//! FIFA 17 SBC render intervention (feature = "fifa17").
//!
//! Makes the FUT **SBC menu render real data** from inside the process. Full spec
//! (all addresses, RVA math, call order, crash risks, staged test plan):
//!   fifa17-recon/docs/sbc-hook-dll-spec.md
//!
//! Everything here is **inert by default** and gated by env vars:
//!   OPENFUT_SBC_HOOK=1       -> arm the deferred worker (resolve + log; READ-ONLY)
//!   OPENFUT_SBC_ARM_ONLY=1   -> Tier-0 negative control: write BYTE[B+0x28]=1 (renders EMPTY)
//!   OPENFUT_SBC_POPULATE=1   -> legacy Tier-1 gate: BLOCKED (logs corrected trace gap, returns)
//!
//! CardsDLL_Win64_retail.dll is loaded lazily (only on entering Ultimate Team), so we
//! defer off the loader lock and poll for it in a background thread.
//!
//! ── Address model (static VAs; PE image base 0x180000000) ────────────────────────
//! All values below are RVAs (VA_static - 0x180000000); live = cards_base + rva.
//! See the spec for the verified disassembly behind each one.

use core::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use windows_sys::Win32::System::LibraryLoader::GetModuleHandleA;
use windows_sys::Win32::System::Memory::{
    VirtualQuery, MEMORY_BASIC_INFORMATION, MEM_COMMIT, PAGE_EXECUTE_READ, PAGE_EXECUTE_READWRITE,
    PAGE_EXECUTE_WRITECOPY, PAGE_GUARD, PAGE_NOACCESS, PAGE_READWRITE, PAGE_WRITECOPY,
};

// ── RVAs (verified byte-exact against /tmp/fut/cardsdll.dll this pass) ────────────
const IMAGE_BASE: usize = 0x180000000;

/// FNV prologue used as the slide-proof control (must match the on-disk PE bytes).
const CTRL_RVA: usize = 0x180d00; // VA 0x180180d00
const CTRL_BYTES: &[u8] = &[
    0x48, 0x83, 0xec, 0x28, 0x48, 0x85, 0xc9, 0x74, 0x50, 0x45, 0x33, 0xc0,
];

const A_SLOT_RVA: usize = 0x2e6398; // *(0x1802e6398) = A (FUT root singleton)
const A_VTABLE_RVA: usize = 0x21c2a0;
const B_OFF: usize = 0x1f9d8; //        B = A + 0x1f9d8 (SBC request/ready TTL cache)
const B_VTABLE_RVA: usize = 0x1fae70;
const B_READY_OFF: usize = 0x28; //     B+0x28 ready byte (the isValid gate)
const B_COLL_OFF: usize = 0x08; //      B+0x08 collection ptr (MUST stay 0 — see spec §4/C5)
const M_CACHE_OFF: usize = 0x20a68; //  M = *(A + 0x20a68) (render source; per-session heap)
const M_COUNT_OFF: usize = 0x50; //     WORD[M+0x50] category count
const B_DTOR_RVA: usize = 0x63040;
const B_ISVALID_RVA: usize = 0x65d40;
const B_CLEAR_RVA: usize = 0x65d20;
const B_READY_EXPECTED_BEFORE_ARM: u8 = 0;

#[allow(dead_code)]
const AVT_M_GETTER: usize = 0x9b0; //   A.vtable[+0x9b0] = 0x18011b7d0 (M lazy getter)
#[allow(dead_code)]
const AVT_B_GETTER: usize = 0x4e8; //   A.vtable[+0x4e8] = 0x18011c1f0 (B getter thunk)

