// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

use crate::OfferInfo;
use crate::RestoreError;
use crate::RestoredChannel;
use crate::VmbusMessageSource;
use guid::Guid;
use mesh::payload::Protobuf;
use vmbus_channel::bus::OfferKey;
use vmbus_core::protocol;
use vmbus_core::protocol::ChannelId;
use vmbus_core::protocol::FeatureFlags;
use vmbus_core::protocol::GpadlId;
use vmbus_core::VersionInfo;

impl<T: VmbusMessageSource> super::ClientTask<T> {
    pub fn handle_save(&mut self) -> SavedState {
        // It's the responsibility of the caller to ensure the client is in a state where it's
        // possible to save.
        SavedState {
            client_state: self.state.into(),
            channels: self
                .inner
                .channels
                .iter()
                .map(|(id, v)| {
                    assert!(
                        v.modify_response_send.is_none(),
                        "Cannot save a channel that is being modified."
                    );
                    let key = offer_key(&v.offer);
                    tracing::info!(%key, %v.state, "channel saved");

                    Channel {
                        id: id.0,
                        state: ChannelState::save(&v.state),
                        offer: v.offer.into(),
                    }
                })
                .collect(),
            gpadls: self
                .inner
                .gpadls
                .iter()
                .map(|(&(channel_id, gpadl_id), gpadl_state)| Gpadl {
                    gpadl_id: gpadl_id.0,
                    channel_id: channel_id.0,
                    state: GpadlState::save(gpadl_state),
                })
                .collect(),
        }
    }

    pub fn handle_restore(
        &mut self,
        saved_state: SavedState,
    ) -> Result<(Option<VersionInfo>, Vec<RestoredChannel>), RestoreError> {
        let mut restored_channels = Vec::new();
        self.state = saved_state.client_state.try_into()?;
        for saved_channel in saved_state.channels {
            if let Some(offer_info) = self.restore_channel(saved_channel) {
                let key = offer_key(&offer_info.offer);
                tracing::info!(%key, state = %saved_channel.state, "channel restored");
                restored_channels.push(RestoredChannel {
                    offer: offer_info,
                    open: saved_channel.state == ChannelState::Opened,
                });
            }
            if let Some(channel) = self.inner.channels.get_mut(&ChannelId(saved_channel.id)) {
                channel.state = saved_channel.state.restore()
            }
        }

        if let super::ClientState::RequestingOffers(_) = &self.state {
            self.request_offers_send
                .send(Some(super::Offer::AllOffersDelivered));
        }

        for gpadl in saved_state.gpadls {
            let channel_id = ChannelId(gpadl.channel_id);
            let gpadl_id = GpadlId(gpadl.gpadl_id);
            let gpadl_state = gpadl.state.restore();
            let tearing_down = matches!(gpadl_state, super::GpadlState::TearingDown);

            if self
                .inner
                .gpadls
                .insert((channel_id, gpadl_id), gpadl_state)
                .is_some()
            {
                return Err(RestoreError::DuplicateGpadlId(gpadl_id.0));
            }

            if tearing_down
                && self
                    .inner
                    .teardown_gpadls
                    .insert(gpadl_id, Some(channel_id))
                    .is_some()
            {
                unreachable!("gpadl ID validated above");
            }
        }

        Ok((self.state.get_version(), restored_channels))
    }

    fn restore_channel(&mut self, channel: Channel) -> Option<OfferInfo> {
        self.create_channel_core(channel.offer.into(), channel.state.restore())
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub struct SavedState {
    #[mesh(1)]
    pub client_state: ClientState,
    #[mesh(2)]
    pub channels: Vec<Channel>,
    #[mesh(3)]
    pub gpadls: Vec<Gpadl>,
}

#[derive(Clone, Debug, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub enum ClientState {
    #[mesh(1)]
    Disconnected,
    #[mesh(2)]
    Connected {
        #[mesh(1)]
        version: u32,
        #[mesh(2)]
        feature_flags: u32,
    },
}

impl From<super::ClientState> for ClientState {
    fn from(state: super::ClientState) -> Self {
        // It is the responsibility of the caller to ensure the client is in a state where it's
        // possible to save.
        match state {
            super::ClientState::Disconnected => ClientState::Disconnected,
            super::ClientState::Connecting(..) => {
                unreachable!("Cannot save in Connecting state.")
            }
            super::ClientState::Connected(info) => ClientState::Connected {
                version: info.version as u32,
                feature_flags: info.feature_flags.into(),
            },
            super::ClientState::RequestingOffers(..) => {
                unreachable!("Cannot save in RequestingOffers state.")
            }
            super::ClientState::Disconnecting(..) => {
                unreachable!("Cannot save in Disconnecting state.")
            }
        }
    }
}

impl TryFrom<ClientState> for super::ClientState {
    type Error = RestoreError;

    fn try_from(state: ClientState) -> Result<Self, Self::Error> {
        let result = match state {
            ClientState::Disconnected => Self::Disconnected,
            ClientState::Connected {
                version,
                feature_flags,
            } => {
                let version = super::SUPPORTED_VERSIONS
                    .iter()
                    .find(|v| version == **v as u32)
                    .copied()
                    .ok_or(RestoreError::UnsupportedVersion(version))?;

                let feature_flags = FeatureFlags::from(feature_flags);
                if feature_flags.contains_unsupported_bits() {
                    return Err(RestoreError::UnsupportedFeatureFlags(feature_flags.into()));
                }

