{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://open-mbee.github.io/OpenSysML/reference/engine-protocol.schema.json",
  "title": "OpenSysML external engine protocol, version 1",
  "description": "Every message the host and an external engine exchange over standard input and output, one JSON-RPC 2.0 object per line. A line the host writes validates against hostMessage; a line the engine writes validates against engineMessage.",
  "oneOf": [
    { "$ref": "#/$defs/hostMessage" },
    { "$ref": "#/$defs/engineMessage" }
  ],
  "$defs": {
    "jsonrpc": { "const": "2.0" },
    "id": {
      "description": "A request's number, chosen by the host; the answer repeats it.",
      "type": "integer",
      "minimum": 1
    },

    "hostMessage": {
      "description": "What the host sends: the describe, covers and run requests, and the cancel notification.",
      "oneOf": [
        { "$ref": "#/$defs/describeRequest" },
        { "$ref": "#/$defs/coversRequest" },
        { "$ref": "#/$defs/runRequest" },
        { "$ref": "#/$defs/cancelNotification" }
      ]
    },
    "engineMessage": {
      "description": "What the engine sends: the progress notification and a response to each request.",
      "oneOf": [
        { "$ref": "#/$defs/progressNotification" },
        { "$ref": "#/$defs/response" }
      ]
    },

    "describeRequest": {
      "type": "object",
      "properties": {
        "jsonrpc": { "$ref": "#/$defs/jsonrpc" },
        "id": { "$ref": "#/$defs/id" },
        "method": { "const": "describe" },
        "params": { "$ref": "#/$defs/describeParams" }
      },
      "required": ["jsonrpc", "id", "method", "params"],
      "additionalProperties": false
    },
    "describeParams": {
      "type": "object",
      "properties": {
        "protocols": {
          "description": "The protocol versions the host serves.",
          "type": "array",
          "items": { "type": "integer", "minimum": 1 },
          "minItems": 1
        }
      },
      "required": ["protocols"],
      "additionalProperties": false
    },
    "coversRequest": {
      "type": "object",
      "properties": {
        "jsonrpc": { "$ref": "#/$defs/jsonrpc" },
        "id": { "$ref": "#/$defs/id" },
        "method": { "const": "covers" },
        "params": { "$ref": "#/$defs/coversParams" }
      },
      "required": ["jsonrpc", "id", "method", "params"],
      "additionalProperties": false
    },
    "coversParams": {
      "type": "object",
      "properties": {
        "question": { "$ref": "#/$defs/question" },
        "model": { "$ref": "#/$defs/model" }
      },
      "required": ["question", "model"],
      "additionalProperties": false
    },
    "runRequest": {
      "type": "object",
      "properties": {
        "jsonrpc": { "$ref": "#/$defs/jsonrpc" },
        "id": { "$ref": "#/$defs/id" },
        "method": { "const": "run" },
        "params": { "$ref": "#/$defs/runParams" }
      },
      "required": ["jsonrpc", "id", "method", "params"],
      "additionalProperties": false
    },
    "runParams": {
      "type": "object",
      "properties": {
        "question": { "$ref": "#/$defs/question" },
        "model": { "$ref": "#/$defs/model" },
        "bounds": {
          "description": "The bounds the entry declares it takes, fixed at the budget's limits; 0 leaves one open.",
          "type": "array",
          "items": { "$ref": "#/$defs/bound" }
        },
        "budget": { "$ref": "#/$defs/budget" }
      },
      "required": ["question", "model", "bounds", "budget"],
      "additionalProperties": false
    },
    "cancelNotification": {
      "type": "object",
      "properties": {
        "jsonrpc": { "$ref": "#/$defs/jsonrpc" },
        "method": { "const": "cancel" },
        "params": { "$ref": "#/$defs/cancelParams" }
      },
      "required": ["jsonrpc", "method", "params"],
      "additionalProperties": false
    },
    "cancelParams": {
      "type": "object",
      "properties": {
        "id": { "$ref": "#/$defs/id" }
      },
      "required": ["id"],
      "additionalProperties": false
    },

    "progressNotification": {
      "type": "object",
      "properties": {
        "jsonrpc": { "$ref": "#/$defs/jsonrpc" },
        "method": { "const": "progress" },
        "params": { "$ref": "#/$defs/progressParams" }
      },
      "required": ["jsonrpc", "method", "params"],
      "additionalProperties": false
    },
    "progressParams": {
      "type": "object",
      "properties": {
        "id": { "$ref": "#/$defs/id" },
        "runs": { "type": "integer", "minimum": 0 },
        "depth": { "type": "integer", "minimum": 0 },
        "steps": { "type": "integer", "minimum": 0 },
        "text": { "type": "string" }
      },
      "required": ["id"],
      "additionalProperties": false
    },
    "response": {
      "description": "The answer to a request: its id with a result or an error, never both.",
      "type": "object",
      "properties": {
        "jsonrpc": { "$ref": "#/$defs/jsonrpc" },
        "id": { "$ref": "#/$defs/id" },
        "result": {
          "oneOf": [
            { "$ref": "#/$defs/description" },
            { "$ref": "#/$defs/coversResult" },
            { "$ref": "#/$defs/result" }
          ]
        },
        "error": { "$ref": "#/$defs/error" }
      },
      "required": ["jsonrpc", "id"],
      "oneOf": [
        { "required": ["result"] },
        { "required": ["error"] }
      ],
      "additionalProperties": false
    },
    "error": {
      "type": "object",
      "properties": {
        "code": { "enum": ["unsupported", "budget", "internal"] },
        "message": { "type": "string" }
      },
      "required": ["code", "message"],
      "additionalProperties": false
    },