// Callable RVAs (for the Tier-1 populate sequence — see spec §6/§8). Kept for
// reference/wiring; not invoked while Tier-1 is blocked.
#[allow(dead_code)]
mod rva {
    pub const M_LAZY_GETTER: usize = 0x11b7d0;
    pub const ISVALID: usize = 0x65d40;
    pub const DESER_SBS_SETS: usize = 0x17b2b0;
    pub const SAX_CTX_INIT: usize = 0x1c63e0;
    pub const REGISTRY_GETTER: usize = 0xd7170;
    pub const MANAGER_GETTER: usize = 0x9c80;
    pub const CLEAR_M: usize = 0x15f3a0;
    pub const CAT_CTOR: usize = 0x159da0;
    pub const CAT_DESER: usize = 0x17ab80;
    pub const CAT_FINALIZE: usize = 0x160e50;
    pub const APPEND: usize = 0x15a770;
    pub const CAT_DTOR: usize = 0x1105d0;
    pub const IDX_REBUILD_1: usize = 0x160e00;
    pub const IDX_REBUILD_2: usize = 0x160f30;
    pub const IDX_REBUILD_3: usize = 0x161020;
    pub const REFRESH_DISPATCH: usize = 0x1a4a70; // Scaleform events 0x756c-0x7574
}

static ARMED: AtomicBool = AtomicBool::new(false);
static ARM_ONLY: AtomicBool = AtomicBool::new(false);
static POPULATE: AtomicBool = AtomicBool::new(false);
static DONE: AtomicBool = AtomicBool::new(false);
static CARDS_BASE: AtomicUsize = AtomicUsize::new(0);
static STATE: AtomicUsize = AtomicUsize::new(RuntimeState::Disabled as usize);

// Full SBC state model. The live repair jumps Resolved -> Validated -> Committed;
// Intercepted/Parsed document the intermediate states but are never entered.
#[allow(dead_code)]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
#[repr(usize)]
enum RuntimeState {
    Disabled,
    Resolved,
    Intercepted,
    Parsed,
    Validated,
    Committed,
    Failed,
}

fn valid_transition(from: RuntimeState, to: RuntimeState) -> bool {
    matches!(
        (from, to),
        (RuntimeState::Disabled, RuntimeState::Resolved)
            | (RuntimeState::Resolved, RuntimeState::Intercepted)
            | (RuntimeState::Intercepted, RuntimeState::Parsed)
            | (RuntimeState::Parsed, RuntimeState::Validated)
            // Resolve-only/Tier-0 validates without installing an interceptor.
            | (RuntimeState::Resolved, RuntimeState::Validated)
            | (RuntimeState::Validated, RuntimeState::Committed)
            | (_, RuntimeState::Failed)
    )
}

fn transition(from: RuntimeState, to: RuntimeState) -> bool {
    valid_transition(from, to)
        && STATE
            .compare_exchange(
                from as usize,
                to as usize,
                Ordering::AcqRel,
                Ordering::Acquire,
            )
            .is_ok()
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
enum ValidationError {
    AddressOverflow,
    AUnreadable,
    AVtableMismatch,
    AGetterMismatch,
    BVtableMismatch,
    BDtorMismatch,
    BIsValidMismatch,
    BClearMismatch,
    MSlotUnreadable,
    ReadyByteUnexpected,
    CollectionUnreadable,
    CollectionNotNull,
    ReadyByteNotWritable,
}

#[derive(Clone, Copy, Debug)]
struct RuntimeSnapshot {
    a: usize,
    a_vtable: usize,
    a_b_getter: usize,
    b: usize,
    b_vtable: usize,
    b_dtor: usize,
    b_isvalid: usize,
    b_clear: usize,
    b_ready: u8,
    b_coll: usize,
    m: usize,
}

fn expected_va(base: usize, rva: usize) -> Result<usize, ValidationError> {
    base.checked_add(rva)
        .ok_or(ValidationError::AddressOverflow)
}

