/* sample.c — consumer seqlock reads: frame sampling, cursor, geometry, status.
 *
 * Every guest read goes through gva_read into a local copy; we never hold a
 * gva_ptr across a seqlock window (it is borrowed and not atomic for re-check).
 * The discipline is the mirror of the producer's publish order in atomic-shim.h,
 * but an independent body — this is consumer code, not shared producer code.
 *
 * Lossy by contract: when a writer keeps a window busy past VGPUP_SEQLOCK_RETRIES
 * we return 0 (skip), never block. Blocking longer would be behavioural timing
 * (control's concern), which has no place in the sensor.
 *
 * All reads go under r->proc_cr3 (the producer's user-AS cr3, cached in the
 * handle at discovery), NOT the System kcr3. A <0 from any gva_read means a page
 * is gone — the producer process may have restarted; we propagate <0 and the
 * caller re-discovers (see vgpu_perception.h "Two epochs + producer restart").
 */

#include "perception-internal.h"
#include <stdio.h>   /* TEMP debug (revert): stderr skip-reason trace */

/* Read one cold-line / packed field at producer offset `off` into dst under the
 * producer's user-AS cr3. */
static int read_field(vmie_mem* m, uintptr_t cr3, uint64_t region_gva,
                      size_t off, void* dst, size_t n)
{
    return gva_read(m, cr3, (uintptr_t)region_gva + off, dst, n) < 0 ? -1 : 0;
}

int vgpup_sample_frame(vgpup_region* r, vmie_mem* m,
                       uint8_t* dst, size_t cap, vgpup_frame_info* info)
{
    unsigned attempt;
    static unsigned long _dc = 0;            /* TEMP debug: 1/240 call gate */
    int _dbg = ((_dc++ % 240u) == 0u);

    if (!r || !m || !dst || !info) { return -1; }

    for (attempt = 0; attempt < VGPUP_SEQLOCK_RETRIES; ++attempt) {
        uint32_t   latest = 0, seq_before = 0, seq_after = 0;
        vgpu_desc_t d;
        uint64_t   slot_gva, seq_gva, desc_gva;
        size_t     frame_bytes;

        /* latest (acquire-equivalent: its own read) */
        if (read_field(m, r->proc_cr3, r->region_gva,
                       offsetof(vgpu_producer_t, latest), &latest, sizeof latest) < 0) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG ret=-1 latest-read-fail\n");
            return -1;
        }
        if (latest == VGPU_LATEST_NONE || latest >= VGPU_SLOT_COUNT) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG ret=0 A latest=%u\n", latest);
            return 0;
        }

        seq_gva  = r->region_gva + offsetof(vgpu_producer_t, seq) + (uint64_t)latest * sizeof(uint32_t);
        desc_gva = r->region_gva + offsetof(vgpu_producer_t, desc) + (uint64_t)latest * sizeof(vgpu_desc_t);

        if (vgpup_read_seq(m, r->proc_cr3, seq_gva, &seq_before) < 0) { return -1; }
        if (vgpup_seq_is_writing(seq_before)) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG cont B att=%u latest=%u seqB=%u (writing)\n", attempt, latest, seq_before);
            continue;   /* writer in slot */
        }

        if (gva_read(m, (uintptr_t)r->proc_cr3, (uintptr_t)desc_gva, &d, sizeof d) < 0) { return -1; }

        /* dedup by frame_id: nothing newer than what we already sampled */
        if (d.frame_id <= r->last_frame_id) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG ret=0 C dedup dfid=%llu last=%llu\n",
                              (unsigned long long)d.frame_id, (unsigned long long)r->last_frame_id);
            return 0;
        }

        /* descriptor sanity within the read window (tight BGRA, bounded dims) */
        if (d.format != VGPU_FMT_BGRA8888 || d.stride != d.width * 4u ||
            d.width == 0u || d.width > VGPU_MAX_WIDTH ||
            d.height == 0u || d.height > VGPU_MAX_HEIGHT) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG cont D torn att=%u w=%u h=%u s=%u f=%u\n",
                              attempt, d.width, d.height, d.stride, d.format);
            continue;   /* likely a torn read; retry */
        }

        frame_bytes = (size_t)d.height * d.stride;
        if (frame_bytes > VGPU_SLOT_STRIDE) { return 0; }   /* impossible-large → skip */
        if (frame_bytes > cap) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG ret=0 F fbytes=%zu cap=%zu\n", frame_bytes, cap);
            return 0;   /* would not fit → lossy drop */
        }

        slot_gva = r->ring_gva + (uint64_t)latest * VGPU_SLOT_STRIDE;
        if (gva_read(m, (uintptr_t)r->proc_cr3, (uintptr_t)slot_gva, dst, frame_bytes) < 0) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG ret=-1 G slot-read-fail latest=%u fbytes=%zu\n", latest, frame_bytes);
            return -1;
        }

