package config

import (
	"flag"
	"fmt"
)

// Extract the program configuration from the command-line arguments.
func FromArgs() (*Config, error) {
	// Parse flags.
	verbose := flag.Bool("v", false, "Verbosity. If set, the program will print logs.")
	explanation := flag.Bool("x", false, "Explanation. Whether or not to show all reduction steps.")
	flag.Parse()

	// Parse non-flag arguments.
	if flag.NArg() == 0 {
		return nil, fmt.Errorf("no input given")
	} else if flag.NArg() > 1 {
		return nil, fmt.Errorf("more than 1 command-line argument")
	}

	// Parse source type.
	var source Source
	if flag.Arg(0) == "-" {
		source = StdinSource{}
	} else {
		source = StringSource{data: flag.Arg(0)}
	}

	return &Config{
		Source:      source,
		Verbose:     *verbose,
		Explanation: *explanation,
	}, nil
}