added gis-spa couples gis reduction plateau

policyengine_canada/parameters/gov/cra/benefits/gis_spa/gis_reduction/gis_spa_couple_plateau_rate.yaml

@@ -0,0 +1,10 @@
+description: GIS reduction rate for the 'plateau' range for a GIS recipient married to a SPA recipient.
+values:
+  2021-01-01: 0
+metadata:
+  period: year
+  label: GIS reduction rate for the 'plateau' range for a GIS recipient married to a SPA recipient.
+  documentataion: Corresponds to GISRRM and GISRLM in the SPSD/M Variable Guide
+  reference:
+  - title: SPSD/M Variable Guide
+

policyengine_canada/parameters/gov/cra/benefits/gis_spa/gis_reduction/two_pensioners.yaml

@@ -1,4 +1,4 @@
-description: Reduction threshold and rate for pensioners married to pensioners. Applies to COUPLE_BOTH_OAS or COUPLE_ONE_OAS_SPA_ELIGIBLE. Note that this calculates on couples combined income, whereas the other GIS cateogires calculate on the lone pensioner's income. Correponds to GISRRM in the SPSD/M.
+description: Reduction threshold and rate for pensioners married to pensioners. Applies to COUPLE_BOTH_OAS. Note that this calculates on couples combined income, whereas the other GIS cateogires calculate on the lone pensioner's income. Correponds to GISRRM in the SPSD/M.
 brackets:
   - threshold:
       2021-01-01: 0

policyengine_canada/tests/gov/cra/benefits/gis_spa/gis_reduction.yaml

@@ -6,7 +6,7 @@
   output:
     gis_reduction: 100
 
-- name: OAS pensioner whose spouse is SPA eligible
+- name: OAS pensioner whose spouse is SPA eligible, with combined income too low to trigger the plateau in the reduction
   period: 2023
   input:
     gis_spa_category: "COUPLE_ONE_OAS_SPA_ELIGIBLE"
@@ -16,6 +16,17 @@
   output:
     gis_reduction: 1_000
 
+- name: Couple with combined income that exceeds the upper plateau threshold given by breakeven_spa_eligible. So the GIS reduction starts again after the plateau. 
+  period: 2023
+  absolute_error_margin: .01
+  input:
+    gis_spa_category: "COUPLE_ONE_OAS_SPA_ELIGIBLE"
+    individual_net_income: 20_048
+    spouse_net_income: 20_000
+    gis_cap: 30000
+  output:
+    gis_reduction: 7487.68
+
 - name: Two OAS pensioners
   period: 2023
   input:

policyengine_canada/tests/gov/cra/benefits/gis_spa/gis_reduction_spa_couple.yaml

@@ -0,0 +1,42 @@
+- name: Couple with combined income less than the plateau threshold. 
+  period: 2023
+  absolute_error_margin: .01
+  input:
+    gis_spa_category: "COUPLE_ONE_OAS_SPA_ELIGIBLE"
+    individual_net_income: 2_048
+    spouse_net_income: 2_000
+  output:
+    gis_reduction_spa_couple: 1_000
+
+- name: Couple with combined income inside the plateau threshold. So the GIS reduction is frozen at the reduction you would have if your income were the crossover amount.
+  period: 2023
+  absolute_error_margin: .01
+  input:
+    gis_spa_category: "COUPLE_ONE_OAS_SPA_ELIGIBLE"
+    individual_net_income: 15_048
+    spouse_net_income: 15_000
+  output:
+    gis_reduction_spa_couple: 6_469.86
+
+- name: Couple with combined income that exceeds the upper plateau threshold given by breakeven_spa_eligible. So the GIS reduction starts again after the plateau. 
+  period: 2023
+  absolute_error_margin: .01
+  input:
+    gis_spa_category: "COUPLE_ONE_OAS_SPA_ELIGIBLE"
+    individual_net_income: 20_048
+    spouse_net_income: 20_000
+  output:
+    gis_reduction_spa_couple: 7487.68
+
+- name: Automatically 0 if you're not the right gis-spa category
+  period: 2023
+  absolute_error_margin: .01
+  input:
+    gis_spa_category: "COUPLE_ONE_OAS_SPA_INELIGIBLE"
+    individual_net_income: 20_048
+    spouse_net_income: 20_000
+  output:
+    gis_reduction_spa_couple: 0
+
+
+

