-- DESCRIPTION: Two-button recursive keyboard experiment

local KEYS = {
    "Q", "W", "E", "R", "T", "Y", "U", "I", "O", "P",
    "A", "S", "D", "F", "G", "H", "J", "K", "L",
    "Z", "X", "C", "V", "B", "N", "M"
}
local MAX_TEXT_BYTES = 80

local text = ""
local candidates = {}
local history = {}
local uppercase = false
local needsDraw = true
local firstDraw = true

local function copyKeys(source, first, last)
    local result = {}
    for index = first, last do result[#result + 1] = source[index] end
    return result
end

local function resetCandidates()
    candidates = copyKeys(KEYS, 1, #KEYS)
    history = {}
end

local function halves()
    local midpoint = math.ceil(#candidates / 2)
    return copyKeys(candidates, 1, midpoint), copyKeys(candidates, midpoint + 1, #candidates)
end

local function append(value)
    if #text + #value <= MAX_TEXT_BYTES then text = text .. value end
end

local function chooseHalf(left)
    local leftHalf, rightHalf = halves()
    history[#history + 1] = candidates
    candidates = left and leftHalf or rightHalf

    if #candidates == 1 then
        local letter = candidates[1]
        append(uppercase and letter or letter:lower())
        resetCandidates()
    end
    needsDraw = true
end

local function undo()
    if #history == 0 then
        sys.exit()
        return
    end
    candidates = history[#history]
    history[#history] = nil
    needsDraw = true
end

local function drawPanel(x, y, width, height, title, values)
    gui.drawRoundedRect(x, y, width, height, 2, 8, COLOR_BLACK)
    gui.drawText(FONT_UI_10, x + 12, y + 32, title, COLOR_BLACK, STYLE_BOLD)
    gui.drawText(FONT_UI_12, x + 12, y + math.floor(height / 2), table.concat(values), COLOR_BLACK, STYLE_NORMAL)
end

local function render()
    local width = gui.width()
    local height = gui.height()
    local margin = 20
    local gap = 12
    local panelWidth = math.floor((width - margin * 2 - gap) / 2)
    local panelTop = 185
    local panelHeight = math.min(220, height - panelTop - 100)
    local leftHalf, rightHalf = halves()

    gui.clear()
    gui.drawCenteredText(FONT_UI_12, 24, "Binary Keyboard", COLOR_BLACK, STYLE_BOLD)
    gui.drawRoundedRect(margin, 65, width - margin * 2, 82, 2, 8, COLOR_BLACK)
    local visibleText = text == "" and "Type with the side buttons" or text:sub(-38)
    gui.drawText(FONT_UI_12, margin + 12, 96, visibleText, COLOR_BLACK, STYLE_NORMAL)

    local progress = string.rep("•", #history)
    gui.drawCenteredText(FONT_UI_10, 155, progress == "" and "Choose a half" or progress, COLOR_BLACK, STYLE_NORMAL)
    drawPanel(margin, panelTop, panelWidth, panelHeight, "LEFT SIDE", leftHalf)
    drawPanel(margin + panelWidth + gap, panelTop, panelWidth, panelHeight, "RIGHT SIDE", rightHalf)

    gui.drawButtonHints(#history == 0 and "Exit" or "Undo", "Space", "Delete", uppercase and "lower" or "UPPER")
    gui.refresh(firstDraw and REFRESH_HALF or REFRESH_FAST)
    firstDraw = false
    needsDraw = false
end

function init()
    text = ""
    uppercase = false
    firstDraw = true
    needsDraw = true
    resetCandidates()
end

function draw()
    if input.wasPressed("up") then
        chooseHalf(true)
    elseif input.wasPressed("down") then
        chooseHalf(false)
    elseif input.wasPressed("back") then
        undo()
    elseif input.wasPressed("confirm") then
        append(" ")
        resetCandidates()
        needsDraw = true
    elseif input.wasPressed("left") then
        if #text > 0 then text = text:sub(1, -2) end
        resetCandidates()
        needsDraw = true
    elseif input.wasPressed("right") then
        uppercase = not uppercase
        needsDraw = true
    end

    if needsDraw then render() end
end