//! Crate-level RPC error type.
//!
//! Hoisted from per-module enums in M2 wave 2 — see `design/followups.md` F8.
//! Every parser/encoder in `mxaccess-rpc` returns this single shared
//! [`RpcError`] so consumers can match on one error surface across PDU
//! decode, OBJREF parse, ORPC `ResolveOxid` body decode, and
//! `IRemUnknown::RemQueryInterface` response decode.
//!
//! Variants here are the union of what M1 wave 1 defined locally in
//! `pdu.rs` and `objref.rs` (`design/followups.md` F8 source list),
//! plus a generic [`RpcError::Decode`] for one-off conditions wave 2's
//! ORPC parsers need (referent-id mismatches, conformant-array max-count
//! underflow, NDR alignment overrun) without growing the enum further.

use thiserror::Error;

/// Errors raised by any codec under `mxaccess-rpc`.
#[derive(Debug, Error, PartialEq, Eq)]
#[non_exhaustive]
pub enum RpcError {
    /// Buffer was shorter than required to decode the type.
    #[error("short read: expected {expected} bytes, got {actual}")]
    ShortRead { expected: usize, actual: usize },

    /// Packet type byte at offset 2 (`DceRpcPdu.cs:52`) did not match the
    /// expected `DceRpcPacketType` for the parser invoked.
    #[error("unexpected packet type {actual}, expected {expected}")]
    UnexpectedPacketType { expected: u8, actual: u8 },

    /// Packet type byte was not a known [`crate::pdu::PacketType`] value.
    #[error("unknown packet type byte {0}")]
    UnknownPacketType(u8),

    /// `header.frag_length` is inconsistent with the supplied buffer or
    /// `auth_length` (`DceRpcPdu.cs:94,150,188,226,101-104,156-159,195-198`).
    #[error(
        "fragment length {frag_length} inconsistent with buffer length {buffer_len} \
         (auth_length={auth_length})"
    )]
    InvalidFragmentLength {
        frag_length: usize,
        buffer_len: usize,
        auth_length: usize,
    },

    /// A bind PDU's per-context list ran past `frag_length`
    /// (`DceRpcPdu.cs:237`) or a syntax identifier was truncated
    /// (`DceRpcPdu.cs:354`).
    #[error("truncated bind body at offset {offset}; need {need} bytes, frag_length={frag_length}")]
    TruncatedBindBody {
        offset: usize,
        need: usize,
        frag_length: usize,
    },

    /// Auth-trailer offset is below the 16-byte header
    /// (`DceRpcPdu.cs:341-345`).
    #[error("invalid auth trailer offset {offset}")]
    InvalidAuthTrailer { offset: usize },

    /// Tried to extract an auth value from a PDU whose `auth_length` is 0
    /// (`DceRpcPdu.cs:336-339`).
    #[error("PDU has no auth value")]
    MissingAuthValue,

    /// Generic decode failure with a position and reason. Used by ORPC
    /// body decoders for one-off conditions that don't justify a typed
    /// variant (e.g. NDR conformant-array max-count underflow per
    /// `ObjectExporterMessages.cs:66-69`, referent-id of zero with no
    /// trailing status per `:57-61`, NDR alignment overrun, etc.).
    #[error("decode at offset {offset} ({reason}); buffer len {buffer_len}")]
    Decode {
        offset: usize,
        reason: &'static str,
        buffer_len: usize,
    },
}