-- Neovim preview for Luma files.
--
-- Set LUMA_MARKDOWN_BIN to the path of the generated executable, or make
-- luma_markdown available on PATH:
--   export LUMA_MARKDOWN_BIN="$PWD/luma_markdown"

local preview_buf = nil
local preview_win = nil
local active_job = nil
local update_id = 0

local function ensure_preview_buffer()
  if preview_buf and vim.api.nvim_buf_is_valid(preview_buf) then return end

  preview_buf = vim.api.nvim_create_buf(false, true)
  vim.api.nvim_buf_set_option(preview_buf, "buftype", "nofile")
  vim.api.nvim_buf_set_option(preview_buf, "bufhidden", "hide")
  vim.api.nvim_buf_set_option(preview_buf, "swapfile", false)
  vim.api.nvim_buf_set_option(preview_buf, "filetype", "markdown")
end

local function show_preview(src_buf, output)
  ensure_preview_buffer()
  vim.api.nvim_buf_set_lines(preview_buf, 0, -1, false, output)

  if not preview_win or not vim.api.nvim_win_is_valid(preview_win) then
    local src_win = vim.fn.bufwinid(src_buf)
    if src_win == -1 then return end

    vim.api.nvim_set_current_win(src_win)
    vim.cmd "rightbelow vsplit"
    preview_win = vim.api.nvim_get_current_win()
    vim.api.nvim_win_set_buf(preview_win, preview_buf)

    vim.api.nvim_set_current_win(src_win)
  end
end

local function update_luma_preview()
  local src_buf = vim.api.nvim_get_current_buf()
  local lines = vim.api.nvim_buf_get_lines(src_buf, 0, -1, false)
  local changedtick = vim.api.nvim_buf_get_changedtick(src_buf)
  local cmd = vim.env.LUMA_MARKDOWN_BIN or "luma_markdown"

  update_id = update_id + 1
  local this_update = update_id

  if active_job then
    vim.fn.jobstop(active_job)
    active_job = nil
  end

  local output = {}
  local errors = {}
  local job
  job = vim.fn.jobstart({ cmd }, {
    stdin = "pipe",
    stdout_buffered = true,
    stderr_buffered = true,
    on_stdout = function(_, data)
      if data then vim.list_extend(output, data) end
    end,
    on_stderr = function(_, data)
      if data then vim.list_extend(errors, data) end
    end,
    on_exit = function(_, exit_code)
      if active_job == job then active_job = nil end
      if this_update ~= update_id then return end
      if not vim.api.nvim_buf_is_valid(src_buf) then return end
      if vim.api.nvim_buf_get_changedtick(src_buf) ~= changedtick then return end

      if exit_code ~= 0 then
        local message = table.concat(errors, "\n")
        if message ~= "" then
          vim.notify("Luma preview failed: " .. message, vim.log.levels.ERROR)
        end
        return
      end

      -- io.println adds a final newline; systemlist used to remove it.
      if output[#output] == "" then table.remove(output) end
      show_preview(src_buf, output)
    end,
  })

  if job <= 0 then
    vim.notify("Could not start Luma preview: " .. cmd, vim.log.levels.ERROR)
    return
  end

  active_job = job
  vim.fn.chansend(job, table.concat(lines, "\n"))
  vim.fn.chanclose(job, "stdin")
end

vim.api.nvim_create_autocmd("BufWritePost", {
  pattern = "*.luma",
  callback = update_luma_preview,
})

vim.api.nvim_create_user_command("LumaPreview", update_luma_preview, {})

local timer = nil
local function debounced_update()
  if timer then timer:stop() end
  timer = vim.defer_fn(update_luma_preview, 150)
end

vim.api.nvim_create_autocmd({ "TextChanged", "TextChangedI" }, {
  pattern = "*.luma",
  callback = debounced_update,
})