local vim = assert(vim)
local M = {}

local cons = "tnshrdlcumwfgypkbvjxqz" -- 21
local vowel = "aeiou" -- 5

local hsel1 = "tnshrdlcumwfgypkbvjxqz" -- 21
local hsel2 = "aeiou" -- 5

local function char_at(s, i)
  local m = (i % #s) + 1
  return string.sub(s, m, m)
end

local function new_panel(buf, row, col, width, height)
  local w = vim.api.nvim_open_win(buf, false, {
    relative = 'win',
    row = row,
    col = col,
    width = width,
    height = height,
    focusable = false,
    style = 'minimal'
  })
  vim.api.nvim_win_set_option(w, "winhighlight", "Normal:WarpNormal")
  return w
end

M.open_vertical = function()
  local current_win = vim.api.nvim_get_current_win()
  local height = vim.api.nvim_win_get_height(current_win)
  local topline = vim.fn.line('w0')
  local width_of_garbage = vim.fn.getwininfo(current_win)[1].textoff

  M.row_map = {}

  M.vert_buf = vim.api.nvim_create_buf(0, 1)
  local line = 0
  M.vert_lines = {}
  local real_width = math.max(3, width_of_garbage)
  while line < height do
    local t = char_at(cons, line) .. char_at(vowel, line)
    table.insert(M.vert_lines, (' '):rep(real_width - 3) .. t .. ' ')
    M.row_map[t] = topline + line
    line = line + 1
  end
  vim.api.nvim_buf_set_lines(M.vert_buf, 0, -1, 0, M.vert_lines)
  return new_panel(M.vert_buf, 0, 0, real_width, height);
end

M.open_horiz = function()
  local current_win = vim.api.nvim_get_current_win()
  local curpos = vim.api.nvim_win_get_cursor(0)
  local topline = vim.fn.line('w0')

  local width_of_garbage = vim.fn.getwininfo(current_win)[1].textoff
  local width = vim.api.nvim_win_get_width(current_win) - width_of_garbage

  M.horiz_bufnr = vim.api.nvim_create_buf(0, 1)
  local col = 0
  local line = ''

  local v = ''
  local c = nil
  local i = 0
  local line_at = vim.fn.getline(curpos[1])
  M.col_map = {}
  local max_width = math.min(width, #line_at + 1)
  while col < max_width do
    v = char_at(hsel1, i)
    if c then
      if M.col_map[v .. c] then break end
      M.col_map[c .. v] = col - 1
    end
    c = char_at(hsel2, i)
    if M.col_map[c .. v] then break end
    line = line .. v
    col = col + 1
    if col < max_width then
      line = line .. c
      M.col_map[v .. c] = col - 1
      col = col + 1
      i = i + 1
    end
  end

  vim.api.nvim_buf_set_lines(M.horiz_bufnr, 0, -1, 0, {' ' .. line})
  M.horiz_line = line

  return new_panel(M.horiz_bufnr, curpos[1] - topline + 1, width_of_garbage - 1,
                   max_width + 2, 1)
end

M.filter_horiz_string = function(ch)
  local new_horiz_line = ''
  local i = 1

  while i <= #M.horiz_line do
    local curch = char_at(M.horiz_line, i - 1)
    if curch == ch then
      new_horiz_line = new_horiz_line .. char_at(M.horiz_line, i)
    else
      new_horiz_line = new_horiz_line .. ' '
    end
    i = i + 1
  end
  vim.api.nvim_buf_set_lines(M.horiz_bufnr, 0, -1, 0, {' ' .. new_horiz_line})
end

M.filter_vert_text = function(ch)
  local new_vert_text = {}
  for _, t in pairs(M.vert_lines) do
    local str = t:gsub("^%s*" .. ch, function(m) return (' '):rep(#m) end)

    if t:match('^%s*' .. ch) then
      table.insert(new_vert_text, str)
    else
      table.insert(new_vert_text, "")
    end
  end
  M.vert_lines = new_vert_text
  vim.api.nvim_buf_set_lines(M.vert_buf, 0, -1, 0, M.vert_lines)
end

local function next_char()
  vim.cmd("redraw!")
  return vim.fn.nr2char(vim.fn.getchar())
end

M.run = function()
  local current_pos = vim.api.nvim_win_get_cursor(0)
  local old_scroll = vim.o.scrolloff
  vim.o.scrolloff = 0

  (function()
    local w

    local cleanup = function(win)
      vim.api.nvim_buf_delete(vim.api.nvim_win_get_buf(win), {force = true})
    end

    local read_row = function()
      w = M.open_vertical()
      local vch1 = next_char()
      if vch1 == '\x1b' then
        return
      elseif vch1 == '.' then
        return current_pos[1]
      else
        M.filter_vert_text(vch1)
        local vch2 = next_char()
        if vch1 == '\x1b' then return end
        return M.row_map[vch1 .. vch2]
      end
    end

    local r = read_row()
    if w then
      cleanup(w)
      w = nil
    end

    if not r then return end

    vim.api.nvim_win_set_cursor(0, {r, current_pos[2]})

    local read_col = function()
      w = M.open_horiz()
      local hch1 = next_char()

      if hch1 == '\x1b' then
        return nil
      elseif hch1 == '.' then
        return current_pos[2]
      elseif not hch1:match('[a-z]') then
        return hch1
      else
        M.filter_horiz_string(hch1)

        local hch2 = next_char()
        if hch2 == '\x1b' then return end
        return M.col_map[hch1 .. hch2]
      end
    end

    local c = read_col()
    if w then cleanup(w) end
    if not c then return end

    if c == '$' or c == '^' then
      vim.cmd("normal! " .. c)
    elseif type(c) == 'string' then
      vim.cmd("normal! f" .. c)
    else
      vim.cmd("normal! " .. (c + 1) .. "|") -- handle multibyte characters
    end
  end)()

  vim.o.scrolloff = old_scroll
end

return M