-- Get file to edit
local tArgs = { ... }
if #tArgs == 0 then
    print( "Usage: edit <path>" )
    return
end

mon = peripheral.wrap("right")

-- Error checking
local sPath = shell.resolve( tArgs[1] )
local bReadOnly = fs.isReadOnly( sPath )
if fs.exists( sPath ) and fs.isDir( sPath ) then
    print( "Cannot edit a directory." )
    return
end

local x,y = 1,1
local w,h = mon.getSize()
local scrollX, scrollY = 0,0

local tLines = {}
local bRunning = true

-- Colours
local highlightColour, keywordColour, commentColour, textColour, bgColour
if mon.isColour() then
    bgColour = colours.black
    textColour = colours.white
    highlightColour = colours.yellow
    keywordColour = colours.yellow
    commentColour = colours.green
    stringColour = colours.red
else
    bgColour = colours.black
    textColour = colours.white
    highlightColour = colours.white
    keywordColour = colours.white
    commentColour = colours.white
    stringColour = colours.white
end

-- Menus
local bMenu = false
local nMenuItem = 1
local tMenuItems
if bReadOnly then
    tMenuItems = { "Exit", "Print" }
else
    tMenuItems = { "Save", "Exit", "Print" }
end

local sStatus = "Press Ctrl to access menu"

local function load( _sPath )
    tLines = {}
    if fs.exists( _sPath ) then
        local file = io.open( _sPath, "r" )
        local sLine = file:read()
        while sLine do
            table.insert( tLines, sLine )
            sLine = file:read()
        end
        file:close()
    end

    if #tLines == 0 then
        table.insert( tLines, "" )
    end
end

local function save( _sPath )
    -- Create intervening folder
    local sDir = sPath:sub(1, sPath:len() - fs.getName(sPath):len() )
    if not fs.exists( sDir ) then
        fs.makeDir( sDir )
    end

    -- Save
    local file = nil
    local function innerSave()
        file = fs.open( _sPath, "w" )
        if file then
            for n, sLine in ipairs( tLines ) do
                file.write( sLine .. "\n" )
            end
        else
            error( "Failed to open ".._sPath )
        end
    end

    local ok = pcall( innerSave )
    if file then
        file.close()
    end
    return ok
end

local tKeywords = {
    ["and"] = true,
    ["break"] = true,
    ["do"] = true,
    ["else"] = true,
    ["elseif"] = true,
    ["end"] = true,
    ["false"] = true,
    ["for"] = true,
    ["function"] = true,
    ["if"] = true,
    ["in"] = true,
    ["local"] = true,
    ["nil"] = true,
    ["not"] = true,
    ["or"] = true,
    ["repeat"] = true,
    ["return"] = true,
    ["then"] = true,
    ["true"] = true,
    ["until"]= true,
    ["while"] = true,
}

local function tryWrite( sLine, regex, colour )
    local match = string.match( sLine, regex )
    if match then
        if type(colour) == "number" then
            mon.setTextColour( colour )
        else
            mon.setTextColour( colour(match) )
        end
        mon.write( match )
        mon.setTextColour( textColour )
        return string.sub( sLine, string.len(match) + 1 )
    end
    return nil
end

local function writeHighlighted( sLine )
    while string.len(sLine) > 0 do
        sLine =
            tryWrite( sLine, "^%-%-%[%[.-%]%]", commentColour ) or
            tryWrite( sLine, "^%-%-.*", commentColour ) or
            tryWrite( sLine, "^\".-[^\\]\"", stringColour ) or
            tryWrite( sLine, "^\'.-[^\\]\'", stringColour ) or
            tryWrite( sLine, "^%[%[.-%]%]", stringColour ) or
            tryWrite( sLine, "^[%w_]+", function( match )
                if tKeywords[ match ] then
                    return keywordColour
                end
                return textColour
            end ) or
            tryWrite( sLine, "^[^%w_]", textColour )
    end
end

local function redrawText()
    for y=1,h-1 do
        mon.setCursorPos( 1 - scrollX, y )
        mon.clearLine()

        local sLine = tLines[ y + scrollY ]
        if sLine ~= nil then
            writeHighlighted( sLine )
        end
    end
    mon.setCursorPos( x - scrollX, y - scrollY )
end

local function redrawLine(_nY)
    local sLine = tLines[_nY]
    mon.setCursorPos( 1 - scrollX, _nY - scrollY )
    mon.clearLine()
    writeHighlighted( sLine )
    mon.setCursorPos( x - scrollX, _nY - scrollY )
end

local function redrawMenu()
    -- Clear line
    mon.setCursorPos( 1, h )
    mon.clearLine()

