--- @brief
---
--- WARNING: This is an experimental feature intended to replace the builtin message + cmdline
--- presentation layer.
---
--- To enable this feature (default opts shown):
--- ```lua
--- require('vim._core.ui2').enable({
---   enable = true, -- Whether to enable or disable the UI.
---   msg = { -- Options related to the message module.
---     ---@type 'cmd'|'msg' Default message target, either in the
---     ---cmdline or in a separate ephemeral message window.
---     ---@type string|table<string, 'cmd'|'msg'|'pager'> Default message target
---     ---or table mapping |ui-messages| kinds and triggers to a target.
---     targets = 'cmd',
---     cmd = { -- Options related to messages in the cmdline window.
---       height = 0.5 -- Maximum height while expanded for messages beyond 'cmdheight'.
---     },
---     dialog = { -- Options related to dialog window.
---       height = 0.5, -- Maximum height.
---     },
---     msg = { -- Options related to msg window.
---       height = 0.5, -- Maximum height.
---       timeout = 4000, -- Time a message is visible in the message window.
---     },
---     pager = { -- Options related to message window.
---       height = 1, -- Maximum height.
---     },
---   },
--- })
--- ```
---
--- There are four special windows/buffers for presenting messages and cmdline:
--- - "cmd": Cmdline. Also used for 'showcmd', 'showmode', 'ruler', and messages by default.
--- - "msg": Message window, shows ephemeral messages useful for 'cmdheight' == 0.
--- - "pager": Pager window, shows |:messages| and certain messages that are never "collapsed".
--- - "dialog": Dialog window, shows modal prompts that expect user input.
---
--- The buffer 'filetype' is set to the above-listed id ("cmd", "msg", …).
--- Handle the |FileType| event to configure any local options for these
--- windows and their respective buffers.
---
--- Unlike the legacy |hit-enter| prompt, messages exceeding 'cmdheight' are
--- instead "collapsed", followed by a `[+x]` "spill" indicator, where `x`
--- indicates the spilled lines. To see the full messages, do either:
--- - ENTER immediately after interactive |:| cmdline shows a message and returns to |Normal-mode|.
--- - |g<| at any time.

local api = vim.api
local M = {
  ns = api.nvim_create_namespace('nvim.ui2'),
  augroup = api.nvim_create_augroup('nvim.ui2', {}),
  cmdheight = vim.o.cmdheight, -- 'cmdheight' option value set by user.
  redrawing = false, -- True when redrawing to display UI event.
  wins = { cmd = -1, dialog = -1, msg = -1, pager = -1 },
  bufs = { cmd = -1, dialog = -1, msg = -1, pager = -1 },
  cfg = {
    enable = true,
    msg = { -- Options related to the message module.
      target = 'cmd', ---@type 'cmd'|'msg' Default message target if not present in targets.
      targets = {}, ---@type table<string, 'cmd'|'msg'|'pager'> Kind specific message targets.
      cmd = { -- Options related to messages in the cmdline window.
        height = 0.5, -- Maximum height while expanded for messages beyond 'cmdheight'.
      },
      dialog = { -- Options related to dialog window.
        height = 0.5, -- Maximum height.
      },
      msg = { -- Options related to msg window.
        height = 0.5, -- Maximum height.
        timeout = 4000, -- Time a message is visible in the message window.
      },
      pager = { -- Options related to message window.
        height = 1, -- Maximum height.
      },
    },
  },
}

---Ensure target buffers and windows are still valid.
function M.check_targets()
  local curtab = api.nvim_get_current_tabpage()
  for i, type in ipairs({ 'cmd', 'dialog', 'msg', 'pager' }) do
    local buf = api.nvim_buf_is_valid(M.bufs[type]) and M.bufs[type]
    local win = api.nvim_win_is_valid(M.wins[type]) and M.wins[type]
    local floating = win and api.nvim_win_get_config(win).zindex
    local setopt = not buf or not win or not floating
    M.bufs[type] = buf or api.nvim_create_buf(false, false)

    if not win or not floating then
      -- Open a new window when closed or no longer floating (e.g. wincmd J).
      local cfg = { col = 0, row = 1, width = 10000, height = 1, mouse = false, noautocmd = true }
      cfg.focusable = false
      cfg.style = 'minimal'
      cfg.relative = 'laststatus'
      cfg.anchor = type ~= 'cmd' and 'SE' or nil
      cfg.mouse = type == 'pager' or nil
      cfg.border = type ~= 'msg' and 'none' or nil
      cfg._cmdline_offset = type == 'cmd' and 0 or nil
      cfg.hide = type ~= 'cmd' or M.cmdheight == 0 or nil
      -- kZIndexMessages < cmd zindex < kZIndexCmdlinePopupMenu (grid_defs.h), pager below others.
      cfg.zindex = 201 - i
      M.wins[type] = api.nvim_open_win(M.bufs[type], false, cfg)
    elseif api.nvim_win_get_tabpage(M.wins[type]) ~= curtab then
      api.nvim_win_set_config(M.wins[type], { win = api.nvim_tabpage_get_win(curtab) })
    end
    if win and floating and api.nvim_win_get_buf(win) ~= M.bufs[type] then
      api.nvim_win_set_buf(win, M.bufs[type])
      setopt = true
    end

