_nodes()
                .with_context(|| format!("get nodes"))? {
                let node = Node::from_capnp_migrate(node_reader)?;
                let dominated = by_uuid.get(&node.uuid)
                    .map(|n| node.version >= n.version)
                    .unwrap_or(true);
                if dominated {
                    by_uuid.insert(node.uuid, node);
                }
            }
        }

        // Group live (non-deleted) nodes by key
        let mut by_key: HashMap<String, Vec<Node>> = HashMap::new();
        for node in by_uuid.into_values() {
            if !node.deleted {
                by_key.entry(node.key.clone()).or_default().push(node);
            }
        }

        // Keep only duplicates
        by_key.retain(|_, nodes| nodes.len() > 1);
        Ok(by_key)
    }

    /// Append nodes to the log file. Returns the offset where the message was written.
    pub fn append_nodes(&mut self, nodes: &[Node]) -> Result<u64> {
        let mut msg = message::Builder::new_default();
        {
            let log = msg.init_root::<memory_capnp::node_log::Builder>();
            let mut list = log.init_nodes(nodes.len() as u32);
            for (i, node) in nodes.iter().enumerate() {
                node.to_capnp(list.reborrow().get(i as u32));
            }
        }
        let mut buf = Vec::new();
        serialize::write_message(&mut buf, &msg)
            .with_context(|| format!("serialize nodes"))?;

        let path = nodes_path();
        let file = fs::OpenOptions::new()
            .create(true).append(true).open(&path)
            .with_context(|| format!("open {}", path.display()))?;

        // Get offset before writing
        let offset = file.metadata().map(|m| m.len()).unwrap_or(0);

        use std::io::Write;
        (&file).write_all(&buf)
            .with_context(|| format!("write nodes"))?;

        self.loaded_nodes_size = file.metadata().map(|m| m.len()).unwrap_or(0);
        Ok(offset)
    }

    /// Append relations to the log file.
    pub fn append_relations(&mut self, relations: &[Relation]) -> Result<()> {
        let mut msg = message::Builder::new_default();
        {
            let log = msg.init_root::<memory_capnp::relation_log::Builder>();
            let mut list = log.init_relations(relations.len() as u32);
            for (i, rel) in relations.iter().enumerate() {
                rel.to_capnp(list.reborrow().get(i as u32));
            }
        }
        let mut buf = Vec::new();
        serialize::write_message(&mut buf, &msg)
            .with_context(|| format!("serialize relations"))?;

        let path = relations_path();
        let file = fs::OpenOptions::new()
            .create(true).append(true).open(&path)
            .with_context(|| format!("open {}", path.display()))?;
        use std::io::Write;
        (&file).write_all(&buf)
            .with_context(|| format!("write relations"))?;

        self.loaded_rels_size = file.metadata().map(|m| m.len()).unwrap_or(0);
        Ok(())
    }

    /// Placeholder - indices will be updated on write with redb.
    pub fn save(&self) -> Result<()> {
        Ok(())
    }
}

/// Check and repair corrupt capnp log files.
///
/// Reads each message sequentially, tracking file position. On the first
/// corrupt message, truncates the file to the last good position. Also
/// removes stale caches so the next load replays from the repaired log.
pub fn fsck() -> Result<()> {
    let mut any_corrupt = false;

    for (path, kind) in [
        (nodes_path(), "node"),
        (relations_path(), "relation"),
    ] {
        if !path.exists() { continue; }

        let file = fs::File::open(&path)
            .with_context(|| format!("open {}", path.display()))?;
        let file_len = file.metadata()
            .with_context(|| format!("stat {}", path.display()))?.len();
        let mut reader = BufReader::new(file);

        let mut good_messages = 0u64;
        let mut last_good_pos = 0u64;

        loop {
            let pos = reader.stream_position()
                .with_context(|| format!("tell {}", path.display()))?;

            let msg = match serialize::read_message(&mut reader, message::ReaderOptions::new()) {
                Ok(m) => m,
                Err(_) => {
                    // read_message fails at EOF (normal) or on corrupt framing
                    if pos < file_len {
                        // Not at EOF — corrupt framing
                        eprintln!("{}: corrupt message at offset {}, truncating", kind, pos);
                        any_corrupt = true;
                        drop(reader);
                        let file = fs::OpenOptions::new().write(true).open(&path)
                            .with_context(|| format!("open for truncate"))?;
                        file.set_len(pos)
                            .with_context(|| format!("truncate {}", path.display()))?;
                        eprintln!("{}: truncated from {} to {} bytes ({} good messages)",
                            kind, file_len, pos, good_messages);
                    }
                    break;
                }
            };

