//! Object store (spec §13.1, §13.3, §13.4): loose objects, one file per

//! object under `objects/loose/<hh>/<rest>`, and packs, `pack-<id>.pack`

//! with a sorted `pack-<id>.idx`, holding zstd-compressed objects. Reads

//! check loose objects first, then every pack; every read re-hashes.

//!

//! Pack file: `OXYPACK1` then entries of

//! `type u8 | flags u8 (bit 0: zstd) | stored_len u32 | raw_len u32 | ref 32 | body`.

//! Index file: `OXYIDX01` then `count u32` then sorted entries of

//! `ref 32 | offset u64 | stored_len u32 | raw_len u32 | type u8 | flags u8`.

use crate::attest::Attest;

use crate::hash::{hash_object, header, ObjectRef, ObjectType};

use crate::identity::{Identity, Signature};

use crate::objects::{Change, ObjectError, StateObject};

use rand::RngCore;

use std::cell::RefCell;

use std::fs;

use std::io::{self, Read, Seek, SeekFrom, Write};

use std::path::{Path, PathBuf};

const PACK_MAGIC: &[u8; 8] = b"OXYPACK1";

const IDX_MAGIC: &[u8; 8] = b"OXYIDX01";

const IDX_ENTRY: usize = 32 + 8 + 4 + 4 + 1 + 1;

const FLAG_ZSTD: u8 = 1;

const ZSTD_LEVEL: i32 = 3;

#[derive(Clone, Copy, Debug)]

struct PackEntry {

    offset: u64,

    stored_len: u32,

    raw_len: u32,

    ty: ObjectType,

    flags: u8,

}

/// One pack's index, fully in memory and sorted by ObjectRef.

#[derive(Debug)]

struct PackIndex {

    path: PathBuf,

    refs: Vec<ObjectRef>,

    entries: Vec<PackEntry>,

}

impl PackIndex {

    fn load(idx_path: &Path, pack_path: &Path) -> Result<PackIndex> {

        let data = fs::read(idx_path)?;

        let bad = |m: &str| StoreError::Corrupt(ObjectRef::ZERO, format!("{}: {m}", idx_path.display()));

        if data.len() < 12 || &data[..8] != IDX_MAGIC {

            return Err(bad("bad index header"));

        }

        let count = u32::from_le_bytes(data[8..12].try_into().unwrap()) as usize;

        if data.len() != 12 + count * IDX_ENTRY {

            return Err(bad("index length mismatch"));

        }

        let mut refs = Vec::with_capacity(count);

        let mut entries = Vec::with_capacity(count);

        for i in 0..count {

            let e = &data[12 + i * IDX_ENTRY..12 + (i + 1) * IDX_ENTRY];

            let r = ObjectRef::from_slice(&e[..32]).unwrap();

            if let Some(prev) = refs.last() {

                if r <= *prev {

                    return Err(bad("index not sorted"));

                }

            }

            refs.push(r);

            entries.push(PackEntry {

                offset: u64::from_le_bytes(e[32..40].try_into().unwrap()),

                stored_len: u32::from_le_bytes(e[40..44].try_into().unwrap()),

                raw_len: u32::from_le_bytes(e[44..48].try_into().unwrap()),

                ty: ObjectType::ALL.get(e[48] as usize).copied().ok_or_else(|| bad("unknown object type"))?,

                flags: e[49],

            });

        }

        Ok(PackIndex { path: pack_path.to_path_buf(), refs, entries })

    }

    fn find(&self, r: &ObjectRef) -> Option<PackEntry> {

        self.refs.binary_search(r).ok().map(|i| self.entries[i])

    }

    fn read(&self, r: &ObjectRef, e: PackEntry) -> Result<(ObjectType, Vec<u8>)> {

        let mut f = fs::File::open(&self.path)?;

        f.seek(SeekFrom::Start(e.offset))?;

        let mut stored = vec![0u8; e.stored_len as usize];

        f.read_exact(&mut stored)?;

        let body = if e.flags & FLAG_ZSTD != 0 {

            zstd::bulk::decompress(&stored, e.raw_len as usize).map_err(|err| StoreError::Corrupt(*r, format!("zstd: {err}")))?

