// Copyright 2019 Google Inc. Use of this source code is governed by an
// MIT-style license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT.

syntax = "proto3";

package sass.embedded_protocol;

// The wrapper type for all messages sent from the host to the compiler. This
// provides a `oneof` that makes it possible to determine the type of each
// inbound message.
message InboundMessage {
  // A request that compiles an entrypoint to CSS.
  message CompileRequest {
    // This compilation's request id. This is included in messages sent from the
    // compiler to the host. Mandatory.
    uint32 id = 1;

    // An input stylesheet provided as plain text, rather than loaded from the
    // filesystem.
    message StringInput {
      // The contents of the stylesheet.
      string source = 1;

      // The location from which `source` was loaded. If this is empty, it
      // indicates that the URL is unknown.
      //
      // This must be a URL recognized by `importer`, if it's passed.
      string url = 2;

      // The syntax to use to parse `source`.
      Syntax syntax = 3;

      // The importer to use to resolve imports relative to `url`.
      Importer importer = 4;
    }

    // The input stylesheet to parse. Mandatory.
    oneof input {
      // A stylesheet loaded from its contents.
      StringInput string = 2;

      // A stylesheet loaded from the given path on the filesystem.
      string path = 3;
    }

    // Possible ways to format the CSS output. The compiler is not required to
    // support all possible options; if the host requests an unsupported style,
    // the compiler should choose the closest supported style.
    enum OutputStyle {
      // Each selector and declaration is written on its own line.
      EXPANDED = 0;

      // The entire stylesheet is written on a single line, with as few
      // characters as possible.
      COMPRESSED = 1;

      // CSS rules and declarations are indented to match the nesting of the
      // Sass source.
      NESTED = 2;

      // Each CSS rule is written on its own single line, along with all its
      // declarations.
      COMPACT = 3;
    }

    // How to format the CSS output.
    OutputStyle style = 4;

    // Whether to generate a source map. Note that this will *not* add a source
    // map comment to the stylesheet; that's up to the host or its users.
    bool source_map = 5;

    // A wrapper message that represents either a user-defined importer or a
    // load path on disk. This must be a wrapper because `oneof` types can't be
    // `repeated`.
    message Importer {
      // The possible types of importer. Mandatory.
      oneof importer {
        // A built-in importer that loads Sass files within the given directory
        // on disk.
        string path = 1;

        // A unique ID for a user-defined importer. This ID will be included in
        // outbound `CanonicalizeRequest` and `ImportRequest` messages to
        // indicate which importer is being called. The host is responsible for
        // generating this ID and ensuring that it's unique across all
        // importers registered for this compilation.
        uint32 importer_id = 2;

        // A unique ID for a special kind of user-defined importer that tells
        // the compiler where to look for files on the physical filesystem, but
        // leaves the details of resolving partials and extensions and loading
        // the file from disk up to the compiler itself.
        //
        // This ID will be included in outbound `FileImportRequest` messages to
        // indicate which importer is being called. The host is responsible for
        // generating this ID and ensuring that it's unique across all importers
        // registered for this compilation.
        uint32 file_importer_id = 3;
      }
    }

    // Importers (including load paths on the filesystem) to use when resolving
    // imports that can't be resolved relative to the file that contains it. Each
    // importer is checked in order until one recognizes the imported URL.
    repeated Importer importers = 6;

    // Signatures for custom global functions whose behavior is defined by the
    // host. These must be valid Sass function signatures that could appear in
    // after `@function` in a Sass stylesheet, such as
    // `mix($color1, $color2, $weight: 50%)`.
    //
    // Compilers must ensure that pure-Sass functions take precedence over
    // custom global functions. They must also reject any custom function names
    // that conflict with function names built into the Sass language.
    repeated string global_functions = 7;
  }

  // A response indicating the result of canonicalizing an imported URL.
  message CanonicalizeResponse {
    uint32 id = 1;

    // The result of canonicalization. Optional. If this is `null`, it indicates
    // that the importer either did not recognize the URL, or could not find a
    // stylesheet at the location it referred to.
    oneof result {
      // The successfully canonicalized URL. This must be an absolute URL,
      // including scheme.
      string url = 2;

      // An error message explaining why canonicalization failed.
      //
      // This indicates that a stylesheet was found, but a canonical URL for it
      // could not be determined. If no stylesheet was found, `result` should be
      // `null` instead.
      string error = 3;
    }
  }

  // A response indicating the result of importing a canonical URL.
  message ImportResponse {
    uint32 id = 1;

