//! Configuration for the gRPC transport.

use std::{collections::HashMap, net::SocketAddr, path::PathBuf, time::Duration};

use tidaldb::replication::shard::ShardId;

use crate::error::GrpcTransportError;

/// Maximum payload size in bytes (64 MiB).
///
/// **Source of truth:** the engine crate's `InProcessTransport::MAX_PAYLOAD_BYTES`
/// (`tidaldb`, `replication/in_process.rs`). Both transports must reject the same
/// over-size payloads so behavior does not diverge by which transport a deployment
/// uses. That engine constant is currently private (module-local in `in_process.rs`),
/// so it cannot be `use`d here directly; the value is mirrored and pinned by the
/// compile-time cross-check below. If the engine ever exposes it (e.g. as
/// `tidaldb::replication::MAX_PAYLOAD_BYTES`), replace this literal with a re-export
/// of that constant and delete the cross-check.
pub const MAX_PAYLOAD_BYTES: usize = 64 * 1024 * 1024;

/// Compile-time guard pinning [`MAX_PAYLOAD_BYTES`] to the engine's 64 MiB limit.
///
/// This catches accidental drift in the mirrored literal at build time (it is the
/// best available cross-check while the engine constant stays private). If this
/// fails to compile, the two crates' payload limits have diverged: reconcile them,
/// preferring to make the engine's constant the single referenced source of truth.
const _: () = assert!(
    MAX_PAYLOAD_BYTES == 64 * 1024 * 1024,
    "tidal-net MAX_PAYLOAD_BYTES must match the engine's InProcessTransport limit (64 MiB)"
);

/// Configuration for a single [`GrpcTransport`](crate::GrpcTransport) instance.
#[derive(Debug, Clone)]
pub struct GrpcTransportConfig {
    /// This node's shard identity.
    pub local_shard: ShardId,
    /// Address to bind the gRPC server on.
    pub listen_addr: SocketAddr,
    /// Peer shard advertised addresses (`shard_id` -> `host:port`).
    ///
    /// A bare `host:port` string, NOT a pre-resolved [`SocketAddr`]. This is
    /// load-bearing for DNS peers (m11p5): [`PeerPool::new`] builds the tonic
    /// URI from the string, so `Channel::from_shared("http://hostname:port")`
    /// makes hyper re-resolve DNS on every (re)connect. A pre-resolved IP
    /// literal would pin the peer to whatever address it had at boot — the
    /// k8s pod-rescheduled-onto-a-new-IP case becomes structurally
    /// unreachable until process restart. A literal IP `host:port` is still
    /// accepted (and re-resolves trivially to itself), so every pre-m11p5
    /// topology keeps working byte-for-byte.
    ///
    /// [`PeerPool::new`]: crate::client::PeerPool::new
    pub peers: HashMap<ShardId, String>,
    /// TLS configuration. `None` requires `insecure = true`.
    pub tls: Option<TlsConfig>,
    /// Allow plaintext connections (no TLS).
    pub insecure: bool,
    /// Capacity of the inbound segment channel.
    pub channel_capacity: usize,
    /// Maximum payload size in bytes.
    pub max_payload_bytes: usize,
    /// Number of consecutive failures before the circuit breaker opens.
    pub circuit_breaker_threshold: u32,
    /// Duration the circuit breaker stays open before allowing a probe.
    pub circuit_breaker_reset: Duration,
    /// Maximum time to establish a TCP/TLS connection to a peer before the
    /// attempt fails fast (and the failure trips the circuit breaker). Without
    /// this, a peer whose host is up but whose port silently blackholes the
    /// SYN would stall the single-threaded shipper indefinitely.
    pub connect_timeout: Duration,
    /// Maximum time for a single `ship_segment` RPC (connect + send + response)
    /// before it is aborted as a transient failure. Bounds the per-call latency
    /// the shipper can ever incur on a stalled peer.
    pub request_timeout: Duration,
    /// HTTP/2 PING keep-alive interval on the client channel. Idle and active
    /// connections send a PING this often; a peer that stops responding is
    /// detected within `keep_alive_interval + keep_alive_timeout` instead of
    /// hanging on a half-open connection.
    pub keep_alive_interval: Duration,
    /// How long to wait for a keep-alive PING ACK before declaring the
    /// connection dead and tearing it down.
    pub keep_alive_timeout: Duration,
    /// Delay before a FAILED catch-up pull is retried by the transport's
    /// timer (m11p4). The event path alone (re-trigger on the next pushed
    /// segment) deadlocks an IDLE cluster: a follower whose pull failed —
    /// e.g. the leader's gRPC server was not yet ready during a rolling
    /// restart — waited for a push that never came and stayed lagged
    /// indefinitely (the 2026-06-11 p3 rollout incident). The timer is the
    /// proactive wake-up alongside that event path; pulls stay single-flight
    /// and rate-limited regardless of which path triggers them.
    pub catchup_retry_interval: Duration,
    /// How often the cert-rotation reloader polls the TLS files for a content
    /// change (m11p7). Only spawned when TLS is configured; ignored on the
    /// plaintext path. Content-hash polling (not inotify) is the robust signal
    /// for Kubernetes secret rotation, which swaps a `..data` symlink atomically
    /// — a mode inotify watchers routinely miss. Default 30s; tests set it low
    /// to exercise rotation-under-load fast.
    pub rotation_poll_interval: Duration,
    /// Maximum wall-clock time a single INBOUND TLS handshake may take before it
    /// is abandoned (m11p7 hardening). The TCP accept happens before any client
    /// cert is verified, so a peer that completes the connect but stalls the TLS
    /// `ClientHello` (a slowloris) would otherwise pin a task + socket
    /// indefinitely, pre-auth. Default 10s; only used on the mTLS path.
    pub handshake_timeout: Duration,
    /// Maximum number of inbound TLS handshakes allowed in flight at once
    /// (m11p7 hardening). Bounds the task/fd cost of a connection flood against
    /// the replication port: when the limit is reached, a freshly-accepted
    /// connection is dropped (load-shed) before its handshake is attempted,
    /// rather than each spawning an unbounded task. Default 256; only the mTLS
    /// path enforces it.
    pub max_concurrent_handshakes: usize,
}

