vfsi-core 0.1.7

use super::support::FsReadResult as OwnedReadResult;
use super::*;
use std::path::Path;

/// One consuming read operation. Construction performs no I/O or allocation.
/// Caller buffers are borrowed only until `Vfsi::vread` returns, including on errors.
pub struct ReadOp<'a, H: crate::api::FileHandle + 'a> {
    source: OpSource<'a, H>,
}
enum OpSource<'a, H: crate::api::FileHandle + 'a> {
    Whole(&'a Path),
    Range(H::ReadRequest<'a>, usize),
    Into(H::ReadIntoRequest<'a>, usize),
}
impl<H: crate::api::FileHandle> std::fmt::Debug for ReadOp<'_, H> {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match &self.source {
            OpSource::Whole(path) => formatter.debug_tuple("ReadOp::whole").field(path).finish(),
            OpSource::Range(_, length) => formatter
                .debug_struct("ReadOp::range")
                .field("length", length)
                .finish_non_exhaustive(),
            OpSource::Into(_, length) => formatter
                .debug_struct("ReadOp::into")
                .field("length", length)
                .finish_non_exhaustive(),
        }
    }
}
impl<'a, H: crate::api::FileHandle + 'a> From<&'a str> for ReadOp<'a, H> {
    fn from(path: &'a str) -> Self {
        Self::whole(path)
    }
}
impl<'a, H: crate::api::FileHandle + 'a> From<&'a Path> for ReadOp<'a, H> {
    fn from(path: &'a Path) -> Self {
        Self::whole(path)
    }
}
impl<'a, H: crate::api::FileHandle + 'a> ReadOp<'a, H> {
    /// Collect a complete file; fail instead of truncating at the byte budget.
    pub fn whole<P: AsRef<Path> + ?Sized>(path: &'a P) -> Self {
        Self {
            source: OpSource::Whole(path.as_ref()),
        }
    }
    /// Allocate a positional range. Short progress and EOF are reported explicitly.
    pub fn range(file: &'a H, offset: u64, length: usize) -> Self {
        Self {
            source: OpSource::Range(file.read_request_at(offset, length), length),
        }
    }
    /// Fill caller storage at an absolute offset, without changing the cursor.
    /// The request length is exactly `buffer.len()`.
    pub fn into(file: &'a H, offset: u64, buffer: &'a mut [u8]) -> Self {
        let length = buffer.len();
        Self {
            source: OpSource::Into(file.read_request_at_into(offset, buffer), length),
        }
    }
    /// Inspect a complete-file path from an external `Vfsi` implementation.
    pub fn whole_file_path(&self) -> Option<&'a Path> {
        match &self.source {
            OpSource::Whole(path) => Some(*path),
            _ => None,
        }
    }
    /// Borrow an allocating range request from an external implementation.
    pub fn range_ref(&self) -> Option<&H::ReadRequest<'a>> {
        match &self.source {
            OpSource::Range(request, _) => Some(request),
            _ => None,
        }
    }
    /// Borrow a caller-buffer request exclusively from an external implementation.
    pub fn buffer_request_mut(&mut self) -> Option<&mut H::ReadIntoRequest<'a>> {
        match &mut self.source {
            OpSource::Into(request, _) => Some(request),
            _ => None,
        }
    }
}

/// Progress for one operation, with no borrowed references to caller storage.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ReadResult {
    /// Resolved absolute offset; zero for a complete-file operation.
    pub(crate) offset: u64,
    /// Number of valid bytes in owned data or the caller's buffer.
    pub(crate) read: usize,
    /// True when the backend observed end of file.
    pub(crate) eof: bool,
    /// Owned contents for `whole`/`range`; `None` for `into`, including empty reads.
    pub(crate) data: Option<Vec<u8>>,
}

impl ReadResult {
    /// Owned contents. The byte count is derived, never independently supplied.
    pub fn owned(offset: u64, data: Vec<u8>, eof: bool) -> Self {
        Self {
            offset,
            read: data.len(),
            eof,
            data: Some(data),
        }
    }
    /// Progress in caller storage, for implementing `Vfsi`. The implementation
    /// must ensure `read` does not exceed the corresponding destination length.
    pub const fn buffered(offset: u64, read: usize, eof: bool) -> Self {
        Self {
            offset,
            read,
            eof,
            data: None,
        }
    }
    pub const fn offset(&self) -> u64 {
        self.offset
    }
    pub const fn read(&self) -> usize {
        self.read
    }
    pub const fn eof(&self) -> bool {
        self.eof
    }
    pub fn data(&self) -> Option<&[u8]> {
        self.data.as_deref()
    }
    pub fn into_data(self) -> Option<Vec<u8>> {
        self.data
    }
    pub const fn is_buffered(&self) -> bool {
        self.data.is_none()
    }
}

