{
  "openapi": "3.1.1",
  "info": {
    "title": "Kann KI das? Agent Sponsorship API",
    "version": "1.0.0",
    "description": "Machine-readable availability and buyer-confirmed Stripe Checkout for fixed sponsor placements."
  },
  "servers": [
    {
      "url": "https://kannkidas.de/api"
    }
  ],
  "paths": {
    "/slots": {
      "get": {
        "operationId": "listSponsorSlots",
        "summary": "List live sponsor-slot availability",
        "responses": {
          "200": {
            "description": "Current slot states",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/SlotList"
                }
              }
            }
          }
        }
      }
    },
    "/v1": {
      "get": {
        "operationId": "getPaidSponsorBuyerBrief",
        "summary": "Fetch a sponsor buyer brief through x402",
        "description": "Protocol-conformance endpoint on Base Sepolia testnet. Commercial sponsor placements remain EUR purchases through buyer-confirmed Stripe hosted Checkout.",
        "responses": {
          "200": {
            "description": "Paid buyer brief and live slot availability",
            "headers": {
              "PAYMENT-RESPONSE": {
                "schema": {
                  "type": "string",
                  "contentEncoding": "base64"
                }
              }
            }
          },
          "402": {
            "description": "x402 v2 payment requirements",
            "headers": {
              "PAYMENT-REQUIRED": {
                "required": true,
                "schema": {
                  "type": "string",
                  "contentEncoding": "base64"
                }
              }
            }
          }
        }
      }
    },
    "/agent/register": {
      "post": {
        "operationId": "registerAgentClient",
        "summary": "Register an OAuth client for an agent",
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/RegistrationRequest"
              }
            }
          }
        },
        "responses": {
          "201": {
            "description": "Client credentials returned once"
          },
          "400": {
            "description": "Invalid registration",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Error"
                }
              }
            }
          }
        }
      }
    },
    "/oauth/token": {
      "post": {
        "operationId": "issueAgentAccessToken",
        "summary": "Issue an opaque access token using client credentials",
        "security": [
          {
            "clientBasic": []
          }
        ],
        "requestBody": {
          "required": true,
          "content": {
            "application/x-www-form-urlencoded": {
              "schema": {
                "type": "object",
                "required": [
                  "grant_type"
                ],
                "properties": {
                  "grant_type": {
                    "const": "client_credentials"
                  },
                  "scope": {
                    "type": "string",
                    "default": "sponsorship:read"
                  }
                }
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "Short-lived bearer token"
          },
          "401": {
            "description": "Invalid client",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Error"
                }
              }
            }
          }
        }
      }
    },
    "/agent/purchases": {
      "post": {
        "operationId": "createSponsorPurchase",
        "summary": "Create an idempotent Stripe Checkout Session",
        "description": "Call only after the buyer explicitly confirms a live slot, price and term. Payment details are collected by Stripe.",
        "security": [
          {
            "oauth2": [
              "sponsorship:write"
            ]
          }
        ],
        "parameters": [
          {
            "name": "Idempotency-Key",
            "in": "header",
            "required": true,
            "schema": {
              "type": "string",
              "minLength": 8,
              "maxLength": 128
            }
          }
        ],
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/PurchaseRequest"
              }
            }
          }
        },
        "x-payment-info": {
          "intent": "session",
          "method": "stripe",
          "amount": 99000,
          "currency": "EUR",
          "methods": [
            {
              "method": "stripe",
              "type": "hosted_checkout"
            }
          ]
        },
        "responses": {
          "201": {
            "description": "Checkout created",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Purchase"
                }
              }
            }
          },
          "401": {
            "description": "Bearer token missing or invalid",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Error"
                }
              }
            }
          },
          "409": {
            "description": "Slot unavailable",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Error"
                }
              }
            }
          }
        }
      }
    },
    "/agent/purchases/{purchase_id}": {
      "get": {
        "operationId": "getSponsorPurchase",
        "summary": "Read a purchase without exposing buyer PII",
        "security": [
          {
            "oauth2": [
              "sponsorship:read"
            ]
          }
        ],
        "parameters": [
          {
            "name": "purchase_id",
            "in": "path",
            "required": true,
            "schema": {
              "type": "string"
            }
          }
        ],
        "responses": {
          "200": {
            "description": "Purchase state",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Purchase"
                }
              }
            }
          },
          "404": {
            "description": "Unknown purchase",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Error"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "securitySchemes": {
      "clientBasic": {
        "type": "http",
        "scheme": "basic"
      },
      "oauth2": {
        "type": "oauth2",
        "flows": {
          "clientCredentials": {
            "tokenUrl": "https://kannkidas.de/api/oauth/token",
            "scopes": {
              "sponsorship:read": "Read own purchase status",
              "sponsorship:write": "Create a confirmed checkout"
            }
          }
        }
      }
    },
    "schemas": {
      "Error": {
        "type": "object",
        "required": [
          "message"
        ],
        "properties": {
          "message": {
            "type": "string"
          }
        }
      },
      "RegistrationRequest": {
        "type": "object",
        "additionalProperties": false,
        "required": [
          "name"
        ],
        "properties": {
          "name": {
            "type": "string",
            "minLength": 3,
            "maxLength": 80
          },
          "scopes": {
            "type": "array",
            "minItems": 1,
            "uniqueItems": true,
            "items": {
              "enum": [
                "sponsorship:read",
                "sponsorship:write"
              ]
            },
            "default": [
              "sponsorship:read"
            ]
          }
        }
      },
      "PurchaseRequest": {
        "$ref": "https://kannkidas.de/schema/agent-purchase.json"
      },
      "Purchase": {
        "type": "object",
        "required": [
          "purchase_id",
          "slot_id",
          "status",
          "status_url"
        ],
        "properties": {
          "purchase_id": {
            "type": "string"
          },
          "slot_id": {
            "type": "string"
          },
          "status": {
            "enum": [
              "checkout_created",
              "paid",
              "expired"
            ]
          },
          "checkout_url": {
            "type": "string",
            "format": "uri"
          },
          "status_url": {
            "type": "string",
            "format": "uri"
          },
          "expires_at": {
            "type": "string",
            "format": "date-time"
          },
          "amount": {
            "type": "integer",
            "const": 99000
          },
          "currency": {
            "type": "string",
            "const": "EUR"
          }
        }
      },
      "SlotList": {
        "type": "object",
        "required": [
          "slots"
        ],
        "properties": {
          "slots": {
            "type": "array",
            "items": {
              "type": "object",
              "required": [
                "id",
                "status"
              ],
              "properties": {
                "id": {
                  "type": "string"
                },
                "status": {
                  "enum": [
                    "available",
                    "held",
                    "sold",
                    "active"
                  ]
                }
              }
            }
          }
        }
      }
    }
  }
}