/// This interface defines all of the types and methods for implementing
/// HTTP Requests and Responses, both incoming and outgoing, as well as
/// their headers, trailers, and bodies.
interface types {
  use wasi:clocks/monotonic-clock@0.2.0.{duration};
  use wasi:io/streams@0.2.0.{input-stream, output-stream};
  use wasi:io/error@0.2.0.{error as io-error};
  use wasi:io/poll@0.2.0.{pollable};

  /// This type corresponds to HTTP standard Methods.
  variant method {
    get,
    head,
    post,
    put,
    delete,
    connect,
    options,
    trace,
    patch,
    other(string)
  }

  /// This type corresponds to HTTP standard Related Schemes.
  variant scheme {
    HTTP,
    HTTPS,
    other(string)
  }

  /// These cases are inspired by the IANA HTTP Proxy Error Types:
  ///   https://www.iana.org/assignments/http-proxy-status/http-proxy-status.xhtml#table-http-proxy-error-types
  variant error-code {
    DNS-timeout,
    DNS-error(DNS-error-payload),
    destination-not-found,
    destination-unavailable,
    destination-IP-prohibited,
    destination-IP-unroutable,
    connection-refused,
    connection-terminated,
    connection-timeout,
    connection-read-timeout,
    connection-write-timeout,
    connection-limit-reached,
    TLS-protocol-error,
    TLS-certificate-error,
    TLS-alert-received(TLS-alert-received-payload),
    HTTP-request-denied,
    HTTP-request-length-required,
    HTTP-request-body-size(option<u64>),
    HTTP-request-method-invalid,
    HTTP-request-URI-invalid,
    HTTP-request-URI-too-long,
    HTTP-request-header-section-size(option<u32>),
    HTTP-request-header-size(option<field-size-payload>),
    HTTP-request-trailer-section-size(option<u32>),
    HTTP-request-trailer-size(field-size-payload),
    HTTP-response-incomplete,
    HTTP-response-header-section-size(option<u32>),
    HTTP-response-header-size(field-size-payload),
    HTTP-response-body-size(option<u64>),
    HTTP-response-trailer-section-size(option<u32>),
    HTTP-response-trailer-size(field-size-payload),
    HTTP-response-transfer-coding(option<string>),
    HTTP-response-content-coding(option<string>),
    HTTP-response-timeout,
    HTTP-upgrade-failed,
    HTTP-protocol-error,
    loop-detected,
    configuration-error,
    /// This is a catch-all error for anything that doesn't fit cleanly into a
    /// more specific case. It also includes an optional string for an
    /// unstructured description of the error. Users should not depend on the
    /// string for diagnosing errors, as it's not required to be consistent
    /// between implementations.
    internal-error(option<string>)
  }

  /// Defines the case payload type for `DNS-error` above:
  record DNS-error-payload {
    rcode: option<string>,
    info-code: option<u16>
  }

  /// Defines the case payload type for `TLS-alert-received` above:
  record TLS-alert-received-payload {
    alert-id: option<u8>,
    alert-message: option<string>
  }

  /// Defines the case payload type for `HTTP-response-{header,trailer}-size` above:
  record field-size-payload {
    field-name: option<string>,
    field-size: option<u32>
  }

  /// Attempts to extract a http-related `error` from the wasi:io `error`
  /// provided.
  ///
  /// Stream operations which return
  /// `wasi:io/stream/stream-error::last-operation-failed` have a payload of
  /// type `wasi:io/error/error` with more information about the operation
  /// that failed. This payload can be passed through to this function to see
  /// if there's http-related information about the error to return.
  ///
  /// Note that this function is fallible because not all io-errors are
  /// http-related errors.
  http-error-code: func(err: borrow<io-error>) -> option<error-code>;

  /// This type enumerates the different kinds of errors that may occur when
  /// setting or appending to a `fields` resource.
  variant header-error {
    /// This error indicates that a `field-key` or `field-value` was
    /// syntactically invalid when used with an operation that sets headers in a
    /// `fields`.
    invalid-syntax,

    /// This error indicates that a forbidden `field-key` was used when trying
    /// to set a header in a `fields`.
    forbidden,

    /// This error indicates that the operation on the `fields` was not
    /// permitted because the fields are immutable.
    immutable,
  }

