/*
 * mktypst - dumb typst document generator.
 *
 * generates a typst document that imports and applies an mktypst template,
 * so you can start writing instead of pasting the same preamble every time.
 *
 * Author:  hachem <im@hachem.wtf>
 * Version: 0.1.0
 */

#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#define mktypst_program "mktypst"
#define mktypst_version "0.1.0"
#define mktypst_tagline "dumb typst document generator"
#define mktypst_package "@local/hachem:0.1.0"

enum Template
{
    template_paper,
    template_letter,
    template_count
};

struct Template_Info
{
    const char* key;
    const char* name;
};

struct Config
{
    const char* name;
    enum Template tmpl;
    const char* title;
    const char* author;
    const char* date;
    int use_stdout;
    int force;
};

static const struct Template_Info templates[template_count] =
{
    [template_paper]  = { .key = "paper",  .name = "paper" },
    [template_letter] = { .key = "letter", .name = "letter" },
};

static void print_version(void)
{
    (void) printf("%s %s\n", mktypst_program, mktypst_version);
}

static void print_usage(FILE* stream)
{
    (void) fprintf(
        stream,
        "%s %s - %s\n"
        "\n"
        "generates a typst document that imports and applies an mktypst\n"
        "template, so you can start writing instead of pasting a preamble.\n"
        "\n"
        "usage: %s [-t template] [-T title] [-a author] [-d date] [-f] <name>\n"
        "       %s [-v | -h]\n"
        "\n"
        "options:\n"
        "  -t, --template NAME  template to apply (default paper)\n"
        "  -T, --title TITLE    document title (default: the name)\n"
        "  -a, --author NAME    author name (default: git config user.name)\n"
        "  -d, --date DATE      document date (default: current month)\n"
        "  -f, --force          overwrite an existing file\n"
        "      --stdout         write to stdout instead of a .typ file\n"
        "  -v, --version        print version and bail\n"
        "  -h, --help           print this and bail\n"
        "\n"
        "by hachem <im@hachem.wtf>\n",
        mktypst_program, mktypst_version, mktypst_tagline,
        mktypst_program, mktypst_program);
}

static void error(const char* message, const char* detail)
{
    if (detail != NULL)
        (void) fprintf(stderr, "%s: error: %s: %s\n", mktypst_program, message, detail);
    else
        (void) fprintf(stderr, "%s: error: %s\n", mktypst_program, message);
}

/* match a value-taking option. handles both "--opt val" and "--opt=val".
 * returns 1 and sets *value on a match, -1 if the value is missing, else 0. */
static int opt_value(const char* arg, const char* shortname, const char* longname,
                     int argc, char** argv, int* i, const char** value)
{
    if (strcmp(arg, shortname) == 0 || strcmp(arg, longname) == 0)
    {
        if (*i + 1 >= argc)
            return -1;

        *value = argv[++(*i)];
        return 1;
    }

    size_t longlen = strlen(longname);

    if (strncmp(arg, longname, longlen) == 0 && arg[longlen] == '=')
    {
        *value = arg + longlen + 1;
        return 1;
    }

    return 0;
}

static int find_template(const char* key, enum Template* out)
{
    for (enum Template tmpl = 0; tmpl < template_count; tmpl++)
        if (strcmp(templates[tmpl].key, key) == 0)
        {
            *out = tmpl;
            return 1;
        }

    return 0;
}

/* the project name with a trailing ".typ" trimmed, used as the default title. */
static const char* stem_of(const char* name)
{
    static char buf[256];

    (void) snprintf(buf, sizeof buf, "%s", name);

    size_t len = strlen(buf);

    if (len >= 4 && strcmp(buf + len - 4, ".typ") == 0)
        buf[len - 4] = '\0';

    return buf;
}

/* best-effort author: git's configured name, else $USER. */
static const char* author_name(void)
{
    static char buf[256];

    buf[0] = '\0';

    FILE* pipe = popen("git config user.name", "r");

    if (pipe != NULL)
    {
        if (fgets(buf, (int) sizeof buf, pipe) != NULL)
        {
            size_t len = strlen(buf);

            if (len > 0 && buf[len - 1] == '\n')
                buf[len - 1] = '\0';
        }

        (void) pclose(pipe);
    }

    if (buf[0] == '\0')
    {
        const char* user = getenv("USER");

        (void) snprintf(buf, sizeof buf, "%s", user != NULL ? user : "Author");
    }

    return buf;
}

static const char* current_date(void)
{
    static char buf[64];

    time_t now = time(NULL);
    struct tm* local = localtime(&now);

    if (local == NULL || strftime(buf, sizeof buf, "%B %Y", local) == 0)
        (void) snprintf(buf, sizeof buf, "undated");

    return buf;
}

static void write_paper(FILE* out, const struct Config* config)
{
    (void) fprintf(
        out,
        "#import \"%s\": paper\n"
        "\n"
        "#show: paper.with(\n"
        "  title: \"%s\",\n"
        "  date: \"%s\",\n"
        "  authors: (\n"
        "    (name: \"%s\", location: []),\n"
        "  ),\n"
        ")\n"
        "\n"
        "= Introduction\n",
        mktypst_package, config->title, config->date, config->author);
}

