Basic emulator

-- BASIC-Emulator "RetroOS"
local program = {}
local vars = {}
local loop_stack = {}
local PIN = "1234" -- Dein PIN für LOGOUT

local themes = {
    {name = "C64 Style", bg = colors.blue, fg = colors.white},
    {name = "CBM PET", bg = colors.black, fg = colors.lime},
    {name = "Apple II", bg = colors.black, fg = colors.green},
    {name = "Spectrum", bg = colors.white, fg = colors.black},
    {name = "DOS Mode", bg = colors.black, fg = colors.lightGray}
}

local currentTheme = themes[1]

-- Grafische Hilfsfunktionen
local function drawBox(w, h, title)
    term.clear()
    local tw, th = term.getSize()
    local x, y = math.floor((tw-w)/2), math.floor((th-h)/2)
    term.setBackgroundColor(colors.gray)
    term.setCursorPos(x, y)
    for i=1, h do
        term.setCursorPos(x, y + i - 1)
        term.write(string.rep(" ", w))
    end
    term.setCursorPos(x+1, y)
    term.write(title)
end

local function promptPin()
    drawBox(20, 5, " SYSTEM SPERRE ")
    term.setCursorPos(5, 3)
    term.write("PIN eingeben:")
    term.setCursorPos(5, 4)
    local input = read("*")
    if input == PIN then return true end
    return false
end

local function selectTheme()
    local selection = 1
    while true do
        term.setBackgroundColor(colors.black)
        term.clear()
        term.setCursorPos(1, 1)
        print("--- Waehle dein Retro-System ---")
        for i, t in ipairs(themes) do
            print((i == selection and "> " or "  ") .. t.name)
        end
        local _, key = os.pullEvent("key")
        if key == keys.up then selection = math.max(1, selection - 1)
        elseif key == keys.down then selection = math.min(#themes, selection + 1)
        elseif key == keys.enter then
            currentTheme = themes[selection]
            break
        end
    end
end

-- Parser Funktionen
local function execute()
    local lines = {}
    for k in pairs(program) do table.insert(lines, k) end
    table.sort(lines)

    local ip = 1
    while ip <= #lines do
        local cmd = program[lines[ip]]:upper()
        local tokens = {}
        for token in cmd:gmatch("%S+") do table.insert(tokens, token) end

        -- Befehlsverarbeitung
        if tokens[1] == "PRINT" then
            local text = cmd:sub(7)
            if vars[text] then print(vars[text])
            elseif text:sub(1,1) == "\"" then print(text:sub(2, -2))
            else print(text) end

        elseif tokens[1] == "LET" or tokens[2] == "=" then
            local var, val = cmd:match("(%a+)%s*=%s*(%d+)")
            vars[var] = tonumber(val)

        elseif tokens[1] == "IF" then
            local var, op, val, thenLine = cmd:match("IF%s+(%a+)%s*([<>=]+)%s*(%d+)%s+THEN%s+(%d+)")
            local condition = false
            if op == "=" and vars[var] == tonumber(val) then condition = true
            elseif op == ">" and vars[var] > tonumber(val) then condition = true
            elseif op == "<" and vars[var] < tonumber(val) then condition = true end

            if condition then
                for i, l in ipairs(lines) do if l == tonumber(thenLine) then ip = i - 1 end end
            end

        elseif tokens[1] == "GOTO" then
            local target = tonumber(tokens[2])
            for i, l in ipairs(lines) do if l == target then ip = i - 1 end end

        elseif tokens[1] == "CLS" then term.clear(); term.setCursorPos(1,1)
        elseif tokens[1] == "REM" then -- Kommentar (ignoriert)
        elseif tokens[1] == "END" then break
        end

        ip = ip + 1
        sleep(0.05)
    end
end

-- Hauptprogramm
selectTheme()
term.setBackgroundColor(currentTheme.bg)
term.setTextColor(currentTheme.fg)
term.clear()
term.setCursorPos(1, 1)

print("RetroOS v1.0 - BASIC Emulation")
while true do
    write("> ")
    local input = read()
    if input:upper() == "RUN" then execute()
    elseif input:upper() == "LOGOUT" then
        if promptPin() then break
        else print("Falscher PIN!") end
    elseif input:upper() == "LIST" then
        for _, n in ipairs((function() local l={}; for k in pairs(program) do table.insert(l,k) end; table.sort(l); return l end)()) do
            print(n .. " " .. program[n])
        end
    else
        local lineNum = tonumber(input:match("^(%d+)"))
        if lineNum then program[lineNum] = input:match("^%d+%s+(.*)")
        else print("SYNTAX ERROR") end
    end
end
term.clear()