{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://drafts.opds.io/schema/feed.schema.json",
  "title": "OPDS Feed",
  "type": "object",
  "properties": {
    "metadata": {
      "description": "Contains feed-level metadata such as title or number of items",
      "$ref": "feed-metadata.schema.json"
    },
    "links": {
      "description": "Feed-level links such as search or pagination",
      "type": "array",
      "items": {
        "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
      },
      "uniqueItems": true,
      "minItems": 1,
      "contains": {
        "properties": {
          "rel": {
            "anyOf": [
              {
                "type": "string",
                "const": "self"
              },
              {
                "type": "array",
                "contains": {
                  "const": "self"
                }
              }
            ]
          }
        },
        "required": [
          "rel"
        ]
      }
    },
    "publications": {
      "description": "A list of publications that can be acquired",
      "type": "array",
      "items": {
        "$ref": "publication.schema.json"
      },
      "uniqueItems": true,
      "minItems": 1
    },
    "navigation": {
      "description": "Navigation for the catalog using links",
      "type": "array",
      "items": {
        "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
      },
      "uniqueItems": true,
      "minItems": 1,
      "allOf": [
        {
          "description": "Each Link Object in a navigation collection must contain a title",
          "items": {
            "required": [
              "title"
            ]
          }
        }
      ]
    },
    "facets": {
      "description": "Facets are meant to re-order or obtain a subset for the current list of publications",
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "metadata": {
            "$ref": "feed-metadata.schema.json"
          },
          "links": {
            "type": "array",
            "items": {
              "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
            },
            "uniqueItems": true,
            "minItems": 1
          }
        }
      },
      "uniqueItems": true,
      "minItems": 1
    },
    "groups": {
      "description": "Groups provide a curated experience, grouping publications or navigation links together",
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "metadata": {
            "$ref": "feed-metadata.schema.json"
          },
          "links": {
            "type": "array",
            "items": {
              "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
            },
            "uniqueItems": true,
            "minItems": 1
          },
          "publications": {
            "type": "array",
            "items": {
              "$ref": "publication.schema.json"
            },
            "uniqueItems": true,
            "minItems": 1
          },
          "navigation": {
            "type": "array",
            "items": {
              "$ref": "https://readium.org/webpub-manifest/schema/link.schema.json"
            },
            "uniqueItems": true,
            "minItems": 1
          }
        },
        "required": [
          "metadata"
        ]
      }
    }
  },
  "required": [
    "metadata",
    "links"
  ],
  "additionalProperties": {
    "$ref": "https://readium.org/webpub-manifest/schema/subcollection.schema.json"
  },
  "anyOf": [
    {
      "required": [
        "publications"
      ]
    },
    {
      "required": [
        "navigation"
      ]
    },
    {
      "required": [
        "groups"
      ]
    }
  ]
}