package main

import (
	"strings"
	"bytes"
	"os"
	"fmt"
	"bufio"
	"regexp"
	"flag"
)

var outFile bytes.Buffer

func errorExit(e error, msg string) {
	if e != nil {
		fmt.Print(msg)
		os.Exit(1)
	}
}

func buildComment(ln string, eof bool) string {
	var out strings.Builder
	if eof && ln == "" {
		return out.String()
	}
	out.Grow(20 + len(ln))
	out.WriteString("i")
	out.WriteString(strings.TrimRight(ln, "\n\r"))
	out.WriteString("\tfalse\tnull.host\t1")
	if !eof {
		out.WriteString("\n")
	}
	return out.String()
}

func deconstructComment(ln string) string {
	text := strings.SplitN(ln, "\t", 2)
	comment := text[0]
	if len(comment) > 1 {
		return comment[1:] + "\n"
	}
	return "\n"
}

func readFile(path string, buildComments bool) {
	file, err := os.Open(path)
	errorExit(err, fmt.Sprintf("Unable to open file for reading: %s", path))
	defer file.Close()

	re := regexp.MustCompile(`.+\t.*\t.*\t.*`)
	reader := bufio.NewReader(file)

	if buildComments {
		for {
			l, e := reader.ReadString('\n')
			eof := e != nil
			if exp := re.MatchString(l); exp {
				outFile.WriteString(l)
			} else {
				outFile.WriteString(buildComment(l, eof))
			}
			if eof {
				break
			}
		}
	} else {
		for {
			l, e := reader.ReadString('\n')
			if exp := re.MatchString(l); exp && l[0] == 'i' {
				outFile.WriteString(deconstructComment(l))
			} else {
				outFile.WriteString(l)
			}
			if e != nil {
				break
			}
		}
	}
}

func writeFile(path string) {
	file, err := os.OpenFile(path, os.O_WRONLY | os.O_CREATE | os.O_TRUNC, 0)
	errorExit(err, fmt.Sprintf("Unable to open file for writing: %s", path))
	defer file.Close()
	file.Write(outFile.Bytes())
}

func PrintHelp() {
	art := `gfu - gophermap formatting utility

syntax: gfu [flags...] [filepath]

example: gfu -d ~/gopher/phlog/gophermap

        default
        convert plain text lines to type 'i'

`
	fmt.Fprint(os.Stderr, art)
	flag.PrintDefaults()
}

func main() {
	deconstructCommentLinks := flag.Bool("d", false, "Deconstruct a gophermap's comments back to regular text")
	header := flag.String("head","","Path to a file containing header content")
	footer := flag.String("foot","","Path to a file containing footer content")
	flag.Usage = PrintHelp

	flag.Parse()
	
	args := flag.Args()
	
	if l := len(args); l != 1 {
		fmt.Printf("Incorrect number of arguments. Expected 1, got %d", l)
		os.Exit(1)
	}

	if *header != "" {
		fmt.Println("Header functionality is not built yet, proceeding with general gophermap conversion...")
	}

	if *footer != "" {
		fmt.Println("Footer functionality is not built yet, proceeding with general gophermap conversion...")
	}

	readFile(args[0], !*deconstructCommentLinks)
	writeFile(args[0])
	os.Exit(0)
}