package main

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"log"
	"mime"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strconv"
)

func main() {
	ReadAndDownload(".", os.Stdin)
}

func ReadAndDownload(root string, r io.Reader) {
	var n int
	var name string
	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		txt := scanner.Text()

		if name == "" || txt == "" {
			name = txt
			n = 0
			continue
		}
		err := download(n, root, name, txt)
		if err != nil {
			log.Println(err)
		}
		n++
	}
}

func download(n int, root, name, uri string) error {
	u, err := url.Parse(uri)
	if err != nil {
		return fmt.Errorf("parsing uri %s: %v", uri, err)
	}
	ext := filepath.Ext(u.Path)

	response, err := http.Get(uri)
	switch {
	case err != nil:
		return fmt.Errorf("downloading file %s: %v", uri, err)
	case response.StatusCode != http.StatusOK:
		return fmt.Errorf("downloading file %s: status code %d", uri, response.StatusCode)
	default:
		defer response.Body.Close()
	}

	var r io.Reader = response.Body
	if ext == "" {
		var err error
		ext, r, err = guessExt(response.Body)
		if err != nil {
			return err
		}
	}

	filename := filepath.Join(root, name+strconv.Itoa(n)+ext)
	f, err := os.Create(filename)
	if err != nil {
		return err
	}

	_, err = io.Copy(f, r)
	return err
}

func guessExt(r io.Reader) (string, io.Reader, error) {
	head, headCopy := make([]byte, 512), make([]byte, 512)
	n, readErr := io.ReadFull(r, head)
	head = head[:n]
	copy(headCopy, head)
	hr := bytes.NewReader(headCopy)

	t := http.DetectContentType(head)
	ext, err := mime.ExtensionsByType(t)

	if readErr == io.EOF || readErr == io.ErrUnexpectedEOF {
		return ext[0], hr, nil
	}

	if err != nil {
		return "", nil, err
	}

	return ext[0], io.MultiReader(hr, r), nil
}