//! `NmxOperationStatusMessage` — completion / status-word frames.
//!
//! Direct port of `src/MxNativeCodec/NmxOperationStatusMessage.cs`.
//!
//! Two on-the-wire shapes are recognised by the inner-body parser:
//!
//! 1. **5-byte status-word frame** — `00 00 SS SS CC` where `SS SS` is a u16
//!    LE status code and `CC` is a completion code. The single proven mapping
//!    is `00 00 50 80 00` → [`MxStatus::WRITE_COMPLETE_OK`]
//!    (`NmxOperationStatusMessage.cs:48-62`,
//!    `design/40-protocol-invariants.md:346`).
//! 2. **1-byte completion-only frame** — a single byte `CC`. Three values are
//!    observed in the wild (`0x00`, `0x41`, `0xEF`) but the byte→status
//!    mapping is unproven; they are preserved verbatim per
//!    `design/70-risks-and-open-questions.md` R3/R4 and
//!    `NmxOperationStatusMessage.cs:36-46,69-76`.
//!
//! The .NET reference also exposes `TryParseProcessDataReceivedBody`, which
//! peels an outer `NmxObservedEnvelope` before delegating to the inner-body
//! parser. The outer envelope codec has not yet been ported to Rust; only
//! [`NmxOperationStatusMessage::try_parse_inner`] is provided here. When
//! `NmxObservedEnvelope` lands, add `try_parse_process_data_received_body` as
//! a thin wrapper.

// Direct byte indexing — see reference_handle.rs for rationale.
#![allow(clippy::indexing_slicing)]

use crate::error::CodecError;
use crate::status::{MxStatus, MxStatusCategory, MxStatusSource};

/// Which of the two recognised inner-frame shapes was decoded
/// (`NmxOperationStatusMessage.cs:3-7`).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum NmxOperationStatusFormat {
    /// Single-byte completion frame (`NmxOperationStatusMessage.cs:5,36-46`).
    CompletionOnly,
    /// 5-byte `00 00 SS SS CC` status-word frame
    /// (`NmxOperationStatusMessage.cs:6,48-62`).
    StatusWord,
}

/// Decoded operation-status frame
/// (`NmxOperationStatusMessage.cs:9-15` — record fields).
///
/// The four payload fields preserve the raw on-wire bytes; [`Self::status`]
/// carries the promoted [`MxStatus`] when a known mapping exists, or an
/// unpromoted placeholder otherwise (see `CompletionOnly` and the fallback
/// branch of `StatusWord`).
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct NmxOperationStatusMessage {
    /// Which inner frame shape was observed.
    pub format: NmxOperationStatusFormat,
    /// First byte of the 5-byte frame (`NmxOperationStatusMessage.cs:54`).
    /// `0` for `CompletionOnly` frames.
    pub command: u8,
    /// `inner[2..4]` u16 LE for `StatusWord` (`NmxOperationStatusMessage.cs:50`).
    /// `0` for `CompletionOnly` frames.
    pub status_code: u16,
    /// Completion byte. `inner[0]` for `CompletionOnly`
    /// (`NmxOperationStatusMessage.cs:38`); `inner[4]` for `StatusWord`
    /// (`NmxOperationStatusMessage.cs:51`).
    pub completion_code: u8,
    /// Promoted status. The only proven promotion is
    /// `status_code == 0x8050 && completion_code == 0x00 → WRITE_COMPLETE_OK`
    /// (`NmxOperationStatusMessage.cs:57`,
    /// `design/40-protocol-invariants.md:346`). Every other shape is wrapped
    /// in an `Unknown`/`Unknown` placeholder with the raw byte preserved in
    /// `detail`.
    pub status: MxStatus,
}

impl NmxOperationStatusMessage {
    /// `true` for the proven `00 00 50 80 00` frame
    /// (`NmxOperationStatusMessage.cs:16-18`).
    pub fn is_mx_access_write_complete(&self) -> bool {
        self.format == NmxOperationStatusFormat::StatusWord
            && self.status_code == 0x8050
            && self.completion_code == 0x00
    }

