//! Serving and talking to remotes (spec §10.2, §16).

use super::*;

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct PullReport {
    pub heads: Vec<ChangeHash>,
    pub changed: bool,
    pub checked_out: bool,
}

impl Repo {
    // ------------------------------------------------------------ serving (spec §16)

    fn ref_attest_path(&self, bookmark: &str) -> PathBuf {
        self.oxy.join("attest").join(bookmark)
    }

    /// The latest reference attestation stored for a bookmark.
    pub fn latest_ref_attest(&self, bookmark: &str) -> Result<Option<(ObjectRef, SignedAttest)>> {
        match fs::read_to_string(self.ref_attest_path(bookmark)) {
            Ok(h) => {
                let r = ObjectRef::from_hex(h.trim()).ok_or_else(|| RepoError::Msg("corrupt attestation pointer".into()))?;
                Ok(Some((r, SignedAttest { attest: self.store.get_attest(&r)?, sigs: self.store.signatures(&r)? })))
            }
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(None),
            Err(e) => Err(e.into()),
        }
    }

    fn set_ref_attest(&self, bookmark: &str, r: &ObjectRef) -> Result<()> {
        fs::create_dir_all(self.oxy.join("attest"))?;
        write_atomic(&self.ref_attest_path(bookmark), r.to_hex().as_bytes())
    }

    pub fn remote_refs(&self) -> Result<Vec<RemoteRef>> {
        let view = self.view()?;
        let mut out = Vec::new();
        for (name, state) in &view.bookmarks {
            let latest = self.latest_ref_attest(name)?.map(|(_, a)| a);
            let last_serial = latest.as_ref().and_then(|a| match a.attest.body {
                AttestBody::Ref { serial, .. } => Some(serial),
                _ => None,
            });
            let attestation = latest.filter(|a| matches!(&a.attest.body, AttestBody::Ref { new_state, .. } if new_state == state));
            out.push(RemoteRef { name: name.clone(), state: *state, heads: self.store.get_state(state)?.heads, attestation, last_serial });
        }
        Ok(out)
    }

    /// Every change reachable from `heads` that is in the store.
    fn closure_in_store(&self, heads: &[ChangeHash]) -> Result<BTreeSet<ChangeHash>> {
        let mut seen = BTreeSet::new();
        let mut stack: Vec<ChangeHash> = heads.to_vec();
        while let Some(h) = stack.pop() {
            if seen.contains(&h) || !self.store.has(&h) {
                continue;
            }
            seen.insert(h);
            stack.extend(self.store.get_change(&h)?.deps);
        }
        Ok(seen)
    }

    /// `closure(want) \ closure(have)`, dependencies first (spec §16.2).
    pub fn negotiate(&self, have: &[ChangeHash], want: &[ChangeHash]) -> Result<Vec<ChangeHash>> {
        let have = self.closure_in_store(have)?;
        let mut out = Vec::new();
        let mut done: BTreeSet<ChangeHash> = have.clone();
        // Iterative post-order DFS.
        let mut stack: Vec<(ChangeHash, bool)> = want.iter().rev().map(|h| (*h, false)).collect();
        while let Some((h, expanded)) = stack.pop() {
            if done.contains(&h) {
                continue;
            }
            if !self.store.has(&h) {
                return fail(format!("change {} is not in this repository", h.short(12)));
            }
            if expanded {
                done.insert(h);
                out.push(h);
                continue;
            }
            stack.push((h, true));
            for d in self.store.get_change(&h)?.deps {
                if !done.contains(&d) {
                    stack.push((d, false));
                }
            }
        }
        Ok(out)
    }

    /// Bundle changes (in the given dependency order) with their signatures,
    /// seals, identities, blobs, chunks.
    pub fn bundle_for(&self, changes: &[ChangeHash]) -> Result<Bundle> {
        let mut bundle = Bundle::default();
        let mut objects: BTreeSet<ObjectRef> = BTreeSet::new();
        let mut seals: BTreeSet<ObjectRef> = BTreeSet::new();
        let add_object = |r: &ObjectRef, objects: &mut BTreeSet<ObjectRef>| {
            if !r.is_zero() && self.store.has(r) {
                objects.insert(*r);
            }
        };
        for h in changes {
            let c = self.store.get_change(h)?;
            let sigs = self.store.signatures(h)?;
            add_object(&c.author, &mut objects);
            for s in &sigs {
                add_object(&s.key, &mut objects);
            }
            for e in &c.edits {
                if let Edit::Replace { old, new, .. } = e {
                    for b in [old, new].into_iter().flatten() {
                        if self.store.has(b) {
                            objects.insert(*b);
                            if let Ok(blob) = Blob::decode(&self.store.get_typed(b, ObjectType::Blob)?) {
                                objects.extend(blob.chunks.iter().copied());
                            }
                        }
                    }
                }
            }
            for s in self.store.seals_for(h)? {
                seals.insert(s);
            }
            bundle.changes.push((c, sigs));
        }
        for r in seals {
            let attest = self.store.get_attest(&r)?;
            let sigs = self.store.signatures(&r)?;
            for s in &sigs {
                add_object(&s.key, &mut objects);
            }
            bundle.attests.push(SignedAttest { attest, sigs });
        }
        for r in objects {
            let (ty, body) = self.store.get(&r)?;
            bundle.objects.push((ty, body));
        }
        Ok(bundle)
    }

