/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

use std::collections::{HashMap, HashSet};

use crate::bso_record::EncryptedBso;
use crate::client::{SetupStorageClient, Sync15ClientResponse};
use crate::collection_keys::CollectionKeys;
use crate::error::{self, ErrorKind, ErrorResponse};
use crate::key_bundle::KeyBundle;
use crate::record_types::{MetaGlobalEngine, MetaGlobalRecord};
use crate::request::{InfoCollections, InfoConfiguration};
use crate::util::ServerTimestamp;
use interrupt_support::Interruptee;
use serde_derive::*;
use sync_guid::Guid;

use self::SetupState::*;

const STORAGE_VERSION: usize = 5;

/// Maps names to storage versions for engines to include in a fresh
/// `meta/global` record. We include engines that we don't implement
/// because they'll be disabled on other clients if we omit them
/// (bug 1479929).
const DEFAULT_ENGINES: &[(&str, usize)] = &[
    ("passwords", 1),
    ("clients", 1),
    ("addons", 1),
    ("addresses", 1),
    ("bookmarks", 2),
    ("creditcards", 1),
    ("forms", 1),
    ("history", 1),
    ("prefs", 2),
    ("tabs", 1),
];

// Declined engines to include in a fresh `meta/global` record.
const DEFAULT_DECLINED: &[&str] = &[];

/// State that we require the app to persist to storage for us.
/// It's a little unfortunate we need this, because it's only tracking
/// "declined engines", and even then, only needed in practice when there's
/// no meta/global so we need to create one. It's extra unfortunate because we
/// want to move away from "globally declined" engines anyway, moving towards
/// allowing engines to be enabled or disabled per client rather than globally.
///
/// Apps are expected to treat this as opaque, so we support serializing it.
/// Note that this structure is *not* used to *change* the declined engines
/// list - that will be done in the future, but the API exposed for that
/// purpose will also take a mutable PersistedGlobalState.
#[derive(Debug, Serialize, Deserialize)]
#[serde(tag = "schema_version")]
pub enum PersistedGlobalState {
    /// V1 was when we persisted the entire GlobalState, keys and all!

    /// V2 is just tracking the globally declined list.
    /// None means "I've no idea" and theoretically should only happen on the
    /// very first sync for an app.
    V2 { declined: Option<Vec<String>> },
}

impl Default for PersistedGlobalState {
    #[inline]
    fn default() -> PersistedGlobalState {
        PersistedGlobalState::V2 { declined: None }
    }
}

#[derive(Debug, Default, Clone, PartialEq)]
pub(crate) struct EngineChangesNeeded {
    pub local_resets: HashSet<String>,
    pub remote_wipes: HashSet<String>,
}

#[derive(Debug, Default, Clone, PartialEq)]
struct RemoteEngineState {
    info_collections: HashSet<String>,
    declined: HashSet<String>,
}

#[derive(Debug, Default, Clone, PartialEq)]
struct EngineStateInput {
    local_declined: HashSet<String>,
    remote: Option<RemoteEngineState>,
    user_changes: HashMap<String, bool>,
}

#[derive(Debug, Default, Clone, PartialEq)]
struct EngineStateOutput {
    // The new declined.
    declined: HashSet<String>,
    // Which engines need resets or wipes.
    changes_needed: EngineChangesNeeded,
}

fn compute_engine_states(input: EngineStateInput) -> EngineStateOutput {
    use crate::util::*;
    log::debug!("compute_engine_states: input {:?}", input);
    let (must_enable, must_disable) = partition_by_value(&input.user_changes);
    let have_remote = input.remote.is_some();
    let RemoteEngineState {
        info_collections,
        declined: remote_declined,
    } = input.remote.clone().unwrap_or_default();

    let both_declined_and_remote = set_intersection(&info_collections, &remote_declined);
    if !both_declined_and_remote.is_empty() {
        // Should we wipe these too?
        log::warn!(
            "Remote state contains engines which are in both info/collections and meta/global's declined: {:?}",
            both_declined_and_remote,
        );
    }

    let most_recent_declined_list = if have_remote {
        &remote_declined
    } else {
        &input.local_declined
    };

    let result_declined = set_difference(
        &set_union(most_recent_declined_list, &must_disable),
        &must_enable,
    );

    let output = EngineStateOutput {
        changes_needed: EngineChangesNeeded {
            // Anything now declined which wasn't in our declined list before gets a reset.
            local_resets: set_difference(&result_declined, &input.local_declined),
            // Anything remote that we just declined gets a wipe. In the future
            // we might want to consider wiping things in both remote declined
            // and info/collections, but we'll let other clients pick up their
            // own mess for now.
            remote_wipes: set_intersection(&info_collections, &must_disable),
        },
        declined: result_declined,
    };
    // No PII here and this helps debug problems.
    log::debug!("compute_engine_states: output {:?}", output);
    output
}

impl PersistedGlobalState {
    fn set_declined(&mut self, new_declined: Vec<String>) {
        match self {
            Self::V2 { ref mut declined } => *declined = Some(new_declined),
        }
    }
    pub(crate) fn get_declined(&self) -> &[String] {
        match self {
            Self::V2 { declined: Some(d) } => &d,
            Self::V2 { declined: None } => &[],
        }
    }
}

