// Adapted from Aptos::storage::schemadb;
// While most of the Sovereign SDK will be available under both
// MIT and APACHE 2.0 licenses, this file is
// licensed under APACHE 2.0 only.

//! A type-safe interface over [`DB`](crate::DB) column families.

use std::fmt::Debug;

use crate::CodecError;

/// Crate users are expected to know [column
/// family](https://github.com/EighteenZi/rocksdb_wiki/blob/master/Column-Families.md)
/// names beforehand, so they can have `static` lifetimes.
pub type ColumnFamilyName = &'static str;

/// A [`Schema`] is a type-safe interface over a specific column family in a
/// [`DB`](crate::DB). It always a key type ([`KeyCodec`]) and a value type ([`ValueCodec`]).
pub trait Schema: Debug + Send + Sync + 'static + Sized {
    /// The column family name associated with this struct.
    /// Note: all schemas within the same SchemaDB must have distinct column family names.
    const COLUMN_FAMILY_NAME: ColumnFamilyName;

    /// Type of the key.
    type Key: KeyCodec<Self>;

    /// Type of the value.
    type Value: ValueCodec<Self>;
}

/// A [`core::result::Result`] alias with [`CodecError`] as the error type.
pub type Result<T, E = CodecError> = core::result::Result<T, E>;

/// This trait defines a type that can serve as a [`Schema::Key`].
///
/// [`KeyCodec`] is a marker trait with a blaket implementation for all types
/// that are both [`KeyEncoder`] and [`KeyDecoder`]. Having [`KeyEncoder`] and
/// [`KeyDecoder`] as two standalone traits on top of [`KeyCodec`] may seem
/// superflous, but it allows for zero-copy key encoding under specific
/// circumstances. E.g.:
///
/// ```rust
/// use anyhow::Context;
///
/// use sov_schema_db::define_schema;
/// use sov_schema_db::schema::{
///     Schema, KeyEncoder, KeyDecoder, ValueCodec, Result,
/// };
///
/// define_schema!(PersonAgeByName, String, u32, "person_age_by_name");
///
/// impl KeyEncoder<PersonAgeByName> for String {
///     fn encode_key(&self) -> Result<Vec<u8>> {
///         Ok(self.as_bytes().to_vec())
///     }
/// }
///
/// /// What about encoding a `&str`, though? We'd have to copy it into a
/// /// `String` first, which is not ideal. But we can do better:
/// impl<'a> KeyEncoder<PersonAgeByName> for &'a str {
///     fn encode_key(&self) -> Result<Vec<u8>> {
///         Ok(self.as_bytes().to_vec())
///     }
/// }
///
/// impl KeyDecoder<PersonAgeByName> for String {
///     fn decode_key(data: &[u8]) -> Result<Self> {
///         Ok(String::from_utf8(data.to_vec()).context("Can't read key")?)
///     }
/// }
///
/// impl ValueCodec<PersonAgeByName> for u32 {
///     fn encode_value(&self) -> Result<Vec<u8>> {
///         Ok(self.to_le_bytes().to_vec())
///     }
///
///     fn decode_value(data: &[u8]) -> Result<Self> {
///         let mut buf = [0u8; 4];
///         buf.copy_from_slice(data);
///         Ok(u32::from_le_bytes(buf))
///     }
/// }
/// ```
pub trait KeyCodec<S: Schema + ?Sized>: KeyEncoder<S> + KeyDecoder<S> {}

impl<T, S: Schema + ?Sized> KeyCodec<S> for T where T: KeyEncoder<S> + KeyDecoder<S> {}

/// Implementors of this trait can be used to encode keys in the given [`Schema`].
pub trait KeyEncoder<S: Schema + ?Sized>: Sized + PartialEq + Debug {
    /// Converts `self` to bytes to be stored in RocksDB.
    fn encode_key(&self) -> Result<Vec<u8>>;
}

/// Implementors of this trait can be used to decode keys in the given [`Schema`].
pub trait KeyDecoder<S: Schema + ?Sized>: Sized + PartialEq + Debug {
    /// Converts bytes fetched from RocksDB to `Self`.
    fn decode_key(data: &[u8]) -> Result<Self>;
}

