"""Unit tests for SyncEngine.

Tests queue management, sync flow, error handling, and retry logic
for the local-to-remote synchronization system.
"""

import json
import sqlite3
from datetime import UTC, datetime, timedelta

# ============================================================================
# FIXTURES
# ============================================================================
from typing import Any
from unittest.mock import AsyncMock, MagicMock

import pytest

from tests.test_constants import COUNT_FOUR, COUNT_THREE, COUNT_TWO


@pytest.fixture
def sync_db(tmp_path: Any) -> None:
    """Fixture: Sync Database.

    Provides: SQLite database with sync tables
    """
    db_path = tmp_path / "sync.db"
    conn = sqlite3.connect(db_path)
    cursor = conn.cursor()

    # Sync queue table
    cursor.execute("""
        CREATE TABLE sync_queue (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            entity_type TEXT NOT NULL,
            entity_id TEXT NOT NULL,
            operation TEXT NOT NULL,
            payload TEXT NOT NULL,
            created_at TEXT NOT NULL,
            retry_count INTEGER DEFAULT 0,
            last_error TEXT,
            UNIQUE(entity_type, entity_id, operation)
        )
    """)

    # Sync state table
    cursor.execute("""
        CREATE TABLE sync_state (
            key TEXT PRIMARY KEY,
            value TEXT NOT NULL,
            updated_at TEXT NOT NULL
        )
    """)

    conn.commit()
    conn.close()

    return db_path


@pytest.fixture
def mock_api_client() -> None:
    """Mock API client for testing sync operations."""
    client = MagicMock()
    client.upload_changes = AsyncMock(return_value={"success": True, "conflicts": []})
    client.download_changes = AsyncMock(return_value={"changes": [], "server_time": datetime.now(UTC).isoformat()})
    client.is_online = MagicMock(return_value=True)
    return client


@pytest.fixture
def sample_queue_entry() -> None:
    """Sample sync queue entry."""
    return {
        "entity_type": "item",
        "entity_id": "item-001",
        "operation": "create",
        "payload": json.dumps({"title": "New Item", "status": "todo", "type": "story"}),
        "created_at": datetime.now(UTC).isoformat(),
        "retry_count": 0,
        "last_error": None,
    }


# ============================================================================
# TEST CLASSES - Queue Management
# ============================================================================


class TestSyncEngineQueueManagement:
    """Test Suite: Sync Engine - Queue Management.

    Tests adding, retrieving, and removing entries from sync queue
    """

    @pytest.mark.unit
    def test_add_to_queue(self, sync_db: Any, sample_queue_entry: Any) -> None:
        """TC-SE.1.1: Add to Queue - Success.

        Given: Change occurred locally
        When: Change is added to queue
        Then: Entry is persisted
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Act
        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at, retry_count)
            VALUES (?, ?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
                sample_queue_entry["retry_count"],
            ),
        )
        conn.commit()

        # Assert
        cursor.execute("SELECT * FROM sync_queue WHERE entity_id = ?", (sample_queue_entry["entity_id"],))
        result = cursor.fetchone()
        conn.close()

        assert result is not None
        assert result[1] == "item"
        assert result[3] == "create"

    @pytest.mark.unit
    def test_get_pending_items(self, sync_db: Any) -> None:
        """TC-SE.1.2: Get Pending Items - Returns All Unsynced.

        Given: Multiple items in queue
        When: Pending items are requested
        Then: All items are returned in order
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Add multiple items
        for i in range(3):
            cursor.execute(
                """
                INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at)
                VALUES (?, ?, ?, ?, ?)
            """,
                ("item", f"item-{i:03d}", "create", json.dumps({"id": i}), datetime.now(UTC).isoformat()),
            )
        conn.commit()

        # Act
        cursor.execute("SELECT * FROM sync_queue ORDER BY id ASC")
        results = cursor.fetchall()
        conn.close()

        # Assert
        assert len(results) == COUNT_THREE
        assert results[0][2] == "item-000"
        assert results[2][2] == "item-002"

    @pytest.mark.unit
    def test_remove_from_queue(self, sync_db: Any, sample_queue_entry: Any) -> None:
        """TC-SE.1.3: Remove from Queue - After Successful Sync.