        } else {

            stored

        };

        if body.len() != e.raw_len as usize || hash_object(e.ty, &body) != *r {

            return Err(StoreError::Corrupt(*r, "packed object does not match its reference".into()));

        }

        Ok((e.ty, body))

    }

}

fn type_index(ty: ObjectType) -> u8 {

    ObjectType::ALL.iter().position(|t| *t == ty).unwrap() as u8

}

/// What `pack_loose` did.

#[derive(Debug, Clone, Default, PartialEq, Eq)]

pub struct PackReport {

    pub objects: usize,

    pub raw_bytes: u64,

    pub packed_bytes: u64,

}

#[derive(Debug, thiserror::Error)]

pub enum StoreError {

    #[error("io: {0}")]

    Io(#[from] io::Error),

    #[error("corrupt object {0}: {1}")]

    Corrupt(ObjectRef, String),

    #[error("object {0}")]

    Object(#[from] ObjectError),

    #[error("object {0} is a {1}, expected {2}")]

    WrongType(ObjectRef, &'static str, &'static str),

    #[error("object {0} not found")]

    NotFound(ObjectRef),

}

pub type Result<T> = std::result::Result<T, StoreError>;

#[derive(Debug)]

pub struct Store {

    dir: PathBuf,

    packs: RefCell<Vec<PackIndex>>,

}

impl Store {

    pub fn open(dir: impl Into<PathBuf>) -> io::Result<Store> {

        let dir = dir.into();

        fs::create_dir_all(dir.join("loose"))?;

        let store = Store { dir, packs: RefCell::new(Vec::new()) };

        store.reload_packs().map_err(|e| io::Error::other(e.to_string()))?;

        Ok(store)

    }

    fn reload_packs(&self) -> Result<()> {

        let mut packs = Vec::new();

        let mut names: Vec<PathBuf> = fs::read_dir(&self.dir)?

            .filter_map(|e| e.ok().map(|e| e.path()))

            .filter(|p| p.extension().is_some_and(|x| x == "idx") && p.file_name().is_some_and(|n| n.to_string_lossy().starts_with("pack-")))

            .collect();

        names.sort();

        for idx in names {

            let pack = idx.with_extension("pack");

            if pack.is_file() {

                packs.push(PackIndex::load(&idx, &pack)?);

            }

        }

        *self.packs.borrow_mut() = packs;

        Ok(())

    }

    pub fn pack_count(&self) -> usize {

        self.packs.borrow().len()

    }

    fn find_packed(&self, r: &ObjectRef) -> Option<(usize, PackEntry)> {

        self.packs.borrow().iter().enumerate().find_map(|(i, p)| p.find(r).map(|e| (i, e)))

    }

    /// Loose objects on disk, with their paths.

    fn loose_objects(&self) -> io::Result<Vec<(ObjectRef, PathBuf)>> {

        let mut out = Vec::new();

        let loose = self.dir.join("loose");

        for d in fs::read_dir(&loose)? {

            let d = d?;

            if !d.file_type()?.is_dir() {

                continue;

            }

            let prefix = d.file_name().to_string_lossy().to_string();

            for f in fs::read_dir(d.path())? {

                let f = f?;

                let name = f.file_name().to_string_lossy().to_string();

                if let Some(r) = ObjectRef::from_hex(&format!("{prefix}{name}")) {

                    out.push((r, f.path()));

                }

            }

        }

        out.sort();

        Ok(out)

    }

    pub fn loose_count(&self) -> io::Result<usize> {

        Ok(self.loose_objects()?.len())

    }

    /// Move every loose object into a new pack (spec §13.4). Loose files are

    /// deleted only after the pack and its index are durable.

    pub fn pack_loose(&self) -> Result<PackReport> {

        let loose = self.loose_objects()?;

        if loose.is_empty() {

            return Ok(PackReport::default());

        }

        let mut nonce = [0u8; 8];

        rand::rngs::OsRng.fill_bytes(&mut nonce);

        let id = hex::encode(nonce);

        let pack_path = self.dir.join(format!("pack-{id}.pack"));

        let idx_path = self.dir.join(format!("pack-{id}.idx"));

        let tmp_pack = self.dir.join(format!("tmp-{id}.pack"));

        let tmp_idx = self.dir.join(format!("tmp-{id}.idx"));

        let mut report = PackReport::default();

        let mut index: Vec<(ObjectRef, PackEntry)> = Vec::with_capacity(loose.len());

