Interpolate between two scenarios #1684
Description
@aaccensi I had a go at refining the changes required for interpolation:
Description
Refactor the interpolation setup to support interpolating between two scenarios (a start scenario and an end scenario) rather than from default values to a scenario. This enables creating intermediate-year scenarios between two user-defined scenarios.
Current Behavior
- Interpolates from default start values → original scenario values
- Uses
input.start_value_for(@scenario)as the baseline
Proposed Improvement
- Interpolates from start_scenario values → end_scenario values
- Validates both scenarios have the same area_code
Implementation Ideas
1. Modify Scenario::YearInterpolator Class:
a. Update the initializer and call method:
- Add optional start_scenario parameter
- Store as instance variable
def self.call(scenario, year, current_user = nil, start_scenario = nil)
new(scenario, year, current_user, start_scenario).run
end
def initialize(scenario, year, current_user, start_scenario = nil)
@scenario = scenario
@year = year
@current_user = current_user
@start_scenario = start_scenario
end
b. Update validation to validate start scenario - add to validate!, add a validate_start_scenario!
c. Update interpolation logic:
- Modify interpolate_input_collection to calculate years correctly
- Modify interpolate_input to use start_scenario values when available ( I think we can fall back to dataset values for now if the start scenario is not given)
2. Modify Api::V3::ScenariosController#interpolate
a. Accept optional start_scenario_id parameter
b. Update permitted parameters
3. Tests and documentation
- Write tests for changes
- Document changes to the interpolation endpoint
Further enhancements
Outlined above is a MVP for these changes - if we want to go further, we could introduce a batch interpolation endpoint which accepts multiple target years in a single request to make multiple interpolated scenarios at once and enforces a 6 scenario limit.