  /// Field keys are always strings.
  type field-key = string;

  /// Field values should always be ASCII strings. However, in
  /// reality, HTTP implementations often have to interpret malformed values,
  /// so they are provided as a list of bytes.
  type field-value = list<u8>;

  /// This following block defines the `fields` resource which corresponds to
  /// HTTP standard Fields. Fields are a common representation used for both
  /// Headers and Trailers.
  ///
  /// A `fields` may be mutable or immutable. A `fields` created using the
  /// constructor, `from-list`, or `clone` will be mutable, but a `fields`
  /// resource given by other means (including, but not limited to,
  /// `incoming-request.headers`, `outgoing-request.headers`) might be be
  /// immutable. In an immutable fields, the `set`, `append`, and `delete`
  /// operations will fail with `header-error.immutable`.
  resource fields {

    /// Construct an empty HTTP Fields.
    ///
    /// The resulting `fields` is mutable.
    constructor();

    /// Construct an HTTP Fields.
    ///
    /// The resulting `fields` is mutable.
    ///
    /// The list represents each key-value pair in the Fields. Keys
    /// which have multiple values are represented by multiple entries in this
    /// list with the same key.
    ///
    /// The tuple is a pair of the field key, represented as a string, and
    /// Value, represented as a list of bytes. In a valid Fields, all keys
    /// and values are valid UTF-8 strings. However, values are not always
    /// well-formed, so they are represented as a raw list of bytes.
    ///
    /// An error result will be returned if any header or value was
    /// syntactically invalid, or if a header was forbidden.
    from-list: static func(
      entries: list<tuple<field-key,field-value>>
    ) -> result<fields, header-error>;

    /// Get all of the values corresponding to a key. If the key is not present
    /// in this `fields`, an empty list is returned. However, if the key is
    /// present but empty, this is represented by a list with one or more
    /// empty field-values present.
    get: func(name: field-key) -> list<field-value>;

    /// Returns `true` when the key is present in this `fields`. If the key is
    /// syntactically invalid, `false` is returned.
    has: func(name: field-key) -> bool;

    /// Set all of the values for a key. Clears any existing values for that
    /// key, if they have been set.
    ///
    /// Fails with `header-error.immutable` if the `fields` are immutable.
    set: func(name: field-key, value: list<field-value>) -> result<_, header-error>;

    /// Delete all values for a key. Does nothing if no values for the key
    /// exist.
    ///
    /// Fails with `header-error.immutable` if the `fields` are immutable.
    delete: func(name: field-key) -> result<_, header-error>;

    /// Append a value for a key. Does not change or delete any existing
    /// values for that key.
    ///
    /// Fails with `header-error.immutable` if the `fields` are immutable.
    append: func(name: field-key, value: field-value) -> result<_, header-error>;

    /// Retrieve the full set of keys and values in the Fields. Like the
    /// constructor, the list represents each key-value pair.
    ///
    /// The outer list represents each key-value pair in the Fields. Keys
    /// which have multiple values are represented by multiple entries in this
    /// list with the same key.
    entries: func() -> list<tuple<field-key,field-value>>;

    /// Make a deep copy of the Fields. Equivelant in behavior to calling the
    /// `fields` constructor on the return value of `entries`. The resulting
    /// `fields` is mutable.
    clone: func() -> fields;
  }

  /// Headers is an alias for Fields.
  type headers = fields;

  /// Trailers is an alias for Fields.
  type trailers = fields;

  /// Represents an incoming HTTP Request.
  resource incoming-request {

    /// Returns the method of the incoming request.
    method: func() -> method;

    /// Returns the path with query parameters from the request, as a string.
    path-with-query: func() -> option<string>;

    /// Returns the protocol scheme from the request.
    scheme: func() -> option<scheme>;

    /// Returns the authority from the request, if it was present.
    authority: func() -> option<string>;

    /// Get the `headers` associated with the request.
    ///
    /// The returned `headers` resource is immutable: `set`, `append`, and
    /// `delete` operations will fail with `header-error.immutable`.
    ///
    /// The `headers` returned are a child resource: it must be dropped before
    /// the parent `incoming-request` is dropped. Dropping this
    /// `incoming-request` before all children are dropped will trap.
    headers: func() -> headers;

