--***************************************************************************
--                  Don G's Celx/Lua Date Converter script                  *
--                             (version 1.0)                                *
--                                                                          *
--  This script allows the user to enter either a calendar date or julian   *
--  date/time, and then returns the date converted to the other format.     *
--                                                                          *
--***************************************************************************


--***************************************************************************
--                            Global Variables                              *
--***************************************************************************
  userKeypress = ""  -- Used with keyboard entry
  julianDate   = 0
  calendarDate = 0


--***************************************************************************
--                         Keyboard Input Callback                          *
--                                                                          *
-- This function is called automatically by Celestia when celestia:         *
-- requestkeyboard() is set to true.                                        *
--                                                                          *
--***************************************************************************
  function celestia_keyboard_callback(char)
    userKeypress = char
    return true  -- Tell Celestia we will handle this keypress
  end


--***************************************************************************
--                   getUserInput from the keyboard                         *
--                                                                          *
--  This function allows the user to enter a single line of text in reply   *
--  to your prompt for information ('prompt' is a string value).            *
--***************************************************************************
  function getUserInput(prompt)
    local inputLine = ""

    if prompt == nil then
       celestia:print("getUserInput Error: Please include prompt text.",
                       5, -1, -1, 1, 5)
       wait(5)
       return ""
    end

    -- Count line feed characters (\n) in the prompt text...
    local x         = 0
    local nlcount   = 0
    local charpos   = 1
    local promptRow = 3

    charcount = string.len(prompt)
    for charpos = 1, charcount do
      x = string.find(prompt, "\n", charpos, plain)
      if x ~= nil then
         nlcount = nlcount + 1
         charpos = x + 1
      end
    end

    -- Compute what row to begin displaying prompt on...
    if nlcount > 0 then
       promptRow = promptRow + nlcount
    end

    origTimeScale = celestia:gettimescale()  -- Get the current time-scale
    celestia:settimescale(0)                 -- Pause time
    userKeypress = ""                        -- Clear the userKeypress var
    celestia:requestkeyboard(true)           -- Enable keyboard input

    while true do                            -- Loop until we get Enter key
      -- Display the prompt...
      celestia:print(prompt .. inputLine, 100, -1, -1, 1, promptRow)
      wait(0.01)

      -- What key did the user press...
      if userKeypress == "\013" then      -- Enter key, we're done
         break

      elseif userKeypress == "\008" then  -- Backspace key, remove last char
         local strlen = string.len(inputLine)
         if strlen <= 1 then
            inputLine = ""
         else
            inputLine = string.sub(inputLine, 1, strlen - 1)
         end

      else  -- Add the character to inputLine...
         inputLine = inputLine .. userKeypress

      end
      userKeypress = ""

    end

    celestia:requestkeyboard(false)       -- Disable keyboard input
    celestia:settimescale(origTimeScale)  -- Reset the time scale
    return inputLine
  end


--***************************************************************************
--                             getCalendarDate                              *
--                                                                          *
--  This function allows the user to enter a Julian date and returns the    *
--  Calendar date.                                                            *
--***************************************************************************
  function getCalendarDate()
    local error  = ""
    local prompt = ""

    while true do
      prompt = error .. "\n"
        .. "Enter 0 (zero) to exit.\n"
        .. "Enter Julian date/time: "

      local userInput = getUserInput(prompt)

      if userInput == "0" or userInput == "" then
         return "0"  -- User terminated the function
      end

      -- Validate the user entered date, and get it if it's okay...
      local num = tonumber(userInput)
      if num == nil then
         num = 0
      end
         
      if num < 1 then
         error = "ERROR: The Julian date/time cannot be zero."
      else
        calendarDate = celestia:fromjulianday(num)
        error = "0"
      end

      if error == "0" then
         return userInput  -- Date was successfully set
      end
      
    end  -- (while)
  end    -- (function)


--***************************************************************************
--                              getJulianDate                               *
--                                                                          *
--  This function allows the user to enter a Calendar date and returns the  *
--  Julian date.                                                            *
--***************************************************************************
  function getJulianDate()
    local error  = ""
    local prompt = ""

    while true do
      prompt = error .. "\n"
        .. "Enter 0 (zero) to exit.\n"
        .. "Include leading zeros, time is UTC 24-hour clock\n"
        .. "Format: YYYY-MM-DD-HH-MM-SS.SSS\n"
        .. "Enter Calendar date/time: "

      local userInput = getUserInput(prompt)

      if userInput == "0" or userInput == "" then
         return "0"  -- User terminated the function
      end