    if setopt then
      -- Set options without firing OptionSet and BufFilePost.
      vim._with({ win = M.wins[type], noautocmd = true }, function()
        api.nvim_set_option_value('eventignorewin', 'all,-FileType', { scope = 'local' })
        api.nvim_set_option_value('wrap', true, { scope = 'local' })
        api.nvim_set_option_value('linebreak', false, { scope = 'local' })
        api.nvim_set_option_value('smoothscroll', true, { scope = 'local' })
        api.nvim_set_option_value('breakindent', false, { scope = 'local' })
        api.nvim_set_option_value('foldenable', false, { scope = 'local' })
        api.nvim_set_option_value('showbreak', '', { scope = 'local' })
        api.nvim_set_option_value('spell', false, { scope = 'local' })
        api.nvim_set_option_value('swapfile', false, { scope = 'local' })
        api.nvim_set_option_value('modifiable', true, { scope = 'local' })
        api.nvim_set_option_value('bufhidden', 'hide', { scope = 'local' })
        api.nvim_set_option_value('buftype', 'nofile', { scope = 'local' })
        -- Use MsgArea except in the msg window. Hide Search highlighting except in the pager.
        local search_hide = 'Search:,CurSearch:,IncSearch:'
        local hl = 'Normal:MsgArea,' .. search_hide
        if type == 'pager' then
          hl = 'Normal:MsgArea'
        elseif type == 'msg' then
          hl = search_hide
        end
        api.nvim_set_option_value('winhighlight', hl, { scope = 'local' })
      end)
      api.nvim_buf_set_name(M.bufs[type], ('[%s]'):format(type:sub(1, 1):upper() .. type:sub(2)))
      -- Fire FileType with window context to let the user reconfigure local options.
      vim._with({ win = M.wins[type] }, function()
        api.nvim_set_option_value('filetype', type, { scope = 'local' })
      end)

      if type == 'pager' then
        -- Close pager with `q`, same as `checkhealth`
        api.nvim_buf_set_keymap(M.bufs.pager, 'n', 'q', '<Cmd>wincmd c<CR>', {})
      elseif type == M.cfg.msg.target then
        M.msg.prev_msg = '' -- Will no longer be visible.
      end
    end
  end
end

local function ui_callback(redraw_msg, event, ...)
  local handler = M.msg[event] or M.cmd[event] --[[@as function]]
  M.check_targets()
  handler(...)
  -- Cmdline mode, non-fast message and non-empty showcmd require an immediate redraw.
  if M.cmd[event] or redraw_msg or (event == 'msg_showcmd' and select(1, ...)[1]) then
    M.redrawing = true
    api.nvim__redraw({
      flush = handler ~= M.cmd.cmdline_hide or nil,
      cursor = handler == M.cmd[event] and true or nil,
      win = handler == M.cmd[event] and M.wins.cmd or nil,
    })
    M.redrawing = false
  end
end
local scheduled_ui_callback = vim.schedule_wrap(ui_callback)

---@nodoc
function M.enable(opts)
  vim.validate('opts', opts, 'table', true)
  M.cfg = vim.tbl_deep_extend('keep', opts, M.cfg)
  M.cfg.msg.target = type(M.cfg.msg.targets) == 'string' and M.cfg.msg.targets or M.cfg.msg.target
  M.cfg.msg.targets = type(M.cfg.msg.targets) == 'table' and M.cfg.msg.targets or {}
  if #vim.api.nvim_list_uis() == 0 then
    return -- Don't prevent stdout messaging when no UIs are attached.
  end

  if M.cfg.enable == false then
    -- Detach and cleanup windows, buffers and autocommands.
    for _, win in pairs(M.wins) do
      pcall(api.nvim_win_close, win, true)
    end
    for _, buf in pairs(M.bufs) do
      pcall(api.nvim_buf_delete, buf, {})
    end
    api.nvim_clear_autocmds({ group = M.augroup })
    vim.ui_detach(M.ns)
    return
  end

  M.cmd = require('vim._core.ui2.cmdline')
  M.msg = require('vim._core.ui2.messages')
  vim.ui_attach(M.ns, { ext_messages = true, set_cmdheight = false }, function(event, ...)
    if not (M.msg[event] or M.cmd[event]) then
      return
    end
    -- Ensure cmdline is placed after a scheduled message in block mode.
    if vim.in_fast_event() or (event == 'cmdline_show' and M.cmd.srow > 0) then
      scheduled_ui_callback(false, event, ...)
    else
      ui_callback(event == 'msg_show', event, ...)
    end
    return true
  end)

  -- The visibility and appearance of the cmdline and message window is
  -- dependent on some option values. Reconfigure windows when option value
  -- has changed and after VimEnter when the user configured value is known.
  -- TODO: Reconsider what is needed when this module is enabled by default early in startup.
  local function check_cmdheight(value)
    M.check_targets()
    -- 'cmdheight' set; (un)hide cmdline window and set its height.
    local cfg = { height = math.max(value, 1), hide = value == 0 }
    api.nvim_win_set_config(M.wins.cmd, cfg)
    M.cmdheight = value
  end

  if vim.v.vim_did_enter == 0 then
    vim.schedule(function()
      check_cmdheight(vim.o.cmdheight)
    end)
  end

  api.nvim_create_autocmd('OptionSet', {
    group = M.augroup,
    pattern = { 'cmdheight', 'laststatus' },
    callback = function(ev)
      if ev.match == 'cmdheight' then
        check_cmdheight(vim.v.option_new)
      end
      M.msg.set_pos()
    end,
    desc = 'Set cmdline and message window dimensions for changed option values.',
  })

  api.nvim_create_autocmd({ 'VimResized', 'TabEnter' }, {
    group = M.augroup,
    callback = function()
      M.check_targets()
      M.msg.set_pos()
    end,
    desc = 'Set cmdline and message window dimensions after shell resize or tabpage change.',
  })
end

return M