    /// Gives the `incoming-body` associated with this request. Will only
    /// return success at most once, and subsequent calls will return error.
    consume: func() -> result<incoming-body>;
  }

  /// Represents an outgoing HTTP Request.
  resource outgoing-request {

    /// Construct a new `outgoing-request` with a default `method` of `GET`, and
    /// `none` values for `path-with-query`, `scheme`, and `authority`.
    ///
    /// * `headers` is the HTTP Headers for the Request.
    ///
    /// It is possible to construct, or manipulate with the accessor functions
    /// below, an `outgoing-request` with an invalid combination of `scheme`
    /// and `authority`, or `headers` which are not permitted to be sent.
    /// It is the obligation of the `outgoing-handler.handle` implementation
    /// to reject invalid constructions of `outgoing-request`.
    constructor(
      headers: headers
    );

    /// Returns the resource corresponding to the outgoing Body for this
    /// Request.
    ///
    /// Returns success on the first call: the `outgoing-body` resource for
    /// this `outgoing-request` can be retrieved at most once. Subsequent
    /// calls will return error.
    body: func() -> result<outgoing-body>;

    /// Get the Method for the Request.
    method: func() -> method;
    /// Set the Method for the Request. Fails if the string present in a
    /// `method.other` argument is not a syntactically valid method.
    set-method: func(method: method) -> result;

    /// Get the combination of the HTTP Path and Query for the Request.
    /// When `none`, this represents an empty Path and empty Query.
    path-with-query: func() -> option<string>;
    /// Set the combination of the HTTP Path and Query for the Request.
    /// When `none`, this represents an empty Path and empty Query. Fails is the
    /// string given is not a syntactically valid path and query uri component.
    set-path-with-query: func(path-with-query: option<string>) -> result;

    /// Get the HTTP Related Scheme for the Request. When `none`, the
    /// implementation may choose an appropriate default scheme.
    scheme: func() -> option<scheme>;
    /// Set the HTTP Related Scheme for the Request. When `none`, the
    /// implementation may choose an appropriate default scheme. Fails if the
    /// string given is not a syntactically valid uri scheme.
    set-scheme: func(scheme: option<scheme>) -> result;

    /// Get the HTTP Authority for the Request. A value of `none` may be used
    /// with Related Schemes which do not require an Authority. The HTTP and
    /// HTTPS schemes always require an authority.
    authority: func() -> option<string>;
    /// Set the HTTP Authority for the Request. A value of `none` may be used
    /// with Related Schemes which do not require an Authority. The HTTP and
    /// HTTPS schemes always require an authority. Fails if the string given is
    /// not a syntactically valid uri authority.
    set-authority: func(authority: option<string>) -> result;

    /// Get the headers associated with the Request.
    ///
    /// The returned `headers` resource is immutable: `set`, `append`, and
    /// `delete` operations will fail with `header-error.immutable`.
    ///
    /// This headers resource is a child: it must be dropped before the parent
    /// `outgoing-request` is dropped, or its ownership is transfered to
    /// another component by e.g. `outgoing-handler.handle`.
    headers: func() -> headers;
  }

  /// Parameters for making an HTTP Request. Each of these parameters is
  /// currently an optional timeout applicable to the transport layer of the
  /// HTTP protocol.
  ///
  /// These timeouts are separate from any the user may use to bound a
  /// blocking call to `wasi:io/poll.poll`.
  resource request-options {
    /// Construct a default `request-options` value.
    constructor();

    /// The timeout for the initial connect to the HTTP Server.
    connect-timeout: func() -> option<duration>;

    /// Set the timeout for the initial connect to the HTTP Server. An error
    /// return value indicates that this timeout is not supported.
    set-connect-timeout: func(duration: option<duration>) -> result;

    /// The timeout for receiving the first byte of the Response body.
    first-byte-timeout: func() -> option<duration>;

    /// Set the timeout for receiving the first byte of the Response body. An
    /// error return value indicates that this timeout is not supported.
    set-first-byte-timeout: func(duration: option<duration>) -> result;

    /// The timeout for receiving subsequent chunks of bytes in the Response
    /// body stream.
    between-bytes-timeout: func() -> option<duration>;

    /// Set the timeout for receiving subsequent chunks of bytes in the Response
    /// body stream. An error return value indicates that this timeout is not
    /// supported.
    set-between-bytes-timeout: func(duration: option<duration>) -> result;
  }

