// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

//! Definitions for describing the format protobuf messages. These can be used
//! to generate `.proto` files that are binary compatible with the associated
//! Rust types.

mod writer;

#[cfg(feature = "std")]
pub use writer::DescriptorWriter;

use crate::DefaultEncoding;
use core::fmt::Display;

/// A trait for a self-describing protobuf message field.
pub trait DescribeField<T> {
    /// The type of the field.
    const FIELD_TYPE: FieldType<'static>;
    /// The type name of the field in a packed context.
    const PACKED_TYPE: Option<&'static str> = None;
}

/// A trait for a self-describing protobuf message.
///
/// This can be derived for `T` by deriving [`Protobuf`](crate::Protobuf) and
/// adding the attribute `#[mesh(package = "my.package.name")]`.
pub trait DescribeMessage<T> {
    /// The message description.
    const DESCRIPTION: MessageDescription<'static>;
}

/// A description of a message type.
#[derive(Copy, Clone)]
pub enum MessageDescription<'a> {
    /// An internally-defined type, described by the descriptor.
    Internal(&'a TopLevelDescriptor<'a>),
    /// An externally-defined type.
    External {
        /// The fully-qualified name of the message type.
        name: &'a str,
        /// The import path of the `.proto` file.
        import_path: &'a str,
    },
}

/// A type URL, used in [`ProtobufAny`](super::message::ProtobufAny) (which
/// shares an encoding with `google.protobuf.Any`).
#[derive(Debug, Copy, Clone)]
pub struct TypeUrl<'a> {
    package: &'a str,
    name: &'a str,
}

impl TypeUrl<'_> {
    fn eq(&self, type_url: &str) -> bool {
        let type_url = type_url.strip_prefix("https://").unwrap_or(type_url);
        if let Some((package, name)) = type_url
            .strip_prefix("type.googleapis.com/")
            .and_then(|ty| ty.rsplit_once('.'))
        {
            self.package == package && self.name == name
        } else {
            false
        }
    }
}

impl Display for TypeUrl<'_> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "type.googleapis.com/{}.{}", self.package, self.name)
    }
}

impl PartialEq<str> for TypeUrl<'_> {
    fn eq(&self, other: &str) -> bool {
        self.eq(other)
    }
}

impl PartialEq<TypeUrl<'_>> for str {
    fn eq(&self, other: &TypeUrl<'_>) -> bool {
        other.eq(self)
    }
}

impl MessageDescription<'_> {
    /// Returns the type URL to use with `google.protobuf.Any`.
    pub const fn type_url(&self) -> TypeUrl<'_> {
        match *self {
            MessageDescription::Internal(tld) => TypeUrl {
                package: tld.package,
                name: tld.message.name,
            },
            MessageDescription::External { name, .. } => TypeUrl { package: "", name },
        }
    }
}

/// Returns the top-level message descriptor for a type with a default encoding.
pub const fn message_description<T: DefaultEncoding>() -> MessageDescription<'static>
where
    T::Encoding: DescribeMessage<T>,
{
    <T::Encoding as DescribeMessage<T>>::DESCRIPTION
}

/// The description of a field type.
#[derive(Debug, Copy, Clone)]
pub struct FieldType<'a> {
    kind: FieldKind<'a>,
    sequence_type: Option<SequenceType<'a>>,
    annotation: &'a str,
}

#[derive(Debug, Copy, Clone)]
enum SequenceType<'a> {
    Optional,
    Repeated,
    Map(&'a str),
}

#[derive(Debug, Copy, Clone)]
enum FieldKind<'a> {
    Builtin(&'a str),
    Local(&'a str),
    External {
        name: &'a str,
        import_path: &'static str,
    },
    Message(fn() -> MessageDescription<'a>),
    Tuple(&'a [FieldType<'a>]),
    KeyValue(&'a [FieldType<'a>; 2]),
}

impl<'a> FieldType<'a> {
    /// Returns a repeated version of this field type.
    ///
    /// Panics if the field type is already a sequence type.
    pub const fn repeated(mut self) -> Self {
        assert!(self.sequence_type.is_none());
        self.sequence_type = Some(SequenceType::Repeated);
        self
    }

    /// Returns a optional version of this field type.
    ///
    /// Panics if the field type is already a sequence type.
    pub const fn optional(mut self) -> Self {
        assert!(self.sequence_type.is_none());
        self.sequence_type = Some(SequenceType::Optional);
        self
    }

    /// Sets an annotation to show up in the .proto file.
    pub const fn annotate(mut self, annotation: &'a str) -> Self {
        self.annotation = annotation;
        self
    }

    /// Returns a map type.
    ///
    /// If `key` is not a builtin numeric scalar or string type, or if `value`
    /// is an optional or repeated type, then this will result in a repeated
    /// tuple instead of a protobuf `map` type. The encodings for these are the
    /// same, but `.proto` `map` types are constrained to mappings from scalars
    /// to non-optional/repeated scalars and messages.
    pub const fn map(kv: &'a [FieldType<'a>; 2]) -> Self {
        let [key, value] = kv;
        if !key.is_sequence() && !value.is_sequence() {
            if let FieldKind::Builtin(ty) = key.kind {
                if let b"uint32" | b"int32" | b"sint32" | b"uint64" | b"sint64" | b"int64"
                | b"fixed32" | b"fixed64" | b"sfixed32" | b"sfixed64" | b"bool" | b"string" =
                    ty.as_bytes()
                {
                    return Self {
                        kind: value.kind,
                        sequence_type: Some(SequenceType::Map(ty)),
                        annotation: "",
                    };
                }
            }
        }
        Self {
            kind: FieldKind::KeyValue(kv),
            sequence_type: Some(SequenceType::Repeated),
            annotation: "",
        }
    }

