#!/usr/bin/ruby

require "pathname"
Dir.chdir(Pathname.new(__FILE__).dirname.to_s)

require "mail"

mail_size_limit= 16*1024
user_size_limit= 1024**2
users_dir= Pathname.new("user")

raw_incoming_mail= STDIN.read(mail_size_limit)
incoming_mail= Mail.new(raw_incoming_mail)

user= [incoming_mail.from].flatten[0].gsub('"', "")
exit 1 unless user
exit 1 unless user=~ /@/
subject= incoming_mail.subject
exit 1 unless subject
user_dir= users_dir + user.split("@", 2).reverse.join("___")
size_file= user_dir + ".size"
tmp_size_file= user_dir + ".size_tmp"

def send_response(original_mail, response_string, attachment= nil, response_subject=nil)
    Mail.deliver do |mail|
        to original_mail.from
        from original_mail.to
        subject response_subject || "Re: #{original_mail.subject}"
        add_file attachment if attachment
        body <<EOF
#{response_string}

--------
available commands:
signup
list
put
get <filename>
delete <filename>
share <filename> <user>
EOF
    end
end

def send_error(original_mail, error_string)
    Mail.deliver do |mail|
        to original_mail.from
        from original_mail.to
        subject "error Re: #{original_mail.subject}"
        body <<EOF
I am sorry to inform you, that your requested command could not be executed.
The reason is:

#{error_string}
EOF
    end
end

case subject
when "signup"
    if user_dir.directory?
        send_error(incoming_mail, "your are already signed up")
        exit
    end
    unless (user_dir+"../.signup_allowed").file?
        send_error(incoming_mail, "signup is currently disabled")
        exit
    end
    user_dir.mkdir
    size_file.open("w") { |f| f.puts 0 }
    send_response(incoming_mail, "signup successfull")
when "list"
    unless user_dir.directory?
        send_error(incoming_mail, "you are not signed up")
        exit
    end
    file_listing= "your_files:\n" +
    user_dir.children.select do |file|
        file.basename.to_s[0] != ?.
    end.collect do |file|
        "#{file.basename} #{file.size/1024.0}Kb"
    end.join("\n")
    send_response(incoming_mail, file_listing)
when /\Aget ([A-Za-z0-9_-]+(\.[a-z0-9]+)?)\Z/
    file_name= $1
    file_path= user_dir+file_name
    unless user_dir.directory?
        send_error(incoming_mail, "you are not signed up")
        exit
    end
    unless file_path.file?
        send_error(incoming_mail, "the requested file does not exist")
        exit
    end
    send_response(incoming_mail, "here is your requested file", file_path.to_s)
when /\Ashare ([A-Za-z0-9_-]+(\.[a-z0-9]+)?) ([A-Za-z0-9][A-Za-z0-9._-]*@([A-Za-z0-9-]+\.)+[A-Za-z]+)\Z/
    file_name= $1
    second_user= $3
    file_path= user_dir+file_name
    unless user_dir.directory?
        send_error(incoming_mail, "you are not signed up")
        exit
    end
    unless file_path.file?
        send_error(incoming_mail, "the requested file does not exist")
        exit
    end
    second_user_dir= users_dir + second_user.split("@", 2).reverse.join("___")
    second_size_file= second_user_dir + ".size"
    second_file_path= second_user_dir + file_name
    unless second_size_file.file?
        send_error(incoming_mail, "the given user is not signed up")
        exit
    end
    if second_file_path.exist?
        send_error(incoming_mail, "file cannot be shared for unknown reasons")
        exit
    end
    second_file_path.make_symlink(file_path.to_s.sub("user/", "../"))
    send_response(incoming_mail, "file shared", file_path.to_s)
when /\Adelete ([A-Za-z0-9_-]+(\.[a-z0-9]+)?)\Z/
    file_name= $1
    file_path= user_dir+file_name
    user_size= begin
        size_file.read.to_i
    rescue Errno::ENOENT
        send_error(incoming_mail, "you are not signed up")
        exit
    end
    unless file_name[0] != ?. and file_path.file?
        send_error(incoming_mail, "the requested file does not exist")
        exit
    end
    user_size-= file_path.size
    file_path.unlink
    tmp_size_file.open("w") { |f| f.puts user_size }
    tmp_size_file.rename(size_file)
    send_response(incoming_mail, "file deleted")
when "put"
    user_size= begin
        size_file.read.to_i
    rescue Errno::ENOENT
        send_error(incoming_mail, "you are not signed up")
        exit
    end
    attachment= incoming_mail.attachments[0]
    unless attachment and attachment.filename=~ /\A([A-Za-z0-9_-]+(\.[a-z0-9]+)?)\Z/
        send_error(incoming_mail, "no valid attachment found")
        exit
    end
    file_path= user_dir+attachment.filename
    if file_path.exist?
        send_error(incoming_mail, "file already exists")
        exit
    end
    attachement_body= attachment.body.decoded
    user_size+= attachement_body.size
    if user_size > user_size_limit
        send_error(incoming_mail, "you have no space left")
        exit
    end
    tmp_size_file.open("w") { |f| f.puts user_size }
    tmp_size_file.rename(size_file)
    file_path.open("w") { |f| f.write attachement_body }
    send_response(incoming_mail, "file saved")
end