icydb_core/db/

session.rs

//! Module: session
//! Responsibility: user-facing query/write execution facade over db executors.
//! Does not own: planning semantics, cursor validation rules, or storage mutation protocol.
//! Boundary: converts fluent/query intent calls into executor operations and response DTOs.

#[cfg(test)]
use crate::db::{DataStore, IndexStore};
use crate::{
    db::{
        Db, EntityResponse, EntitySchemaDescription, FluentDeleteQuery, FluentLoadQuery,
        MissingRowPolicy, PagedGroupedExecutionWithTrace, PagedLoadExecutionWithTrace, PlanError,
        Query, QueryError, QueryTracePlan, StoreRegistry, TraceExecutionStrategy,
        WriteBatchResponse,
        access::AccessStrategy,
        commit::EntityRuntimeHooks,
        cursor::decode_optional_cursor_token,
        describe::describe_entity_model,
        executor::{
            DeleteExecutor, ExecutablePlan, ExecutionStrategy, ExecutorPlanError, LoadExecutor,
            SaveExecutor,
        },
        query::{
            builder::aggregate::AggregateExpr, explain::ExplainAggregateTerminalPlan,
            plan::QueryMode,
        },
    },
    error::InternalError,
    obs::sink::{MetricsSink, with_metrics_sink},
    traits::{CanisterKind, EntityKind, EntityValue},
};
use std::thread::LocalKey;

// Map executor-owned plan-surface failures into query-owned plan errors.
fn map_executor_plan_error(err: ExecutorPlanError) -> QueryError {
    match err {
        ExecutorPlanError::Cursor(err) => QueryError::from(PlanError::from(*err)),
    }
}

// Decode one optional external cursor token and map decode failures into the
// query-plan cursor error boundary.
fn decode_optional_cursor_bytes(cursor_token: Option<&str>) -> Result<Option<Vec<u8>>, QueryError> {
    decode_optional_cursor_token(cursor_token).map_err(|err| QueryError::from(PlanError::from(err)))
}

///
/// DbSession
///
/// Session-scoped database handle with policy (debug, metrics) and execution routing.
///

pub struct DbSession<C: CanisterKind> {
    db: Db<C>,
    debug: bool,
    metrics: Option<&'static dyn MetricsSink>,
}

impl<C: CanisterKind> DbSession<C> {
    /// Construct one session facade for a database handle.
    #[must_use]
    pub(crate) const fn new(db: Db<C>) -> Self {
        Self {
            db,
            debug: false,
            metrics: None,
        }
    }

    /// Construct one session facade from store registry and runtime hooks.
    #[must_use]
    pub const fn new_with_hooks(
        store: &'static LocalKey<StoreRegistry>,
        entity_runtime_hooks: &'static [EntityRuntimeHooks<C>],
    ) -> Self {
        Self::new(Db::new_with_hooks(store, entity_runtime_hooks))
    }

    /// Enable debug execution behavior where supported by executors.
    #[must_use]
    pub const fn debug(mut self) -> Self {
        self.debug = true;
        self
    }

    /// Attach one metrics sink for all session-executed operations.
    #[must_use]
    pub const fn metrics_sink(mut self, sink: &'static dyn MetricsSink) -> Self {
        self.metrics = Some(sink);
        self
    }

    fn with_metrics<T>(&self, f: impl FnOnce() -> T) -> T {
        if let Some(sink) = self.metrics {
            with_metrics_sink(sink, f)
        } else {
            f()
        }
    }

    // Shared save-facade wrapper keeps metrics wiring and response shaping uniform.
    fn execute_save_with<E, T, R>(
        &self,
        op: impl FnOnce(SaveExecutor<E>) -> Result<T, InternalError>,
        map: impl FnOnce(T) -> R,
    ) -> Result<R, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        let value = self.with_metrics(|| op(self.save_executor::<E>()))?;

        Ok(map(value))
    }

    // Shared save-facade wrappers keep response shape explicit at call sites.
    fn execute_save_entity<E>(
        &self,
        op: impl FnOnce(SaveExecutor<E>) -> Result<E, InternalError>,
    ) -> Result<E, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_with(op, std::convert::identity)
    }

    fn execute_save_batch<E>(
        &self,
        op: impl FnOnce(SaveExecutor<E>) -> Result<Vec<E>, InternalError>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_with(op, WriteBatchResponse::new)
    }

    fn execute_save_view<E>(
        &self,
        op: impl FnOnce(SaveExecutor<E>) -> Result<E::ViewType, InternalError>,
    ) -> Result<E::ViewType, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_with(op, std::convert::identity)
    }