fn validate_snapshot(base: usize, s: &RuntimeSnapshot) -> Result<(), ValidationError> {
    if s.a == 0
        || s.b
            != s.a
                .checked_add(B_OFF)
                .ok_or(ValidationError::AddressOverflow)?
    {
        return Err(ValidationError::AUnreadable);
    }
    if s.a_vtable != expected_va(base, A_VTABLE_RVA)? {
        return Err(ValidationError::AVtableMismatch);
    }
    if s.a_b_getter != expected_va(base, 0x11c1f0)? {
        return Err(ValidationError::AGetterMismatch);
    }
    if s.b_vtable != expected_va(base, B_VTABLE_RVA)? {
        return Err(ValidationError::BVtableMismatch);
    }
    if s.b_dtor != expected_va(base, B_DTOR_RVA)? {
        return Err(ValidationError::BDtorMismatch);
    }
    if s.b_isvalid != expected_va(base, B_ISVALID_RVA)? {
        return Err(ValidationError::BIsValidMismatch);
    }
    if s.b_clear != expected_va(base, B_CLEAR_RVA)? {
        return Err(ValidationError::BClearMismatch);
    }
    if s.b_ready != B_READY_EXPECTED_BEFORE_ARM {
        return Err(ValidationError::ReadyByteUnexpected);
    }
    if s.b_coll != 0 {
        return Err(ValidationError::CollectionNotNull);
    }
    let _ = s.m; // The guarded snapshot read proves the M slot itself is readable.
    Ok(())
}

/// Fault-safe pointer read: returns None unless `ptr` lands
/// in a committed, readable page and the full 8 bytes fit inside the region.
unsafe fn read_ptr(ptr: usize) -> Option<usize> {
    if ptr < 0x10000 || ptr & 7 != 0 {
        return None;
    }
    let mut mbi: MEMORY_BASIC_INFORMATION = core::mem::zeroed();
    let n = VirtualQuery(
        ptr as _,
        &mut mbi,
        core::mem::size_of::<MEMORY_BASIC_INFORMATION>(),
    );
    if n == 0 || mbi.State != MEM_COMMIT {
        return None;
    }
    if mbi.Protect & (PAGE_NOACCESS | PAGE_GUARD) != 0 {
        return None;
    }
    if ptr + 8 > mbi.BaseAddress as usize + mbi.RegionSize {
        return None;
    }
    Some(core::ptr::read_volatile(ptr as *const usize))
}

/// Guarded byte read.
unsafe fn read_u8(ptr: usize) -> Option<u8> {
    if ptr < 0x10000 {
        return None;
    }
    let mut mbi: MEMORY_BASIC_INFORMATION = core::mem::zeroed();
    let n = VirtualQuery(
        ptr as _,
        &mut mbi,
        core::mem::size_of::<MEMORY_BASIC_INFORMATION>(),
    );
    if n == 0 || mbi.State != MEM_COMMIT || mbi.Protect & (PAGE_NOACCESS | PAGE_GUARD) != 0 {
        return None;
    }
    if ptr + 1 > mbi.BaseAddress as usize + mbi.RegionSize {
        return None;
    }
    Some(core::ptr::read_volatile(ptr as *const u8))
}

/// A Tier-0 write is allowed only when the complete byte lies in a committed,
/// non-guarded region whose current protection explicitly permits writes.
unsafe fn writable_u8(ptr: usize) -> bool {
    if ptr < 0x10000 {
        return false;
    }
    let mut mbi: MEMORY_BASIC_INFORMATION = core::mem::zeroed();
    let n = VirtualQuery(
        ptr as _,
        &mut mbi,
        core::mem::size_of::<MEMORY_BASIC_INFORMATION>(),
    );
    if n == 0 || mbi.State != MEM_COMMIT || mbi.Protect & (PAGE_NOACCESS | PAGE_GUARD) != 0 {
        return false;
    }
    let protection = mbi.Protect & 0xff;
    let writable = matches!(
        protection,
        PAGE_READWRITE | PAGE_WRITECOPY | PAGE_EXECUTE_READWRITE | PAGE_EXECUTE_WRITECOPY
    );
    writable
        && ptr
            .checked_add(1)
            .is_some_and(|end| end <= (mbi.BaseAddress as usize).saturating_add(mbi.RegionSize))
}

