package main

import (
  "flag"
  "fmt"
  "os"
  "os/user"
  "path/filepath"
  "strings"
)

const (
	argsError = 1
  fileError = iota
  lexError
  compileError
)

func fileExists(p string) (bool, error) {
  _, err := os.Stat(p)
  if err == nil { return true, nil }
  if os.IsNotExist(err) { return false, nil }
  return false, err
}

func setIn() {
  args := flag.Args()
  if len(args) == 0 {
    fmt.Fprintf(os.Stderr, "No input file\n")
    os.Exit(argsError)
  } else if len(args) > 1 {
    fmt.Fprintf(os.Stderr, "Too many input files (%d), needed 1\n", len(args))
    os.Exit(argsError)
  }
  in = absFilepath(args[0])
  exists, err := fileExists(in)
  if err != nil {
    fmt.Fprintf(os.Stderr, "Could not open file\n\t%s", err.Error())
    os.Exit(fileError)
  } else if !exists {
    fmt.Fprintf(os.Stderr, "%q does not exist\n", in)
    os.Exit(fileError)
  }
}

func setOut(o string) {
  if o == "" {
    out = "out.rom"
  } else {
    out = o
  }
}

func isHexValue(v byte) bool {
  if (v >= 0x30 && v <= 0x39) || (v >= 0x41 && v <= 0x46) || (v >= 0x61 && v <= 0x66) {
    return true
  }
  return false
}

func isHex(s string) bool {
  if len(s) != 2 {
    return false
  }
  for _, b := range []byte(s) {
    if !isHexValue(b) {
      return false
    }
  }
  return true
}

func loadFile(p string) string {
	b, err := os.ReadFile(p)
	if err != nil {
    fmt.Fprintf(os.Stderr, err.Error())
    os.Exit(fileError)
	}
  return string(b)
}

func absFilepath(p string) string {
	if strings.HasPrefix(p, "~") {
		if p == "~" || strings.HasPrefix(p, "~/") {
			homedir, _ := os.UserHomeDir()
			if len(p) <= 2 {
				p = homedir
			} else if len(p) > 2 {
				p = filepath.Join(homedir, p[2:])
			}
		} else {
			i := strings.IndexRune(p, '/')
			var u string
			var remainder string
			if i < 0 {
				u = p[1:]
				remainder = ""
			} else {
				u = p[1:i]
				remainder = p[i:]
			}
			usr, err := user.Lookup(u)
			if err != nil {
				p = filepath.Join("/home", u, remainder)
			} else {
				p = filepath.Join(usr.HomeDir, remainder)
			}
		}
	} else if !strings.HasPrefix(p, "/") {
		wd, _ := os.Getwd()
		p = filepath.Join(wd, p)
	}

	path, _ := filepath.Abs(p)
	return path
}