    // ---------------------------------------------------------------------
    // Query entry points (public, fluent)
    // ---------------------------------------------------------------------

    /// Start a fluent load query with default missing-row policy (`Ignore`).
    #[must_use]
    pub const fn load<E>(&self) -> FluentLoadQuery<'_, E>
    where
        E: EntityKind<Canister = C>,
    {
        FluentLoadQuery::new(self, Query::new(MissingRowPolicy::Ignore))
    }

    /// Start a fluent load query with explicit missing-row policy.
    #[must_use]
    pub const fn load_with_consistency<E>(
        &self,
        consistency: MissingRowPolicy,
    ) -> FluentLoadQuery<'_, E>
    where
        E: EntityKind<Canister = C>,
    {
        FluentLoadQuery::new(self, Query::new(consistency))
    }

    /// Start a fluent delete query with default missing-row policy (`Ignore`).
    #[must_use]
    pub fn delete<E>(&self) -> FluentDeleteQuery<'_, E>
    where
        E: EntityKind<Canister = C>,
    {
        FluentDeleteQuery::new(self, Query::new(MissingRowPolicy::Ignore).delete())
    }

    /// Start a fluent delete query with explicit missing-row policy.
    #[must_use]
    pub fn delete_with_consistency<E>(
        &self,
        consistency: MissingRowPolicy,
    ) -> FluentDeleteQuery<'_, E>
    where
        E: EntityKind<Canister = C>,
    {
        FluentDeleteQuery::new(self, Query::new(consistency).delete())
    }

    /// Return one stable, human-readable index listing for the entity schema.
    ///
    /// Output format mirrors SQL-style introspection:
    /// - `PRIMARY KEY (field)`
    /// - `INDEX name (field_a, field_b)`
    /// - `UNIQUE INDEX name (field_a, field_b)`
    #[must_use]
    pub fn show_indexes<E>(&self) -> Vec<String>
    where
        E: EntityKind<Canister = C>,
    {
        let mut indexes = Vec::with_capacity(E::MODEL.indexes.len().saturating_add(1));
        indexes.push(format!("PRIMARY KEY ({})", E::MODEL.primary_key.name));

        for index in E::MODEL.indexes {
            let kind = if index.unique {
                "UNIQUE INDEX"
            } else {
                "INDEX"
            };
            let fields = index.fields.join(", ");
            indexes.push(format!("{kind} {} ({fields})", index.name));
        }

        indexes
    }

    /// Return one structured schema description for the entity.
    ///
    /// This is a typed `DESCRIBE`-style introspection surface consumed by
    /// developer tooling and pre-EXPLAIN debugging.
    #[must_use]
    pub fn describe_entity<E>(&self) -> EntitySchemaDescription
    where
        E: EntityKind<Canister = C>,
    {
        describe_entity_model(E::MODEL)
    }

    // ---------------------------------------------------------------------
    // Low-level executors (crate-internal; execution primitives)
    // ---------------------------------------------------------------------

    #[must_use]
    pub(crate) const fn load_executor<E>(&self) -> LoadExecutor<E>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        LoadExecutor::new(self.db, self.debug)
    }

    #[must_use]
    pub(crate) const fn delete_executor<E>(&self) -> DeleteExecutor<E>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        DeleteExecutor::new(self.db, self.debug)
    }

    #[must_use]
    pub(crate) const fn save_executor<E>(&self) -> SaveExecutor<E>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        SaveExecutor::new(self.db, self.debug)
    }

    // ---------------------------------------------------------------------
    // Query diagnostics / execution (internal routing)
    // ---------------------------------------------------------------------

    /// Execute one scalar load/delete query and return materialized response rows.
    pub fn execute_query<E>(&self, query: &Query<E>) -> Result<EntityResponse<E>, QueryError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        let plan = query.plan()?.into_executable();

        let result = match query.mode() {
            QueryMode::Load(_) => self.with_metrics(|| self.load_executor::<E>().execute(plan)),
            QueryMode::Delete(_) => self.with_metrics(|| self.delete_executor::<E>().execute(plan)),
        };

        result.map_err(QueryError::execute)
    }

    // Shared load-query terminal wrapper: build plan, run under metrics, map
    // execution errors into query-facing errors.
    pub(crate) fn execute_load_query_with<E, T>(
        &self,
        query: &Query<E>,
        op: impl FnOnce(LoadExecutor<E>, ExecutablePlan<E>) -> Result<T, InternalError>,
    ) -> Result<T, QueryError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        let plan = query.plan()?.into_executable();

        self.with_metrics(|| op(self.load_executor::<E>(), plan))
            .map_err(QueryError::execute)
    }

