// Simulator backend: flash is emulated in a file (SKEY_FLASH_FILE), randomness
// comes from the OS, and HID packets travel over stdin/stdout.
//
// The button: without SKEY_BUTTON_FILE every request is approved. With it,
// creating that file is a press (its mtime is the press time), and the
// simulator deletes it when the press is used.
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/random.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>

#include "host.h"
#include "platform.h"

static uint8_t flash[STORAGE_SIZE];
static const char *flash_path;
static const char *button_path;
static struct timespec start;

void platform_init(void) {
    flash_path = getenv("SKEY_FLASH_FILE");
    if (!flash_path) flash_path = "skey_flash.bin";
    button_path = getenv("SKEY_BUTTON_FILE");
    memset(flash, 0xff, sizeof(flash));
    FILE *f = fopen(flash_path, "rb");
    if (f) {
        if (fread(flash, 1, sizeof(flash), f) != sizeof(flash)) memset(flash, 0xff, sizeof(flash));
        fclose(f);
    }
    clock_gettime(CLOCK_MONOTONIC, &start);
}

uint32_t platform_millis(void) {
    struct timespec now;
    clock_gettime(CLOCK_MONOTONIC, &now);
    return (uint32_t)((now.tv_sec - start.tv_sec) * 1000 + (now.tv_nsec - start.tv_nsec) / 1000000);
}

void platform_random(uint8_t *buf, size_t len) {
    while (len > 0) {
        ssize_t n = getrandom(buf, len, 0);
        if (n < 0) platform_panic("getrandom failed");
        buf += n;
        len -= (size_t)n;
    }
}

void platform_panic(const char *msg) {
    fprintf(stderr, "skey_sim: %s\n", msg);
    abort();
}

bool platform_button_take_press(uint32_t max_age_ms) {
    struct stat st;
    struct timespec now;
    if (!button_path) return true;
    if (stat(button_path, &st) != 0) return false;
    unlink(button_path);
    clock_gettime(CLOCK_REALTIME, &now);
    int64_t age_ms = (int64_t)(now.tv_sec - st.st_mtim.tv_sec) * 1000 + (now.tv_nsec - st.st_mtim.tv_nsec) / 1000000;
    return age_ms <= (int64_t)max_age_ms;
}

void platform_led(bool on) {
    (void)on;
}

void platform_wink(void) {
    fprintf(stderr, "skey_sim: wink\n");
}

static void save_flash(void) {
    FILE *f = fopen(flash_path, "wb");
    if (!f || fwrite(flash, 1, sizeof(flash), f) != sizeof(flash)) platform_panic("cannot write flash file");
    fclose(f);
}

void platform_flash_read(uint32_t offset, void *buf, size_t len) {
    if (offset > STORAGE_SIZE || len > STORAGE_SIZE - offset) platform_panic("flash read out of range");
    memcpy(buf, flash + offset, len);
}

void platform_flash_erase(uint32_t offset) {
    if (offset % STORAGE_SECTOR_SIZE || offset >= STORAGE_SIZE) platform_panic("bad flash erase");
    memset(flash + offset, 0xff, STORAGE_SECTOR_SIZE);
    save_flash();
}

// Behaves like NOR flash: whole pages only, and programming only clears bits.
void platform_flash_program(uint32_t offset, const void *buf, size_t len) {
    const uint8_t *src = buf;
    if (offset % STORAGE_PAGE_SIZE || len % STORAGE_PAGE_SIZE || offset > STORAGE_SIZE ||
        len > STORAGE_SIZE - offset)
        platform_panic("bad flash program");
    for (size_t i = 0; i < len; i++) flash[offset + i] &= src[i];
    save_flash();
}

void platform_hid_send(const uint8_t packet[HID_PACKET_SIZE]) {
    fwrite(packet, 1, HID_PACKET_SIZE, stdout);
    fflush(stdout);
}

bool host_receive(uint8_t packet[HID_PACKET_SIZE], int timeout_ms) {
    struct pollfd pfd = {.fd = STDIN_FILENO, .events = POLLIN};
    if (poll(&pfd, 1, timeout_ms) <= 0) return false;
    for (size_t got = 0; got < HID_PACKET_SIZE;) {
        ssize_t n = read(STDIN_FILENO, packet + got, HID_PACKET_SIZE - got);
        if (n <= 0) exit(0);  // the host closed the pipe: unplugged
        got += (size_t)n;
    }
    return true;
}

bool platform_hid_receive(uint8_t packet[HID_PACKET_SIZE]) {
    return host_receive(packet, 0);
}