  /// Represents the ability to send an HTTP Response.
  ///
  /// This resource is used by the `wasi:http/incoming-handler` interface to
  /// allow a Response to be sent corresponding to the Request provided as the
  /// other argument to `incoming-handler.handle`.
  resource response-outparam {

    /// Set the value of the `response-outparam` to either send a response,
    /// or indicate an error.
    ///
    /// This method consumes the `response-outparam` to ensure that it is
    /// called at most once. If it is never called, the implementation
    /// will respond with an error.
    ///
    /// The user may provide an `error` to `response` to allow the
    /// implementation determine how to respond with an HTTP error response.
    set: static func(
      param: response-outparam,
      response: result<outgoing-response, error-code>,
    );
  }

  /// This type corresponds to the HTTP standard Status Code.
  type status-code = u16;

  /// Represents an incoming HTTP Response.
  resource incoming-response {

    /// Returns the status code from the incoming response.
    status: func() -> status-code;

    /// Returns the headers from the incoming response.
    ///
    /// The returned `headers` resource is immutable: `set`, `append`, and
    /// `delete` operations will fail with `header-error.immutable`.
    ///
    /// This headers resource is a child: it must be dropped before the parent
    /// `incoming-response` is dropped.
    headers: func() -> headers;

    /// Returns the incoming body. May be called at most once. Returns error
    /// if called additional times.
    consume: func() -> result<incoming-body>;
  }

  /// Represents an incoming HTTP Request or Response's Body.
  ///
  /// A body has both its contents - a stream of bytes - and a (possibly
  /// empty) set of trailers, indicating that the full contents of the
  /// body have been received. This resource represents the contents as
  /// an `input-stream` and the delivery of trailers as a `future-trailers`,
  /// and ensures that the user of this interface may only be consuming either
  /// the body contents or waiting on trailers at any given time.
  resource incoming-body {

    /// Returns the contents of the body, as a stream of bytes.
    ///
    /// Returns success on first call: the stream representing the contents
    /// can be retrieved at most once. Subsequent calls will return error.
    ///
    /// The returned `input-stream` resource is a child: it must be dropped
    /// before the parent `incoming-body` is dropped, or consumed by
    /// `incoming-body.finish`.
    ///
    /// This invariant ensures that the implementation can determine whether
    /// the user is consuming the contents of the body, waiting on the
    /// `future-trailers` to be ready, or neither. This allows for network
    /// backpressure is to be applied when the user is consuming the body,
    /// and for that backpressure to not inhibit delivery of the trailers if
    /// the user does not read the entire body.
    %stream: func() -> result<input-stream>;

    /// Takes ownership of `incoming-body`, and returns a `future-trailers`.
    /// This function will trap if the `input-stream` child is still alive.
    finish: static func(this: incoming-body) -> future-trailers;
  }

  /// Represents a future which may eventaully return trailers, or an error.
  ///
  /// In the case that the incoming HTTP Request or Response did not have any
  /// trailers, this future will resolve to the empty set of trailers once the
  /// complete Request or Response body has been received.
  resource future-trailers {

    /// Returns a pollable which becomes ready when either the trailers have
    /// been received, or an error has occured. When this pollable is ready,
    /// the `get` method will return `some`.
    subscribe: func() -> pollable;

    /// Returns the contents of the trailers, or an error which occured,
    /// once the future is ready.
    ///
    /// The outer `option` represents future readiness. Users can wait on this
    /// `option` to become `some` using the `subscribe` method.
    ///
    /// The outer `result` is used to retrieve the trailers or error at most
    /// once. It will be success on the first call in which the outer option
    /// is `some`, and error on subsequent calls.
    ///
    /// The inner `result` represents that either the HTTP Request or Response
    /// body, as well as any trailers, were received successfully, or that an
    /// error occured receiving them. The optional `trailers` indicates whether
    /// or not trailers were present in the body.
    ///
    /// When some `trailers` are returned by this method, the `trailers`
    /// resource is immutable, and a child. Use of the `set`, `append`, or
    /// `delete` methods will return an error, and the resource must be
    /// dropped before the parent `future-trailers` is dropped.
    get: func() -> option<result<result<option<trailers>, error-code>>>;
  }

