//! rsapi — the kernel↔binary ABI (ADR 0006).
//!
//! One versioned `Exports` table is constructed per invocation and handed
//! to the binary's entry point.  The header starts with a magic and a
//! `version: u32` so a future kernel can keep old binaries working
//! (dispatch on the version, never on struct layout).
//!
//! Everything here is `no_std`-clean: plain structs and function pointers,
//! no allocation, no rsnix dependency — binaries link only this crate.

#![no_std]

/// Table magic: "RSEX".
pub const EXPORTS_MAGIC: u32 = 0x5245_5853;

/// ABI revision.  Bump on any signature change; the kernel refuses to run
/// binaries whose required major exceeds its own.
pub const ABI_VERSION: u32 = 2;

/// Entry-point signature.  `extern "C"` on the x86_64-unknown-uefi
/// target is the Win64 convention: the three arguments arrive in
/// RCX/RDX/R8 on both sides of the table.
pub type EntryPoint = extern "C" fn(exports: &'static Exports, argc: usize, argv: *const Arg) -> i32;

/// One C-style argv element: pointer + length (rs-dos strings are not
/// NUL-terminated in memory).
#[derive(Clone, Copy)]
pub struct Arg {
    pub ptr: *const u8,
    pub len: usize,
}

/// A line of text handed across the ABI (stream I/O).
#[derive(Clone, Copy)]
pub struct Line {
    pub ptr: *const u8,
    pub len: usize,
}

impl Line {
    /// Borrow as a &str.
    pub fn as_str(&self) -> &'static str {
        unsafe { core::str::from_utf8_unchecked(core::slice::from_raw_parts(self.ptr, self.len)) }
    }
}

/// Outcome of `get_line`.
#[derive(Clone, Copy, PartialEq, Eq)]
pub enum StreamResult {
    Line,
    Eof,
    Abort,
}

// ---------------------------------------------------------------------------
// v2 types
// ---------------------------------------------------------------------------

/// Opaque file/directory handle returned by `fs_resolve` / `fs_create`.
pub type FsHandle = i32;

/// One directory entry returned by `fs_dir_next`.
#[repr(C)]
#[derive(Clone, Copy)]
pub struct DirEntry {
    pub name: Line,
    pub is_dir: bool,
    pub _pad: u8,
    pub size: u64,
}

/// Real-time clock snapshot.
#[repr(C)]
#[derive(Clone, Copy)]
pub struct RtcTime {
    pub year: u16,
    pub month: u8,
    pub day: u8,
    pub hour: u8,
    pub minute: u8,
    pub second: u8,
    pub _pad: u8,
}

/// Memory statistics (heap + page allocator).
#[repr(C)]
#[derive(Clone, Copy)]
pub struct MemStats {
    pub heap_total: u64,
    pub heap_free: u64,
    pub pages_total: u64,
    pub pages_free: u64,
}

/// One PCI device discovered at probe time.
#[repr(C)]
#[derive(Clone, Copy)]
pub struct PciDevice {
    pub bus: u8,
    pub device: u8,
    pub function: u8,
    pub class: u8,
    pub subclass: u8,
    pub vendor: u16,
    pub device_id: u16,
}

/// Kernel version information.
#[derive(Clone, Copy)]
pub struct KernelVersion {
    pub name: Line,
    pub major: u16,
    pub minor: u16,
    pub patch: u16,
}

// ---------------------------------------------------------------------------
// Exports table — v2
// ---------------------------------------------------------------------------

/// The function table a binary receives.  Layout is fixed by `version`;
/// new functions are appended, existing ones never move.
#[repr(C)]
pub struct Exports {
    // ---- header ----
    pub magic: u32,
    pub version: u32,

    // ---- console / streams (v1) ----
    pub put_line: fn(line: Line) -> bool,
    pub get_line: fn(out: &mut Line) -> StreamResult,

    // ---- lifecycle (v1) ----
    pub log_line: fn(line: Line),
    pub exit: fn(code: i32) -> !,

    // ---- filesystem queries (v2) ----
    /// Resolve a path to a handle; returns -1 on error.
    pub fs_resolve: fn(path: Line) -> FsHandle,
    /// Iterate directory entries: returns true and fills `out` while
    /// entries remain; returns false when exhausted.  Resets position.
    pub fs_dir_next: fn(handle: FsHandle, out: &mut DirEntry) -> bool,
    /// Create a file (is_dir=false) or directory (is_dir=true) at path.
    /// Returns 0 on success, -1 on error.
    pub fs_create: fn(path: Line, is_dir: bool) -> i32,
    /// Remove a file or empty directory.  Returns 0 on success.
    pub fs_remove: fn(path: Line) -> i32,
    /// Read `len` bytes from `handle` at `pos`.  Returns bytes actually
    /// read, or -1 on error.
    pub fs_read: fn(handle: FsHandle, buf: *mut u8, pos: u64, len: u64) -> i64,
    /// Write `len` bytes to `handle` at `pos`.  Returns bytes written.
    pub fs_write: fn(handle: FsHandle, buf: *const u8, pos: u64, len: u64) -> i64,
    /// Get file/directory size in bytes.
    pub fs_size: fn(handle: FsHandle) -> u64,
    /// Close a handle (currently a no-op; reserved for future fd mgmt).
    pub fs_close: fn(handle: FsHandle),

    // ---- hardware queries (v2) ----
    pub rtc_now: fn(out: &mut RtcTime),
    pub mem_stats: fn(out: &mut MemStats),
    /// Enumerate PCI: returns number of devices discovered.
    pub pci_probe: fn() -> u32,
    /// Get one PCI device by index (0-based).  Returns true on success.
    pub pci_device: fn(index: u32, out: &mut PciDevice) -> bool,
    /// Copy up to `cap` bytes of the kernel log ring into `buf`.
    /// Returns bytes copied.
    pub klog_dump: fn(buf: *mut u8, cap: u64) -> u64,
    /// Fill `out` with kernel version info.
    pub kernel_version: fn(out: &mut KernelVersion),
}