    // The stylesheet's contents were loaded successfully.
    message ImportSuccess {
      // The text of the stylesheet. Mandatory.
      string contents = 1;

      // The syntax of `contents`. Mandatory.
      Syntax syntax = 2;

      // An absolute, browser-accessible URL indicating the resolved location of
      // the imported stylesheet. Optional.
      //
      // This should be a `file:` URL if one is available, but an `http:` URL is
      // acceptable as well. If no URL is supplied, a `data:` URL is generated
      // automatically from `contents`.
      //
      // If this is provided, it must be an absolute URL, including scheme.
      string sourceMapUrl = 3;
    }

    // The result of loading the URL. Mandatory.
    oneof result {
      // The contents of the loaded stylesheet.
      ImportSuccess success = 2;

      // An error message explaining why the URL could not be loaded.
      string error = 3;
    }
  }

  // A response indicating the result of redirecting a URL to the filesystem.
  message FileImportResponse {
    uint32 id = 1;

    // The result of loading the URL. Mandatory.
    oneof result {
      // The absolute `file:` URL to look for the file on the physical
      // filesystem.
      //
      // The host must ensure that this URL follows the format for an absolute
      // `file:` URL on the current operating system without a hostname, and the
      // compiler must verify this to the best of its ability. See
      // https://en.wikipedia.org/wiki/File_URI_scheme for details on the
      // format.
      //
      // The compiler must handle turning this into a canonical URL by resolving
      // it for partials, file extensions, and index files. The compiler must
      // then loading the contents of the resulting canonical URL from the
      // filesystem.
      string file_url = 2;

      // An error message explaining why the URL could not be loaded.
      string error = 3;
    }
  }

  // A response indicating the result of calling a custom Sass function defined
  // in the host.
  message FunctionCallResponse {
    uint32 id = 1;

    // The result of calling the function. Mandatory.
    oneof result {
      // The return value of a successful function call.
      Value success = 2;

      // An error message explaining why the function call failed.
      string error = 3;
    }
  }

  // Possible syntaxes for a Sass stylesheet.
  enum Syntax {
    // The CSS-superset `.scss` syntax.
    SCSS = 0;

    // The indented `.sass` syntax.
    INDENTED = 1;

    // Plain CSS syntax that doesn't support any special Sass features.
    CSS = 2;
  }

  // The wrapped message. Mandatory.
  oneof message {
    CompileRequest compileRequest = 2;
    CanonicalizeResponse canonicalizeResponse = 3;
    ImportResponse importResponse = 4;
    FileImportResponse fileImportResponse = 5;
    FunctionCallResponse functionCallResponse = 6;
  }
}

// The wrapper type for all messages sent from the compiler to the host. This
// provides a `oneof` that makes it possible to determine the type of each
// outbound message.
message OutboundMessage {
  // A response that contains the result of a compilation.
  message CompileResponse {
    // The compilation's request id. Mandatory.
    int32 id = 1;

    // A message indicating that the Sass file was successfully compiled to CSS.
    message CompileSuccess {
      // The compiled CSS.
      string css = 1;

      // The JSON-encoded source map, or the empty string if
      // `CompileRequest.source_map` was `false`.
      //
      // The compiler must not add a `"file"` key to this source map. It's the
      // host's (or the host's user's) responsibility to determine how the
      // generated CSS can be reached from the source map.
      string source_map = 2;
    }

    // A message indicating that the Sass file could not be successfully
    // compiled to CSS.
    message CompileFailure {
      // A message describing the reason for the failure.
      string message = 1;

      // The span associated with the failure. Optional.
      SourceSpan span = 2;

      // The stack trace associated with the failure.
      //
      // The empty string indicates that no stack trace is available. Otherwise,
      // the format of this stack trace is not specified and is likely to be
      // inconsistent between implementations.
      string stack_trace = 3;
    }

    // The success or failure result of the compilation. Mandatory.
    oneof result {
      // The result of a successful compilation.
      CompileSuccess success = 2;

      // The result of a failed compilation.
      CompileFailure failure = 3;
    }
  }

  // An event indicating that a message should be displayed to the user.
  message LogEvent {
    // The request id for the compilation that triggered the message. Mandatory.
    uint32 compilation_id = 1;

    // The type of message.
    enum Type {
      // A warning for something other than a deprecated Sass feature. Often
      // emitted due to a stylesheet using the `@warn` rule.
      WARNING = 0;

      // A warning indicating that the stylesheet is using a deprecated Sass
      // feature. Compilers should not add text like "deprecation warning" to
      // deprecation warnings; it's up to the host to determine how to signal
      // that to the user.
      DEPRECATION_WARNING = 1;

