kcode-k1-invites 0.2.2

use base64::{Engine as _, engine::general_purpose::URL_SAFE_NO_PAD};
use hmac::{Hmac, Mac};
use kcode_k1_invite_projection::{ApplyOutcome, InviteAction, InviteProjection};
use kcode_k1_peering::K1Peering;
use kcode_k1_transaction::SubsystemId;
use kcode_k1_transaction_id::TxId;
use kcode_k1_txn_ordering::{K1TxnOrdering, Subsystem};
use sha2::Sha256;
use std::collections::{HashMap, HashSet};
use std::path::Path;
use std::str::FromStr;
use std::sync::{Arc, Condvar, Mutex, MutexGuard};
use zeroize::Zeroize;

const SUBSYSTEM_NAME: &str = "k1-invites-subsystem";
const ISSUE_LENGTH: usize = 34;
const CONSUME_HEADER_LENGTH: usize = 78;
const REOPEN_REQUIRED: &str = "k1-invites is unavailable; reopen required";

type HmacSha256 = Hmac<Sha256>;

pub struct InviteCode {
    bytes: [u8; 6],
}

impl InviteCode {
    pub fn expose(&self) -> String {
        URL_SAFE_NO_PAD.encode(self.bytes.as_slice())
    }
}

impl FromStr for InviteCode {
    type Err = String;

    fn from_str(value: &str) -> Result<Self, Self::Err> {
        let mut code = InviteCode { bytes: [0; 6] };
        if value.len() != 8 {
            return Err("invalid invite code".to_owned());
        }
        let written = match URL_SAFE_NO_PAD.decode_slice(value, &mut code.bytes) {
            Ok(written) => written,
            Err(_) => return Err("invalid invite code".to_owned()),
        };
        if written != code.bytes.len() {
            return Err("invalid invite code".to_owned());
        }
        let mut canonical = [0_u8; 8];
        let encoded = match URL_SAFE_NO_PAD.encode_slice(&code.bytes, &mut canonical) {
            Ok(encoded) => encoded,
            Err(_) => {
                canonical.zeroize();
                return Err("invalid invite code".to_owned());
            }
        };
        if encoded != canonical.len() || canonical.as_slice() != value.as_bytes() {
            canonical.zeroize();
            return Err("invalid invite code".to_owned());
        }
        canonical.zeroize();
        Ok(code)
    }
}

impl Drop for InviteCode {
    fn drop(&mut self) {
        self.bytes.zeroize();
    }
}

pub struct InviteVerifierKey {
    bytes: [u8; 32],
}

impl InviteVerifierKey {
    pub fn from_bytes(bytes: [u8; 32]) -> Self {
        Self { bytes }
    }
}

impl Drop for InviteVerifierKey {
    fn drop(&mut self) {
        self.bytes.zeroize();
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum InviteStatus {
    Unknown,
    Unused,
    Consumed,
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub struct UserId(TxId);

impl UserId {
    pub const fn from_tx_id(txid: TxId) -> Self {
        Self(txid)
    }

    pub const fn as_tx_id(self) -> TxId {
        self.0
    }
}

#[derive(Clone, Copy, Eq, Hash, PartialEq)]
pub struct RegistrationKey([u8; 32]);

impl RegistrationKey {
    pub fn from_bytes(bytes: [u8; 32]) -> Self {
        Self(bytes)
    }

    pub fn as_bytes(&self) -> &[u8; 32] {
        &self.0
    }
}

#[derive(Clone, Eq, PartialEq)]
pub struct Registration {
    user_id: UserId,
    registration_key: RegistrationKey,
    data: Arc<Vec<u8>>,
}

impl Registration {
    pub fn user_id(&self) -> UserId {
        self.user_id
    }

    pub fn registration_key(&self) -> RegistrationKey {
        self.registration_key
    }

    pub fn data(&self) -> &[u8] {
        self.data.as_slice()
    }
}

pub struct K1Invites {
    subsystem: Arc<InviteSubsystem>,
    _ordering: Arc<K1TxnOrdering>,
    peering: Arc<K1Peering>,
    verifier_key: InviteVerifierKey,
}