    "description": {
      "description": "The engine's answer to describe, checked field by field against its manifest entry.",
      "type": "object",
      "properties": {
        "name": { "type": "string", "minLength": 1 },
        "version": { "type": "string", "minLength": 1 },
        "protocol": { "type": "integer", "minimum": 1 },
        "answers": { "type": "array", "items": { "$ref": "#/$defs/questionKind" }, "minItems": 1 },
        "subjects": { "description": "Declaration kinds the engine answers about, the notation's keyword without def: action, state, calc, ...", "type": "array", "items": { "type": "string" } },
        "bounds": { "type": "array", "items": { "$ref": "#/$defs/boundName" } },
        "witness": { "$ref": "#/$defs/witnessKind" },
        "model": { "type": "array", "items": { "$ref": "#/$defs/modelForm" } },
        "authority": { "$ref": "#/$defs/strength" },
        "concurrent": { "type": "boolean" }
      },
      "required": ["name", "version", "protocol", "answers"],
      "additionalProperties": false
    },
    "coversResult": {
      "type": "object",
      "properties": {
        "covers": { "type": "boolean" },
        "reason": { "type": "string" }
      },
      "required": ["covers"],
      "additionalProperties": false
    },
    "result": {
      "description": "The engine's answer to run. The strength is what the engine claims; the host decides what stands.",
      "type": "object",
      "properties": {
        "claim": { "$ref": "#/$defs/claim" },
        "strength": { "$ref": "#/$defs/strength" },
        "bounds": { "type": "array", "items": { "$ref": "#/$defs/bound" } },
        "witness": { "$ref": "#/$defs/witness" },
        "executions": { "type": "array", "items": { "$ref": "#/$defs/witness" } },
        "reason": { "type": "string" },
        "values": { "type": "array", "items": { "$ref": "#/$defs/value" } },
        "inputs": { "type": "array", "items": { "$ref": "#/$defs/input" } },
        "assumptions": { "type": "array", "items": { "type": "string" } },
        "elapsed": { "description": "Milliseconds.", "type": "integer", "minimum": 0 }
      },
      "required": ["claim", "strength"],
      "additionalProperties": false
    },
    "input": {
      "description": "One feature of the initial state as the engine accounts for it: free over its domain or pinned, the value a witness chose spelled as notation.",
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "type": { "type": "string" },
        "sort": { "type": "string" },
        "domain": { "type": "string" },
        "free": { "type": "boolean" },
        "optional": { "type": "boolean" },
        "value": { "type": "string" }
      },
      "required": ["name"],
      "additionalProperties": false
    },
    "witness": {
      "description": "A schedule witness (one schedule, two for sensitive) or an assignment witness (inputs alone).",
      "type": "object",
      "properties": {
        "schedules": {
          "description": "Schedules in the replay: format, `step N: <token>@<node> first of ...` lines.",
          "type": "array",
          "items": { "type": "string" }
        },
        "at": {
          "description": "The move a violation is evaluated at; absent means the schedule's end.",
          "type": "integer",
          "minimum": 0
        },
        "feature": { "description": "The feature two sensitive schedules diverge on.", "type": "string" },
        "inputs": { "type": "array", "items": { "$ref": "#/$defs/value" } }
      },
      "additionalProperties": false
    },