impl GrpcTransportConfig {
    /// Reject a config whose numeric invariants would silently break the
    /// transport rather than fail loudly.
    ///
    /// # Errors
    ///
    /// Returns [`GrpcTransportError::Internal`] if any of the following holds.
    /// Each is a misconfiguration that, left unchecked, degrades into a silent
    /// fault the operator cannot see at runtime:
    ///
    /// - `channel_capacity == 0`: [`tokio::sync::mpsc::channel`] panics on a
    ///   zero capacity, so the transport would not even start — surface it as a
    ///   typed error here instead of a panic deep in [`GrpcTransport::new`].
    /// - any timeout is `Duration::ZERO` (`connect_timeout`, `request_timeout`,
    ///   `keep_alive_interval`, `keep_alive_timeout`): a zero deadline aborts
    ///   every attempt instantly, turning the fail-fast design into a transport
    ///   that can never ship a single segment.
    /// - `max_payload_bytes == 0` or `> MAX_PAYLOAD_BYTES`: a zero ceiling
    ///   rejects every segment; a ceiling above the engine's wire limit lets the
    ///   client/server codec accept a payload the peer will refuse, so both ends
    ///   must agree on the same in-range bound.
    /// - `circuit_breaker_reset == Duration::ZERO`: a breaker that reopens with
    ///   no cool-down hammers a down peer with no backoff.
    /// - any peer address is not a syntactic `host:port` (empty/malformed host
    ///   or a port outside `1..=65535`): a bad peer string surfaces only as
    ///   "invalid URI" deep in [`PeerPool::new`] otherwise — catch the config
    ///   typo here, naming the offending peer. The check is hostname-tolerant
    ///   (it mirrors the server crate's `validate_host_port`): a DNS name is a
    ///   valid peer address, an IP literal is too, but reachability is NOT
    ///   probed (siblings boot in any order).
    ///
    /// `circuit_breaker_threshold == 0` is intentionally allowed: the breaker
    /// treats a zero threshold as "open on the first failure" (fail-fast), a
    /// legitimate—if aggressive—policy rather than a degenerate one.
    ///
    /// [`GrpcTransport::new`]: crate::transport::GrpcTransport::new
    pub fn validate(&self) -> Result<(), GrpcTransportError> {
        if self.channel_capacity == 0 {
            return Err(GrpcTransportError::Internal(
                "channel_capacity must be > 0 (a zero-capacity mpsc channel panics)".into(),
            ));
        }
        for (name, d) in [
            ("connect_timeout", self.connect_timeout),
            ("request_timeout", self.request_timeout),
            ("keep_alive_interval", self.keep_alive_interval),
            ("keep_alive_timeout", self.keep_alive_timeout),
        ] {
            if d.is_zero() {
                return Err(GrpcTransportError::Internal(format!(
                    "{name} must be > 0 (a zero deadline aborts every attempt instantly)"
                )));
            }
        }
        if self.max_payload_bytes == 0 || self.max_payload_bytes > MAX_PAYLOAD_BYTES {
            return Err(GrpcTransportError::Internal(format!(
                "max_payload_bytes must be in 1..={MAX_PAYLOAD_BYTES}, got {}",
                self.max_payload_bytes
            )));
        }
        if self.circuit_breaker_reset.is_zero() {
            return Err(GrpcTransportError::Internal(
                "circuit_breaker_reset must be > 0 (a zero cool-down hammers a down peer)".into(),
            ));
        }
        if self.catchup_retry_interval.is_zero() {
            return Err(GrpcTransportError::Internal(
                "catchup_retry_interval must be > 0 (a zero delay turns the \
                 catch-up retry timer into a hot loop against the source)"
                    .into(),
            ));
        }
        if self.rotation_poll_interval.is_zero() {
            return Err(GrpcTransportError::Internal(
                "rotation_poll_interval must be > 0 (a zero delay turns the \
                 cert-rotation reloader into a hot loop re-reading the TLS files)"
                    .into(),
            ));
        }
        if self.handshake_timeout.is_zero() {
            return Err(GrpcTransportError::Internal(
                "handshake_timeout must be > 0 (a zero deadline rejects every \
                 inbound TLS handshake instantly)"
                    .into(),
            ));
        }
        if self.max_concurrent_handshakes == 0 {
            return Err(GrpcTransportError::Internal(
                "max_concurrent_handshakes must be > 0 (a zero bound load-sheds \
                 every inbound connection, refusing all peers)"
                    .into(),
            ));
        }
        for (shard, addr) in &self.peers {
            validate_peer_addr(*shard, addr)?;
        }
        Ok(())
    }
}

