//! Implementation of event enum and event content enum macros.

use proc_macro2::{Span, TokenStream};
use quote::{format_ident, quote, ToTokens};
use syn::{Attribute, Data, DataEnum, DeriveInput, Ident, LitStr};

use crate::{
    event_parse::{EventEnumDecl, EventEnumEntry, EventKind, EventKindVariation},
    util::{has_prev_content_field, EVENT_FIELDS},
};

/// Create a content enum from `EventEnumInput`.
pub fn expand_event_enums(input: &EventEnumDecl) -> syn::Result<TokenStream> {
    use EventKindVariation as V;

    let ruma_events = crate::import_ruma_events();

    let mut res = TokenStream::new();

    let kind = input.kind;
    let attrs = &input.attrs;
    let events: Vec<_> = input.events.iter().map(|entry| entry.ev_type.clone()).collect();
    let variants: Vec<_> =
        input.events.iter().map(EventEnumEntry::to_variant).collect::<syn::Result<_>>()?;

    let events = &events;
    let variants = &variants;
    let ruma_events = &ruma_events;

    res.extend(expand_event_enum(kind, V::Full, events, attrs, variants, ruma_events));
    res.extend(expand_content_enum(kind, events, attrs, variants, ruma_events));

    if matches!(kind, EventKind::Ephemeral | EventKind::Message | EventKind::State) {
        res.extend(expand_event_enum(kind, V::Sync, events, attrs, variants, ruma_events));
        res.extend(expand_from_full_event(kind, V::Full, variants));
        res.extend(expand_into_full_event(kind, V::Sync, variants, ruma_events));
    }

    if matches!(kind, EventKind::State) {
        res.extend(expand_event_enum(kind, V::Stripped, events, attrs, variants, ruma_events));
        res.extend(expand_event_enum(kind, V::Initial, events, attrs, variants, ruma_events));
    }

    if matches!(kind, EventKind::Message | EventKind::State) {
        res.extend(expand_event_enum(kind, V::Redacted, events, attrs, variants, ruma_events));
        res.extend(expand_event_enum(kind, V::RedactedSync, events, attrs, variants, ruma_events));
        res.extend(expand_redact(kind, V::Full, variants, ruma_events));
        res.extend(expand_redact(kind, V::Sync, variants, ruma_events));
        res.extend(expand_possibly_redacted_enum(kind, V::Full, ruma_events));
        res.extend(expand_possibly_redacted_enum(kind, V::Sync, ruma_events));
        res.extend(expand_from_full_event(kind, V::Redacted, variants));
        res.extend(expand_into_full_event(kind, V::RedactedSync, variants, ruma_events));
    }

    Ok(res)
}

fn expand_event_enum(
    kind: EventKind,
    var: EventKindVariation,
    events: &[LitStr],
    attrs: &[Attribute],
    variants: &[EventEnumVariant],
    ruma_events: &TokenStream,
) -> TokenStream {
    let serde = quote! { #ruma_events::exports::serde };

    let event_struct = kind.to_event_ident(var).unwrap();
    let ident = kind.to_event_enum_ident(var).unwrap();

    let variant_decls = variants.iter().map(|v| v.decl());
    let content: Vec<_> =
        events.iter().map(|event| to_event_path(event, kind, var, ruma_events)).collect();
    let custom_variant = if var.is_redacted() {
        quote! {
            /// A redacted event not defined by the Matrix specification
            #[doc(hidden)]
            _Custom(
                #ruma_events::#event_struct<#ruma_events::custom::RedactedCustomEventContent>,
            ),
        }
    } else {
        quote! {
            /// An event not defined by the Matrix specification
            #[doc(hidden)]
            _Custom(#ruma_events::#event_struct<#ruma_events::custom::CustomEventContent>),
        }
    };

    let deserialize_impl = expand_deserialize_impl(kind, var, events, variants, ruma_events);
    let field_accessor_impl = expand_accessor_methods(kind, var, variants, ruma_events);
    let from_impl = expand_from_impl(&ident, &content, variants);

    quote! {
        #( #attrs )*
        #[derive(Clone, Debug, #serde::Serialize)]
        #[serde(untagged)]
        #[allow(clippy::large_enum_variant)]
        #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
        pub enum #ident {
            #(
                #[doc = #events]
                #variant_decls(#content),
            )*
            #custom_variant
        }