            // Validate the message content too
            let valid = if kind == "node" {
                msg.get_root::<memory_capnp::node_log::Reader>()
                    .and_then(|l| l.get_nodes().map(|_| ()))
                    .is_ok()
            } else {
                msg.get_root::<memory_capnp::relation_log::Reader>()
                    .and_then(|l| l.get_relations().map(|_| ()))
                    .is_ok()
            };

            if valid {
                good_messages += 1;
                last_good_pos = reader.stream_position()
                    .with_context(|| format!("tell {}", path.display()))?;
            } else {
                eprintln!("{}: corrupt message content at offset {}, truncating to {}",
                    kind, pos, last_good_pos);
                any_corrupt = true;
                drop(reader);
                let file = fs::OpenOptions::new().write(true).open(&path)
                    .with_context(|| format!("open for truncate"))?;
                file.set_len(last_good_pos)
                    .with_context(|| format!("truncate {}", path.display()))?;
                eprintln!("{}: truncated from {} to {} bytes ({} good messages)",
                    kind, file_len, last_good_pos, good_messages);
                break;
            }
        }

        if !any_corrupt {
            eprintln!("{}: {} messages, all clean", kind, good_messages);
        }
    }

    if any_corrupt {
        eprintln!("repair complete — run `poc-memory status` to verify");
    } else {
        eprintln!("store is clean");
    }

    Ok(())
}

/// Rebuild redb index from capnp log.
/// Scans the log, tracking offsets, and records latest version of each node.
fn rebuild_index(db_path: &Path, capnp_path: &Path) -> Result<redb::Database> {
    // Remove old database if it exists
    if db_path.exists() {
        fs::remove_file(db_path)
            .with_context(|| format!("remove old db {}", db_path.display()))?;
    }

    let database = index::open_db(db_path)?;

    if !capnp_path.exists() {
        return Ok(database);
    }

    // Track latest (offset, uuid, version, deleted) per key
    let mut latest: HashMap<String, (u64, [u8; 16], u32, bool)> = HashMap::new();

    let file = fs::File::open(capnp_path)
        .with_context(|| format!("open {}", capnp_path.display()))?;
    let mut reader = BufReader::new(file);

    loop {
        let offset = reader.stream_position()?;
        let msg = match serialize::read_message(&mut reader, message::ReaderOptions::new()) {
            Ok(m) => m,
            Err(_) => break,
        };

        let log = match msg.get_root::<memory_capnp::node_log::Reader>() {
            Ok(l) => l,
            Err(_) => continue,
        };

        let nodes = match log.get_nodes() {
            Ok(n) => n,
            Err(_) => continue,
        };
        for node_reader in nodes {
            let key = node_reader.get_key().ok()
                .and_then(|t| t.to_str().ok())
                .unwrap_or("")
                .to_string();
            if key.is_empty() { continue; }

            let version = node_reader.get_version();
            let deleted = node_reader.get_deleted();

            let mut uuid = [0u8; 16];
            if let Ok(data) = node_reader.get_uuid() {
                if data.len() >= 16 {
                    uuid.copy_from_slice(&data[..16]);
                }
            }

            // Keep if newer version
            let dominated = latest.get(&key)
                .map(|(_, _, v, _)| version >= *v)
                .unwrap_or(true);
            if dominated {
                latest.insert(key, (offset, uuid, version, deleted));
            }
        }
    }

    // Write index entries for non-deleted nodes
    {
        let txn = database.begin_write()?;
        {
            let mut nodes_table = txn.open_table(index::NODES)?;
            let mut uuid_table = txn.open_table(index::UUID_TO_KEY)?;

            for (key, (offset, uuid, _, deleted)) in latest {
                if !deleted {
                    nodes_table.insert(key.as_str(), offset)?;
                    uuid_table.insert(uuid.as_slice(), key.as_str())?;
                }
            }
        }
        txn.commit()?;
    }

    Ok(database)
}