{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://basicstack.de/schemas/expense/canonical/v1.0.0.json",
  "title": "Expense (canonical) v1.0.0",
  "description": "Kanonische Reisekostenstruktur. Bindet die Benutzerfreigabe. Technische Senken-Mappings dürfen die hier definierten Felder nicht in ihrer geschäftlichen Bedeutung ändern — insbesondere total_amount, currency und expense_items[].amount.",
  "type": "object",
  "additionalProperties": false,
  "required": ["schema", "workflow_id", "employee_id", "trip", "currency", "total_amount", "expense_items", "project_assignment"],
  "properties": {
    "schema": {
      "type": "object",
      "additionalProperties": false,
      "required": ["name", "version"],
      "properties": {
        "name": { "const": "expense.canonical" },
        "version": { "const": "1.0.0" }
      }
    },
    "workflow_id": {
      "type": "string",
      "pattern": "^WF-[0-9]{4}-[0-9]{4,}$",
      "description": "Prozess-ID, konstant über die gesamte Reisekostenabrechnung."
    },
    "employee_id": {
      "type": "string",
      "pattern": "^EMP-[0-9]+$",
      "description": "Interne Mitarbeiter-ID. Nicht die SAP-Personalnummer — die wird senken-seitig zugeordnet."
    },
    "trip": {
      "type": "object",
      "additionalProperties": false,
      "required": ["start_date", "end_date", "destination"],
      "properties": {
        "start_date": { "type": "string", "format": "date" },
        "end_date":   { "type": "string", "format": "date" },
        "destination": { "type": "string", "minLength": 1, "maxLength": 200 },
        "purpose":     { "type": "string", "maxLength": 500 }
      }
    },
    "currency": {
      "type": "string",
      "pattern": "^[A-Z]{3}$",
      "description": "ISO 4217 Währungscode (z.B. EUR)."
    },
    "total_amount": {
      "type": "string",
      "pattern": "^-?[0-9]+\\.[0-9]{2}$",
      "description": "Summe aller expense_items, als Dezimal-String mit zwei Nachkommastellen (JSON Number vermeidet Rundungsfehler)."
    },
    "expense_items": {
      "type": "array",
      "minItems": 1,
      "maxItems": 200,
      "items": {
        "type": "object",
        "additionalProperties": false,
        "required": ["type", "amount", "incurred_on"],
        "properties": {
          "type": {
            "type": "string",
            "enum": ["HOTEL", "MEALS", "TRANSPORT_FLIGHT", "TRANSPORT_RAIL", "TRANSPORT_CAR", "PARKING", "COMMUNICATION", "CONFERENCE_FEE", "OTHER"]
          },
          "amount":      { "type": "string", "pattern": "^-?[0-9]+\\.[0-9]{2}$" },
          "incurred_on": { "type": "string", "format": "date" },
          "description": { "type": "string", "maxLength": 500 },
          "receipt_ref": {
            "type": "string",
            "pattern": "^pii://[A-Za-z0-9/._-]+$",
            "description": "Referenz in den PII-Store (verschlüsselter S3-Bucket), nicht der Beleg selbst."
          }
        }
      }
    },
    "project_assignment": {
      "type": "object",
      "additionalProperties": false,
      "required": ["project_code", "cost_center", "source_attestation_ref"],
      "properties": {
        "project_code": { "type": "string", "pattern": "^P-[0-9]+$" },
        "cost_center":  { "type": "string", "pattern": "^CC-[0-9]+$" },
        "source_attestation_ref": {
          "type": "string",
          "pattern": "^sha256:[0-9a-f]{64}$",
          "description": "SHA-256 der Query Attestation (ds:expense-db-app / project_assignments), aus der dieses Projekt stammt. Zwingend, damit Verification nachweisen kann, dass das gewählte Projekt tatsächlich in der dem Benutzer vorgelegten Liste war."
        }
      }
    }
  }
}