{
  "functions": [
    {
      "isLoggedIn()": "auth.username !== null"
    },
    {
      "createOnly()": "next.exists() && !prev.exists()"
    },
    {
      "deleteOnly()": "prev.exists() && !next.exists()"
    },
    {
      "createOrDelete()": "createOnly() || deleteOnly()"
    }
  ],
  "schema": {
    "definitions": {
      "message": {
        "type": "object",
        "properties": {
          "from": {
            "type": "string",
            "constraint": "(auth.username == next     && createOnly()) || ($userid === auth.username && deleteOnly())"
          },
          "to": {
            "type": "string",
            "constraint": "createOrDelete()"
          },
          "message": {
            "type": "string",
            "constraint": "createOrDelete()"
          }
        },
        "required": [
          "from",
          "to",
          "message"
        ],
        "additionalProperties": false,
        "examples": [
          {
            "from": "bill",
            "to": "tom",
            "message": "hey Tom!"
          }
        ],
        "nonexamples": [
          {
            "to": "tom",
            "message": "hey Tom!"
          }
        ]
      }
    },
    "type": "object",
    "properties": {
      "users": {
        "type": "object",
        "$userid": {
          "type": "object",
          "properties": {
            "inbox": {
              "type": "object",
              "$message": {
                "$ref": "#/definitions/message"
              }
            },
            "outbox": {
              "type": "object",
              "$message": {
                "$ref": "#/definitions/message"
              }
            }
          }
        }
      }
    },
    "additionalProperties": false
  },
  "access": [
    {
      "location": "users/$userid/inbox/",
      "write": "createOnly() && isLoggedIn()"
    },
    {
      "location": "users/$userid/inbox/",
      "write": "deleteOnly() && $userid === auth.username"
    },
    {
      "location": "users/$userid/outbox/",
      "write": true
    },
    {
      "location": "users/$userid",
      "read": "$userid === auth.username"
    }
  ]
}