---@class mini.diff.jj.CacheEntry
---@field fs_event uv.uv_fs_event_t?
---@field timer uv.uv_timer_t?

local MiniDiff = require("mini.diff")

---@overload fun(args: string[], cwd: string): vim.SystemCompleted
---@overload fun(args: string[], cwd: string, on_exit: fun(out: vim.SystemCompleted)): vim.SystemObj
---@param args string[]
---@param cwd string
---@param on_exit? fun(out: vim.SystemCompleted)
local function jj(args, cwd, on_exit)
  local obj = vim.system(
    vim.list_extend({ "jj", "--ignore-working-copy" }, args),
    { text = true, cwd = cwd },
    on_exit
  )
  if on_exit then
    return obj
  else
    return obj:wait()
  end
end

---@type table<number, mini.diff.jj.CacheEntry?>
local cache = {}

---@param buf_id integer
---@return string
local function buf_path(buf_id) return vim.uv.fs_realpath(vim.api.nvim_buf_get_name(buf_id)) or "" end

---@param cwd string
---@return string?
local function repo_root(cwd)
  local result = jj({ "root" }, cwd)
  if result.code == 0 and result.stdout ~= nil then return vim.trim(result.stdout) end
end

local function invalidate(buf_id)
  local entry = cache[buf_id]
  if entry then
    if entry.fs_event then entry.fs_event:stop() end
    if entry.timer then entry.timer:stop() end
    cache[buf_id] = nil
  end
end

---@param buf_id integer
---@param file_path string
---@param cwd string
local function set_ref_text(buf_id, file_path, cwd)
  local stat = vim.uv.fs_stat(cwd)
  if not stat or stat.type ~= "directory" then return end

  ---@param text string | string[] | nil
  local function set_text(text)
    vim.schedule(function() MiniDiff.set_ref_text(buf_id, text) end)
  end

  jj({ "file", "show", "-r", "@-", file_path }, cwd, function(res)
    if res.code == 0 then return set_text(res.stdout) end

    -- Ignore if file is untracked in `@`.
    jj({ "file", "list", "-r", "@", file_path }, cwd, function(list)
      local tracked = list.code == 0 and list.stdout ~= nil and vim.trim(list.stdout) ~= ""
      set_text(tracked and "" or nil)
    end)
  end)
end

---@param buf_id integer
---@param file_path string
---@return boolean?
local function watch(buf_id, file_path)
  local cwd = vim.fs.dirname(file_path)
  local repo = repo_root(cwd)
  if not repo then return false end

  local watch_path = vim.fs.joinpath(repo, ".jj/working_copy")
  local fs_event = vim.uv.new_fs_event()
  local timer = vim.uv.new_timer()

  local function tick()
    if not timer then return end
    timer:stop()
    timer:start(50, 0, function() set_ref_text(buf_id, file_path, cwd) end)
  end

  local function on_change(_, filename)
    if filename == "checkout" and timer then tick() end
  end

  if fs_event then fs_event:start(watch_path, {}, on_change) end

  invalidate(buf_id)
  cache[buf_id] = { fs_event = fs_event, timer = timer }

  set_ref_text(buf_id, file_path, cwd)

  return true
end

---@param buf_id integer
---@return boolean?
local function attach(buf_id)
  if cache[buf_id] then return false end
  local path = buf_path(buf_id)
  if path == "" then return false end
  return watch(buf_id, path)
end

---@param buf_id integer
local function detach(buf_id) invalidate(buf_id) end

return { name = "jj", attach = attach, detach = detach }