local ui = require("ui")

local M = {}

local KEY_W, KEY_H, KEY_GAP, ROW_GAP = 26, 30, 4, 5
local SIDE_W, MODE_W, SPACE_W, OK_W = 40, 54, 174, 58
local PAGES = {
  lower = {"qwertyuiop", "asdfghjkl", "zxcvbnm"},
  upper = {"QWERTYUIOP", "ASDFGHJKL", "ZXCVBNM"},
  numbers = {"1234567890", "-/:;()$&@", ".,?!'"},
  symbols = {"[]{}#%^*+=", "_\\|~<>$&@", ".,?!'"},
}

-- Keyed by node id, because the node itself is sixteen bytes in the firmware and holds
-- nothing a keyboard cares about.
local state = {}

local function chars(page, row)
  return PAGES[page][row]
end

local function rowWidth(count)
  return count * KEY_W + (count - 1) * KEY_GAP
end

local function centeredX(rect, width)
  return rect.x + (rect.w - width) // 2
end

local function thirdRow(page, rect)
  local value = chars(page, 3)
  local width = SIDE_W * 2 + KEY_GAP * 2 + rowWidth(#value)
  return value, centeredX(rect, width)
end

-- Pure geometry: which key covers a point, given a page and the rectangle the board was
-- placed in. Kept free of the node tree so the host tests can exercise the maths that
-- actually decides what a tap enters.
function M.keyAt(page, rect, x, y)
  local localY = y - rect.y
  if localY < 0 then return end
  local row = localY // (KEY_H + ROW_GAP) + 1
  if row > 4 or localY % (KEY_H + ROW_GAP) >= KEY_H then return end

  if row <= 2 then
    local value = chars(page, row)
    local localX = x - centeredX(rect, rowWidth(#value))
    if localX < 0 then return end
    local column = localX // (KEY_W + KEY_GAP) + 1
    if column <= #value and localX % (KEY_W + KEY_GAP) < KEY_W then
      return (row - 1) * 10 + column, "char", value:sub(column, column)
    end
    return
  end

  if row == 3 then
    local value, start = thirdRow(page, rect)
    local localX = x - start
    if localX < 0 then return end
    if localX < SIDE_W then
      return 90, (page == "lower" or page == "upper") and "shift" or "symbols"
    end
    localX = localX - SIDE_W - KEY_GAP
    local width = rowWidth(#value)
    if localX >= 0 and localX < width then
      local column = localX // (KEY_W + KEY_GAP) + 1
      if localX % (KEY_W + KEY_GAP) < KEY_W then
        return 20 + column, "char", value:sub(column, column)
      end
      return
    end
    localX = localX - width - KEY_GAP
    if localX >= 0 and localX < SIDE_W then return 91, "backspace" end
    return
  end

  local width = MODE_W + SPACE_W + OK_W + KEY_GAP * 2
  local localX = x - centeredX(rect, width)
  if localX < 0 then return end
  if localX < MODE_W then return 100, "mode" end
  localX = localX - MODE_W - KEY_GAP
  if localX >= 0 and localX < SPACE_W then return 101, "space" end
  localX = localX - SPACE_W - KEY_GAP
  if localX >= 0 and localX < OK_W then return 102, "submit" end
end

local function drawArrow(x, y, width, color, down)
  local middle = x + width // 2
  if down then
    gui.drawLine(middle, y + 8, middle, y + 20, color)
    gui.drawLine(middle - 5, y + 15, middle, y + 20, color)
    gui.drawLine(middle, y + 20, middle + 5, y + 15, color)
  else
    gui.drawLine(middle, y + 9, middle, y + 21, color)
    gui.drawLine(middle - 5, y + 14, middle, y + 9, color)
    gui.drawLine(middle, y + 9, middle + 5, y + 14, color)
  end
end

local function drawKey(id, label, x, y, width, pressed)
  local theme = ui.theme
  local gradient = pressed and theme.face_pressed or theme.face
  local color = pressed and theme.accent_fg or theme.fg
  gui.roundRect(x, y, width, KEY_H, theme.radius, theme.bg, gradient[1], gradient[2], color)
  if label == "shift" then
    drawArrow(x, y, width, color, state[id].page == "upper")
  else
    gui.drawText(label, x + (width - gui.getTextWidth(label)) // 2,
                 y + (KEY_H - gui.getFontHeight()) // 2, color, gradient[2])
  end
end

