//! Implementations of the MessageEventContent and StateEventContent derive macro.

use std::borrow::Cow;

use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote};
use syn::{
    parse::{Parse, ParseStream},
    DeriveInput, Ident, LitStr, Token,
};

use crate::event_parse::{EventKind, EventKindVariation};

mod kw {
    // This `content` field is kept when the event is redacted.
    syn::custom_keyword!(skip_redaction);
    // Do not emit any redacted event code.
    syn::custom_keyword!(custom_redacted);
    // The kind of event content this is.
    syn::custom_keyword!(kind);
}

/// Parses attributes for `*EventContent` derives.
///
/// `#[ruma_event(type = "m.room.alias")]`
enum EventMeta {
    /// Variant holds the "m.whatever" event type.
    Type(LitStr),

    Kind(EventKind),

    /// Fields marked with `#[ruma_event(skip_redaction)]` are kept when the event is
    /// redacted.
    SkipRedacted,

    /// This attribute signals that the events redacted form is manually implemented and should not
    /// be generated.
    CustomRedacted,
}

impl EventMeta {
    fn get_event_type(&self) -> Option<&LitStr> {
        match self {
            Self::Type(t) => Some(t),
            _ => None,
        }
    }

    fn get_event_kind(&self) -> Option<EventKind> {
        match self {
            Self::Kind(k) => Some(*k),
            _ => None,
        }
    }
}

impl Parse for EventMeta {
    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
        let lookahead = input.lookahead1();
        if lookahead.peek(Token![type]) {
            let _: Token![type] = input.parse()?;
            let _: Token![=] = input.parse()?;
            input.parse().map(EventMeta::Type)
        } else if lookahead.peek(kw::kind) {
            let _: kw::kind = input.parse()?;
            let _: Token![=] = input.parse()?;
            EventKind::parse(input).map(EventMeta::Kind)
        } else if lookahead.peek(kw::skip_redaction) {
            let _: kw::skip_redaction = input.parse()?;
            Ok(EventMeta::SkipRedacted)
        } else if lookahead.peek(kw::custom_redacted) {
            let _: kw::custom_redacted = input.parse()?;
            Ok(EventMeta::CustomRedacted)
        } else {
            Err(lookahead.error())
        }
    }
}

struct MetaAttrs(Vec<EventMeta>);

impl MetaAttrs {
    fn is_custom(&self) -> bool {
        self.0.iter().any(|a| matches!(a, &EventMeta::CustomRedacted))
    }

    fn get_event_type(&self) -> Option<&LitStr> {
        self.0.iter().find_map(|a| a.get_event_type())
    }

    fn get_event_kind(&self) -> Option<EventKind> {
        self.0.iter().find_map(|a| a.get_event_kind())
    }
}

impl Parse for MetaAttrs {
    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
        let attrs = syn::punctuated::Punctuated::<EventMeta, Token![,]>::parse_terminated(input)?;
        Ok(Self(attrs.into_iter().collect()))
    }
}

/// Create an `EventContent` implementation for a struct.
pub fn expand_event_content(
    input: &DeriveInput,
    ruma_events: &TokenStream,
) -> syn::Result<TokenStream> {
    let content_attr = input
        .attrs
        .iter()
        .filter(|attr| attr.path.is_ident("ruma_event"))
        .map(|attr| attr.parse_args::<MetaAttrs>())
        .collect::<syn::Result<Vec<_>>>()?;

    let mut event_types: Vec<_> =
        content_attr.iter().filter_map(|attrs| attrs.get_event_type()).collect();
    let event_type = match event_types.as_slice() {
        [] => {
            return Err(syn::Error::new(
                Span::call_site(),
                "no event type attribute found, \
                 add `#[ruma_event(type = \"any.room.event\", kind = Kind)]` \
                 below the event content derive",
            ));
        }
        [_] => event_types.pop().unwrap(),
        _ => {
            return Err(syn::Error::new(
                Span::call_site(),
                "multiple event type attribute found, there can only be one",
            ));
        }
    };

    let mut event_kinds: Vec<_> =
        content_attr.iter().filter_map(|attrs| attrs.get_event_kind()).collect();
    let event_kind = match event_kinds.as_slice() {
        [] => None,
        [_] => Some(event_kinds.pop().unwrap()),
        _ => {
            return Err(syn::Error::new(
                Span::call_site(),
                "multiple event kind attribute found, there can only be one",
            ));
        }
    };

    // We only generate redacted content structs for state and message events
    let redacted_event_content = needs_redacted(&content_attr, event_kind)
        .then(|| generate_redacted_event_content(input, event_type, ruma_events, event_kind))
        .transpose()?;

    let event_content_impl = generate_event_content_impl(&input.ident, event_type, ruma_events);
    let static_event_content_impl = event_kind.map(|k| {
        generate_static_event_content_impl(&input.ident, k, false, event_type, ruma_events)
    });
    let marker_trait_impl =
        event_kind.map(|k| generate_marker_trait_impl(k, &input.ident, ruma_events)).transpose()?;
    let type_aliases = event_kind
        .map(|k| generate_event_type_aliases(k, &input.ident, &event_type.value(), ruma_events))
        .transpose()?;