    -- Draw line numbers
    mon.setCursorPos( w - string.len( "Ln "..y ) + 1, h )
    mon.setTextColour( highlightColour )
    mon.write( "Ln " )
    mon.setTextColour( textColour )
    mon.write( y )

    mon.setCursorPos( 1, h )
    if bMenu then
        -- Draw menu
        mon.setTextColour( textColour )
        for nItem,sItem in pairs( tMenuItems ) do
            if nItem == nMenuItem then
                mon.setTextColour( highlightColour )
                mon.write( "[" )
                mon.setTextColour( textColour )
                mon.write( sItem )
                mon.setTextColour( highlightColour )
                mon.write( "]" )
                mon.setTextColour( textColour )
            else
                mon.write( " "..sItem.." " )
            end
        end
    else
        -- Draw status
        mon.setTextColour( highlightColour )
        mon.write( sStatus )
        mon.setTextColour( textColour )
    end

    -- Reset cursor
    mon.setCursorPos( x - scrollX, y - scrollY )
end

local tMenuFuncs = {
    Save=function()
        if bReadOnly then
            sStatus = "Access denied"
        else
            local ok, err = save( sPath )
            if ok then
                sStatus="Saved to "..sPath
            else
                sStatus="Error saving to "..sPath
            end
        end
        redrawMenu()
    end,
    Print=function()
        local printer = peripheral.find( "printer" )
        if not printer then
            sStatus = "No printer attached"
            return
        end

        local nPage = 0
        local sName = fs.getName( sPath )
        if printer.getInkLevel() < 1 then
            sStatus = "Printer out of ink"
            return
        elseif printer.getPaperLevel() < 1 then
            sStatus = "Printer out of paper"
            return
        end

        local screenmoninal = mon.current()
        local printermoninal = {
            getCursorPos = printer.getCursorPos,
            setCursorPos = printer.setCursorPos,
            getSize = printer.getPageSize,
            write = printer.write,
        }
        printermoninal.scroll = function()
            if nPage == 1 then
                printer.setPageTitle( sName.." (page "..nPage..")" )
            end

            while not printer.newPage() do
                if printer.getInkLevel() < 1 then
                    sStatus = "Printer out of ink, please refill"
                elseif printer.getPaperLevel() < 1 then
                    sStatus = "Printer out of paper, please refill"
                else
                    sStatus = "Printer output tray full, please empty"
                end

                mon.redirect( screenmoninal )
                redrawMenu()
                mon.redirect( printermoninal )

                local timer = os.startTimer(0.5)
                sleep(0.5)
            end

            nPage = nPage + 1
            if nPage == 1 then
                printer.setPageTitle( sName )
            else
                printer.setPageTitle( sName.." (page "..nPage..")" )
            end
        end

        bMenu = false
        mon.redirect( printermoninal )
        local ok, error = pcall( function()
            mon.scroll()
            for n, sLine in ipairs( tLines ) do
                print( sLine )
            end
        end )
        mon.redirect( screenmoninal )
        if not ok then
            print( error )
        end

        while not printer.endPage() do
            sStatus = "Printer output tray full, please empty"
            redrawMenu()
            sleep( 0.5 )
        end
        bMenu = true

        if nPage > 1 then
            sStatus = "Printed "..nPage.." Pages"
        else
            sStatus = "Printed 1 Page"
        end
        redrawMenu()
    end,
    Exit=function()
        bRunning = false
    end
}

