{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://drafts.opds.io/schema/publication.schema.json",
  "title": "OPDS Publication",
  "type": "object",
  "properties": {
    "metadata": {
      "$ref": "https://readium.org/webpub-manifest/schema/metadata.schema.json"
    },
    "links": {
      "type": "array",
      "items": {
        "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
      },
      "contains": {
        "description": "A publication must contain at least one acquisition link.",
        "properties": {
          "rel": {
            "anyOf": [
              {
                "$ref": "#/$defs/acquisition"
              },
              {
                "type": "array",
                "contains": {
                  "$ref": "#/$defs/acquisition"
                }
              }
            ]
          }
        }
      }
    },
    "images": {
      "description": "Images are meant to be displayed to the user when browsing publications",
      "type": "array",
      "items": {
        "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
      },
      "minItems": 1,
      "allOf": [
        {
          "description": "At least one image resource must use one of the following formats: image/jpeg, image/avif, image/png or image/gif.",
          "contains": {
            "properties": {
              "type": {
                "enum": [
                  "image/jpeg",
                  "image/webp",
                  "image/avif",
                  "image/png",
                  "image/jxl",
                  "image/gif"
                ]
              }
            }
          }
        }
      ]
    }
  },
  "required": [
    "metadata",
    "links"
  ],
  "$defs": {
    "acquisition": {
      "type": "string",
      "enum": [
        "acquisition",
        "borrow",
        "buy",
        "preview",
        "subscribe",
        "http://opds-spec.org/acquisition",
        "http://opds-spec.org/acquisition/buy",
        "http://opds-spec.org/acquisition/open-access",
        "http://opds-spec.org/acquisition/borrow",
        "http://opds-spec.org/acquisition/sample",
        "http://opds-spec.org/acquisition/subscribe"
      ]
    }
  }
}