name: hydration
type: processor
status: beta
categories: [ Utility, Integration ]
summary: A common hydration pattern.
description: Hydrates content from structured messages based on an ID field.

fields:
  - name: cache
    description: A cache resource to use.
    type: string
  - name: id_path
    description: A dot path pointing to the identifier to use for hydration.
    type: string
  - name: content_path
    description: A dot path pointing to the value to cache and hydrate.
    type: string

mapping: |
  map cache_get {
    root.branch.request_map = """
      root = if this.%v.type() == "null" {
        this.%v
      } else {
        deleted()
      }
    """.format(this.content_path, this.id_path)

    root.branch.processors = [
      {
        "cache": {
          "operator": "get",
          "resource": this.cache,
          "key": "${! content() }",
        }
      }
    ]

    root.branch.result_map = "root.%v = content().string()".format(this.content_path)
  }

  map cache_set {
    root.branch.request_map = """
      meta id = this.%v
      root = this.%v | deleted()
    """.format(this.id_path, this.content_path)

    root.branch.processors = [
      {
        "cache": {
          "operator": "set",
          "resource": this.cache,
          "key": """${! meta("id") }""",
          "value": "${! content() }",
        }
      }
    ]
  }

  root.try = [
    this.apply("cache_set"),
    this.apply("cache_get"),
  ]

  # The following is only used for testing config field type coercion
  let cache_type = this.cache.type()
  let id_type = this.id_path.type()
  let content_type = this.content_path.type()
  root = if $cache_type != "string" || $id_type != "string" || $content_type != "string" {
    throw("Fields were coerced into incorrect types: cache(%v), id_path(%v), content_path(%v)".format($cache_type, $id_type, $content_type))
  }

tests:
  - name: Basic fields
    config:
      cache: foocache
      id_path: article.id
      content_path: article.content

    expected:
      try:
        - branch:
            request_map: |-2
              
                  meta id = this.article.id
                  root = this.article.content | deleted()
                
            processors:
              - cache:
                  operator: set
                  resource: foocache
                  key: ${! meta("id") }
                  value: ${! content() }

        - branch:
            request_map: |-2
              
                  root = if this.article.content.type() == "null" {
                    this.article.id
                  } else {
                    deleted()
                  }
                
            processors:
              - cache:
                  operator: get
                  resource: foocache
                  key: ${! content() }
            result_map: root.article.content = content().string()

  - name: Type coercion
    config:
      cache: 10
      id_path: false
      content_path: 20.475