        /* re-check the slot seq: unchanged and still even → snapshot consistent */
        if (vgpup_read_seq(m, r->proc_cr3, seq_gva, &seq_after) < 0) { return -1; }
        if (seq_after != seq_before || vgpup_seq_is_writing(seq_after)) {
            if (_dbg) fprintf(stderr, "VGPUP_DBG cont H att=%u latest=%u seqB=%u seqA=%u\n",
                              attempt, latest, seq_before, seq_after);
            continue;   /* the slot was rewritten under us — retry */
        }

        info->desc.width        = d.width;
        info->desc.height       = d.height;
        info->desc.stride       = d.stride;
        info->desc.format       = d.format;
        info->desc.frame_id     = d.frame_id;
        info->desc.timestamp_ns = d.timestamp_ns;
        info->bytes             = frame_bytes;

        r->last_frame_id = d.frame_id;
        return 1;
    }
    if (_dbg) fprintf(stderr, "VGPUP_DBG ret=0 I retry-exhaust (%u attempts all busy)\n", VGPUP_SEQLOCK_RETRIES);
    return 0;   /* writer kept the slot busy past the retry limit — skip */
}

int vgpup_read_cursor(vgpup_region* r, vmie_mem* m, vgpup_cursor* out)
{
    unsigned attempt;

    if (!r || !m || !out) { return -1; }

    /* The producer bumps cursor_seq LAST (acquire), so we read the cursor line
     * first and gate on cursor_seq being even and unchanged across the window. */
    for (attempt = 0; attempt < VGPUP_SEQLOCK_RETRIES; ++attempt) {
        uint32_t seq_before = 0, seq_after = 0;
        uint32_t visible = 0, hotspot = 0, glyph = 0, id = 0;
        uint64_t pos = 0;

        if (vgpup_read_seq(m, r->proc_cr3, r->region_gva + offsetof(vgpu_producer_t, cursor_seq),
                           &seq_before) < 0) { return -1; }
        if (vgpup_seq_is_writing(seq_before)) { continue; }

        if (read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cursor_visible), &visible, sizeof visible) < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cursor_pos),     &pos,     sizeof pos)     < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cursor_hotspot), &hotspot, sizeof hotspot) < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cursor_glyph),   &glyph,   sizeof glyph)   < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cursor_id),      &id,      sizeof id)      < 0) {
            return -1;
        }

        if (vgpup_read_seq(m, r->proc_cr3, r->region_gva + offsetof(vgpu_producer_t, cursor_seq),
                           &seq_after) < 0) { return -1; }
        if (seq_after != seq_before || vgpup_seq_is_writing(seq_after)) { continue; }

        out->seq     = seq_after;
        out->visible = visible;
        out->x       = vgpup_cursor_x(pos);
        out->y       = vgpup_cursor_y(pos);
        out->hot_x   = vgpup_lo16(hotspot);
        out->hot_y   = vgpup_hi16(hotspot);
        out->glyph_w = vgpup_lo16(glyph);
        out->glyph_h = vgpup_hi16(glyph);
        out->id      = id;
        return 1;
    }
    return 0;
}

int vgpup_read_geometry(vgpup_region* r, vmie_mem* m, vgpup_geometry* out)
{
    unsigned attempt;

    if (!r || !m || !out) { return -1; }

    for (attempt = 0; attempt < VGPUP_SEQLOCK_RETRIES; ++attempt) {
        uint32_t seq_before = 0, seq_after = 0;
        int32_t  virt_x = 0, virt_y = 0, cap_x = 0, cap_y = 0;
        uint32_t virt_w = 0, virt_h = 0, dpi = 0, refresh_mhz = 0;

        if (vgpup_read_seq(m, r->proc_cr3, r->region_gva + offsetof(vgpu_producer_t, geom_seq),
                           &seq_before) < 0) { return -1; }
        if (vgpup_seq_is_writing(seq_before)) { continue; }

        if (read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, virt_x),      &virt_x,      sizeof virt_x)      < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, virt_y),      &virt_y,      sizeof virt_y)      < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, virt_w),      &virt_w,      sizeof virt_w)      < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, virt_h),      &virt_h,      sizeof virt_h)      < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cap_x),       &cap_x,       sizeof cap_x)       < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, cap_y),       &cap_y,       sizeof cap_y)       < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, dpi),         &dpi,         sizeof dpi)         < 0 ||
            read_field(m, r->proc_cr3, r->region_gva, offsetof(vgpu_producer_t, refresh_mhz), &refresh_mhz, sizeof refresh_mhz) < 0) {
            return -1;
        }

        if (vgpup_read_seq(m, r->proc_cr3, r->region_gva + offsetof(vgpu_producer_t, geom_seq),
                           &seq_after) < 0) { return -1; }
        if (seq_after != seq_before || vgpup_seq_is_writing(seq_after)) { continue; }

        out->virt_x      = virt_x;
        out->virt_y      = virt_y;
        out->virt_w      = virt_w;
        out->virt_h      = virt_h;
        out->cap_x       = cap_x;
        out->cap_y       = cap_y;
        out->dpi         = dpi;
        out->refresh_mhz = refresh_mhz;
        return 1;
    }
    return 0;
}

int vgpup_read_status(vgpup_region* r, vmie_mem* m, vgpup_status* out)
{
    vgpu_producer_t p;

    if (!r || !m || !out) { return -1; }

    /* Cold line: single naturally-aligned atomic fields with no seqlock. Read
     * the whole producer block once and pick the cold fields — "fresh enough"
     * by the lossy contract. */
    if (gva_read(m, (uintptr_t)r->proc_cr3, (uintptr_t)r->region_gva, &p, sizeof p) < 0) { return -1; }

    out->heartbeat         = p.heartbeat;
    out->run_epoch         = p.run_epoch;
    out->status            = p.status;
    out->backend           = p.backend;
    out->error_code        = p.error_code;
    out->applied_fps       = p.applied_fps;
    out->supported_formats = p.supported_formats;
    out->ctrl_ack          = p.ctrl_ack;
    out->full_frame_ack    = p.full_frame_ack;
    out->content_change_ns = p.content_change_ns;

    r->run_epoch = p.run_epoch;   /* feed the session-break detector */
    return 0;
}