/// Holds global Sync state, including server upload limits, the
/// last-fetched collection modified times, `meta/global` record, and
/// encrypted copies of the crypto/keys resourse (which we hold as encrypted
/// both to avoid keeping them in memory longer than necessary, and guard against
/// the wrong (ie, a different user's) root key being passed in.
#[derive(Debug, Clone)]
pub struct GlobalState {
    pub config: InfoConfiguration,
    pub collections: InfoCollections,
    pub global: MetaGlobalRecord,
    pub global_timestamp: ServerTimestamp,
    pub keys: EncryptedBso,
}

/// Creates a fresh `meta/global` record, using the default engine selections,
/// and declined engines from our PersistedGlobalState.
fn new_global(pgs: &PersistedGlobalState) -> error::Result<MetaGlobalRecord> {
    let sync_id = Guid::random();
    let mut engines: HashMap<String, _> = HashMap::new();
    for (name, version) in DEFAULT_ENGINES.iter() {
        let sync_id = Guid::random();
        engines.insert(
            (*name).to_string(),
            MetaGlobalEngine {
                version: *version,
                sync_id,
            },
        );
    }
    // We only need our PersistedGlobalState to fill out a new meta/global - if
    // we previously saw a meta/global then we would have updated it with what
    // it was at the time.
    let declined = match pgs {
        PersistedGlobalState::V2 { declined: Some(d) } => d.clone(),
        _ => DEFAULT_DECLINED.iter().map(ToString::to_string).collect(),
    };

    Ok(MetaGlobalRecord {
        sync_id,
        storage_version: STORAGE_VERSION,
        engines,
        declined,
    })
}

fn fixup_meta_global(global: &mut MetaGlobalRecord) -> bool {
    let mut changed_any = false;
    for &(name, version) in DEFAULT_ENGINES.iter() {
        let had_engine = global.engines.contains_key(name);
        let should_have_engine = !global.declined.iter().any(|c| c == name);
        if had_engine != should_have_engine {
            if should_have_engine {
                log::debug!("SyncID for engine {:?} was missing", name);
                global.engines.insert(
                    name.to_string(),
                    MetaGlobalEngine {
                        version,
                        sync_id: Guid::random(),
                    },
                );
            } else {
                log::debug!("SyncID for engine {:?} was present, but shouldn't be", name);
                global.engines.remove(name);
            }
            changed_any = true;
        }
    }
    changed_any
}

pub struct SetupStateMachine<'a> {
    client: &'a dyn SetupStorageClient,
    root_key: &'a KeyBundle,
    pgs: &'a mut PersistedGlobalState,
    // `allowed_states` is designed so that we can arrange for the concept of
    // a "fast" sync - so we decline to advance if we need to setup from scratch.
    // The idea is that if we need to sync before going to sleep we should do
    // it as fast as possible. However, in practice this isn't going to do
    // what we expect - a "fast sync" that finds lots to do is almost certainly
    // going to take longer than a "full sync" that finds nothing to do.
    // We should almost certainly remove this and instead allow for a "time
    // budget", after which we get interrupted. Later...
    allowed_states: Vec<&'static str>,
    sequence: Vec<&'static str>,
    engine_updates: Option<&'a HashMap<String, bool>>,
    interruptee: &'a dyn Interruptee,
    pub(crate) changes_needed: Option<EngineChangesNeeded>,
}

impl<'a> SetupStateMachine<'a> {
    /// Creates a state machine for a "classic" Sync 1.5 client that supports
    /// all states, including uploading a fresh `meta/global` and `crypto/keys`
    /// after a node reassignment.
    pub fn for_full_sync(
        client: &'a dyn SetupStorageClient,
        root_key: &'a KeyBundle,
        pgs: &'a mut PersistedGlobalState,
        engine_updates: Option<&'a HashMap<String, bool>>,
        interruptee: &'a dyn Interruptee,
    ) -> SetupStateMachine<'a> {
        SetupStateMachine::with_allowed_states(
            client,
            root_key,
            pgs,
            interruptee,
            engine_updates,
            vec![
                "Initial",
                "InitialWithConfig",
                "InitialWithInfo",
                "InitialWithMetaGlobal",
                "Ready",
                "FreshStartRequired",
                "WithPreviousState",
            ],
        )
    }