impl K1Invites {
    pub fn open(
        root: &Path,
        ordering: Arc<K1TxnOrdering>,
        peering: Arc<K1Peering>,
        verifier_key: InviteVerifierKey,
    ) -> Result<Self, String> {
        let projection = InviteProjection::open(root)?;
        let snapshot = projection.snapshot()?;
        let checkpoint = snapshot.checkpoint;
        let mut state = FacadeState::new();
        state
            .issues
            .try_reserve(snapshot.issues.len())
            .map_err(|_| allocation_error())?;
        state
            .issue_commitments
            .try_reserve(snapshot.issues.len())
            .map_err(|_| allocation_error())?;
        state
            .registrations
            .try_reserve(snapshot.registrations.len())
            .map_err(|_| allocation_error())?;
        state
            .registration_keys
            .try_reserve(snapshot.registrations.len())
            .map_err(|_| allocation_error())?;
        for issue in snapshot.issues {
            if state.issues.contains_key(&issue.commitment)
                || state.issue_commitments.contains_key(&issue.issue_id)
            {
                return Err("invite projection snapshot is inconsistent".to_owned());
            }
            state.issues.insert(issue.commitment, issue.issue_id);
            state
                .issue_commitments
                .insert(issue.issue_id, issue.commitment);
        }
        for accepted in snapshot.registrations {
            let commitment = accepted.commitment;
            if state.issue_commitments.get(&accepted.issue_id) != Some(&commitment) {
                return Err("invite projection snapshot is inconsistent".to_owned());
            }
            let registration_key = RegistrationKey::from_bytes(accepted.registration_key);
            if state.registrations.contains_key(&commitment)
                || state.registration_keys.contains_key(&registration_key)
            {
                return Err("invite projection snapshot is inconsistent".to_owned());
            }
            state.registrations.insert(
                commitment,
                Registration {
                    user_id: UserId(accepted.user_id),
                    registration_key,
                    data: Arc::new(accepted.data),
                },
            );
            state.registration_keys.insert(registration_key, commitment);
        }
        let subsystem = Arc::new(InviteSubsystem {
            projection: Mutex::new(projection),
            state: Mutex::new(state),
        });
        let callback: Arc<dyn Subsystem> = subsystem.clone();
        ordering.register_subsystem(subsystem_id()?, checkpoint, callback)?;
        subsystem.ensure_available()?;
        Ok(Self {
            subsystem,
            _ordering: ordering,
            peering,
            verifier_key,
        })
    }

    pub fn status(&self, code: &InviteCode) -> Result<InviteStatus, String> {
        let commitment = invite_commitment(&self.verifier_key, &code.bytes)?;
        let state = lock_unpoison(&self.subsystem.state);
        if !state.available {
            return Err(REOPEN_REQUIRED.to_owned());
        }
        Ok(status_from_state(&state, commitment))
    }

    pub fn create(&self) -> Result<(TxId, InviteCode), String> {
        enum Resolution {
            Return(Result<TxId, String>),
            Retry,
        }

        loop {
            self.subsystem.ensure_available()?;
            let subsystem_id = subsystem_id()?;
            let mut code = InviteCode { bytes: [0_u8; 6] };
            getrandom::fill(&mut code.bytes).map_err(|error| error.to_string())?;
            let commitment = invite_commitment(&self.verifier_key, &code.bytes)?;
            let reserved = {
                let mut state = lock_unpoison(&self.subsystem.state);
                if !state.available {
                    return Err(REOPEN_REQUIRED.to_owned());
                }
                if state.issues.contains_key(&commitment)
                    || state.pending_issues.contains(&commitment)
                {
                    false
                } else {
                    state
                        .pending_issues
                        .try_reserve(1)
                        .map_err(|_| allocation_error())?;
                    state.pending_issues.insert(commitment);
                    true
                }
            };
            if !reserved {
                continue;
            }
            let payload = issue_payload(commitment);
            let submission = self.peering.submit_txn(subsystem_id, &payload);
            let resolution = {
                let mut state = lock_unpoison(&self.subsystem.state);
                let pending_was_present = state.pending_issues.remove(&commitment);
                if !pending_was_present {
                    state.available = false;
                    Resolution::Return(Err(REOPEN_REQUIRED.to_owned()))
                } else if !state.available {
                    Resolution::Return(Err(REOPEN_REQUIRED.to_owned()))
                } else {
                    match submission {
                        Ok(returned_id) => match state.issues.get(&commitment).copied() {
                            Some(accepted_id) if accepted_id == returned_id => {
                                Resolution::Return(Ok(returned_id))
                            }
                            Some(_) => Resolution::Retry,
                            None => Resolution::Return(Err(
                                "issue transaction was not the winning Issue".to_owned(),
                            )),
                        },
                        Err(error) => match state.issues.get(&commitment).copied() {
                            Some(accepted_id) => Resolution::Return(Ok(accepted_id)),
                            None => Resolution::Return(Err(error)),
                        },
                    }
                }
            };
            match resolution {
                Resolution::Return(result) => return result.map(|id| (id, code)),
                Resolution::Retry => continue,
            }
        }
    }