// Fault-safe executable-range check retained with the address model; not currently wired.
#[allow(dead_code)]
unsafe fn executable_range(ptr: usize, len: usize) -> bool {
    let Some(end) = ptr.checked_add(len) else {
        return false;
    };
    let mut mbi: MEMORY_BASIC_INFORMATION = core::mem::zeroed();
    let n = VirtualQuery(
        ptr as _,
        &mut mbi,
        core::mem::size_of::<MEMORY_BASIC_INFORMATION>(),
    );
    if n == 0 || mbi.State != MEM_COMMIT || mbi.Protect & (PAGE_NOACCESS | PAGE_GUARD) != 0 {
        return false;
    }
    let protection = mbi.Protect & 0xff;
    matches!(
        protection,
        PAGE_EXECUTE_READ | PAGE_EXECUTE_READWRITE | PAGE_EXECUTE_WRITECOPY
    ) && end <= (mbi.BaseAddress as usize).saturating_add(mbi.RegionSize)
}

/// Guarded 16-bit read (M category count is a WORD).
unsafe fn read_u16(ptr: usize) -> Option<u16> {
    let lo = read_u8(ptr)? as u16;
    let hi = read_u8(ptr + 1)? as u16;
    Some(lo | (hi << 8))
}

/// Resolve CardsDLL's runtime base, or 0. Tries the exact loaded name; the ToolHelp
/// fallback (name-contains "CardsDLL") lives in the spec — add it if EA ever renames.
unsafe fn resolve_cards_base() -> usize {
    let h = GetModuleHandleA(c"CardsDLL_Win64_retail.dll".as_ptr().cast());
    if !h.is_null() {
        return h as usize;
    }
    // Also try the short form some tooling reports.
    let h2 = GetModuleHandleA(c"CardsDLL.dll".as_ptr().cast());
    if !h2.is_null() {
        return h2 as usize;
    }
    0
}

#[inline]
fn va(base: usize, rva: usize) -> usize {
    base + rva
}

/// Prove the module didn't move: the FNV control prologue must match the on-disk PE.
unsafe fn control_matches(base: usize) -> bool {
    let p = va(base, CTRL_RVA);
    for (i, &want) in CTRL_BYTES.iter().enumerate() {
        match read_u8(p + i) {
            Some(got) if got == want => {}
            _ => return false,
        }
    }
    true
}

/// Take one guarded identity snapshot. A failure to read any identity-bearing field is
/// distinct from a value mismatch and aborts before mutation.
unsafe fn runtime_snapshot(base: usize) -> Result<RuntimeSnapshot, ValidationError> {
    let a_slot = expected_va(base, A_SLOT_RVA)?;
    let a = read_ptr(a_slot)
        .filter(|&value| value != 0)
        .ok_or(ValidationError::AUnreadable)?;
    let a_vtable = read_ptr(a).ok_or(ValidationError::AVtableMismatch)?;
    let a_b_getter = read_ptr(
        a_vtable
            .checked_add(AVT_B_GETTER)
            .ok_or(ValidationError::AddressOverflow)?,
    )
    .ok_or(ValidationError::AGetterMismatch)?;
    let b = a
        .checked_add(B_OFF)
        .ok_or(ValidationError::AddressOverflow)?;
    let b_vtable = read_ptr(b).ok_or(ValidationError::BVtableMismatch)?;
    let b_dtor = read_ptr(b_vtable).ok_or(ValidationError::BDtorMismatch)?;
    let b_isvalid = read_ptr(
        b_vtable
            .checked_add(8)
            .ok_or(ValidationError::AddressOverflow)?,
    )
    .ok_or(ValidationError::BIsValidMismatch)?;
    let b_clear = read_ptr(
        b_vtable
            .checked_add(16)
            .ok_or(ValidationError::AddressOverflow)?,
    )
    .ok_or(ValidationError::BClearMismatch)?;
    let b_ready = read_u8(
        b.checked_add(B_READY_OFF)
            .ok_or(ValidationError::AddressOverflow)?,
    )
    .ok_or(ValidationError::ReadyByteUnexpected)?;
    let b_coll = read_ptr(
        b.checked_add(B_COLL_OFF)
            .ok_or(ValidationError::AddressOverflow)?,
    )
    .ok_or(ValidationError::CollectionUnreadable)?;
    let m = read_ptr(
        a.checked_add(M_CACHE_OFF)
            .ok_or(ValidationError::AddressOverflow)?,
    )
    .ok_or(ValidationError::MSlotUnreadable)?;
    Ok(RuntimeSnapshot {
        a,
        a_vtable,
        a_b_getter,
        b,
        b_vtable,
        b_dtor,
        b_isvalid,
        b_clear,
        b_ready,
        b_coll,
        m,
    })
}