    /// Build one trace payload for a query without executing it.
    ///
    /// This lightweight surface is intended for developer diagnostics:
    /// plan hash, access strategy summary, and planner/executor route shape.
    pub fn trace_query<E>(&self, query: &Query<E>) -> Result<QueryTracePlan, QueryError>
    where
        E: EntityKind<Canister = C>,
    {
        let compiled = query.plan()?;
        let explain = compiled.explain();
        let plan_hash = explain.fingerprint().to_string();

        let executable = compiled.into_executable();
        let access_strategy = AccessStrategy::from_plan(executable.access()).debug_summary();
        let execution_strategy = match query.mode() {
            QueryMode::Load(_) => Some(trace_execution_strategy(
                executable
                    .execution_strategy()
                    .map_err(QueryError::execute)?,
            )),
            QueryMode::Delete(_) => None,
        };

        Ok(QueryTracePlan::new(
            plan_hash,
            access_strategy,
            execution_strategy,
            explain,
        ))
    }

    /// Build one aggregate-terminal explain payload without executing the query.
    pub(crate) fn explain_load_query_terminal_with<E>(
        query: &Query<E>,
        aggregate: AggregateExpr,
    ) -> Result<ExplainAggregateTerminalPlan, QueryError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        // Phase 1: build one compiled query once and project logical explain output.
        let compiled = query.plan()?;
        let query_explain = compiled.explain();
        let terminal = aggregate.kind();

        // Phase 2: derive the executor route label for this aggregate terminal.
        let executable = compiled.into_executable();
        let execution = executable.explain_aggregate_terminal_execution_descriptor(aggregate);

        Ok(ExplainAggregateTerminalPlan::new(
            query_explain,
            terminal,
            execution,
        ))
    }

    /// Execute one scalar paged load query and return optional continuation cursor plus trace.
    pub(crate) fn execute_load_query_paged_with_trace<E>(
        &self,
        query: &Query<E>,
        cursor_token: Option<&str>,
    ) -> Result<PagedLoadExecutionWithTrace<E>, QueryError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        // Phase 1: build/validate executable plan and reject grouped plans.
        let plan = query.plan()?.into_executable();
        match plan.execution_strategy().map_err(QueryError::execute)? {
            ExecutionStrategy::PrimaryKey => {
                return Err(QueryError::execute(invariant(
                    "cursor pagination requires explicit or grouped ordering",
                )));
            }
            ExecutionStrategy::Ordered => {}
            ExecutionStrategy::Grouped => {
                return Err(QueryError::execute(invariant(
                    "grouped plans require execute_grouped(...)",
                )));
            }
        }

        // Phase 2: decode external cursor token and validate it against plan surface.
        let cursor_bytes = decode_optional_cursor_bytes(cursor_token)?;
        let cursor = plan
            .prepare_cursor(cursor_bytes.as_deref())
            .map_err(map_executor_plan_error)?;

        // Phase 3: execute one traced page and encode outbound continuation token.
        let (page, trace) = self
            .with_metrics(|| {
                self.load_executor::<E>()
                    .execute_paged_with_cursor_traced(plan, cursor)
            })
            .map_err(QueryError::execute)?;
        let next_cursor = page
            .next_cursor
            .map(|token| {
                let Some(token) = token.as_scalar() else {
                    return Err(QueryError::execute(invariant(
                        "scalar load pagination emitted grouped continuation token",
                    )));
                };

                token.encode().map_err(|err| {
                    QueryError::execute(InternalError::serialize_internal(format!(
                        "failed to serialize continuation cursor: {err}"
                    )))
                })
            })
            .transpose()?;

        Ok(PagedLoadExecutionWithTrace::new(
            page.items,
            next_cursor,
            trace,
        ))
    }

    /// Execute one grouped query page with optional grouped continuation cursor.
    ///
    /// This is the explicit grouped execution boundary; scalar load APIs reject
    /// grouped plans to preserve scalar response contracts.
    pub fn execute_grouped<E>(
        &self,
        query: &Query<E>,
        cursor_token: Option<&str>,
    ) -> Result<PagedGroupedExecutionWithTrace, QueryError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        // Phase 1: build/validate executable plan and require grouped shape.
        let plan = query.plan()?.into_executable();
        if !matches!(
            plan.execution_strategy().map_err(QueryError::execute)?,
            ExecutionStrategy::Grouped
        ) {
            return Err(QueryError::execute(invariant(
                "execute_grouped requires grouped logical plans",
            )));
        }

