/* Build: cc -std=c11 -Wall -Wextra convert.c -o convert $(pkg-config --cflags --libs libcurl) */
#include <curl/curl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct Buffer {
    unsigned char *data;
    size_t length;
};

static size_t receive_bytes(char *data, size_t size, size_t count, void *user)
{
    struct Buffer *buffer = user;
    if (size && count > SIZE_MAX / size)
        return 0;
    size_t length = size * count;
    if (length > SIZE_MAX - buffer->length)
        return 0;
    if (!length)
        return 0;
    unsigned char *next = realloc(buffer->data, buffer->length + length);
    if (!next)
        return 0;
    memcpy(next + buffer->length, data, length);
    buffer->data = next;
    buffer->length += length;
    return length;
}

static CURLcode add_text(curl_mime *form, const char *name, const char *value)
{
    curl_mimepart *part = curl_mime_addpart(form);
    if (!part)
        return CURLE_OUT_OF_MEMORY;
    CURLcode result = curl_mime_name(part, name);
    return result == CURLE_OK
        ? curl_mime_data(part, value, CURL_ZERO_TERMINATED) : result;
}

#define CHECK_CURL(call) do { \
    CURLcode code = (call); \
    if (code != CURLE_OK) { \
        fprintf(stderr, "Request failed: %s\n", curl_easy_strerror(code)); \
        goto cleanup; \
    } \
} while (0)

int main(int argc, char **argv)
{
    const char *mode = argc > 1 ? argv[1] : "url";
    const char *input = argc > 2 ? argv[2] : "https://example.com/";
    const char *output = argc > 3 ? argv[3] : "output.pdf";
    if (argc > 4 || (argc == 2) ||
            (strcmp(mode, "url") && strcmp(mode, "file") && strcmp(mode, "text"))) {
        fprintf(stderr, "Usage: %s [url|file|text INPUT [OUTPUT.pdf]]\n", argv[0]);
        return EXIT_FAILURE;
    }
    const char *username = getenv("API_USERNAME");
    const char *api_key = getenv("API_KEY");
    if (!username || !*username || !api_key || !*api_key) {
        fputs("Set API_USERNAME and API_KEY. Both may be demo for testing.\n", stderr);
        return EXIT_FAILURE;
    }

    CURLcode initialized = curl_global_init(CURL_GLOBAL_DEFAULT);
    if (initialized != CURLE_OK) {
        fprintf(stderr, "libcurl initialization failed: %s\n",
                curl_easy_strerror(initialized));
        return EXIT_FAILURE;
    }
    int result = EXIT_FAILURE;
    CURL *curl = curl_easy_init();
    curl_mime *form = NULL;
    struct Buffer response = {NULL, 0};
    long status = 0;
    if (!curl || !(form = curl_mime_init(curl))) {
        fputs("Cannot allocate the request.\n", stderr);
        goto cleanup;
    }

    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_URL, "https://api.pdfcrowd.com/convert/24.04/"));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_USERNAME, username));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_PASSWORD, api_key));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_HTTPAUTH, CURLAUTH_BASIC));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 30L));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_TIMEOUT, 120L));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, receive_bytes));
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_WRITEDATA, &response));

    CHECK_CURL(add_text(form, "input_format", "html"));
    CHECK_CURL(add_text(form, "output_format", "pdf"));
    CHECK_CURL(add_text(form, "content_viewport_width", "balanced"));
    CHECK_CURL(add_text(form, "page_size", "A4"));
    if (!strcmp(mode, "file")) {
        curl_mimepart *part = curl_mime_addpart(form);
        if (!part) {
            fputs("Cannot allocate the file upload.\n", stderr);
            goto cleanup;
        }
        CHECK_CURL(curl_mime_name(part, "file"));
        CHECK_CURL(curl_mime_filedata(part, input));
    } else {
        CHECK_CURL(add_text(form, mode, input));
    }
    CHECK_CURL(curl_easy_setopt(curl, CURLOPT_MIMEPOST, form));
    CHECK_CURL(curl_easy_perform(curl));
    CHECK_CURL(curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &status));
    if (status != 200) {
        fprintf(stderr, "PDFCrowd returned HTTP %ld:\n", status);
        if (response.length)
            fwrite(response.data, 1, response.length, stderr);
        fputc('\n', stderr);
        goto cleanup;
    }

    FILE *file = fopen(output, "wb");
    if (!file) {
        perror("Cannot open the output file");
        goto cleanup;
    }
    size_t written = fwrite(response.data, 1, response.length, file);
    int closed = fclose(file);
    if (written != response.length || closed != 0) {
        fputs("Could not write the complete PDF.\n", stderr);
        goto cleanup;
    }
    printf("Saved %s\n", output);
    result = EXIT_SUCCESS;

cleanup:
    if (curl)
        curl_easy_cleanup(curl);
    curl_mime_free(form);
    free(response.data);
    curl_global_cleanup();
    return result;
}