    /// Parse an inner body — either 1 byte (`CompletionOnly`) or 5 bytes
    /// (`StatusWord` with leading `00 00`).
    ///
    /// Mirrors `NmxOperationStatusMessage.TryParseInner`
    /// (`NmxOperationStatusMessage.cs:34-67`).
    ///
    /// # Errors
    ///
    /// Returns [`CodecError::ShortRead`] when the buffer length matches no
    /// recognised shape. The .NET reference returns `false` and a `null!`
    /// out-param; the Rust port surfaces the failure as a typed error so
    /// callers can distinguish "not an operation-status frame" from
    /// "successfully parsed". Match on the error to mirror the bool API.
    pub fn try_parse_inner(inner: &[u8]) -> Result<Self, CodecError> {
        if inner.len() == 1 {
            // CompletionOnly — `NmxOperationStatusMessage.cs:36-46`.
            let completion_code = inner[0];
            return Ok(Self {
                format: NmxOperationStatusFormat::CompletionOnly,
                command: 0,
                status_code: 0,
                completion_code,
                status: create_unpromoted_completion_status(completion_code),
            });
        }

        if inner.len() == 5 && inner[0] == 0x00 && inner[1] == 0x00 {
            // StatusWord — `NmxOperationStatusMessage.cs:48-62`.
            let status_code = u16::from(inner[2]) | (u16::from(inner[3]) << 8);
            let completion_code = inner[4];

            // Only the (0x8050, 0x00) shape is promoted to a typed status.
            // Every other (status_code, completion_code) pair is preserved as
            // an Unknown/Unknown placeholder with the raw byte in `detail`,
            // mirroring `NmxOperationStatusMessage.cs:57-61`.
            //
            // The .NET fallback packs `detail` as:
            //   completion_code == 0x00 ? (short)status_code : completion_code
            // We replicate the same selection here, including the
            // `unchecked((short)statusCode)` reinterpretation (i.e. the u16's
            // bit pattern as i16).
            let status = if status_code == 0x8050 && completion_code == 0x00 {
                MxStatus::WRITE_COMPLETE_OK
            } else {
                let detail = if completion_code == 0x00 {
                    // Reinterpret the u16 status_code as i16 (two's complement).
                    status_code as i16
                } else {
                    i16::from(completion_code)
                };
                MxStatus {
                    success: 0,
                    category: MxStatusCategory::Unknown,
                    detected_by: MxStatusSource::Unknown,
                    detail,
                }
            };

            return Ok(Self {
                format: NmxOperationStatusFormat::StatusWord,
                command: inner[0],
                status_code,
                completion_code,
                status,
            });
        }

        Err(CodecError::ShortRead {
            // 1 or 5 are the two valid lengths; report the smaller for the
            // diagnostic. Callers that need the strict bool API should pattern
            // match on `Err(_) => false`.
            expected: 1,
            actual: inner.len(),
        })
    }
}

/// Build the unpromoted placeholder status used by `CompletionOnly` frames
/// (`NmxOperationStatusMessage.cs:69-76`).
fn create_unpromoted_completion_status(completion_code: u8) -> MxStatus {
    MxStatus {
        success: 0,
        category: MxStatusCategory::Unknown,
        detected_by: MxStatusSource::Unknown,
        detail: i16::from(completion_code),
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used, clippy::indexing_slicing)]
mod tests {
    use super::*;

    #[test]
    fn write_complete_ok_frame() {
        // The proven 5-byte mapping (`design/40-protocol-invariants.md:346`).
        let frame = [0x00, 0x00, 0x50, 0x80, 0x00];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.format, NmxOperationStatusFormat::StatusWord);
        assert_eq!(msg.command, 0x00);
        assert_eq!(msg.status_code, 0x8050);
        assert_eq!(msg.completion_code, 0x00);
        assert_eq!(msg.status, MxStatus::WRITE_COMPLETE_OK);
        assert!(msg.is_mx_access_write_complete());
    }

