pg_tviews 0.1.0-beta.11

use pgrx::datum::DatumWithOid;
use pgrx::prelude::*;
use std::collections::HashMap;

/// Propagation Engine: Parent Discovery for Dependent Views
///
/// This module provides parent discovery for the transaction-level queue:
/// - **Parent Discovery**: Finds views that depend on changed entities
/// - **Affected Row Identification**: Locates rows impacted by changes
///
/// Used by the `PRE_COMMIT` handler (`src/queue/`) to iteratively discover
/// and enqueue parent TVIEWs for refresh.
use crate::queue::RefreshKey;

/// Find parent keys that depend on the given entity+pk (without refreshing them)
///
/// Propagation that returns keys instead of
/// performing immediate recursive refreshes.
///
/// # Example
///
/// ```rust
/// let key = RefreshKey::pk("user", 1);
/// let parents = find_parents_for(&key)?;
/// // Returns: [
/// //   RefreshKey::pk("post", 10),
/// //   RefreshKey::pk("post", 20),
/// //   RefreshKey::pk("comment", 5),
/// // ]
/// // These are all the tv_post and tv_comment rows where fk_user = 1
/// ```
pub fn find_parents_for(
    key: &RefreshKey,
    graph: &crate::queue::EntityDepGraph,
) -> crate::TViewResult<Vec<RefreshKey>> {
    // Find all parent entities that depend on this entity (from cached graph)
    let parent_entities = find_parent_entities(&key.entity, graph)?;

    if parent_entities.is_empty() {
        return Ok(Vec::new());
    }

    // Propagation only applies to PK-based keys; DISTINCT ON dedup keys
    // do not carry a FK value that parent TVIEWs can use for lookup.
    if key.is_dedup() {
        return Ok(Vec::new());
    }

    // Pre-allocate parent_keys: conservatively estimate 8 parents per entity on average
    let expected_parents = parent_entities.len().saturating_mul(8);
    let mut parent_keys = Vec::with_capacity(expected_parents);

    // For each parent entity, find affected rows
    for parent_entity in parent_entities {
        let affected_pks = find_affected_pks(&parent_entity, &key.entity, key.pk)?;

        // Convert to RefreshKeys
        for pk in affected_pks {
            parent_keys.push(RefreshKey::pk(&parent_entity, pk));
        }
    }

    Ok(parent_keys)
}

/// Find parent keys for multiple child keys in a single batched operation (P-07).
///
/// This is the **optimized version of find_parents_for** that batches multiple keys
/// into fewer SPI queries. Instead of calling find_affected_pks once per key,
/// it groups keys by (parent_entity, child_entity) and issues ONE query per group
/// using PostgreSQL's `= ANY($1)` operator.
///
/// # Performance
/// - **Before**: N keys × M parent entities = N*M SPI queries
/// - **After**: N keys × M parent entities = M SPI queries (batched)
/// - **Example**: 3 changed user PKs with 2 parent entities (post, comment)
///   - Before: 6 queries (3 × 2)
///   - After: 2 queries (1 per parent entity)
///
/// # Arguments
/// * `keys` - Multiple RefreshKey values to propagate
/// * `graph` - Cached entity dependency graph
///
/// # Returns
/// Map from each input key to its discovered parent keys
pub fn find_parents_batch(
    keys: &[RefreshKey],
    graph: &crate::queue::EntityDepGraph,
) -> crate::TViewResult<HashMap<RefreshKey, Vec<RefreshKey>>> {
    // Pre-allocate result HashMap: expect ~2 parent entities per key on average
    let mut result: HashMap<RefreshKey, Vec<RefreshKey>> = HashMap::with_capacity(keys.len());

    // Filter to PK-only keys (dedup keys don't propagate)
    // Pre-allocate with capacity for all keys (worst case: all are PK-based)
    let pk_keys: Vec<_> = keys.iter().filter(|k| !k.is_dedup()).cloned().collect();

    if pk_keys.is_empty() {
        return Ok(result);
    }

    // Build batch groups: (parent_entity, child_entity) -> Vec<child_pk>
    let batch_groups = build_batch_groups(&pk_keys, graph)?;

    // Execute one query per group
    for ((parent_entity, child_entity), child_pks) in batch_groups {
        let affected_pk_map = find_affected_pks_batch(&parent_entity, &child_entity, &child_pks)?;

        // Map results back to original keys
        for key in &pk_keys {
            if key.entity == child_entity
                && let Some(affected_pks) = affected_pk_map.get(&key.pk)
            {
                for pk in affected_pks {
                    result
                        .entry(key.clone())
                        .or_insert_with(|| Vec::with_capacity(8))
                        .push(RefreshKey::pk(&parent_entity, *pk));
                }
            }
        }
    }