        {

            let mut f = io::BufWriter::new(fs::File::create(&tmp_pack)?);

            f.write_all(PACK_MAGIC)?;

            let mut offset = PACK_MAGIC.len() as u64;

            for (r, _) in &loose {

                let (ty, body) = self.get(r)?;

                let compressed = zstd::bulk::compress(&body, ZSTD_LEVEL).map_err(|e| StoreError::Corrupt(*r, format!("zstd: {e}")))?;

                let (flags, stored) = if compressed.len() < body.len() { (FLAG_ZSTD, compressed) } else { (0, body.clone()) };

                let header_len = 1 + 1 + 4 + 4 + 32;

                f.write_all(&[type_index(ty), flags])?;

                f.write_all(&(stored.len() as u32).to_le_bytes())?;

                f.write_all(&(body.len() as u32).to_le_bytes())?;

                f.write_all(&r.0)?;

                f.write_all(&stored)?;

                index.push((*r, PackEntry { offset: offset + header_len, stored_len: stored.len() as u32, raw_len: body.len() as u32, ty, flags }));

                offset += header_len + stored.len() as u64;

                report.objects += 1;

                report.raw_bytes += body.len() as u64;

                report.packed_bytes += stored.len() as u64;

            }

            f.flush()?;

            f.get_ref().sync_all()?;

        }

        {

            let mut f = io::BufWriter::new(fs::File::create(&tmp_idx)?);

            f.write_all(IDX_MAGIC)?;

            f.write_all(&(index.len() as u32).to_le_bytes())?;

            for (r, e) in &index {

                f.write_all(&r.0)?;

                f.write_all(&e.offset.to_le_bytes())?;

                f.write_all(&e.stored_len.to_le_bytes())?;

                f.write_all(&e.raw_len.to_le_bytes())?;

                f.write_all(&[type_index(e.ty), e.flags])?;

            }

            f.flush()?;

            f.get_ref().sync_all()?;

        }

        fs::rename(&tmp_pack, &pack_path)?;

        fs::rename(&tmp_idx, &idx_path)?;

        self.reload_packs()?;

        for (_, path) in &loose {

            fs::remove_file(path)?;

            if let Some(dir) = path.parent() {

                let _ = fs::remove_dir(dir);

            }

        }

        Ok(report)

    }

    pub fn dir(&self) -> &Path {

        &self.dir

    }

    fn path_for(&self, r: &ObjectRef) -> PathBuf {

        let h = r.to_hex();

        self.dir.join("loose").join(&h[..2]).join(&h[2..])

    }

    pub fn has(&self, r: &ObjectRef) -> bool {

        self.path_for(r).is_file() || self.find_packed(r).is_some()

    }

    /// Store `body` as an object of type `ty`; idempotent.

    pub fn put(&self, ty: ObjectType, body: &[u8]) -> Result<ObjectRef> {

        let r = hash_object(ty, body);

        let path = self.path_for(&r);

        if path.is_file() || self.find_packed(&r).is_some() {

            return Ok(r);

        }

        fs::create_dir_all(path.parent().unwrap())?;

        let mut nonce = [0u8; 8];

        rand::rngs::OsRng.fill_bytes(&mut nonce);

        let tmp = self.dir.join("loose").join(format!("tmp-{}", hex::encode(nonce)));

        {

            let mut f = fs::File::create(&tmp)?;

            f.write_all(&header(ty, body.len()))?;

            f.write_all(body)?;

            f.sync_all()?;

        }

        fs::rename(&tmp, &path)?;

        Ok(r)

    }

    /// Read and verify an object, loose or packed.

    pub fn get(&self, r: &ObjectRef) -> Result<(ObjectType, Vec<u8>)> {

        let path = self.path_for(r);

        let data = match fs::read(&path) {

            Ok(d) => d,

            Err(e) if e.kind() == io::ErrorKind::NotFound => {

                return match self.find_packed(r) {

                    Some((i, e)) => self.packs.borrow()[i].read(r, e),

                    None => Err(StoreError::NotFound(*r)),

                };

