//! Typed handle around an opened gateway session.
//!
//! [`Session`] wraps an `OpenSession` reply (just the session id) plus a
//! cloned [`GatewayClient`] and offers Rust-shaped methods for the
//! command surface that the worker exposes — `Register`, `AddItem`,
//! bulk subscribe variants, `Write`/`Write2`, and the event stream.
//!
//! Bulk commands enforce a 1000-item cap before contacting the worker, in
//! line with the gateway's documented `MAX_BULK_ITEMS`.

use crate::client::{EventStream, GatewayClient};
use crate::error::{ensure_protocol_success, Error};
use crate::generated::mxaccess_gateway::v1::mx_command::Payload;
use crate::generated::mxaccess_gateway::v1::mx_command_reply;
use crate::generated::mxaccess_gateway::v1::{
    AddItem2Command, AddItemBulkCommand, AddItemCommand, AdviseCommand, AdviseItemBulkCommand,
    CloseSessionRequest, MxCommand, MxCommandKind, MxCommandReply, MxCommandRequest,
    MxValue as ProtoMxValue, OpenSessionRequest, RegisterCommand, RemoveItemBulkCommand,
    RemoveItemCommand, StreamEventsRequest, SubscribeBulkCommand, SubscribeResult, UnAdviseCommand,
    UnAdviseItemBulkCommand, UnsubscribeBulkCommand, Write2Command, WriteCommand,
};
use crate::value::MxValue;

const MAX_BULK_ITEMS: usize = 1_000;

/// Handle to an opened gateway session.
///
/// `Session` carries the gateway-issued session id and a cloned
/// [`GatewayClient`]. All methods are async and stateless on the client
/// side: the gateway tracks per-session worker state. Drop the handle and
/// call [`Session::close`] to release the worker; the gateway also reaps
/// orphaned sessions on its own schedule.
#[derive(Clone)]
pub struct Session {
    id: String,
    client: GatewayClient,
}

impl Session {
    pub(crate) fn new(id: impl Into<String>, client: GatewayClient) -> Self {
        Self {
            id: id.into(),
            client,
        }
    }

    /// Borrow the gateway-assigned session id.
    pub fn id(&self) -> &str {
        &self.id
    }

    /// Convenience constructor that issues `OpenSession` with the supplied
    /// client session name and returns the resulting [`Session`].
    ///
    /// # Errors
    ///
    /// Propagates errors from
    /// [`GatewayClient::open_session`](crate::client::GatewayClient::open_session).
    pub async fn open(client: GatewayClient, client_session_name: &str) -> Result<Self, Error> {
        client
            .open_session(OpenSessionRequest {
                client_session_name: client_session_name.to_owned(),
                ..OpenSessionRequest::default()
            })
            .await
    }

    /// Issue `CloseSession` against this session id.
    ///
    /// # Errors
    ///
    /// Returns [`Error::ProtocolStatus`] if the gateway returns a non-OK
    /// envelope and any transport/status errors propagated by tonic.
    pub async fn close(&self) -> Result<(), Error> {
        let reply = self
            .client
            .close_session_raw(CloseSessionRequest {
                session_id: self.id.clone(),
                client_correlation_id: "rust-client-close-session".to_owned(),
            })
            .await?;
        ensure_protocol_success("close session", reply.protocol_status.as_ref())?;
        Ok(())
    }

    /// Run MXAccess `Register` and return the assigned `ServerHandle`.
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] if the worker reports a non-OK status,
    /// plus transport/status errors from tonic.
    pub async fn register(&self, client_name: &str) -> Result<i32, Error> {
        let reply = self
            .invoke(
                MxCommandKind::Register,
                Payload::Register(RegisterCommand {
                    client_name: client_name.to_owned(),
                }),
            )
            .await?;

        Ok(register_server_handle(&reply))
    }

    /// Run MXAccess `AddItem` against `server_handle` and return the
    /// assigned `ItemHandle`.
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] when MXAccess rejects the item
    /// definition, plus transport/status errors from tonic.
    pub async fn add_item(&self, server_handle: i32, item_definition: &str) -> Result<i32, Error> {
        let reply = self
            .invoke(
                MxCommandKind::AddItem,
                Payload::AddItem(AddItemCommand {
                    server_handle,
                    item_definition: item_definition.to_owned(),
                }),
            )
            .await?;

