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use proc_macro2::{Span, TokenStream as TokenStream2};
use quote::{quote, ToTokens, TokenStreamExt};
use syn::{
    parse::{Parse, ParseStream},
    DeriveInput, Ident,
};

use super::ToSqlConfig;

/// A parsed `#[derive(PostgresHash)]` item.
///
/// It should be used with [`syn::parse::Parse`] functions.
///
/// Using [`quote::ToTokens`] will output the declaration for a `pgx::datum::sql_entity_graph::InventoryPostgresHash`.
///
/// On structs:
///
/// ```rust
/// use syn::{Macro, parse::Parse, parse_quote, parse};
/// use quote::{quote, ToTokens};
/// use pgx_utils::sql_entity_graph::PostgresHash;
///
/// # fn main() -> eyre::Result<()> {
/// let parsed: PostgresHash = parse_quote! {
///     #[derive(PostgresHash)]
///     struct Example<'a> {
///         demo: &'a str,
///     }
/// };
/// let sql_graph_entity_tokens = parsed.to_token_stream();
/// # Ok(())
/// # }
/// ```
///
/// On enums:
///
/// ```rust
/// use syn::{Macro, parse::Parse, parse_quote, parse};
/// use quote::{quote, ToTokens};
/// use pgx_utils::sql_entity_graph::PostgresHash;
///
/// # fn main() -> eyre::Result<()> {
/// let parsed: PostgresHash = parse_quote! {
///     #[derive(PostgresHash)]
///     enum Demo {
///         Example,
///     }
/// };
/// let sql_graph_entity_tokens = parsed.to_token_stream();
/// # Ok(())
/// # }
/// ```
#[derive(Debug, Clone)]
pub struct PostgresHash {
    pub name: Ident,
    pub to_sql_config: ToSqlConfig,
}

impl PostgresHash {
    pub fn new(name: Ident, to_sql_config: ToSqlConfig) -> Self {
        Self {
            name,
            to_sql_config,
        }
    }

    pub fn from_derive_input(derive_input: DeriveInput) -> Result<Self, syn::Error> {
        let to_sql_config =
            ToSqlConfig::from_attributes(derive_input.attrs.as_slice())?.unwrap_or_default();
        Ok(Self::new(derive_input.ident, to_sql_config))
    }
}

impl Parse for PostgresHash {
    fn parse(input: ParseStream) -> Result<Self, syn::Error> {
        use syn::Item;

        let parsed = input.parse()?;
        let (ident, attrs) = match &parsed {
            Item::Enum(item) => (item.ident.clone(), item.attrs.as_slice()),
            Item::Struct(item) => (item.ident.clone(), item.attrs.as_slice()),
            _ => return Err(syn::Error::new(input.span(), "expected enum or struct")),
        };
        let to_sql_config = ToSqlConfig::from_attributes(attrs)?.unwrap_or_default();
        Ok(Self::new(ident, to_sql_config))
    }
}

impl ToTokens for PostgresHash {
    fn to_tokens(&self, tokens: &mut TokenStream2) {
        let name = &self.name;
        let sql_graph_entity_fn_name = syn::Ident::new(
            &format!("__pgx_internals_hash_{}", self.name),
            Span::call_site(),
        );
        let to_sql_config = &self.to_sql_config;
        let inv = quote! {
            #[no_mangle]
            pub extern "C" fn  #sql_graph_entity_fn_name() -> pgx::datum::sql_entity_graph::SqlGraphEntity {
                use core::any::TypeId;
                extern crate alloc;
                use alloc::vec::Vec;
                use alloc::vec;
                let submission = pgx::datum::sql_entity_graph::PostgresHashEntity {
                    name: stringify!(#name),
                    file: file!(),
                    line: line!(),
                    full_path: core::any::type_name::<#name>(),
                    module_path: module_path!(),
                    id: TypeId::of::<#name>(),
                    to_sql_config: #to_sql_config,
                };
                pgx::datum::sql_entity_graph::SqlGraphEntity::Hash(submission)
            }
        };
        tokens.append_all(inv);
    }
}