feat: add find_last_slot_per_block method to schedule repositories and update related logic

k-tv-backend/infra/src/schedule_repository/postgres.rs

@@ -1,9 +1,11 @@
 use async_trait::async_trait;
 use chrono::{DateTime, Utc};
 
-use domain::{ChannelId, DomainError, DomainResult, GeneratedSchedule, PlaybackRecord, ScheduleRepository};
+use std::collections::HashMap;
 
-use super::mapping::{map_schedule, PlaybackRecordRow, ScheduleRow, SlotRow};
+use domain::{BlockId, ChannelId, DomainError, DomainResult, GeneratedSchedule, MediaItemId, PlaybackRecord, ScheduleRepository};
+
+use super::mapping::{map_schedule, LastSlotRow, PlaybackRecordRow, ScheduleRow, SlotRow};
 
 pub struct PostgresScheduleRepository {
     pool: sqlx::Pool<sqlx::Postgres>,
@@ -143,6 +145,41 @@ impl ScheduleRepository for PostgresScheduleRepository {
         rows.into_iter().map(PlaybackRecord::try_from).collect()
     }
 
+    async fn find_last_slot_per_block(
+        &self,
+        channel_id: ChannelId,
+    ) -> DomainResult<HashMap<BlockId, MediaItemId>> {
+        let channel_id_str = channel_id.to_string();
+        let rows: Vec<LastSlotRow> = sqlx::query_as(
+            "SELECT ss.source_block_id, ss.item \
+             FROM scheduled_slots ss \
+             INNER JOIN generated_schedules gs ON gs.id = ss.schedule_id \
+             WHERE gs.channel_id = $1 \
+               AND ss.start_at = ( \
+                   SELECT MAX(ss2.start_at) \
+                   FROM scheduled_slots ss2 \
+                   INNER JOIN generated_schedules gs2 ON gs2.id = ss2.schedule_id \
+                   WHERE ss2.source_block_id = ss.source_block_id \
+                     AND gs2.channel_id = $2 \
+               )",
+        )
+        .bind(&channel_id_str)
+        .bind(&channel_id_str)
+        .fetch_all(&self.pool)
+        .await
+        .map_err(|e| DomainError::RepositoryError(e.to_string()))?;
+
+        let mut map = HashMap::new();
+        for row in rows {
+            let block_id = uuid::Uuid::parse_str(&row.source_block_id)
+                .map_err(|e| DomainError::RepositoryError(format!("Invalid block UUID: {}", e)))?;
+            let item: domain::MediaItem = serde_json::from_str(&row.item)
+                .map_err(|e| DomainError::RepositoryError(format!("Invalid slot item JSON: {}", e)))?;
+            map.insert(block_id, item.id);
+        }
+        Ok(map)
+    }
+
     async fn save_playback_record(&self, record: &PlaybackRecord) -> DomainResult<()> {
         sqlx::query(
             r#"