{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://schemas.fablepool.org/v1/problem.schema.json",
  "title": "FablePool ProblemVersion",
  "description": "Canonical storage format for one immutable version of a community problem. Includes the shared rich-content model used by all FablePool schemas.",
  "type": "object",
  "required": ["schemaVersion", "kind", "title", "locale", "license", "difficulty", "tags", "statement", "answerSpec"],
  "additionalProperties": false,
  "properties": {
    "schemaVersion": { "const": "1" },
    "kind": { "const": "problem" },
    "problemId": {
      "description": "Stable identity of the problem family (UUID). Absent in not-yet-saved drafts and in import bundles before id assignment.",
      "type": "string",
      "format": "uuid"
    },
    "versionLabel": {
      "description": "Human-readable version label assigned by the platform, e.g. 'v3'. Informational only; authoritative version identity lives in the database.",
      "type": "string",
      "maxLength": 32
    },
    "slug": {
      "type": "string",
      "pattern": "^[a-z0-9]+(?:-[a-z0-9]+)*$",
      "minLength": 3,
      "maxLength": 80
    },
    "title": { "type": "string", "minLength": 3, "maxLength": 200 },
    "summary": {
      "description": "Plain-text teaser shown in lists and search results. No markup.",
      "type": "string",
      "maxLength": 500
    },
    "locale": {
      "description": "BCP 47 language tag of this version's content.",
      "type": "string",
      "pattern": "^[a-zA-Z]{2,3}(-[a-zA-Z0-9]{2,8})*$"
    },
    "translationOf": {
      "description": "If this version is a translation, the problemId of the source-locale problem.",
      "type": "string",
      "format": "uuid"
    },
    "license": {
      "description": "Content license. The platform only accepts CC BY-SA 4.0 or more permissive CC licenses compatible with it.",
      "type": "string",
      "enum": ["CC-BY-SA-4.0", "CC-BY-4.0", "CC0-1.0"]
    },
    "attribution": { "$ref": "#/$defs/Attribution" },
    "tags": {
      "type": "array",
      "minItems": 1,
      "maxItems": 12,
      "uniqueItems": true,
      "items": { "type": "string", "pattern": "^[a-z0-9]+(?:-[a-z0-9]+)*$", "maxLength": 50 }
    },
    "topics": {
      "description": "Slugs of curated taxonomy topics (Topic entities), e.g. 'number-theory'.",
      "type": "array",
      "maxItems": 5,
      "uniqueItems": true,
      "items": { "type": "string", "pattern": "^[a-z0-9]+(?:-[a-z0-9]+)*$", "maxLength": 50 }
    },
    "difficulty": {
      "type": "object",
      "required": ["level"],
      "additionalProperties": false,
      "properties": {
        "level": { "type": "integer", "minimum": 1, "maximum": 5 },
        "label": { "type": "string", "enum": ["intro", "easy", "medium", "hard", "expert"] }
      }
    },
    "estimatedMinutes": { "type": "integer", "minimum": 1, "maximum": 240 },
    "prerequisites": {
      "type": "array",
      "maxItems": 10,
      "items": { "$ref": "#/$defs/Prerequisite" }
    },
    "statement": { "$ref": "#/$defs/RichContent" },
    "answerSpec": { "$ref": "attempt-answer.schema.json#/$defs/AnswerSpec" },
    "hints": {
      "type": "array",
      "maxItems": 8,
      "items": { "$ref": "hint-solution.schema.json#/$defs/Hint" }
    },
    "solutions": {
      "type": "array",
      "maxItems": 5,
      "items": { "$ref": "hint-solution.schema.json#/$defs/Solution" }
    },
    "assets": {
      "description": "Manifest of MediaAssets referenced by content blocks. Every image/audio block must reference an assetId listed here.",
      "type": "array",
      "maxItems": 30,
      "items": { "$ref": "#/$defs/AssetRef" }
    },
    "changelog": {
      "description": "Author-written summary of what changed relative to the parent version.",
      "type": "string",
      "maxLength": 2000
    },
    "x-extensions": {
      "description": "Namespaced experimental extensions. Keys must be reverse-DNS style. Renderers must ignore unknown extensions.",
      "type": "object",
      "propertyNames": { "pattern": "^[a-z0-9-]+(\\.[a-z0-9-]+)+$" }
    }
  },
  "$defs": {
    "Prerequisite": {
      "type": "object",
      "required": ["refType", "ref"],
      "additionalProperties": false,
      "properties": {
        "refType": { "type": "string", "enum": ["problem", "course", "topic"] },
        "ref": {
          "description": "UUID for problem/course, topic slug for topic.",
          "type": "string",
          "maxLength": 80
        },
        "note": { "type": "string", "maxLength": 200 }
      }
    },
    "Attribution": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "authors": {
          "type": "array",
          "minItems": 1,
          "maxItems": 20,
          "items": {
            "type": "object",
            "required": ["name"],
            "additionalProperties": false,
            "properties": {
              "name": { "type": "string", "minLength": 1, "maxLength": 120 },
