-- DESCRIPTION: Two-button recursive keyboard experiment

local ROWS = {
    { "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" }
}

-- Spatial Rank - Halving must split the keyboard left/right on screen, so keys sort by their
-- centered column position, with the row index only breaking ties.
local KEYS = {}
local keyRank = {}
for rowIndex, row in ipairs(ROWS) do
    for columnIndex, key in ipairs(row) do
        KEYS[#KEYS + 1] = key
        keyRank[key] = (columnIndex - (#row + 1) / 2) * 10 + rowIndex
    end
end
table.sort(KEYS, function(a, b) return keyRank[a] < keyRank[b] end)
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

-- Side Lookup - Rendering needs per-key shading, but candidates are stored in layout order.
local function sides()
    local leftHalf, rightHalf = halves()
    local result = {}
    for _, key in ipairs(leftHalf) do result[key] = "left" end
    for _, key in ipairs(rightHalf) do result[key] = "right" end
    return result
end

local function drawKeyboard(width, top, bottom)
    local gap = 6
    local margin = 16
    local keyWidth = math.floor((width - margin * 2 - gap * 9) / 10)
    local keyHeight = math.min(56, math.floor((bottom - top - gap * 2) / 3))
    local side = sides()

    for rowIndex, row in ipairs(ROWS) do
        local rowWidth = #row * keyWidth + (#row - 1) * gap
        local startX = math.floor((width - rowWidth) / 2)
        local y = top + (rowIndex - 1) * (keyHeight + gap)

        for columnIndex, key in ipairs(row) do
            local keySide = side[key]
            if keySide then
                local x = startX + (columnIndex - 1) * (keyWidth + gap)
                local shaded = keySide == "right"
                gui.fillRoundedRect(x, y, keyWidth, keyHeight, 4, shaded and COLOR_DARK_GRAY or COLOR_WHITE)
                gui.drawRoundedRect(x, y, keyWidth, keyHeight, 1, 4, COLOR_BLACK)
                local label = uppercase and key or key:lower()
                local textX = x + math.floor((keyWidth - gui.getTextWidth(FONT_NOTOSANS_16, label, STYLE_BOLD)) / 2)
                gui.drawText(FONT_NOTOSANS_16, textX, y + math.floor(keyHeight / 2) - 10, label,
                    shaded and COLOR_WHITE or COLOR_BLACK, STYLE_BOLD)
            end
        end
    end
end

local function render()
    local width = gui.width()
    local height = gui.height()
    local margin = 20

    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)

    gui.drawCenteredText(FONT_UI_10, 170, "UP = plain left    DOWN = shaded right", COLOR_BLACK, STYLE_NORMAL)
    drawKeyboard(width, 195, height - 90)

    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