    pub fn consume_with_data(
        &self,
        code: &InviteCode,
        registration_key: RegistrationKey,
        data: &[u8],
    ) -> Result<UserId, String> {
        self.subsystem.ensure_available()?;
        let commitment = invite_commitment(&self.verifier_key, &code.bytes)?;
        let shared_data = Arc::new(fallible_copy(data)?);
        let candidate_cell = Arc::new(PendingResult::new());
        let role = {
            let mut state = lock_unpoison(&self.subsystem.state);
            if !state.available {
                return Err(REOPEN_REQUIRED.to_owned());
            }
            if let Some(accepted) = state.registrations.get(&commitment) {
                ConsumeRole::Accepted(accepted.clone())
            } else if let Some(pending) = state.pending_consumes.get(&commitment) {
                ConsumeRole::Pending {
                    registration_key: pending.registration_key,
                    data: pending.data.clone(),
                    cell: pending.cell.clone(),
                }
            } else {
                let issue_id = state
                    .issues
                    .get(&commitment)
                    .copied()
                    .ok_or_else(|| "unknown invite code".to_owned())?;
                if state.registration_keys.contains_key(&registration_key)
                    || state
                        .pending_registration_keys
                        .contains_key(&registration_key)
                {
                    return Err("registration key is already used by another invite".to_owned());
                }
                state
                    .pending_consumes
                    .try_reserve(1)
                    .map_err(|_| allocation_error())?;
                state
                    .pending_registration_keys
                    .try_reserve(1)
                    .map_err(|_| allocation_error())?;
                state.pending_consumes.insert(
                    commitment,
                    PendingConsume {
                        registration_key,
                        data: shared_data.clone(),
                        cell: candidate_cell.clone(),
                    },
                );
                state
                    .pending_registration_keys
                    .insert(registration_key, commitment);
                ConsumeRole::Leader {
                    issue_id,
                    data: shared_data.clone(),
                    cell: candidate_cell.clone(),
                }
            }
        };
        match role {
            ConsumeRole::Accepted(accepted) => {
                if accepted.registration_key == registration_key && accepted.data.as_slice() == data
                {
                    Ok(accepted.user_id)
                } else {
                    Err("invite was already consumed with different registration data".to_owned())
                }
            }
            ConsumeRole::Pending {
                registration_key: pending_key,
                data: pending_data,
                cell,
            } => {
                if pending_key != registration_key || pending_data.as_slice() != data {
                    return Err("invite has a conflicting consume request in progress".to_owned());
                }
                wait_for_pending(&cell)
            }
            ConsumeRole::Leader {
                issue_id,
                data,
                cell,
            } => {
                let payload = match consume_payload(
                    issue_id,
                    commitment,
                    registration_key,
                    data.as_slice(),
                ) {
                    Ok(payload) => payload,
                    Err(error) => {
                        return self.abandon_pending(commitment, registration_key, &cell, error);
                    }
                };
                let subsystem_id = match subsystem_id() {
                    Ok(subsystem_id) => subsystem_id,
                    Err(error) => {
                        return self.abandon_pending(commitment, registration_key, &cell, error);
                    }
                };
                if let Err(error) = self.subsystem.ensure_available() {
                    return self.abandon_pending(commitment, registration_key, &cell, error);
                }
                let submission = self.peering.submit_txn(subsystem_id, &payload);
                self.complete_pending(
                    commitment,
                    registration_key,
                    data.as_slice(),
                    &cell,
                    submission,
                )
            }
        }
    }

    pub fn registrations(&self) -> Result<Vec<Registration>, String> {
        self.subsystem.ensure_available()?;
        let snapshot = {
            let projection = lock_unpoison(&self.subsystem.projection);
            projection.snapshot()
        };
        let snapshot = match snapshot {
            Ok(snapshot) => snapshot,
            Err(error) => {
                self.subsystem.mark_unavailable();
                return Err(error);
            }
        };
        self.subsystem.ensure_available()?;
        let mut registrations = Vec::new();
        registrations
            .try_reserve_exact(snapshot.registrations.len())
            .map_err(|_| allocation_error())?;
        for accepted in snapshot.registrations {
            registrations.push(Registration {
                user_id: UserId(accepted.user_id),
                registration_key: RegistrationKey::from_bytes(accepted.registration_key),
                data: Arc::new(accepted.data),
            });
        }
        Ok(registrations)
    }

    fn abandon_pending(
        &self,
        commitment: [u8; 32],
        registration_key: RegistrationKey,
        cell: &Arc<PendingResult>,
        error: String,
    ) -> Result<UserId, String> {
        let consistent = self.remove_pending(commitment, registration_key, cell);
        let result = if consistent {
            Err(error)
        } else {
            Err(REOPEN_REQUIRED.to_owned())
        };
        publish_pending(cell, &result);
        result
    }