        Given: Item in queue
        When: Sync succeeds
        Then: Item is removed from queue
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at)
            VALUES (?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
            ),
        )
        conn.commit()

        # Act
        cursor.execute("DELETE FROM sync_queue WHERE entity_id = ?", (sample_queue_entry["entity_id"],))
        conn.commit()

        # Assert
        cursor.execute("SELECT * FROM sync_queue WHERE entity_id = ?", (sample_queue_entry["entity_id"],))
        result = cursor.fetchone()
        conn.close()

        assert result is None

    @pytest.mark.unit
    def test_update_retry_count(self, sync_db: Any, sample_queue_entry: Any) -> None:
        """TC-SE.1.4: Update Retry Count - After Failed Sync.

        Given: Item in queue
        When: Sync fails
        Then: Retry count is incremented
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at, retry_count)
            VALUES (?, ?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
                0,
            ),
        )
        conn.commit()

        # Act
        cursor.execute(
            """
            UPDATE sync_queue
            SET retry_count = retry_count + 1, last_error = ?
            WHERE entity_id = ?
        """,
            ("Network error", sample_queue_entry["entity_id"]),
        )
        conn.commit()

        # Assert
        cursor.execute(
            "SELECT retry_count, last_error FROM sync_queue WHERE entity_id = ?",
            (sample_queue_entry["entity_id"],),
        )
        result = cursor.fetchone()
        conn.close()

        assert result[0] == 1
        assert result[1] == "Network error"

    @pytest.mark.unit
    def test_filter_by_max_retries(self, sync_db: Any) -> None:
        """TC-SE.1.5: Filter by Max Retries - Skip Failed Items.

        Given: Items with various retry counts
        When: Queue is filtered by max retries
        Then: Only eligible items are returned
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Add items with different retry counts
        retry_counts = [0, 1, 2, 3, 5]  # Max retries = 3
        for i, count in enumerate(retry_counts):
            cursor.execute(
                """
                INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at, retry_count)
                VALUES (?, ?, ?, ?, ?, ?)
            """,
                ("item", f"item-{i:03d}", "create", json.dumps({"id": i}), datetime.now(UTC).isoformat(), count),
            )
        conn.commit()

        # Act
        max_retries = 3
        cursor.execute(
            """
            SELECT * FROM sync_queue WHERE retry_count <= ?
        """,
            (max_retries,),
        )
        results = cursor.fetchall()
        conn.close()

        # Assert
        assert len(results) == COUNT_FOUR  # Only items with retry_count <= COUNT_THREE


# ============================================================================
# TEST CLASSES - Sync Flow
# ============================================================================


class TestSyncEngineSyncFlow:
    """Test Suite: Sync Engine - Sync Flow.

    Tests complete sync process including upload and download phases
    """

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_upload_phase_success(self, sync_db: Any, mock_api_client: Any, sample_queue_entry: Any) -> None:
        """TC-SE.2.1: Upload Phase - Success.

        Given: Pending changes in queue
        When: Upload sync is triggered
        Then: Changes are sent to server
        And: Queue is cleared
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at)
            VALUES (?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
            ),
        )
        conn.commit()

        # Act
        cursor.execute("SELECT * FROM sync_queue")
        pending = cursor.fetchall()

        # Simulate upload
        changes = [
            {"entity_type": row[1], "entity_id": row[2], "operation": row[3], "payload": json.loads(row[4])}
            for row in pending
        ]

        result = await mock_api_client.upload_changes(changes)

        # Simulate queue cleanup on success
        if result["success"]:
            cursor.execute("DELETE FROM sync_queue WHERE entity_id = ?", (sample_queue_entry["entity_id"],))
            conn.commit()

        # Assert
        cursor.execute("SELECT * FROM sync_queue")
        remaining = cursor.fetchall()
        conn.close()

        assert result["success"] is True
        assert len(remaining) == 0
        mock_api_client.upload_changes.assert_called_once()

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_download_phase_success(self, sync_db: Any, mock_api_client: Any) -> None:
        """TC-SE.2.2: Download Phase - Success.

