fterm.lua

local api = vim.api
local cmd = vim.cmd
local fn = vim.fn

local W = {}
local base_opt = {
    relative = 'editor',
    style = 'minimal'
}

cmd('hi def link FTerm Normal')

function create_borders(height, width)
    local border_lines = { '┌' .. string.rep('─', width) .. '┐' }
    local middle_line = '|' .. string.rep(' ', width) .. '|'
    for i=1, height do
      table.insert(border_lines, middle_line)
    end
    table.insert(border_lines, '└' .. string.rep('─', width) .. '┘')

    return border_lines
end

function open_float()
    vim.g.last_win = fn.nvim_get_current_win()
    vim.g.last_buf = fn.nvim_get_current_buf()
    vim.g.last_pos = fn.winsaveview()

    -- get dimensions
    local width = api.nvim_get_option("columns")
    local height = api.nvim_get_option("lines")

    -- calculate our floating window size
    local win_width = math.ceil(width * 0.8)
    local win_height = math.ceil(height * 0.8 - 4)

    -- and its starting position
    local col = math.ceil((width - win_width) / 2)
    local row = math.ceil((height - win_height) / 2 - 1)

    local opt = vim.tbl_extend('keep', base_opt, {
        width = win_width,
        height = win_height,
        col = col,
        row = row,
    })

    local padding_opt = vim.tbl_extend('keep', base_opt, {
        width = win_width + 2,
        height = win_height + 2,
        col = col - 1,
        row = row - 1,
    })

    local padding_buf = api.nvim_create_buf(false, true)
    local borders = create_borders(win_height, win_width)
    api.nvim_buf_set_lines(padding_buf, 0, -1, false, borders)
    local padding_win = api.nvim_open_win(padding_buf, true, padding_opt)
    fn.nvim_win_set_option(padding_win, 'winhl', 'Normal:FTerm')

    local buf = api.nvim_create_buf(false, true)
    local win = api.nvim_open_win(buf, true, opt)
    fn.nvim_win_set_option(win, 'winhl', 'Normal:FTerm')

    fn.termopen(os.getenv('SHELL'))
    cmd("startinsert")
    cmd("autocmd! TermClose <buffer> lua close_float()")

    W = { win, padding_win }
end

function close_float()
    if next(W) == nil then
        do return end
    end

    for _, win in ipairs(W) do
        if api.nvim_win_is_valid(win) then
            api.nvim_win_close(win, {})
        end
    end

    W = {}
end

function toggle_float()
    if next(W) == nil then
        open_float()
        do return end
    end

    close_float()

    if next(vim.g.last_pos) then
        -- cmd("wincmd l")
        -- fn.setpos('.', last_pos)
        -- cmd("keepalt b"..last_buf)
        -- fn.winrestview(vim.g.last_pos)
        -- last_pos = nil
        -- print(vim.inspect(vim.g.last_win))
        -- cmd(string.format('exe %d . "wincmd c"', vim.g.last_win))
    end

    -- print(vim.inspect(W))
end

cmd [[ command! WinOpen lua open_float() ]]
cmd [[ command! WinToggle lua toggle_float() ]]
cmd [[ command! WinClose lua close_float() ]]