    #[test]
    fn status_word_unknown_with_completion_zero_packs_status_code_as_i16() {
        // status_code 0x8051, completion 0x00 — not the proven mapping; falls
        // through to the unpromoted branch with detail = (i16)0x8051 = -32687.
        // Mirrors `NmxOperationStatusMessage.cs:61` (`unchecked((short)statusCode)`).
        let frame = [0x00, 0x00, 0x51, 0x80, 0x00];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.format, NmxOperationStatusFormat::StatusWord);
        assert_eq!(msg.status_code, 0x8051);
        assert_eq!(msg.completion_code, 0x00);
        assert_eq!(msg.status.category, MxStatusCategory::Unknown);
        assert_eq!(msg.status.detected_by, MxStatusSource::Unknown);
        assert_eq!(msg.status.detail, 0x8051u16 as i16);
        assert!(!msg.is_mx_access_write_complete());
    }

    #[test]
    fn status_word_unknown_with_nonzero_completion_packs_completion_in_detail() {
        // completion_code != 0 — detail = completion_code as i16
        // (`NmxOperationStatusMessage.cs:61`).
        let frame = [0x00, 0x00, 0x50, 0x80, 0x42];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.completion_code, 0x42);
        assert_eq!(msg.status.detail, 0x42);
        assert_eq!(msg.status.category, MxStatusCategory::Unknown);
        assert!(!msg.is_mx_access_write_complete());
    }

    #[test]
    fn completion_only_zero_byte() {
        // 1-byte 0x00 — preserved verbatim per design R3/R4.
        let frame = [0x00];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.format, NmxOperationStatusFormat::CompletionOnly);
        assert_eq!(msg.command, 0);
        assert_eq!(msg.status_code, 0);
        assert_eq!(msg.completion_code, 0x00);
        assert_eq!(msg.status.detail, 0x00);
        assert_eq!(msg.status.category, MxStatusCategory::Unknown);
        // `CompletionOnly` is never promoted to WriteCompleteOk.
        assert!(!msg.is_mx_access_write_complete());
    }

    #[test]
    fn completion_only_0x41_byte() {
        // 1-byte 0x41 — observed in the wild, mapping unproven
        // (`design/70-risks-and-open-questions.md` R4).
        let frame = [0x41];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.format, NmxOperationStatusFormat::CompletionOnly);
        assert_eq!(msg.completion_code, 0x41);
        assert_eq!(msg.status.detail, 0x41);
        assert_eq!(msg.status.category, MxStatusCategory::Unknown);
    }

    #[test]
    fn completion_only_0xef_byte() {
        // 1-byte 0xEF — observed in the wild, mapping unproven
        // (`design/70-risks-and-open-questions.md` R4).
        let frame = [0xEF];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.format, NmxOperationStatusFormat::CompletionOnly);
        assert_eq!(msg.completion_code, 0xEF);
        // 0xEF as i16 is 0x00EF (zero-extended), not -17.
        assert_eq!(msg.status.detail, 0xEF);
    }

    #[test]
    fn rejects_unknown_length() {
        // 0 / 2 / 3 / 4 / 6 bytes — all non-recognised shapes.
        for len in [0_usize, 2, 3, 4, 6, 16] {
            let buf = vec![0u8; len];
            assert!(
                NmxOperationStatusMessage::try_parse_inner(&buf).is_err(),
                "length {len} should be rejected"
            );
        }
    }

    #[test]
    fn rejects_5_byte_frame_without_leading_zeros() {
        // 5 bytes with non-zero leading bytes — not a StatusWord frame
        // (`NmxOperationStatusMessage.cs:48` requires `inner[0] == 0 && inner[1] == 0`).
        let frame = [0x01, 0x00, 0x50, 0x80, 0x00];
        assert!(NmxOperationStatusMessage::try_parse_inner(&frame).is_err());
        let frame = [0x00, 0x01, 0x50, 0x80, 0x00];
        assert!(NmxOperationStatusMessage::try_parse_inner(&frame).is_err());
    }

    #[test]
    fn status_code_is_little_endian() {
        // `inner[2..4]` is read as u16 LE — `inner[2] | (inner[3] << 8)`.
        // 0xAA at [2], 0xBB at [3] → 0xBBAA.
        let frame = [0x00, 0x00, 0xAA, 0xBB, 0x00];
        let msg = NmxOperationStatusMessage::try_parse_inner(&frame).unwrap();
        assert_eq!(msg.status_code, 0xBBAA);
    }
}