use heck::SnakeCase;
use proc_macro2::{Ident, TokenStream};
use quote::{quote, quote_spanned};
use syn::{punctuated::Punctuated, token::Comma, Data, DataEnum, Fields, Lit, Meta, Variant};

/// Method to derive a Primary Key for a Model using the [PrimaryKeyTrait](sea_orm::PrimaryKeyTrait)
pub fn expand_derive_primary_key(ident: Ident, data: Data) -> syn::Result<TokenStream> {
    let variants = match data {
        syn::Data::Enum(DataEnum { variants, .. }) => variants,
        _ => {
            return Ok(quote_spanned! {
                ident.span() => compile_error!("you can only derive DerivePrimaryKey on enums");
            })
        }
    };

    if variants.is_empty() {
        return Ok(quote_spanned! {
            ident.span() => compile_error!("Entity must have a primary key column. See <https://github.com/SeaQL/sea-orm/issues/485> for details.");
        });
    }

    let variant: Vec<TokenStream> = variants
        .iter()
        .map(|Variant { ident, fields, .. }| match fields {
            Fields::Named(_) => quote! { #ident{..} },
            Fields::Unnamed(_) => quote! { #ident(..) },
            Fields::Unit => quote! { #ident },
        })
        .collect();

    let name: Vec<TokenStream> = variants
        .iter()
        .map(|v| {
            let mut column_name = v.ident.to_string().to_snake_case();
            for attr in v.attrs.iter() {
                if let Some(ident) = attr.path.get_ident() {
                    if ident != "sea_orm" {
                        continue;
                    }
                } else {
                    continue;
                }
                if let Ok(list) = attr.parse_args_with(Punctuated::<Meta, Comma>::parse_terminated)
                {
                    for meta in list.iter() {
                        if let Meta::NameValue(nv) = meta {
                            if let Some(name) = nv.path.get_ident() {
                                if name == "column_name" {
                                    if let Lit::Str(litstr) = &nv.lit {
                                        column_name = litstr.value();
                                    }
                                }
                            }
                        }
                    }
                }
            }
            quote! { #column_name }
        })
        .collect();

    Ok(quote!(
        #[automatically_derived]
        impl sea_orm::Iden for #ident {
            fn unquoted(&self, s: &mut dyn std::fmt::Write) {
                write!(s, "{}", self.as_str()).unwrap();
            }
        }

        #[automatically_derived]
        impl sea_orm::IdenStatic for #ident {
            fn as_str(&self) -> &str {
                match self {
                    #(Self::#variant => #name),*
                }
            }
        }

        #[automatically_derived]
        impl sea_orm::PrimaryKeyToColumn for #ident {
            type Column = Column;

            fn into_column(self) -> Self::Column {
                match self {
                    #(Self::#variant => Self::Column::#variant,)*
                }
            }

            fn from_column(col: Self::Column) -> Option<Self> {
                match col {
                    #(Self::Column::#variant => Some(Self::#variant),)*
                    _ => None,
                }
            }
        }
    ))
}