//! matrix-sdk `Client` setup for the daemon: take the per-agent access
//! token [`crate::credential`] resolved, probe `whoami` to recover the
//! agent's matrix `user_id` + `device_id`, restore the matrix-sdk
//! session, return the Client ready to start sync.
//!
//! 🩸 The token arrives as a [`Token`] and never as a path this module
//! reads — where it came from is [`crate::credential`]'s question, and the
//! only thing said about it here is its [`crate::credential::Origin`].
//!
//! No OAuth dance / cross-signing setup (in contrast to damocles-daemon's
//! ccc.de connection): for the swarm's tuwunel the swarm already minted the
//! token + user/device as its appservice and handed us the bearer. matrix-sdk's `restore_session` with a constructed
//! `MatrixSession` skips the login flow entirely.
//!
//! E2EE is enabled via `with_encryption_settings`. Crypto keys are persisted
//! in the sqlite store under `state_dir` (survives container restarts, lost on
//! `--purge`).
//!
//! Cross-signing is bootstrapped best-effort after session restore
//! (`ensure_cross_signing`) so the agent's device stops showing as
//! "unverified" in other users' Matrix clients: the in-hive tuwunel accepts
//! the initial device-signing-key upload on the bearer token alone (no UIAA
//! re-auth). A homeserver that DID require UIAA just fails the call, which is
//! swallowed — the session stays exactly as unverified as before.
//!
//! Server-side key backup is turned on or recovered by `ensure_recovery`, with
//! the passphrase `swarm-controller` mints per account, so a crypto store lost
//! to a purge or a token reset gets its history back.

use std::path::Path;

use anyhow::{Context, Result, anyhow, bail};
use matrix_sdk::{
    Client, SessionMeta, SessionTokens,
    authentication::matrix::MatrixSession,
    encryption::{BackupDownloadStrategy, EncryptionSettings},
    ruma::{OwnedDeviceId, OwnedUserId},
};
use serde::Deserialize;
use tokio::fs;

use crate::credential::{Passphrase, Token};

/// Sentinel returned when `build_and_restore` detects that the token is
/// permanently invalid (`M_UNKNOWN_TOKEN`). The token has already been
/// discarded ([`Token::discard_stale`]). Retrying the same token at once
/// won't help — the account needs a new one, which the daemon's periodic
/// retry of a down secondary picks up.
///
/// Distinct from the general `anyhow::Error` path so callers can use
/// `err.downcast_ref::<PermanentBringUpError>()` to distinguish "retry
/// won't help" from a transient network/DNS/5xx failure.
#[derive(Debug)]
pub struct PermanentBringUpError(pub String);

impl std::fmt::Display for PermanentBringUpError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(&self.0)
    }
}

impl std::error::Error for PermanentBringUpError {}

/// Subset of the `/_matrix/client/v3/account/whoami` response we care
/// about. matrix-spec field names; `device_id` is optional per spec
/// (servers MAY omit it for legacy bearer scopes) but tuwunel always
/// returns it.
#[derive(Debug, Deserialize)]
struct WhoamiResponse {
    user_id: String,
    device_id: Option<String>,
}