    Ok(result)
}

/// Build batch groups for propagation query (unit-testable logic).
///
/// Groups keys by (parent_entity, child_entity) to minimize queries.
/// Returns: Map<(parent, child), Vec<child_pk>>
fn build_batch_groups(
    keys: &[RefreshKey],
    graph: &crate::queue::EntityDepGraph,
) -> crate::TViewResult<HashMap<(String, String), Vec<i64>>> {
    // Pre-allocate groups HashMap: expect ~2-4 unique (parent, child) pairs on average
    let mut groups: HashMap<(String, String), Vec<i64>> = HashMap::with_capacity(4);

    for key in keys {
        // Get parent entities for this child from the cached graph
        let parent_entities = graph.parents.get(&key.entity).cloned().unwrap_or_default();

        for parent_entity in parent_entities {
            groups
                .entry((parent_entity, key.entity.clone()))
                .or_insert_with(|| Vec::with_capacity(8))
                .push(key.pk);
        }
    }

    Ok(groups)
}

/// Find all PKs in a parent TVIEW that reference any of the given child PKs (batched).
///
/// This uses PostgreSQL's `= ANY($1)` to check multiple FKs in one query.
/// Returns a map from child_pk to the list of parent PKs referencing it.
fn find_affected_pks_batch(
    parent_entity: &str,
    child_entity: &str,
    child_pks: &[i64],
) -> spi::Result<HashMap<i64, Vec<i64>>> {
    let fk_col = format!("fk_{child_entity}");
    let parent_table = format!("tv_{parent_entity}");
    let parent_pk_col = format!("pk_{parent_entity}");

    // Use = ANY($1) to batch multiple child PKs into one query
    let query =
        format!("SELECT {fk_col}, {parent_pk_col} FROM {parent_table} WHERE {fk_col} = ANY($1)");

    Spi::connect(|client| {
        // Convert child_pks to a PostgreSQL array datum
        let pks_array = child_pks.to_vec();
        let args = vec![unsafe {
            DatumWithOid::new(
                pks_array,
                PgOid::BuiltIn(PgBuiltInOids::INT8ARRAYOID).value(),
            )
        }];

        let rows = client.select(&query, None, &args)?;
        // Pre-allocate result HashMap: expect entries for each unique child_pk
        let mut result: HashMap<i64, Vec<i64>> = HashMap::with_capacity(child_pks.len());

        for row in rows {
            if let (Some(child_pk), Some(parent_pk)) = (
                row[fk_col.as_str()].value::<i64>()?,
                row[parent_pk_col.as_str()].value::<i64>()?,
            ) {
                result
                    .entry(child_pk)
                    .or_insert_with(|| Vec::with_capacity(4))
                    .push(parent_pk);
            }
        }

        Ok(result)
    })
}

/// Find all parent entities that depend on the given entity (from cached graph).
///
/// Example: `find_parent_entities`("user") -> `["post", "comment"]`
/// This means `tv_post` and `tv_comment` both have FK references to `tv_user`
fn find_parent_entities(
    child_entity: &str,
    graph: &crate::queue::EntityDepGraph,
) -> spi::Result<Vec<String>> {
    // Look up parent entities from cached graph (no SPI query)
    Ok(graph.parents.get(child_entity).cloned().unwrap_or_default())
}

/// Find all PKs in the parent TVIEW that reference the given child PK.
///
/// Example: `find_affected_pks`("post", "user", 1)
/// Returns all `pk_post` values where `fk_user` = 1
fn find_affected_pks(
    parent_entity: &str,
    child_entity: &str,
    child_pk: i64,
) -> spi::Result<Vec<i64>> {
    let fk_col = format!("fk_{child_entity}");
    let parent_table = format!("tv_{parent_entity}");
    let parent_pk_col = format!("pk_{parent_entity}");

    // Table/column names are from pg_tview_meta (internal); child_pk is parameterized
    let query = format!("SELECT {parent_pk_col} FROM {parent_table} WHERE {fk_col} = $1");
    let args = vec![unsafe {
        DatumWithOid::new(child_pk, PgOid::BuiltIn(PgBuiltInOids::INT8OID).value())
    }];

    Spi::connect(|client| {
        let rows = client.select(&query, None, &args)?;
        let mut pks = Vec::new();

        for row in rows {
            if let Some(pk) = row[parent_pk_col.as_str()].value::<i64>()? {
                pks.push(pk);
            }
        }

        Ok(pks)
    })
}

#[cfg(any(test, feature = "pg_test"))]
#[pg_schema]
mod tests {
    use super::*;
    use pgrx::prelude::Spi;

