-- Menu API
-- by RichardG867

local menu = {
    display = function(self)
        selCharLength = #self.selChar
        baseY = 0
        maxX, maxY = term.getSize()

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

        if self.title ~= nil then
            baseY = #self.title + 1

            for i = 1, #self.title do
                print(self.title[i]:sub(1, maxX-1))
            end
        end

        columns = math.ceil(#self.entries / (maxY - baseY))
        columnWidth = math.floor(maxX / columns)
        curColumn = 1
        entryOffset = {}
        entryRow = {}

        j = 1
        for i = 1, #self.entries do
            if baseY + j > maxY then
                curColumn = curColumn + 1
                j = 1
            end

            entryOffset[i] = (curColumn - 1) * columnWidth
            entryRow[i] = j
            if self.entries[i] ~= "" then
                term.setCursorPos(entryOffset[i] + selCharLength + 1, baseY + j)
                term.write(self.entries[i]:sub(1, columnWidth-selCharLength-1))
            end
            j = j + 1
        end

        curEntry = 1
        while curEntry > 0 and self.entries[curEntry] == "" do
            curEntry = curEntry + 1
        end
        if curEntry > #self.entries then error("Empty entry list") end

        while true do
            term.setCursorPos(entryOffset[curEntry] + 1, baseY + entryRow[curEntry])
            term.write(self.selChar)

            event, key = os.pullEvent("key")
            clearSel = 0

            if key == 200 then
                clearSel = curEntry
                curEntry = curEntry - 1

                while curEntry > 0 and self.entries[curEntry] == "" do
                    curEntry = curEntry - 1
                end
                if curEntry < 1 then curEntry = clearSel end
            elseif key == 208 then
                clearSel = curEntry
                curEntry = curEntry + 1

                while curEntry <= #self.entries and self.entries[curEntry] == "" do
                    curEntry = curEntry + 1
                end
                if curEntry > #self.entries then curEntry = clearSel end
            elseif key == 28 then
                term.clear()
                term.setCursorPos(1,1)
                return curEntry
            end

            if clearSel > 0 then
                term.setCursorPos(entryOffset[clearSel] + 1, baseY + entryRow[clearSel])
                term.write(string.rep(" ",selCharLength))
            end
        end
    end,
    setSelChar = function(self, char)
        self.selChar = char
    end,
    tostring = function(self)
        return "Menu["..#self.entries.."]"
    end
}

local metatable = {
    __index = menu,
    __tostring = menu.tostring
}

function new(title, entries)
    if entries == nil or #entries < 1 then
        error("Empty entry list")
    end

    local newmenu = {
        title = title or nil,
        entries = entries,
        selChar = "> "
    }

    setmetatable(newmenu, metatable)
    return newmenu
end