/// Build + restore a matrix-sdk `Client` for the per-agent bearer
/// `token`. The Client points at `homeserver`, persists its sqlite cache
/// under `state_dir`, and is ready for sync once returned.
///
/// Steps:
/// 1. Plain reqwest GET to `/_matrix/client/v3/account/whoami` with
///    the bearer — this gives us back the matrix `user_id` +
///    `device_id` (the registration response had them but only the
///    token was kept; whoami is the cheapest recovery path
///    and avoids matrix-sdk's circular requirement of needing a
///    session to call whoami).
/// 2. Build the real Client with the sqlite store + `restore_session`
///    using a synthetic `MatrixSession`.
///
/// # Errors
///
/// Returns an error if the `whoami` request fails, or if the matrix-sdk
/// client fails to build or restore the session.
pub async fn build_and_restore(
    homeserver: &str,
    token: &Token,
    state_dir: &Path,
    is_primary: bool,
) -> Result<Client> {
    let (user_id, device_id) = match whoami(homeserver, token.expose()).await {
        Ok(ids) => ids,
        Err(e) => {
            let msg = format!("{e:#}");
            if msg.contains("M_UNKNOWN_TOKEN") {
                // Homeserver rejected our token — stale session after a homeserver
                // state wipe or token expiry. Discard it so we don't loop on it
                // (which for a store-held credential is a log line and nothing
                // else — see `Token::discard_stale`). The rest of the handling
                // depends on whether this is the primary (hive-internal) account
                // or a secondary one, because a single bad secondary token must
                // NOT take down the whole daemon (and with it every healthy
                // account).
                token.discard_stale().await;
                if is_primary {
                    tracing::warn!(
                        credential = %token.origin(),
                        "matrix token rejected (M_UNKNOWN_TOKEN); discarding stale token"
                    );
                    // Primary: also drop the matrix-sdk sqlite state keyed to the
                    // now-invalid session, then exit 0; the swarm's backfill
                    // re-mints the token and systemd restarts us once it
                    // exists (store re-check timer, or the path watcher). Exit 0 (not
                    // Err) keeps systemd's Restart=on-failure from looping; the
                    // call site is before any tasks are spawned so there's
                    // nothing to clean up.
                    if let Err(re) = fs::remove_dir_all(state_dir).await {
                        tracing::warn!(
                            path = %state_dir.display(),
                            err = %re,
                            "failed to remove sdk state dir; next startup may fail with stale state"
                        );
                    }
                    std::process::exit(0);
                }
                // Secondary: a file token is gone, a store token is untouched; the
                // daemon tries the account again later and reads the token afresh.
                // The sdk state stays in place in case the operator re-provisions a
                // token for the same device.
                // Return a PermanentBringUpError so the caller can distinguish
                // "retrying now won't help" from a transient network/DNS failure.
                // Every try of a down secondary lands here, so the warning is the
                // caller's, once per outage.
                tracing::debug!(
                    credential = %token.origin(),
                    "matrix token rejected (M_UNKNOWN_TOKEN); discarded stale token"
                );
                return Err(anyhow::Error::new(PermanentBringUpError(
                    "matrix token rejected (M_UNKNOWN_TOKEN); discarded stale token, leaving account down".into(),
                )));
            }
            return Err(e);
        }
    };

    fs::create_dir_all(state_dir)
        .await
        .with_context(|| format!("mkdir matrix state dir {}", state_dir.display()))?;
    let client = Client::builder()
        .homeserver_url(homeserver)
        .sqlite_store(state_dir, None)
        .with_encryption_settings(EncryptionSettings {
            backup_download_strategy: BackupDownloadStrategy::OneShot,
            ..EncryptionSettings::default()
        })
        .build()
        .await
        .with_context(|| format!("build matrix client for {homeserver}"))?;
    let session = MatrixSession {
        meta: SessionMeta { user_id, device_id },
        tokens: SessionTokens {
            access_token: token.expose().to_owned(),
            refresh_token: None,
        },
    };
    client
        .restore_session(session)
        .await
        .context("restore matrix session")?;
    tracing::info!(
        user = %client.user_id().map(ToString::to_string).unwrap_or_default(),
        device = %client.device_id().map(ToString::to_string).unwrap_or_default(),
        "matrix session restored"
    );
    Ok(client)
}

/// Bare-reqwest whoami probe — used at startup to recover the
/// `user_id` + `device_id` the registration response carried but
/// hive-c0re didn't persist alongside the access token. Cheaper than
/// teaching the hive-c0re side to persist them, plus matches what a
/// fresh deployment with a hand-rolled token (`HIVE_MATRIX_TOKEN_FILE`
/// pointing somewhere unexpected) needs anyway.
async fn whoami(homeserver: &str, token: &str) -> Result<(OwnedUserId, OwnedDeviceId)> {
    let url = format!("{homeserver}/_matrix/client/v3/account/whoami");
    let resp = reqwest::Client::builder()
        .timeout(std::time::Duration::from_secs(10))
        .build()
        .context("build whoami reqwest client")?
        .get(&url)
        .bearer_auth(token)
        .send()
        .await
        .with_context(|| format!("GET {url}"))?;
    let status = resp.status();
    if !status.is_success() {
        let body = resp.text().await.unwrap_or_default();
        return Err(anyhow!("whoami GET {url} → HTTP {status}, body: {body}"));
    }
    let body: WhoamiResponse = resp.json().await.context("parse whoami response")?;
    let user_id: OwnedUserId = body
        .user_id
        .parse()
        .with_context(|| format!("invalid user_id in whoami: {}", body.user_id))?;
    let device_id_raw = body
        .device_id
        .ok_or_else(|| anyhow!("whoami response missing device_id"))?;
    let device_id: OwnedDeviceId = device_id_raw.into();
    Ok((user_id, device_id))
}