        Given: Server has new changes
        When: Download sync is triggered
        Then: Changes are retrieved
        And: Last sync time is updated
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        last_sync = (datetime.now(UTC) - timedelta(hours=1)).isoformat()

        # Act
        result = await mock_api_client.download_changes(since=last_sync)

        # Update last sync time
        cursor.execute(
            """
            INSERT OR REPLACE INTO sync_state (key, value, updated_at)
            VALUES (?, ?, ?)
        """,
            ("last_sync", result["server_time"], datetime.now(UTC).isoformat()),
        )
        conn.commit()

        # Assert
        cursor.execute("SELECT value FROM sync_state WHERE key = ?", ("last_sync",))
        stored_sync_time = cursor.fetchone()
        conn.close()

        assert stored_sync_time is not None
        mock_api_client.download_changes.assert_called_once()

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_bidirectional_sync(self, sync_db: Any, mock_api_client: Any, sample_queue_entry: Any) -> None:
        """TC-SE.2.3: Bidirectional Sync - Upload then Download.

        Given: Local changes and remote changes exist
        When: Full sync is triggered
        Then: Upload completes first
        And: Download completes second
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at)
            VALUES (?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
            ),
        )
        conn.commit()

        # Act - Upload phase
        cursor.execute("SELECT * FROM sync_queue")
        pending = cursor.fetchall()
        changes = [{"entity_id": row[2]} for row in pending]

        upload_result = await mock_api_client.upload_changes(changes)

        if upload_result["success"]:
            cursor.execute("DELETE FROM sync_queue")
            conn.commit()

        # Download phase
        await mock_api_client.download_changes()

        # Assert
        cursor.execute("SELECT * FROM sync_queue")
        queue_after = cursor.fetchall()
        conn.close()

        assert upload_result["success"] is True
        assert len(queue_after) == 0
        assert mock_api_client.upload_changes.called
        assert mock_api_client.download_changes.called

    @pytest.mark.unit
    def test_offline_mode_queue_persistence(self, sync_db: Any, sample_queue_entry: Any) -> None:
        """TC-SE.2.4: Offline Mode - Queue Persistence.

        Given: Device is offline
        When: Changes are made locally
        Then: Changes are queued
        And: Queue persists across sessions
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Act - Add to queue while offline
        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at)
            VALUES (?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
            ),
        )
        conn.commit()
        conn.close()

        # Simulate app restart - reconnect to DB
        conn2 = sqlite3.connect(sync_db)
        cursor2 = conn2.cursor()

        # Assert - Queue still has items
        cursor2.execute("SELECT * FROM sync_queue")
        results = cursor2.fetchall()
        conn2.close()

        assert len(results) == 1
        assert results[0][2] == sample_queue_entry["entity_id"]


# ============================================================================
# TEST CLASSES - Error Handling
# ============================================================================


class TestSyncEngineErrorHandling:
    """Test Suite: Sync Engine - Error Handling.

    Tests handling of network errors, conflicts, and retry logic
    """

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_network_error_retry(self, sync_db: Any, sample_queue_entry: Any) -> None:
        """TC-SE.3.1: Network Error - Retry Logic.

        Given: Network error during sync
        When: Sync fails
        Then: Retry count is incremented
        And: Item remains in queue
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at, retry_count)
            VALUES (?, ?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
                0,
            ),
        )
        conn.commit()

        # Act - Simulate network error
        error_message = "Connection timeout"
        cursor.execute(
            """
            UPDATE sync_queue
            SET retry_count = retry_count + 1, last_error = ?
            WHERE entity_id = ?
        """,
            (error_message, sample_queue_entry["entity_id"]),
        )
        conn.commit()

        # Assert
        cursor.execute(
            "SELECT retry_count, last_error FROM sync_queue WHERE entity_id = ?",
            (sample_queue_entry["entity_id"],),
        )
        result = cursor.fetchone()
        conn.close()

        assert result[0] == 1
        assert result[1] == error_message

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_max_retries_reached(self, sync_db: Any, sample_queue_entry: Any) -> None:
        """TC-SE.3.2: Max Retries Reached - Stop Retrying.