        #deserialize_impl
        #field_accessor_impl
        #from_impl
    }
}

fn expand_deserialize_impl(
    kind: EventKind,
    var: EventKindVariation,
    events: &[LitStr],
    variants: &[EventEnumVariant],
    ruma_events: &TokenStream,
) -> TokenStream {
    let serde = quote! { #ruma_events::exports::serde };
    let serde_json = quote! { #ruma_events::exports::serde_json };

    let ident = kind.to_event_enum_ident(var).unwrap();
    let event_struct = kind.to_event_ident(var).unwrap();

    let variant_attrs = variants.iter().map(|v| {
        let attrs = &v.attrs;
        quote! { #(#attrs)* }
    });
    let self_variants = variants.iter().map(|v| v.ctor(quote! { Self }));
    let content = events.iter().map(|event| to_event_path(event, kind, var, ruma_events));

    let custom_deserialize = if var.is_redacted() {
        quote! {
            event => {
                let event = #serde_json::from_str::<#ruma_events::#event_struct<
                    #ruma_events::custom::RedactedCustomEventContent,
                >>(json.get())
                .map_err(D::Error::custom)?;

                Ok(Self::_Custom(event))
            },
        }
    } else {
        quote! {
            event => {
                let event =
                    #serde_json::from_str::<
                        #ruma_events::#event_struct<#ruma_events::custom::CustomEventContent>
                    >(json.get())
                    .map_err(D::Error::custom)?;

                Ok(Self::_Custom(event))
            },
        }
    };

    quote! {
        impl<'de> #serde::de::Deserialize<'de> for #ident {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: #serde::de::Deserializer<'de>,
            {
                use #serde::de::Error as _;

                let json = Box::<#serde_json::value::RawValue>::deserialize(deserializer)?;
                let #ruma_events::EventTypeDeHelper { ev_type, .. } =
                    #ruma_events::from_raw_json_value(&json)?;

                match &*ev_type {
                    #(
                        #variant_attrs #events => {
                            let event = #serde_json::from_str::<#content>(json.get())
                                .map_err(D::Error::custom)?;
                            Ok(#self_variants(event))
                        },
                    )*
                    #custom_deserialize
                }
            }
        }
    }
}

fn expand_from_impl(
    ty: &Ident,
    content: &[TokenStream],
    variants: &[EventEnumVariant],
) -> TokenStream {
    let from_impls = content.iter().zip(variants).map(|(content, variant)| {
        let ident = &variant.ident;
        let attrs = &variant.attrs;

        quote! {
            #[automatically_derived]
            #(#attrs)*
            impl ::std::convert::From<#content> for #ty {
                fn from(c: #content) -> Self {
                    Self::#ident(c)
                }
            }
        }
    });

    quote! { #( #from_impls )* }
}

fn expand_from_full_event(
    kind: EventKind,
    var: EventKindVariation,
    variants: &[EventEnumVariant],
) -> TokenStream {
    let ident = kind.to_event_enum_ident(var).unwrap();
    let sync = kind.to_event_enum_ident(var.to_sync().unwrap()).unwrap();

    let ident_variants = variants.iter().map(|v| v.match_arm(&ident));
    let self_variants = variants.iter().map(|v| v.ctor(quote! { Self }));

    quote! {
        #[automatically_derived]
        impl ::std::convert::From<#ident> for #sync {
            fn from(event: #ident) -> Self {
                match event {
                    #(
                        #ident_variants(event) => {
                            #self_variants(::std::convert::From::from(event))
                        },
                    )*
                    #ident::_Custom(event) => {
                        Self::_Custom(::std::convert::From::from(event))
                    },
                }
            }
        }
    }
}