/// Best-effort: bootstrap this account's cross-signing identity so its
/// device stops showing as "unverified" in other users' Matrix clients.
///
/// `bootstrap_cross_signing_if_needed(None)` is idempotent — it queries the
/// account's existing keys and only uploads the master / self-signing /
/// user-signing key set when no cross-signing identity exists yet. That
/// upload also self-signs the current device, which is what actually clears
/// the unverified warning. On a restart with the identity already present
/// it's a no-op.
///
/// The `None` is the UIAA auth: the in-hive tuwunel accepts the initial
/// `device_signing/upload` on the bearer token alone (no interactive
/// re-auth). If a homeserver required UIAA the call returns a `UiaaResponse`
/// error we can't satisfy with a bare bearer token — so this is best-effort:
/// the failure is logged and swallowed, leaving the session no worse off than
/// before. Never breaks account bring-up.
///
/// This only signs the *current* device against a freshly-bootstrapped
/// identity. A device under an already existing identity is a no-op here; it
/// is signed by [`ensure_recovery`]'s `recover`, which imports the
/// self-signing key from secret storage, and stays unverified for an account
/// with no recovery passphrase.
pub async fn ensure_cross_signing(client: &Client, account: &str) {
    match client
        .encryption()
        .bootstrap_cross_signing_if_needed(None)
        .await
    {
        Ok(()) => {
            tracing::info!(
                account,
                "matrix cross-signing ensured (device self-verified)"
            );
        }
        Err(e) => {
            tracing::warn!(
                account,
                error = %format!("{e:#}"),
                "matrix cross-signing bootstrap failed; session stays unverified (non-fatal)"
            );
        }
    }
}

/// What [`ensure_recovery`] did.
enum Backup {
    /// This device was already connected to the account's backup.
    AlreadyOn,
    /// The server had no backup; one was created, with secret storage that
    /// `passphrase` opens.
    Enabled,
    /// The server had a backup; the keys secret storage holds for it, and
    /// for cross-signing if it holds those, were imported.
    Restored,
}

/// Best-effort: turn on server-side key backup for this account, or recover
/// from the backup it already has, with the account's recovery `passphrase`.
///
/// Run after [`ensure_cross_signing`], so a newly bootstrapped identity's
/// private keys are local when `enable` exports them into secret storage, and
/// an existing identity is left for `recover` to import. After a recover the
/// room keys download in the background (`BackupDownloadStrategy::OneShot`).
///
/// Every failure is logged and swallowed, as in [`ensure_cross_signing`]: the
/// account comes up as it would have without backup. That includes secret
/// storage this passphrase does not open, which is never replaced: with a
/// backup, `recover` fails; without one, this refuses.
pub async fn ensure_recovery(client: &Client, account: &str, passphrase: &Passphrase) {
    match recover_or_enable(client, passphrase.expose()).await {
        Ok(Backup::AlreadyOn) => {
            tracing::debug!(account, "matrix key backup already on for this device");
        }
        Ok(Backup::Enabled) => tracing::info!(
            account,
            passphrase = %passphrase.path(),
            "matrix recovery enabled: server-side key backup created"
        ),
        Ok(Backup::Restored) => tracing::info!(
            account,
            passphrase = %passphrase.path(),
            "matrix recovery: recovered from the server-side key backup; room keys download in the background"
        ),
        Err(e) => tracing::warn!(
            account,
            passphrase = %passphrase.path(),
            error = %format!("{e:#}"),
            "matrix recovery failed; key backup stays off (non-fatal)"
        ),
    }
}