    /// Creates a state machine for a fast sync, which only uses locally
    /// cached global state, and bails if `meta/global` or `crypto/keys`
    /// are missing or out-of-date. This is useful in cases where it's
    /// important to get to ready as quickly as possible, like syncing before
    /// sleep, or when conserving time or battery life.
    pub fn for_fast_sync(
        client: &'a dyn SetupStorageClient,
        root_key: &'a KeyBundle,
        pgs: &'a mut PersistedGlobalState,
        engine_updates: Option<&'a HashMap<String, bool>>,
        interruptee: &'a dyn Interruptee,
    ) -> SetupStateMachine<'a> {
        SetupStateMachine::with_allowed_states(
            client,
            root_key,
            pgs,
            interruptee,
            engine_updates,
            vec!["Ready", "WithPreviousState"],
        )
    }

    /// Creates a state machine for a read-only sync, where the client can't
    /// upload `meta/global` or `crypto/keys`. Useful for clients that only
    /// sync specific collections, like Lockbox.
    pub fn for_readonly_sync(
        client: &'a dyn SetupStorageClient,
        root_key: &'a KeyBundle,
        pgs: &'a mut PersistedGlobalState,
        interruptee: &'a dyn Interruptee,
    ) -> SetupStateMachine<'a> {
        SetupStateMachine::with_allowed_states(
            client,
            root_key,
            pgs,
            interruptee,
            // No engine updates for a readonly sync
            None,
            // We don't allow a FreshStart in a read-only sync.
            vec![
                "Initial",
                "InitialWithConfig",
                "InitialWithInfo",
                "InitialWithMetaGlobal",
                "Ready",
                "WithPreviousState",
            ],
        )
    }

    fn with_allowed_states(
        client: &'a dyn SetupStorageClient,
        root_key: &'a KeyBundle,
        pgs: &'a mut PersistedGlobalState,
        interruptee: &'a dyn Interruptee,
        engine_updates: Option<&'a HashMap<String, bool>>,
        allowed_states: Vec<&'static str>,
    ) -> SetupStateMachine<'a> {
        SetupStateMachine {
            client,
            root_key,
            pgs,
            sequence: Vec::new(),
            allowed_states,
            engine_updates,
            interruptee,
            changes_needed: None,
        }
    }

    fn advance(&mut self, from: SetupState) -> error::Result<SetupState> {
        match from {
            // Fetch `info/configuration` with current server limits, and
            // `info/collections` with collection last modified times.
            Initial => {
                let config = match self.client.fetch_info_configuration()? {
                    Sync15ClientResponse::Success { record, .. } => record,
                    Sync15ClientResponse::Error(ErrorResponse::NotFound { .. }) => {
                        InfoConfiguration::default()
                    }
                    other => return Err(other.create_storage_error().into()),
                };
                Ok(InitialWithConfig { config })
            }

            // XXX - we could consider combining these Initial* states, because we don't
            // attempt to support filling in "missing" global state - *any* 404 in them
            // means `FreshStart`.
            // IOW, in all cases, they either `Err()`, move to `FreshStartRequired`, or
            // advance to a specific next state.
            InitialWithConfig { config } => {
                match self.client.fetch_info_collections()? {
                    Sync15ClientResponse::Success {
                        record: collections,
                        ..
                    } => Ok(InitialWithInfo {
                        config,
                        collections,
                    }),
                    // If the server doesn't have a `crypto/keys`, start over
                    // and reupload our `meta/global` and `crypto/keys`.
                    Sync15ClientResponse::Error(ErrorResponse::NotFound { .. }) => {
                        Ok(FreshStartRequired { config })
                    }
                    other => Err(other.create_storage_error().into()),
                }
            }

            InitialWithInfo {
                config,
                collections,
            } => {
                match self.client.fetch_meta_global()? {
                    Sync15ClientResponse::Success {
                        record: mut global,
                        last_modified: mut global_timestamp,
                        ..
                    } => {
                        // If the server has a newer storage version, we can't
                        // sync until our client is updated.
                        if global.storage_version > STORAGE_VERSION {
                            return Err(ErrorKind::ClientUpgradeRequired.into());
                        }

