//! Core model for netdoc parsing

use super::*;

/// A document or section that can be parsed

///

/// Normally [derived](derive_deftly_template_NetdocParseable).

pub trait NetdocParseable: Sized {

    /// Document type for errors, normally its intro keyword

    fn doctype_for_error() -> &'static str;

    /// Is `Keyword` an intro Item Keyword for this kind of document?

    ///

    /// This is used with 1-keyword lookahead, to allow us to push or pop

    /// the parsing state into or out of a sub-document.

    ///

    /// For signatures sections, this should report *every* recognised keyword.

    fn is_intro_item_keyword(kw: KeywordRef<'_>) -> bool;

    /// Parse the document from a stream of Items

    ///

    /// Should stop before reading any keyword matching `stop_at`.

    /// (Except, right at the start.)

    ///

    /// Should also stop before reading a 2nd intro keyword,

    /// so that successive calls to this function can parse

    /// successive sub-documents of this kind.

    ///

    /// Otherwise, should continue until EOF.

    ///

    /// Must check whether the first item is this document's `is_intro_item_keyword`,

    /// and error if not.

    fn from_items(input: &mut ItemStream<'_>, stop_at: stop_at!()) -> Result<Self, ErrorProblem>;

    /// Is `Keyword` a structural keyword for this kind of document?

    ///

    /// Returns `Some(IsStructural)` for:

    ///   - this type's intro item keyword (`is_intro_item_keyword`)

    ///   - the intro items or structural items for any of its sub-documents and sections

    ///     `#[deftly(netdoc(subdoc))]`

    ///

    /// (This means it returns true for *any* item in a signatures subdocument

    /// ie any field in a struct decorated `#[deftly(netdoc(signatures))]`

    /// since those are considered intro items.)

    ///

    /// Used for avoiding parsing ambiguity when a netdoc from a semi-trusted source

    /// is embedded into another netdoc.

    /// See <https://spec.torproject.org/dir-spec/creating-key-certificates.html#nesting>.

    ///

    /// # Return type and relationship to `is_intro_item_keyword`

    ///

    /// Returns `Option<IsStructural>`

    /// so that it has a different type to [`NetdocParseable::is_intro_item_keyword`],

    /// preventing accidental confusion between the two kinds of keyword property enquiry.

    ///

    /// Our parsing algorithms actually only care about *intro keywords* for sub-documents.

    /// We don't need to worry about anything else;

    /// notably, we don't need to care about other structural items within those sub-documents.

    ///

    /// Except for authcerts in votes,, which are nested documents

    /// with partially trusted content.

    /// That is what this method is for.

    ///

    /// So, we privilege `is_intro_item_keyword` by having it return `bool`

    /// and by the affordances in [`StopAt`].

    fn is_structural_keyword(kw: KeywordRef<'_>) -> Option<IsStructural>;

}

/// A collection of fields that can be parsed within a section

///

/// None of the items can be structural.

///

/// Normally [derived](derive_deftly_template_NetdocParseableFields).

pub trait NetdocParseableFields: Sized {

    /// The partially-parsed set of items.

    type Accumulator: Sized + Debug + Send + Sync + 'static;

    /// Is this one of the keywords in this struct

    fn is_item_keyword(kw: KeywordRef<'_>) -> bool;

    /// Accumulate an item in this struct

    ///

    /// # Panics

    ///

    /// The caller must have first checked the `item`'s keyword with `is_item_keyword`.

    /// If this *isn't* an item for this structure, may panic.

    fn accumulate_item(acc: &mut Self::Accumulator, item: UnparsedItem<'_>) -> Result<(), EP>;

    /// Finish

    ///

    /// Resolves the `Accumulator` into the output type.

    /// Generally, this means throwing an error if expected fields were not present.

    fn finish(acc: Self::Accumulator) -> Result<Self, EP>;

}

/// An item (value) that can be parsed in a netdoc

///

/// This is the type `T` of a field `item: T` in a netdoc type.

///

/// An implementation is provided for tuples of `ItemArgumentParseable`,

/// which parses each argument in turn,

/// ignores additional arguments,

/// and rejects any Object.

///

/// Typically derived with

/// [`#[derive_deftly(ItemValueParseable)]`](derive_deftly_template_ItemValueParseable).

///

/// Signature items are special, and implement [`SignatureItemParseable`] instead.

pub trait ItemValueParseable: Sized {

    /// Parse the item's value

    fn from_unparsed(item: UnparsedItem<'_>) -> Result<Self, ErrorProblem>;

}

/// An (individual) argument that can be parsed from in a netdoc

///

/// An implementations is provided for **`T: FromStr`**,

/// which expects a single argument and passes it to `FromStr`.

///

/// For netdoc arguments whose specified syntax spans multiple space-separated words,

/// use a manual implementation or a wrapper type.

pub trait ItemArgumentParseable: Sized {

    /// Parse the argument

    fn from_args<'s>(args: &mut ArgumentStream<'s>) -> Result<Self, ArgumentError>;

}

/// An Object value that be parsed from a netdoc

pub trait ItemObjectParseable: Sized {

    /// Check that the Label is right

    fn check_label(label: &str) -> Result<(), ErrorProblem>;

    /// Convert the bytes of the Object (which was present) into the actual value

    ///

    /// `input` has been base64-decoded.

    fn from_bytes(input: &[u8]) -> Result<Self, ErrorProblem>;

}

/// Token indicating that a keyword is structural

///

/// Returned by [`NetdocParseable::is_structural_keyword`]

#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]

#[allow(clippy::exhaustive_structs)]

pub struct IsStructural;

//---------- provided blanket impls ----------

impl<T: NormalItemArgument> ItemArgumentParseable for T {

}

impl<T: ItemValueParseable> ItemValueParseable for Arc<T> {

}

impl<T: NetdocParseable> NetdocParseable for Arc<T> {

}

impl<T: NetdocParseableFields> NetdocParseableFields for Arc<T> {

    type Accumulator = T::Accumulator;

}

/// implement [`ItemValueParseable`] for a particular tuple size

macro_rules! item_value_parseable_for_tuple {

    { $($i:literal)* } => { paste! {

        impl< $( [<T$i>]: ItemArgumentParseable, )* >

            ItemValueParseable for ( $( [<T$i>], )* )

        {

        }

    } }

}

item_value_parseable_for_tuple! {}

item_value_parseable_for_tuple! { 0 }

item_value_parseable_for_tuple! { 0 1 }

item_value_parseable_for_tuple! { 0 1 2 }

item_value_parseable_for_tuple! { 0 1 2 3 }

item_value_parseable_for_tuple! { 0 1 2 3 4 }

item_value_parseable_for_tuple! { 0 1 2 3 4 5 }

item_value_parseable_for_tuple! { 0 1 2 3 4 5 6 }

item_value_parseable_for_tuple! { 0 1 2 3 4 5 6 7 }

item_value_parseable_for_tuple! { 0 1 2 3 4 5 6 7 8 }

item_value_parseable_for_tuple! { 0 1 2 3 4 5 6 7 8 9 }