//! matrix-sdk `Client` setup for the daemon: read the per-agent access
//! token from the state-dir file `hive-c0re::matrix::ensure_user_for`
//! wrote, probe `whoami` to recover the agent's matrix `user_id` +
//! `device_id`, restore the matrix-sdk session, return the Client ready
//! to start sync.
//!
//! No OAuth dance / cross-signing setup (in contrast to damocles-daemon's
//! ccc.de connection): for the in-hive tuwunel the `registration_token`
//! UIAA flow already minted the token + user/device, hive-c0re just
//! handed us the bearer in a file. matrix-sdk's `restore_session` with
//! a constructed `MatrixSession` skips the login flow entirely.
//!
//! E2EE is enabled via `with_encryption_settings(EncryptionSettings::default())`.
//! 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. Automatic
//! key backup is still left at its default (disabled).

use std::path::Path;

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

/// Sentinel returned when `build_and_restore` detects that the token is
/// permanently invalid (`M_UNKNOWN_TOKEN`). The token has already been
/// removed from disk. Callers should NOT retry — the account needs
/// re-provisioning by hive-c0re.
///
/// 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 at `token_file`. The Client points at `homeserver`, persists
/// its sqlite cache under `state_dir`, and is ready for sync once
/// returned.
///
/// Steps:
/// 1. Read the bearer token from `token_file` (trim trailing whitespace).
/// 2. 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 hive-c0re
///    only persisted the token; whoami is the cheapest recovery path
///    and avoids matrix-sdk's circular requirement of needing a
///    session to call whoami).
/// 3. Build the real Client with the sqlite store + `restore_session`
///    using a synthetic `MatrixSession`.
///
/// # Errors
///
/// Returns an error if the token file is missing or empty, 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_file: &Path,
    state_dir: &Path,
    is_primary: bool,
) -> Result<Client> {
    let token = fs::read_to_string(token_file)
        .await
        .with_context(|| format!("read matrix token from {}", token_file.display()))?
        .trim()
        .to_owned();
    if token.is_empty() {
        return Err(anyhow!("matrix token at {} is empty", token_file.display()));
    }

    let (user_id, device_id) = match whoami(homeserver, &token).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. Delete the stale token file so we
                // don't loop on it. 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).
                tracing::warn!(
                    path = %token_file.display(),
                    is_primary,
                    "matrix token rejected (M_UNKNOWN_TOKEN); removing stale token"
                );
                let _ = fs::remove_file(token_file).await;
                if is_primary {
                    // Primary: also drop the matrix-sdk sqlite state keyed to the
                    // now-invalid session, then exit 0 so hive-c0re's `ensure_all`
                    // re-provisions the account and the systemd.paths watcher
                    // restarts us once the fresh token file appears. 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: token removed (so it's cleanly skipped next boot
                // rather than re-erroring); leave the sdk state in place in case
                // the operator re-provisions a fresh token for the same device.
                // Return a PermanentBringUpError so the caller can distinguish
                // "don't retry" from a transient network/DNS failure.
                return Err(anyhow::Error::new(PermanentBringUpError(
                    "matrix token rejected (M_UNKNOWN_TOKEN); removed stale token, skipping account".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::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,
            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.
///
/// Known gap (self-verify only): this signs the *current* device against a
/// freshly-bootstrapped identity. A device re-provisioned under an already
/// existing identity (new `device_id`, e.g. after a token reissue) would need
/// the cross-signing secret keys via secret storage to re-sign itself —
/// tracked as the longer-term mutual-verification follow-up.
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)"
            );
        }
    }
}

/// 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)");
        }
    }
}