                        // If the server has an older storage version, wipe and
                        // reupload.
                        if global.storage_version < STORAGE_VERSION {
                            Ok(FreshStartRequired { config })
                        } else {
                            log::info!("Have info/collections and meta/global. Computing new engine states");
                            let initial_global_declined: HashSet<String> =
                                global.declined.iter().cloned().collect();
                            let result = compute_engine_states(EngineStateInput {
                                local_declined: self.pgs.get_declined().iter().cloned().collect(),
                                user_changes: self.engine_updates.cloned().unwrap_or_default(),
                                remote: Some(RemoteEngineState {
                                    declined: initial_global_declined.clone(),
                                    info_collections: collections.keys().cloned().collect(),
                                }),
                            });
                            // Persist the new declined.
                            self.pgs
                                .set_declined(result.declined.iter().cloned().collect());
                            // If the declined engines differ from remote, fix that.
                            let fixed_declined = if result.declined != initial_global_declined {
                                global.declined = result.declined.iter().cloned().collect();
                                log::info!(
                                    "Uploading new declined {:?} to meta/global with timestamp {:?}",
                                    global.declined,
                                    global_timestamp,
                                );
                                true
                            } else {
                                false
                            };
                            // If there are missing syncIds, we need to fix those as well
                            let fixed_ids = if fixup_meta_global(&mut global) {
                                log::info!(
                                    "Uploading corrected meta/global with timestamp {:?}",
                                    global_timestamp,
                                );
                                true
                            } else {
                                false
                            };

                            if fixed_declined || fixed_ids {
                                global_timestamp =
                                    self.client.put_meta_global(global_timestamp, &global)?;
                                log::debug!("new global_timestamp: {:?}", global_timestamp);
                            }
                            // Update the set of changes needed.
                            if self.changes_needed.is_some() {
                                // Should never happen (we prevent state machine
                                // loops elsewhere) but if it did, the info is stale
                                // anyway.
                                log::warn!("Already have a set of changes needed, Overwriting...");
                            }
                            self.changes_needed = Some(result.changes_needed);
                            Ok(InitialWithMetaGlobal {
                                config,
                                collections,
                                global,
                                global_timestamp,
                            })
                        }
                    }
                    Sync15ClientResponse::Error(ErrorResponse::NotFound { .. }) => {
                        Ok(FreshStartRequired { config })
                    }
                    other => Err(other.create_storage_error().into()),
                }
            }

            InitialWithMetaGlobal {
                config,
                collections,
                global,
                global_timestamp,
            } => {
                // Now try and get keys etc - if we fresh-start we'll re-use declined.
                match self.client.fetch_crypto_keys()? {
                    Sync15ClientResponse::Success {
                        record,
                        last_modified,
                        ..
                    } => {
                        // Note that collection/keys is itself a bso, so the
                        // json body also carries the timestamp. If they aren't
                        // identical something has screwed up and we should die.
                        assert_eq!(last_modified, record.modified);
                        let state = GlobalState {
                            config,
                            collections,
                            global,
                            global_timestamp,
                            keys: record,
                        };
                        Ok(Ready { state })
                    }
                    // If the server doesn't have a `crypto/keys`, start over
                    // and reupload our `meta/global` and `crypto/keys`.
                    Sync15ClientResponse::Error(ErrorResponse::NotFound { .. }) => {
                        Ok(FreshStartRequired { config })
                    }
                    other => Err(other.create_storage_error().into()),
                }
            }

            // We've got old state that's likely to be OK.
            // We keep things simple here - if there's evidence of a new/missing
            // meta/global or new/missing keys we just restart from scratch.
            WithPreviousState { old_state } => match self.client.fetch_info_collections()? {
                Sync15ClientResponse::Success {
                    record: collections,
                    ..
                } => Ok(
                    if self.engine_updates.is_none()
                        && is_same_timestamp(old_state.global_timestamp, &collections, "meta")
                        && is_same_timestamp(old_state.keys.modified, &collections, "crypto")
                    {
                        Ready {
                            state: GlobalState {
                                collections,
                                ..old_state
                            },
                        }
                    } else {
                        InitialWithConfig {
                            config: old_state.config,
                        }
                    },
                ),
                _ => Ok(InitialWithConfig {
                    config: old_state.config,
                }),
            },

            Ready { state } => Ok(Ready { state }),

            FreshStartRequired { config } => {
                // Wipe the server.
                log::info!("Fresh start: wiping remote");
                self.client.wipe_all_remote()?;

                // Upload a fresh `meta/global`...
                log::info!("Uploading meta/global");
                let computed = compute_engine_states(EngineStateInput {
                    local_declined: self.pgs.get_declined().iter().cloned().collect(),
                    user_changes: self.engine_updates.cloned().unwrap_or_default(),
                    remote: None,
                });
                self.pgs
                    .set_declined(computed.declined.iter().cloned().collect());

                self.changes_needed = Some(computed.changes_needed);

                let new_global = new_global(self.pgs)?;

                self.client
                    .put_meta_global(ServerTimestamp::default(), &new_global)?;