      // A message generated by the user for their own debugging purposes.
      DEBUG = 2;
    }
    Type type = 2;

    // The text of the message.
    string message = 3;

    // The span associated with this message. Optional.
    SourceSpan span = 4;

    // The stack trace associated with this message.
    //
    // The empty string indicates that no stack trace is available. Otherwise,
    // the format of this stack trace is not specified and is likely to be
    // inconsistent between implementations.
    string stack_trace = 5;
  }

  // A request for a custom importer to convert an imported URL to its canonical
  // format.
  //
  // If the URL is not recognized by this importer, or if no stylesheet is found
  // at that URL, `CanonicalizeResponse.result` must be `null`.
  //
  // Canonical URLs must be absolute, including a scheme. If the import is
  // referring to a Sass file on disk, the importer is encouraged to respond
  // with a `CanonicalizeResponse.result.file`, in which case the host will
  // handle the logic of resolving partials, file extensions, and index files.
  //
  // If Sass has already loaded a stylesheet with the returned canonical URL, it
  // re-uses the existing parse tree. This means that importers must ensure that
  // the same canonical URL always refers to the same stylesheet, *even across
  // different importers*. Importers must also ensure that any canonicalized
  // URLs they return can be passed back to `CanonicalizeRequest` and will be
  // returned unchanged.
  //
  // If this importer's URL format supports file extensions, it should
  // canonicalize them the same way as the default filesystem importer:
  //
  // * The importer should look for stylesheets by adding the prefix `_` to the
  //   URL's basename, and by adding the extensions `.sass` and `.scss` if the
  //   URL doesn't already have one of those extensions. For example, if the URL
  //   was `foo/bar/baz`, the importer would look for:
  //
  //   * `foo/bar/baz.sass`
  //   * `foo/bar/baz.scss`
  //   * `foo/bar/_baz.sass`
  //   * `foo/bar/_baz.scss`
  //
  //   If the URL was foo/bar/baz.scss, the importer would just look for:
  //
  //   * `foo/bar/baz.scss`
  //   * `foo/bar/_baz.scss`
  //
  //   If the importer finds a stylesheet at more than one of these URLs, it
  //   should respond with a `CanonicalizeResponse.result.error` indicating that
  //   the import is ambiguous. Note that if the extension is explicitly
  //   specified, a stylesheet with another extension may exist without error.
  //
  // * If none of the possible paths is valid, the importer should perform the
  //   same resolution on the URL followed by `/index`. In the example above, it
  //   would look for:
  //
  //   * `foo/bar/baz/_index.sass`
  //   * `foo/bar/baz/index.sass`
  //   * `foo/bar/baz/_index.scss`
  //   * `foo/bar/baz/index.scss`
  //
  //   As above, if the importer finds a stylesheet at more than one of these
  //   URLs, it should respond with a `CanonicalizeResponse.result.error`
  //   indicating that the import is ambiguous.
  message CanonicalizeRequest {
    uint32 id = 1;

    // The request id for the compilation that triggered the message. Mandatory.
    uint32 compilation_id = 2;

    // The unique ID of the importer being invoked. This must match an importer
    // ID passed to this compilation in `CompileRequest.importers` or
    // `CompileRequest.input.string.importer`. Mandatory.
    uint32 importer_id = 3;

    // The URL of the import to be canonicalized. This may be either absolute or
    // relative.
    //
    // When loading a URL, the host must first try resolving that URL relative
    // to the canonical URL of the current file, and canonicalizing the result
    // using the importer that loaded the current file. If this returns `null`,
    // the host must then try canonicalizing the original URL with each importer
    // in order until one returns something other than `null`. That is the
    // result of the import.
    string url = 4;
  }

  // A request for a custom importer to load the contents of a stylesheet.
  message ImportRequest {
    uint32 id = 1;

    // The request id for the compilation that triggered the message. Mandatory.
    uint32 compilation_id = 2;

    // The unique ID of the importer being invoked. This must match an
    // `Importer.importer_id` passed to this compilation in
    // `CompileRequest.importers` or `CompileRequest.input.string.importer`.
    // Mandatory.
    uint32 importer_id = 3;

    // The canonical URL of the import. This is guaranteed to be a URL returned
    // by a `CanonicalizeRequest` to this importer.
    string url = 4;
  }

  // A request for a custom filesystem importer to load the contents of a
  // stylesheet.
  message FileImportRequest {
    uint32 id = 1;