local function doMenuItem( _n )
    tMenuFuncs[tMenuItems[_n]]()
    if bMenu then
        bMenu = false
        mon.setCursorBlink( true )
    end
    redrawMenu()
end

local function setCursor( x, y )
    local screenX = x - scrollX
    local screenY = y - scrollY

    local bRedraw = false
    if screenX < 1 then
        scrollX = x - 1
        screenX = 1
        bRedraw = true
    elseif screenX > w then
        scrollX = x - w
        screenX = w
        bRedraw = true
    end

    if screenY < 1 then
        scrollY = y - 1
        screenY = 1
        bRedraw = true
    elseif screenY > h-1 then
        scrollY = y - (h-1)
        screenY = h-1
        bRedraw = true
    end

    if bRedraw then
        redrawText()
    end
    mon.setCursorPos( screenX, screenY )

    -- Statusbar now pertains to menu, it would probably be safe to redraw the menu on every key event.
    redrawMenu()
end

-- Actual program functionality begins
load(sPath)

mon.setBackgroundColour( bgColour )
mon.clear()
mon.setCursorPos(x,y)
mon.setCursorBlink( true )

redrawText()
redrawMenu()

-- Handle input
while bRunning do
    local sEvent, param, param2, param3 = os.pullEvent()
    if sEvent == "key" then
        if param == keys.up then
            -- Up
            if not bMenu then
                if y > 1 then
                    -- Move cursor up
                    y = y - 1
                    x = math.min( x, string.len( tLines[y] ) + 1 )
                    setCursor( x, y )
                end
            end
        elseif param == keys.down then
            -- Down
            if not bMenu then
                -- Move cursor down
                if y < #tLines then
                    y = y + 1
                    x = math.min( x, string.len( tLines[y] ) + 1 )
                    setCursor( x, y )
                end
            end
        elseif param == keys.tab then
            -- Tab
            if not bMenu and not bReadOnly then
                -- Indent line
                tLines[y]="  "..tLines[y]
                x = x + 2
                setCursor( x, y )
                redrawLine(y)
            end
        elseif param == keys.pageUp then
            -- Page Up
            if not bMenu then
                -- Move up a page
                if y - (h - 1) >= 1 then
                    y = y - (h - 1)
                else
                    y = 1
                end
                x = math.min( x, string.len( tLines[y] ) + 1 )
                setCursor( x, y )
            end
        elseif param == keys.pageDown then
            -- Page Down
            if not bMenu then
                -- Move down a page
                if y + (h - 1) <= #tLines then
                    y = y + (h - 1)
                else
                    y = #tLines
                end
                x = math.min( x, string.len( tLines[y] ) + 1 )
                setCursor( x, y )
            end
        elseif param == keys.home then
            -- Home
            if not bMenu then
                -- Move cursor to the beginning
                x=1
                setCursor(x,y)
            end
        elseif param == keys["end"] then
            -- End
            if not bMenu then
                -- Move cursor to the end
                x = string.len( tLines[y] ) + 1
                setCursor(x,y)
            end
        elseif param == keys.left then
            -- Left
            if not bMenu then
                if x > 1 then
                    -- Move cursor left
                    x = x - 1
                elseif x==1 and y>1 then
                    x = string.len( tLines[y-1] ) + 1
                    y = y - 1
                end
                setCursor( x, y )
            else
                -- Move menu left
                nMenuItem = nMenuItem - 1
                if nMenuItem < 1 then
                    nMenuItem = #tMenuItems
                end
                redrawMenu()
            end
        elseif param == keys.right then
            -- Right
            if not bMenu then
                if x < string.len( tLines[y] ) + 1 then
                    -- Move cursor right
                    x = x + 1
                elseif x==string.len( tLines[y] ) + 1 and y<#tLines then
                    x = 1
                    y = y + 1
                end
                setCursor( x, y )
            else
                -- Move menu right
                nMenuItem = nMenuItem + 1
                if nMenuItem > #tMenuItems then
                    nMenuItem = 1
                end
                redrawMenu()
            end
        elseif param == keys.delete then
            -- Delete
            if not bMenu and not bReadOnly then
                if  x < string.len( tLines[y] ) + 1 then
                    local sLine = tLines[y]
                    tLines[y] = string.sub(sLine,1,x-1) .. string.sub(sLine,x+1)
                    redrawLine(y)
                elseif y<#tLines then
                    tLines[y] = tLines[y] .. tLines[y+1]
                    table.remove( tLines, y+1 )
                    redrawText()
                    redrawMenu()
                end
            end
        elseif param == keys.backspace then
            -- Backspace
            if not bMenu and not bReadOnly then
                if x > 1 then
                    -- Remove character
                    local sLine = tLines[y]
                    tLines[y] = string.sub(sLine,1,x-2) .. string.sub(sLine,x)
                    redrawLine(y)