        // Phase 2: decode external grouped cursor token and validate against plan.
        let cursor_bytes = decode_optional_cursor_bytes(cursor_token)?;
        let cursor = plan
            .prepare_grouped_cursor(cursor_bytes.as_deref())
            .map_err(map_executor_plan_error)?;

        // Phase 3: execute grouped page and encode outbound grouped continuation token.
        let (page, trace) = self
            .with_metrics(|| {
                self.load_executor::<E>()
                    .execute_grouped_paged_with_cursor_traced(plan, cursor)
            })
            .map_err(QueryError::execute)?;
        let next_cursor = page
            .next_cursor
            .map(|token| {
                let Some(token) = token.as_grouped() else {
                    return Err(QueryError::execute(invariant(
                        "grouped pagination emitted scalar continuation token",
                    )));
                };

                token.encode().map_err(|err| {
                    QueryError::execute(InternalError::serialize_internal(format!(
                        "failed to serialize grouped continuation cursor: {err}"
                    )))
                })
            })
            .transpose()?;

        Ok(PagedGroupedExecutionWithTrace::new(
            page.rows,
            next_cursor,
            trace,
        ))
    }

    // ---------------------------------------------------------------------
    // High-level write API (public, intent-level)
    // ---------------------------------------------------------------------

    /// Insert one entity row.
    pub fn insert<E>(&self, entity: E) -> Result<E, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_entity(|save| save.insert(entity))
    }

    /// Insert a single-entity-type batch atomically in one commit window.
    ///
    /// If any item fails pre-commit validation, no row in the batch is persisted.
    ///
    /// This API is not a multi-entity transaction surface.
    pub fn insert_many_atomic<E>(
        &self,
        entities: impl IntoIterator<Item = E>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_batch(|save| save.insert_many_atomic(entities))
    }

    /// Insert a batch with explicitly non-atomic semantics.
    ///
    /// WARNING: fail-fast and non-atomic. Earlier inserts may commit before an error.
    pub fn insert_many_non_atomic<E>(
        &self,
        entities: impl IntoIterator<Item = E>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_batch(|save| save.insert_many_non_atomic(entities))
    }

    /// Replace one existing entity row.
    pub fn replace<E>(&self, entity: E) -> Result<E, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_entity(|save| save.replace(entity))
    }

    /// Replace a single-entity-type batch atomically in one commit window.
    ///
    /// If any item fails pre-commit validation, no row in the batch is persisted.
    ///
    /// This API is not a multi-entity transaction surface.
    pub fn replace_many_atomic<E>(
        &self,
        entities: impl IntoIterator<Item = E>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_batch(|save| save.replace_many_atomic(entities))
    }

    /// Replace a batch with explicitly non-atomic semantics.
    ///
    /// WARNING: fail-fast and non-atomic. Earlier replaces may commit before an error.
    pub fn replace_many_non_atomic<E>(
        &self,
        entities: impl IntoIterator<Item = E>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_batch(|save| save.replace_many_non_atomic(entities))
    }

    /// Update one existing entity row.
    pub fn update<E>(&self, entity: E) -> Result<E, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_entity(|save| save.update(entity))
    }

    /// Update a single-entity-type batch atomically in one commit window.
    ///
    /// If any item fails pre-commit validation, no row in the batch is persisted.
    ///
    /// This API is not a multi-entity transaction surface.
    pub fn update_many_atomic<E>(
        &self,
        entities: impl IntoIterator<Item = E>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_batch(|save| save.update_many_atomic(entities))
    }

    /// Update a batch with explicitly non-atomic semantics.
    ///
    /// WARNING: fail-fast and non-atomic. Earlier updates may commit before an error.
    pub fn update_many_non_atomic<E>(
        &self,
        entities: impl IntoIterator<Item = E>,
    ) -> Result<WriteBatchResponse<E>, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_batch(|save| save.update_many_non_atomic(entities))
    }

    /// Insert one view value and return the stored view.
    pub fn insert_view<E>(&self, view: E::ViewType) -> Result<E::ViewType, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_view::<E>(|save| save.insert_view(view))
    }

    /// Replace one view value and return the stored view.
    pub fn replace_view<E>(&self, view: E::ViewType) -> Result<E::ViewType, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_view::<E>(|save| save.replace_view(view))
    }

    /// Update one view value and return the stored view.
    pub fn update_view<E>(&self, view: E::ViewType) -> Result<E::ViewType, InternalError>
    where
        E: EntityKind<Canister = C> + EntityValue,
    {
        self.execute_save_view::<E>(|save| save.update_view(view))
    }

