// Framebuffer snapshot shim: preloaded into xochitl, it captures the e-paper
// framebuffer (via setBuffers) and, when the trigger file /tmp/fbdump appears,
// saves the current framebuffer to /home/root/fbdump.png. Used to recover the
// real Calligraphy nib angle by measuring xochitl's actual rendered strokes.

#define _GNU_SOURCE 1
#include <QImage>
#include <tuple>
#include <dlfcn.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/stat.h>
#include <cstdio>

namespace {
uchar *g_bits = nullptr;
int g_w = 0, g_h = 0, g_bpl = 0, g_fmt = 0;
bool g_started = false;

void *dumper(void *)
{
    fprintf(stderr, "FBSHIM dumper thread started\n");
    for (;;) {
        usleep(400000);
        struct stat st;
        if (g_bits && stat("/tmp/fbdump", &st) == 0) {
            QImage snap = QImage(g_bits, g_w, g_h, g_bpl, QImage::Format(g_fmt)).copy();
            bool ok = snap.save("/home/root/fbdump.png");
            if (!ok) ok = snap.save("/home/root/fbdump.bmp", "BMP");
            ::unlink("/tmp/fbdump");
            fprintf(stderr, "FBDUMP %dx%d saved ok=%d\n", g_w, g_h, int(ok));
        }
    }
    return nullptr;
}
}

extern "C" void _ZN13EPFramebuffer10setBuffersESt5tupleIJ6QImageS1_EEPS1_(
    void *self, void *tuplePtr, void *imgPtr)
{
    static void (*real)(void *, void *, void *) = nullptr;
    if (!real)
        real = (void (*)(void *, void *, void *))dlsym(
            RTLD_NEXT, "_ZN13EPFramebuffer10setBuffersESt5tupleIJ6QImageS1_EEPS1_");
    auto *t = reinterpret_cast<std::tuple<QImage, QImage> *>(tuplePtr);
    const QImage &a = std::get<0>(*t);
    g_bits = const_cast<uchar *>(a.constBits());
    g_w = a.width(); g_h = a.height(); g_bpl = a.bytesPerLine(); g_fmt = int(a.format());
    fprintf(stderr, "FBSHIM setBuffers %dx%d fmt=%d\n", g_w, g_h, g_fmt);
    if (!g_started) {
        g_started = true;
        pthread_t th;
        pthread_create(&th, nullptr, dumper, nullptr);
    }
    if (real) real(self, tuplePtr, imgPtr);
}