fn set_failed(error: ValidationError) {
    STATE.store(RuntimeState::Failed as usize, Ordering::Release);
    crate::write_log(&format!(
        "SBC_HOOK: runtime validation FAILED: {error:?} -- no write\n"
    ));
}

/// Public entry: called from `fifa17::install`. Spawns the deferred worker if
/// OPENFUT_SBC_HOOK=1; otherwise logs "disabled" and returns (fully inert).
pub fn install() {
    let armed = std::env::var("OPENFUT_SBC_HOOK")
        .map(|v| v == "1")
        .unwrap_or(false);
    ARMED.store(armed, Ordering::Relaxed);
    if !armed {
        STATE.store(RuntimeState::Disabled as usize, Ordering::Relaxed);
        crate::write_log("SBC_HOOK: disabled (set OPENFUT_SBC_HOOK=1 to enable)\n");
        return;
    }
    ARM_ONLY.store(
        std::env::var("OPENFUT_SBC_ARM_ONLY")
            .map(|v| v == "1")
            .unwrap_or(false),
        Ordering::Relaxed,
    );
    POPULATE.store(
        std::env::var("OPENFUT_SBC_POPULATE")
            .map(|v| v == "1")
            .unwrap_or(false),
        Ordering::Relaxed,
    );
    crate::write_log("SBC_HOOK: ARMED (deferred worker spawning)\n");
    std::thread::spawn(|| unsafe { worker() });
}

/// Deferred worker: waits (up to ~5 min) for CardsDLL to load — it only appears when
/// the user enters Ultimate Team — then runs the resolve/log (+ optional Tier-0 arm)
/// exactly once.
unsafe fn worker() {
    let mut base = 0usize;
    for _ in 0..600u32 {
        base = resolve_cards_base();
        if base != 0 {
            break;
        }
        std::thread::sleep(std::time::Duration::from_millis(500));
    }
    if base == 0 {
        crate::write_log("SBC_HOOK: CardsDLL_Win64_retail.dll never loaded — giving up\n");
        return;
    }
    CARDS_BASE.store(base, Ordering::Relaxed);
    let slide = base.wrapping_sub(IMAGE_BASE);
    let ctrl_ok = control_matches(base);
    crate::write_log(&format!(
        "SBC_HOOK: CardsDLL base={base:#x} slide={slide:#x} CONTROL={}\n",
        if ctrl_ok { "OK" } else { "MISMATCH-ABORT" }
    ));
    if !ctrl_ok {
        STATE.store(RuntimeState::Failed as usize, Ordering::Release);
        return; // module map moved -> offsets untrustworthy (spec §1)
    }

    if !transition(RuntimeState::Disabled, RuntimeState::Resolved) {
        crate::write_log("SBC_HOOK: invalid state transition to Resolved -- no write\n");
        STATE.store(RuntimeState::Failed as usize, Ordering::Release);
        return;
    }