    /// Store a bundle's contents. With `strict`, every change must
    /// authenticate (signature or seal by its author or a delegate).
    pub fn import_bundle(&self, bundle: &Bundle, strict: bool) -> Result<Vec<ChangeHash>> {
        for (ty, body) in &bundle.objects {
            match ty {
                ObjectType::Chunk | ObjectType::Blob | ObjectType::Identity | ObjectType::State => {
                    self.store.put(*ty, body)?;
                }
                other => return fail(format!("bundle may not carry {} objects", other.name())),
            }
        }
        for sa in &bundle.attests {
            let r = self.store.put_attest(&sa.attest)?;
            for sig in &sa.sigs {
                self.store.put_signature(&r, sig)?;
            }
            if let AttestBody::Seal { hashes } = &sa.attest.body {
                for h in hashes {
                    self.store.index_seal(h, &r)?;
                }
            }
        }
        let incoming: BTreeSet<ChangeHash> = bundle.changes.iter().map(|(c, _)| c.hash()).collect();
        let mut imported = Vec::new();
        for (c, sigs) in &bundle.changes {
            let h = c.hash();
            for d in &c.deps {
                if !self.store.has(d) && !incoming.contains(d) {
                    return fail(format!("change {} depends on {}, which is neither stored nor in the bundle", h.short(12), d.short(12)));
                }
            }
            self.store.put_change(c)?;
            for sig in sigs {
                self.store.put_signature(&h, sig)?;
            }
            imported.push(h);
        }
        if strict {
            for h in &imported {
                if !matches!(self.authenticate_change(h)?, SignatureStatus::Valid { .. }) {
                    return fail(format!("change {} is not authenticated by its author", h.short(12)));
                }
            }
        }
        Ok(imported)
    }

    /// Verify a reference attestation against an update it claims to describe.
    /// `allow_equal` lets a client re-read the attestation it already has; a
    /// server receiving a push requires a strictly greater serial.
    fn check_ref_attest(&self, sa: &SignedAttest, name: &str, old_state: &ObjectRef, new_state: &ObjectRef, last_serial: Option<u64>, allow_equal: bool) -> std::result::Result<u64, String> {
        let AttestBody::Ref { name: n, old_state: o, new_state: nw, serial } = &sa.attest.body else {
            return Err("attestation is not a ref attestation".into());
        };
        if n != name || o != old_state || nw != new_state {
            return Err("attestation does not describe this update".into());
        }
        if sa.attest.repo != self.id().map_err(|e| e.to_string())? {
            return Err("attestation is for a different repository".into());
        }
        if let Some(last) = last_serial {
            if *serial < last || (*serial == last && !allow_equal) {
                return Err(format!("attestation serial {serial} is not greater than the last seen {last}"));
            }
        }
        let r = sa.attest.hash();
        let sig = sa.sigs.first().ok_or("attestation carries no signature")?;
        let id = self.store.get_identity(&sig.key).map_err(|_| format!("unknown key {}", sig.key.short(12)))?;
        verify_signature(&id, sig, Domain::Attest, &r).map_err(|e| e.to_string())?;
        Ok(*serial)
    }