    /// TEST ONLY: clear all registered data and index stores for this database.
    #[cfg(test)]
    #[doc(hidden)]
    pub fn clear_stores_for_tests(&self) {
        self.db.with_store_registry(|reg| {
            // Test cleanup only: clearing all stores is set-like and does not
            // depend on registry iteration order.
            for (_, store) in reg.iter() {
                store.with_data_mut(DataStore::clear);
                store.with_index_mut(IndexStore::clear);
            }
        });
    }
}

fn invariant(message: impl Into<String>) -> InternalError {
    InternalError::query_executor_invariant(message)
}

const fn trace_execution_strategy(strategy: ExecutionStrategy) -> TraceExecutionStrategy {
    match strategy {
        ExecutionStrategy::PrimaryKey => TraceExecutionStrategy::PrimaryKey,
        ExecutionStrategy::Ordered => TraceExecutionStrategy::Ordered,
        ExecutionStrategy::Grouped => TraceExecutionStrategy::Grouped,
    }
}

///
/// TESTS
///

#[cfg(test)]
mod tests {
    use super::*;
    use crate::db::cursor::CursorPlanError;

    // Assert query-surface cursor errors remain wrapped under QueryError::Plan(PlanError::Cursor).
    fn assert_query_error_is_cursor_plan(
        err: QueryError,
        predicate: impl FnOnce(&CursorPlanError) -> bool,
    ) {
        assert!(matches!(
            err,
            QueryError::Plan(plan_err)
                if matches!(
                    plan_err.as_ref(),
                    PlanError::Cursor(inner) if predicate(inner.as_ref())
                )
        ));
    }

    // Assert both session conversion paths preserve the same cursor-plan variant payload.
    fn assert_cursor_mapping_parity(
        build: impl Fn() -> CursorPlanError,
        predicate: impl Fn(&CursorPlanError) -> bool + Copy,
    ) {
        let mapped_via_executor = map_executor_plan_error(ExecutorPlanError::from(build()));
        assert_query_error_is_cursor_plan(mapped_via_executor, predicate);

        let mapped_via_plan = QueryError::from(PlanError::from(build()));
        assert_query_error_is_cursor_plan(mapped_via_plan, predicate);
    }

    #[test]
    fn session_cursor_error_mapping_parity_boundary_arity() {
        assert_cursor_mapping_parity(
            || CursorPlanError::continuation_cursor_boundary_arity_mismatch(2, 1),
            |inner| {
                matches!(
                    inner,
                    CursorPlanError::ContinuationCursorBoundaryArityMismatch {
                        expected: 2,
                        found: 1
                    }
                )
            },
        );
    }

    #[test]
    fn session_cursor_error_mapping_parity_window_mismatch() {
        assert_cursor_mapping_parity(
            || CursorPlanError::continuation_cursor_window_mismatch(8, 3),
            |inner| {
                matches!(
                    inner,
                    CursorPlanError::ContinuationCursorWindowMismatch {
                        expected_offset: 8,
                        actual_offset: 3
                    }
                )
            },
        );
    }

    #[test]
    fn session_cursor_error_mapping_parity_decode_reason() {
        assert_cursor_mapping_parity(
            || {
                CursorPlanError::invalid_continuation_cursor(
                    crate::db::codec::cursor::CursorDecodeError::OddLength,
                )
            },
            |inner| {
                matches!(
                    inner,
                    CursorPlanError::InvalidContinuationCursor {
                        reason: crate::db::codec::cursor::CursorDecodeError::OddLength
                    }
                )
            },
        );
    }

    #[test]
    fn session_cursor_error_mapping_parity_primary_key_type_mismatch() {
        assert_cursor_mapping_parity(
            || {
                CursorPlanError::continuation_cursor_primary_key_type_mismatch(
                    "id",
                    "ulid",
                    Some(crate::value::Value::Text("not-a-ulid".to_string())),
                )
            },
            |inner| {
                matches!(
                    inner,
                    CursorPlanError::ContinuationCursorPrimaryKeyTypeMismatch {
                        field,
                        expected,
                        value: Some(crate::value::Value::Text(value))
                    } if field == "id" && expected == "ulid" && value == "not-a-ulid"
                )
            },
        );
    }

    #[test]
    fn session_cursor_error_mapping_parity_matrix_preserves_cursor_variants() {
        // Keep one matrix-level canary test name so cross-module audit references remain stable.
        assert_cursor_mapping_parity(
            || CursorPlanError::continuation_cursor_boundary_arity_mismatch(2, 1),
            |inner| {
                matches!(
                    inner,
                    CursorPlanError::ContinuationCursorBoundaryArityMismatch {
                        expected: 2,
                        found: 1
                    }
                )
            },
        );
    }
}