    // Resolve and validate A -> B, M. The vtable method checks make it substantially
    // harder for a coincidental heap pointer to pass after a binary/layout mismatch.
    let snapshot = match runtime_snapshot(base).and_then(|snapshot| {
        validate_snapshot(base, &snapshot)?;
        Ok(snapshot)
    }) {
        Ok(snapshot) => snapshot,
        Err(error) => {
            set_failed(error);
            return;
        }
    };
    if !transition(RuntimeState::Resolved, RuntimeState::Validated) {
        crate::write_log("SBC_HOOK: invalid state transition to Validated -- no write\n");
        STATE.store(RuntimeState::Failed as usize, Ordering::Release);
        return;
    }
    let a = snapshot.a;
    let b = snapshot.b;
    let m = snapshot.m;
    let m_count = (m != 0).then(|| read_u16(m + M_COUNT_OFF)).flatten();
    crate::write_log(&format!(
        "SBC_HOOK: A={a:#x} B={b:#x} B+0x28(ready)={:?} B+0x08(coll)={:?} M=*(A+0x20a68)={:?} WORD[M+0x50]={:?}\n",
        Some(snapshot.b_ready), opt_hex(Some(snapshot.b_coll)), opt_hex(Some(m)), m_count,
    ));

    // Tier-0 — arm-only negative control. Write ONLY BYTE[B+0x28]=1; leave B+0x08=0 so
    // isValid takes the short-circuit (spec §4). Renders the menu EMPTY (M null/empty) —
    // this is the baseline, NOT the fix. One-shot.
    if ARM_ONLY.load(Ordering::Relaxed) {
        if DONE.swap(true, Ordering::Relaxed) {
            return;
        }
        // Re-snapshot immediately before mutation to reduce the time-of-check/time-of-use
        // window. In particular, the exact patch byte must still be 0 and B+0x08 null.
        let write_snapshot = match runtime_snapshot(base).and_then(|snapshot| {
            validate_snapshot(base, &snapshot)?;
            if !writable_u8(snapshot.b + B_READY_OFF) {
                return Err(ValidationError::ReadyByteNotWritable);
            }
            Ok(snapshot)
        }) {
            Ok(snapshot) => snapshot,
            Err(error) => {
                set_failed(error);
                return;
            }
        };
        crate::write_log(&format!(
            "SBC_HOOK: Tier-0 arm-only -> writing BYTE[{:#x}]=1 (expect EMPTY render, no modal)\n",
            write_snapshot.b + B_READY_OFF
        ));
        core::ptr::write_volatile((write_snapshot.b + B_READY_OFF) as *mut u8, 1u8);
        match read_u8(write_snapshot.b + B_READY_OFF) {
            Some(1) if transition(RuntimeState::Validated, RuntimeState::Committed) => {}
            _ => {
                set_failed(ValidationError::ReadyByteUnexpected);
                return;
            }
        }
        crate::write_log(
            "SBC_HOOK: Tier-0 arm-only DONE (open the SBC menu; ~2 placeholder tiles expected)\n",
        );
        return;
    }

    // Legacy Tier-1 gate — deliberately blocked. The fresh live exchange proves FIFA
    // already owns a real response and SAX reader for /sbs/sets. The next milestone is
    // passive tracing of the native response-to-deserializer dispatch, not construction
    // of a reader. Cold-calling with a fabricated reader would CLEAR M and/or segfault.
    if POPULATE.load(Ordering::Relaxed) {
        crate::write_log(
            "SBC_HOOK: legacy Tier-1 populate is BLOCKED — capture the genuine response \
             and reader at the native dispatch boundary first (see client-hook plan M3/M4). \
             No deser call made; fabricated readers can clear M or crash.\n",
        );
    }
}

fn opt_hex(o: Option<usize>) -> String {
    match o {
        Some(v) => format!("{v:#x}"),
        None => "<unreadable>".to_string(),
    }
}