        Ok(add_item_handle(&reply))
    }

    /// Run MXAccess `AddItem2` (item with a caller-supplied context string)
    /// and return the assigned `ItemHandle`.
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::add_item`].
    pub async fn add_item2(
        &self,
        server_handle: i32,
        item_definition: &str,
        item_context: &str,
    ) -> Result<i32, Error> {
        let reply = self
            .invoke(
                MxCommandKind::AddItem2,
                Payload::AddItem2(AddItem2Command {
                    server_handle,
                    item_definition: item_definition.to_owned(),
                    item_context: item_context.to_owned(),
                }),
            )
            .await?;

        Ok(add_item2_handle(&reply))
    }

    /// Run MXAccess `RemoveItem` for the given handle pair.
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] on a non-OK worker status, plus the
    /// usual transport/status errors.
    pub async fn remove_item(&self, server_handle: i32, item_handle: i32) -> Result<(), Error> {
        self.invoke(
            MxCommandKind::RemoveItem,
            Payload::RemoveItem(RemoveItemCommand {
                server_handle,
                item_handle,
            }),
        )
        .await?;
        Ok(())
    }

    /// Run MXAccess `Advise` to start receiving change notifications for
    /// the given item.
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] when the worker reports a non-OK status.
    pub async fn advise(&self, server_handle: i32, item_handle: i32) -> Result<(), Error> {
        self.invoke(
            MxCommandKind::Advise,
            Payload::Advise(AdviseCommand {
                server_handle,
                item_handle,
            }),
        )
        .await?;
        Ok(())
    }

    /// Run MXAccess `UnAdvise` to stop change notifications for the given
    /// item.
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] when the worker reports a non-OK status.
    pub async fn un_advise(&self, server_handle: i32, item_handle: i32) -> Result<(), Error> {
        self.invoke(
            MxCommandKind::UnAdvise,
            Payload::UnAdvise(UnAdviseCommand {
                server_handle,
                item_handle,
            }),
        )
        .await?;
        Ok(())
    }

    /// Bulk variant of [`Session::add_item`]. Each tag address yields one
    /// `SubscribeResult` in the returned vector.
    ///
    /// # Errors
    ///
    /// Returns [`Error::InvalidArgument`] when the input exceeds the
    /// gateway's 1000-item bulk cap, plus the usual command-level errors.
    pub async fn add_item_bulk(
        &self,
        server_handle: i32,
        tag_addresses: Vec<String>,
    ) -> Result<Vec<SubscribeResult>, Error> {
        ensure_bulk_size("tag_addresses", tag_addresses.len())?;
        let reply = self
            .invoke(
                MxCommandKind::AddItemBulk,
                Payload::AddItemBulk(AddItemBulkCommand {
                    server_handle,
                    tag_addresses,
                }),
            )
            .await?;

        Ok(bulk_results(reply, BulkReplyKind::AddItemBulk))
    }

    /// Bulk variant of [`Session::advise`].
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::add_item_bulk`].
    pub async fn advise_item_bulk(
        &self,
        server_handle: i32,
        item_handles: Vec<i32>,
    ) -> Result<Vec<SubscribeResult>, Error> {
        ensure_bulk_size("item_handles", item_handles.len())?;
        let reply = self
            .invoke(
                MxCommandKind::AdviseItemBulk,
                Payload::AdviseItemBulk(AdviseItemBulkCommand {
                    server_handle,
                    item_handles,
                }),
            )
            .await?;

        Ok(bulk_results(reply, BulkReplyKind::AdviseItemBulk))
    }

    /// Bulk variant of [`Session::remove_item`].
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::add_item_bulk`].
    pub async fn remove_item_bulk(
        &self,
        server_handle: i32,
        item_handles: Vec<i32>,
    ) -> Result<Vec<SubscribeResult>, Error> {
        ensure_bulk_size("item_handles", item_handles.len())?;
        let reply = self
            .invoke(
                MxCommandKind::RemoveItemBulk,
                Payload::RemoveItemBulk(RemoveItemBulkCommand {
                    server_handle,
                    item_handles,
                }),
            )
            .await?;