                // ...And a fresh `crypto/keys`.
                let new_keys = CollectionKeys::new_random()?.to_encrypted_bso(&self.root_key)?;
                self.client
                    .put_crypto_keys(ServerTimestamp::default(), &new_keys)?;

                // TODO(lina): Can we pass along server timestamps from the PUTs
                // above, and avoid re-fetching the `m/g` and `c/k` we just
                // uploaded?
                // OTOH(mark): restarting the state machine keeps life simple and rare.
                Ok(InitialWithConfig { config })
            }
        }
    }

    /// Runs through the state machine to the ready state.
    pub fn run_to_ready(&mut self, state: Option<GlobalState>) -> error::Result<GlobalState> {
        let mut s = match state {
            Some(old_state) => WithPreviousState { old_state },
            None => Initial,
        };
        loop {
            self.interruptee.err_if_interrupted()?;
            let label = &s.label();
            log::trace!("global state: {:?}", label);
            match s {
                Ready { state } => {
                    self.sequence.push(label);
                    return Ok(state);
                }
                // If we already started over once before, we're likely in a
                // cycle, and should try again later. Intermediate states
                // aren't a problem, just the initial ones.
                FreshStartRequired { .. } | WithPreviousState { .. } | Initial => {
                    if self.sequence.contains(&label) {
                        // Is this really the correct error?
                        return Err(ErrorKind::SetupRace.into());
                    }
                }
                _ => {
                    if !self.allowed_states.contains(&label) {
                        return Err(ErrorKind::SetupRequired.into());
                    }
                }
            };
            self.sequence.push(label);
            s = self.advance(s)?;
        }
    }
}

/// States in the remote setup process.
/// TODO(lina): Add link once #56 is merged.
#[derive(Debug)]
#[allow(clippy::large_enum_variant)]
enum SetupState {
    // These "Initial" states are only ever used when starting from scratch.
    Initial,
    InitialWithConfig {
        config: InfoConfiguration,
    },
    InitialWithInfo {
        config: InfoConfiguration,
        collections: InfoCollections,
    },
    InitialWithMetaGlobal {
        config: InfoConfiguration,
        collections: InfoCollections,
        global: MetaGlobalRecord,
        global_timestamp: ServerTimestamp,
    },
    WithPreviousState {
        old_state: GlobalState,
    },
    Ready {
        state: GlobalState,
    },
    FreshStartRequired {
        config: InfoConfiguration,
    },
}

impl SetupState {
    fn label(&self) -> &'static str {
        match self {
            Initial { .. } => "Initial",
            InitialWithConfig { .. } => "InitialWithConfig",
            InitialWithInfo { .. } => "InitialWithInfo",
            InitialWithMetaGlobal { .. } => "InitialWithMetaGlobal",
            Ready { .. } => "Ready",
            WithPreviousState { .. } => "WithPreviousState",
            FreshStartRequired { .. } => "FreshStartRequired",
        }
    }
}

/// Whether we should skip fetching an item. Used when we already have timestamps
/// and want to check if we should reuse our existing state. The state's fairly
/// cheap to recreate and very bad to use if it is wrong, so we insist on the
/// *exact* timestamp matching and not a simple "later than" check.
fn is_same_timestamp(local: ServerTimestamp, collections: &InfoCollections, key: &str) -> bool {
    collections.get(key).map_or(false, |ts| local == *ts)
}

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

    use crate::bso_record::{BsoRecord, EncryptedBso, EncryptedPayload, Payload};
    use crate::record_types::CryptoKeysRecord;
    use interrupt_support::NeverInterrupts;

    struct InMemoryClient {
        info_configuration: error::Result<Sync15ClientResponse<InfoConfiguration>>,
        info_collections: error::Result<Sync15ClientResponse<InfoCollections>>,
        meta_global: error::Result<Sync15ClientResponse<MetaGlobalRecord>>,
        crypto_keys: error::Result<Sync15ClientResponse<BsoRecord<EncryptedPayload>>>,
    }

    impl SetupStorageClient for InMemoryClient {
        fn fetch_info_configuration(
            &self,
        ) -> error::Result<Sync15ClientResponse<InfoConfiguration>> {
            match &self.info_configuration {
                Ok(client_response) => Ok(client_response.clone()),
                Err(_) => Ok(Sync15ClientResponse::Error(ErrorResponse::ServerError {
                    status: 500,
                    route: "test/path".into(),
                })),
            }
        }

        fn fetch_info_collections(&self) -> error::Result<Sync15ClientResponse<InfoCollections>> {
            match &self.info_collections {
                Ok(collections) => Ok(collections.clone()),
                Err(_) => Ok(Sync15ClientResponse::Error(ErrorResponse::ServerError {
                    status: 500,
                    route: "test/path".into(),
                })),
            }
        }