/// The homeserver and device calls [`recover_or_enable`] decides from, so a
/// test can stand in for matrix-sdk.
trait KeyBackup {
    /// Wait for the e2ee tasks a restored client starts in the background.
    async fn settle(&self);
    /// Whether this device is already connected to the account's backup.
    async fn on_this_device(&self) -> bool;
    /// Whether the homeserver holds a key backup version.
    async fn backup_on_server(&self) -> Result<bool>;
    /// Whether the account has a default secret-storage key.
    async fn secret_storage_on_server(&self) -> Result<bool>;
    /// Open secret storage with `passphrase` and import what it holds.
    async fn recover(&self, passphrase: &str) -> Result<()>;
    /// Create a backup and new secret storage that `passphrase` opens.
    async fn enable(&self, passphrase: &str) -> Result<()>;
}

impl KeyBackup for Client {
    async fn settle(&self) {
        self.encryption().wait_for_e2ee_initialization_tasks().await;
    }

    async fn on_this_device(&self) -> bool {
        self.encryption().backups().are_enabled().await
    }

    async fn backup_on_server(&self) -> Result<bool> {
        Ok(self.encryption().backups().fetch_exists_on_server().await?)
    }

    async fn secret_storage_on_server(&self) -> Result<bool> {
        Ok(self.encryption().secret_storage().is_enabled().await?)
    }

    async fn recover(&self, passphrase: &str) -> Result<()> {
        Ok(self.encryption().recovery().recover(passphrase).await?)
    }

    async fn enable(&self, passphrase: &str) -> Result<()> {
        // The recovery key `enable` returns is not kept: the passphrase opens
        // the same secret storage.
        self.encryption()
            .recovery()
            .enable()
            .with_passphrase(passphrase)
            .await?;
        Ok(())
    }
}

/// The body of [`ensure_recovery`], with its outcome returned rather than
/// logged.
///
/// ⚠️ `enable` makes a new secret-storage key and sets it as the account's
/// default, whatever default was there. With no backup but secret storage
/// present, this refuses rather than enable: that default key is someone
/// else's, and replacing it locks their recovery key out.
async fn recover_or_enable(account: &impl KeyBackup, passphrase: &str) -> Result<Backup> {
    // A device restored from its own store reconnects to the backup in a
    // background task; asking before it finishes says no.
    account.settle().await;
    if account.on_this_device().await {
        return Ok(Backup::AlreadyOn);
    }
    if account
        .backup_on_server()
        .await
        .context("asking the homeserver for the account's key backup")?
    {
        account
            .recover(passphrase)
            .await
            .context("recovering from the key backup")?;
        return Ok(Backup::Restored);
    }
    if account
        .secret_storage_on_server()
        .await
        .context("asking the homeserver for the account's secret storage")?
    {
        bail!(
            "the account has secret storage but no key backup; not enabling, \
             which would replace a default secret-storage key this daemon did not create"
        );
    }
    account
        .enable(passphrase)
        .await
        .context("enabling key backup")?;
    Ok(Backup::Enabled)
}

