package main

import (
	"bufio"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"unicode"
)

func main() {
	// Load the configuration file, if any

	// Run command loop
	myshell_loop()

	// Perform any shutdown/cleanup
}

func myshell_loop() {
	for {
		// Read command
		fmt.Printf("myshell> ")
		line := read_line()

		// Parse command
		args := split_line(line)

		// Execute command
		output, err := execute(args)
		if err != nil {
			fmt.Println("error during exec command:", err)
		} else {
			fmt.Printf(string(output))
		}
	}
	// Loop back to read command
}

func read_line() string {
	// Read the command line
	reader := bufio.NewReader(os.Stdin)
	input, err := reader.ReadString('\n')
	if err != nil {
		fmt.Println("Error reading command line: ", err)
	}

	// Remove the newline character
	input = strings.TrimSuffix(input, "\r\n")
	input = strings.TrimSuffix(input, "\n")

	return input
}

// Split the line into arguments
func split_line(line string) []string {
	fieldSeparator := func(c rune) bool {
		return unicode.IsSpace(c) || c == '\a'
	}
	args := strings.FieldsFunc(line, fieldSeparator)

	return args
}

var builtin_cmds = map[string]func([]string) ([]byte, error){
	"cd": myshell_cd,
	"exit": myshell_exit,
}

// Execute the command
func execute(args []string) ([]byte, error) {
	// Check for builtin commands
	if cmd, ok := builtin_cmds[args[0]]; ok {
		return cmd(args)
	}

	cmd := exec.Command("sh", "-c", strings.Join(args, " "))
	output, err := cmd.CombinedOutput()
	return output, err
}

func myshell_cd(args []string) ([]byte, error) {
	if len(args) < 2 {
		return nil, fmt.Errorf("cd: missing argument")
	}
	err := os.Chdir(args[1])
	return nil, err
}

func myshell_exit(args []string) ([]byte, error) {
	os.Exit(0)
	return nil, nil
}