//! Derive macros for the Compact codec traits.

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#![cfg_attr(not(test), warn(unused_crate_dependencies))]
#![allow(unreachable_pub, missing_docs)]
#![cfg_attr(docsrs, feature(doc_cfg))]

use proc_macro::TokenStream;
use quote::{format_ident, quote};
use syn::{
    bracketed,
    parse::{Parse, ParseStream},
    parse_macro_input, DeriveInput, Result, Token,
};

mod arbitrary;
mod compact;

#[derive(Clone)]
pub(crate) struct ZstdConfig {
    compressor: syn::Path,
    decompressor: syn::Path,
}

/// Derives the `Compact` trait for custom structs, optimizing serialization with a possible
/// bitflag struct.
///
/// ## Implementation:
/// The derived `Compact` implementation leverages a bitflag struct when needed to manage the
/// presence of certain field types, primarily for compacting fields efficiently. This bitflag
/// struct records information about fields that require a small, fixed number of bits for their
/// encoding, such as `bool`, `Option<T>`, or other small types.
///
/// ### Bit Sizes for Fields:
/// The amount of bits used to store a field size is determined by the field's type. For specific
/// types, a fixed number of bits is allocated (from `fn get_bit_size`):
/// - `bool`, `Option<T>`, `TransactionKind`, `Signature`: **1 bit**
/// - `TxType`: **2 bits**
/// - `u64`, `BlockNumber`, `TxNumber`, `ChainId`, `NumTransactions`: **4 bits**
/// - `u128`: **5 bits**
/// - `U256`: **6 bits**
///
/// ### Warning: Extending structs, unused bits and backwards compatibility:
/// When the bitflag only has one bit left (for example, when adding many `Option<T>` fields),
/// you should introduce a new struct (e.g., `TExtension`) with additional fields, and use
/// `Option<TExtension>` in the original struct. This approach allows further field extensions while
/// maintaining backward compatibility.
///
/// ### Limitations:
/// - Fields not listed above, or types such `Vec`, or large composite types, should manage their
///   own encoding and do not rely on the bitflag struct.
/// - `Bytes` fields and any types containing a `Bytes` field should be placed last to ensure
///   efficient decoding.
#[proc_macro_derive(Compact, attributes(maybe_zero, reth_codecs))]
pub fn derive(input: TokenStream) -> TokenStream {
    compact::derive(parse_macro_input!(input as DeriveInput), None)
}

/// Adds `zstd` compression to derived [`Compact`].
#[proc_macro_derive(CompactZstd, attributes(maybe_zero, reth_codecs, reth_zstd))]
pub fn derive_zstd(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);

    let mut compressor = None;
    let mut decompressor = None;

    for attr in &input.attrs {
        if attr.path().is_ident("reth_zstd") &&
            let Err(err) = attr.parse_nested_meta(|meta| {
                if meta.path.is_ident("compressor") {
                    let value = meta.value()?;
                    let path: syn::Path = value.parse()?;
                    compressor = Some(path);
                } else if meta.path.is_ident("decompressor") {
                    let value = meta.value()?;
                    let path: syn::Path = value.parse()?;
                    decompressor = Some(path);
                } else {
                    return Err(meta.error("unsupported attribute"));
                }
                Ok(())
            })
        {
            return err.to_compile_error().into();
        }
    }

    let (Some(compressor), Some(decompressor)) = (compressor, decompressor) else {
        return quote! {
            compile_error!("missing compressor or decompressor attribute");
        }
        .into();
    };

    compact::derive(input, Some(ZstdConfig { compressor, decompressor }))
}

/// Generates tests for given type.
///
/// If `compact` or `rlp` is passed to `add_arbitrary_tests`, there will be proptest roundtrip tests
/// generated. An integer value passed will limit the number of proptest cases generated (default:
/// 256).
///
/// Examples:
/// * `#[add_arbitrary_tests]`: will derive arbitrary with no tests.
/// * `#[add_arbitrary_tests(rlp)]`: will derive arbitrary and generate rlp roundtrip proptests.
/// * `#[add_arbitrary_tests(rlp, 10)]`: will derive arbitrary and generate rlp roundtrip proptests.
///   Limited to 10 cases.
/// * `#[add_arbitrary_tests(compact, rlp)]`. will derive arbitrary and generate rlp and compact
///   roundtrip proptests.
#[proc_macro_attribute]
pub fn add_arbitrary_tests(args: TokenStream, input: TokenStream) -> TokenStream {
    let ast = parse_macro_input!(input as DeriveInput);

    let tests =
        arbitrary::maybe_generate_tests(args, &ast.ident, &format_ident!("{}Tests", ast.ident));
    quote! {
        #ast
        #tests
    }
    .into()
}

struct GenerateTestsInput {
    args: TokenStream,
    ty: syn::Type,
    mod_name: syn::Ident,
}

impl Parse for GenerateTestsInput {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        input.parse::<Token![#]>()?;

        let args;
        bracketed!(args in input);

        let args = args.parse::<proc_macro2::TokenStream>()?;
        let ty = input.parse()?;

        input.parse::<Token![,]>()?;
        let mod_name = input.parse()?;

        Ok(Self { args: args.into(), ty, mod_name })
    }
}

/// Generates tests for given type based on passed parameters.
///
/// See `arbitrary::maybe_generate_tests` for more information.
///
/// Examples:
/// * `generate_tests!(#[rlp] MyType, MyTypeTests)`: will generate rlp roundtrip tests for `MyType`
///   in a module named `MyTypeTests`.
/// * `generate_tests!(#[compact, 10] MyType, MyTypeTests)`: will generate compact roundtrip tests
///   for `MyType` limited to 10 cases.
#[proc_macro]
pub fn generate_tests(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as GenerateTestsInput);

    arbitrary::maybe_generate_tests(input.args, &input.ty, &input.mod_name).into()
}