        Given: Item has reached max retry count
        When: Queue is processed
        Then: Item is skipped
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        max_retries = 3
        cursor.execute(
            """
            INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at, retry_count, last_error)
            VALUES (?, ?, ?, ?, ?, ?, ?)
        """,
            (
                sample_queue_entry["entity_type"],
                sample_queue_entry["entity_id"],
                sample_queue_entry["operation"],
                sample_queue_entry["payload"],
                sample_queue_entry["created_at"],
                max_retries + 1,  # Exceeded max
                "Multiple failures",
            ),
        )
        conn.commit()

        # Act - Filter items eligible for retry
        cursor.execute("SELECT * FROM sync_queue WHERE retry_count <= ?", (max_retries,))
        eligible = cursor.fetchall()
        conn.close()

        # Assert - Item is not eligible
        assert len(eligible) == 0

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_conflict_detection(self, mock_api_client: Any) -> None:
        """TC-SE.3.3: Conflict Detection - Server Returns Conflict.

        Given: Concurrent modification on server
        When: Upload is attempted
        Then: Conflict is detected
        And: Conflict resolution is triggered
        """
        # Arrange
        mock_api_client.upload_changes = AsyncMock(
            return_value={
                "success": False,
                "conflicts": [
                    {"entity_id": "item-001", "local_version": 2, "remote_version": 3, "reason": "version_mismatch"},
                ],
            },
        )

        changes = [{"entity_id": "item-001", "version": 2}]

        # Act
        result = await mock_api_client.upload_changes(changes)

        # Assert
        assert result["success"] is False
        assert len(result["conflicts"]) == 1
        assert result["conflicts"][0]["reason"] == "version_mismatch"

    @pytest.mark.unit
    def test_exponential_backoff(self) -> None:
        """TC-SE.3.4: Exponential Backoff - Increasing Delays.

        Given: Multiple retry attempts
        When: Backoff delay is calculated
        Then: Delay increases exponentially
        """
        # Arrange
        base_delay = 1.0
        max_delay = 60.0

        # Act
        delays = []
        for retry_count in range(5):
            delay = min(base_delay * (2**retry_count), max_delay)
            delays.append(delay)

        # Assert
        assert delays[0] == 1.0  # 2^0 = 1
        assert delays[1] == float(COUNT_TWO + 0.0)  # 2^1 = 2
        assert delays[2] == float(COUNT_FOUR + 0.0)  # 2^2 = 4
        assert delays[3] == 8.0  # 2^3 = 8
        assert delays[4] == 16.0  # 2^4 = 16

    @pytest.mark.unit
    @pytest.mark.asyncio
    async def test_partial_sync_failure(self, sync_db: Any, _mock_api_client: Any) -> None:
        """TC-SE.3.5: Partial Sync Failure - Some Items Succeed.

        Given: Multiple items to sync
        When: Some items fail
        Then: Successful items are removed from queue
        And: Failed items remain with incremented retry count
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Add multiple items
        for i in range(3):
            cursor.execute(
                """
                INSERT INTO sync_queue (entity_type, entity_id, operation, payload, created_at)
                VALUES (?, ?, ?, ?, ?)
            """,
                ("item", f"item-{i:03d}", "create", json.dumps({"id": i}), datetime.now(UTC).isoformat()),
            )
        conn.commit()

        # Simulate partial success (item-000 and item-001 succeed, item-002 fails)
        successful_ids = ["item-000", "item-001"]
        failed_id = "item-002"

        # Act - Remove successful items
        for entity_id in successful_ids:
            cursor.execute("DELETE FROM sync_queue WHERE entity_id = ?", (entity_id,))

        # Increment retry for failed item
        cursor.execute(
            """
            UPDATE sync_queue
            SET retry_count = retry_count + 1, last_error = ?
            WHERE entity_id = ?
        """,
            ("Server error", failed_id),
        )
        conn.commit()

        # Assert
        cursor.execute("SELECT entity_id, retry_count FROM sync_queue")
        remaining = cursor.fetchall()
        conn.close()

        assert len(remaining) == 1
        assert remaining[0][0] == failed_id
        assert remaining[0][1] == 1


# ============================================================================
# TEST CLASSES - Sync State Management
# ============================================================================


class TestSyncEngineSyncState:
    """Test Suite: Sync Engine - Sync State Management.

