{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://schemas.fablepool.org/v1/lesson-content.json",
  "title": "FablePool Lesson Content",
  "description": "The structured payload stored in Lesson.content (inside a CourseVersion). A lesson is an ordered sequence of segments interleaving prose, embedded problems and reflection checkpoints.",
  "type": "object",
  "required": ["schema", "segments"],
  "additionalProperties": false,
  "properties": {
    "schema": { "const": "fablepool.lesson/1" },
    "objectives": {
      "type": "array",
      "maxItems": 20,
      "items": { "type": "string", "minLength": 1, "maxLength": 300 },
      "description": "Learning objectives shown at the top of the lesson and used by recommendations."
    },
    "estimated_minutes": { "type": "integer", "minimum": 1, "maximum": 600 },
    "segments": {
      "type": "array",
      "minItems": 1,
      "maxItems": 200,
      "items": { "$ref": "#/$defs/segment" }
    }
  },
  "$defs": {
    "segment": {
      "oneOf": [
        { "$ref": "#/$defs/contentSegment" },
        { "$ref": "#/$defs/problemSegment" },
        { "$ref": "#/$defs/checkpointSegment" }
      ]
    },
    "contentSegment": {
      "type": "object",
      "required": ["kind", "document"],
      "additionalProperties": false,
      "properties": {
        "kind": { "const": "content" },
        "document": { "$ref": "https://schemas.fablepool.org/v1/content-document.json" }
      }
    },
    "problemSegment": {
      "type": "object",
      "required": ["kind", "problem"],
      "additionalProperties": false,
      "properties": {
        "kind": { "const": "problem" },
        "problem": {
          "type": "string",
          "format": "uuid",
          "description": "Problem id. Resolved to that problem's published version at delivery time; the export pipeline pins the exact version."
        },
        "required": {
          "type": "boolean",
          "default": true,
          "description": "Whether this problem must be answered to complete the lesson."
        },
        "context": {
          "type": "string",
          "maxLength": 500,
          "description": "Short bridge text shown above the embedded problem."
        }
      }
    },
    "checkpointSegment": {
      "type": "object",
      "required": ["kind", "prompt"],
      "additionalProperties": false,
      "description": "A self-reflection pause; the response is private to the learner and not graded.",
      "properties": {
        "kind": { "const": "checkpoint" },
        "title": { "type": "string", "maxLength": 200 },
        "prompt": { "$ref": "https://schemas.fablepool.org/v1/content-document.json" }
      }
    }
  }
}