refactor: extract shared file-status query logic into utility function

- Created app/utils/file_queries.py with apply_status_filter function
- Updated app/api/files.py to use shared function
- Updated app/views/files.py to use shared function
- Removed unused 'or_' import from app/api/files.py
- Added comprehensive tests in tests/test_file_queries.py
- All tests pass (10 new tests, 14 existing tests verified)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/utils/file_queries.py

@@ -0,0 +1,72 @@
+"""
+Shared file query utilities for filtering files by processing status.
+
+This module contains reusable query logic for filtering FileRecord objects
+based on their processing status (pending, processing, failed, completed).
+"""
+
+from typing import Optional
+
+from sqlalchemy import or_
+from sqlalchemy.orm import Query, Session
+
+from app.models import FileRecord, ProcessingLog
+
+
+def apply_status_filter(query: Query, db: Session, status: Optional[str]) -> Query:
+    """
+    Apply status filter to a FileRecord query.
+
+    This function modifies a SQLAlchemy query to filter files based on their
+    processing status by examining associated ProcessingLog entries.
+
+    Args:
+        query: The base SQLAlchemy query for FileRecord objects
+        db: Database session for creating subqueries
+        status: Status filter to apply. Valid values:
+            - "pending": Files with no ProcessingLog entries
+            - "processing": Files with in_progress logs
+            - "failed": Files with failure logs
+            - "completed": Files with success logs but no failures or in_progress
+            - None: No filter applied (returns query unchanged)
+
+    Returns:
+        Modified query with status filter applied
+
+    Examples:
+        >>> query = db.query(FileRecord)
+        >>> query = apply_status_filter(query, db, "completed")
+        >>> files = query.all()
+    """
+    if not status:
+        return query
+
+    # Subquery to get file IDs matching the status
+    if status == "pending":
+        # Files with no logs
+        subq = db.query(ProcessingLog.file_id).distinct()
+        query = query.filter(~FileRecord.id.in_(subq))
+    elif status == "processing":
+        # Files with in_progress logs
+        subq = db.query(ProcessingLog.file_id).filter(ProcessingLog.status == "in_progress").distinct()
+        query = query.filter(FileRecord.id.in_(subq))
+    elif status == "failed":
+        # Files with failure logs
+        subq = db.query(ProcessingLog.file_id).filter(ProcessingLog.status == "failure").distinct()
+        query = query.filter(FileRecord.id.in_(subq))
+    elif status == "completed":
+        # Files with success logs but no failures or in_progress
+        success_files = db.query(ProcessingLog.file_id).filter(ProcessingLog.status == "success").distinct().subquery()
+
+        failed_files = (
+            db.query(ProcessingLog.file_id)
+            .filter(or_(ProcessingLog.status == "failure", ProcessingLog.status == "in_progress"))
+            .distinct()
+            .subquery()
+        )
+
+        query = query.filter(FileRecord.id.in_(db.query(success_files.c.file_id))).filter(
+            ~FileRecord.id.in_(db.query(failed_files.c.file_id))
+        )
+
+    return query