// LNP/BP client-side-validation foundation libraries implementing LNPBP
// specifications & standards (LNPBP-4, 7, 8, 9, 42, 81)
//
// Written in 2019-2022 by
//     Dr. Maxim Orlovsky <orlovsky@pandoracore.com>
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to
// the public domain worldwide. This software is distributed without
// any warranty.
//
// You should have received a copy of the Apache 2.0 License along with this
// software. If not, see <https://opensource.org/licenses/Apache-2.0>.

//! Encoding and data preparation for commitment procedures in
//! client-side-validation as defined by [LNPBP-9] standard.
//!
//! Client-side-validation commitment process requires special encoding of
//! the data. While [`strict_encoding`] is the main standard for atomic data
//! types in client-side-validation world and should be used during internal
//! protocol-specific data validation, commitments may require processes of
//! merklization arrays of data items, or hiding confidential parts of the
//! data via hashing, pedersen commitments and so on. Thus, additinally to
//! strict encoding, a set of different encodings and data convolution and
//! hiding procedures are defined in this `commit_encode` module of the
//! `commit_verify` library. This includes:
//! - **merklization** procedures operating special types of tagged hashes and
//!   committing to the depth of each node
//! - **commit conceal** procedures, making data confidential (transforming
//!   types into confidential versions)
//! - **commit encoding**, which should *conceal* all the data and merklize
//!   arrays, and only them performing their *strict encoding*
//! - **consensus commitment**, which wraps all of the above as a final API,
//!   producing of a single commitment to the client-validated data.
//!
//! [LNPBP-9]: https://github.com/LNP-BP/LNPBPs/blob/master/lnpbp-0009.md

use std::io;

use bitcoin_hashes::HashEngine;

use crate::{CommitVerify, PrehashedProtocol};

/// Prepares the data to the *consensus commit* procedure by first running
/// necessary conceal and merklization procedures, and them performing strict
/// encoding for the resulted data.
pub trait CommitEncode {
    /// Encodes the data for the commitment by writing them directly into a
    /// [`io::Write`] writer instance
    fn commit_encode<E: io::Write>(&self, e: E) -> usize;

    /// Serializes data for the commitment in-memory into a newly allocated
    /// array
    fn commit_serialize(&self) -> Vec<u8> {
        let mut vec = Vec::new();
        self.commit_encode(&mut vec);
        vec
    }
}

/// Convenience macro for commit-encoding list of the data
#[macro_export]
macro_rules! commit_encode_list {
    ( $encoder:ident; $($item:expr),+ ) => {
        {
            let mut len = 0usize;
            $(
                len += $item.commit_encode(&mut $encoder);
            )+
            len
        }
    }
}

/// Marker trait defining specific encoding strategy which should be used for
/// automatic implementation of [`CommitEncode`].
pub trait Strategy {
    /// Specific strategy. List of supported strategies:
    /// - [`strategies::UsingStrict`]
    /// - [`strategies::UsingConceal`]
    /// - [`strategies::UsingHash`]
    type Strategy;
}

/// Strategies simplifying implementation of [`CommitEncode`] trait.
///
/// Implemented after concept by Martin Habovštiak <martin.habovstiak@gmail.com>
pub mod strategies {
    use bitcoin_hashes::Hash;

    use super::*;

    /// Encodes by running strict *encoding procedure* on the raw data without
    /// any pre-processing.
    ///
    /// Should not be used for array types (require manual [`CommitEncode`]
    /// implementation involving merklization) or data which may contain
    /// confidential or sensitive information (use [`UsingConceal`] in this
    /// case).
    pub struct UsingStrict;

    /// Encodes data by first converting them into confidential version
    /// (*concealing*) by running [`CommitConceal::commit_conceal`] first and
    /// returning its result serialized with strict encoding rules.
    pub struct UsingConceal;

    /// Encodes data by first hashing them with the provided hash function `H`
    /// and then returning its result serialized with strict encoding rules.
    pub struct UsingHash<H>(std::marker::PhantomData<H>)
    where
        H: Hash + strict_encoding::StrictEncode;

    impl<T> CommitEncode for amplify::Holder<T, UsingStrict>
    where
        T: strict_encoding::StrictEncode,
    {
        fn commit_encode<E: io::Write>(&self, e: E) -> usize {
            self.as_inner().strict_encode(e).expect(
                "Strict encoding must not fail for types using \
                 `strategy::UsingStrict`",
            )
        }
    }

    impl<T> CommitEncode for amplify::Holder<T, UsingConceal>
    where
        T: CommitConceal,
        <T as CommitConceal>::ConcealedCommitment: CommitEncode,
    {
        fn commit_encode<E: io::Write>(&self, e: E) -> usize {
            self.as_inner().commit_conceal().commit_encode(e)
        }
    }