        fn fetch_meta_global(&self) -> error::Result<Sync15ClientResponse<MetaGlobalRecord>> {
            match &self.meta_global {
                Ok(global) => Ok(global.clone()),
                // TODO(lina): Special handling for 404s, we want to ensure we
                // handle missing keys and other server errors correctly.
                Err(_) => Ok(Sync15ClientResponse::Error(ErrorResponse::ServerError {
                    status: 500,
                    route: "test/path".into(),
                })),
            }
        }

        fn put_meta_global(
            &self,
            xius: ServerTimestamp,
            global: &MetaGlobalRecord,
        ) -> error::Result<ServerTimestamp> {
            // Ensure that the meta/global record we uploaded is "fixed up"
            assert!(DEFAULT_ENGINES
                .iter()
                .filter(|e| e.0 != "logins")
                .all(|&(k, _v)| global.engines.contains_key(k)));
            assert!(!global.engines.contains_key("logins"));
            assert_eq!(global.declined, vec!["logins".to_string()]);
            // return a different timestamp.
            Ok(ServerTimestamp(xius.0 + 1))
        }

        fn fetch_crypto_keys(&self) -> error::Result<Sync15ClientResponse<EncryptedBso>> {
            match &self.crypto_keys {
                Ok(keys) => Ok(keys.clone()),
                // TODO(lina): Same as above, for 404s.
                Err(_) => Ok(Sync15ClientResponse::Error(ErrorResponse::ServerError {
                    status: 500,
                    route: "test/path".into(),
                })),
            }
        }

        fn put_crypto_keys(
            &self,
            xius: ServerTimestamp,
            _keys: &EncryptedBso,
        ) -> error::Result<()> {
            assert_eq!(xius, ServerTimestamp(888_800));
            Err(ErrorKind::StorageHttpError(ErrorResponse::ServerError {
                status: 500,
                route: "crypto/keys".to_string(),
            })
            .into())
        }

        fn wipe_all_remote(&self) -> error::Result<()> {
            Ok(())
        }
    }

    fn mocked_success_ts<T>(t: T, ts: i64) -> error::Result<Sync15ClientResponse<T>> {
        Ok(Sync15ClientResponse::Success {
            status: 200,
            record: t,
            last_modified: ServerTimestamp(ts),
            route: "test/path".into(),
        })
    }

    fn mocked_success<T>(t: T) -> error::Result<Sync15ClientResponse<T>> {
        mocked_success_ts(t, 0)
    }

    // for tests, we want a BSO with a specific timestamp, which we never
    // need in non-test-code as the timestamp comes from the server.
    impl CollectionKeys {
        pub fn to_encrypted_bso_with_timestamp(
            &self,
            root_key: &KeyBundle,
            modified: ServerTimestamp,
        ) -> error::Result<EncryptedBso> {
            let record = CryptoKeysRecord {
                id: "keys".into(),
                collection: "crypto".into(),
                default: self.default.to_b64_array(),
                collections: self
                    .collections
                    .iter()
                    .map(|kv| (kv.0.clone(), kv.1.to_b64_array()))
                    .collect(),
            };
            let mut bso =
                crate::CleartextBso::from_payload(Payload::from_record(record)?, "crypto");
            bso.modified = modified;
            Ok(bso.encrypt(root_key)?)
        }
    }

    #[test]
    fn test_state_machine_ready_from_empty() {
        let root_key = KeyBundle::new_random().unwrap();
        let keys = CollectionKeys {
            timestamp: ServerTimestamp(123_400),
            default: KeyBundle::new_random().unwrap(),
            collections: HashMap::new(),
        };
        let mg = MetaGlobalRecord {
            sync_id: "syncIDAAAAAA".into(),
            storage_version: 5usize,
            engines: vec![(
                "bookmarks",
                MetaGlobalEngine {
                    version: 1usize,
                    sync_id: "syncIDBBBBBB".into(),
                },
            )]
            .into_iter()
            .map(|(key, value)| (key.to_owned(), value))
            .collect(),
            // We ensure that the record we upload doesn't have a logins record.
            declined: vec!["logins".to_string()],
        };
        let client = InMemoryClient {
            info_configuration: mocked_success(InfoConfiguration::default()),
            info_collections: mocked_success(InfoCollections::new(
                vec![("meta", 123_456), ("crypto", 145_000)]
                    .into_iter()
                    .map(|(key, value)| (key.to_owned(), ServerTimestamp(value)))
                    .collect(),
            )),
            meta_global: mocked_success_ts(mg, 999_000),
            crypto_keys: mocked_success_ts(
                keys.to_encrypted_bso_with_timestamp(&root_key, ServerTimestamp(888_000))
                    .expect("should always work in this test"),
                888_000,
            ),
        };
        let mut pgs = PersistedGlobalState::V2 { declined: None };

        let mut state_machine =
            SetupStateMachine::for_full_sync(&client, &root_key, &mut pgs, None, &NeverInterrupts);
        assert!(
            state_machine.run_to_ready(None).is_ok(),
            "Should drive state machine to ready"
        );
        assert_eq!(
            state_machine.sequence,
            vec![
                "Initial",
                "InitialWithConfig",
                "InitialWithInfo",
                "InitialWithMetaGlobal",
                "Ready",
            ],
            "Should cycle through all states"
        );
    }