/// This trait defines a type that can serve as a [`Schema::Value`].
pub trait ValueCodec<S: Schema + ?Sized>: Sized + PartialEq + Debug {
    /// Converts `self` to bytes to be stored in DB.
    fn encode_value(&self) -> Result<Vec<u8>>;
    /// Converts bytes fetched from DB to `Self`.
    fn decode_value(data: &[u8]) -> Result<Self>;
}

/// A utility macro to define [`Schema`] implementors. You must specify the
/// [`Schema`] implementor's name, the key type, the value type, and the column
/// family name.
///
/// # Example
///
/// ```rust
/// use anyhow::Context;
///
/// use sov_schema_db::define_schema;
/// use sov_schema_db::schema::{
///     Schema, KeyEncoder, KeyDecoder, ValueCodec, Result,
/// };
///
/// define_schema!(PersonAgeByName, String, u32, "person_age_by_name");
///
/// impl KeyEncoder<PersonAgeByName> for String {
///     fn encode_key(&self) -> Result<Vec<u8>> {
///         Ok(self.as_bytes().to_vec())
///     }
/// }
///
/// impl KeyDecoder<PersonAgeByName> for String {
///     fn decode_key(data: &[u8]) -> Result<Self> {
///         Ok(String::from_utf8(data.to_vec()).context("Can't read key")?)
///     }
/// }
///
/// impl ValueCodec<PersonAgeByName> for u32 {
///     fn encode_value(&self) -> Result<Vec<u8>> {
///         Ok(self.to_le_bytes().to_vec())
///     }
///
///     fn decode_value(data: &[u8]) -> Result<Self> {
///         let mut buf = [0u8; 4];
///         buf.copy_from_slice(data);
///         Ok(u32::from_le_bytes(buf))
///     }
/// }
/// ```
#[macro_export]
macro_rules! define_schema {
    ($schema_type:ident, $key_type:ty, $value_type:ty, $cf_name:expr) => {
        #[derive(Debug)]
        pub(crate) struct $schema_type;

        impl $crate::schema::Schema for $schema_type {
            type Key = $key_type;
            type Value = $value_type;

            const COLUMN_FAMILY_NAME: $crate::schema::ColumnFamilyName = $cf_name;
        }
    };
}

#[cfg(feature = "fuzzing")]
pub mod fuzzing {
    use proptest::collection::vec;
    use proptest::prelude::*;

    use super::{KeyDecoder, KeyEncoder, Schema, ValueCodec};

    /// Helper used in tests to assert a (key, value) pair for a certain [`Schema`] is able to convert
    /// to bytes and convert back.
    pub fn assert_encode_decode<S: Schema>(key: &S::Key, value: &S::Value) {
        {
            let encoded = key.encode_key().expect("Encoding key should work.");
            let decoded = S::Key::decode_key(&encoded).expect("Decoding key should work.");
            assert_eq!(*key, decoded);
        }
        {
            let encoded = value.encode_value().expect("Encoding value should work.");
            let decoded = S::Value::decode_value(&encoded).expect("Decoding value should work.");
            assert_eq!(*value, decoded);
        }
    }

    /// Helper used in tests and fuzzers to make sure a schema never panics when decoding random bytes.
    #[allow(unused_must_use)]
    pub fn assert_no_panic_decoding<S: Schema>(bytes: &[u8]) {
        S::Key::decode_key(bytes);
        S::Value::decode_value(bytes);
    }

    pub fn arb_small_vec_u8() -> impl Strategy<Value = Vec<u8>> {
        vec(any::<u8>(), 0..2048)
    }

    #[macro_export]
    macro_rules! test_no_panic_decoding {
        ($schema_type:ty) => {
            use proptest::prelude::*;
            use sov_schema_db::schema::fuzzing::{arb_small_vec_u8, assert_no_panic_decoding};

            proptest! {
                #[test]
                fn test_no_panic_decoding(bytes in arb_small_vec_u8()) {
                    assert_no_panic_decoding::<$schema_type>(&bytes)
                }
            }
        };
    }
}