        Ok(bulk_results(reply, BulkReplyKind::RemoveItemBulk))
    }

    /// Bulk variant of [`Session::un_advise`].
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::add_item_bulk`].
    pub async fn un_advise_item_bulk(
        &self,
        server_handle: i32,
        item_handles: Vec<i32>,
    ) -> Result<Vec<SubscribeResult>, Error> {
        ensure_bulk_size("item_handles", item_handles.len())?;
        let reply = self
            .invoke(
                MxCommandKind::UnAdviseItemBulk,
                Payload::UnAdviseItemBulk(UnAdviseItemBulkCommand {
                    server_handle,
                    item_handles,
                }),
            )
            .await?;

        Ok(bulk_results(reply, BulkReplyKind::UnAdviseItemBulk))
    }

    /// Bulk `Subscribe` (atomic add-and-advise) for a list of tag addresses.
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::add_item_bulk`].
    pub async fn subscribe_bulk(
        &self,
        server_handle: i32,
        tag_addresses: Vec<String>,
    ) -> Result<Vec<SubscribeResult>, Error> {
        ensure_bulk_size("tag_addresses", tag_addresses.len())?;
        let reply = self
            .invoke(
                MxCommandKind::SubscribeBulk,
                Payload::SubscribeBulk(SubscribeBulkCommand {
                    server_handle,
                    tag_addresses,
                }),
            )
            .await?;

        Ok(bulk_results(reply, BulkReplyKind::SubscribeBulk))
    }

    /// Bulk `Unsubscribe` (atomic un-advise-and-remove) for a list of
    /// item handles.
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::add_item_bulk`].
    pub async fn unsubscribe_bulk(
        &self,
        server_handle: i32,
        item_handles: Vec<i32>,
    ) -> Result<Vec<SubscribeResult>, Error> {
        ensure_bulk_size("item_handles", item_handles.len())?;
        let reply = self
            .invoke(
                MxCommandKind::UnsubscribeBulk,
                Payload::UnsubscribeBulk(UnsubscribeBulkCommand {
                    server_handle,
                    item_handles,
                }),
            )
            .await?;

        Ok(bulk_results(reply, BulkReplyKind::UnsubscribeBulk))
    }

    /// Run MXAccess `Write` (single-value, no caller-supplied timestamp).
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] for non-OK worker statuses, plus the
    /// usual transport/status errors.
    pub async fn write(
        &self,
        server_handle: i32,
        item_handle: i32,
        value: MxValue,
        user_id: i32,
    ) -> Result<(), Error> {
        self.invoke(
            MxCommandKind::Write,
            Payload::Write(WriteCommand {
                server_handle,
                item_handle,
                value: Some(value.into_proto()),
                user_id,
            }),
        )
        .await?;
        Ok(())
    }

    /// Run MXAccess `Write2` (single-value with caller-supplied timestamp).
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::write`].
    pub async fn write2(
        &self,
        server_handle: i32,
        item_handle: i32,
        value: MxValue,
        timestamp_value: MxValue,
        user_id: i32,
    ) -> Result<(), Error> {
        self.invoke(
            MxCommandKind::Write2,
            Payload::Write2(Write2Command {
                server_handle,
                item_handle,
                value: Some(value.into_proto()),
                timestamp_value: Some(timestamp_value.into_proto()),
                user_id,
            }),
        )
        .await?;
        Ok(())
    }

    /// Open the per-session event stream from the beginning.
    ///
    /// # Errors
    ///
    /// Returns the `tonic::Status` mapped through [`Error::from`] when the
    /// gateway rejects the subscription.
    pub async fn events(&self) -> Result<EventStream, Error> {
        self.events_after(0).await
    }

    /// Open the per-session event stream, requesting only events whose
    /// `worker_sequence` is greater than `after_worker_sequence`. Pass `0`
    /// to receive every buffered event.
    ///
    /// # Errors
    ///
    /// Same conditions as [`Session::events`].
    pub async fn events_after(&self, after_worker_sequence: u64) -> Result<EventStream, Error> {
        self.client
            .stream_events(StreamEventsRequest {
                session_id: self.id.clone(),
                after_worker_sequence,
            })
            .await
    }