fn expand_into_full_event(
    kind: EventKind,
    var: EventKindVariation,
    variants: &[EventEnumVariant],
    ruma_events: &TokenStream,
) -> TokenStream {
    let ruma_identifiers = quote! { #ruma_events::exports::ruma_identifiers };

    let ident = kind.to_event_enum_ident(var).unwrap();
    let full = kind.to_event_enum_ident(var.to_full().unwrap()).unwrap();

    let self_variants = variants.iter().map(|v| v.match_arm(quote! { Self }));
    let full_variants = variants.iter().map(|v| v.ctor(&full));

    quote! {
        #[automatically_derived]
        impl #ident {
            /// Convert this sync event into a full event (one with a `room_id` field).
            pub fn into_full_event(
                self,
                room_id: #ruma_identifiers::RoomId
            ) -> #full {
                match self {
                    #(
                        #self_variants(event) => {
                            #full_variants(event.into_full_event(room_id))
                        },
                    )*
                    Self::_Custom(event) => {
                        #full::_Custom(event.into_full_event(room_id))
                    },
                }
            }
        }
    }
}

/// Create a content enum from `EventEnumInput`.
fn expand_content_enum(
    kind: EventKind,
    events: &[LitStr],
    attrs: &[Attribute],
    variants: &[EventEnumVariant],
    ruma_events: &TokenStream,
) -> TokenStream {
    let serde = quote! { #ruma_events::exports::serde };
    let serde_json = quote! { #ruma_events::exports::serde_json };

    let ident = kind.to_content_enum();

    let event_type_str = events;

    let content: Vec<_> =
        events.iter().map(|ev| to_event_content_path(kind, ev, None, ruma_events)).collect();

    let variant_decls = variants.iter().map(|v| v.decl()).collect::<Vec<_>>();

    let variant_attrs = variants.iter().map(|v| {
        let attrs = &v.attrs;
        quote! { #(#attrs)* }
    });
    let variant_arms = variants.iter().map(|v| v.match_arm(quote! { Self })).collect::<Vec<_>>();
    let variant_ctors = variants.iter().map(|v| v.ctor(quote! { Self }));

    let marker_trait_impl = expand_marker_trait_impl(kind, ruma_events);
    let from_impl = expand_from_impl(&ident, &content, variants);

    quote! {
        #( #attrs )*
        #[derive(Clone, Debug, #serde::Serialize)]
        #[serde(untagged)]
        #[allow(clippy::large_enum_variant)]
        #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
        pub enum #ident {
            #(
                #[doc = #event_type_str]
                #variant_decls(#content),
            )*
            #[doc(hidden)]
            _Custom {
                #[serde(skip)]
                event_type: ::std::string::String,
            },
        }

        #[automatically_derived]
        impl #ruma_events::EventContent for #ident {
            fn event_type(&self) -> &::std::primitive::str {
                match self {
                    #( #variant_arms(content) => content.event_type(), )*
                    Self::_Custom { event_type } => &event_type,
                }
            }

            fn from_parts(
                event_type: &::std::primitive::str,
                input: &#serde_json::value::RawValue,
            ) -> #serde_json::Result<Self> {
                match event_type {
                    #(
                        #variant_attrs #event_type_str => {
                            let content = #content::from_parts(event_type, input)?;
                            ::std::result::Result::Ok(#variant_ctors(content))
                        }
                    )*
                    ty => {
                        ::std::result::Result::Ok(Self::_Custom { event_type: ty.to_owned() })
                    }
                }
            }
        }