    fn complete_pending(
        &self,
        commitment: [u8; 32],
        registration_key: RegistrationKey,
        data: &[u8],
        cell: &Arc<PendingResult>,
        submission: Result<TxId, String>,
    ) -> Result<UserId, String> {
        let (available, accepted, consistent) = {
            let mut state = lock_unpoison(&self.subsystem.state);
            let available = state.available;
            let accepted = state.registrations.get(&commitment).cloned();
            let consistent = pending_matches(&state, commitment, registration_key, cell);
            state.pending_consumes.remove(&commitment);
            if state.pending_registration_keys.get(&registration_key) == Some(&commitment) {
                state.pending_registration_keys.remove(&registration_key);
            }
            if !consistent {
                state.available = false;
            }
            (available, accepted, consistent)
        };
        let result = if !available || !consistent {
            Err(REOPEN_REQUIRED.to_owned())
        } else {
            match submission {
                Err(error) => match accepted {
                    Some(accepted)
                        if accepted.registration_key == registration_key
                            && accepted.data.as_slice() == data =>
                    {
                        Ok(accepted.user_id)
                    }
                    _ => Err(error),
                },
                Ok(returned_id) => {
                    if let Some(accepted) = accepted {
                        if accepted.user_id.as_tx_id() == returned_id
                            && accepted.registration_key == registration_key
                            && accepted.data.as_slice() == data
                        {
                            Ok(accepted.user_id)
                        } else {
                            Err("consume transaction was not the accepted registration".to_owned())
                        }
                    } else {
                        Err("consume transaction was a semantic loser".to_owned())
                    }
                }
            }
        };
        publish_pending(cell, &result);
        result
    }

    fn remove_pending(
        &self,
        commitment: [u8; 32],
        registration_key: RegistrationKey,
        cell: &Arc<PendingResult>,
    ) -> bool {
        let mut state = lock_unpoison(&self.subsystem.state);
        let consistent = pending_matches(&state, commitment, registration_key, cell);
        state.pending_consumes.remove(&commitment);
        if state.pending_registration_keys.get(&registration_key) == Some(&commitment) {
            state.pending_registration_keys.remove(&registration_key);
        }
        if !consistent {
            state.available = false;
        }
        consistent
    }
}

struct InviteSubsystem {
    projection: Mutex<InviteProjection>,
    state: Mutex<FacadeState>,
}

impl InviteSubsystem {
    fn ensure_available(&self) -> Result<(), String> {
        if lock_unpoison(&self.state).available {
            Ok(())
        } else {
            Err(REOPEN_REQUIRED.to_owned())
        }
    }

    fn apply_if_available(&self, action: InviteAction) -> Result<ApplyOutcome, String> {
        let projection = lock_unpoison(&self.projection);
        self.ensure_available()?;
        projection.apply(action)
    }

    fn mark_unavailable(&self) {
        lock_unpoison(&self.state).available = false;
    }

    fn fault(&self, error: String) -> Result<(), String> {
        self.mark_unavailable();
        Err(error)
    }

    fn accept_issue(&self, id: TxId, commitment: [u8; 32]) -> Result<(), String> {
        let mut state = lock_unpoison(&self.state);
        if !state.available {
            return Err(REOPEN_REQUIRED.to_owned());
        }
        if state.issues.contains_key(&commitment) || state.issue_commitments.contains_key(&id) {
            state.available = false;
            return Err("accepted Issue contradicted invite indexes".to_owned());
        }
        if state.issues.try_reserve(1).is_err() || state.issue_commitments.try_reserve(1).is_err() {
            state.available = false;
            return Err(allocation_error());
        }
        state.issues.insert(commitment, id);
        state.issue_commitments.insert(id, commitment);
        Ok(())
    }

    fn accept_registration(
        &self,
        id: TxId,
        issue_id: TxId,
        commitment: [u8; 32],
        registration_key: [u8; 32],
        data: &[u8],
    ) -> Result<(), String> {
        let copied_data = match fallible_copy(data) {
            Ok(data) => Arc::new(data),
            Err(error) => return self.fault(error),
        };
        let registration_key = RegistrationKey::from_bytes(registration_key);
        let mut state = lock_unpoison(&self.state);
        if !state.available {
            return Err(REOPEN_REQUIRED.to_owned());
        }
        if state.issues.get(&commitment) != Some(&issue_id)
            || state.issue_commitments.get(&issue_id) != Some(&commitment)
            || state.registrations.contains_key(&commitment)
            || state.registration_keys.contains_key(&registration_key)
        {
            state.available = false;
            return Err("accepted registration contradicted invite indexes".to_owned());
        }
        if state.registrations.try_reserve(1).is_err()
            || state.registration_keys.try_reserve(1).is_err()
        {
            state.available = false;
            return Err(allocation_error());
        }
        state.registrations.insert(
            commitment,
            Registration {
                user_id: UserId(id),
                registration_key,
                data: copied_data,
            },
        );
        state.registration_keys.insert(registration_key, commitment);
        Ok(())
    }
}

