/*
 * keygen2.c - Generate SSH keys using libssh
 * Author: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
 */

/*
 * Copyright (c) 2019 Red Hat, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see http://www.gnu.org/licenses/.
 */

#include "config.h"

#include <libssh/libssh.h>
#include <stdio.h>
#include <stdlib.h>
#include <argp.h>
#include <errno.h>
#include <string.h>
#include <ctype.h>
#include <fcntl.h>

#include <sys/stat.h>

struct arguments_st {
    enum ssh_keytypes_e type;
    unsigned long bits;
    char *file;
    char *passphrase;
};

static struct argp_option options[] = {
    {
        .name  = "bits",
        .key   = 'b',
        .arg   = "BITS",
        .flags = 0,
        .doc   = "The size of the key to be generated. "
                 "If omitted, a default value is used depending on the TYPE. "
                 "Accepted values are: "
                 "1024, 2048, 3072 (default), 4096, and 8192 for TYPE=\"rsa\"; "
                 "256 (default), 384, and 521 for TYPE=\"ecdsa\"; "
                 "1024 (default) and 2048 for TYPE=\"dsa\"; "
                 "can be omitted for TYPE=\"ed25519\" "
                 "(it will be ignored if provided).\n",
        .group = 0
    },
    {
        .name  = "file",
        .key   = 'f',
        .arg   = "FILE",
        .flags = 0,
        .doc   = "The output file. "
                 "If not provided, the used file name will be generated "
                 "according to the key type as \"id_TYPE\" "
                 "(e.g. \"id_rsa\" for type \"rsa\"). "
                 "The public key file name is generated from the private key "
                 "file name by appending \".pub\".\n",
        .group = 0
    },
    {
        .name  = "passphrase",
        .key   = 'p',
        .arg   = "PASSPHRASE",
        .flags = 0,
        .doc   = "The passphrase used to encrypt the private key. "
                 "If omitted the file will not be encrypted.\n",
        .group = 0
    },
    {
        .name  = "type",
        .key   = 't',
        .arg   = "TYPE",
        .flags = 0,
        .doc   = "The type of the key to be generated. "
                 "Accepted values are: "
                 "\"rsa\", \"ecdsa\", \"ed25519\", and \"dsa\".\n",
        .group = 0
    },
    {
        /* End of the options */
        0
    },
};

/* Parse a single option. */
static error_t parse_opt (int key, char *arg, struct argp_state *state)
{
    /* Get the input argument from argp_parse, which we
     * know is a pointer to our arguments structure.
     */
    struct arguments_st *arguments = NULL;
    error_t rc = 0;

    if (state == NULL) {
        return EINVAL;
    }

    arguments = state->input;
    if (arguments == NULL) {
        fprintf(stderr, "Error: NULL pointer to arguments structure "
                "provided\n");
        rc = EINVAL;
        goto end;
    }

    switch (key) {
        case 'b':
            errno = 0;
            arguments->bits = strtoul(arg, NULL, 10);
            if (errno != 0) {
                rc = errno;
                goto end;
            }
            break;
        case 'f':
            arguments->file = strdup(arg);
            if (arguments->file == NULL) {
                fprintf(stderr, "Error: Out of memory\n");
                rc = ENOMEM;
                goto end;
            }
            break;
        case 'p':
            arguments->passphrase = strdup(arg);
            if (arguments->passphrase == NULL) {
                fprintf(stderr, "Error: Out of memory\n");
                rc = ENOMEM;
                goto end;
            }
            break;
        case 't':
            if (!strcmp(arg, "rsa")) {
                arguments->type = SSH_KEYTYPE_RSA;
            }
            else if (!strcmp(arg, "dsa")) {
                arguments->type = SSH_KEYTYPE_DSS;
            }
            else if (!strcmp(arg, "ecdsa")) {
                arguments->type = SSH_KEYTYPE_ECDSA;
            }
            else if (!strcmp(arg, "ed25519")) {
                arguments->type = SSH_KEYTYPE_ED25519;
            }
            else {
                fprintf(stderr, "Error: Invalid key type\n");
                argp_usage(state);
                rc = EINVAL;
                goto end;
            }
            break;
        case ARGP_KEY_ARG:
            if (state->arg_num > 0) {
                /* Too many arguments. */
                printf("Error: Too many arguments\n");
                argp_usage(state);
            }
            break;
        case ARGP_KEY_END:
            break;
        default:
            return ARGP_ERR_UNKNOWN;
    }