                    x = x - 1
                    setCursor( x, y )
                elseif y > 1 then
                    -- Remove newline
                    local sPrevLen = string.len( tLines[y-1] )
                    tLines[y-1] = tLines[y-1] .. tLines[y]
                    table.remove( tLines, y )
                    redrawText()

                    x = sPrevLen + 1
                    y = y - 1
                    setCursor( x, y )
                end
            end
        elseif param == keys.enter then
            -- Enter
            if not bMenu and not bReadOnly then
                -- Newline
                local sLine = tLines[y]
                local _,spaces=string.find(sLine,"^[ ]+")
                if not spaces then
                    spaces=0
                end
                tLines[y] = string.sub(sLine,1,x-1)
                table.insert( tLines, y+1, string.rep(' ',spaces)..string.sub(sLine,x) )
                redrawText()

                x = spaces+1
                y = y + 1
                setCursor( x, y )
            elseif bMenu then
                -- Menu selection
                doMenuItem( nMenuItem )
            end
        elseif param == keys.leftCtrl or param == keys.rightCtrl then
            -- Menu toggle
            bMenu = not bMenu
            if bMenu then
                mon.setCursorBlink( false )
            else
                mon.setCursorBlink( true )
            end
            redrawMenu()
        end

    elseif sEvent == "char" then
        if not bMenu and not bReadOnly then
            -- Input text
            local sLine = tLines[y]
            tLines[y] = string.sub(sLine,1,x-1) .. param .. string.sub(sLine,x)
            redrawLine(y)

            x = x + 1
            setCursor( x, y )
        elseif bMenu then
            -- Select menu items
            for n,sMenuItem in ipairs( tMenuItems ) do
                if string.lower(string.sub(sMenuItem,1,1)) == string.lower(param) then
                    doMenuItem( n )
                    break
                end
            end
        end

    elseif sEvent == "paste" then
        if not bMenu and not bReadOnly then
            -- Input text
            local sLine = tLines[y]
            tLines[y] = string.sub(sLine,1,x-1) .. param .. string.sub(sLine,x)
            redrawLine(y)

            x = x + string.len( param )
            setCursor( x, y )
        end

    elseif sEvent == "mouse_click" then
        if not bMenu then
            if param == 1 then
                -- Left click
                local cx,cy = param2, param3
                if cy < h then
                    y = math.min( math.max( scrollY + cy, 1 ), #tLines )
                    x = math.min( math.max( scrollX + cx, 1 ), string.len( tLines[y] ) + 1 )
                    setCursor( x, y )
                end
            end
        end

    elseif sEvent == "mouse_scroll" then
        if not bMenu then
            if param == -1 then
                -- Scroll up
                if scrollY > 0 then
                    -- Move cursor up
                    scrollY = scrollY - 1
                    redrawText()
                end

            elseif param == 1 then
                -- Scroll down
                local nMaxScroll = #tLines - (h-1)
                if scrollY < nMaxScroll then
                    -- Move cursor down
                    scrollY = scrollY + 1
                    redrawText()
                end

            end
        end

    elseif sEvent == "mon_resize" then
        w,h = mon.getSize()
        setCursor( x, y )
        redrawMenu()
        redrawText()

    end
end

-- Cleanup
mon.clear()
mon.setCursorBlink( false )
mon.setCursorPos( 1, 1 )