impl Subsystem for InviteSubsystem {
    fn submit_txn(&self, id: TxId, payload: &[u8]) -> Result<(), String> {
        self.ensure_available()?;
        let parsed = match parse_payload(id, payload) {
            Ok(parsed) => parsed,
            Err(error) => return self.fault(error),
        };
        let action = match projection_action(parsed) {
            Ok(action) => action,
            Err(error) => return self.fault(error),
        };
        let outcome = match self.apply_if_available(action) {
            Ok(outcome) => outcome,
            Err(error) => return self.fault(error),
        };
        match outcome {
            ApplyOutcome::IssueAccepted(issue) => match parsed {
                ParsedAction::Issue { id, commitment }
                    if issue.issue_id == id && issue.commitment == commitment =>
                {
                    self.accept_issue(issue.issue_id, issue.commitment)
                }
                _ => self.fault("projection Issue outcome contradicted action".to_owned()),
            },
            ApplyOutcome::RegistrationAccepted(accepted) => match parsed {
                ParsedAction::Consume {
                    id,
                    issue_id,
                    commitment,
                    registration_key,
                    data,
                } if accepted.user_id == id
                    && accepted.issue_id == issue_id
                    && accepted.commitment == commitment
                    && accepted.registration_key == registration_key
                    && accepted.data.as_slice() == data =>
                {
                    self.accept_registration(
                        accepted.user_id,
                        accepted.issue_id,
                        accepted.commitment,
                        accepted.registration_key,
                        accepted.data.as_slice(),
                    )
                }
                _ => self.fault("projection registration outcome contradicted action".to_owned()),
            },
            ApplyOutcome::Noop => Ok(()),
        }
    }

    fn reorg(&self) -> Result<(), String> {
        self.mark_unavailable();
        let projection = lock_unpoison(&self.projection);
        projection.discard()
    }
}

struct FacadeState {
    available: bool,
    issues: HashMap<[u8; 32], TxId>,
    issue_commitments: HashMap<TxId, [u8; 32]>,
    registrations: HashMap<[u8; 32], Registration>,
    registration_keys: HashMap<RegistrationKey, [u8; 32]>,
    pending_issues: HashSet<[u8; 32]>,
    pending_consumes: HashMap<[u8; 32], PendingConsume>,
    pending_registration_keys: HashMap<RegistrationKey, [u8; 32]>,
}

impl FacadeState {
    fn new() -> Self {
        Self {
            available: true,
            issues: HashMap::new(),
            issue_commitments: HashMap::new(),
            registrations: HashMap::new(),
            registration_keys: HashMap::new(),
            pending_issues: HashSet::new(),
            pending_consumes: HashMap::new(),
            pending_registration_keys: HashMap::new(),
        }
    }
}

struct PendingConsume {
    registration_key: RegistrationKey,
    data: Arc<Vec<u8>>,
    cell: Arc<PendingResult>,
}

struct PendingResult {
    outcome: Mutex<Option<Result<UserId, String>>>,
    ready: Condvar,
}

impl PendingResult {
    fn new() -> Self {
        Self {
            outcome: Mutex::new(None),
            ready: Condvar::new(),
        }
    }
}

enum ConsumeRole {
    Accepted(Registration),
    Pending {
        registration_key: RegistrationKey,
        data: Arc<Vec<u8>>,
        cell: Arc<PendingResult>,
    },
    Leader {
        issue_id: TxId,
        data: Arc<Vec<u8>>,
        cell: Arc<PendingResult>,
    },
}

#[derive(Clone, Copy)]
enum ParsedAction<'a> {
    Issue {
        id: TxId,
        commitment: [u8; 32],
    },
    Consume {
        id: TxId,
        issue_id: TxId,
        commitment: [u8; 32],
        registration_key: [u8; 32],
        data: &'a [u8],
    },
}

fn parse_payload<'a>(id: TxId, payload: &'a [u8]) -> Result<ParsedAction<'a>, String> {
    if payload.len() < 2 || payload[0] != 2 {
        return Err("malformed k1-invites payload".to_owned());
    }
    match payload[1] {
        1 if payload.len() == ISSUE_LENGTH => Ok(ParsedAction::Issue {
            id,
            commitment: array_32(&payload[2..34]),
        }),
        2 if payload.len() >= CONSUME_HEADER_LENGTH => Ok(ParsedAction::Consume {
            id,
            issue_id: tx_id_from_slice(&payload[2..14]),
            commitment: array_32(&payload[14..46]),
            registration_key: array_32(&payload[46..78]),
            data: &payload[78..],
        }),
        _ => Err("malformed k1-invites payload".to_owned()),
    }
}