end:
    return rc;
}

static int validate_args(struct arguments_st *args)
{
    int rc = 0;

    if (args == NULL) {
        return EINVAL;
    }

    switch(args->type) {
        case SSH_KEYTYPE_RSA:
            switch(args->bits) {
                case 0:
                    /* If not provided, use default value */
                    args->bits = 3072;
                    break;
                case 1024:
                case 2048:
                case 3072:
                case 4096:
                case 8192:
                    break;
                default:
                    fprintf(stderr, "Error: Invalid bits parameter provided\n");
                    rc = EINVAL;
                    break;
            }

            if (args->file == NULL) {
                args->file = strdup("id_rsa");
                if (args->file == NULL) {
                    rc = ENOMEM;
                    break;
                }
            }

            break;
        case SSH_KEYTYPE_ECDSA:
            switch(args->bits) {
                case 0:
                    /* If not provided, use default value */
                    args->bits = 256;
                    break;
                case 256:
                case 384:
                case 521:
                    break;
                default:
                    fprintf(stderr, "Error: Invalid bits parameter provided\n");
                    rc = EINVAL;
                    break;
            }
            if (args->file == NULL) {
                args->file = strdup("id_ecdsa");
                if (args->file == NULL) {
                    rc = ENOMEM;
                    break;
                }
            }

            break;
        case SSH_KEYTYPE_DSS:
            switch(args->bits) {
                case 0:
                    /* If not provided, use default value */
                    args->bits = 1024;
                    break;
                case 1024:
                case 2048:
                    break;
                default:
                    fprintf(stderr, "Error: Invalid bits parameter provided\n");
                    rc = EINVAL;
                    break;
            }
            if (args->file == NULL) {
                args->file = strdup("id_dsa");
                if (args->file == NULL) {
                    rc = ENOMEM;
                    break;
                }
            }

            break;
        case SSH_KEYTYPE_ED25519:
            /* Ignore value and overwrite with a zero */
            args->bits = 0;

            if (args->file == NULL) {
                args->file = strdup("id_ed25519");
                if (args->file == NULL) {
                    rc = ENOMEM;
                    break;
                }
            }

            break;
        default:
            fprintf(stderr, "Error: unknown key type\n");
            rc = EINVAL;
            break;
    }

    return rc;
}

/* Program documentation. */
static char doc[] = "Generate an SSH key pair. "
                    "The \"--type\" (short: \"-t\") option is required.";

/* Our argp parser */
static struct argp argp = {options, parse_opt, NULL, doc, NULL, NULL, NULL};

int main(int argc, char *argv[])
{
    ssh_key key = NULL;
    int rc = 0;
    char overwrite[1024] = "";

    char *pubkey_file = NULL;

    struct arguments_st arguments = {
        .type = SSH_KEYTYPE_UNKNOWN,
        .bits = 0,
        .file = NULL,
        .passphrase = NULL,
    };

    if (argc < 2) {
        argp_help(&argp, stdout, ARGP_HELP_DOC | ARGP_HELP_USAGE, argv[0]);
        goto end;
    }

    rc = argp_parse(&argp, argc, argv, 0, 0, &arguments);
    if (rc != 0) {
        goto end;
    }

