/*
	gcc -o dump_eml.exe dump_eml_attachments.c
*/
 
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<stdint.h>
 
static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
                                'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
                                'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
                                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
                                'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                                'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                                'w', 'x', 'y', 'z', '0', '1', '2', '3',
                                '4', '5', '6', '7', '8', '9', '+', '/'};
static char *decoding_table = NULL;
static int mod_table[] = {0, 2, 1};
 
unsigned char *base64_decode(const char *data,
                             size_t input_length,
                             size_t *output_length);
void build_decoding_table();
void base64_cleanup();
 
int open_and_extract_from_eml(char *filename,char *path_destino);
int isEmptyLine(char *line);
char *content_disposition = "Content-Disposition: attachment;";
 
int main(int argc, char **argv )	{
	if(argc != 3)	{
		printf("Uso: %s <Carpeta_con_EMLs> <Carpeta_destino_adjuntos>\n",argv[0]);
		exit(0);
	}
	open_and_extract_from_eml(argv[1],argv[2]);
	return 0;
}
 
int  open_and_extract_from_eml(char *filename,char *path_destino)	{
	FILE *eml_file, *temp_file;
	char *dest_file,*temp0,*temp1;
	char *line,*buffer_base64 = NULL,*buffer_decoded;
	char *full_writen_file;
	int len_dest_file_name,offset,len_content_disposition,len_base64_line,len_base64_buffer, len_output,len_path_destino,entrar;
	len_content_disposition = strlen(content_disposition);
	len_path_destino = strlen(path_destino);
	line = malloc(1024);
	eml_file = fopen(filename,"rb");
	offset = 0;
	while(!feof(eml_file) && fgets(line,1024,eml_file) != NULL)	{
		if(memcmp(line,content_disposition,len_content_disposition) == 0)	{
			printf("Encontrado: %s",line);
			temp0 = strstr(line,"filename=");
			if(temp0 ==NULL )	{
				//tal vez la proxima linea?
				memset(line,0,1024);
				fgets(line,1024,eml_file);
			}
 
			temp0 = strstr(line,"filename=");
			if(temp0 !=NULL )	{
				temp1 = strstr(temp0 +10,"\"");
				if(temp1 == NULL)	{
					//No hay " finales
					exit(0);
				}
				len_dest_file_name = temp1 - (line + (temp0 - line) + 10 );
				//printf("len_dest_file_name %i\n",len_dest_file_name);
				dest_file = malloc(len_dest_file_name+1);
				strncpy(dest_file,(line + (temp0 - line) + 10),len_dest_file_name);
				dest_file[len_dest_file_name] = '\0';
 
				memset(line,0,1024);
				fgets(line,1024,eml_file);
				//printf("Nueva linea leida \"%s\"",line);
				if(!isEmptyLine(line))	{
					//Deberia de ser una linea vacia;
					exit(0);
				}
				buffer_base64 = NULL;
				offset = 0;
				memset(line,0,1024);
				entrar = 1;
				while(entrar && fgets(line,1024,eml_file) != NULL &&  !isEmptyLine(line) )	{	//leemos hasta la proxima linea vacia o hasta encontrar un '=' al final de la linea
					len_base64_line = strlen(line);
					buffer_base64 = realloc(buffer_base64,offset+len_base64_line+1);
					if(line[len_base64_line-1] == '\n'  || line[len_base64_line-1] == '\r'){
						line[len_base64_line-1] ='\0';
						len_base64_line--;
					}
					if(line[len_base64_line-1] == '\n'  || line[len_base64_line-1] == '\r'){
						line[len_base64_line-1] ='\0';
						len_base64_line--;
					}
 
					memcpy(buffer_base64+offset,line,len_base64_line);
					offset+=len_base64_line;
					if(line[len_base64_line-1] == '=')	{
						entrar = 0;
					}
					memset(line,0,1024);
				}
				buffer_base64[offset] = '\0';
				//printf("Encoded buffer: %s\n",buffer_base64);
				len_base64_buffer = strlen(buffer_base64);
				buffer_decoded = base64_decode(buffer_base64,len_base64_buffer,&len_output);
				buffer_decoded[len_output] = '\0';
				/*
				printf("OK\n");
				printf("Decoded buffer: %s\n",buffer_decoded);
				printf("Path destino: %s\n",path_destino);
				printf("len_dest_file_name: %i\n",len_dest_file_name);
				printf("len_path_destino: %i\n",len_path_destino);
				*/
				full_writen_file = malloc(len_dest_file_name + len_path_destino+10);
				sprintf(full_writen_file,"%s/%s",path_destino,dest_file);
				printf("Destino: %s\n",full_writen_file);
				temp_file = fopen(full_writen_file,"wb");
				fwrite(buffer_decoded,1,len_output,temp_file);
				fclose(temp_file);
 
				free(buffer_base64);
				free(dest_file);
				free(full_writen_file);
			}
			else	{
				printf("Se encontro %s, pero no se encontro Filename omitiendo!\n",content_disposition);
			}
		}
		memset(line,0,1024);
	}
	free(line);
}
 
int isEmptyLine(char *line)	{
	if(line[0] == '\0' || line[0] == '\n' || line[0] == '\r')
		return 1;
	return 0;
}
 
unsigned char *base64_decode(const char *data,
                             size_t input_length,
                             size_t *output_length) {
 
    if (decoding_table == NULL) build_decoding_table();
 
    if (input_length % 4 != 0) return NULL;
 
    *output_length = input_length / 4 * 3;
    if (data[input_length - 1] == '=') (*output_length)--;
    if (data[input_length - 2] == '=') (*output_length)--;
 
    unsigned char *decoded_data = malloc(*output_length);
    if (decoded_data == NULL) return NULL;
 
    for (int i = 0, j = 0; i < input_length;) {
 
        uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
 
        uint32_t triple = (sextet_a << 3 * 6)
        + (sextet_b << 2 * 6)
        + (sextet_c << 1 * 6)
        + (sextet_d << 0 * 6);
 
        if (j < *output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        if (j < *output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        if (j < *output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
    }
 
    return decoded_data;
}
 
void build_decoding_table() {
    decoding_table = malloc(256);
    for (int i = 0; i < 64; i++)
        decoding_table[(unsigned char) encoding_table[i]] = i;
}
 
 
void base64_cleanup() {
    free(decoding_table);
}