// Licensed to the Apache Software Foundation (ASF) under one

// or more contributor license agreements.  See the NOTICE file

// distributed with this work for additional information

// regarding copyright ownership.  The ASF licenses this file

// to you under the Apache License, Version 2.0 (the

// "License"); you may not use this file except in compliance

// with the License.  You may obtain a copy of the License at

//

//   http://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing,

// software distributed under the License is distributed on an

// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY

// KIND, either express or implied.  See the License for the

// specific language governing permissions and limitations

// under the License.

use arrow_buffer::Buffer;

use arrow_schema::ArrowError;

/// The maximum number of bytes that can be stored inline in a byte view.

///

/// See [`ByteView`] and [`GenericByteViewArray`] for more information on the

/// layout of the views.

///

/// [`GenericByteViewArray`]: https://docs.rs/arrow/latest/arrow/array/struct.GenericByteViewArray.html

pub const MAX_INLINE_VIEW_LEN: u32 = 12;

/// Helper to access views of [`GenericByteViewArray`] (`StringViewArray` and

/// `BinaryViewArray`) where the length is greater than 12 bytes.

///

/// See Also:

/// * [`GenericByteViewArray`] for more information on the layout of the views.

/// * [`validate_binary_view`] and [`validate_string_view`] to validate

///

/// # Example: Create a new u128 view

///

/// ```rust

/// # use arrow_data::ByteView;;

/// // Create a view for a string of length 20

/// // first four bytes are "Rust"

/// // stored in buffer 3

/// // at offset 42

/// let prefix = "Rust";

/// let view = ByteView::new(20, prefix.as_bytes())

///   .with_buffer_index(3)

///   .with_offset(42);

///

/// // create the final u128

/// let v = view.as_u128();

/// assert_eq!(v, 0x2a000000037473755200000014);

/// ```

///

/// # Example: decode a `u128` into its constituent fields

/// ```rust

/// # use arrow_data::ByteView;

/// // Convert a u128 to a ByteView

/// // See validate_{string,binary}_view functions to validate

/// let v = ByteView::from(0x2a000000037473755200000014);

///

/// assert_eq!(v.length, 20);

/// assert_eq!(v.prefix, 0x74737552);

/// assert_eq!(v.buffer_index, 3);

/// assert_eq!(v.offset, 42);

/// ```

///

/// [`GenericByteViewArray`]: https://docs.rs/arrow/latest/arrow/array/struct.GenericByteViewArray.html

#[derive(Debug, Copy, Clone, Default)]

#[repr(C)]

pub struct ByteView {

    /// The length of the string/bytes.

    pub length: u32,

    /// First 4 bytes of string/bytes data.

    pub prefix: u32,

    /// The buffer index.

    pub buffer_index: u32,

    /// The offset into the buffer.

    pub offset: u32,

}

impl ByteView {

    /// Construct a [`ByteView`] for data `length` of bytes with the specified prefix.

    ///

    /// See example on [`ByteView`] docs

    ///

    /// Notes:

    /// * the length should always be greater than [`MAX_INLINE_VIEW_LEN`]

    ///   (Data less than 12 bytes is stored as an inline view)

    /// * buffer and offset are set to `0`

    ///

    /// # Panics

    /// If the prefix is not exactly 4 bytes

    #[inline]

    pub fn new(length: u32, prefix: &[u8]) -> Self {

        debug_assert!(length > MAX_INLINE_VIEW_LEN);

        Self {

            length,

            prefix: u32::from_le_bytes(prefix.try_into().unwrap()),

            buffer_index: 0,

            offset: 0,

        }

    }

    /// Set the [`Self::buffer_index`] field

    #[inline]

    pub fn with_buffer_index(mut self, buffer_index: u32) -> Self {

        self.buffer_index = buffer_index;

        self

    }

    /// Set the [`Self::offset`] field

    #[inline]

    pub fn with_offset(mut self, offset: u32) -> Self {

        self.offset = offset;

        self

    }

    #[inline(always)]

    /// Convert `ByteView` to `u128` by concatenating the fields

    pub fn as_u128(self) -> u128 {

        (self.length as u128)

            | ((self.prefix as u128) << 32)

            | ((self.buffer_index as u128) << 64)

            | ((self.offset as u128) << 96)

    }

}

impl From<u128> for ByteView {

    #[inline]

    fn from(value: u128) -> Self {

        Self {

            length: value as u32,

            prefix: (value >> 32) as u32,

            buffer_index: (value >> 64) as u32,

            offset: (value >> 96) as u32,

        }

    }

}

impl From<ByteView> for u128 {

    #[inline]

    fn from(value: ByteView) -> Self {

        value.as_u128()

    }

}

/// Validates the combination of `views` and `buffers` is a valid BinaryView

pub fn validate_binary_view(views: &[u128], buffers: &[Buffer]) -> Result<(), ArrowError> {

    validate_view_impl(views, buffers, |_, _| Ok(()))

}

/// Validates the combination of `views` and `buffers` is a valid StringView

pub fn validate_string_view(views: &[u128], buffers: &[Buffer]) -> Result<(), ArrowError> {

    validate_view_impl(views, buffers, |idx, b| {

        std::str::from_utf8(b).map_err(|e| {

            ArrowError::InvalidArgumentError(format!(

                "Encountered non-UTF-8 data at index {idx}: {e}"

            ))

        })?;

        Ok(())

    })

}

fn validate_view_impl<F>(views: &[u128], buffers: &[Buffer], f: F) -> Result<(), ArrowError>

where

    F: Fn(usize, &[u8]) -> Result<(), ArrowError>,

{

    for (idx, v) in views.iter().enumerate() {

        let len = *v as u32;

        if len <= MAX_INLINE_VIEW_LEN {

            if len < MAX_INLINE_VIEW_LEN && (v >> (32 + len * 8)) != 0 {

                return Err(ArrowError::InvalidArgumentError(format!(

                    "View at index {idx} contained non-zero padding for string of length {len}",

                )));

            }

            f(idx, &v.to_le_bytes()[4..4 + len as usize])?;

        } else {

            let view = ByteView::from(*v);

            let data = buffers.get(view.buffer_index as usize).ok_or_else(|| {

                ArrowError::InvalidArgumentError(format!(

                    "Invalid buffer index at {idx}: got index {} but only has {} buffers",

                    view.buffer_index,

                    buffers.len()

                ))

            })?;

            let start = view.offset as usize;

            let end = start + len as usize;

            let b = data.get(start..end).ok_or_else(|| {

                ArrowError::InvalidArgumentError(format!(

                    "Invalid buffer slice at {idx}: got {start}..{end} but buffer {} has length {}",

                    view.buffer_index,

                    data.len()

                ))

            })?;

            if !b.starts_with(&view.prefix.to_le_bytes()) {

                return Err(ArrowError::InvalidArgumentError(

                    "Mismatch between embedded prefix and data".to_string(),

                ));

            }

            f(idx, b)?;

        }

    }

    Ok(())

}