    /// Returns a field type for a message whose top-level descriptor is
    /// returned by `f`.
    ///
    /// This is abstracted through a function to allow for recursive types.
    /// Currently Rust does not allow a `const` to refer to a `static`, but it
    /// does allow a `const` to refer to a function that returns a `&'static`.
    pub const fn message(f: fn() -> MessageDescription<'a>) -> Self {
        Self {
            kind: FieldKind::Message(f),
            sequence_type: None,
            annotation: "",
        }
    }

    /// Returns a field type for a local message type with `name`.
    pub const fn local(name: &'a str) -> Self {
        Self {
            kind: FieldKind::Local(name),
            sequence_type: None,
            annotation: "",
        }
    }

    /// Returns a field type for a builtin type, such as `uint32`.
    pub const fn builtin(name: &'a str) -> Self {
        Self {
            kind: FieldKind::Builtin(name),
            sequence_type: None,
            annotation: "",
        }
    }

    /// Returns a field type for an anonymous tuple.
    pub const fn tuple(field_types: &'a [Self]) -> Self {
        // Use well-known types instead of new anonymous ones when possible.
        match field_types {
            [] => {
                return Self::external("google.protobuf.Empty", "google/protobuf/empty.proto");
            }
            &[
                Self {
                    kind: FieldKind::Builtin(ty),
                    sequence_type: None,
                    annotation,
                },
            ] if annotation.is_empty() => {
                let wrapper = match ty.as_bytes() {
                    b"double" => Some("google.protobuf.DoubleValue"),
                    b"float" => Some("google.protobuf.FloatValue"),
                    b"int64" => Some("google.protobuf.Int64Value"),
                    b"uint64" => Some("google.protobuf.UInt64Value"),
                    b"int32" => Some("google.protobuf.Int32Value"),
                    b"uint32" => Some("google.protobuf.UInt32Value"),
                    b"bool" => Some("google.protobuf.BoolValue"),
                    b"string" => Some("google.protobuf.StringValue"),
                    b"bytes" => Some("google.protobuf.BytesValue"),
                    _ => None,
                };
                if let Some(wrapper) = wrapper {
                    return Self::external(wrapper, "google/protobuf/wrappers.proto");
                }
            }
            _ => {}
        }
        Self {
            kind: FieldKind::Tuple(field_types),
            sequence_type: None,
            annotation: "",
        }
    }

    /// Returns a field type for an external type with the given fully-qualified
    /// name and protoc import path.
    pub const fn external(name: &'a str, import_path: &'static str) -> Self {
        Self {
            kind: FieldKind::External { name, import_path },
            sequence_type: None,
            annotation: "",
        }
    }

    /// Returns true if this is a sequence type (optional or repeated).
    pub const fn is_sequence(&self) -> bool {
        self.sequence_type.is_some()
    }

    /// Returns true if this type can use a packed encoding in a repeated
    /// context.
    pub const fn can_pack(&self) -> bool {
        if self.sequence_type.is_some() {
            return false;
        }
        match self.kind {
            FieldKind::Builtin(v) => matches!(
                v.as_bytes(),
                b"double" | b"float" | b"int64" | b"uint64" | b"int32" | b"uint32" | b"bool"
            ),
            _ => false,
        }
    }
}

/// A descriptor for a message field.
#[derive(Debug, Copy, Clone)]
pub struct FieldDescriptor<'a> {
    field_type: FieldType<'a>,
    field_number: u32,
    comment: &'a str,
    name: &'a str,
}

impl<'a> FieldDescriptor<'a> {
    /// Returns a new descriptor.
    pub const fn new(
        comment: &'a str,
        field_type: FieldType<'a>,
        name: &'a str,
        field_number: u32,
    ) -> Self {
        Self {
            field_type,
            field_number,
            comment,
            name,
        }
    }
}

/// A description of a protobuf `oneof`.
#[derive(Debug, Copy, Clone)]
pub struct OneofDescriptor<'a> {
    name: &'a str,
    variants: &'a [FieldDescriptor<'a>],
}

impl<'a> OneofDescriptor<'a> {
    /// Returns a new descriptor.
    pub const fn new(name: &'a str, variants: &'a [FieldDescriptor<'a>]) -> Self {
        Self { name, variants }
    }
}

/// A message descriptor.
#[derive(Debug, Copy, Clone)]
pub struct MessageDescriptor<'a> {
    comment: &'a str,
    name: &'a str,
    fields: &'a [FieldDescriptor<'a>],
    oneofs: &'a [OneofDescriptor<'a>],
    messages: &'a [MessageDescriptor<'a>],
}

impl<'a> MessageDescriptor<'a> {
    /// Creates a new message descriptor.
    pub const fn new(
        name: &'a str,
        comment: &'a str,
        fields: &'a [FieldDescriptor<'a>],
        oneofs: &'a [OneofDescriptor<'a>],
        messages: &'a [MessageDescriptor<'a>],
    ) -> Self {
        Self {
            comment,
            name,
            fields,
            oneofs,
            messages,
        }
    }
}

/// A message descriptor for a message rooted directly in a package (and not
/// nested in another message type).
#[derive(Debug, Copy, Clone)]
pub struct TopLevelDescriptor<'a> {
    package: &'a str,
    message: &'a MessageDescriptor<'a>,
}

impl<'a> TopLevelDescriptor<'a> {
    /// Returns a new descriptor.
    pub const fn message(package: &'a str, message: &'a MessageDescriptor<'a>) -> Self {
        Self { package, message }
    }
}
