Implement tax handling for branches by adding tax percent to regions, updating product sell costs, and enhancing UI for tax summaries in BranchView

backend/sql/update_product_sell_costs.sql

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+-- Backup original sell_cost values (just in case)
+-- Run this once: will add a column original_sell_cost and copy existing sell_cost into it
+ALTER TABLE IF EXISTS falukant_type.product
+  ADD COLUMN IF NOT EXISTS original_sell_cost numeric;
+
+UPDATE falukant_type.product
+SET sell_cost = sell_cost * ((6 * 7 / 100) + 100);
+
+-- Compute min and max cumulative tax across all regions
+WITH RECURSIVE ancestors AS (
+  SELECT id AS start_id, id, parent_id, tax_percent FROM falukant_data.region
+  UNION ALL
+  SELECT a.start_id, r.id, r.parent_id, r.tax_percent
+  FROM falukant_data.region r
+  JOIN ancestors a ON r.id = a.parent_id
+), totals AS (
+  SELECT start_id, COALESCE(SUM(tax_percent),0) AS total FROM ancestors GROUP BY start_id
+), mm AS (
+  SELECT COALESCE(MIN(total),0) AS min_total, COALESCE(MAX(total),0) AS max_total FROM totals
+)
+SELECT * FROM mm;
+
+-- Choose one of the following update blocks to run:
+
+-- 1) MIN-STRATEGY: increase sell_cost so that taxes at the minimal cumulative tax have no effect
+-- (this will set sell_cost = CEIL(original_sell_cost * (1 / (1 - min_total/100))))
+
+-- BEGIN MIN-STRATEGY
+-- WITH mm AS (
+--   WITH RECURSIVE ancestors AS (
+--     SELECT id AS start_id, id, parent_id, tax_percent FROM falukant_data.region
+--     UNION ALL
+--     SELECT a.start_id, r.id, r.parent_id, r.tax_percent
+--     FROM falukant_data.region r
+--     JOIN ancestors a ON r.id = a.parent_id
+--   ), totals AS (
+--     SELECT start_id, COALESCE(SUM(tax_percent),0) AS total FROM ancestors GROUP BY start_id
+--   )
+--   SELECT COALESCE(MIN(total),0) AS min_total FROM totals
+-- )
+-- UPDATE falukant_type.product
+-- SET sell_cost = CEIL(original_sell_cost * (CASE WHEN (1 - (SELECT min_total FROM mm)/100) <= 0 THEN 1 ELSE (1 / (1 - (SELECT min_total FROM mm)/100)) END));
+-- END MIN-STRATEGY
+
+-- 2) MAX-STRATEGY: increase sell_cost so that taxes at the maximal cumulative tax have no effect
+-- (this will set sell_cost = CEIL(original_sell_cost * (1 / (1 - max_total/100))))
+
+-- BEGIN MAX-STRATEGY
+-- WITH mm AS (
+--   WITH RECURSIVE ancestors AS (
+--     SELECT id AS start_id, id, parent_id, tax_percent FROM falukant_data.region
+--     UNION ALL
+--     SELECT a.start_id, r.id, r.parent_id, r.tax_percent
+--     FROM falukant_data.region r
+--     JOIN ancestors a ON r.id = a.parent_id
+--   ), totals AS (
+--     SELECT start_id, COALESCE(SUM(tax_percent),0) AS total FROM ancestors GROUP BY start_id
+--   )
+--   SELECT COALESCE(MAX(total),0) AS max_total FROM totals
+-- )
+-- UPDATE falukant_type.product
+-- SET sell_cost = CEIL(original_sell_cost * (CASE WHEN (1 - (SELECT max_total FROM mm)/100) <= 0 THEN 1 ELSE (1 / (1 - (SELECT max_total FROM mm)/100)) END));
+-- END MAX-STRATEGY
+
+-- Notes:
+-- 1) Uncomment exactly one strategy block (MIN or MAX) and run the script.
+-- 2) The script creates `original_sell_cost` as a backup; keep it for safety.
+-- 3) CEIL is used to avoid undercompensating due to rounding. If you prefer ROUND use ROUND(...).
+-- 4) Test on a staging DB first.