fn projection_action(parsed: ParsedAction<'_>) -> Result<InviteAction, String> {
    match parsed {
        ParsedAction::Issue { id, commitment } => Ok(InviteAction::Issue { id, commitment }),
        ParsedAction::Consume {
            id,
            issue_id,
            commitment,
            registration_key,
            data,
        } => Ok(InviteAction::Consume {
            id,
            issue_id,
            commitment,
            registration_key,
            data: fallible_copy(data)?,
        }),
    }
}

fn invite_commitment(verifier_key: &InviteVerifierKey, code: &[u8; 6]) -> Result<[u8; 32], String> {
    let mut mac = HmacSha256::new_from_slice(&verifier_key.bytes)
        .map_err(|_| "invalid invite verifier key".to_owned())?;
    mac.update(b"k1-invite-v2");
    mac.update(code);
    let output = mac.finalize().into_bytes();
    let mut commitment = [0_u8; 32];
    commitment.copy_from_slice(&output);
    Ok(commitment)
}

fn status_from_state(state: &FacadeState, commitment: [u8; 32]) -> InviteStatus {
    if state.registrations.contains_key(&commitment) {
        InviteStatus::Consumed
    } else if state.issues.contains_key(&commitment) {
        InviteStatus::Unused
    } else {
        InviteStatus::Unknown
    }
}

fn issue_payload(commitment: [u8; 32]) -> [u8; ISSUE_LENGTH] {
    let mut payload = [0_u8; ISSUE_LENGTH];
    payload[0] = 2;
    payload[1] = 1;
    payload[2..].copy_from_slice(&commitment);
    payload
}

fn consume_payload(
    issue_id: TxId,
    commitment: [u8; 32],
    registration_key: RegistrationKey,
    data: &[u8],
) -> Result<Vec<u8>, String> {
    let total = CONSUME_HEADER_LENGTH
        .checked_add(data.len())
        .ok_or_else(|| "consume payload length overflow".to_owned())?;
    let mut payload = Vec::new();
    payload
        .try_reserve_exact(total)
        .map_err(|_| allocation_error())?;
    payload.extend_from_slice(&[2, 2]);
    payload.extend_from_slice(issue_id.as_bytes());
    payload.extend_from_slice(&commitment);
    payload.extend_from_slice(registration_key.as_bytes());
    payload.extend_from_slice(data);
    Ok(payload)
}

fn subsystem_id() -> Result<SubsystemId, String> {
    SubsystemId::from_str(SUBSYSTEM_NAME).map_err(|error| error.to_string())
}

fn tx_id_from_slice(bytes: &[u8]) -> TxId {
    let mut raw = [0_u8; 12];
    raw.copy_from_slice(bytes);
    TxId::from_bytes(raw)
}

fn array_32(bytes: &[u8]) -> [u8; 32] {
    let mut array = [0_u8; 32];
    array.copy_from_slice(bytes);
    array
}

fn fallible_copy(bytes: &[u8]) -> Result<Vec<u8>, String> {
    let mut copied = Vec::new();
    copied
        .try_reserve_exact(bytes.len())
        .map_err(|_| allocation_error())?;
    copied.extend_from_slice(bytes);
    Ok(copied)
}

fn allocation_error() -> String {
    "memory allocation failed".to_owned()
}

fn pending_matches(
    state: &FacadeState,
    commitment: [u8; 32],
    registration_key: RegistrationKey,
    cell: &Arc<PendingResult>,
) -> bool {
    state
        .pending_consumes
        .get(&commitment)
        .is_some_and(|pending| {
            pending.registration_key == registration_key && Arc::ptr_eq(&pending.cell, cell)
        })
        && state.pending_registration_keys.get(&registration_key) == Some(&commitment)
}

fn publish_pending(cell: &PendingResult, result: &Result<UserId, String>) {
    {
        let mut outcome = lock_unpoison(&cell.outcome);
        *outcome = Some(result.clone());
    }
    cell.ready.notify_all();
}

fn wait_for_pending(cell: &PendingResult) -> Result<UserId, String> {
    let mut outcome = lock_unpoison(&cell.outcome);
    loop {
        if let Some(result) = outcome.as_ref() {
            return result.clone();
        }
        outcome = match cell.ready.wait(outcome) {
            Ok(outcome) => outcome,
            Err(poisoned) => poisoned.into_inner(),
        };
    }
}

fn lock_unpoison<T>(mutex: &Mutex<T>) -> MutexGuard<'_, T> {
    match mutex.lock() {
        Ok(guard) => guard,
        Err(poisoned) => poisoned.into_inner(),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn tx_id(byte: u8) -> TxId {
        TxId::from_bytes([byte; 12])
    }

