//! Read-only protocol discovery and value-query responses.

use kaptan_config::{
    ConfigManager, ConfigModel, ConfigState, ConfigValue, FieldDescriptor, FieldId, Generation,
    ProfileStore,
};

use super::{import::SnapshotImporter, session::ConfigProtocol};
use crate::{ProtocolError, ValueSource};

/// Bounded descriptor page returned by a schema discovery request.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct DescriptorPage {
    /// Request being answered.
    pub request_id: u32,
    /// First requested descriptor index.
    pub first: u16,
    /// Number of descriptors present in `descriptors`.
    pub len: u8,
    /// Fixed-capacity response page; `None` slots are unused.
    pub descriptors: [Option<&'static FieldDescriptor>; 4],
}

/// One typed value read from an explicitly selected configuration snapshot.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct ValueResponse {
    /// Request being answered.
    pub request_id: u32,
    /// Transaction session for transaction values, otherwise zero.
    pub session_id: u32,
    /// Current transaction revision, otherwise zero.
    pub revision: u32,
    /// Requested stable field identity.
    pub field: FieldId,
    /// Declared scalar value.
    pub value: ConfigValue,
}

/// Correlated protocol/schema discovery response.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct ConfigInfo {
    /// Request being answered.
    pub request_id: u32,
    /// Boot-active generation, or `None` for the factory profile.
    pub active_generation: Option<Generation>,
    /// Last committed generation, or `None` for the factory profile.
    pub committed_generation: Option<Generation>,
    /// Exact schema identifier expected by profile import.
    pub schema_id: [u8; 16],
    /// Version carried inside the one raw CBOR profile blob.
    pub profile_format: u16,
    /// Number of editable fields in the registry.
    pub field_count: u16,
    /// Current configuration lifecycle state.
    pub state: ConfigState,
    /// Deployment capabilities such as bounded CBOR import.
    pub capability_flags: u8,
}

/// Exact response produced by the custom configuration service.
#[derive(Clone, Copy, Debug, PartialEq)]
pub enum ServiceResponse {
    /// Correlated protocol/schema discovery response.
    Info(ConfigInfo),
    /// Completion for a mutating operation or rejected query.
    Result(crate::ConfigReply),
    /// Bounded self-describing schema page.
    Descriptors(DescriptorPage),
    /// One typed scalar value.
    Value(ValueResponse),
}

impl<I> ConfigProtocol<I> {
    /// Returns static descriptor metadata by stable schema index.
    pub fn descriptor<C, S>(
        &self,
        manager: &ConfigManager<C, S>,
        index: u16,
    ) -> Option<&'static FieldDescriptor>
    where
        C: ConfigModel,
        S: ProfileStore<C>,
    {
        manager.descriptor(index)
    }

    /// Reads one typed value without opening or changing a transaction.
    pub fn value<C, S>(
        &self,
        manager: &ConfigManager<C, S>,
        source: ValueSource,
        field: FieldId,
    ) -> Option<ConfigValue>
    where
        C: ConfigModel,
        S: ProfileStore<C>,
    {
        match source {
            ValueSource::Active => manager.active_value(field),
            ValueSource::Committed => manager.committed_value(field),
            ValueSource::Transaction => manager.transaction_value(field),
        }
    }

    pub(super) fn descriptors<C, S>(
        &self,
        manager: &ConfigManager<C, S>,
        request_id: u32,
        first: u16,
        requested: u16,
    ) -> DescriptorPage
    where
        C: ConfigModel,
        S: ProfileStore<C>,
    {
        let mut descriptors = [None; 4];
        let count = requested.min(descriptors.len() as u16);
        let mut len = 0;
        for offset in 0..count {
            let Some(index) = first.checked_add(offset) else {
                break;
            };
            let Some(descriptor) = manager.descriptor(index) else {
                break;
            };
            descriptors[usize::from(len)] = Some(descriptor);
            len += 1;
        }
        DescriptorPage {
            request_id,
            first,
            len,
            descriptors,
        }
    }

    pub(super) fn info<C, S>(&self, manager: &ConfigManager<C, S>, request_id: u32) -> ConfigInfo
    where
        C: ConfigModel,
        S: ProfileStore<C>,
        I: SnapshotImporter<C>,
    {
        ConfigInfo {
            request_id,
            active_generation: manager.active_generation(),
            committed_generation: manager.committed_generation(),
            schema_id: C::SCHEMA_ID,
            profile_format: I::PROFILE_FORMAT,
            field_count: manager.field_count(),
            state: self.state,
            capability_flags: self.capability_flags_for::<C>(),
        }
    }

    pub(super) fn value_response<C, S>(
        &self,
        manager: &ConfigManager<C, S>,
        owner: u64,
        request_id: u32,
        session_id: u32,
        field: FieldId,
        source: ValueSource,
    ) -> ServiceResponse
    where
        C: ConfigModel,
        S: ProfileStore<C>,
    {
        let (value, reply_session, revision) = match source {
            ValueSource::Active => (manager.active_value(field), 0, 0),
            ValueSource::Committed => (manager.committed_value(field), 0, 0),
            ValueSource::Transaction => {
                let Some(session) = self.session else {
                    return ServiceResponse::Result(self.rejected_for(
                        request_id,
                        session_id,
                        ProtocolError::InvalidSession,
                    ));
                };
                if session.id != session_id || session.owner != owner {
                    return ServiceResponse::Result(self.rejected_for(
                        request_id,
                        session_id,
                        ProtocolError::InvalidSession,
                    ));
                }
                (
                    manager.transaction_value(field),
                    session.id,
                    session.revision,
                )
            }
        };
        let Some(value) = value else {
            return ServiceResponse::Result(self.rejected_for(
                request_id,
                session_id,
                ProtocolError::UnknownField(field),
            ));
        };
        ServiceResponse::Value(ValueResponse {
            request_id,
            session_id: reply_session,
            revision,
            field,
            value,
        })
    }
}