/// Legacy Tier-1 scaffold. **Never call this with a fabricated reader.** The intended
/// implementation is now a guarded synchronous dispatch repair that borrows the genuine
/// response and reader from the real HTTP transaction on its native thread.
///
/// Sequence once `reader` (a primed SAX reader over canned sbs/sets JSON) exists:
///   let base = CARDS_BASE.load(Relaxed);
///   let deser: unsafe extern "system" fn(*mut u8, *mut u8) -> bool =
///       transmute(va(base, rva::DESER_SBS_SETS));
///   deser(core::ptr::null_mut(), reader);   // self-locates mgr, clears+appends+finalizes+commits M
///   // then Tier-0 arm: BYTE[B+0x28]=1, leave B+0x08=0
///   // then refresh so 0x1800b5eda re-reads WORD[M+0x50]
#[allow(dead_code)]
unsafe fn populate_m(_reader: *mut u8) {
    // Intentionally unimplemented: the passive trace must prove the response/reader
    // ownership and exact virtual-dispatch boundary before any parser call is enabled.
    unreachable!(
        "populate_m requires a proven native dispatch contract; see client-hook plan M3/M4"
    );
}

#[cfg(test)]
mod tests {
    use super::*;

    fn valid_snapshot(base: usize) -> RuntimeSnapshot {
        let a = 0x1000_0000usize;
        RuntimeSnapshot {
            a,
            a_vtable: base + A_VTABLE_RVA,
            a_b_getter: base + 0x11c1f0,
            b: a + B_OFF,
            b_vtable: base + B_VTABLE_RVA,
            b_dtor: base + B_DTOR_RVA,
            b_isvalid: base + B_ISVALID_RVA,
            b_clear: base + B_CLEAR_RVA,
            b_ready: B_READY_EXPECTED_BEFORE_ARM,
            b_coll: 0,
            m: 0,
        }
    }

    #[test]
    fn accepts_exact_runtime_identity_with_null_uninitialized_m() {
        let base = 0x7fff_0000_0000usize;
        assert_eq!(validate_snapshot(base, &valid_snapshot(base)), Ok(()));
    }

    #[test]
    fn rejects_wrong_a_or_b_class_identity() {
        let base = 0x7fff_0000_0000usize;
        let mut snapshot = valid_snapshot(base);
        snapshot.a_vtable += 8;
        assert_eq!(
            validate_snapshot(base, &snapshot),
            Err(ValidationError::AVtableMismatch)
        );

        let mut snapshot = valid_snapshot(base);
        snapshot.b_vtable += 8;
        assert_eq!(
            validate_snapshot(base, &snapshot),
            Err(ValidationError::BVtableMismatch)
        );
    }

    #[test]
    fn rejects_changed_patch_byte_or_live_collection() {
        let base = 0x7fff_0000_0000usize;
        let mut snapshot = valid_snapshot(base);
        snapshot.b_ready = 1;
        assert_eq!(
            validate_snapshot(base, &snapshot),
            Err(ValidationError::ReadyByteUnexpected)
        );

        let mut snapshot = valid_snapshot(base);
        snapshot.b_coll = 0x1234_0000;
        assert_eq!(
            validate_snapshot(base, &snapshot),
            Err(ValidationError::CollectionNotNull)
        );
    }

    #[test]
    fn state_machine_is_forward_only_and_fail_closed() {
        assert!(valid_transition(
            RuntimeState::Disabled,
            RuntimeState::Resolved
        ));
        assert!(valid_transition(
            RuntimeState::Resolved,
            RuntimeState::Validated
        ));
        assert!(valid_transition(
            RuntimeState::Validated,
            RuntimeState::Committed
        ));
        assert!(valid_transition(RuntimeState::Parsed, RuntimeState::Failed));
        assert!(!valid_transition(
            RuntimeState::Validated,
            RuntimeState::Resolved
        ));
        assert!(!valid_transition(
            RuntimeState::Failed,
            RuntimeState::Resolved
        ));
        assert!(!valid_transition(
            RuntimeState::Resolved,
            RuntimeState::Committed
        ));
    }
}