    #[test]
    fn user_id_converts_from_and_to_tx_id() {
        let txid = tx_id(6);
        assert_eq!(UserId::from_tx_id(txid).as_tx_id(), txid);
    }

    #[test]
    fn invite_status_uses_only_accepted_state() {
        let commitment = [4; 32];
        let registration_key = RegistrationKey::from_bytes([5; 32]);
        let mut state = FacadeState::new();

        assert_eq!(status_from_state(&state, commitment), InviteStatus::Unknown);
        state.issues.insert(commitment, tx_id(1));
        assert_eq!(status_from_state(&state, commitment), InviteStatus::Unused);

        state.pending_consumes.insert(
            commitment,
            PendingConsume {
                registration_key,
                data: Arc::new(b"pending".to_vec()),
                cell: Arc::new(PendingResult::new()),
            },
        );
        assert_eq!(status_from_state(&state, commitment), InviteStatus::Unused);

        state.registrations.insert(
            commitment,
            Registration {
                user_id: UserId(tx_id(2)),
                registration_key,
                data: Arc::new(b"accepted".to_vec()),
            },
        );
        assert_eq!(
            status_from_state(&state, commitment),
            InviteStatus::Consumed
        );

        let copied = InviteStatus::Consumed;
        assert_eq!(copied, InviteStatus::Consumed);
        assert_eq!(format!("{copied:?}"), "Consumed");
    }

    #[test]
    fn public_status_survives_restart() {
        use std::sync::atomic::{AtomicU64, Ordering};

        static NEXT_TEMP_ROOT: AtomicU64 = AtomicU64::new(0);

        let unique = NEXT_TEMP_ROOT.fetch_add(1, Ordering::Relaxed);
        let root = std::env::temp_dir().join(format!(
            "kcode-k1-invites-status-{}-{unique}",
            std::process::id()
        ));
        let ordering_root = root.join("ordering");
        let peering_root = root.join("peering");
        let invites_root = root.join("invites");

        let ordering =
            Arc::new(K1TxnOrdering::open(&ordering_root).expect("open temporary ordering"));
        let peering = Arc::new(
            K1Peering::open(&peering_root, Arc::clone(&ordering)).expect("open temporary peering"),
        );
        let invites = K1Invites::open(
            &invites_root,
            Arc::clone(&ordering),
            Arc::clone(&peering),
            InviteVerifierKey::from_bytes([7; 32]),
        )
        .expect("open temporary invites");

        let unknown = InviteCode::from_str("AAAAAAAA").expect("canonical unknown code");
        assert_eq!(
            invites.status(&unknown).expect("unknown status"),
            InviteStatus::Unknown
        );

        let (_, code) = invites.create().expect("create invite");
        let retained_code = code.expose();
        assert_eq!(
            invites.status(&code).expect("unused status"),
            InviteStatus::Unused
        );
        invites
            .consume_with_data(&code, RegistrationKey::from_bytes([8; 32]), b"account")
            .expect("consume invite");
        assert_eq!(
            invites.status(&code).expect("consumed status"),
            InviteStatus::Consumed
        );

        drop(invites);
        drop(peering);
        drop(ordering);

        let ordering =
            Arc::new(K1TxnOrdering::open(&ordering_root).expect("reopen temporary ordering"));
        let peering = Arc::new(
            K1Peering::open(&peering_root, Arc::clone(&ordering))
                .expect("reopen temporary peering"),
        );
        let invites = K1Invites::open(
            &invites_root,
            Arc::clone(&ordering),
            Arc::clone(&peering),
            InviteVerifierKey::from_bytes([7; 32]),
        )
        .expect("reopen temporary invites");
        let code = InviteCode::from_str(&retained_code).expect("parse retained code");
        assert_eq!(
            invites.status(&code).expect("restarted status"),
            InviteStatus::Consumed
        );

        drop(invites);
        drop(peering);
        drop(ordering);
        std::fs::remove_dir_all(&root).expect("remove temporary root");
    }

    #[test]
    fn invite_code_is_strict_and_round_trips() {
        let code = InviteCode {
            bytes: [0, 1, 2, 253, 254, 255],
        };
        let exposed = code.expose();
        assert_eq!(exposed.len(), 8);
        let parsed = InviteCode::from_str(&exposed).expect("canonical code");
        assert_eq!(parsed.expose(), exposed);
        for invalid in ["", "AAAAAAA", "AAAAAAAA=", "AAAAAAAAA", "AAAAAA+/", "åååå"] {
            assert!(InviteCode::from_str(invalid).is_err());
        }
    }

