DROP VIEW quantity_unit_conversions_resolved;
CREATE VIEW quantity_unit_conversions_resolved
AS

SELECT *
FROM (

-- 1. Product "purchase to stock" conversion factor
SELECT
	-1 AS id, -- Dummy, LessQL needs an id column
	p.id AS product_id,
	p.qu_id_purchase AS from_qu_id,
	qu_from.name AS from_qu_name,
	qu_from.name_plural AS from_qu_name_plural,
	p.qu_id_stock AS to_qu_id,
	qu_to.name AS to_qu_name,
	qu_to.name_plural AS to_qu_name_plural,
	CASE WHEN p.qu_id_stock = p.qu_id_purchase THEN 1.0 ELSE p.qu_factor_purchase_to_stock END AS factor, -- Enforce a factor of 1 when QU stock = QU purchase
	'1 product purchase to stock factor' AS source
FROM products p
JOIN quantity_units qu_from
	ON p.qu_id_purchase = qu_from.id
JOIN quantity_units qu_to
	ON p.qu_id_stock = qu_to.id
UNION -- Inversed
SELECT
	-1 AS id, -- Dummy, LessQL needs an id column
	p.id AS product_id,
	p.qu_id_stock AS from_qu_id,
	qu_to.name AS from_qu_name,
	qu_to.name_plural AS from_qu_name_plural,
	p.qu_id_purchase AS to_qu_id,
	qu_from.name AS to_qu_name,
	qu_from.name_plural AS to_qu_name_plural,
	1 / p.qu_factor_purchase_to_stock AS factor,
	'1 product purchase to stock factor (inversed)' AS source
FROM products p
JOIN quantity_units qu_from
	ON p.qu_id_purchase = qu_from.id
JOIN quantity_units qu_to
	ON p.qu_id_stock = qu_to.id
WHERE p.qu_id_stock != p.qu_id_purchase -- => Only when QU stock is not the same as QU purchase

UNION

-- 2. Product specific QU overrides
SELECT
	-1 AS id, -- Dummy, LessQL needs an id column
	p.id AS product_id,
	quc.from_qu_id AS from_qu_id,
	qu_from.name AS from_qu_name,
	qu_from.name_plural AS from_qu_name_plural,
	quc.to_qu_id AS to_qu_id,
	qu_to.name AS to_qu_name,
	qu_to.name_plural AS to_qu_name_plural,
	quc.factor AS factor,
	'2 product override' AS source
FROM products p
JOIN quantity_unit_conversions quc
	ON p.id = quc.product_id
JOIN quantity_units qu_from
	ON quc.from_qu_id = qu_from.id
JOIN quantity_units qu_to
	ON quc.to_qu_id = qu_to.id

UNION

-- 3. Default (direct) QU conversion factors
SELECT
	-1 AS id, -- Dummy, LessQL needs an id column
	p.id AS product_id,
	p.qu_id_stock AS from_qu_id,
	qu_from.name AS from_qu_name,
	qu_from.name_plural AS from_qu_name_plural,
	quc.to_qu_id AS to_qu_id,
	qu_to.name AS to_qu_name,
	qu_to.name_plural AS to_qu_name_plural,
	quc.factor AS factor,
	'3 default direct factor' AS source
FROM products p
JOIN quantity_unit_conversions quc
	ON p.qu_id_stock = quc.from_qu_id
	AND quc.product_id IS NULL
JOIN quantity_units qu_from
	ON quc.from_qu_id = qu_from.id
JOIN quantity_units qu_to
	ON quc.to_qu_id = qu_to.id

UNION

-- 4. Default (indirect) QU conversion factors
SELECT
	-1 AS id, -- Dummy, LessQL needs an id column
	p.id AS product_id,
	(SELECT from_qu_id FROM quantity_unit_conversions WHERE to_qu_id = quc.to_qu_id AND product_id = p.id) AS from_qu_id,
	qu_from.name AS from_qu_name,
	qu_from.name_plural AS from_qu_name_plural,
	quc.from_qu_id AS to_qu_id,
	qu_to.name AS to_qu_name,
	qu_to.name_plural AS to_qu_name_plural,
	(SELECT factor FROM quantity_unit_conversions WHERE to_qu_id = quc.to_qu_id AND product_id = p.id) / quc.factor AS factor,
	'4 default indirect factor' AS source
FROM products p
JOIN product_qu_relations pqr
	ON p.id = pqr.product_id
JOIN quantity_unit_conversions quc
	ON pqr.qu_id = quc.from_qu_id
	AND quc.product_id IS NULL
JOIN quantity_units qu_from
	ON (SELECT from_qu_id FROM quantity_unit_conversions WHERE to_qu_id = quc.to_qu_id AND product_id = p.id) = qu_from.id
JOIN quantity_units qu_to
	ON quc.from_qu_id = qu_to.id
WHERE NOT EXISTS(SELECT 1 FROM quantity_unit_conversions qucx WHERE qucx.product_id = p.id AND qucx.from_qu_id = pqr.qu_id) -- => Product override exists

) x
ORDER BY source;