/// Aggregate logical byte budget, defaulting to the client's policy (16 MiB).
/// Range request lengths must fit even if EOF returns fewer bytes. Complete
/// files share the remaining returned-data budget and fail rather than truncate.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ReadOptions {
    max_total_bytes: Option<std::num::NonZeroUsize>,
}
impl ReadOptions {
    /// Inherit the client's aggregate read budget.
    pub const fn new() -> Self {
        Self {
            max_total_bytes: None,
        }
    }
    /// Override the aggregate budget for this call; `None` restores inheritance.
    /// Only nonzero overrides are representable. Stream larger files instead
    /// of raising this when bounded memory is required.
    pub const fn max_total_bytes(mut self, bytes: Option<std::num::NonZeroUsize>) -> Self {
        self.max_total_bytes = bytes;
        self
    }
    /// None inherits the client's configured read budget.
    pub const fn total_byte_limit(self) -> Option<std::num::NonZeroUsize> {
        self.max_total_bytes
    }
    /// Resolve an inherited aggregate budget against the client's default.
    pub fn limit_or(self, default: usize) -> usize {
        self.max_total_bytes
            .map_or(default, std::num::NonZeroUsize::get)
    }
}

impl Default for ReadOptions {
    fn default() -> Self {
        Self::new()
    }
}
pub fn consume_ops<'a, H: crate::api::FileHandle + 'a>(
    ops: impl IntoIterator<Item = ReadOp<'a, H>>,
    budget: usize,
    owned: impl FnOnce(&[ReadRequest<'a, H::ReadRequest<'a>>], usize) -> Result<Vec<OwnedReadResult>>,
    buffers: impl FnOnce(
        &mut [H::ReadIntoRequest<'a>],
        usize,
    ) -> Result<Vec<crate::api::ReadIntoResult>>,
) -> Result<Vec<ReadResult>> {
    let mut owned_ops = Vec::new();
    let mut owned_indices = Vec::new();
    let mut buffer_ops = Vec::new();
    let mut buffer_indices = Vec::new();
    let mut requested = 0usize;
    let mut count = 0usize;
    for (index, op) in ops.into_iter().enumerate() {
        count += 1;
        let length = match &op.source {
            OpSource::Whole(_) => 0,
            OpSource::Range(_, length) | OpSource::Into(_, length) => *length,
        };
        requested = requested
            .checked_add(length)
            .filter(|bytes| *bytes <= budget)
            .ok_or_else(|| Error::client(index, libc::EFBIG as u32))?;
        match op.source {
            OpSource::Whole(path) => {
                owned_ops.push(ReadRequest::whole_file(path));
                owned_indices.push(index);
            }
            OpSource::Range(request, _) => {
                owned_ops.push(ReadRequest::range(request));
                owned_indices.push(index);
            }
            OpSource::Into(request, _) => {
                buffer_ops.push(request);
                buffer_indices.push(index);
            }
        }
    }
    let remap = |error: Error, indices: &[usize]| match error.index() {
        Some(index) if index < indices.len() => error.with_index(indices[index]),
        Some(_) => Error::transport(None, "invalid vread_native backend error index"),
        None => error,
    };
    let buffered = if buffer_ops.is_empty() {
        Vec::new()
    } else {
        buffers(&mut buffer_ops, budget).map_err(|e| remap(e, &buffer_indices))?
    };
    drop(buffer_ops);
    if buffered.len() != buffer_indices.len() {
        return Err(Error::transport(
            None,
            "invalid vread_native buffer result count",
        ));
    }
    let mut remaining = budget;
    for result in &buffered {
        remaining = remaining
            .checked_sub(result.read)
            .ok_or_else(|| Error::transport(None, "vread_native backend exceeded byte budget"))?;
    }
    let allocated = if owned_ops.is_empty() {
        Vec::new()
    } else {
        owned(&owned_ops, remaining).map_err(|e| remap(e, &owned_indices))?
    };
    if allocated.len() != owned_indices.len() {
        return Err(Error::transport(
            None,
            "invalid vread_native owned result count",
        ));
    }
    let mut output: Vec<Option<ReadResult>> = (0..count).map(|_| None).collect();
    for (index, result) in buffer_indices.into_iter().zip(buffered) {
        output[index] = Some(ReadResult {
            offset: result.offset,
            read: result.read,
            eof: result.eof,
            data: None,
        });
    }
    for (index, result) in owned_indices.into_iter().zip(allocated) {
        remaining = remaining
            .checked_sub(result.data.len())
            .ok_or_else(|| Error::transport(None, "vread_native backend exceeded byte budget"))?;
        output[index] = Some(ReadResult {
            offset: result.offset,
            read: result.data.len(),
            eof: result.eof,
            data: Some(result.data),
        });
    }
    output
        .into_iter()