  /// Represents an outgoing HTTP Response.
  resource outgoing-response {

    /// Construct an `outgoing-response`, with a default `status-code` of `200`.
    /// If a different `status-code` is needed, it must be set via the
    /// `set-status-code` method.
    ///
    /// * `headers` is the HTTP Headers for the Response.
    constructor(headers: headers);

    /// Get the HTTP Status Code for the Response.
    status-code: func() -> status-code;

    /// Set the HTTP Status Code for the Response. Fails if the status-code
    /// given is not a valid http status code.
    set-status-code: func(status-code: status-code) -> result;

    /// Get the headers associated with the Request.
    ///
    /// The returned `headers` resource is immutable: `set`, `append`, and
    /// `delete` operations will fail with `header-error.immutable`.
    ///
    /// This headers resource is a child: it must be dropped before the parent
    /// `outgoing-request` is dropped, or its ownership is transfered to
    /// another component by e.g. `outgoing-handler.handle`.
    headers: func() -> headers;

    /// Returns the resource corresponding to the outgoing Body for this Response.
    ///
    /// Returns success on the first call: the `outgoing-body` resource for
    /// this `outgoing-response` can be retrieved at most once. Subsequent
    /// calls will return error.
    body: func() -> result<outgoing-body>;
  }

  /// Represents an outgoing HTTP Request or Response's Body.
  ///
  /// A body has both its contents - a stream of bytes - and a (possibly
  /// empty) set of trailers, inducating the full contents of the body
  /// have been sent. This resource represents the contents as an
  /// `output-stream` child resource, and the completion of the body (with
  /// optional trailers) with a static function that consumes the
  /// `outgoing-body` resource, and ensures that the user of this interface
  /// may not write to the body contents after the body has been finished.
  ///
  /// If the user code drops this resource, as opposed to calling the static
  /// method `finish`, the implementation should treat the body as incomplete,
  /// and that an error has occured. The implementation should propogate this
  /// error to the HTTP protocol by whatever means it has available,
  /// including: corrupting the body on the wire, aborting the associated
  /// Request, or sending a late status code for the Response.
  resource outgoing-body {

    /// Returns a stream for writing the body contents.
    ///
    /// The returned `output-stream` is a child resource: it must be dropped
    /// before the parent `outgoing-body` resource is dropped (or finished),
    /// otherwise the `outgoing-body` drop or `finish` will trap.
    ///
    /// Returns success on the first call: the `output-stream` resource for
    /// this `outgoing-body` may be retrieved at most once. Subsequent calls
    /// will return error.
    write: func() -> result<output-stream>;

    /// Finalize an outgoing body, optionally providing trailers. This must be
    /// called to signal that the response is complete. If the `outgoing-body`
    /// is dropped without calling `outgoing-body.finalize`, the implementation
    /// should treat the body as corrupted.
    ///
    /// Fails if the body's `outgoing-request` or `outgoing-response` was
    /// constructed with a Content-Length header, and the contents written
    /// to the body (via `write`) does not match the value given in the
    /// Content-Length.
    finish: static func(
      this: outgoing-body,
      trailers: option<trailers>
    ) -> result<_, error-code>;
  }

  /// Represents a future which may eventaully return an incoming HTTP
  /// Response, or an error.
  ///
  /// This resource is returned by the `wasi:http/outgoing-handler` interface to
  /// provide the HTTP Response corresponding to the sent Request.
  resource future-incoming-response {
    /// Returns a pollable which becomes ready when either the Response has
    /// been received, or an error has occured. When this pollable is ready,
    /// the `get` method will return `some`.
    subscribe: func() -> pollable;

    /// Returns the incoming HTTP Response, or an error, once one is ready.
    ///
    /// The outer `option` represents future readiness. Users can wait on this
    /// `option` to become `some` using the `subscribe` method.
    ///
    /// The outer `result` is used to retrieve the response or error at most
    /// once. It will be success on the first call in which the outer option
    /// is `some`, and error on subsequent calls.
    ///
    /// The inner `result` represents that either the incoming HTTP Response
    /// status and headers have recieved successfully, or that an error
    /// occured. Errors may also occur while consuming the response body,
    /// but those will be reported by the `incoming-body` and its
    /// `output-stream` child.
    get: func() -> option<result<result<incoming-response, error-code>>>;

  }
}