//! Borsh utils
use {
    borsh::{
        maybestd::io::{Error, Write},
        schema::{BorshSchema, Declaration, Definition, Fields},
        BorshDeserialize, BorshSerialize,
    },
    std::collections::HashMap,
};

/// Get packed length for the given BorchSchema Declaration
fn get_declaration_packed_len(
    declaration: &str,
    definitions: &HashMap<Declaration, Definition>,
) -> usize {
    match definitions.get(declaration) {
        Some(Definition::Array { length, elements }) => {
            *length as usize * get_declaration_packed_len(elements, definitions)
        }
        Some(Definition::Enum { variants }) => {
            1 + variants
                .iter()
                .map(|(_, declaration)| get_declaration_packed_len(declaration, definitions))
                .max()
                .unwrap_or(0)
        }
        Some(Definition::Struct { fields }) => match fields {
            Fields::NamedFields(named_fields) => named_fields
                .iter()
                .map(|(_, declaration)| get_declaration_packed_len(declaration, definitions))
                .sum(),
            Fields::UnnamedFields(declarations) => declarations
                .iter()
                .map(|declaration| get_declaration_packed_len(declaration, definitions))
                .sum(),
            Fields::Empty => 0,
        },
        Some(Definition::Sequence {
            elements: _elements,
        }) => panic!("Missing support for Definition::Sequence"),
        Some(Definition::Tuple { elements }) => elements
            .iter()
            .map(|element| get_declaration_packed_len(element, definitions))
            .sum(),
        None => match declaration {
            "u8" | "i8" => 1,
            "u16" | "i16" => 2,
            "u32" | "i32" => 4,
            "u64" | "i64" => 8,
            "u128" | "i128" => 16,
            "nil" => 0,
            _ => panic!("Missing primitive type: {}", declaration),
        },
    }
}

/// Get the worst-case packed length for the given BorshSchema
///
/// Note: due to the serializer currently used by Borsh, this function cannot
/// be used on-chain in the Safecoin BPF execution environment.
pub fn get_packed_len<S: BorshSchema>() -> usize {
    let schema_container = S::schema_container();
    get_declaration_packed_len(&schema_container.declaration, &schema_container.definitions)
}

/// Deserializes without checking that the entire slice has been consumed
///
/// Normally, `try_from_slice` checks the length of the final slice to ensure
/// that the deserialization uses up all of the bytes in the slice.
///
/// Note that there is a potential issue with this function. Any buffer greater than
/// or equal to the expected size will properly deserialize. For example, if the
/// user passes a buffer destined for a different type, the error won't get caught
/// as easily.
pub fn try_from_slice_unchecked<T: BorshDeserialize>(data: &[u8]) -> Result<T, Error> {
    let mut data_mut = data;
    let result = T::deserialize(&mut data_mut)?;
    Ok(result)
}

/// Helper struct which to count how much data would be written during serialization
#[derive(Default)]
struct WriteCounter {
    count: usize,
}

impl Write for WriteCounter {
    fn write(&mut self, data: &[u8]) -> Result<usize, Error> {
        let amount = data.len();
        self.count += amount;
        Ok(amount)
    }

    fn flush(&mut self) -> Result<(), Error> {
        Ok(())
    }
}

/// Get the packed length for the serialized form of this object instance.
///
/// Useful when working with instances of types that contain a variable-length
/// sequence, such as a Vec or HashMap.  Since it is impossible to know the packed
/// length only from the type's schema, this can be used when an instance already
/// exists, to figure out how much space to allocate in an account.
pub fn get_instance_packed_len<T: BorshSerialize>(instance: &T) -> Result<usize, Error> {
    let mut counter = WriteCounter::default();
    instance.serialize(&mut counter)?;
    Ok(counter.count)
}

#[cfg(test)]
mod tests {
    use {
        super::*,
        borsh::{maybestd::io::ErrorKind, BorshSchema, BorshSerialize},
        std::{collections::HashMap, mem::size_of},
    };

    #[derive(PartialEq, Clone, Debug, BorshSerialize, BorshDeserialize, BorshSchema)]
    enum TestEnum {
        NoValue,
        Value(u32),
        StructValue {
            #[allow(dead_code)]
            number: u64,
            #[allow(dead_code)]
            array: [u8; 8],
        },
    }

    // for test simplicity
    impl Default for TestEnum {
        fn default() -> Self {
            Self::NoValue
        }
    }

    #[derive(Default, BorshSerialize, BorshDeserialize, BorshSchema)]
    struct TestStruct {
        pub array: [u64; 16],
        pub number_u128: u128,
        pub number_u32: u32,
        pub tuple: (u8, u16),
        pub enumeration: TestEnum,
    }

    #[derive(Debug, PartialEq, BorshSerialize, BorshDeserialize, BorshSchema)]
    struct Child {
        pub data: [u8; 64],
    }

    #[derive(Debug, PartialEq, BorshSerialize, BorshDeserialize, BorshSchema)]
    struct Parent {
        pub data: Vec<Child>,
    }