              "userId": { "type": "string", "format": "uuid" },
              "url": { "type": "string", "format": "uri", "pattern": "^https://" },
              "role": { "type": "string", "enum": ["author", "translator", "illustrator", "editor"] }
            }
          }
        },
        "forkedFrom": {
          "type": "object",
          "required": ["problemId", "versionId"],
          "additionalProperties": false,
          "properties": {
            "problemId": { "type": "string", "format": "uuid" },
            "versionId": { "type": "string", "format": "uuid" },
            "title": { "type": "string", "maxLength": 200 },
            "url": { "type": "string", "format": "uri", "pattern": "^https://" }
          }
        },
        "externalSources": {
          "description": "Citations for adapted material. Required by policy when content is adapted from a compatible external OER.",
          "type": "array",
          "maxItems": 10,
          "items": {
            "type": "object",
            "required": ["title", "license"],
            "additionalProperties": false,
            "properties": {
              "title": { "type": "string", "maxLength": 300 },
              "author": { "type": "string", "maxLength": 200 },
              "url": { "type": "string", "format": "uri", "pattern": "^https://" },
              "license": { "type": "string", "maxLength": 50 }
            }
          }
        }
      }
    },
    "AssetRef": {
      "type": "object",
      "required": ["assetId", "mediaType", "sha256"],
      "additionalProperties": false,
      "properties": {
        "assetId": { "type": "string", "pattern": "^[a-zA-Z0-9_-]{8,64}$" },
        "mediaType": {
          "type": "string",
          "enum": ["image/png", "image/jpeg", "image/webp", "image/svg+xml", "image/gif", "audio/mpeg", "audio/ogg"]
        },
        "sha256": { "type": "string", "pattern": "^[a-f0-9]{64}$" },
        "byteSize": { "type": "integer", "minimum": 1, "maximum": 10485760 },
        "originalFilename": { "type": "string", "maxLength": 255 }
      }
    },

    "RichContent": {
      "description": "Ordered list of block nodes. This is the shared content model for statements, hints, solutions, lessons, and discussion-free contexts.",
      "type": "array",
      "maxItems": 200,
      "items": { "$ref": "#/$defs/Block" }
    },
    "Block": {
      "oneOf": [
        { "$ref": "#/$defs/ParagraphBlock" },
        { "$ref": "#/$defs/HeadingBlock" },
        { "$ref": "#/$defs/MathBlock" },
        { "$ref": "#/$defs/CodeBlock" },
        { "$ref": "#/$defs/ImageBlock" },
        { "$ref": "#/$defs/ListBlock" },
        { "$ref": "#/$defs/TableBlock" },
        { "$ref": "#/$defs/CalloutBlock" },
        { "$ref": "#/$defs/QuoteBlock" },
        { "$ref": "#/$defs/WidgetBlock" },
        { "$ref": "#/$defs/DividerBlock" }
      ]
    },
    "ParagraphBlock": {
      "type": "object",
      "required": ["type", "content"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "paragraph" },
        "content": { "$ref": "#/$defs/InlineContent" }
      }
    },
    "HeadingBlock": {
      "type": "object",
      "required": ["type", "level", "content"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "heading" },
        "level": {
          "description": "2–4 only. Level 1 is reserved for the document title rendered by the platform chrome.",
          "type": "integer",
          "minimum": 2,
          "maximum": 4
        },
        "content": { "$ref": "#/$defs/InlineContent" }
      }
    },
    "MathBlock": {
      "type": "object",
      "required": ["type", "latex", "alt"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "math" },
        "latex": { "type": "string", "minLength": 1, "maxLength": 5000 },
        "alt": {
          "description": "Spoken-form description for screen readers, e.g. 'the integral from 0 to 1 of x squared dx'. Required for display math.",
          "type": "string",
          "minLength": 1,
          "maxLength": 1000
        },
        "numbered": { "type": "boolean", "default": false }
      }
    },
    "CodeBlock": {
      "type": "object",
      "required": ["type", "language", "code"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "code" },
        "language": {
          "type": "string",
          "enum": ["python", "javascript", "typescript", "c", "cpp", "java", "rust", "go", "haskell", "sql", "pseudocode", "text"]
        },
        "code": { "type": "string", "maxLength": 20000 },
        "caption": { "type": "string", "maxLength": 300 },
        "highlightLines": {
          "type": "array",
          "maxItems": 50,
          "items": { "type": "integer", "minimum": 1 }
        }
      }
    },
    "ImageBlock": {
      "type": "object",
      "required": ["type", "assetId", "alt"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "image" },
        "assetId": { "type": "string", "pattern": "^[a-zA-Z0-9_-]{8,64}$" },