    #[test]
    fn commitment_uses_the_exact_domain_and_code_bytes() {
        let key = InviteVerifierKey::from_bytes([7; 32]);
        let code = [1, 2, 3, 4, 5, 6];
        let actual = invite_commitment(&key, &code).expect("commitment");
        let mut mac = HmacSha256::new_from_slice(&[7; 32]).expect("key");
        mac.update(b"k1-invite-v2");
        mac.update(&code);
        let expected = mac.finalize().into_bytes();
        assert_eq!(&actual[..], &expected[..]);
    }

    #[test]
    fn version_two_wire_round_trips() {
        let callback_id = tx_id(9);
        let issue_id = tx_id(4);
        let commitment = [3; 32];
        let key = RegistrationKey::from_bytes([5; 32]);
        let issue = issue_payload(commitment);
        match parse_payload(callback_id, &issue).expect("Issue") {
            ParsedAction::Issue {
                id,
                commitment: parsed,
            } => {
                assert_eq!(id, callback_id);
                assert_eq!(parsed, commitment);
            }
            ParsedAction::Consume { .. } => panic!("wrong action"),
        }
        let consume =
            consume_payload(issue_id, commitment, key, b"opaque\0bytes").expect("Consume payload");
        assert_eq!(consume.len(), CONSUME_HEADER_LENGTH + 12);
        match parse_payload(callback_id, &consume).expect("Consume") {
            ParsedAction::Consume {
                id,
                issue_id: parsed_issue,
                commitment: parsed_commitment,
                registration_key,
                data,
            } => {
                assert_eq!(id, callback_id);
                assert_eq!(parsed_issue, issue_id);
                assert_eq!(parsed_commitment, commitment);
                assert_eq!(registration_key, [5; 32]);
                assert_eq!(data, b"opaque\0bytes");
            }
            ParsedAction::Issue { .. } => panic!("wrong action"),
        }
    }

    #[test]
    fn malformed_payloads_are_rejected() {
        let id = tx_id(1);
        let mut extended_issue = vec![0; ISSUE_LENGTH + 1];
        extended_issue[0] = 2;
        extended_issue[1] = 1;
        let mut short_consume = vec![0; CONSUME_HEADER_LENGTH - 1];
        short_consume[0] = 2;
        short_consume[1] = 2;
        let malformed = vec![
            Vec::new(),
            vec![2],
            vec![1, 1],
            vec![2, 3],
            vec![2, 1],
            extended_issue,
            short_consume,
        ];
        for payload in malformed {
            assert!(parse_payload(id, &payload).is_err());
        }
    }

    #[test]
    fn apply_waiting_behind_reorg_linearization_does_not_reach_projection() {
        use std::sync::atomic::{AtomicU64, Ordering};
        use std::sync::mpsc;
        use std::thread;

        static NEXT_TEMP_ROOT: AtomicU64 = AtomicU64::new(0);

        let unique = NEXT_TEMP_ROOT.fetch_add(1, Ordering::Relaxed);
        let root = std::env::temp_dir().join(format!(
            "kcode-k1-invites-reorg-{}-{unique}",
            std::process::id()
        ));
        let projection = InviteProjection::open(&root).expect("open temporary projection");
        let subsystem = Arc::new(InviteSubsystem {
            projection: Mutex::new(projection),
            state: Mutex::new(FacadeState::new()),
        });
        let projection_guard = lock_unpoison(&subsystem.projection);
        let worker_subsystem = Arc::clone(&subsystem);
        let (ready_sender, ready_receiver) = mpsc::channel();
        let worker = thread::spawn(move || {
            ready_sender.send(()).expect("signal helper readiness");
            worker_subsystem.apply_if_available(InviteAction::Issue {
                id: tx_id(8),
                commitment: [9; 32],
            })
        });

        ready_receiver.recv().expect("receive helper readiness");
        subsystem.mark_unavailable();
        drop(projection_guard);

        match worker.join().expect("join helper thread") {
            Err(error) => assert_eq!(error, REOPEN_REQUIRED),
            Ok(_) => panic!("unavailable helper unexpectedly applied the Issue"),
        }
        drop(subsystem);

        let projection = InviteProjection::open(&root).expect("reopen temporary projection");
        let snapshot = projection
            .snapshot()
            .expect("snapshot temporary projection");
        assert!(snapshot.checkpoint.is_none());
        assert!(snapshot.issues.is_empty());
        assert!(snapshot.registrations.is_empty());
        drop(projection);
        std::fs::remove_dir_all(&root).expect("remove temporary projection");
    }
}