/// Syntactic check that a peer's advertised address is a `host:port` the tonic
/// URI builder ([`PeerPool::new`](crate::client::PeerPool::new)) can turn into
/// a valid endpoint, mirroring the server crate's `validate_host_port`:
///
/// - an optional `http://` / `https://` prefix is tolerated (the scheme the
///   pool prepends is derived from TLS, but a prefixed value must not be
///   silently doubled into `http://http://…`),
/// - the host must be non-empty and contain no whitespace or `/`,
/// - the port must parse as a non-zero `u16` (port 0 is never a peer-reachable
///   address).
///
/// A DNS name passes (the m11p5 point): reachability is NOT probed here —
/// siblings boot in any order, so an unresolvable-at-startup peer is normal.
fn validate_peer_addr(shard: ShardId, addr: &str) -> Result<(), GrpcTransportError> {
    let bare = addr
        .strip_prefix("http://")
        .or_else(|| addr.strip_prefix("https://"))
        .unwrap_or(addr)
        .trim_end_matches('/');
    let bad = |why: &str| {
        Err(GrpcTransportError::Internal(format!(
            "peer {shard:?} address '{addr}' is not a valid host:port ({why})"
        )))
    };
    let Some((host, port)) = bare.rsplit_once(':') else {
        return bad("missing ':port'");
    };
    if host.is_empty() || host.contains([' ', '/']) {
        return bad("empty or malformed host");
    }
    match port.parse::<u16>() {
        Ok(0) => bad("port 0 is not reachable by peers"),
        Ok(_) => Ok(()),
        Err(_) => bad("port must be 1-65535"),
    }
}