static void write_letter(FILE* out, const struct Config* config)
{
    (void) fprintf(
        out,
        "#import \"%s\": letter\n"
        "\n"
        "#show: letter.with(\n"
        "  sender: (\n"
        "    name: [%s],\n"
        "    address: [Votre adresse \\ Code postal, ville],\n"
        "  ),\n"
        "  recipient: (\n"
        "    name: [Destinataire],\n"
        "    address: [Son adresse \\ Code postal, ville],\n"
        "  ),\n"
        "  place: \"Paris\",\n"
        "  date: \"%s\",\n"
        "  subject: [%s],\n"
        ")\n"
        "\n"
        "Corps de la lettre.\n",
        mktypst_package, config->author, config->date, config->title);
}

static void write_document(FILE* out, const struct Config* config)
{
    switch (config->tmpl)
    {
        case template_paper:
            write_paper(out, config);
            break;

        case template_letter:
            write_letter(out, config);
            break;

        default:
            break;
    }
}

static void output_path(const char* name, char* buf, size_t size)
{
    size_t len = strlen(name);

    if (len >= 4 && strcmp(name + len - 4, ".typ") == 0)
        (void) snprintf(buf, size, "%s", name);
    else
        (void) snprintf(buf, size, "%s.typ", name);
}

static int generate(const struct Config* config)
{
    if (config->use_stdout)
    {
        write_document(stdout, config);
        return 0;
    }

    char path[1024];
    output_path(config->name, path, sizeof path);

    if (!config->force && access(path, F_OK) == 0)
    {
        error("file already exists (use -f to overwrite)", path);
        return -1;
    }

    FILE* file = fopen(path, "w");

    if (file == NULL)
    {
        error("cannot create file", path);
        return -1;
    }

    write_document(file, config);

    if (fclose(file) != 0)
    {
        error("cannot write file", path);
        return -1;
    }

    (void) printf("created %s (%s)\n", path, templates[config->tmpl].name);
    (void) printf("  typst watch %s\n", path);

    return 0;
}

static int parse_args(int argc, char** argv, struct Config* config)
{
    const char* template_arg = NULL;
    const char* name = NULL;

    for (int i = 1; i < argc; i++)
    {
        const char* arg = argv[i];

        if (strcmp(arg, "-h") == 0 || strcmp(arg, "--help") == 0)
        {
            print_usage(stdout);
            return -1;
        }

        if (strcmp(arg, "-v") == 0 || strcmp(arg, "--version") == 0)
        {
            print_version();
            return -1;
        }

        if (strcmp(arg, "--stdout") == 0)
        {
            config->use_stdout = 1;
            continue;
        }

        if (strcmp(arg, "-f") == 0 || strcmp(arg, "--force") == 0)
        {
            config->force = 1;
            continue;
        }

        int matched = 0;

        matched = opt_value(arg, "-t", "--template", argc, argv, &i, &template_arg);
        if (matched != 0)
        {
            if (matched < 0) { error("missing argument for", arg); return 1; }
            continue;
        }

        matched = opt_value(arg, "-T", "--title", argc, argv, &i, &config->title);
        if (matched != 0)
        {
            if (matched < 0) { error("missing argument for", arg); return 1; }
            continue;
        }

        matched = opt_value(arg, "-a", "--author", argc, argv, &i, &config->author);
        if (matched != 0)
        {
            if (matched < 0) { error("missing argument for", arg); return 1; }
            continue;
        }

        matched = opt_value(arg, "-d", "--date", argc, argv, &i, &config->date);
        if (matched != 0)
        {
            if (matched < 0) { error("missing argument for", arg); return 1; }
            continue;
        }

        if (arg[0] == '-' && arg[1] != '\0')
        {
            error("unknown option", arg);
            return 1;
        }

        if (name != NULL)
        {
            error("unexpected extra argument", arg);
            return 1;
        }

        name = arg;
    }

    if (name == NULL)
    {
        error("missing document name", NULL);
        return 1;
    }

    config->name = name;

    if (template_arg != NULL && !find_template(template_arg, &config->tmpl))
    {
        error("unknown template", template_arg);
        return 1;
    }

    if (config->title == NULL)
        config->title = stem_of(name);

    if (config->author == NULL)
        config->author = author_name();

    if (config->date == NULL)
        config->date = current_date();

    return 0;
}

int main(int argc, char** argv)
{
    (void) setlocale(LC_TIME, "");

    struct Config config =
    {
        .name = NULL,
        .tmpl = template_paper,
        .title = NULL,
        .author = NULL,
        .date = NULL,
        .use_stdout = 0,
        .force = 0,
    };

    int status = parse_args(argc, argv, &config);

    if (status < 0)
        return EXIT_SUCCESS;

    if (status > 0)
    {
        print_usage(stderr);
        return EXIT_FAILURE;
    }

    if (generate(&config) != 0)
        return EXIT_FAILURE;

    return EXIT_SUCCESS;
}