HexEdit

local guideBar = "|Pos.|00|01|02|03|04|05|06|07|ASCIIRep|"
local sepBar =   "|----|--|--|--|--|--|--|--|--|--------|"
local horizBar = string.rep("-", 39)
local sX, sY = term.getSize()

local args = {...}

if not term.isColor() then
    print("Sorry, but you must an Advanced Computer is required to use this program.")
    return
end

if #args <= 0 then
    print("USAGE: "..fs.getName(shell.getRunningProgram()).." [file]")
    return
end

local function writeScreen(bytes, offsetLines, fileName)
    local byteLines = {}

    local function writeLine(bLine, offset, y)
        term.setCursorPos(1, y)
        local line = "|"
        local strOffset = string.format("%X", offset)
        for i=#strOffset, 3 do
            strOffset = "0"..strOffset
        end
        line = line..strOffset.."|"
        local asciiRep = ""
        for i=1, 8 do
            if bLine[i] ~= nil then
                local t = string.format("%X", bLine[i])
                if #t == 1 then
                    t = "0"..t
                end
                line = line..t.."|"
                if bLine[i] >= 0x20 and bLine[i] <= 0x7E then
                    asciiRep = asciiRep..string.char(bLine[i])
                else
                    asciiRep = asciiRep.."."
                end
            else
                line = line.."  ".."|"
                asciiRep = asciiRep.." "
            end
        end
        line = line..asciiRep.."|"
        term.clearLine()
        term.write(line)
    end

    for i=1, math.ceil(#bytes / 8) do
        byteLines[i] = { --[[ ["offset"] = (i-1)*8 ]] }
        for j=1, 8 do
            byteLines[i][j] = bytes[ ((i-1)*8)+j ]
        end
    end

    term.clear()
    term.setCursorPos(1,1)

    term.write("Current File: \""..fileName.."\" Size: "..#bytes.." bytes") -- Better to cut off the filename rather than completely wrecking the UI
    print(guideBar)
    print(sepBar)
    for i=4, sY do
        if byteLines[(i-3)+offsetLines] then
            writeLine( byteLines[(i-3)+offsetLines], ((i-4)+offsetLines)*8, i )
        else
            writeLine( {}, ((i-4)+offsetLines)*8, i )
        end
    end
    term.setCursorPos(41, 2)
    term.write("E to exit")
    term.setCursorPos(41, 3)
    term.write("(and save)")
    term.setCursorPos(41, 5)
    term.write("Q to quit")
    term.setCursorPos(41, 6)
    term.write("(no save)")
    term.setCursorPos(41, 8)
    term.write("S to save")
    term.setCursorPos(41, 9)
    term.write("(no quit)")
end

local handle = fs.open(args[1], "rb")
local bytes = {}
while true do
    local byte = handle.read()
    if byte then
        table.insert(bytes, byte)
    else
        break
    end
    term.setCursorPos(1, 1)
    term.clear()
    print("Loading file.")
    print(#bytes.." out of approximately "..fs.getSize(args[1]).." bytes loaded.")
    print(math.ceil((#bytes / fs.getSize(args[1]))*100).."% complete.")
    os.queueEvent("")
    os.pullEvent()
end
handle.close()

local function save(b)
    local handle = fs.open(args[1], "wb")
    for i=1, #bytes do
        term.setCursorPos(1, 1)
        term.clearLine()
        term.write("Writing: "..i.." of "..#b.." ("..math.ceil((i/#b)*100).."%)")
        handle.write(b[i])
        os.queueEvent("")
        os.pullEvent()
    end
    handle.close()
end

local lineOffset = 0
while true do
    --local byteOffset = lineOffset * 8
    writeScreen(bytes, lineOffset, args[1])
    local event, a1, x, y = os.pullEvent()
    if event == "char" then
        if a1 == "e" or a1 == "E" then
            save(bytes)
            break
        elseif a1 == "q" or a1 == "Q" then
            break
        elseif a1 == "s" or a1 == "S" then
            save(bytes)
        end
    elseif event == "mouse_click" then
        if (not (y >= 1 and y <= 3)) and (x >6 and x < 39) then
            term.setCursorPos(1,1)
            term.write("Current File: \""..args[1].."\" Size: "..#bytes.." bytes !EDITING!")
            -- Get clicked cell:
            if x > 30 then
                local cell = x - 30
                term.setCursorPos(((cell-1)*3)+7, y)
                term.setBackgroundColor(colors.blue)
                term.write("  ")
                term.setCursorPos(x, y)
                term.setBackgroundColor(colors.red)
                term.write(" ")
                term.setBackgroundColor(colors.black)
                term.setCursorPos(x, y)
                term.setCursorBlink(true)
                local b = 0
                while true do
                    local event, c = os.pullEvent()
                    if event == "char" then
                        b = string.byte(c)
                        break
                    elseif event == "key" then
                        if c == keys.backspace or c == keys.delete then
                            b = nil
                            break
                        end
                    end
                end
                bytes[ (lineOffset+(y-4))*8+cell ] = b
                term.setCursorBlink(false)
            else--[[if x > 6 and x < 39 then]]
                local cell = math.ceil((x-5)/3)
                term.setCursorPos(((cell-1)*3)+7, y)
                term.setBackgroundColor(colors.red)
                term.write("  ")
                term.setCursorPos(30+cell, y)
                term.setBackgroundColor(colors.blue)
                term.write(" ")
                term.setBackgroundColor(colors.black)
                term.setCursorPos(((cell-1)*3)+7, y)
                term.setCursorBlink(true)
                local st = ""
                while true do
                    local event, c = os.pullEvent()
                    if event == "char" and tonumber(c, 16) then
                        st = st..c
                    elseif event == "key" and (c == keys.backspace or c == keys.delete) then
                        if #st == 0 then
                            break
                        else
                            st = string.sub(st, 1, #st-1)
                        end
                    end
                    term.setCursorPos(((cell-1)*3)+7, y)
                    term.write(st)
                    if #st >= 2 then
                        break
                    end
                end
                bytes[ (lineOffset+(y-4))*8+cell ] = tonumber(st, 16)
                term.setCursorBlink(false)
            end
            term.setCursorPos(1,1)
            term.write("Current File: \""..args[1].."\" Size: "..#bytes.." bytes")
        end
        -- > 30, < 39
    elseif event == "mouse_scroll" then
        lineOffset = lineOffset+a1
        if lineOffset < 0 then
            lineOffset = 0
        end
    end
end

--[[
term.setCursorPos(1,1)
term.write("Current File: \""..args[1].."\" Size: "..#bytes.." bytes !WRITING!")

local handle = fs.open(args[1], "wb")
for i=1, #bytes do
    handle.write(bytes[i])
    os.queueEvent("")
    os.pullEvent()
end
handle.close()
]]

term.clear()
term.setCursorPos(1,1)