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docs/moved-boxes-task.md

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+## Goal
+Obtain correct count of boxes (and, ideally, their contained items count) that had their state changed from InStock to Donated in a certain timeframe.
+The boxes are registered in a specific base.
+The results shall group counts by box product (that's a simplification, actually it's product category), and target location ID.
+
+## Example data
+### history table
+
+Changes of box properties (state, location, product, number of items)
+
+```
+changedate | record_id | changes        | from_int | to_int
+2023-01-01 |         9 | Record created |     NULL |   NULL
+2023-01-01 |        12 | Record created |     NULL |   NULL
+2023-01-01 |        20 | Record created |     NULL |   NULL
+2023-01-01 |        25 | Record created |     NULL |   NULL
+2023-01-10 |        12 | box_state_id   |        1 |      5
+2023-01-10 |        12 | location_id    |        1 |      2
+2023-01-15 |        20 | location_id    |        1 |      2
+2023-01-15 |        20 | box_state_id   |        1 |      5
+2023-02-11 |        12 | box_state_id   |        5 |      1
+2023-02-11 |        12 | location_id    |        2 |      1
+2023-03-01 |        12 | items          |       30 |     15
+2023-03-19 |        25 | box_state_id   |        1 |      5
+2023-03-19 |        25 | location_id    |        4 |      5
+2023-03-21 |        12 | product_id     |        2 |      3
+2023-03-30 |        12 | box_state_id   |        1 |      5
+2023-03-30 |        12 | location_id    |        1 |      2
+```
+
+Explanation: Locations have a default box state that is assigned to a box moved into the location. On e.g. 2023-01-10, box 12 is moved from the InStock location 1 to the Donated location 2, as a result two rows are added to the history table (update of box state and box location). It can not be relied on the order of the two entries.
+On 2023-02-11, the same box 12 is moved back, and later a couple of items are removed, and the product ID is updated.
+
+### stock table
+
+Holds current box properties (as of 2023-03-30):
+
+```
+id | location_id | product_id | items | box_state_id
+ 9 |           1 |          1 |    10 |            1
+12 |           2 |          3 |    15 |            5
+20 |           2 |          1 |    99 |            5
+25 |           5 |          5 |    20 |            5
+```
+
+On 2023-01-01 it looked like this:
+
+```
+id | location_id | product_id | items | box_state_id
+ 9 |           1 |          1 |    10 |            1
+12 |           1 |          2 |    30 |            1
+20 |           1 |          1 |    99 |            1
+25 |           4 |          4 |    20 |            1
+```
+
+### locations table
+
+```
+id | base_id | default_box_state_id
+ 1 |       1 |                    1
+ 2 |       1 |                    5
+ 3 |       1 |                    2
+ 4 |       2 |                    1
+ 5 |       2 |                    5
+```
+
+## Problem statement
+
+*What is the best data format to answer the following questions in a straightforward and correct way?*
+
+1. How many boxes (and items), grouped by product and target location, have been moved in base 1 in January 2023?
+    - product ID 1, location ID 2: 1 box (99 items)
+    - product ID 2, location ID 2: 1 box (30 items)
+1. How many boxes (and items), grouped by product and target location, have been moved in base 1 in January&February 2023?
+    - product ID 1, location ID 2: 1 box (99 items)
+1. How many boxes (and items), grouped by product and target location, have been moved in base 1 in the first quarter of 2023?
+    - product ID 1, location ID 2: 1 box (99 items)
+    - product ID 3, location ID 2: 1 box (15 items)
+
+What updates to the existing data structures (history / box table), and/or the business logic would leverage answering these questions?
+
+### Extra
+
+- How to find all boxes in my base that had their state changed from InStock to Donated, then back to InStock, and finally their product changed?
+
+### Current output data format
+
+Currently we propose a data format with columns for change date, target location ID, product ID, and number of moved boxes.