<?php
declare(strict_types=1);

use PHPUnit\Framework\TestCase;

/**
 * Tests for WPDO_Migration_Engine — 7-state static lifecycle controller.
 *
 * Validates valid/invalid transitions, rollback, and status.
 * High-level operations (migrate/verify/cutover) require a registered
 * migration instance and are tested at the transition level here.
 */
class MigrationEngineTest extends TestCase {

	protected function setUp(): void {
		$GLOBALS['_wp_options'] = [];
		// Reset static migrations registry.
		$ref = new ReflectionClass( WPDO_Migration_Engine::class );
		$m   = $ref->getProperty( 'migrations' );
		$m->setAccessible( true );
		$m->setValue( null, [] );
	}

	// ── can_transition ───────────────────────────────────────────────────────

	/** @dataProvider valid_transitions_provider */
	public function test_can_transition_returns_true_for_valid_paths( string $from, string $to ): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', $from );
		$this->assertTrue(
			WPDO_Migration_Engine::can_transition( 'hot_hp_listing', $to ),
			"Expected valid transition: $from → $to"
		);
	}

	public static function valid_transitions_provider(): array {
		return [
			[ 'idle',      'dual_write'  ],
			[ 'dual_write', 'backfill'   ],
			[ 'backfill',  'verify'      ],
			[ 'backfill',  'dual_write'  ], // backfill can go back to dual_write.
			[ 'verify',    'cutover'     ],
			[ 'verify',    'dual_write'  ], // verify can step back.
			[ 'cutover',   'cleanup'     ],
			[ 'cleanup',   'complete'    ],
			// Any state → idle is always allowed (rollback path).
			[ 'cutover',   'idle'        ],
			[ 'complete',  'idle'        ],
		];
	}

	/** @dataProvider invalid_transitions_provider */
	public function test_can_transition_returns_false_for_invalid_paths( string $from, string $to ): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', $from );
		$this->assertFalse(
			WPDO_Migration_Engine::can_transition( 'hot_hp_listing', $to ),
			"Expected invalid transition: $from → $to"
		);
	}

	public static function invalid_transitions_provider(): array {
		return [
			[ 'idle',     'cutover'  ], // Must traverse intermediate states.
			[ 'complete', 'backfill' ], // Cannot go backwards except to idle.
			[ 'idle',     'complete' ],
		];
	}

	// ── transition ───────────────────────────────────────────────────────────

	public function test_transition_updates_state_on_valid_path(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'idle' );
		$result = WPDO_Migration_Engine::transition( 'hot_hp_listing', 'dual_write' );
		$this->assertTrue( $result );
		$this->assertSame( 'dual_write', WPDO_Feature_Flags::get( 'hot_hp_listing' ) );
	}

	public function test_transition_returns_false_and_preserves_state_on_invalid_path(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'idle' );
		$result = WPDO_Migration_Engine::transition( 'hot_hp_listing', 'complete' );
		$this->assertFalse( $result );
		$this->assertSame( 'idle', WPDO_Feature_Flags::get( 'hot_hp_listing' ) );
	}

	// ── rollback ─────────────────────────────────────────────────────────────

	public function test_rollback_resets_state_to_idle(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'cutover' );
		$result = WPDO_Migration_Engine::rollback( 'hot_hp_listing' );
		$this->assertSame( 'idle', $result['status'] );
		$this->assertSame( 'idle', WPDO_Feature_Flags::get( 'hot_hp_listing' ) );
	}

	public function test_rollback_from_idle_returns_idle_status(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'idle' );
		$result = WPDO_Migration_Engine::rollback( 'hot_hp_listing' );
		// Engine returns idle status with "already idle" message (not error).
		$this->assertSame( 'idle', $result['status'] );
	}

	// ── status ────────────────────────────────────────────────────────────────

	public function test_status_returns_current_state(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'backfill' );
		$status = WPDO_Migration_Engine::status( 'hot_hp_listing' );
		$this->assertSame( 'backfill', $status['state'] );
		$this->assertSame( 'hot_hp_listing', $status['module'] );
	}

	// ── cleanup / enable require prior states ───────────────────────────────

	public function test_cleanup_fails_when_not_in_cutover(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'backfill' );
		$result = WPDO_Migration_Engine::cleanup( 'hot_hp_listing' );
		$this->assertSame( 'error', $result['status'] );
	}

	public function test_enable_fails_when_not_in_cleanup(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'cutover' );
		$result = WPDO_Migration_Engine::enable( 'hot_hp_listing' );
		$this->assertSame( 'error', $result['status'] );
	}

	public function test_enable_succeeds_from_cleanup(): void {
		WPDO_Feature_Flags::set( 'hot_hp_listing', 'cleanup' );
		$result = WPDO_Migration_Engine::enable( 'hot_hp_listing' );
		$this->assertSame( 'complete', $result['status'] );
		$this->assertSame( 'complete', WPDO_Feature_Flags::get( 'hot_hp_listing' ) );
	}

	// ── migrate without registered migration ────────────────────────────────

	public function test_migrate_without_registration_returns_error(): void {
		$result = WPDO_Migration_Engine::migrate( 'hot_unregistered' );
		$this->assertSame( 'error', $result['status'] );
	}
}