    Ok(quote! {
        #redacted_event_content
        #event_content_impl
        #static_event_content_impl
        #marker_trait_impl
        #type_aliases
    })
}

fn generate_redacted_event_content(
    input: &DeriveInput,
    event_type: &LitStr,
    ruma_events: &TokenStream,
    event_kind: Option<EventKind>,
) -> Result<TokenStream, syn::Error> {
    let ruma_identifiers = quote! { #ruma_events::exports::ruma_identifiers };
    let serde = quote! { #ruma_events::exports::serde };
    let serde_json = quote! { #ruma_events::exports::serde_json };

    let ident = &input.ident;
    let doc = format!("Redacted form of [`{}`]", ident);
    let redacted_ident = format_ident!("Redacted{}", ident);

    let kept_redacted_fields =
        if let syn::Data::Struct(syn::DataStruct {
            fields: syn::Fields::Named(syn::FieldsNamed { named, .. }),
            ..
        }) = &input.data
        {
            // this is to validate the `#[ruma_event(skip_redaction)]` attribute
            named
                .iter()
                .flat_map(|f| &f.attrs)
                .filter(|a| a.path.is_ident("ruma_event"))
                .find_map(|a| {
                    if let Err(e) = a.parse_args::<EventMeta>() {
                        Some(Err(e))
                    } else {
                        None
                    }
                })
                .unwrap_or(Ok(()))?;

            let mut fields: Vec<_> = named
                .iter()
                .filter(|f| {
                    matches!(
                        f.attrs.iter().find_map(|a| a.parse_args::<EventMeta>().ok()),
                        Some(EventMeta::SkipRedacted)
                    )
                })
                .cloned()
                .collect();

            // don't re-emit our `ruma_event` attributes
            for f in &mut fields {
                f.attrs.retain(|a| !a.path.is_ident("ruma_event"));
            }
            fields
        } else {
            vec![]
        };

    let redaction_struct_fields = kept_redacted_fields.iter().flat_map(|f| &f.ident);

    let (redacted_fields, redacted_return) = if kept_redacted_fields.is_empty() {
        (quote! { ; }, quote! { Ok(#redacted_ident {}) })
    } else {
        (
            quote! {
                { #( #kept_redacted_fields, )* }
            },
            quote! {
                Err(#serde::de::Error::custom(
                    format!("this redacted event has fields that cannot be constructed")
                ))
            },
        )
    };

    let (has_deserialize_fields, has_serialize_fields) = if kept_redacted_fields.is_empty() {
        (quote! { #ruma_events::HasDeserializeFields::False }, quote! { false })
    } else {
        (quote! { #ruma_events::HasDeserializeFields::True }, quote! { true })
    };

    let constructor = kept_redacted_fields.is_empty().then(|| {
        let doc = format!("Creates an empty {}.", redacted_ident);
        quote! {
            impl #redacted_ident {
                #[doc = #doc]
                pub fn new() -> Self {
                    Self
                }
            }
        }
    });

    let redacted_event_content =
        generate_event_content_impl(&redacted_ident, event_type, ruma_events);

    let marker_trait_impl = match event_kind {
        Some(EventKind::Message) => quote! {
            #[automatically_derived]
            impl #ruma_events::RedactedMessageEventContent for #redacted_ident {}
        },
        Some(EventKind::State) => quote! {
            #[automatically_derived]
            impl #ruma_events::RedactedStateEventContent for #redacted_ident {}
        },
        _ => TokenStream::new(),
    };

    let static_event_content_impl = event_kind.map(|k| {
        generate_static_event_content_impl(&redacted_ident, k, true, event_type, ruma_events)
    });

    Ok(quote! {
        // this is the non redacted event content's impl
        #[automatically_derived]
        impl #ruma_events::RedactContent for #ident {
            type Redacted = #redacted_ident;

            fn redact(self, version: &#ruma_identifiers::RoomVersionId) -> #redacted_ident {
                #redacted_ident {
                    #( #redaction_struct_fields: self.#redaction_struct_fields, )*
                }
            }
        }

        #[doc = #doc]
        #[derive(Clone, Debug, #serde::Deserialize, #serde::Serialize)]
        #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
        pub struct #redacted_ident #redacted_fields

        #constructor

        #redacted_event_content

        #[automatically_derived]
        impl #ruma_events::RedactedEventContent for #redacted_ident {
            fn empty(ev_type: &str) -> #serde_json::Result<Self> {
                if ev_type != #event_type {
                    return Err(#serde::de::Error::custom(
                        format!("expected event type `{}`, found `{}`", #event_type, ev_type)
                    ));
                }

                #redacted_return
            }

            fn has_serialize_fields(&self) -> bool {
                #has_serialize_fields
            }

            fn has_deserialize_fields() -> #ruma_events::HasDeserializeFields {
                #has_deserialize_fields
            }
        }