    // The request id for the compilation that triggered the message. Mandatory.
    uint32 compilation_id = 2;

    // The unique ID of the importer being invoked. This must match an
    // `Importer.file_importer_id` passed to this compilation in
    // `CompileRequest.importers` or `CompileRequest.input.string.importer`.
    // Mandatory.
    uint32 importer_id = 3;

    // The canonical URL of the import. This is guaranteed to be a URL returned
    // by a `CanonicalizeRequest` to this importer.
    string url = 4;
  }

  // A request to invoke a custom Sass function and return its result.
  message FunctionCallRequest {
    uint32 id = 1;

    // The request id for the compilation that triggered the message. Mandatory.
    uint32 compilation_id = 2;

    // An identifier that indicates which function to invoke. Mandatory.
    oneof identifier {
      // The name of the function to invoke.
      //
      // This must match the name of a function signature the host passed to the
      // corresponding `CompileRequest.global_functions` call, including hyphens
      // and underscores.
      string name = 3;

      // The opaque ID of the function to invoke.
      //
      // This must match the ID of a `Value.HostFunction` that the host passed
      // to the compiler.
      uint32 function_id = 4;
    }

    // The arguments passed to the function, in the order they appear in the
    // function signature passed to `CompileRequest.global_functions`. Mandatory.
    //
    // The compiler must ensure that a valid number of arguments are passed for
    // the given signature, that default argument values are instantiated
    // appropriately, and that variable argument lists (`$args...`) are passed
    // as `Value.ArgumentList`s.
    repeated Value arguments = 5;
  }

  // The wrapped message. Mandatory.
  oneof message {
    ProtocolError error = 1;
    CompileResponse compileResponse = 2;
    LogEvent logEvent = 3;
    CanonicalizeRequest canonicalizeRequest = 4;
    ImportRequest importRequest = 5;
    FileImportRequest fileImportRequest = 6;
    FunctionCallRequest functionCallRequest = 7;
  }
}

// An error reported when an endpoint violates the embedded Sass protocol.
message ProtocolError {
  // Potential types of errors.
  enum ErrorType {
    // A message was received that couldn't be decoded as an `InboundMessage`
    // (for the compiler) or `OutboundMessage` (for the host).
    PARSE = 0;

    // A message was received that violated a documented restriction, such as
    // not providing a mandatory field.
    PARAMS = 1;

    // Something unexpected went wrong within the endpoint.
    INTERNAL = 2;
  }
  ErrorType type = 1;

  // The ID of the request that had an error. This MUST be `-1` if the request
  // ID couldn't be determined, or if the error is being reported for a response
  // or an event.
  int32 id = 2;

  // A human-readable message providing more detail about the error.
  string message = 3;
}

// A chunk of a source file.
message SourceSpan {
  // The text covered by the source span. Compilers must guarantee that this is
  // the text between `start.offset` and `end.offset` in the source file
  // referred to by `url`.
  string text = 1;

  // A single point in a source file.
  message SourceLocation {
    // The 0-based offset of this location within the source file. Mandatory.
    uint32 offset = 1;

    // The 0-based line number of this location within the source file.
    // Mandatory.
    uint32 line = 2;

    // The 0-based column number of this location within its line. Mandatory.
    uint32 column = 3;
  }

  // The location of the first character in this span. Mandatory.
  SourceLocation start = 2;

  // The location of the first character after this span. Optional.
  //
  // If this is omitted, it indicates that the span is empty and points
  // immediately before `start`. In that case, `text` must be empty.
  //
  // This must not point to a location before `start`.
  SourceLocation end = 3;

  // The URL of the file to which this span refers.
  //
  // This may be empty, indicating that the span refers to a
  // `CompileRequest.StringInput` file that doesn't specify a URL.
  string url = 4;

  // Additional source text surrounding this span.
  //
  // If this isn't empty, it must contain `text`. Furthermore, `text` must begin
  // at column `start.column` of a line in `context`.
  //
  // This usually contains the full lines the span begins and ends on if the
  // span itself doesn't cover the full lines.
  string context = 5;
}

// A SassScript value, passed to and returned by functions.
message Value {
  // A SassScript string value.
  message String {
    // The contents of the string. Mandatory.
    string text = 1;

    // Whether the string is quoted or unquoted. Mandatory.
    bool quoted = 2;
  }

  // A SassScript number value.
  message Number {
    // The number's numeric value. Mandatory.
    double value = 1;

