NASA EPIC Earth Imagery Retrieval

arazzo: 1.0.1
info:
  title: NASA EPIC Earth Imagery Retrieval
  summary: List the dates EPIC actually has imagery for, then pull both natural and enhanced color metadata for one of them.
  description: >-
    The date-catalog-first pattern for the Earth Polychromatic Imaging Camera.
    DSCOVR does not return full-disc imagery every day, so requesting an
    arbitrary date is a coin flip. EPIC publishes a dedicated endpoint listing
    every date it holds natural color imagery for, and this workflow reads that
    catalog first, selects a date from it, and then pulls both the natural color
    and enhanced color metadata for that same date so a caller can compare the
    two renderings of an identical capture. Every step spells out its request
    inline so the flow can be read and executed without opening the underlying
    OpenAPI description.
  version: 1.0.0
sourceDescriptions:
- name: epicApi
  url: ../openapi/nasa-epic-api-openapi.yml
  type: openapi
workflows:
- workflowId: epic-earth-imagery-retrieval
  summary: Resolve an available EPIC date and retrieve its natural and enhanced color imagery metadata.
  description: >-
    Reads the catalog of dates for which EPIC holds natural color imagery,
    takes the first available date, and retrieves both the natural color and
    enhanced color image metadata for that date.
  inputs:
    type: object
    required:
    - apiKey
    properties:
      apiKey:
        type: string
        description: NASA API key from api.nasa.gov. DEMO_KEY works for low-volume testing.
        default: DEMO_KEY
  steps:
  - stepId: listAvailableDates
    description: >-
      Read the catalog of every date for which EPIC holds natural color
      imagery. This is the only reliable way to pick a date that will actually
      return images, since DSCOVR does not capture usable full-disc imagery
      every day.
    operationId: getEpicNaturalDates
    parameters:
    - name: api_key
      in: query
      value: $inputs.apiKey
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      availableDates: $response.body
      selectedDate: $response.body#/0/date
  - stepId: getNaturalColorImagery
    description: >-
      Retrieve natural color image metadata for the selected date. Each entry
      carries the image filename, the caption, the centroid coordinates of the
      Earth disc, and the spacecraft, lunar, and solar J2000 positions at
      capture time.
    operationId: getEpicNaturalByDate
    parameters:
    - name: date
      in: path
      value: $steps.listAvailableDates.outputs.selectedDate
    - name: api_key
      in: query
      value: $inputs.apiKey
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      naturalImages: $response.body
      naturalIdentifier: $response.body#/0/identifier
      naturalImageName: $response.body#/0/image
      naturalCaption: $response.body#/0/caption
      naturalCaptureDate: $response.body#/0/date
      centroidLat: $response.body#/0/centroid_coordinates/lat
      centroidLon: $response.body#/0/centroid_coordinates/lon
  - stepId: getEnhancedColorImagery
    description: >-
      Retrieve enhanced color image metadata for the same date so the caller
      can pair each natural color capture with its contrast-enhanced rendering
      of the same moment.
    operationId: getEpicEnhancedByDate
    parameters:
    - name: date
      in: path
      value: $steps.listAvailableDates.outputs.selectedDate
    - name: api_key
      in: query
      value: $inputs.apiKey
    successCriteria:
    - condition: $statusCode == 200
    outputs:
      enhancedImages: $response.body
      enhancedIdentifier: $response.body#/0/identifier
      enhancedImageName: $response.body#/0/image
      enhancedCaptureDate: $response.body#/0/date
  outputs:
    selectedDate: $steps.listAvailableDates.outputs.selectedDate
    naturalImageName: $steps.getNaturalColorImagery.outputs.naturalImageName
    naturalCaption: $steps.getNaturalColorImagery.outputs.naturalCaption
    centroidLat: $steps.getNaturalColorImagery.outputs.centroidLat
    centroidLon: $steps.getNaturalColorImagery.outputs.centroidLon
    enhancedImageName: $steps.getEnhancedColorImagery.outputs.enhancedImageName