    #[test]
    fn test_from_previous_state_declined() {
        let _ = env_logger::try_init();
        // The state-machine sequence where we didn't use the previous state
        // (ie, where the state machine restarted)
        let sm_seq_restarted = vec![
            "WithPreviousState",
            "InitialWithConfig",
            "InitialWithInfo",
            "InitialWithMetaGlobal",
            "Ready",
        ];
        // The state-machine sequence where we used the previous state.
        let sm_seq_used_previous = vec!["WithPreviousState", "Ready"];

        // do the actual test.
        fn do_test(
            client: &dyn SetupStorageClient,
            root_key: &KeyBundle,
            mut pgs: &mut PersistedGlobalState,
            engine_updates: Option<&HashMap<String, bool>>,
            old_state: GlobalState,
            expected_states: &[&str],
        ) {
            let mut state_machine = SetupStateMachine::for_full_sync(
                client,
                root_key,
                &mut pgs,
                engine_updates,
                &NeverInterrupts,
            );
            assert!(
                state_machine.run_to_ready(Some(old_state)).is_ok(),
                "Should drive state machine to ready"
            );
            assert_eq!(state_machine.sequence, expected_states);
        }

        // and all the complicated setup...
        let ts_metaglobal = 123_456;
        let ts_keys = 145_000;
        let root_key = KeyBundle::new_random().unwrap();
        let keys = CollectionKeys {
            timestamp: ServerTimestamp(ts_keys + 1),
            default: KeyBundle::new_random().unwrap(),
            collections: HashMap::new(),
        };
        let mg = MetaGlobalRecord {
            sync_id: "syncIDAAAAAA".into(),
            storage_version: 5usize,
            engines: vec![(
                "bookmarks",
                MetaGlobalEngine {
                    version: 1usize,
                    sync_id: "syncIDBBBBBB".into(),
                },
            )]
            .into_iter()
            .map(|(key, value)| (key.to_owned(), value))
            .collect(),
            // We ensure that the record we upload doesn't have a logins record.
            declined: vec!["logins".to_string()],
        };
        let collections = InfoCollections::new(
            vec![("meta", ts_metaglobal), ("crypto", ts_keys)]
                .into_iter()
                .map(|(key, value)| (key.to_owned(), ServerTimestamp(value)))
                .collect(),
        );
        let client = InMemoryClient {
            info_configuration: mocked_success(InfoConfiguration::default()),
            info_collections: mocked_success(collections.clone()),
            meta_global: mocked_success_ts(mg.clone(), ts_metaglobal),
            crypto_keys: mocked_success_ts(
                keys.to_encrypted_bso_with_timestamp(&root_key, ServerTimestamp(ts_keys))
                    .expect("should always work in this test"),
                ts_keys,
            ),
        };

        // First a test where the "previous" global state is OK to reuse.
        {
            let mut pgs = PersistedGlobalState::V2 { declined: None };
            // A "previous" global state.
            let old_state = GlobalState {
                config: InfoConfiguration::default(),
                collections: collections.clone(),
                global: mg.clone(),
                global_timestamp: ServerTimestamp(ts_metaglobal),
                keys: keys
                    .to_encrypted_bso_with_timestamp(&root_key, ServerTimestamp(ts_keys))
                    .expect("should always work in this test"),
            };
            do_test(
                &client,
                &root_key,
                &mut pgs,
                None,
                old_state,
                &sm_seq_used_previous,
            );
        }

        // Now where the meta/global record on the server is later.
        {
            let mut pgs = PersistedGlobalState::V2 { declined: None };
            // A "previous" global state.
            let old_state = GlobalState {
                config: InfoConfiguration::default(),
                collections: collections.clone(),
                global: mg.clone(),
                global_timestamp: ServerTimestamp(999_999),
                keys: keys
                    .to_encrypted_bso_with_timestamp(&root_key, ServerTimestamp(ts_keys))
                    .expect("should always work in this test"),
            };
            do_test(
                &client,
                &root_key,
                &mut pgs,
                None,
                old_state,
                &sm_seq_restarted,
            );
        }

