ConfigFileOpen <- function(file_path, silent = FALSE) {
  # This function loads all the data contained in the configuration file 
  # specified as parameter 'configfile' in the function Load() of 
  # s2dverification.
  # Extends the environment given as parameter with the variables and 
  # functions needed for the configuration file mechanism to work.
  # Check ?ConfigFileOpen for a detailed explanation on how to prepare
  # your own configuration file.
  #
  # Expected defined variables in the specified environment:
  #  - configfile
  #  - var
  #  - exp
  #  - obs
  # The relevant variables and function that extend the environment are the 
  # following:
  #  - ConfigPutInDictionary
  #  - ConfigReplaceVariablesInString
  #  - ConfigGetDatasetInfo
  #  - is_file_per_member_exp
  #  - is_file_per_member_obs
  #  - is_file_per_dataset_obs
  #  - exp_info
  #  - obs_info
  #  - is_2d_var
  #
  # Args:
  #   environment: Environment to be extended
  #
  # Returns:
  #   This function returns nothing but extends the specified environment instead.
  #
  # History:
  #   0.1  #  2015-01  (N. Manubens, nicolau.manubens@ic3.cat)  # Original code

  if (!silent) {
    print(paste("* Reading configuration file:", file_path))
  }
  # Read the data from the configuration file.
  ## Remove comments, tabulations, spaces, empty lines, ...
  all_lines <- readLines(file_path)
  all_lines <- gsub("\t", "", all_lines)
  all_lines <- gsub(" ", "", all_lines)
  all_lines <- all_lines[-grep("^#", all_lines)]
  all_lines <- all_lines[-grep("^$", all_lines)]
  ## Detect key lines
  key_positions <- grep("^!!", all_lines)

  ## Check that the format of the configuration file is right.
  if (length(key_positions) != 12) {
    stop('Error: The configuration file is corrupted or outdated: the key lines do not match the expected pattern.')
  }

  ## Start parsing the configuration.
  ## Parse the 2-dimensional (atmospheric) and global mean (oceanic) variable 
  ## entries and keep them in two vectors
  if (key_positions[1] + 1 < key_positions[2]) {
    two_d_var_lines <- all_lines[(key_positions[1] + 1):(key_positions[2] - 1)]
    two_d_vars <- unlist(strsplit(two_d_var_lines, ","))
  } else {
    two_d_vars <- c()
  }
  if (key_positions[2] + 1 < key_positions[3]) {
    global_mean_var_lines <- all_lines[(key_positions[2] + 1):(key_positions[3] - 1)]
    global_mean_vars <- unlist(strsplit(gsub(" ", "", global_mean_var_lines), ","))
  } else {
    global_mean_vars <- c()
  }

  # The variables that are used in the configuration filed are kept in 
  # 'definitions', an associative array (key-value array or dictionary).
  definitions <- c()
  ## Parse the variables definitions in the whole configuration file
  if (key_positions[3] + 1 < key_positions[4]) {
    exp_table_definitions <- all_lines[(key_positions[3] + 1):(key_positions[4] - 1)]
  } else {
    exp_table_definitions <- c()
  }
  if (key_positions[5] + 1 < key_positions[6]) {
    file_per_member_exp_table_definitions <- all_lines[(key_positions[5] + 1):(key_positions[6] - 1)]
  } else {
    file_per_member_exp_table_definitions <- c()
  }
  if (key_positions[7] + 1 < key_positions[8]) {
    obs_table_definitions <- all_lines[(key_positions[7] + 1):(key_positions[8] - 1)]
  } else {
    obs_table_definitions <- c()
  }
  if (key_positions[9] + 1 < key_positions[10]) {
    file_per_member_obs_table_definitions <- all_lines[(key_positions[9] + 1):(key_positions[10] - 1)]
  } else {
    file_per_member_obs_table_definitions <- c()
  }
  if (key_positions[11] + 1 < key_positions[12]) {
    file_per_dataset_obs_table_definitions <- all_lines[(key_positions[11] + 1):(key_positions[12] - 1)]
  } else {
    file_per_dataset_obs_table_definitions <- c()
  }
  all_definitions <- c(exp_table_definitions, file_per_member_exp_table_definitions, obs_table_definitions)
  all_definitions <- c(all_definitions, file_per_member_obs_table_definitions, file_per_dataset_obs_table_definitions)
  if (length(grep("=", all_definitions)) == length(all_definitions)) {
    for (definition in all_definitions) {
      if (length(which(strsplit(definition, "")[[1]] == "=")) == 1) {
        var_name <- strsplit(definition, "=")[[1]][1]
        var_value <- strsplit(definition, "=")[[1]][2]
        if ((length(which(strsplit(var_value, "")[[1]] == "$")) %% 2) == 0) {
          definitions <- ConfigPutInDictionary(definitions, var_name, var_value)
        } else {
          stop('Error: The configuration file is corrupted: there are incorrect variable definition lines in the definition zones. A closing "$" symbol may be missing.')
        }
      } else {
        stop('Error: The configuration file is corrupted: there are incorrect definition lines in the definition zones.')
      }
    }
  } else {
    stop('Error: The configuration file is corrupted: there are malformed definition lines in the definition zones.')
  }

