{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://mlsysbook.ai/periodic-table/table.schema.json",
  "title": "Periodic Table of ML Systems",
  "description": "Single source of truth for the Periodic Table of ML Systems. Consumed by the standalone HTML emitter and the StaffML React app. Cross-reference invariants (bond resolution, formula resolution, no cell collisions) are enforced by the validator script in addition to this schema.",
  "type": "object",
  "required": ["version", "title", "blocks", "rows", "elements", "compounds"],
  "additionalProperties": false,
  "properties": {
    "version":  { "type": "string", "pattern": "^\\d+\\.\\d+(\\.\\d+)?$" },
    "title":    { "type": "string" },
    "subtitle": { "type": "string" },

    "blocks": {
      "type": "array",
      "minItems": 1,
      "items": {
        "type": "object",
        "required": ["key", "name", "sub", "color", "cols"],
        "additionalProperties": false,
        "properties": {
          "key":   { "type": "string", "enum": ["R", "C", "X", "K", "M"] },
          "name":  { "type": "string" },
          "sub":   { "type": "string" },
          "color": { "type": "string", "pattern": "^#[0-9a-fA-F]{6}$" },
          "cols":  {
            "type": "array",
            "minItems": 1,
            "items": { "type": "integer", "minimum": 1, "maximum": 18 }
          }
        }
      }
    },

    "rows": {
      "type": "array",
      "minItems": 1,
      "items": {
        "type": "object",
        "required": ["index", "key", "name"],
        "additionalProperties": false,
        "properties": {
          "index":   { "type": "integer", "minimum": 1, "maximum": 8 },
          "key":     { "type": "string", "pattern": "^[a-z_]+$" },
          "name":    { "type": "string" },
          "tagline": { "type": "string" }
        }
      }
    },

    "elements": {
      "type": "array",
      "minItems": 1,
      "items": {
        "type": "object",
        "required": ["id", "sym", "name", "block", "row", "col", "desc", "bonds", "why"],
        "additionalProperties": false,
        "properties": {
          "id":    { "type": "integer", "minimum": 1 },
          "sym":   { "type": "string", "pattern": "^[A-Z][a-z]$" },
          "name":  { "type": "string", "minLength": 1 },
          "block": { "type": "string", "enum": ["R", "C", "X", "K", "M"] },
          "row":   { "type": "integer", "minimum": 1, "maximum": 8 },
          "col":   { "type": "integer", "minimum": 1, "maximum": 18 },
          "year":  { "type": ["string", "null"] },
          "desc":  { "type": "string", "minLength": 1 },
          "bonds": {
            "type": "array",
            "items": { "type": "string", "pattern": "^[A-Z][a-z]$" }
          },
          "why":   { "type": "string", "minLength": 1 }
        }
      }
    },

    "compounds": {
      "type": "array",
      "items": {
        "type": "object",
        "required": ["section", "items"],
        "additionalProperties": false,
        "properties": {
          "section": { "type": "string" },
          "hint":    { "type": "string" },
          "items": {
            "type": "array",
            "items": {
              "type": "object",
              "required": ["name", "formula"],
              "additionalProperties": false,
              "properties": {
                "name":    { "type": "string" },
                "formula": { "type": "string", "minLength": 1 }
              }
            }
          }
        }
      }
    },

    "known_collisions": {
      "type": "array",
      "description": "Documented intentional symbol collisions. Lookup behavior is last-wins; consumers may disambiguate by id or by (row, col).",
      "items": {
        "type": "object",
        "required": ["sym", "ids", "note"],
        "additionalProperties": false,
        "properties": {
          "sym":  { "type": "string", "pattern": "^[A-Z][a-z]$" },
          "ids":  {
            "type": "array",
            "minItems": 2,
            "items": { "type": "integer", "minimum": 1 }
          },
          "note": { "type": "string" }
        }
      }
    }
  }
}