    // The number's numerator units.
    //
    // The endpoint sending the number must ensure that no numerator units are
    // [compatible][] with any denominator units. Such compatible units must be
    // simplified away according to the multiplicative factor between them
    // defined in the CSS Values and Units spec.
    //
    // [compatible]: https://www.w3.org/TR/css-values-4/#compat
    repeated string numerators = 2;

    // The number's denominator units.
    repeated string denominators = 3;
  }

  // A SassScript color value, represented as red, green, and blue channels.
  message RgbColor {
    // The color's red channel. Mandatory. May not be above 255.
    uint32 red = 1;

    // The color's green channel. Mandatory. May not be above 255.
    uint32 green = 2;

    // The color's blue channel. Mandatory. May not be above 255.
    uint32 blue = 3;

    // The color's alpha channel. Mandatory. Must be between 0 and 1,
    // inclusive.
    double alpha = 4;
  }

  // A SassScript color value, represented as hue, saturation, and lightness channels.
  message HslColor {
    // The color's hue. Mandatory.
    double hue = 1;

    // The color's percent saturation. Mandatory. Must be between 0 and 100,
    // inclusive.
    double saturation = 2;

    // The color's percent lightness. Mandatory. Must be between 0 and 100,
    // inclusive.
    double lightness = 3;

    // The color's alpha channel. Mandatory. Must be between 0 and 1,
    // inclusive.
    double alpha = 4;
  }

  // A SassScript list value.
  message List {
    // Different types of separators a list can have.
    enum Separator {
      // List elements are separated by a comma.
      COMMA = 0;

      // List elements are separated by whitespace.
      SPACE = 1;

      // List elements are separated by a forward slash.
      SLASH = 2;

      // The list's separator hasn't yet been determined.
      //
      // Singleton lists and empty lists don't have separators defiend. This
      // means that list functions will prefer other lists' separators if
      // possible.
      UNDECIDED = 3;
    }

    // The type of separator for this list. Mandatory.
    Separator separator = 1;

    // Whether this list has square brackets. Mandatory.
    bool has_brackets = 2;

    // The elements of this list.
    repeated Value contents = 3;
  }

  // A SassScript map value.
  message Map {
    // A single key/value pair in the map.
    message Entry {
      // The key this entry is associated with. Mandatory.
      Value key = 1;

      // The value associated with this key. Mandatory.
      Value value = 2;
    }

    // The entries in this map. The sending endpoint must guarantee that no two
    // entries have the same key.
    repeated Entry entries = 1;
  }

  // Singleton SassScript values that have no internal state.
  enum Singleton {
    // The SassScript boolean true value.
    TRUE = 0;

    // The SassScript boolean false value.
    FALSE = 1;

    // The SassScript null value.
    NULL = 2;
  }

  // A first-class function defined in the compiler. New `CompilerFunction`s may
  // only be created by the compiler, but the host may pass `CompilerFunction`s
  // back to the compiler as long as their IDs match IDs of functions received
  // by the host during that same compilation.
  message CompilerFunction {
    // A unique ID for this function. This ID can be used in
    // `InboundRequest.FunctionCallRequest` to invoke this function. The
    // compiler is responsible for generating this ID and ensuring it's unique
    // across all functions passed to the host for this compilation. Mandatory.
    uint32 id = 1;
  }

  // An anonymous custom function defined in the host. New `HostFunction`s may
  // only be created by the host, and `HostFunction`s may *never* be passed from
  // the compiler to the host. The compiler must instead pass a
  // `CompilerFunction` that wraps the `HostFunction`.
  message HostFunction {
    // A unique ID for this function. The compiler must pass this ID as
    // `OutboundRequest.FunctionCallRequest.id` when invoking this function. The
    // host is responsible for generating this ID and ensuring it's unique
    // across all functions for *all* compilations. Mandatory.
    uint32 id = 1;

    // The signatures for this function. This must be a valid Sass function
    // signature that could appear in after `@function` in a Sass stylesheet,
    // such as `mix($color1, $color2, $weight: 50%)`. Mandatory.
    //
    // The compiler may not invoke the function by its name, since it's not
    // guaranteed to be globally unique. However, it may use the name to
    // generate the string representation of this function.
    string signature = 2;
  }

  // The value itself. Mandatory.
  //
  // This is wrapped in a message type rather than used directly to reduce
  // repetition, and because oneofs can't be repeated.
  oneof value {
    String string = 1;
    Number number = 2;
    RgbColor rgb_color = 3;
    HslColor hsl_color = 4;
    List list = 5;
    Map map = 6;
    Singleton singleton = 7;
    CompilerFunction compiler_function = 8;
    HostFunction host_function = 9;
  }
}
