// SPDX-License-Identifier: GPL-2.0-only
/*
 * Experimental offline decoder only.
 * The 12-bit unpack and transpose candidates are adapted from Metrohan's
 * gxfp5130-linux decoder.  They are not part of the capture/library path and
 * are not yet verified for this 0x2504 ChicagoHU device.
 */
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define IMAGE_OFFSET 8u
#define PACKED_LENGTH 7680u
#define CRC_LENGTH 4u
#define SAMPLE_COUNT 5120u
#define RAW_WIDTH 64u
#define RAW_HEIGHT 80u
#define TRANSPOSED_WIDTH 80u
#define TRANSPOSED_HEIGHT 64u
#define SAMPLE_MAX 4095u

static uint16_t get_le16(const uint8_t *p)
{
        return (uint16_t)p[0] | ((uint16_t)p[1] << 8);
}

static uint32_t crc32_mpeg2(const uint8_t *data, size_t length)
{
        uint32_t crc = UINT32_MAX;
        size_t i;

        for (i = 0; i < length; i++) {
                unsigned int bit;

                crc ^= (uint32_t)data[i] << 24;
                for (bit = 0; bit < 8; bit++)
                        crc = (crc & UINT32_C(0x80000000))
                                ? (crc << 1) ^ UINT32_C(0x04c11db7)
                                : crc << 1;
        }
        return crc;
}

static uint32_t get_goodix_crc(const uint8_t *p)
{
        return ((uint32_t)p[2] << 24) | ((uint32_t)p[3] << 16) |
               ((uint32_t)p[0] << 8) | (uint32_t)p[1];
}

static int read_file(const char *path, uint8_t **out, size_t *out_length)
{
        FILE *file = fopen(path, "rb");
        long end;
        uint8_t *data;

        if (!file)
                return -errno;
        if (fseek(file, 0, SEEK_END) != 0 || (end = ftell(file)) < 0 ||
            fseek(file, 0, SEEK_SET) != 0) {
                fclose(file);
                return -EIO;
        }
        data = malloc(end > 0 ? (size_t)end : 1u);
        if (!data) {
                fclose(file);
                return -ENOMEM;
        }
        if (end > 0 && fread(data, 1, (size_t)end, file) != (size_t)end) {
                free(data);
                fclose(file);
                return -EIO;
        }
        if (fclose(file) != 0) {
                free(data);
                return -EIO;
        }
        *out = data;
        *out_length = (size_t)end;
        return 0;
}

static void unpack_four(const uint8_t *p, uint16_t out[4])
{
        out[0] = (uint16_t)(((p[0] & 0x0fu) << 8) | p[1]);
        out[1] = (uint16_t)((p[3] << 4) | (p[0] >> 4));
        out[2] = (uint16_t)(((p[5] & 0x0fu) << 8) | p[2]);
        out[3] = (uint16_t)((p[4] << 4) | (p[5] >> 4));
}

static int write_pgm(const char *path, const uint16_t *pixels,
                     size_t width, size_t height, int inverted)
{
        FILE *file = fopen(path, "wb");
        size_t i;

        if (!file)
                return -errno;
        if (fprintf(file, "P5\n%zu %zu\n%u\n",
                    width, height, SAMPLE_MAX) < 0) {
                fclose(file);
                return -EIO;
        }
        for (i = 0; i < width * height; i++) {
                uint16_t value = inverted
                        ? (uint16_t)(SAMPLE_MAX - pixels[i])
                        : pixels[i];
                uint8_t encoded[2] = {
                        (uint8_t)(value >> 8), (uint8_t)value
                };

                if (fwrite(encoded, 1, sizeof(encoded), file) !=
                    sizeof(encoded)) {
                        fclose(file);
                        return -EIO;
                }
        }
        return fclose(file) == 0 ? 0 : -EIO;
}

int main(int argc, char **argv)
{
        const char *path = argc > 1 ? argv[1] : "capture_plaintext.bin";
        uint8_t *frame = NULL;
        size_t frame_length = 0;
        uint16_t *raw = NULL;
        uint16_t *transposed = NULL;
        uint16_t declared;
        const uint8_t *packed;
        const uint8_t *crc_bytes;
        uint32_t calculated_crc;
        uint32_t stored_crc;
        size_t offset;
        size_t sample = 0;
        int ret;

        ret = read_file(path, &frame, &frame_length);
        if (ret) {
                fprintf(stderr, "%s: %s\n", path, strerror(-ret));
                return EXIT_FAILURE;
        }
        if (frame_length < 3u) {
                fprintf(stderr, "input is shorter than the frame header\n");
                ret = -EBADMSG;
                goto out;
        }
        declared = get_le16(frame + 1);
        if (frame[0] != 0x20u || frame_length != 3u + declared ||
            frame_length < IMAGE_OFFSET + PACKED_LENGTH + CRC_LENGTH + 1u) {
                fprintf(stderr,
                        "unexpected frame: cmd=0x%02x declared=%u size=%zu\n",
                        frame[0], declared, frame_length);
                ret = -EBADMSG;
                goto out;
        }

        packed = frame + IMAGE_OFFSET;
        crc_bytes = packed + PACKED_LENGTH;
        calculated_crc = crc32_mpeg2(packed, PACKED_LENGTH);
        stored_crc = get_goodix_crc(crc_bytes);
        if (calculated_crc != stored_crc) {
                fprintf(stderr,
                        "image CRC mismatch: calculated=%08x stored=%08x\n",
                        calculated_crc, stored_crc);
                ret = -EBADMSG;
                goto out;
        }

        raw = calloc(SAMPLE_COUNT, sizeof(*raw));
        transposed = calloc(SAMPLE_COUNT, sizeof(*transposed));
        if (!raw || !transposed) {
                ret = -ENOMEM;
                goto out;
        }

        for (offset = 0; offset < PACKED_LENGTH; offset += 6u) {
                uint16_t values[4];
                size_t i;

                unpack_four(packed + offset, values);
                for (i = 0; i < 4u; i++, sample++) {
                        size_t destination;

                        raw[sample] = values[i];
                        destination = (sample % RAW_WIDTH) *
                                      TRANSPOSED_WIDTH +
                                      sample / RAW_WIDTH;
                        transposed[destination] = values[i];
                }
        }

        ret = write_pgm("candidate_raw.pgm", raw,
                        RAW_WIDTH, RAW_HEIGHT, 0);
        if (!ret)
                ret = write_pgm("candidate_transposed.pgm", transposed,
                                TRANSPOSED_WIDTH, TRANSPOSED_HEIGHT, 0);
        if (!ret)
                ret = write_pgm("candidate_inverted.pgm", raw,
                                RAW_WIDTH, RAW_HEIGHT, 1);
        if (!ret)
                ret = write_pgm("candidate_transposed_inverted.pgm",
                                transposed, TRANSPOSED_WIDTH,
                                TRANSPOSED_HEIGHT, 1);
        if (ret) {
                fprintf(stderr, "PGM write failed: %s\n", strerror(-ret));
                goto out;
        }

        printf("Input CRC valid: 0x%08x\n", calculated_crc);
        printf("Experimental outputs written:\n");
        printf("  candidate_raw.pgm (64x80)\n");
        printf("  candidate_transposed.pgm (80x64)\n");
        printf("  candidate_inverted.pgm (64x80)\n");
        printf("  candidate_transposed_inverted.pgm (80x64)\n");

out:
        free(transposed);
        free(raw);
        free(frame);
        return ret ? EXIT_FAILURE : EXIT_SUCCESS;
}