    /// Test pre-allocation in batch parent discovery.
    ///
    /// Verifies that:
    /// 1. Pre-allocation is correct and doesn't change results
    /// 2. Batching correctly groups by (parent, child) entities
    /// 3. Results match non-batched discovery for same input
    ///
    /// Scenario: Multiple children from same entity with multiple parent entities
    #[pg_test]
    fn test_find_parents_batch_pre_allocation() {
        // Setup: Create tables with multiple FK relationships
        Spi::run("CREATE TABLE tb_user (pk_user BIGSERIAL PRIMARY KEY, name TEXT)").unwrap();
        Spi::run(
            "CREATE TABLE tb_post (
            pk_post BIGSERIAL PRIMARY KEY,
            fk_user BIGINT REFERENCES tb_user(pk_user),
            title TEXT
        )",
        )
        .unwrap();
        Spi::run(
            "CREATE TABLE tb_comment (
            pk_comment BIGSERIAL PRIMARY KEY,
            fk_user BIGINT REFERENCES tb_user(pk_user),
            fk_post BIGINT REFERENCES tb_post(pk_post),
            text TEXT
        )",
        )
        .unwrap();

        // Insert test data
        Spi::run("INSERT INTO tb_user (pk_user, name) VALUES (1, 'Alice'), (2, 'Bob')").unwrap();
        Spi::run("INSERT INTO tb_post (pk_post, fk_user, title) VALUES (1, 1, 'Post 1'), (2, 1, 'Post 2'), (3, 2, 'Post 3')").unwrap();
        Spi::run(
            "INSERT INTO tb_comment (pk_comment, fk_user, fk_post, text)
                  VALUES (1, 1, 1, 'Comment 1'), (2, 1, 2, 'Comment 2'), (3, 2, 3, 'Comment 3')",
        )
        .unwrap();

        // Create dependency TVIEWs
        Spi::run(
            "
            SELECT pg_tviews_create('user', $$
                SELECT pk_user, jsonb_build_object('name', name) AS data
                FROM tb_user
            $$)
        ",
        )
        .unwrap();

        Spi::run(
            "
            SELECT pg_tviews_create('post', $$
                SELECT pk_post, fk_user,
                       jsonb_build_object('title', title, 'author', v_user.data) AS data
                FROM tb_post
                LEFT JOIN v_user ON v_user.pk_user = tb_post.fk_user
            $$)
        ",
        )
        .unwrap();

        Spi::run(
            "
            SELECT pg_tviews_create('comment', $$
                SELECT pk_comment, fk_user, fk_post,
                       jsonb_build_object('text', text) AS data
                FROM tb_comment
            $$)
        ",
        )
        .unwrap();

        // Test: Find parents for multiple user PKs using batched discovery
        let graph = crate::queue::EntityDepGraph::load().unwrap();

        let keys = vec![
            crate::queue::RefreshKey::pk("user", 1),
            crate::queue::RefreshKey::pk("user", 2),
        ];

        // Batched discovery
        let batched_result = find_parents_batch(&keys, &graph).unwrap();

        // Verify results are non-empty
        assert!(!batched_result.is_empty(), "Should find parent entities");

        // For user pk=1, should find posts 1, 2
        let key1 = &keys[0];
        if let Some(parents) = batched_result.get(key1) {
            // Should have multiple post parents
            let post_parents: Vec<_> = parents.iter().filter(|p| p.entity == "post").collect();
            assert!(!post_parents.is_empty(), "User 1 should have post parents");
        }

        // For user pk=2, should find post 3
        let key2 = &keys[1];
        if let Some(parents) = batched_result.get(key2) {
            let post_parents: Vec<_> = parents.iter().filter(|p| p.entity == "post").collect();
            assert!(!post_parents.is_empty(), "User 2 should have post parents");
        }
    }

    /// Test that batch pre-allocation handles empty parent case correctly.
    ///
    /// Verifies that pre-allocations handle the edge case where a child
    /// entity has no parents (no FK references from other entities).
    #[pg_test]
    fn test_find_parents_batch_no_parents() {
        // Setup: Single entity with no FK references
        Spi::run("CREATE TABLE tb_tag (pk_tag BIGSERIAL PRIMARY KEY, name TEXT)").unwrap();
        Spi::run("INSERT INTO tb_tag (pk_tag, name) VALUES (1, 'Tag1'), (2, 'Tag2')").unwrap();

        // Create TVIEW
        Spi::run(
            "
            SELECT pg_tviews_create('tag', $$
                SELECT pk_tag, jsonb_build_object('name', name) AS data
                FROM tb_tag
            $$)
        ",
        )
        .unwrap();

        let graph = crate::queue::EntityDepGraph::load().unwrap();

        let keys = vec![
            crate::queue::RefreshKey::pk("tag", 1),
            crate::queue::RefreshKey::pk("tag", 2),
        ];

        let result = find_parents_batch(&keys, &graph).unwrap();

        // Should return empty or no entries for tag (no parents)
        let has_tag_results = keys.iter().any(|k| result.contains_key(k));

        // Either tag has no parents (expected) or result is empty
        if has_tag_results {
            for parents in result.values() {
                assert!(parents.is_empty(), "Tag should have no parents");
            }
        }
    }
}