            }

            Err(e) => return Err(e.into()),

        };

        let nul = data.iter().position(|&b| b == 0).ok_or_else(|| StoreError::Corrupt(*r, "no header".into()))?;

        let head = std::str::from_utf8(&data[..nul]).map_err(|_| StoreError::Corrupt(*r, "header not UTF-8".into()))?;

        let mut parts = head.split(' ');

        let (Some("oxy1"), Some(ty), Some(len), None) = (parts.next(), parts.next(), parts.next(), parts.next()) else {

            return Err(StoreError::Corrupt(*r, format!("bad header {head:?}")));

        };

        let ty = ObjectType::from_name(ty).ok_or_else(|| StoreError::Corrupt(*r, format!("unknown type {ty}")))?;

        let len: usize = len.parse().map_err(|_| StoreError::Corrupt(*r, "bad length".into()))?;

        let body = &data[nul + 1..];

        if body.len() != len {

            return Err(StoreError::Corrupt(*r, format!("length {} != header {len}", body.len())));

        }

        if hash_object(ty, body) != *r {

            return Err(StoreError::Corrupt(*r, "hash mismatch".into()));

        }

        Ok((ty, body.to_vec()))

    }

    pub fn get_typed(&self, r: &ObjectRef, want: ObjectType) -> Result<Vec<u8>> {

        let (ty, body) = self.get(r)?;

        if ty != want {

            return Err(StoreError::WrongType(*r, ty.name(), want.name()));

        }

        Ok(body)

    }

    pub fn put_change(&self, c: &Change) -> Result<ObjectRef> {

        self.put(ObjectType::Change, &c.encode())

    }

    pub fn get_change(&self, r: &ObjectRef) -> Result<Change> {

        Ok(Change::decode(&self.get_typed(r, ObjectType::Change)?)?)

    }

    pub fn put_chunk(&self, bytes: &[u8]) -> Result<ObjectRef> {

        self.put(ObjectType::Chunk, bytes)

    }

    pub fn put_state(&self, st: &StateObject) -> Result<ObjectRef> {

        self.put(ObjectType::State, &st.encode())

    }

    pub fn get_state(&self, r: &ObjectRef) -> Result<StateObject> {

        Ok(StateObject::decode(&self.get_typed(r, ObjectType::State)?)?)

    }

    pub fn put_attest(&self, a: &Attest) -> Result<ObjectRef> {

        self.put(ObjectType::Attest, &a.encode())

    }

    pub fn get_attest(&self, r: &ObjectRef) -> Result<Attest> {

        Ok(Attest::decode(&self.get_typed(r, ObjectType::Attest)?)?)

    }

    fn seal_index_path(&self, change: &ObjectRef) -> PathBuf {

        let h = change.to_hex();

        self.dir.join("seals").join(&h[..2]).join(&h[2..])

    }

    /// Record that seal attestation `attest` covers `change`.

    pub fn index_seal(&self, change: &ObjectRef, attest: &ObjectRef) -> Result<()> {

        let mut seals = self.seals_for(change)?;

        if seals.contains(attest) {

            return Ok(());

        }

        seals.push(*attest);

        seals.sort();

        let path = self.seal_index_path(change);

        fs::create_dir_all(path.parent().unwrap())?;

        let text: String = seals.iter().map(|s| format!("{}\n", s.to_hex())).collect();

        let tmp = path.with_extension("tmp");

        fs::write(&tmp, text)?;

        fs::rename(&tmp, &path)?;

        Ok(())

    }

    /// Seal attestations known to cover `change`.

    pub fn seals_for(&self, change: &ObjectRef) -> Result<Vec<ObjectRef>> {

        match fs::read_to_string(self.seal_index_path(change)) {

            Ok(t) => Ok(t.lines().filter_map(ObjectRef::from_hex).collect()),

            Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(vec![]),

            Err(e) => Err(e.into()),

        }

    }

    pub fn put_identity(&self, id: &Identity) -> Result<ObjectRef> {

        self.put(ObjectType::Identity, &id.encode())

    }

    pub fn get_identity(&self, r: &ObjectRef) -> Result<Identity> {