{
  "openapi": "3.1.0",
  "info": {
    "title": "OTP Flow API",
    "version": "1.0.0",
    "description": "Send and verify SMS one-time passwords to Indian mobile numbers. Authenticate with `Authorization: Bearer <api_key>`."
  },
  "servers": [
    {
      "url": "https://otpflow.in"
    }
  ],
  "security": [
    {
      "bearerAuth": []
    }
  ],
  "paths": {
    "/send-otp": {
      "post": {
        "operationId": "sendOtp",
        "summary": "Send an OTP by SMS",
        "description": "Sends an OTP to a 10 digit Indian mobile number and returns an otp_id used for verification. If `otp` is omitted a random one of `otp_length` digits is generated.",
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "type": "object",
                "required": [
                  "number",
                  "purpose"
                ],
                "properties": {
                  "number": {
                    "type": "string",
                    "pattern": "^[6-9][0-9]{9}$",
                    "description": "10 digit mobile number"
                  },
                  "purpose": {
                    "type": "string",
                    "minLength": 3,
                    "maxLength": 40
                  },
                  "ttl": {
                    "type": "integer",
                    "minimum": 5,
                    "maximum": 120,
                    "default": 10,
                    "description": "Minutes until the OTP expires"
                  },
                  "otp": {
                    "type": "string",
                    "pattern": "^[0-9]{3,40}$",
                    "description": "Optional custom OTP"
                  },
                  "otp_length": {
                    "type": "integer",
                    "minimum": 3,
                    "maximum": 40,
                    "default": 6,
                    "description": "Length when OTP is generated"
                  }
                }
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "OTP sent",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean"
                    },
                    "message": {
                      "type": "string"
                    },
                    "otp_id": {
                      "type": "string"
                    },
                    "number": {
                      "type": "string"
                    },
                    "purpose": {
                      "type": "string"
                    },
                    "ttl": {
                      "type": "integer"
                    },
                    "expires_at": {
                      "type": "string",
                      "format": "date-time"
                    },
                    "cost": {
                      "type": "number"
                    },
                    "balance": {
                      "type": "number"
                    }
                  }
                }
              }
            }
          },
          "401": {
            "description": "Invalid API key",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "402": {
            "description": "Insufficient balance",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "422": {
            "description": "Validation error",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "429": {
            "description": "Rate limited",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "502": {
            "description": "SMS provider failure (not charged)",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          }
        }
      }
    },
    "/verify-otp": {
      "post": {
        "operationId": "verifyOtp",
        "summary": "Verify an OTP",
        "requestBody": {
          "required": true,
          "content": {
            "application/json": {
              "schema": {
                "type": "object",
                "required": [
                  "otp_id",
                  "otp"
                ],
                "properties": {
                  "otp_id": {
                    "type": "string"
                  },
                  "otp": {
                    "type": "string"
                  }
                }
              }
            }
          }
        },
        "responses": {
          "200": {
            "description": "Verified",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean"
                    },
                    "verified": {
                      "type": "boolean"
                    },
                    "otp_id": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "400": {
            "description": "Incorrect OTP",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "404": {
            "description": "Unknown otp_id",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "409": {
            "description": "Already used",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "410": {
            "description": "Expired",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          },
          "429": {
            "description": "Too many attempts",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean",
                      "const": false
                    },
                    "error": {
                      "type": "string"
                    },
                    "message": {
                      "type": "string"
                    }
                  }
                }
              }
            }
          }
        }
      }
    },
    "/balance": {
      "get": {
        "operationId": "getBalance",
        "summary": "Get wallet balance and current rate",
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "success": {
                      "type": "boolean"
                    },
                    "balance": {
                      "type": "number"
                    },
                    "currency": {
                      "type": "string"
                    },
                    "rate_per_otp": {
                      "type": "number"
                    }
                  }
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "securitySchemes": {
      "bearerAuth": {
        "type": "http",
        "scheme": "bearer"
      }
    }
  }
}