impl Default for GrpcTransportConfig {
    fn default() -> Self {
        Self {
            local_shard: ShardId::SINGLE,
            // Default replication listener. Inside tidalDB's reserved dev band
            // (59520–59529); 59529 is the slot claimed for the gRPC transport.
            listen_addr: "127.0.0.1:59529".parse().expect("valid default addr"),
            peers: HashMap::new(),
            tls: None,
            insecure: true,
            channel_capacity: 1024,
            max_payload_bytes: MAX_PAYLOAD_BYTES,
            circuit_breaker_threshold: 5,
            circuit_breaker_reset: Duration::from_secs(30),
            connect_timeout: Duration::from_secs(5),
            request_timeout: Duration::from_secs(10),
            keep_alive_interval: Duration::from_secs(10),
            keep_alive_timeout: Duration::from_secs(5),
            catchup_retry_interval: Duration::from_secs(30),
            rotation_poll_interval: Duration::from_secs(30),
            handshake_timeout: Duration::from_secs(10),
            max_concurrent_handshakes: 256,
        }
    }
}

/// TLS certificate paths for mutual TLS.
#[derive(Debug, Clone)]
pub struct TlsConfig {
    /// Path to the CA certificate PEM file.
    pub ca_cert: PathBuf,
    /// Path to the server certificate PEM file.
    pub server_cert: PathBuf,
    /// Path to the server private key PEM file.
    pub server_key: PathBuf,
    /// Path to the client certificate PEM file (for mTLS).
    pub client_cert: Option<PathBuf>,
    /// Path to the client private key PEM file (for mTLS).
    pub client_key: Option<PathBuf>,
}

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

    #[test]
    fn default_config_is_valid() {
        // The shipped defaults must pass their own invariant check, otherwise
        // every default-built transport would error at construction.
        GrpcTransportConfig::default()
            .validate()
            .expect("default config must satisfy its own invariants");
    }

    #[test]
    fn zero_channel_capacity_is_rejected() {
        // A zero-capacity mpsc channel panics inside GrpcTransport::new; the
        // typed error must catch it before that panic.
        let cfg = GrpcTransportConfig {
            channel_capacity: 0,
            ..GrpcTransportConfig::default()
        };
        let err = cfg
            .validate()
            .expect_err("zero channel_capacity must be rejected");
        assert!(matches!(err, GrpcTransportError::Internal(_)));
    }

    #[test]
    fn zero_timeouts_are_rejected() {
        let mutators: [fn(&mut GrpcTransportConfig); 4] = [
            |c| c.connect_timeout = Duration::ZERO,
            |c| c.request_timeout = Duration::ZERO,
            |c| c.keep_alive_interval = Duration::ZERO,
            |c| c.keep_alive_timeout = Duration::ZERO,
        ];
        for mutate in mutators {
            let mut cfg = GrpcTransportConfig::default();
            mutate(&mut cfg);
            assert!(
                cfg.validate().is_err(),
                "a zero deadline must be rejected (it aborts every attempt instantly)"
            );
        }
    }

    #[test]
    fn zero_handshake_bounds_are_rejected() {
        // A zero handshake timeout rejects every inbound TLS handshake instantly;
        // a zero concurrency bound load-sheds every connection — both refuse all
        // peers, so the typed config check must catch them.
        let mutators: [fn(&mut GrpcTransportConfig); 2] = [
            |c| c.handshake_timeout = Duration::ZERO,
            |c| c.max_concurrent_handshakes = 0,
        ];
        for mutate in mutators {
            let mut cfg = GrpcTransportConfig::default();
            mutate(&mut cfg);
            assert!(
                cfg.validate().is_err(),
                "a zero handshake bound must be rejected"
            );
        }
    }