        #static_event_content_impl
        #marker_trait_impl
    })
}

fn generate_event_type_aliases(
    event_kind: EventKind,
    ident: &Ident,
    event_type: &str,
    ruma_events: &TokenStream,
) -> syn::Result<TokenStream> {
    // The redaction module has its own event types.
    if ident == "RoomRedactionEventContent" {
        return Ok(quote! {});
    }

    let ident_s = ident.to_string();
    let ev_type_s = ident_s.strip_suffix("Content").ok_or_else(|| {
        syn::Error::new_spanned(ident, "Expected content struct name ending in `Content`")
    })?;

    let type_aliases = [
        EventKindVariation::Full,
        EventKindVariation::Sync,
        EventKindVariation::Stripped,
        EventKindVariation::Initial,
        EventKindVariation::Redacted,
        EventKindVariation::RedactedSync,
    ]
    .iter()
    .filter_map(|&kind| Some((kind, event_kind.try_to_event_ident(kind)?)))
    .map(|(kind, ev_struct)| {
        let ev_type = format_ident!("{}{}", kind, ev_type_s);

        let doc_text = match kind {
            EventKindVariation::Full => "",
            EventKindVariation::Sync => " from a `sync_events` response",
            EventKindVariation::Stripped => " from an invited room preview",
            EventKindVariation::Redacted => " that has been redacted",
            EventKindVariation::RedactedSync => {
                " from a `sync_events` response that has been redacted"
            }
            EventKindVariation::Initial => " for creating a room",
        };
        let ev_type_doc = format!("An `{}` event{}.", event_type, doc_text);

        let content_struct = if kind.is_redacted() {
            Cow::Owned(format_ident!("Redacted{}", ident))
        } else {
            Cow::Borrowed(ident)
        };

        quote! {
            #[doc = #ev_type_doc]
            pub type #ev_type = #ruma_events::#ev_struct<#content_struct>;
        }
    })
    .collect();

    Ok(type_aliases)
}

fn generate_marker_trait_impl(
    event_kind: EventKind,
    ident: &Ident,
    ruma_events: &TokenStream,
) -> syn::Result<TokenStream> {
    let marker_trait = match event_kind {
        EventKind::GlobalAccountData => quote! { GlobalAccountDataEventContent },
        EventKind::RoomAccountData => quote! { RoomAccountDataEventContent },
        EventKind::Ephemeral => quote! { EphemeralRoomEventContent },
        EventKind::Message => quote! { MessageEventContent },
        EventKind::State => quote! { StateEventContent },
        EventKind::ToDevice => quote! { ToDeviceEventContent },
        EventKind::RoomRedaction | EventKind::Presence | EventKind::Decrypted => {
            return Err(syn::Error::new_spanned(
                ident,
                "valid event kinds are GlobalAccountData, RoomAccountData, \
                 EphemeralRoom, Message, State, ToDevice",
            ));
        }
    };

    Ok(quote! {
        #[automatically_derived]
        impl #ruma_events::#marker_trait for #ident {}
    })
}

fn generate_event_content_impl(
    ident: &Ident,
    event_type: &LitStr,
    ruma_events: &TokenStream,
) -> TokenStream {
    let serde = quote! { #ruma_events::exports::serde };
    let serde_json = quote! { #ruma_events::exports::serde_json };

    quote! {
        #[automatically_derived]
        impl #ruma_events::EventContent for #ident {
            fn event_type(&self) -> &str {
                #event_type
            }

            fn from_parts(
                ev_type: &str,
                content: &#serde_json::value::RawValue,
            ) -> #serde_json::Result<Self> {
                if ev_type != #event_type {
                    return Err(#serde::de::Error::custom(
                        format!("expected event type `{}`, found `{}`", #event_type, ev_type)
                    ));
                }

                #serde_json::from_str(content.get())
            }
        }
    }
}

fn generate_static_event_content_impl(
    ident: &Ident,
    event_kind: EventKind,
    redacted: bool,
    event_type: &LitStr,
    ruma_events: &TokenStream,
) -> TokenStream {
    let event_kind = match event_kind {
        EventKind::GlobalAccountData => quote! { GlobalAccountData },
        EventKind::RoomAccountData => quote! { RoomAccountData },
        EventKind::Ephemeral => quote! { EphemeralRoomData },
        EventKind::Message => quote! { Message { redacted: #redacted } },
        EventKind::State => quote! { State { redacted: #redacted } },
        EventKind::ToDevice => quote! { ToDevice },
        EventKind::RoomRedaction | EventKind::Presence | EventKind::Decrypted => {
            unreachable!("not a valid event content kind")
        }
    };

    quote! {
        impl #ruma_events::StaticEventContent for #ident {
            const KIND: #ruma_events::EventKind = #ruma_events::EventKind::#event_kind;
            const TYPE: &'static ::std::primitive::str = #event_type;
        }
    }
}

fn needs_redacted(input: &[MetaAttrs], event_kind: Option<EventKind>) -> bool {
    // `is_custom` means that the content struct does not need a generated
    // redacted struct also. If no `custom_redacted` attrs are found the content
    // needs a redacted struct generated.
    !input.iter().any(|a| a.is_custom())
        && matches!(event_kind, Some(EventKind::Message) | Some(EventKind::State))
}