        // Where keys on the server is later.
        {
            let mut pgs = PersistedGlobalState::V2 { declined: None };
            // A "previous" global state.
            let old_state = GlobalState {
                config: InfoConfiguration::default(),
                collections: collections.clone(),
                global: mg.clone(),
                global_timestamp: ServerTimestamp(ts_metaglobal),
                keys: keys
                    .to_encrypted_bso_with_timestamp(&root_key, ServerTimestamp(999_999))
                    .expect("should always work in this test"),
            };
            do_test(
                &client,
                &root_key,
                &mut pgs,
                None,
                old_state,
                &sm_seq_restarted,
            );
        }

        // Where there are engine-state changes.
        {
            let mut pgs = PersistedGlobalState::V2 { declined: None };
            // A "previous" global state.
            let old_state = GlobalState {
                config: InfoConfiguration::default(),
                collections,
                global: mg,
                global_timestamp: ServerTimestamp(ts_metaglobal),
                keys: keys
                    .to_encrypted_bso_with_timestamp(&root_key, ServerTimestamp(ts_keys))
                    .expect("should always work in this test"),
            };
            let mut engine_updates = HashMap::<String, bool>::new();
            engine_updates.insert("logins".to_string(), false);
            do_test(
                &client,
                &root_key,
                &mut pgs,
                Some(&engine_updates),
                old_state,
                &sm_seq_restarted,
            );
            let declined = match pgs {
                PersistedGlobalState::V2 { declined: d } => d,
            };
            // and check we now consider logins as declined.
            assert_eq!(declined, Some(vec!["logins".to_string()]));
        }
    }

    fn string_set(s: &[&str]) -> HashSet<String> {
        s.iter().map(ToString::to_string).collect()
    }
    fn string_map<T: Clone>(s: &[(&str, T)]) -> HashMap<String, T> {
        s.iter().map(|v| (v.0.to_string(), v.1.clone())).collect()
    }
    #[test]
    fn test_engine_states() {
        assert_eq!(
            compute_engine_states(EngineStateInput {
                local_declined: string_set(&["foo", "bar"]),
                remote: None,
                user_changes: Default::default(),
            }),
            EngineStateOutput {
                declined: string_set(&["foo", "bar"]),
                // No wipes, no resets
                changes_needed: Default::default(),
            }
        );
        assert_eq!(
            compute_engine_states(EngineStateInput {
                local_declined: string_set(&["foo", "bar"]),
                remote: Some(RemoteEngineState {
                    declined: string_set(&["foo"]),
                    info_collections: string_set(&["bar"])
                }),
                user_changes: Default::default(),
            }),
            EngineStateOutput {
                // Now we have `foo`.
                declined: string_set(&["foo"]),
                // No wipes, no resets, should just be a local update.
                changes_needed: Default::default(),
            }
        );
        assert_eq!(
            compute_engine_states(EngineStateInput {
                local_declined: string_set(&["foo", "bar"]),
                remote: Some(RemoteEngineState {
                    declined: string_set(&["foo", "bar", "quux"]),
                    info_collections: string_set(&[])
                }),
                user_changes: Default::default(),
            }),
            EngineStateOutput {
                // Now we have `foo`.
                declined: string_set(&["foo", "bar", "quux"]),
                changes_needed: EngineChangesNeeded {
                    // Should reset `quux`.
                    local_resets: string_set(&["quux"]),
                    // No wipes, though.
                    remote_wipes: string_set(&[]),
                }
            }
        );
        assert_eq!(
            compute_engine_states(EngineStateInput {
                local_declined: string_set(&["bar", "baz"]),
                remote: Some(RemoteEngineState {
                    declined: string_set(&["bar", "baz",]),
                    info_collections: string_set(&["quux"])
                }),
                // Change a declined engine to undeclined.
                user_changes: string_map(&[("bar", true)]),
            }),
            EngineStateOutput {
                declined: string_set(&["baz"]),
                // No wipes, just undecline it.
                changes_needed: Default::default()
            }
        );
        assert_eq!(
            compute_engine_states(EngineStateInput {
                local_declined: string_set(&["bar", "baz"]),
                remote: Some(RemoteEngineState {
                    declined: string_set(&["bar", "baz"]),
                    info_collections: string_set(&["foo"])
                }),
                // Change an engine which exists remotely to declined.
                user_changes: string_map(&[("foo", false)]),
            }),
            EngineStateOutput {
                declined: string_set(&["baz", "bar", "foo"]),
                // No wipes, just undecline it.
                changes_needed: EngineChangesNeeded {
                    // Should reset our local foo
                    local_resets: string_set(&["foo"]),
                    // And wipe the server.
                    remote_wipes: string_set(&["foo"]),
                }
            }
        );
    }
}