/// Best-effort: set this account's matrix avatar from the rasterized icon
/// PNG. The path comes from `HIVE_ICON_PNG` (a nix-built derivation the
/// harness forwards into the daemon env; absent when no icon resolves).
/// Idempotent via a per-account `avatar-icon-hash` file in the account's
/// sdk `state_dir` — a re-upload only happens when the icon bytes change,
/// so daemon restarts don't re-spam the homeserver.
///
/// This replaces the old `matrix-avatar-sync` systemd curl oneshot: the
/// daemon already holds an authenticated `Client` pointed at the correct
/// homeserver, so it uploads over the live connection — no hardcoded URL,
/// no token re-read, no token-file globbing. Any failure is logged and
/// swallowed: avatar trouble must never break account bring-up or sync.
pub async fn sync_avatar(client: &Client, state_dir: &Path, account: &str) {
    let Ok(png_path) = std::env::var("HIVE_ICON_PNG") else {
        return; // no icon forwarded → nothing to sync
    };
    let bytes = match fs::read(&png_path).await {
        Ok(b) => b,
        Err(e) => {
            tracing::warn!(account, path = %png_path, error = %e, "matrix avatar: icon PNG unreadable; skipping");
            return;
        }
    };
    // FNV-1a content hash — enough to answer "did the icon change?" and
    // deterministic across Rust/std versions (unlike `DefaultHasher`, whose
    // output may change between toolchains, spuriously mismatching the
    // persisted hash and re-uploading the same avatar). No crypto strength
    // needed here, so no dependency on a hashing crate.
    let hash = {
        let mut h: u64 = 0xcbf2_9ce4_8422_2325;
        for &b in &bytes {
            h ^= u64::from(b);
            h = h.wrapping_mul(0x0000_0100_0000_01b3);
        }
        format!("{h:016x}")
    };
    let hash_file = state_dir.join("avatar-icon-hash");
    if let Ok(prev) = fs::read_to_string(&hash_file).await
        && prev.trim() == hash
    {
        tracing::debug!(account, "matrix avatar: icon unchanged; skipping upload");
        return;
    }
    match client
        .account()
        .upload_avatar(&mime::IMAGE_PNG, bytes)
        .await
    {
        Ok(mxc) => {
            tracing::info!(account, mxc = %mxc, "matrix avatar set");
            if let Err(e) = fs::write(&hash_file, &hash).await {
                tracing::warn!(account, error = %e, "matrix avatar: set ok but hash write failed (re-uploads next start)");
            }
        }
        Err(e) => {
            tracing::warn!(account, error = %format!("{e:#}"), "matrix avatar: upload failed; skipping (non-fatal)");
        }
    }
}

#[cfg(test)]
mod tests {
    use std::sync::Mutex;

    use super::*;

    /// An account as the homeserver and this device describe it, recording
    /// which of the two writes [`recover_or_enable`] made.
    #[derive(Default)]
    struct Fake {
        on_device: bool,
        backup: bool,
        secret_storage: bool,
        calls: Mutex<Vec<&'static str>>,
    }

    impl KeyBackup for Fake {
        async fn settle(&self) {}

        async fn on_this_device(&self) -> bool {
            self.on_device
        }

        async fn backup_on_server(&self) -> Result<bool> {
            Ok(self.backup)
        }

        async fn secret_storage_on_server(&self) -> Result<bool> {
            Ok(self.secret_storage)
        }

        async fn recover(&self, _: &str) -> Result<()> {
            self.calls.lock().unwrap().push("recover");
            Ok(())
        }

        async fn enable(&self, _: &str) -> Result<()> {
            self.calls.lock().unwrap().push("enable");
            Ok(())
        }
    }

    fn calls(fake: &Fake) -> Vec<&'static str> {
        fake.calls.lock().unwrap().clone()
    }

    #[tokio::test]
    async fn secret_storage_without_a_backup_is_not_enabled_over() {
        // `enable` would replace the account's default secret-storage key,
        // which another client's recovery key opens.
        let fake = Fake {
            secret_storage: true,
            ..Fake::default()
        };
        assert!(recover_or_enable(&fake, "p").await.is_err());
        assert!(calls(&fake).is_empty(), "{:?}", calls(&fake));
    }

    #[tokio::test]
    async fn an_account_with_nothing_on_the_server_is_enabled() {
        // Control for the test above: the guard is the only thing stopping
        // `enable` there.
        let fake = Fake::default();
        assert!(matches!(
            recover_or_enable(&fake, "p").await.unwrap(),
            Backup::Enabled
        ));
        assert_eq!(calls(&fake), ["enable"]);
    }

    #[tokio::test]
    async fn a_backup_on_the_server_is_recovered_not_enabled() {
        let fake = Fake {
            backup: true,
            secret_storage: true,
            ..Fake::default()
        };
        assert!(matches!(
            recover_or_enable(&fake, "p").await.unwrap(),
            Backup::Restored
        ));
        assert_eq!(calls(&fake), ["recover"]);
    }

    #[tokio::test]
    async fn a_device_already_on_the_backup_writes_nothing() {
        let fake = Fake {
            on_device: true,
            backup: true,
            secret_storage: true,
            ..Fake::default()
        };
        assert!(matches!(
            recover_or_enable(&fake, "p").await.unwrap(),
            Backup::AlreadyOn
        ));
        assert!(calls(&fake).is_empty());
    }
}