-- Walks every key, handing each one to `visit`. Painting the whole board and repainting a
-- single key are the same traversal, so a key's position is defined in one place. Pure,
-- for the same reason keyAt is.
function M.eachKey(page, rect, visit)
  local y = rect.y

  for row = 1, 2 do
    local value = chars(page, row)
    local x = centeredX(rect, rowWidth(#value))
    for column = 1, #value do
      visit((row - 1) * 10 + column, value:sub(column, column), x, y, KEY_W)
      x = x + KEY_W + KEY_GAP
    end
    y = y + KEY_H + ROW_GAP
  end

  local value, x = thirdRow(page, rect)
  visit(90, (page == "lower" or page == "upper") and "shift" or
        (page == "numbers" and "#+=" or "123"), x, y, SIDE_W)
  x = x + SIDE_W + KEY_GAP
  for column = 1, #value do
    visit(20 + column, value:sub(column, column), x, y, KEY_W)
    x = x + KEY_W + KEY_GAP
  end
  visit(91, "<-", x, y, SIDE_W)

  y = y + KEY_H + ROW_GAP
  local width = MODE_W + SPACE_W + OK_W + KEY_GAP * 2
  x = centeredX(rect, width)
  visit(100, (page == "lower" or page == "upper") and "123" or "ABC", x, y, MODE_W)
  x = x + MODE_W + KEY_GAP
  visit(101, "space", x, y, SPACE_W)
  x = x + SPACE_W + KEY_GAP
  visit(102, "OK", x, y, OK_W)
end

local function rectOf(id)
  local x, y, w, h = node.getRect(id)
  return {x = x, y = y, w = w, h = h}
end

local function paint(id)
  M.eachKey(state[id].page, rectOf(id), function(key, label, x, y, width)
    drawKey(id, label, x, y, width, false)
  end)
end

-- Repaints one key in place. The keyboard is a single node, so there is no parent to
-- clear and nothing else on screen can have moved.
local function drawOneKey(id, target, pressed)
  M.eachKey(state[id].page, rectOf(id), function(key, label, x, y, width)
    if key == target then drawKey(id, label, x, y, width, pressed) end
  end)
end

local function down(id, x, y)
  local key = M.keyAt(state[id].page, rectOf(id), x, y)
  state[id].activeKey = key
  if key then drawOneKey(id, key, true) end
end

local function unpress(id)
  local key = state[id].activeKey
  state[id].activeKey = nil
  if key then drawOneKey(id, key, false) end
end

local function press(id, x, y)
  local st = state[id]
  local key, action, char = M.keyAt(st.page, rectOf(id), x, y)
  if not key or key ~= st.activeKey then return end

  local function changed()
    if st.on_change then st.on_change(st.value) end
  end

  if action == "char" then
    if #st.value < st.max_length then st.value = st.value .. char; changed() end
  elseif action == "shift" then
    st.page = st.page == "lower" and "upper" or "lower"
    node.invalidate(id)
  elseif action == "symbols" then
    st.page = st.page == "numbers" and "symbols" or "numbers"
    node.invalidate(id)
  elseif action == "mode" then
    st.page = (st.page == "lower" or st.page == "upper") and "numbers" or "lower"
    node.invalidate(id)
  elseif action == "backspace" then
    st.value = st.value:sub(1, -2)
    changed()
  elseif action == "space" then
    if #st.value < st.max_length then st.value = st.value .. " "; changed() end
  elseif action == "submit" and st.on_submit then
    st.on_submit(st.value)
  end
end

-- One custom-painted node keeps a full keyboard off the heap: ordinary ui.button keys
-- would add dozens of nodes and their styles while wifi is already holding buffers.
function M.new(spec)
  spec = spec or {}
  local id = ui.custom{
    h = 4 * KEY_H + 3 * ROW_GAP,
    paint = paint,
    on_down = down,
    on_press = press,
    on_unpress = unpress,
    press_style = false,  -- a key highlights itself; the node never does
  }
  state[id] = {
    value = spec.value or "",
    max_length = spec.max_length or 64,
    page = "lower",
    on_change = spec.on_change,
    on_submit = spec.on_submit,
  }
  return id
end

return M