    #[test]
    fn unchecked_deserialization() {
        let data = vec![
            Child { data: [0u8; 64] },
            Child { data: [1u8; 64] },
            Child { data: [2u8; 64] },
        ];
        let parent = Parent { data };

        // exact size, both work
        let mut byte_vec = vec![0u8; 4 + get_packed_len::<Child>() * 3];
        let mut bytes = byte_vec.as_mut_slice();
        parent.serialize(&mut bytes).unwrap();
        let deserialized = Parent::try_from_slice(&byte_vec).unwrap();
        assert_eq!(deserialized, parent);
        let deserialized = try_from_slice_unchecked::<Parent>(&byte_vec).unwrap();
        assert_eq!(deserialized, parent);

        // too big, only unchecked works
        let mut byte_vec = vec![0u8; 4 + get_packed_len::<Child>() * 10];
        let mut bytes = byte_vec.as_mut_slice();
        parent.serialize(&mut bytes).unwrap();
        let err = Parent::try_from_slice(&byte_vec).unwrap_err();
        assert_eq!(err.kind(), ErrorKind::InvalidData);
        let deserialized = try_from_slice_unchecked::<Parent>(&byte_vec).unwrap();
        assert_eq!(deserialized, parent);
    }

    #[test]
    fn packed_len() {
        assert_eq!(
            get_packed_len::<TestEnum>(),
            size_of::<u8>() + size_of::<u64>() + size_of::<u8>() * 8
        );
        assert_eq!(
            get_packed_len::<TestStruct>(),
            size_of::<u64>() * 16
                + size_of::<u128>()
                + size_of::<u32>()
                + size_of::<u8>()
                + size_of::<u16>()
                + get_packed_len::<TestEnum>()
        );
    }

    #[test]
    fn instance_packed_len_matches_packed_len() {
        let enumeration = TestEnum::StructValue {
            number: u64::MAX,
            array: [255; 8],
        };
        assert_eq!(
            get_packed_len::<TestEnum>(),
            get_instance_packed_len(&enumeration).unwrap(),
        );
        let test_struct = TestStruct {
            enumeration,
            ..TestStruct::default()
        };
        assert_eq!(
            get_packed_len::<TestStruct>(),
            get_instance_packed_len(&test_struct).unwrap(),
        );
        assert_eq!(
            get_packed_len::<u8>(),
            get_instance_packed_len(&0u8).unwrap(),
        );
        assert_eq!(
            get_packed_len::<u16>(),
            get_instance_packed_len(&0u16).unwrap(),
        );
        assert_eq!(
            get_packed_len::<u32>(),
            get_instance_packed_len(&0u32).unwrap(),
        );
        assert_eq!(
            get_packed_len::<u64>(),
            get_instance_packed_len(&0u64).unwrap(),
        );
        assert_eq!(
            get_packed_len::<u128>(),
            get_instance_packed_len(&0u128).unwrap(),
        );
        assert_eq!(
            get_packed_len::<[u8; 10]>(),
            get_instance_packed_len(&[0u8; 10]).unwrap(),
        );
        assert_eq!(
            get_packed_len::<(i8, i16, i32, i64, i128)>(),
            get_instance_packed_len(&(i8::MAX, i16::MAX, i32::MAX, i64::MAX, i128::MAX)).unwrap(),
        );
    }

    #[test]
    fn instance_packed_len_with_vec() {
        let data = vec![
            Child { data: [0u8; 64] },
            Child { data: [1u8; 64] },
            Child { data: [2u8; 64] },
            Child { data: [3u8; 64] },
            Child { data: [4u8; 64] },
            Child { data: [5u8; 64] },
        ];
        let parent = Parent { data };
        assert_eq!(
            get_instance_packed_len(&parent).unwrap(),
            4 + parent.data.len() * get_packed_len::<Child>()
        );
    }

    #[derive(Debug, PartialEq, BorshSerialize, BorshDeserialize, BorshSchema)]
    struct StructWithHashMap {
        data: HashMap<String, TestEnum>,
    }

    #[test]
    fn instance_packed_len_with_varying_sizes_in_hashmap() {
        let mut data = HashMap::new();
        let string1 = "the first string, it's actually really really long".to_string();
        let enum1 = TestEnum::NoValue;
        let string2 = "second string, shorter".to_string();
        let enum2 = TestEnum::Value(u32::MAX);
        let string3 = "third".to_string();
        let enum3 = TestEnum::StructValue {
            number: 0,
            array: [0; 8],
        };
        data.insert(string1.clone(), enum1.clone());
        data.insert(string2.clone(), enum2.clone());
        data.insert(string3.clone(), enum3.clone());
        let instance = StructWithHashMap { data };
        assert_eq!(
            get_instance_packed_len(&instance).unwrap(),
            4 + get_instance_packed_len(&string1).unwrap()
                + get_instance_packed_len(&enum1).unwrap()
                + get_instance_packed_len(&string2).unwrap()
                + get_instance_packed_len(&enum2).unwrap()
                + get_instance_packed_len(&string3).unwrap()
                + get_instance_packed_len(&enum3).unwrap()
        );
    }
}