    /// Accept a push (spec §16.3). Without a trust policy every repository
    /// is unverified, so unsigned changes and unattested updates are accepted;
    /// attestations that are present must still be valid.
    pub fn receive_push(&self, bundle: Bundle, updates: Vec<RefUpdate>) -> Result<Vec<RefResult>> {
        self.import_bundle(&bundle, false)?;
        let (op_ref, op) = self.head_op()?;
        let mut view = op.view.clone();
        let mut results = Vec::new();
        let mut names = Vec::new();
        for u in updates {
            let outcome = self.apply_update(&mut view, &u);
            let (ok, reason) = match outcome {
                Ok(()) => (true, String::new()),
                Err(e) => (false, e),
            };
            if ok {
                names.push(u.name.clone());
            }
            results.push(RefResult { name: u.name, ok, reason });
        }
        if !names.is_empty() {
            self.record_op(&[op_ref], &format!("push received: {}", names.join(" ")), view)?;
        }
        Ok(results)
    }

    fn apply_update(&self, view: &mut View, u: &RefUpdate) -> std::result::Result<(), String> {
        let empty = self.store.put_state(&StateObject::new(vec![])).map_err(|e| e.to_string())?;
        let current = view.bookmarks.get(&u.name).copied().unwrap_or(empty);
        if current != u.old_state {
            return Err("stale: the remote bookmark has moved; pull first".into());
        }
        let new_state = self.store.get_state(&u.new_state).map_err(|_| "new state object is missing".to_string())?;
        for h in &new_state.heads {
            if !self.store.has(h) {
                return Err(format!("head {} is missing", h.short(12)));
            }
        }
        if !u.force {
            let old_heads = self.store.get_state(&current).map_err(|e| e.to_string())?.heads;
            let closure = self.closure_in_store(&new_state.heads).map_err(|e| e.to_string())?;
            if let Some(h) = old_heads.iter().find(|h| !closure.contains(h)) {
                return Err(format!("not a fast-forward: current head {} would be dropped (use --force)", h.short(12)));
            }
        }
        if let Some(sa) = &u.attestation {
            let last = self.latest_ref_attest(&u.name).map_err(|e| e.to_string())?.and_then(|(_, a)| match a.attest.body {
                AttestBody::Ref { serial, .. } => Some(serial),
                _ => None,
            });
            self.check_ref_attest(sa, &u.name, &u.old_state, &u.new_state, last, false)?;
            let r = self.store.put_attest(&sa.attest).map_err(|e| e.to_string())?;
            for sig in &sa.sigs {
                self.store.put_signature(&r, sig).map_err(|e| e.to_string())?;
            }
            self.set_ref_attest(&u.name, &r).map_err(|e| e.to_string())?;
        }
        view.bookmarks.insert(u.name.clone(), u.new_state);
        Ok(())
    }

    // ------------------------------------------------------------ client side

    fn remote_url(&self, name: &str) -> Result<String> {
        self.config.remotes.get(name).cloned().ok_or_else(|| RepoError::Msg(format!("no remote named {name:?}; add one with `oxy remote add`")))
    }

    /// Credentials and trust for a remote: `remote.<name>.token` (else
    /// `$OXY_TOKEN`) and `remote.<name>.ca` (else `$OXY_CA`).
    fn remote_options(&self, name: &str) -> RemoteOptions {
        RemoteOptions {
            token: self.config.remote_tokens.get(name).cloned().or_else(|| std::env::var("OXY_TOKEN").ok()),
            ca: self.config.remote_cas.get(name).map(PathBuf::from).or_else(|| std::env::var("OXY_CA").ok().map(PathBuf::from)),
        }
    }

    fn open_named_remote(&self, name: &str) -> Result<Box<dyn crate::protocol::Remote>> {
        open_remote(&self.remote_url(name)?, &self.remote_options(name))
    }

    fn serial_path(&self, remote: &str, bookmark: &str) -> PathBuf {
        self.oxy.join("remotes").join(remote).join(format!("{bookmark}.serial"))
    }

    fn last_seen_serial(&self, remote: &str, bookmark: &str) -> Option<u64> {
        fs::read_to_string(self.serial_path(remote, bookmark)).ok().and_then(|s| s.trim().parse().ok())
    }

    fn record_serial(&self, remote: &str, bookmark: &str, serial: u64) -> Result<()> {
        let p = self.serial_path(remote, bookmark);
        fs::create_dir_all(p.parent().unwrap())?;
        write_atomic(&p, serial.to_string().as_bytes())
    }

    /// Every head this repository knows: bookmarks, remote tracking, working copy.
    fn known_heads(&self, view: &View) -> Result<Vec<ChangeHash>> {
        let mut have: BTreeSet<ChangeHash> = BTreeSet::new();
        for st in view.bookmarks.values().chain(view.remotes.values().flat_map(|b| b.values())) {
            if let Ok(s) = self.store.get_state(st) {
                have.extend(s.heads);
            }
        }
        have.extend(view.workspaces.values().copied());
        Ok(have.into_iter().collect())
    }