        "alt": {
          "description": "Required alternative text. Use empty string only for purely decorative images.",
          "type": "string",
          "maxLength": 1000
        },
        "caption": { "$ref": "#/$defs/InlineContent" },
        "width": { "type": "integer", "minimum": 1, "maximum": 4096 },
        "height": { "type": "integer", "minimum": 1, "maximum": 4096 }
      }
    },
    "ListBlock": {
      "type": "object",
      "required": ["type", "ordered", "items"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "list" },
        "ordered": { "type": "boolean" },
        "items": {
          "type": "array",
          "minItems": 1,
          "maxItems": 100,
          "items": {
            "type": "object",
            "required": ["content"],
            "additionalProperties": false,
            "properties": {
              "content": { "$ref": "#/$defs/RichContent" }
            }
          }
        }
      }
    },
    "TableBlock": {
      "type": "object",
      "required": ["type", "rows"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "table" },
        "caption": { "type": "string", "maxLength": 300 },
        "header": {
          "type": "array",
          "maxItems": 12,
          "items": { "$ref": "#/$defs/InlineContent" }
        },
        "rows": {
          "type": "array",
          "minItems": 1,
          "maxItems": 100,
          "items": {
            "type": "array",
            "minItems": 1,
            "maxItems": 12,
            "items": { "$ref": "#/$defs/InlineContent" }
          }
        }
      }
    },
    "CalloutBlock": {
      "type": "object",
      "required": ["type", "variant", "content"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "callout" },
        "variant": { "type": "string", "enum": ["note", "tip", "warning", "definition", "theorem", "example"] },
        "title": { "type": "string", "maxLength": 200 },
        "content": { "$ref": "#/$defs/RichContent" }
      }
    },
    "QuoteBlock": {
      "type": "object",
      "required": ["type", "content"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "quote" },
        "content": { "$ref": "#/$defs/RichContent" },
        "attribution": { "type": "string", "maxLength": 200 }
      }
    },
    "WidgetBlock": {
      "description": "Embeds a sandboxed widget. The textFallback is mandatory so content degrades on low-bandwidth/no-JS clients and for assistive technology when the widget declares an 'alternative-task' strategy.",
      "type": "object",
      "required": ["type", "widgetName", "widgetVersion", "textFallback"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "widget" },
        "widgetName": { "type": "string", "pattern": "^[a-z0-9]+(?:-[a-z0-9]+)*$", "maxLength": 80 },
        "widgetVersion": { "type": "string", "pattern": "^\\d+\\.\\d+\\.\\d+$" },
        "params": {
          "description": "Instance parameters; validated against the widget manifest's paramsSchema at save time.",
          "type": "object"
        },
        "heightHint": { "type": "integer", "minimum": 100, "maximum": 1200 },
        "textFallback": { "$ref": "#/$defs/RichContent" }
      }
    },
    "DividerBlock": {
      "type": "object",
      "required": ["type"],
      "additionalProperties": false,
      "properties": { "type": { "const": "divider" } }
    },

    "InlineContent": {
      "type": "array",
      "maxItems": 500,
      "items": { "$ref": "#/$defs/Inline" }
    },
    "Inline": {
      "oneOf": [
        { "$ref": "#/$defs/TextSpan" },
        { "$ref": "#/$defs/InlineMath" },
        { "$ref": "#/$defs/Link" }
      ]
    },
    "TextSpan": {
      "type": "object",
      "required": ["type", "text"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "text" },
        "text": { "type": "string", "maxLength": 5000 },
        "marks": {
          "type": "array",
          "maxItems": 5,
          "uniqueItems": true,
          "items": { "type": "string", "enum": ["bold", "italic", "code", "strike", "sub", "sup"] }
        }
      }
    },
    "InlineMath": {
      "type": "object",
      "required": ["type", "latex"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "math" },
        "latex": { "type": "string", "minLength": 1, "maxLength": 1000 },
        "alt": { "type": "string", "maxLength": 500 }
      }
    },
    "Link": {
      "type": "object",
      "required": ["type", "href", "content"],
      "additionalProperties": false,
      "properties": {
        "type": { "const": "link" },
        "href": {
          "description": "https URLs or internal app paths only. javascript:/data: URIs are rejected by schema and again by the sanitizer.",
          "type": "string",
          "maxLength": 2000,
          "pattern": "^(https://|/)"
        },
        "content": {
          "type": "array",
          "minItems": 1,
          "maxItems": 50,
          "items": { "$ref": "#/$defs/TextSpan" }
        }
      }
    }
  }
}