db: Add utility functions

- Add functions to be used in calculation of yearly_expected_and_vacation for work summary

api/db/functions/get_vacation_for_period.py

@@ -0,0 +1,48 @@
+from alembic_utils.pg_function import PGFunction
+
+
+get_vacation_for_period = PGFunction(
+    schema="public",
+    signature="get_vacation_for_period(start_date date,end_date date,capacity numeric)",
+    definition="""
+        /*
+         * Author: Danielle Mayabb, Dec 2023
+         * Purpose: Provided a time range and daily capacity, gets the amount of vacation hours
+         * available to a user
+         * Notes: When getting the difference of dates, the end date is not included,
+         * so 1 day is added to the calculation
+         * Simplified formula is:
+         * (Number of days in period) / (Number of days in year)
+         * * yearly_vacation_hours * (daily_capacity * 5 / company_fte)
+         * So we determine the fraction of the year for which someone is working (it will be <=1)
+         * Multiply that by total available vacation hours so that if someone is only working part of the year,
+         * they get the correct proportion of vacation
+         * Next, we need to get a fraction for the capacity which is daily_capacity * 5 (for weekly capacity)
+         * divided by company_fte.
+         * This is the percentage of time of FTE someone works.
+         */
+        returns numeric(8,4)
+        as $$
+            /*
+             * First, we need to get some constants:
+             * 1. The amount of yearly vacation hours for the company
+             * 2. What is considered FTE for the company (per week)
+             */
+            declare yearly_vacation_hours int := (select config.yearly_vacation_hours from public.config limit 1);
+            declare company_fte_weekly int := (select config.company_fte from public.config limit 1);
+            BEGIN
+                return(
+                    select (end_date - start_date + 1) /
+                        (
+                        make_date(date_part('year', end_date::date)::int, 12, 31) -
+                        make_date(date_part('year', start_date::date)::int, 01, 01) + 1
+                        )::float
+                    * yearly_vacation_hours
+                    * (capacity * 5 / company_fte_weekly::float)
+                );
+            end;
+            $$
+        LANGUAGE plpgsql
+        ;
+""",
+)

api/db/functions/get_workday_count.py

@@ -0,0 +1,28 @@
+from alembic_utils.pg_function import PGFunction
+
+
+get_workday_count = PGFunction(
+    schema="public",
+    signature="get_workday_count(start_date date, end_date date)",
+    definition="""
+            /*
+            * Author: Danielle Mayabb, Dec 2023
+            * Purpose: Provided a time range, gets the number of work days for the period,
+            * i.e., gets the count of non-weekend days
+            */
+            RETURNS integer
+            as $$
+            BEGIN
+                return (
+                select count(generated_date::date)
+                from generate_series(
+                        start_date,
+                        end_date,
+                        interval '1 day') as generated_date
+                where extract(isodow from generated_date) < 6);
+            END;
+            $$
+            LANGUAGE plpgsql
+            ;
+""",
+)

api/migrations/versions/6a1ad39b566d_add_calculation_functions.py

@@ -0,0 +1,43 @@
+"""Add calculation functions
+
+Revision ID: 6a1ad39b566d
+Revises: 2ac6108453f3
+Create Date: 2024-01-05 11:07:57.026492
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from alembic_utils.pg_function import PGFunction
+from alembic_utils.pg_trigger import PGTrigger
+from db.functions.get_workday_count import get_workday_count
+from db.functions.get_vacation_for_period import get_vacation_for_period
+
+# revision identifiers, used by Alembic.
+revision = "6a1ad39b566d"
+down_revision = "cf4f31d5cd2d"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_entity(get_workday_count)
+    op.create_entity(get_vacation_for_period)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    get_workday_count = PGFunction(
+        schema="public",
+        signature="get_workday_count(start_date date, end_date date)",
+        definition="# ",
+    )
+    op.drop_entity(get_workday_count)
+    get_vacation_for_period = PGFunction(
+        schema="public",
+        signature="get_vacation_for_period(start_date date, end_date date, capacity numeric)",
+        definition="# ",
+    )
+    op.drop_entity(get_vacation_for_period)
+    # ### end Alembic commands ###