    /// Fetch every bookmark of a remote into `remotes/<name>/bookmarks/*` (spec §10.2).
    pub fn fetch(&self, remote_name: &str) -> Result<Vec<(String, Vec<ChangeHash>, usize)>> {
        let remote = self.open_named_remote(remote_name)?;
        if remote.repo_id()? != self.id()? {
            return fail(format!("remote {remote_name:?} is a different repository (repository IDs differ)"));
        }
        let (op_ref, op) = self.head_op()?;
        let mut view = op.view.clone();
        let have = self.known_heads(&view)?;
        let mut report = Vec::new();
        for r in remote.refs()? {
            let needed = remote.negotiate(&have, &r.heads)?;
            let bundle = remote.fetch(&needed)?;
            let imported = self.import_bundle(&bundle, false)?;
            for h in &r.heads {
                if !self.store.has(h) {
                    return fail(format!("remote did not send head {}", h.short(12)));
                }
            }
            let state = self.store.put_state(&StateObject::new(r.heads.clone()))?;
            if state != r.state {
                return fail(format!("remote state {} does not match its heads", r.state.short(12)));
            }
            if let Some(sa) = &r.attestation {
                let AttestBody::Ref { old_state, new_state, .. } = &sa.attest.body else {
                    return fail("remote sent a non-ref attestation for a bookmark");
                };
                let (old_state, new_state) = (*old_state, *new_state);
                let serial = self
                    .check_ref_attest(sa, &r.name, &old_state, &new_state, self.last_seen_serial(remote_name, &r.name), true)
                    .map_err(|e| RepoError::Msg(format!("attestation for {}/{}: {e}", remote_name, r.name)))?;
                if new_state != r.state {
                    return fail(format!("attestation for {}/{} does not cover its current state", remote_name, r.name));
                }
                let ar = self.store.put_attest(&sa.attest)?;
                for sig in &sa.sigs {
                    self.store.put_signature(&ar, sig)?;
                }
                self.record_serial(remote_name, &r.name, serial)?;
            }
            view.remotes.entry(remote_name.to_string()).or_default().insert(r.name.clone(), state);
            report.push((r.name, r.heads, imported.len()));
        }
        if view != op.view {
            self.record_op(&[op_ref], &format!("oxy fetch {remote_name}"), view)?;
        }
        Ok(report)
    }

    /// Fetch, then take the union of the local bookmark's state with the
    /// remote's: no merge change, conflicts become reified (spec §9.4).
    pub fn pull(&self, remote_name: &str) -> Result<PullReport> {
        self.fetch(remote_name)?;
        let (op_ref, op) = self.head_op()?;
        let bookmark = self.config.bookmark.clone();
        let local = self.heads_of(&op.view, &bookmark)?;
        let Some(remote_state) = op.view.remotes.get(remote_name).and_then(|b| b.get(&bookmark)).copied() else {
            return Ok(PullReport { heads: local, changed: false, checked_out: false });
        };
        let remote_heads = self.store.get_state(&remote_state)?.heads;
        let mut all = local.clone();
        all.extend(remote_heads);
        let st = self.load_state(&all)?;
        let mut heads = st.maximal(&all);
        heads.sort();
        let mut sorted_local = local.clone();
        sorted_local.sort();
        if heads == sorted_local {
            return Ok(PullReport { heads, changed: false, checked_out: false });
        }
        let mut view = op.view.clone();
        view.bookmarks.insert(bookmark.clone(), self.store.put_state(&StateObject::new(heads.clone()))?);
        self.record_op(&[op_ref], &format!("oxy pull {remote_name}"), view)?;
        // Follow along if the working copy was clean and on the old heads.
        let snap = self.snapshot("oxy pull")?;
        let clean = snap.wc.tree_ops.is_empty() && snap.wc.edits.is_empty();
        let mut base = snap.base.maximal(&snap.wc.deps);
        base.sort();
        let mut checked_out = false;
        if clean && base == sorted_local {
            self.checkout(&heads, false, "oxy pull (checkout)")?;
            checked_out = true;
        }
        Ok(PullReport { heads, changed: true, checked_out })
    }