        .map(|result| result.ok_or_else(|| Error::transport(None, "vread_native omitted a result")))
        .collect()
}
/// Internal projection for the native owned-result batch path.
pub struct ReadRequest<'a, R> {
    pub(crate) source: Source<'a, R>,
}
pub(crate) enum Source<'a, R> {
    Whole(&'a Path),
    Range(R),
}
impl<'a, R> ReadRequest<'a, R> {
    /// Read a complete path within the aggregate budget, without manual OPEN/CLOSE.
    pub fn whole_file<P: AsRef<Path> + ?Sized>(path: &'a P) -> Self {
        Self {
            source: Source::Whole(path.as_ref()),
        }
    }
    /// Wrap a positional request, preserving short results and EOF.
    pub fn range(request: R) -> Self {
        Self {
            source: Source::Range(request),
        }
    }
    /// Borrow the backend-defined range request, or return `None` for a whole file.
    /// External [`crate::api::Vfsi`] implementations can use this together with
    /// a whole-file dispatch path without exposing handles.
    pub fn range_ref(&self) -> Option<&R> {
        match &self.source {
            Source::Range(request) => Some(request),
            _ => None,
        }
    }
}
impl<'a, R> From<R> for ReadRequest<'a, R> {
    fn from(request: R) -> Self {
        Self::range(request)
    }
}
pub fn read_batch<R>(
    requests: &[ReadRequest<'_, R>],
    budget: usize,
    read_ranges: impl FnOnce(&[&R], usize) -> Result<Vec<OwnedReadResult>>,
    read_paths: impl FnOnce(&[&Path], usize) -> Result<Vec<Vec<u8>>>,
) -> Result<Vec<OwnedReadResult>> {
    if requests.is_empty() {
        return Ok(Vec::new());
    }
    let (mut paths, mut path_indices, mut ranges, mut range_indices) =
        (Vec::new(), Vec::new(), Vec::new(), Vec::new());
    for (i, r) in requests.iter().enumerate() {
        match &r.source {
            Source::Whole(path) => {
                paths.push(*path);
                path_indices.push(i);
            }
            Source::Range(range) => {
                ranges.push(range);
                range_indices.push(i);
            }
        }
    }
    let remap = |e: Error, indices: &[usize]| match e.index() {
        Some(i) if i < indices.len() => e.with_index(indices[i]),
        Some(_) => Error::transport(None, "invalid vread_native backend error index"),
        None => e,
    };
    // Group ranges before complete paths. Reads do not promise a snapshot.
    let range_results = if ranges.is_empty() {
        Vec::new()
    } else {
        read_ranges(&ranges, budget).map_err(|e| remap(e, &range_indices))?
    };
    if range_results.len() != ranges.len() {
        return Err(Error::transport(
            None,
            "invalid vread_native range result count",
        ));
    }
    let mut remaining = budget;
    for r in &range_results {
        remaining = remaining
            .checked_sub(r.data.len())
            .ok_or_else(|| Error::transport(None, "vread_native backend exceeded byte budget"))?;
    }
    let path_results = if paths.is_empty() {
        Vec::new()
    } else {
        read_paths(&paths, remaining).map_err(|e| remap(e, &path_indices))?
    };
    if path_results.len() != paths.len() {
        return Err(Error::transport(
            None,
            "invalid vread_native path result count",
        ));
    }
    for r in &path_results {
        remaining = remaining
            .checked_sub(r.len())
            .ok_or_else(|| Error::transport(None, "vread_native backend exceeded byte budget"))?;
    }
    let mut output: Vec<Option<OwnedReadResult>> = (0..requests.len()).map(|_| None).collect();
    for (i, r) in range_indices.into_iter().zip(range_results) {
        output[i] = Some(r);
    }
    for (i, data) in path_indices.into_iter().zip(path_results) {
        output[i] = Some(OwnedReadResult {
            offset: 0,
            data,
            eof: true,
        });
    }
    output
        .into_iter()
        .map(|r| r.ok_or_else(|| Error::transport(None, "vread_native omitted a result")))
        .collect()
}

#[cfg(test)]
mod option_layout_tests {
    use super::ReadOptions;
    use std::num::NonZeroUsize;
    #[test]
    fn read_options_are_one_word_and_keep_inheritance_distinct() {
        assert_eq!(
            std::mem::size_of::<ReadOptions>(),
            std::mem::size_of::<usize>()
        );
        let mut options = ReadOptions::new();
        assert_eq!(options.limit_or(7), 7);
        for bytes in [1, 42, usize::MAX] {
            let limit = NonZeroUsize::new(bytes);
            options = options.max_total_bytes(limit);
            assert_eq!(options.total_byte_limit(), limit);
            assert_eq!(options.limit_or(7), bytes);
        }
        options = options.max_total_bytes(None);
        assert_eq!(options.total_byte_limit(), None);
        assert_eq!(options.limit_or(7), 7);
        assert_eq!(
            options.limit_or(0),
            0,
            "an inherited zero policy must not become unlimited"
        );
    }
}