        #marker_trait_impl
        #from_impl
    }
}

fn expand_redact(
    kind: EventKind,
    var: EventKindVariation,
    variants: &[EventEnumVariant],
    ruma_events: &TokenStream,
) -> TokenStream {
    let ruma_identifiers = quote! { #ruma_events::exports::ruma_identifiers };

    let ident = kind.to_event_enum_ident(var).unwrap();
    let redacted_enum = kind.to_event_enum_ident(var.to_redacted().unwrap()).unwrap();

    let self_variants = variants.iter().map(|v| v.match_arm(quote! { Self }));
    let redacted_variants = variants.iter().map(|v| v.ctor(&redacted_enum));

    quote! {
        #[automatically_derived]
        impl #ruma_events::Redact for #ident {
            type Redacted = #redacted_enum;

            fn redact(
                self,
                redaction: #ruma_events::room::redaction::SyncRoomRedactionEvent,
                version: &#ruma_identifiers::RoomVersionId,
            ) -> #redacted_enum {
                match self {
                    #(
                        #self_variants(event) => #redacted_variants(
                            #ruma_events::Redact::redact(event, redaction, version),
                        ),
                    )*
                    Self::_Custom(event) => #redacted_enum::_Custom(
                        #ruma_events::Redact::redact(event, redaction, version),
                    )
                }
            }
        }
    }
}

fn expand_possibly_redacted_enum(
    kind: EventKind,
    var: EventKindVariation,
    ruma_events: &TokenStream,
) -> TokenStream {
    let serde = quote! { #ruma_events::exports::serde };
    let serde_json = quote! { #ruma_events::exports::serde_json };

    let ident = format_ident!("AnyPossiblyRedacted{}", kind.to_event_ident(var).unwrap());
    let regular_enum_ident = kind.to_event_enum_ident(var).unwrap();
    let redacted_enum_ident = kind.to_event_enum_ident(var.to_redacted().unwrap()).unwrap();

    quote! {
        /// An enum that holds either regular un-redacted events or redacted events.
        #[derive(Clone, Debug, #serde::Serialize)]
        #[serde(untagged)]
        #[allow(clippy::exhaustive_enums)]
        pub enum #ident {
            /// An un-redacted event.
            Regular(#regular_enum_ident),

            /// A redacted event.
            Redacted(#redacted_enum_ident),
        }

        impl<'de> #serde::de::Deserialize<'de> for #ident {
            fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
            where
                D: #serde::de::Deserializer<'de>,
            {
                let json = Box::<#serde_json::value::RawValue>::deserialize(deserializer)?;
                let #ruma_events::RedactionDeHelper { unsigned } =
                    #ruma_events::from_raw_json_value(&json)?;

                Ok(match unsigned {
                    Some(unsigned) if unsigned.redacted_because.is_some() => {
                        Self::Redacted(#ruma_events::from_raw_json_value(&json)?)
                    }
                    _ => Self::Regular(#ruma_events::from_raw_json_value(&json)?),
                })
            }
        }
    }
}

fn expand_marker_trait_impl(kind: EventKind, ruma_events: &TokenStream) -> TokenStream {
    let marker_trait = match kind {
        EventKind::State => quote! { StateEventContent },
        EventKind::Message => quote! { MessageEventContent },
        EventKind::Ephemeral => quote! { EphemeralRoomEventContent },
        EventKind::GlobalAccountData => quote! { GlobalAccountDataEventContent },
        EventKind::RoomAccountData => quote! { RoomAccountDataEventContent },
        EventKind::ToDevice => quote! { ToDeviceEventContent },
        _ => return TokenStream::new(),
    };

    let ident = kind.to_content_enum();
    quote! {
        #[automatically_derived]
        impl #ruma_events::#marker_trait for #ident {}
    }
}

fn expand_accessor_methods(
    kind: EventKind,
    var: EventKindVariation,
    variants: &[EventEnumVariant],
    ruma_events: &TokenStream,
) -> TokenStream {
    let ident = kind.to_event_enum_ident(var).unwrap();
    let self_variants: Vec<_> = variants.iter().map(|v| v.match_arm(quote! { Self })).collect();

    let content_accessors = (!var.is_redacted()).then(|| {
        let content_enum = kind.to_content_enum();
        let content_variants: Vec<_> = variants.iter().map(|v| v.ctor(&content_enum)).collect();