    Tests tracking of last sync time and sync status
    """

    @pytest.mark.unit
    def test_store_last_sync_time(self, sync_db: Any) -> None:
        """TC-SE.4.1: Store Last Sync Time - Success.

        Given: Sync completes successfully
        When: Last sync time is stored
        Then: Timestamp is persisted
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        sync_time = datetime.now(UTC).isoformat()

        # Act
        cursor.execute(
            """
            INSERT OR REPLACE INTO sync_state (key, value, updated_at)
            VALUES (?, ?, ?)
        """,
            ("last_sync", sync_time, datetime.now(UTC).isoformat()),
        )
        conn.commit()

        # Assert
        cursor.execute("SELECT value FROM sync_state WHERE key = ?", ("last_sync",))
        result = cursor.fetchone()
        conn.close()

        assert result is not None
        assert result[0] == sync_time

    @pytest.mark.unit
    def test_retrieve_last_sync_time(self, sync_db: Any) -> None:
        """TC-SE.4.2: Retrieve Last Sync Time - Success.

        Given: Last sync time exists
        When: Time is retrieved
        Then: Correct timestamp is returned
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        sync_time = datetime.now(UTC).isoformat()
        cursor.execute(
            """
            INSERT INTO sync_state (key, value, updated_at)
            VALUES (?, ?, ?)
        """,
            ("last_sync", sync_time, datetime.now(UTC).isoformat()),
        )
        conn.commit()

        # Act
        cursor.execute("SELECT value FROM sync_state WHERE key = ?", ("last_sync",))
        result = cursor.fetchone()
        conn.close()

        # Assert
        assert result[0] == sync_time

    @pytest.mark.unit
    def test_no_previous_sync(self, sync_db: Any) -> None:
        """TC-SE.4.3: No Previous Sync - Handle Gracefully.

        Given: First sync attempt
        When: Last sync time is requested
        Then: None or default is returned
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Act
        cursor.execute("SELECT value FROM sync_state WHERE key = ?", ("last_sync",))
        result = cursor.fetchone()
        conn.close()

        # Assert
        assert result is None

    @pytest.mark.unit
    def test_store_sync_status(self, sync_db: Any) -> None:
        """TC-SE.4.4: Store Sync Status - Track State.

        Given: Sync operation in progress
        When: Status is updated
        Then: Current state is stored
        """
        # Arrange
        conn = sqlite3.connect(sync_db)
        cursor = conn.cursor()

        # Act
        statuses = ["syncing", "complete", "error"]
        for status in statuses:
            cursor.execute(
                """
                INSERT OR REPLACE INTO sync_state (key, value, updated_at)
                VALUES (?, ?, ?)
            """,
                ("sync_status", status, datetime.now(UTC).isoformat()),
            )
            conn.commit()

        # Assert
        cursor.execute("SELECT value FROM sync_state WHERE key = ?", ("sync_status",))
        result = cursor.fetchone()
        conn.close()

        assert result[0] == "error"  # Last status


# ============================================================================
# NOTES
# ============================================================================

"""
COVERAGE AREAS:

1. Queue Management:
   - Add/remove entries
   - Retrieve pending items
   - Update retry counts
   - Filter by max retries

2. Sync Flow:
   - Upload phase
   - Download phase
   - Bidirectional sync
   - Offline persistence

3. Error Handling:
   - Network errors
   - Retry logic
   - Max retries
   - Conflict detection
   - Exponential backoff
   - Partial failures

4. Sync State:
   - Last sync time tracking
   - Sync status management
   - First sync handling

TODO for full implementation:
- Add SyncEngine class tests (when implemented)
- Add WebSocket real-time sync tests
- Add delta sync tests
- Add concurrent sync tests
- Add bandwidth optimization tests
"""
