South Carolina sales tax cut for people age 85 and older

Fixes PolicyEngine#5387

changelog_entry.yaml

@@ -1,4 +1,4 @@
 - bump: minor
   changes:
     added:
-    - South Carolina sales tax cut for people age 85 and older.
+    - South Carolina sales and use tax, general and elderly.

policyengine_us/parameters/gov/states/sc/tax/sales/exclusion/age_threshold.yaml → policyengine_us/parameters/gov/states/sc/tax/sales_and_use/exclusion/age_threshold.yaml

@@ -1,10 +1,11 @@
-description: South Carolina provides a lower state tax rate for sales and use by individuals of this age and older.
+description: South Carolina provides a lower state sales and use tax rate for filers of this age and older.
 values:
   2021-01-01: 85
 
 metadata:
   unit: year
-  label: South Carolina sales tax exclusion for the elderly
+  period: year
+  label: South Carolina sales and use tax exclusion age threshold
   reference: 
     - title: SC REVENUE RULING 08-5
       href: https://dor.sc.gov/resources-site/lawandpolicy/Advisory%20Opinions/RR08-5.pdf#page=2

policyengine_us/parameters/gov/states/sc/tax/sales/exclusion/percentage.yaml → policyengine_us/parameters/gov/states/sc/tax/sales_and_use/exclusion/percentage.yaml

@@ -1,7 +1,7 @@
-description: South Carolina provides the following percentage of exclusion for sales and use tax.
+description: South Carolina excludes the following percentage of the sales and use tax for elderly filers.
 metadata:
   unit: /1
-  label: South Carolina senior exemption amount
+  label: South Carolina sales and use tax senior exclusion percentage
   reference: 
     - title: SC REVENUE RULING 08-5
       href: https://dor.sc.gov/resources-site/lawandpolicy/Advisory%20Opinions/RR08-5.pdf#page=2

policyengine_us/parameters/gov/states/sc/tax/sales_and_use/general.yaml

@@ -0,0 +1,10 @@
+description: South Carolina imposes a general sales and use tax rate of this amount.
+metadata:
+  unit: /1
+  label: South Carolina general sales and use tax
+  reference: 
+    - title: SC REVENUE RULING 08-5
+      href: https://dor.sc.gov/resources-site/lawandpolicy/Advisory%20Opinions/RR08-5.pdf#page=1
+
+values:
+  2021-01-01: 0.06

policyengine_us/variables/gov/states/sc/tax/sales_and_use/sc_sales_and_use_exclusion_eligible.py

@@ -0,0 +1,17 @@
+from policyengine_us.model_api import *
+
+
+class sc_sales_and_use_exclusion_eligible(Variable):
+    value_type = bool
+    entity = TaxUnit
+    label = "Eligible for South Carolina sales and use tax senior exclusion"
+    definition_period = YEAR
+    reference = "https://dor.sc.gov/resources-site/lawandpolicy/Advisory%20Opinions/RR08-5.pdf#page=2"
+    defined_for = StateCode.SC
+
+    def formula(tax_unit, period, parameters):
+        p = parameters(period).gov.states.sc.tax.sales_and_use.exclusion
+        person = tax_unit.members
+        age = person("age", period)
+        age_eligible = age >= p.age_threshold
+        return age_eligible

policyengine_us/variables/gov/states/sc/tax/sales_and_use/sc_sales_and_use_tax.py

@@ -0,0 +1,22 @@
+from policyengine_us.model_api import *
+
+
+class sc_sales_and_use_tax(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "South Carolina sales and use tax"
+    unit = USD
+    definition_period = YEAR
+    defined_for = StateCode.SC
+
+    def formula(tax_unit, period, parameters):
+        p = parameters(period).gov.states.sc.tax.sales_and_use
+
+        # base amount
+
+        # sales and use tax rate with eligible exclusion
+        eligible = tax_unit("sc_sales_and_use_exclusion_eligible", period)
+        exclusion = p.exclusion.percentage * eligible
+        rate_applied = p.general - exclusion
+
+        # return base amount * rate_applied