      -- Validate the user entered date, and get it if it's okay...
      error = checkDate(userInput)
      
      if error == "0" then
         return userInput  -- Date was successfully set
      end
      
    end  -- (while)
  end    -- (function)


-- Validate user entry...
  function checkDate(userInput)
    if string.len(userInput) ~= 23 then
       return "Error: Please enter all digits, hyphens, leading zeros and decimal places."
    end

    -- Pick out the individual fields we need...
    
    -- YYYY-MM-DD-HH-MM-SS.SSS
    --          11111111112222
    -- 12345678901234567890123
    local year   = string.sub(userInput,  1,  4)
    local month  = string.sub(userInput,  6,  7)
    local day    = string.sub(userInput,  9, 10)
    local hour   = string.sub(userInput, 12, 13)
    local minute = string.sub(userInput, 15, 16)
    local second = string.sub(userInput, 18, 23)

    local num = tonumber(year)
    if num == nil then
       num = 0
    end
         
    if num < 1 then
       return "ERROR: The year cannot be zero."
    end

    num = tonumber(month)
    if num == nil then
       num = 99
    end
         
    if num < 1 or num > 12 then
       return "ERROR: Invalid Month. Must be between 01 and 12"
    end

    num = tonumber(day)
    if num == nil then
       num = 99
    end
         
    if num < 1 or num > 31 then
       return "ERROR: Invalid Day. Must be between 01 and 31"
    end

    num = tonumber(hour)
    if num == nil then
       num = 99
    end
         
    if num > 23 then
       return "ERROR: Invalid Hour. Must be between 00 and 23"
    end

    num = tonumber(minute)
    if num == nil then
       num = 99
    end
         
    if num > 60 then
       return "ERROR: Invalid Minute. Must be between 00 and 59"
    end

    num = tonumber(second)
    if num == nil then
       num = 99
    end
         
    if num > 60 then
       return "ERROR: Invalid Seconds. Must be between 00.000 and 59.999"
    end
       
    -- Finally, get the new date...
    julianDate = celestia:tojulianday(
        tonumber(year),
        tonumber(month),
        tonumber(day),
        tonumber(hour),
        tonumber(minute),
        tonumber(second) )
           
    return "0"
  end


--***************************************************************************
--                Convert a calendar date to a julian date                  *
--***************************************************************************

-- What type of date does the user want to convert?...
   local dateType = ""
   local error    = ""
   local newDate  = ""

   while (string.upper(dateType) ~= "C" and string.upper(dateType) ~= "J") do
     dateType = getUserInput(error .. "\n"
                          .. "Press ESC to exit.\n"
                          .. "What format date do you want to enter?\n"
                          .. "C=Calendar, J=Julian...")

     if  string.upper(dateType) ~= "C"
     and string.upper(dateType) ~= "J" then
         error = "ERROR: Please enter a 'C' or 'J'..."
     end
   end


-- Calendar to Julian conversion...
   if string.upper(dateType) == "C" then
      newDate = getJulianDate()
      if newDate == "0" then
         celestia:flash("User terminated the function.", 5)
         wait (5)
      else
         celestia:print("Calendar Date: ".. newDate .. "\n" ..
                        "Julian Date: "  .. julianDate, 60, -1, -1, 0, 5)
         wait (60)
      end

-- Julian to Calendar conversion...
   elseif string.upper(dateType) == "J" then
      newDate = getCalendarDate()
      if newDate == "0" then
         celestia:flash("User terminated the function.", 5)
         wait (5)
      else
         celestia:print("Calendar Date: "
           .. string.format("%04u", calendarDate.year)    .. "-"
           .. string.format("%02u", calendarDate.month)   .. "-"
           .. string.format("%02u", calendarDate.day)     .. "-"
           .. string.format("%02u", calendarDate.hour)    .. "-"
           .. string.format("%02u", calendarDate.minute)  .. "-"
           .. string.format("%05.3f", calendarDate.seconds)
           .. "\n"
           .. "Julian Date: " .. newDate, 60, -1, -1, 0, 5)
         wait (60)
      end
   end


   celestia:flash("End of script.", 3)
   wait (3)