    /// Issue a raw `Invoke` for an arbitrary command, without filtering on
    /// the protocol status. Useful when callers need the full reply for
    /// commands not yet wrapped by `Session`.
    ///
    /// # Errors
    ///
    /// Returns the `tonic::Status` mapped through [`Error::from`].
    pub async fn invoke_raw(
        &self,
        kind: MxCommandKind,
        payload: Payload,
    ) -> Result<MxCommandReply, Error> {
        self.client
            .invoke_raw(self.command_request(kind, payload))
            .await
    }

    /// Issue an `Invoke` for an arbitrary command and surface a non-OK
    /// reply as [`Error::Command`].
    ///
    /// # Errors
    ///
    /// Returns [`Error::Command`] for non-OK worker statuses plus any
    /// errors propagated by [`invoke_raw`](Self::invoke_raw).
    pub async fn invoke(
        &self,
        kind: MxCommandKind,
        payload: Payload,
    ) -> Result<MxCommandReply, Error> {
        self.client
            .invoke(self.command_request(kind, payload))
            .await
    }

    fn command_request(&self, kind: MxCommandKind, payload: Payload) -> MxCommandRequest {
        MxCommandRequest {
            session_id: self.id.clone(),
            client_correlation_id: format!("rust-client-{}", kind.as_str_name()),
            command: Some(MxCommand {
                kind: kind as i32,
                payload: Some(payload),
            }),
        }
    }
}

fn ensure_bulk_size(name: &'static str, len: usize) -> Result<(), Error> {
    if len > MAX_BULK_ITEMS {
        Err(Error::InvalidArgument {
            name: name.to_owned(),
            detail: format!("bulk commands are limited to {MAX_BULK_ITEMS} item(s)"),
        })
    } else {
        Ok(())
    }
}

fn register_server_handle(reply: &MxCommandReply) -> i32 {
    match reply.payload.as_ref() {
        Some(mx_command_reply::Payload::Register(register)) => register.server_handle,
        _ => reply
            .return_value
            .as_ref()
            .and_then(int32_reply_value)
            .unwrap_or_default(),
    }
}

fn add_item_handle(reply: &MxCommandReply) -> i32 {
    match reply.payload.as_ref() {
        Some(mx_command_reply::Payload::AddItem(add_item)) => add_item.item_handle,
        _ => reply
            .return_value
            .as_ref()
            .and_then(int32_reply_value)
            .unwrap_or_default(),
    }
}

fn add_item2_handle(reply: &MxCommandReply) -> i32 {
    match reply.payload.as_ref() {
        Some(mx_command_reply::Payload::AddItem2(add_item)) => add_item.item_handle,
        _ => reply
            .return_value
            .as_ref()
            .and_then(int32_reply_value)
            .unwrap_or_default(),
    }
}

enum BulkReplyKind {
    AddItemBulk,
    AdviseItemBulk,
    RemoveItemBulk,
    UnAdviseItemBulk,
    SubscribeBulk,
    UnsubscribeBulk,
}

fn bulk_results(reply: MxCommandReply, kind: BulkReplyKind) -> Vec<SubscribeResult> {
    match (reply.payload, kind) {
        (Some(mx_command_reply::Payload::AddItemBulk(reply)), BulkReplyKind::AddItemBulk) => {
            reply.results
        }
        (Some(mx_command_reply::Payload::AdviseItemBulk(reply)), BulkReplyKind::AdviseItemBulk) => {
            reply.results
        }
        (Some(mx_command_reply::Payload::RemoveItemBulk(reply)), BulkReplyKind::RemoveItemBulk) => {
            reply.results
        }
        (
            Some(mx_command_reply::Payload::UnAdviseItemBulk(reply)),
            BulkReplyKind::UnAdviseItemBulk,
        ) => reply.results,
        (Some(mx_command_reply::Payload::SubscribeBulk(reply)), BulkReplyKind::SubscribeBulk) => {
            reply.results
        }
        (
            Some(mx_command_reply::Payload::UnsubscribeBulk(reply)),
            BulkReplyKind::UnsubscribeBulk,
        ) => reply.results,
        _ => Vec::new(),
    }
}

fn int32_reply_value(value: &ProtoMxValue) -> Option<i32> {
    match value.kind.as_ref()? {
        crate::generated::mxaccess_gateway::v1::mx_value::Kind::Int32Value(value) => Some(*value),
        _ => None,
    }
}