{
  "openapi": "3.0.3",
  "info": {
    "title": "Letter Service API",
    "version": "1.0.0",
    "description": "API for generating, sending, and managing letters."
  },
  "servers": [
    {
      "url": "/"
    }
  ],
  "security": [
    {
      "bearerAuth": []
    }
  ],
  "paths": {
    "/health": {
      "get": {
        "summary": "Health check",
        "tags": [
          "System"
        ],
        "security": [],
        "responses": {
          "200": {
            "description": "Service is healthy",
            "content": {
              "application/json": {
                "schema": {
                  "type": "object",
                  "properties": {
                    "status": {
                      "type": "string",
                      "example": "ok"
                    },
                    "uptime": {
                      "type": "number",
                      "example": 123.45
                    }
                  }
                }
              }
            }
          },
          "500": { "$ref": "#/components/responses/InternalServerError" }
        }
      }
    },
    "/letters/{userId}": {
      "parameters": [
        {
          "name": "userId",
          "in": "path",
          "required": true,
          "description": "Unique identifier of a user.",
          "schema": {
            "type": "string",
            "format": "uuid",
            "example": "223e4567-e89b-12d3-a456-426614174111"
          }
        }
      ],
      "get": {
        "summary": "Get all letters for a user",
        "description": "Returns all letters belonging to the specified user across all cases.",
        "tags": [
          "Letters"
        ],
        "responses": {
          "200": {
            "description": "List of letters for the user.",
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/LetterResource"
                  }
                }
              }
            }
          },
          "401": { "$ref": "#/components/responses/Unauthorized" },
          "403": { "$ref": "#/components/responses/Forbidden" },
          "404": { "$ref": "#/components/responses/NotFound" },
          "500": { "$ref": "#/components/responses/InternalServerError" }
        }
      }
    },
    "/letters/{userId}/{caseReferenceNumber}": {
      "parameters": [
        {
          "name": "userId",
          "in": "path",
          "required": true,
          "description": "Unique identifier of the user.",
          "schema": {
            "type": "string",
            "format": "uuid",
            "example": "223e4567-e89b-12d3-a456-426614174111"
          }
        },
        {
          "name": "caseReferenceNumber",
          "in": "path",
          "required": true,
          "description": "Case reference number.",
          "schema": {
            "type": "string",
            "example": "25-70123"
          }
        }
      ],
      "get": {
        "summary": "Get all letters for a case",
        "description": "Returns all letters for a specific case belonging to a specific user.",
        "tags": [
          "Letters"
        ],
        "responses": {
          "200": {
            "description": "List of letters for the case.",
            "content": {
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/LetterResource"
                  }
                }
              }
            }
          },
          "401": { "$ref": "#/components/responses/Unauthorized" },
          "403": { "$ref": "#/components/responses/Forbidden" },
          "404": { "$ref": "#/components/responses/NotFound" },
          "500": { "$ref": "#/components/responses/InternalServerError" }
        }
      }
    },
    "/letters/{userId}/{caseReferenceNumber}/{letterId}": {
      "parameters": [
        {
          "name": "userId",
          "in": "path",
          "required": true,
          "description": "Unique identifier of the user.",
          "schema": {
            "type": "string",
            "format": "uuid",
            "example": "223e4567-e89b-12d3-a456-426614174111"
          }
        },
        {
          "name": "caseReferenceNumber",
          "in": "path",
          "required": true,
          "description": "Case reference number.",
          "schema": {
            "type": "string",
            "example": "25-700123"
          }
        },
        {
          "name": "letterId",
          "in": "path",
          "required": true,
          "description": "Unique identifier of the letter.",
          "schema": {
            "type": "string",
            "format": "uuid",
            "example": "123e4567-e89b-12d3-a456-426614174000"
          }
        },
        {
          "name": "format",
          "in": "query",
          "required": false,
          "description": "Response format",
          "schema": {
            "type": "string",
            "enum": [
              "json",
              "template",
              "pdf"
            ],
            "default": "json"
          }
        }
      ],
      "get": {
        "summary": "Get a specific letter",
        "description": "Returns the details of a specific letter for a given user and case. Available as raw json, an interpolated template or a PDF stream.",
        "tags": [
          "Letters"
        ],
        "responses": {
          "200": {
            "description": "Details of the requested letter.",
            "content": {
