输入历史：上下键翻看历史发言

-- 错误：上下键直接回填不记游标，来回乱跳
function onUp()
    input:setText(history[hIdx])
end
function onDown()
    input:setText(history[hIdx + 1])
end

local history, hIdx = {}, 0
local draft = ""
local function onSend(text)
    if text == "" then return end
    if history[#history] ~= text then
        history[#history + 1] = text
        if #history > 50 then
            table.remove(history, 1)
        end
    end
    hIdx = #history + 1
end
local function onUp()
    if hIdx > 1 then
        if hIdx > #history then draft = input:getText() end
        hIdx = hIdx - 1
        input:setText(history[hIdx])
    end
end
local function onDown()
    if hIdx < #history then
        hIdx = hIdx + 1
        input:setText(history[hIdx])
    elseif hIdx == #history then
        hIdx = hIdx + 1
        input:setText(draft)
    end
end