DROP MATERIALIZED VIEW IF EXISTS dmezentsev.conversion_funnel;
CREATE MATERIALIZED VIEW dmezentsev.conversion_funnel AS 
WITH progress AS (
	-- Прогресс каждого пользователя по каждому курсу
	SELECT 
		e.course_id,
		e.user_id,
		COUNT(DISTINCT l.id) AS total_lessons,
		COUNT(DISTINCT lv.lesson_id) AS viewed_lessons,
		ROUND(COUNT(DISTINCT lv.lesson_id) * 100.0 / NULLIF(COUNT(DISTINCT l.id), 0), 2) AS viewed_pct
	FROM dmezentsev.enrollments e
	LEFT JOIN dmezentsev.lessons l ON e.course_id = l.course_id
	LEFT JOIN dmezentsev.lesson_views lv ON l.id = lv.lesson_id AND e.user_id = lv.user_id
	GROUP BY e.course_id, e.user_id
),

funnel_stats AS (
	-- Статистика по каждому курсу для всех этапов воронки
	SELECT 
		c.id AS course_id,
		c.title AS course_title,
		(SELECT COUNT(*) FROM dmezentsev.users_) AS registered_count,
		COUNT(DISTINCT e.user_id) AS enrolled_count,
		COUNT(DISTINCT CASE WHEN p.viewed_lessons > 0 THEN e.user_id END) AS started_count,
		COUNT(DISTINCT CASE WHEN p.viewed_pct >= 50 THEN e.user_id END) AS mid_progress_count,
		COUNT(DISTINCT CASE WHEN p.viewed_pct = 100 THEN e.user_id END) AS completed_count
	FROM dmezentsev.courses c
	LEFT JOIN dmezentsev.enrollments e ON c.id = e.course_id
	LEFT JOIN progress p ON e.course_id = p.course_id AND e.user_id = p.user_id
	GROUP BY c.id, c.title
)

-- Соединяем этапы с помощью UNION ALL 
SELECT 
	course_id,
	course_title,
	stage_name,
	users_count,
	conversion_from_previous,
	conversion_from_start
FROM (
	-- Этап 1: registered
	SELECT 
		course_id,
		course_title,
		'registered' AS stage_name,
		registered_count AS users_count,
		0 AS conversion_from_previous,
		100.00 AS conversion_from_start,
		1 AS stage_order
	FROM funnel_stats

	UNION ALL

	-- Этап 2: enrolled
	SELECT 
		course_id,
		course_title,
		'enrolled',
		enrolled_count,
		ROUND(100.0 * enrolled_count / NULLIF(registered_count, 0), 2),
		ROUND(100.0 * enrolled_count / NULLIF(registered_count, 0), 2),
		2 AS stage_order
	FROM funnel_stats

	UNION ALL

	-- Этап 3: started
	SELECT 
		course_id,
		course_title,
		'started',
		started_count,
		ROUND(100.0 * started_count / NULLIF(enrolled_count, 0), 2),
		ROUND(100.0 * started_count / NULLIF(registered_count, 0), 2),
		3 AS stage_order
	FROM funnel_stats

	UNION ALL

	-- Этап 4: mid_progress
	SELECT 
		course_id,
		course_title,
		'mid_progress',
		mid_progress_count,
		ROUND(100.0 * mid_progress_count / NULLIF(started_count, 0), 2),
		ROUND(100.0 * mid_progress_count / NULLIF(registered_count, 0), 2),
		4 AS stage_order
	FROM funnel_stats

	UNION ALL

	-- Этап 5: completed
	SELECT 
		course_id,
		course_title,
		'completed',
		completed_count,
		ROUND(100.0 * completed_count / NULLIF(mid_progress_count, 0), 2),
		ROUND(100.0 * completed_count / NULLIF(registered_count, 0), 2),
		5 AS stage_order
	FROM funnel_stats
) AS funnel_rows
ORDER BY course_id, stage_order;