              "application/json": {
                "schema": {
                  "oneOf": [
                    { "$ref": "#/components/schemas/LetterResource" },
                    { "$ref": "#/components/schemas/TemplateResource" }
                  ]
                }
              },
              "application/pdf": {
                "schema": {
                  "type": "string",
                  "format": "binary"
                }
              }
            }
          },
          "400": { "$ref": "#/components/responses/BadRequest" },
          "401": { "$ref": "#/components/responses/Unauthorized" },
          "403": { "$ref": "#/components/responses/Forbidden" },
          "404": { "$ref": "#/components/responses/NotFound" },
          "500": { "$ref": "#/components/responses/InternalServerError" }
        }
      }
    }
  },
  "components": {
    "securitySchemes": {
      "bearerAuth": {
        "type": "http",
        "scheme": "bearer",
        "bearerFormat": "JWT"
      }
    },
    "schemas": {
      "LetterData": {
        "type": "object",
        "description": "Dynamic key-value pairs used to populate the letter template. Required fields will vary depending on letterType.",
        "additionalProperties": {
          "type": "string",
          "example": "Some value"
        },
        "example": {
          "recipientName": "Mr Test Testcase",
          "caseReference": "25-700123",
          "decisionDate": "2024-01-15"
        }
      },
      "LetterResource": {
        "type": "object",
        "description": "Represents a stored letter and its associated metadata.",
        "properties": {
          "userId": {
            "type": "string",
            "format": "uuid",
            "description": "Unique identifier of the user who owns the letter.",
            "example": "223e4567-e89b-12d3-a456-426614174111"
          },
          "caseReferenceNumber": {
            "type": "string",
            "description": "Reference number of the case to which the letter belongs.",
            "example": "25-700123"
          },
          "letterId": {
            "type": "string",
            "format": "uuid",
            "description": "Unique identifier of the letter.",
            "example": "123e4567-e89b-12d3-a456-426614174000"
          },
          "letterType": {
            "type": "string",
            "description": "Code that identifies which letter template was used.",
            "example": "AA01"
          },
          "letterData": {
            "$ref": "#/components/schemas/LetterData"
          }
        },
        "required": [
          "userId",
          "caseReferenceNumber",
          "letterId",
          "letterType",
          "letterData"
        ]
      },
      "TemplateResource": {
        "description": "Represents a stored letter, its associated metadata and the interpolated template instance",
        "allOf": [
          { "$ref": "#/components/schemas/LetterResource" },
          {
            "type": "object",
            "properties": {
              "templateInstance": {
                "type": "object",
                "description": "Interpolated/derived values produced by applying the template.",
                "additionalProperties": true
              }
            },
            "required": ["templateInstance"]
          }
        ]
      },
      "ErrorObject": {
        "type": "object",
        "properties": {
          "status": { "type": "integer", "example": 401 },
          "title": { "type": "string", "example": "401 Unauthorized" },
          "detail": { "type": "string", "example": "No authorization token was found" }
        },
        "required": ["status", "title", "detail"],
        "additionalProperties": false
      },
      "ErrorResponse": {
        "type": "object",
        "properties": {
          "errors": {
            "type": "array",
            "items": { "$ref": "#/components/schemas/ErrorObject" }
          }
        },
        "required": ["errors"],
        "additionalProperties": false
      }
    },
    "responses": {
      "BadRequest": {
        "description": "There is an issue with the request",
        "content": {
          "application/vnd.api+json": {
            "schema": {
              "$ref": "#/components/schemas/ErrorResponse"
            }
          }
        }
      },
      "Unauthorized": {
        "description": "Access token is missing or invalid",
        "content": {
          "application/vnd.api+json": {
            "schema": {
              "$ref": "#/components/schemas/ErrorResponse"
            }
          }
        }
      },
      "Forbidden": {
        "description": "The JWT doesn't permit access to this endpoint",
        "content": {
          "application/vnd.api+json": {
            "schema": {
              "$ref": "#/components/schemas/ErrorResponse"
            }
          }
        }
      },
      "NotFound": {
        "description": "The specified resource was not found",
        "content": {
          "application/vnd.api+json": {
            "schema": {
              "$ref": "#/components/schemas/ErrorResponse"
            }
          }
        }
      },
      "InternalServerError": {
        "description": "Unexpected server error.",
        "content": {
          "application/json": {
            "schema": { "$ref": "#/components/schemas/ErrorResponse" }
          }
        }
      }
    }
  }
}