package main

import (
	"bufio"
	"errors"
	"fmt"
	"io/ioutil"
	"math"
	"os"
	"strings"
)

func usage(retval int) {
	fmt.Printf("directory_merge: moves files from multiple directories " +
		"into a single directory\n");
	fmt.Printf("usage: directory_merge [destination_directory] " +
		"[source_dir 1] ... [source_dir N]\n")
	os.Exit(retval)
}

type RenamePlan struct {
	src string
	dstIdx uint64
}

func (plan *RenamePlan) DstToString(numDigits int) string {
	return fmt.Sprintf("%0" + fmt.Sprintf("%d", numDigits) + "d", plan.dstIdx);
}

func (plan *RenamePlan) String(dstDir string, numDigits int) string {
	return plan.src + " -> " + dstDir + "/" + plan.DstToString(numDigits);
}

func (plan *RenamePlan) Execute(dstDir string, numDigits int) error {
	dstFile := dstDir + "/" + plan.DstToString(numDigits)
	fmt.Printf("Renaming %s to %s.\n", plan.src, dstFile)
	err := os.Rename(plan.src, dstFile)
	if err != nil {
		return errors.New(fmt.Sprintf("Failed to rename %s to %s: %v\n",
			plan.src, dstFile, err.Error()))
	}
	return nil
}

func main() {
	if (len(os.Args) < 3) {
		usage(1)
	}
	dstDir := os.Args[1]
	srcDirs := os.Args[2:]
	renamePlans := make([]*RenamePlan, 0)
	var dstIdx uint64
	for srcDirIdx := range srcDirs {
		// ioutil.ReadDir alphabetizes what it returns
		srcDir := srcDirs[srcDirIdx]
		srcs, err := ioutil.ReadDir(srcDir)
		if err != nil {
			panic(fmt.Sprintf("Error reading directory %s: %s", srcDir, err))
		}
		for srcIdx := range srcs {
			srcPath := srcDir + "/" + srcs[srcIdx].Name()
			dstIdx++
			renamePlan := &RenamePlan {
				src: srcPath,
				dstIdx: dstIdx,
			}
			renamePlans = append(renamePlans, renamePlan)
		}
	}
	numDigits := int(math.Ceil(math.Log10(float64(dstIdx))))
	for renamePlanIdx := range renamePlans {
		fmt.Printf("%s\n", renamePlans[renamePlanIdx].
								String(dstDir, numDigits));
	}
	reader := bufio.NewReader(os.Stdin)
	for {
		fmt.Printf("Execute? (y/n):\n")
		text, _ := reader.ReadString('\n')
		text = strings.TrimSpace(text)
		if text == "y" {
			break
		}
		if text == "n" {
			fmt.Printf("Aborting.\n");
			os.Exit(0)
		}
	}
	for renamePlanIdx := range renamePlans {
		err := renamePlans[renamePlanIdx].Execute(dstDir, numDigits);
		if err != nil {
			panic(err)
		}
	}
	os.Exit(0)
}