                Self::Connected(VersionInfo {
                    version,
                    feature_flags,
                })
            }
        };

        Ok(result)
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub struct Channel {
    #[mesh(1)]
    pub id: u32,
    #[mesh(2)]
    pub state: ChannelState,
    #[mesh(3)]
    pub offer: Offer,
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub enum ChannelState {
    #[mesh(1)]
    Offered,
    #[mesh(2)]
    Opened,
}

impl ChannelState {
    fn save(state: &super::ChannelState) -> Self {
        match state {
            super::ChannelState::Offered => Self::Offered,
            super::ChannelState::Opening(..) => {
                unreachable!("Cannot save channel in opening state.")
            }
            super::ChannelState::Opened => Self::Opened,
        }
    }

    fn restore(self) -> super::ChannelState {
        match self {
            ChannelState::Offered => super::ChannelState::Offered,
            ChannelState::Opened => super::ChannelState::Opened,
        }
    }
}

impl std::fmt::Display for ChannelState {
    fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            ChannelState::Offered => write!(fmt, "Offered"),
            ChannelState::Opened => write!(fmt, "Opened"),
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub enum GpadlState {
    #[mesh(1)]
    Created,
    #[mesh(2)]
    TearingDown,
}

impl GpadlState {
    fn save(value: &super::GpadlState) -> Self {
        match value {
            super::GpadlState::Offered(..) => unreachable!("Cannot save gpadl in offered state."),
            super::GpadlState::Created => Self::Created,
            super::GpadlState::TearingDown => Self::TearingDown,
        }
    }

    fn restore(self) -> super::GpadlState {
        match self {
            GpadlState::Created => super::GpadlState::Created,
            GpadlState::TearingDown => super::GpadlState::TearingDown,
        }
    }
}

#[derive(Clone, Debug, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub struct Gpadl {
    #[mesh(1)]
    pub gpadl_id: u32,
    #[mesh(2)]
    pub channel_id: u32,
    #[mesh(3)]
    pub state: GpadlState,
}

#[derive(Copy, Clone, Debug, PartialEq, Eq, Protobuf)]
#[mesh(package = "vmbus.client")]
pub struct Offer {
    #[mesh(1)]
    pub interface_id: Guid,
    #[mesh(2)]
    pub instance_id: Guid,
    #[mesh(3)]
    pub flags: u16,
    #[mesh(4)]
    pub mmio_megabytes: u16,
    #[mesh(5)]
    pub user_defined: [u8; 120],
    #[mesh(6)]
    pub subchannel_index: u16,
    #[mesh(7)]
    pub mmio_megabytes_optional: u16,
    #[mesh(8)]
    pub channel_id: u32,
    #[mesh(9)]
    pub monitor_id: u8,
    #[mesh(10)]
    pub monitor_allocated: u8,
    #[mesh(11)]
    pub is_dedicated: u16,
    #[mesh(12)]
    pub connection_id: u32,
}

impl From<protocol::OfferChannel> for Offer {
    fn from(offer: protocol::OfferChannel) -> Self {
        Self {
            interface_id: offer.interface_id,
            instance_id: offer.instance_id,
            flags: offer.flags.into(),
            mmio_megabytes: offer.mmio_megabytes,
            user_defined: offer.user_defined.into(),
            subchannel_index: offer.subchannel_index,
            mmio_megabytes_optional: offer.mmio_megabytes_optional,
            channel_id: offer.channel_id.0,
            monitor_id: offer.monitor_id,
            monitor_allocated: offer.monitor_allocated,
            is_dedicated: offer.is_dedicated,
            connection_id: offer.connection_id,
        }
    }
}

impl From<Offer> for protocol::OfferChannel {
    fn from(offer: Offer) -> Self {
        Self {
            interface_id: offer.interface_id,
            instance_id: offer.instance_id,
            flags: offer.flags.into(),
            rsvd: [0; 4],
            mmio_megabytes: offer.mmio_megabytes,
            user_defined: offer.user_defined.into(),
            subchannel_index: offer.subchannel_index,
            mmio_megabytes_optional: offer.mmio_megabytes_optional,
            channel_id: ChannelId(offer.channel_id),
            monitor_id: offer.monitor_id,
            monitor_allocated: offer.monitor_allocated,
            is_dedicated: offer.is_dedicated,
            connection_id: offer.connection_id,
        }
    }
}

fn offer_key(offer: &protocol::OfferChannel) -> OfferKey {
    OfferKey {
        interface_id: offer.interface_id,
        instance_id: offer.instance_id,
        subchannel_index: offer.subchannel_index,
    }
}