        let prev_content = has_prev_content_field(kind, var).then(|| {
            quote! {
                /// Returns the previous content for this event.
                pub fn prev_content(&self) -> Option<#content_enum> {
                    match self {
                        #(
                            #self_variants(event) => {
                                event.prev_content.as_ref().map(|c| #content_variants(c.clone()))
                            },
                        )*
                        Self::_Custom(event) => {
                            event.prev_content.as_ref().map(|c| #content_enum::_Custom {
                                event_type: #ruma_events::EventContent::event_type(c).to_owned(),
                            })
                        },
                    }
                }
            }
        });

        quote! {
            /// Returns the content for this event.
            pub fn content(&self) -> #content_enum {
                match self {
                    #( #self_variants(event) => #content_variants(event.content.clone()), )*
                    Self::_Custom(event) => #content_enum::_Custom {
                        event_type: #ruma_events::EventContent::event_type(&event.content)
                            .to_owned(),
                    },
                }
            }

            #prev_content
        }
    });

    let methods = EVENT_FIELDS.iter().map(|(name, has_field)| {
        has_field(kind, var).then(|| {
            let docs = format!("Returns this event's {} field.", name);
            let ident = Ident::new(name, Span::call_site());
            let field_type = field_return_type(name, var, ruma_events);
            let variants = variants.iter().map(|v| v.match_arm(quote! { Self }));

            quote! {
                #[doc = #docs]
                pub fn #ident(&self) -> &#field_type {
                    match self {
                        #( #variants(event) => &event.#ident, )*
                        Self::_Custom(event) => &event.#ident,
                    }
                }
            }
        })
    });

    quote! {
        #[automatically_derived]
        impl #ident {
            /// Returns the `type` of this event.
            pub fn event_type(&self) -> &::std::primitive::str {
                match self {
                    #( #self_variants(event) =>
                        #ruma_events::EventContent::event_type(&event.content), )*
                    Self::_Custom(event) =>
                        #ruma_events::EventContent::event_type(&event.content),
                }
            }

            #content_accessors

            #( #methods )*
        }
    }
}

fn to_event_path(
    name: &LitStr,
    kind: EventKind,
    var: EventKindVariation,
    ruma_events: &TokenStream,
) -> TokenStream {
    let span = name.span();
    let name = name.value();

    // There is no need to give a good compiler error as `to_camel_case` is called first.
    assert_eq!(&name[..2], "m.");

    let path: Vec<_> = name[2..].split('.').collect();

    let event: String = name[2..]
        .split(&['.', '_'] as &[char])
        .map(|s| s.chars().next().unwrap().to_uppercase().to_string() + &s[1..])
        .collect();

    let path = path.iter().map(|s| Ident::new(s, span));

    let event_name = if kind == EventKind::ToDevice {
        assert_eq!(var, EventKindVariation::Full);
        format_ident!("ToDevice{}Event", event)
    } else {
        format_ident!("{}{}Event", var, event)
    };
    quote! { #ruma_events::#( #path )::*::#event_name }
}

fn to_event_content_path(
    kind: EventKind,
    name: &LitStr,
    prefix: Option<&str>,
    ruma_events: &TokenStream,
) -> TokenStream {
    let span = name.span();
    let name = name.value();

    // There is no need to give a good compiler error as `to_camel_case` is called first.
    assert_eq!(&name[..2], "m.");

    let path: Vec<_> = name[2..].split('.').collect();

    let event: String = name[2..]
        .split(&['.', '_'] as &[char])
        .map(|s| s.chars().next().unwrap().to_uppercase().to_string() + &s[1..])
        .collect();

    let content_str = match kind {
        EventKind::ToDevice => {
            format_ident!("ToDevice{}{}EventContent", prefix.unwrap_or(""), event)
        }
        _ => format_ident!("{}{}EventContent", prefix.unwrap_or(""), event),
    };