    /// Push the current bookmark (spec §16.3), sealing this author's unsigned
    /// changes and attesting the reference when a key is available.
    pub fn push(&self, remote_name: &str, force: bool) -> Result<Vec<RefResult>> {
        let remote = self.open_named_remote(remote_name)?;
        if remote.repo_id()? != self.id()? {
            return fail(format!("remote {remote_name:?} is a different repository (repository IDs differ)"));
        }
        let (op_ref, op) = self.head_op()?;
        let bookmark = self.config.bookmark.clone();
        let local_heads = self.heads_of(&op.view, &bookmark)?;
        let refs = remote.refs()?;
        let empty = self.store.put_state(&StateObject::new(vec![]))?;
        let (remote_state, remote_heads, last_serial) = match refs.iter().find(|r| r.name == bookmark) {
            Some(r) => (r.state, r.heads.clone(), r.last_serial),
            None => (empty, vec![], None),
        };
        let new_state = self.store.put_state(&StateObject::new(local_heads.clone()))?;
        if new_state == remote_state {
            return Ok(vec![RefResult { name: bookmark, ok: true, reason: "already up to date".into() }]);
        }
        for h in &remote_heads {
            if !self.store.has(h) {
                return fail(format!("the remote has change {} which you do not; pull first", h.short(12)));
            }
        }
        if !force {
            let closure = self.closure_in_store(&local_heads)?;
            if let Some(h) = remote_heads.iter().find(|h| !closure.contains(h)) {
                return fail(format!("not a fast-forward: remote head {} is not in your state; pull first or use --force", h.short(12)));
            }
        }
        let to_send = self.negotiate(&remote_heads, &local_heads)?;
        let mut bundle = self.bundle_for(&to_send)?;
        let key = self.secret_key()?.map(|(k, _)| k);
        if let Some(key) = key {
            // Seal this author's changes that carry no valid authenticator.
            let mut unsigned = Vec::new();
            for h in &to_send {
                let c = self.store.get_change(h)?;
                if c.author == key && !matches!(self.authenticate_change(h)?, SignatureStatus::Valid { .. }) {
                    unsigned.push(*h);
                }
            }
            for chunk in unsigned.chunks(crate::attest::MAX_SEAL_HASHES) {
                let sa = self.sign_attest(&Attest::seal(self.id()?, chunk.to_vec()))?;
                bundle.attests.push(sa);
            }
            bundle = self.bundle_for(&to_send)?;
        }
        bundle.objects.push((ObjectType::State, StateObject::new(local_heads.clone()).encode()));
        let attestation = match key {
            Some(_) => Some(self.sign_attest(&Attest {
                repo: self.id()?,
                hlc: Hlc::now(),
                body: AttestBody::Ref { name: bookmark.clone(), old_state: remote_state, new_state, serial: last_serial.unwrap_or(0) + 1 },
            })?),
            None => None,
        };
        let serial = attestation.as_ref().and_then(|a| match a.attest.body {
            AttestBody::Ref { serial, .. } => Some(serial),
            _ => None,
        });
        let results = remote.push(bundle, vec![RefUpdate { name: bookmark.clone(), old_state: remote_state, new_state, force, attestation }])?;
        if results.iter().any(|r| r.ok) {
            let mut view = op.view.clone();
            view.remotes.entry(remote_name.to_string()).or_default().insert(bookmark.clone(), new_state);
            self.record_op(&[op_ref], &format!("oxy push {remote_name}"), view)?;
            if let Some(s) = serial {
                self.record_serial(remote_name, &bookmark, s)?;
            }
        }
        Ok(results)
    }

    /// Clone a remote into `dest`: same repository ID, `origin` remote,
    /// bookmark set to the remote's, working copy checked out.
    pub fn clone(url: &str, dest: &Path) -> Result<Repo> {
        let options = RemoteOptions {
            token: std::env::var("OXY_TOKEN").ok(),
            ca: std::env::var("OXY_CA").ok().map(PathBuf::from),
        };
        let remote = open_remote(url, &options)?;
        let id = remote.repo_id()?;
        let mut repo = Repo::init_with_id(dest, id)?;
        repo.config.set("remote.origin.url", url)?;
        repo.save_config()?;
        repo.fetch("origin")?;
        let (op_ref, op) = repo.head_op()?;
        let bookmark = repo.config.bookmark.clone();
        if let Some(state) = op.view.remotes.get("origin").and_then(|b| b.get(&bookmark)).copied() {
            let heads = repo.store.get_state(&state)?.heads;
            let mut view = op.view.clone();
            view.bookmarks.insert(bookmark, state);
            repo.record_op(&[op_ref], &format!("oxy clone {url}"), view)?;
            repo.checkout(&heads, false, "oxy clone (checkout)")?;
        }
        Ok(repo)
    }
}