    impl<T, H> CommitEncode for amplify::Holder<T, UsingHash<H>>
    where
        H: Hash + strict_encoding::StrictEncode,
        T: strict_encoding::StrictEncode,
    {
        fn commit_encode<E: io::Write>(&self, e: E) -> usize {
            let mut engine = H::engine();
            engine.input(
                &strict_encoding::strict_serialize(self.as_inner()).expect(
                    "Strict encoding of hash strategy-based commitment data \
                     must not fail",
                ),
            );
            let hash = H::from_engine(engine);
            hash.strict_encode(e).expect(
                "Strict encoding must not fail for types using \
                 `strategy::UsingHash`",
            )
        }
    }

    impl<K, V> CommitEncode for (K, V)
    where
        K: CommitEncode,
        V: CommitEncode,
    {
        fn commit_encode<E: io::Write>(&self, mut e: E) -> usize {
            self.0.commit_encode(&mut e) + self.1.commit_encode(&mut e)
        }
    }

    impl<A, B, C> CommitEncode for (A, B, C)
    where
        A: CommitEncode,
        B: CommitEncode,
        C: CommitEncode,
    {
        fn commit_encode<E: io::Write>(&self, mut e: E) -> usize {
            self.0.commit_encode(&mut e)
                + self.1.commit_encode(&mut e)
                + self.2.commit_encode(&mut e)
        }
    }

    impl<T> CommitEncode for T
    where
        T: Strategy + Clone,
        amplify::Holder<T, <T as Strategy>::Strategy>: CommitEncode,
    {
        fn commit_encode<E: io::Write>(&self, e: E) -> usize {
            amplify::Holder::new(self.clone()).commit_encode(e)
        }
    }

    impl Strategy for usize {
        type Strategy = UsingStrict;
    }
    impl Strategy for u8 {
        type Strategy = UsingStrict;
    }
    impl Strategy for u16 {
        type Strategy = UsingStrict;
    }
    impl Strategy for u32 {
        type Strategy = UsingStrict;
    }
    impl Strategy for u64 {
        type Strategy = UsingStrict;
    }
    impl Strategy for i8 {
        type Strategy = UsingStrict;
    }
    impl Strategy for i16 {
        type Strategy = UsingStrict;
    }
    impl Strategy for i32 {
        type Strategy = UsingStrict;
    }
    impl Strategy for i64 {
        type Strategy = UsingStrict;
    }
    impl Strategy for String {
        type Strategy = UsingStrict;
    }
    impl Strategy for &str {
        type Strategy = UsingStrict;
    }
    impl Strategy for &[u8] {
        type Strategy = UsingStrict;
    }
    impl Strategy for Vec<u8> {
        type Strategy = UsingStrict;
    }

    #[cfg(feature = "grin_secp256k1zkp")]
    impl Strategy for secp256k1zkp::pedersen::Commitment {
        type Strategy = strategies::UsingStrict;
    }

    #[cfg(feature = "grin_secp256k1zkp")]
    impl Strategy for secp256k1zkp::pedersen::RangeProof {
        type Strategy = strategies::UsingHash<bitcoin_hashes::sha256::Hash>;
    }

    impl<T> Strategy for &T
    where
        T: Strategy,
    {
        type Strategy = T::Strategy;
    }
}

/// Trait that should perform conversion of a given client-side-validated data
/// type into its confidential version concealing all of its data.
///
/// Since the resulting concealed version must be unequally derived from the
/// original data with negligible risk of collisions, it is a form of
/// *commitment* – thus the procedure called *commit-conceal* and not just a
/// *conceal*.
pub trait CommitConceal {
    /// The resulting confidential type concealing and committing to the
    /// original data
    type ConcealedCommitment;

    /// Performs commit-conceal procedure returning confidential data
    /// concealing and committing to the original data
    fn commit_conceal(&self) -> Self::ConcealedCommitment;
}

/// High-level API used in client-side validation for producing a single
/// commitment to the data, which includes running all necessary procedures like
/// concealment with [`CommitConceal`], merklization, strict encoding,
/// wrapped into [`CommitEncode`], followed by the actual commitment to its
/// output.
pub trait ConsensusCommit: Sized + CommitEncode {
    /// Type of the resulting commitment
    type Commitment: CommitVerify<Vec<u8>, PrehashedProtocol>;

    /// Performs commitment to client-side-validated data
    #[inline]
    fn consensus_commit(&self) -> Self::Commitment {
        let mut encoder = io::Cursor::new(vec![]);
        self.commit_encode(&mut encoder);
        Self::Commitment::commit(&encoder.into_inner())
    }

    /// Verifies commitment to client-side-validated data
    #[inline]
    fn consensus_verify(&self, commitment: &Self::Commitment) -> bool {
        let mut encoder = io::Cursor::new(vec![]);
        self.commit_encode(&mut encoder);
        commitment.verify(&encoder.into_inner())
    }
}