    let path = path.iter().map(|s| Ident::new(s, span));

    quote! {
        #ruma_events::#( #path )::*::#content_str
    }
}

/// Splits the given `event_type` string on `.` and `_` removing the `m.room.` then
/// camel casing to give the `Event` struct name.
fn to_camel_case(name: &LitStr) -> syn::Result<Ident> {
    let span = name.span();
    let name = name.value();

    if &name[..2] != "m." {
        return Err(syn::Error::new(
            span,
            format!("well-known matrix events have to start with `m.` found `{}`", name),
        ));
    }

    let s: String = name[2..]
        .split(&['.', '_'] as &[char])
        .map(|s| s.chars().next().unwrap().to_uppercase().to_string() + &s[1..])
        .collect();

    Ok(Ident::new(&s, span))
}

fn field_return_type(
    name: &str,
    var: EventKindVariation,
    ruma_events: &TokenStream,
) -> TokenStream {
    let ruma_common = quote! { #ruma_events::exports::ruma_common };
    let ruma_identifiers = quote! { #ruma_events::exports::ruma_identifiers };

    match name {
        "origin_server_ts" => quote! { #ruma_common::MilliSecondsSinceUnixEpoch },
        "room_id" => quote! { #ruma_identifiers::RoomId },
        "event_id" => quote! { #ruma_identifiers::EventId },
        "sender" => quote! { #ruma_identifiers::UserId },
        "state_key" => quote! { ::std::primitive::str },
        "unsigned" => {
            if var.is_redacted() {
                quote! { #ruma_events::RedactedUnsigned }
            } else {
                quote! { #ruma_events::Unsigned }
            }
        }
        _ => panic!("the `ruma_events_macros::event_enum::EVENT_FIELD` const was changed"),
    }
}

pub(crate) struct EventEnumVariant {
    pub attrs: Vec<Attribute>,
    pub ident: Ident,
}

impl EventEnumVariant {
    pub(crate) fn to_tokens<T>(&self, prefix: Option<T>, with_attrs: bool) -> TokenStream
    where
        T: ToTokens,
    {
        let mut tokens = TokenStream::new();
        if with_attrs {
            for attr in &self.attrs {
                attr.to_tokens(&mut tokens);
            }
        }
        if let Some(p) = prefix {
            tokens.extend(quote! { #p :: })
        }
        self.ident.to_tokens(&mut tokens);

        tokens
    }

    pub(crate) fn decl(&self) -> TokenStream {
        self.to_tokens::<TokenStream>(None, true)
    }

    pub(crate) fn match_arm(&self, prefix: impl ToTokens) -> TokenStream {
        self.to_tokens(Some(prefix), true)
    }

    pub(crate) fn ctor(&self, prefix: impl ToTokens) -> TokenStream {
        self.to_tokens(Some(prefix), false)
    }
}

impl EventEnumEntry {
    pub(crate) fn to_variant(&self) -> syn::Result<EventEnumVariant> {
        let attrs = self.attrs.clone();
        let ident = to_camel_case(&self.ev_type)?;
        Ok(EventEnumVariant { attrs, ident })
    }
}

pub(crate) fn expand_from_impls_derived(input: DeriveInput) -> TokenStream {
    let variants = match &input.data {
        Data::Enum(DataEnum { variants, .. }) => variants,
        _ => panic!("this derive macro only works with enums"),
    };

    let from_impls = variants.iter().map(|variant| match &variant.fields {
        syn::Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
            let inner_struct = &fields.unnamed.first().unwrap().ty;
            let var_ident = &variant.ident;
            let id = &input.ident;
            quote! {
                #[automatically_derived]
                impl ::std::convert::From<#inner_struct> for #id {
                    fn from(c: #inner_struct) -> Self {
                        Self::#var_ident(c)
                    }
                }
            }
        }
        _ => {
            panic!("this derive macro only works with enum variants with a single unnamed field")
        }
    });

    quote! {
        #( #from_impls )*
    }
}