  # Parse the entries in the tables
  ## These are the indices of the key positions in the vector of key positions
  tables_key_positions <- c(4, 6, 8, 10, 12)
  current_table <- 1
  for (table_key_position in tables_key_positions) {
    datasets <- list(c(), c(), c(), c())

    if (current_table < 3) {
      default_values <- c("$DEFAULT_EXP_MAIN_PATH$", "$DEFAULT_EXP_FILE_PATH$", "$DEFAULT_GRID$", "$DEFAULT_NC_VAR_NAME$", '$DEFAULT_SUFFIX$', '$DEFAULT_VAR_MIN$', '$DEFAULT_VAR_MAX$')
    } else {
      default_values <- c("$DEFAULT_OBS_MAIN_PATH$", "$DEFAULT_OBS_FILE_PATH$", "$DEFAULT_NC_VAR_NAME$", '$DEFAULT_SUFFIX$', '$DEFAULT_VAR_MIN$', '$DEFAULT_VAR_MAX$')
    }
    previous_values <- c(".*", ".*", default_values)
    table_lines <- c()
    table_end <- ifelse(table_key_position == max(tables_key_positions), length(all_lines), key_positions[table_key_position + 1] - 1)
    if ((key_positions[table_key_position] + 1) <= table_end) {
      table_lines <- all_lines[(key_positions[table_key_position] + 1):table_end]
      table_lines <- strsplit(table_lines, ",")
    }

    for (entry in table_lines) {
      if (entry[1] == '"') {
        entry[1] <- previous_values[1]
      }
      if ((length(entry) > 1)) {
        if (entry[2] == '"') {
          entry[2] <- previous_values[2]
        }
      } else {
        stop('Error: The variable column must be defined in all the entries in the tables in the configuration file.')
      }
      for (value_position in 1:length(default_values)) {
        if ((length(entry) > value_position + 1)) {
          if (entry[value_position + 2] == '"') {
            entry[value_position + 2] <- previous_values[value_position + 2]
          }
        } else {
          entry[value_position + 2] <- '*'
        }
      }
      if (entry[1] == '.*') {
        if (entry[2] == '.*') {
          datasets[[1]] <- c(datasets[[1]], list(entry))
        } else {
          datasets[[3]] <- c(datasets[[3]], list(entry))
        }
      } else {
        if (entry[2] == '.*') {
          datasets[[2]] <- c(datasets[[2]], list(entry))
        } else {
          datasets[[4]] <- c(datasets[[4]], list(entry))
        }
      }
      previous_values <- entry
    }

    if (current_table == 1) {
      file_per_startdate_exps <- datasets
    } else if (current_table == 2) {
      file_per_member_exps <- datasets
    } else if (current_table == 3) {
      file_per_month_obs <- datasets
    } else if (current_table == 4) {
      file_per_member_obs <- datasets
    } else if (current_table == 5) {
      file_per_dataset_obs <- datasets
    }

    current_table <- current_table + 1
  }
  
  if (!silent) {
    print("* Config file read successfully.")
  }

  invisible(list(definitions = definitions, two_d_vars = two_d_vars, 
                 global_mean_vars = global_mean_vars, 
                 file_per_startdate_experiments = file_per_startdate_exps, 
                 file_per_member_experiments = file_per_member_exps, 
                 file_per_month_observations = file_per_month_obs,
                 file_per_member_observations = file_per_member_obs,
                 file_per_dataset_observations = file_per_dataset_obs))
}