    rc = validate_args(&arguments);
    if (rc != 0) {
        goto end;
    }

    errno = 0;
    rc = open(arguments.file, O_CREAT | O_EXCL | O_WRONLY, S_IRUSR | S_IWUSR);
    if (rc < 0) {
        if (errno == EEXIST) {
            printf("File \"%s\" exists. Overwrite it? (y|n) ", arguments.file);
            scanf("%1023s", overwrite);
            if (tolower(overwrite[0]) == 'y') {
                rc = open(arguments.file, O_WRONLY);
                if (rc > 0) {
                    close(rc);
                    errno = 0;
                    rc = chmod(arguments.file, S_IRUSR | S_IWUSR);
                    if (rc != 0) {
                        fprintf(stderr,
                                "Error(%d): Could not set file permissions\n",
                                errno);
                        goto end;
                    }
                } else {
                    fprintf(stderr,
                            "Error: Could not create private key file\n");
                    goto end;
                }
            } else {
                goto end;
            }
        } else {
            fprintf(stderr, "Error opening \"%s\" file\n", arguments.file);
            goto end;
        }
    } else {
        close(rc);
    }

    /* Generate a new private key */
    rc = ssh_pki_generate(arguments.type, arguments.bits, &key);
    if (rc != SSH_OK) {
        fprintf(stderr, "Error: Failed to generate keys");
        goto end;
    }

    /* Write the private key */
    rc = ssh_pki_export_privkey_file(key, arguments.passphrase, NULL, NULL,
                                     arguments.file);
    if (rc != SSH_OK) {
        fprintf(stderr, "Error: Failed to write private key file");
        goto end;
    }

    /* If a passphrase was provided, overwrite and free it as it is not needed
     * anymore */
    if (arguments.passphrase != NULL) {
#ifdef HAVE_EXPLICIT_BZERO
        explicit_bzero(arguments.passphrase, strlen(arguments.passphrase));
#else
        bzero(arguments.passphrase, strlen(arguments.passphrase));
#endif
        free(arguments.passphrase);
        arguments.passphrase = NULL;
    }

    pubkey_file = (char *)malloc(strlen(arguments.file) + 5);
    if (pubkey_file == NULL) {
        rc = ENOMEM;
        goto end;
    }

    sprintf(pubkey_file, "%s.pub", arguments.file);

    errno = 0;
    rc = open(pubkey_file,
              O_CREAT | O_EXCL | O_WRONLY,
              S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
    if (rc < 0) {
        if (errno == EEXIST) {
            printf("File \"%s\" exists. Overwrite it? (y|n) ", pubkey_file);
            scanf("%1023s", overwrite);
            if (tolower(overwrite[0]) == 'y') {
                rc = open(pubkey_file, O_WRONLY);
                if (rc > 0) {
                    close(rc);
                    errno = 0;
                    rc = chmod(pubkey_file,
                               S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
                    if (rc != 0) {
                        fprintf(stderr,
                                "Error(%d): Could not set file permissions\n",
                                errno);
                        goto end;
                    }
                } else {
                    fprintf(stderr,
                            "Error: Could not create public key file\n");
                    goto end;
                }
            } else {
                goto end;
            }
        } else {
            fprintf(stderr, "Error opening \"%s\" file\n", pubkey_file);
            goto end;
        }
    } else {
        close(rc);
    }

    /* Write the public key */
    rc = ssh_pki_export_pubkey_file(key, pubkey_file);
    if (rc != SSH_OK) {
        fprintf(stderr, "Error: Failed to write public key file");
        goto end;
    }

end:
    if (key != NULL) {
        ssh_key_free(key);
    }

    if (arguments.file != NULL) {
        free(arguments.file);
    }

    if (arguments.passphrase != NULL) {
#ifdef HAVE_EXPLICIT_BZERO
        explicit_bzero(arguments.passphrase, strlen(arguments.passphrase));
#else
        bzero(arguments.passphrase, strlen(arguments.passphrase));
#endif
        free(arguments.passphrase);
    }

    if (pubkey_file != NULL) {
        free(pubkey_file);
    }
    return rc;
}