#[cfg(any(feature = "blocking-io", feature = "async-io"))]
use crate::MAX_LINE_LEN;
use crate::{PacketLineRef, U16_HEX_BYTES};

/// Allow the read-progress handler to determine how to continue.
///
/// Use [`std::ops::ControlFlow::Continue`] to continue reading the next progress if available.
/// Use [`std::ops::ControlFlow::Break`] to abort all IO even if more would be available, claiming the operation was interrupted.
pub type ProgressAction = std::ops::ControlFlow<()>;

#[cfg(any(feature = "blocking-io", feature = "async-io"))]
pub(crate) type ExhaustiveOutcome<'a> = (
    bool,                                                                     // is_done
    Option<PacketLineRef<'static>>,                                           // stopped_at
    Option<std::io::Result<Result<PacketLineRef<'a>, crate::decode::Error>>>, // actual method result
);

mod error {
    use std::fmt::{Debug, Display, Formatter};

    use bstr::BString;

    /// The error representing an ERR packet line, as possibly wrapped into an `std::io::Error`.
    #[derive(Debug)]
    pub struct Error {
        /// The contents of the ERR line, with `ERR` portion stripped.
        pub message: BString,
    }

    impl Display for Error {
        fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
            Display::fmt(&self.message, f)
        }
    }

    impl std::error::Error for Error {}
}
pub use error::Error;

/// State for `StreamingPeekableIter` implementations.
pub struct StreamingPeekableIterState<T> {
    pub(crate) read: T,
    pub(crate) peek_buf: Vec<u8>,
    #[cfg(any(feature = "blocking-io", feature = "async-io"))]
    pub(crate) buf: Vec<u8>,
    pub(crate) fail_on_err_lines: bool,
    pub(crate) delimiters: &'static [PacketLineRef<'static>],
    pub(crate) is_done: bool,
    pub(crate) stopped_at: Option<PacketLineRef<'static>>,
    #[cfg_attr(all(not(feature = "async-io"), not(feature = "blocking-io")), allow(dead_code))]
    pub(crate) trace: bool,
}

impl<T> StreamingPeekableIterState<T> {
    /// Return a new instance from `read` which will stop decoding packet lines when receiving one of the given `delimiters`.
    /// If `trace` is `true`, all packetlines received or sent will be passed to the facilities of the `gix-trace` crate.
    #[cfg(any(feature = "blocking-io", feature = "async-io"))]
    pub(crate) fn new(read: T, delimiters: &'static [PacketLineRef<'static>], trace: bool) -> Self {
        Self {
            read,
            #[cfg(any(feature = "blocking-io", feature = "async-io"))]
            buf: vec![0; MAX_LINE_LEN],
            peek_buf: Vec::new(),
            delimiters,
            fail_on_err_lines: false,
            is_done: false,
            stopped_at: None,
            trace,
        }
    }

    /// Modify the peek buffer, overwriting the byte at `position` with the given byte to `replace_with` while truncating
    /// it to contain only bytes until the newly replaced `position`.
    ///
    /// This is useful if you would want to remove 'special bytes' hidden behind, say a NULL byte to disappear and allow
    /// standard line readers to read the next line as usual.
    ///
    /// **Note** that `position` does not include the 4 bytes prefix (they are invisible outside the reader)
    pub fn peek_buffer_replace_and_truncate(&mut self, position: usize, replace_with: u8) {
        let position = position + U16_HEX_BYTES;
        self.peek_buf[position] = replace_with;

        let new_len = position + 1;
        self.peek_buf.truncate(new_len);
        self.peek_buf[..4].copy_from_slice(&crate::encode::u16_to_hex((new_len) as u16));
    }

    /// Returns the packet line that stopped the iteration, or
    /// `None` if the end wasn't reached yet, on EOF, or if [`fail_on_err_lines()`][StreamingPeekableIterState::fail_on_err_lines()] was true.
    pub fn stopped_at(&self) -> Option<PacketLineRef<'static>> {
        self.stopped_at
    }

    /// Reset all iteration state allowing to continue a stopped iteration that is not yet at EOF.
    ///
    /// This can happen once a delimiter is reached.
    pub fn reset(&mut self) {
        let delimiters = std::mem::take(&mut self.delimiters);
        self.reset_with(delimiters);
    }

    /// Similar to [`reset()`][StreamingPeekableIterState::reset()] with support to changing the `delimiters`.
    pub fn reset_with(&mut self, delimiters: &'static [PacketLineRef<'static>]) {
        self.delimiters = delimiters;
        self.is_done = false;
        self.stopped_at = None;
    }

    /// If `value` is `true` the provider will check for special `ERR` packet lines and stop iteration when one is encountered.
    ///
    /// Use [`stopped_at()]`[`StreamingPeekableIterState::stopped_at()`] to inspect the cause of the end of the iteration.
    /// ne
    pub fn fail_on_err_lines(&mut self, value: bool) {
        self.fail_on_err_lines = value;
    }

    /// Replace the reader used with the given `read`, resetting all other iteration state as well.
    pub fn replace(&mut self, read: T) -> T {
        let prev = std::mem::replace(&mut self.read, read);
        self.reset();
        self.fail_on_err_lines = false;
        prev
    }
}