# 1. Goal
A coffee roastery operates two roasting plants. Each plant sends a list of roast
batches. The roastery needs one consolidated list. The list shows the totals of
each green coffee lot. A planning program calls the consolidation before it
plans the next roasting week.

# 2. Open questions
None.

# 3. Context
- Plant A and plant B record their roast batches independently. The same batch
  ID can occur in both lists. A batch ID can also occur more than one time in
  one list.
- A batch has a batch ID, a plant, a lot ID, a roast date, and a roasted weight
  in kilograms. The roasted weight has two decimal places.

# 4. Contract
- Create the class {{P}}ROAST_MERGER in package $TMP.
- The class is public and final. The class has a public constructor without
  parameters.
- The class has these public types:
  - TY_BATCH_ID (character, length 10)
  - TY_PLANT (character, length 4)
  - TY_LOT_ID (character, length 8)
  - TY_WEIGHT (packed number, length 7, 2 decimal places)
  - TY_BATCH (structure): BATCH_ID, PLANT, LOT_ID, ROAST_DATE (date),
    ROASTED_KG (TY_WEIGHT)
  - TT_BATCHES: standard table of TY_BATCH with empty key
  - TY_LOT_TOTAL (structure): LOT_ID, BATCH_COUNT (integer), TOTAL_KG
    (TY_WEIGHT), LAST_DATE (date)
  - TT_LOT_TOTALS: standard table of TY_LOT_TOTAL with empty key
- The class has this public method and no other public method:
  MERGE
    IMPORTING it_plant_a TYPE tt_batches
              it_plant_b TYPE tt_batches
    RETURNING VALUE(rt_totals) TYPE tt_lot_totals

# 5. Business rules
The method MERGE applies these rules in this sequence.
1. A batch is invalid if the batch ID is empty, or if the roasted weight is zero
   or negative. Ignore all invalid batches.
2. A batch ID identifies a batch. If the same batch ID occurs more than one
   time, keep the first occurrence. Replace the kept occurrence only if a later
   occurrence has a larger roasted weight. The order of the occurrences is: all
   batches of plant A first, then all batches of plant B.
3. Group the remaining batches by lot ID.
4. For each lot ID calculate:
   - BATCH_COUNT: the number of batches with this lot ID.
   - TOTAL_KG: the sum of the roasted weights of these batches.
   - LAST_DATE: the latest roast date of these batches.
5. The result has one row for each lot ID with at least one batch.
6. The result is sorted by LOT_ID in ascending order.
7. If both input tables are empty, the result is empty.

# 6. Constraints
- Release target: SAP_BASIS 816 (ABAP Platform 2025).
- Coding standards: Clean ABAP. Method length below 40 statements. No global
  variables. No comment that restates the code.
- Out of scope: no database table, no CDS view, no report, no function module,
  no change of the public contract.

# 7. Acceptance
- The class is active and has no syntax error.
- The hidden tests pass.
- Write your own ABAP Unit tests for the class.