Implement API endpoint for generating time series for historical data

Let's implement an API endpoint for generating time series data suitable for producing plots on the frontend.

Chart data for observations data has the following requirements:

charts are plotted for each observations variable (_obsvar) (i.e.: TDd, TDx, etc )
data may be smoothed with some smoothing algorithm (ex: centered 5-year moving average)
plots may include an additional series with aggregated data for each decade in the requested temporal range
plots may include an additional time series which is result of calculating the Mann-Kendall trend, with client-provided input values (start year, end year)

With these requirements in mind, an API endpoint for requesting observation-related time series will look like this:

/api/v2/observations/{station_id}/time-series/{observation-variable-identifier}?
  datetime={datetime}&
  include_observations_data={true/false}&
  smoothing_algorithm={smoothing_algorithm}&
  include_decade_aggregation={true/false}&
  include_mann_kendall_trend={true/false}&
  mann_kendall_trend_start_year={mann_kendall_start_year}&
  mann_kendall_trend_end_year={mann_kendall_end_year}

Where:

station_id is the identifier of the station where data comes from
observation_variable_identifier is the identifier of the obs_var
datetime is a timerange for specifying the temporal interval of the data. This is a string with the same semantics as those defined in OGC API EDR. Defaults to null, which means that the response should cover the full temporal range of data for that station
include_observations_data is a boolean specifying whether the observations data time series is to be returned or not - defaults to true
smoothing_algorithm is a string with the name of the smoothing algorithm to be applied to all observations data. If null then no smoothing is applied - defaults to null
include_decade_aggregation is a boolean specifying whether to return an additional time series with aggregated values by decade. Defaults to false
include_mann_kendall_trend - is a boolean specifying whether to return an additional time series with a trend line that is calculated using the Mann-Kendall method. Defaults to false
mann_kendall_trend_start_year - is a string with the start year for the Mann-Kendall trend line. Defaults to null, which means that the first year of the datetime parameter is used as the start year
mann_kendall_trend_end_year - is a string with the end year for the Mann-Kendall trend line. Defaults to null, which means that the last year of the datetime parameter is used as the last year

The API response would be a JSON object of the form:

{
  "station_id": "{station_id}",
  "mann_kendall_trend": {
    "slope": 0.6,
    "intercept": 3.4,
    "significance": 0.9
  } 
  "values": [
    {
      "value": 5.6,
      "series": "tas_mean",
      "date": "1980-05-01"
    },
    {
      "value": 5.7,
      "series": "tas_mean",
      "date": "1980-06-01",
    },
    {
      "value": 5.4,
      "series": "mann_kendall_trend",
      "date": "1980-06-01",
    },
     {
      "value": 5.4,
      "series": "decade-1981-1990",
      "date": "1981-01-01",
    }
  ]
}

geobeyond / Arpav-PPCV-backend

Implement API endpoint for generating time series for historical data #96