    "question": {
      "type": "object",
      "properties": {
        "kind": { "$ref": "#/$defs/questionKind" },
        "subject": { "description": "The qualified name as the surface spelled it.", "type": "string" },
        "subjectKind": { "description": "The subject's declaration kind as a manifest's subjects spells it; absent when the model does not declare the subject once.", "type": "string" },
        "schedule": { "description": "The scheduling policy as -schedule spells it.", "type": "string" },
        "free": { "type": "array", "items": { "enum": ["schedule", "inputs"] } },
        "condition": { "$ref": "#/$defs/condition" },
        "conditions": { "type": "array", "items": { "$ref": "#/$defs/conditionSet" } },
        "bindings": { "type": "array", "items": { "$ref": "#/$defs/value" } },
        "inputs": { "type": "array", "items": { "$ref": "#/$defs/freeInput" } },
        "sweep": { "$ref": "#/$defs/sweep" }
      },
      "required": ["kind", "subject", "schedule", "free"],
      "additionalProperties": false
    },
    "condition": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "text": { "type": "string" }
      },
      "required": ["name"],
      "additionalProperties": false
    },
    "conditionSet": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "features": { "type": "array", "items": { "$ref": "#/$defs/freeInput" } },
        "assertions": { "type": "array", "items": { "$ref": "#/$defs/condition" } },
        "pinned": { "type": "array", "items": { "$ref": "#/$defs/pinned" } }
      },
      "required": ["name", "features", "assertions"],
      "additionalProperties": false
    },
    "pinned": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "text": { "type": "string" }
      },
      "required": ["name", "text"],
      "additionalProperties": false
    },
    "freeInput": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "type": { "type": "string" },
        "unit": { "type": "string" },
        "domain": { "type": "string" }
      },
      "required": ["name"],
      "additionalProperties": false
    },
    "sweep": {
      "type": "object",
      "properties": {
        "ranges": { "type": "array", "items": { "$ref": "#/$defs/range" } },
        "sampled": { "type": "boolean" },
        "samples": { "type": "integer", "minimum": 0 },
        "seed": { "type": "integer", "minimum": 0 }
      },
      "required": ["ranges"],
      "additionalProperties": false
    },
    "range": {
      "type": "object",
      "properties": {
        "parameter": { "type": "string" },
        "type": { "type": "string" },
        "unit": { "type": "string" },
        "from": { "$ref": "#/$defs/scalar" },
        "to": { "$ref": "#/$defs/scalar" },
        "step": { "$ref": "#/$defs/scalar" }
      },
      "required": ["parameter", "type", "from", "to"],
      "additionalProperties": false
    },
    "value": {
      "description": "A named value as the tool protocol carries one: a number, a truth or a string, with a unit by its short name.",
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "value": { "$ref": "#/$defs/scalar" },
        "unit": { "type": "string" }
      },
      "required": ["name", "value"],
      "additionalProperties": false
    },
    "scalar": { "type": ["number", "boolean", "string"] },
    "bound": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "limit": { "type": "integer" },
        "reached": { "type": "boolean" }
      },
      "required": ["name", "limit"],
      "additionalProperties": false
    },
    "budget": {
      "type": "object",
      "properties": {
        "deadline": { "description": "An absolute time, RFC 3339.", "type": "string", "format": "date-time" },
        "depth": { "type": "integer", "minimum": 0 },
        "steps": { "type": "integer", "minimum": 0 },
        "runs": { "type": "integer", "minimum": 0 },
        "memory": { "type": "integer", "minimum": 0 },
        "jobs": { "type": "integer", "minimum": 0 }
      },
      "additionalProperties": false
    },
    "model": {
      "description": "The model in the forms the entry declared.",
      "type": "object",
      "properties": {
        "sources": { "$ref": "#/$defs/sources" },
        "graphs": { "$ref": "#/$defs/graphs" }
      },
      "additionalProperties": false
    },
    "sources": {
      "type": "object",
      "properties": {
        "library": { "description": "The version of the standard library the host embeds.", "type": "string" },
        "documents": {
          "type": "array",
          "items": {
            "type": "object",
            "properties": {
              "path": { "type": "string" },
              "text": { "type": "string" }
            },
            "required": ["path", "text"],
            "additionalProperties": false
          }
        }
      },
      "required": ["library", "documents"],
      "additionalProperties": false
    },
    "graphs": {
      "description": "The graphs:<version> form: the lowered graphs of the subject and of every behavior it performs. The forms of actions and states are the export's, documented with the version.",
      "type": "object",
      "properties": {
        "version": { "type": "integer", "minimum": 1 },
        "subject": { "type": "string" },
        "actions": {
          "type": "array",
          "items": { "type": "object", "properties": { "name": { "type": "string" }, "kind": { "type": "string" } }, "required": ["name", "kind"] }
        },
        "states": {
          "type": "array",
          "items": { "type": "object", "properties": { "name": { "type": "string" }, "kind": { "type": "string" } }, "required": ["name", "kind"] }
        }
      },
      "required": ["version", "subject"],
      "additionalProperties": false
    },

    "questionKind": {
      "enum": ["evaluate", "outcomes", "holds", "sensitive", "satisfiable", "sweep", "compute"]
    },
    "claim": {
      "enum": ["none", "holds", "violated", "sensitive", "value", "table", "outcomes", "satisfiable", "unsatisfiable", "unbounded"]
    },
    "strength": {
      "enum": ["not covered", "observed", "witnessed", "bounded", "proved"]
    },
    "witnessKind": { "enum": ["schedule", "assignment", "none"] },
    "modelForm": {
      "description": "sources, rdf or graphs:<version>; the host serves graphs:1 and refuses rdf.",
      "type": "string",
      "pattern": "^(sources|rdf|graphs:[1-9][0-9]*)$"
    },
    "boundName": { "enum": ["depth", "steps", "runs", "memory"] }
  }
}