policyengine_canada/variables/gov/cra/benefits/gis_spa/gis/gis_reduction.py

@@ -15,19 +15,20 @@ def formula(person, period, parameters):
         household = person.household
         spouse_net_income = household("spouse_net_income", period)
         gis_base = person("gis_cap", period)
+        gis_reduction_spa_couple = person("gis_reduction_spa_couple", period)
         p = parameters(period).gov.cra.benefits.gis_spa.gis_reduction
 
         reduction = select(
              [
                  gis_spa_category == gis_spa_categories.SINGLE_WITH_OAS,
                  gis_spa_category == gis_spa_categories.COUPLE_BOTH_OAS,
-                 (gis_spa_category == gis_spa_categories.COUPLE_ONE_OAS_SPA_ELIGIBLE) & (gis_base > 0),  # THIS NEEDS TO CHANGE BASED ON THE 'CROSSOVER' THING. # the gis_base > 0 makes sure this person is the eligible one in the couple, since both people in the couple will have the same category.
+                 (gis_spa_category == gis_spa_categories.COUPLE_ONE_OAS_SPA_ELIGIBLE) & (gis_base > 0),  # the gis_base > 0 makes sure this person is the eligible one in the couple, since both people in the couple will have the same category.
                  (gis_spa_category == gis_spa_categories.COUPLE_ONE_OAS_SPA_INELIGIBLE) & (gis_base > 0)
              ],
              [
                  p.one_pensioner.calc(individual_net_income),
                  p.two_pensioners.calc(individual_net_income + spouse_net_income),
-                 p.two_pensioners.calc(individual_net_income + spouse_net_income),
+                 gis_reduction_spa_couple,
                  p.one_pensioner.calc(individual_net_income)
              ],
              default=0,

policyengine_canada/variables/gov/cra/benefits/gis_spa/gis/gis_reduction_spa_couple.py

@@ -0,0 +1,35 @@
+from policyengine_canada.model_api import *
+
+class gis_reduction_spa_couple(Variable):
+    value_type = float
+    entity = Person
+    label = "Guaranteed Income Supplement Reduction for a Recipient with SPA-eligible Spouse"
+    unit = CAD
+    documentation = "The amount by which the base GIS is reduced, based on personal net income and the number of pensioners in the household. This is implemented as a variable, not a parameter, due to the complexity and dependencies of the reduction rate."
+    definition_period = YEAR
+
+    def formula(person, period, parameters):
+        gis_spa_category = person("gis_spa_category", period)
+        gis_spa_categories = gis_spa_category.possible_values
+        individual_net_income = person("individual_net_income", period)
+        household = person.household
+        spouse_net_income = household("spouse_net_income", period)
+        combined_net_income = individual_net_income + spouse_net_income
+        state = person.state
+        crossover = state("gis_spa_crossover", period)
+        breakeven_spa_eligible = state("breakeven_spa_eligible", period)
+        breakeven_spa_ineligible = state("breakeven_spa_ineligible", period)
+        plateau_range = breakeven_spa_eligible - crossover
+        p = parameters(period).gov.cra.benefits.gis_spa.gis_reduction
+
+        # Reduce like other pensioner couples up to the crossover point 
+        first_part  = min(p.two_pensioners.calc(combined_net_income), p.two_pensioners.calc(crossover)) 
+        # Plateau until the spouse's SPA-gis-portion is exhausted, as captured by the variable plateau_range. The first part must be maxed-out for this to be non-zero.
+        second_part = min((combined_net_income - first_part) * p.gis_spa_couple_plateau_rate, plateau_range * p.gis_spa_couple_plateau_rate) * (first_part == (p.two_pensioners.calc(crossover))) 
+        # Start reducing again at the married couple breakeven point for income beyond the crossover maximum. Only be non-zero if there's any income in that range. 
+        third_part  = p.two_pensioners.calc(combined_net_income - (crossover - 48) - plateau_range) * ((combined_net_income > (crossover - plateau_range))) 
+
+     #   return(third_part)
+        return(first_part + second_part + third_part) * (gis_spa_category == gis_spa_categories.COUPLE_ONE_OAS_SPA_ELIGIBLE)
+
+