    #[test]
    fn zero_circuit_breaker_reset_is_rejected() {
        let cfg = GrpcTransportConfig {
            circuit_breaker_reset: Duration::ZERO,
            ..GrpcTransportConfig::default()
        };
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn zero_catchup_retry_interval_is_rejected() {
        // A zero retry delay turns the m11p4 catch-up timer into a hot loop
        // that hammers the stream source.
        let cfg = GrpcTransportConfig {
            catchup_retry_interval: Duration::ZERO,
            ..GrpcTransportConfig::default()
        };
        assert!(cfg.validate().is_err());
    }

    #[test]
    fn payload_ceiling_out_of_range_is_rejected() {
        // Zero rejects every segment; above the engine wire limit lets the codec
        // accept a payload the peer will refuse.
        for bytes in [0, MAX_PAYLOAD_BYTES + 1] {
            let cfg = GrpcTransportConfig {
                max_payload_bytes: bytes,
                ..GrpcTransportConfig::default()
            };
            assert!(
                cfg.validate().is_err(),
                "max_payload_bytes {bytes} is out of the 1..={MAX_PAYLOAD_BYTES} range"
            );
        }
    }

    #[test]
    fn payload_ceiling_at_engine_limit_is_allowed() {
        let cfg = GrpcTransportConfig {
            max_payload_bytes: MAX_PAYLOAD_BYTES,
            ..GrpcTransportConfig::default()
        };
        assert!(cfg.validate().is_ok());
    }

    #[test]
    fn zero_circuit_breaker_threshold_is_allowed() {
        // A zero threshold means "open on the first failure" (fail-fast), a
        // legitimate aggressive policy — not a degenerate config.
        let cfg = GrpcTransportConfig {
            circuit_breaker_threshold: 0,
            ..GrpcTransportConfig::default()
        };
        assert!(cfg.validate().is_ok());
    }

    #[test]
    fn valid_peer_addresses_are_accepted() {
        // IP literal, DNS name, fully-qualified k8s pod DNS, and a
        // scheme-prefixed value must all pass — the m11p5 DNS-peer point is
        // that hostnames are first-class peer addresses.
        for addr in [
            "127.0.0.1:9601",
            "tidal-eu:9601",
            "tidaldb-1.tidaldb-peers.tidaldb-cluster.svc.cluster.local:9601",
            "http://127.0.0.1:9601",
            "https://tidal-eu:9601",
        ] {
            let cfg = GrpcTransportConfig {
                peers: HashMap::from([(ShardId(1), addr.to_string())]),
                ..GrpcTransportConfig::default()
            };
            cfg.validate()
                .unwrap_or_else(|e| panic!("peer addr '{addr}' must be accepted: {e:?}"));
        }
    }

    #[test]
    fn malformed_peer_addresses_are_rejected() {
        // A bad peer string would otherwise surface only as an opaque
        // "invalid URI" deep in PeerPool::new — the config check names the
        // offending peer instead.
        for (addr, why) in [
            ("127.0.0.1", "missing port"),
            ("127.0.0.1:0", "port 0"),
            ("127.0.0.1:99999", "port out of range"),
            (":9601", "empty host"),
            ("10.0.0.1:port", "non-numeric port"),
        ] {
            let cfg = GrpcTransportConfig {
                peers: HashMap::from([(ShardId(1), addr.to_string())]),
                ..GrpcTransportConfig::default()
            };
            let Err(err) = cfg.validate() else {
                panic!("peer addr '{addr}' ({why}) must be rejected");
            };
            assert!(
                matches!(err, GrpcTransportError::Internal(_)),
                "expected an Internal config error for '{addr}', got {err:?}"
            );
        }
    }
}