-- finder.lua — Minimal async fuzzy finder + grep for Neovim ≥ 0.11
-- Non-blocking, debounced, stable selection, correct scrolling, match highlights.
-- Hardened for races, Windows paths, and cwd/root mismatches.

local M = {}

---------------------------------------------------------------------
-- Config
---------------------------------------------------------------------
M.config = {
  file_cmd = nil, -- "fd" | "fdfind" | nil (auto)
  grep_cmd = 'rg', -- ripgrep binary
  page_size = 60, -- soft cap; real viewport height is measured
  debounce_ms = 80,
  cache_ttl_sec = 20,
  max_items = 5000, -- safety cap for massive outputs
  debug = false,
}

---------------------------------------------------------------------
-- State
---------------------------------------------------------------------
local S = {
  active = false,
  mode = nil, -- "files" | "grep"
  root = nil,
  is_git = false,

  cache = {},
  timer = nil,
  ns = vim.api.nvim_create_namespace('finder_ns'),
  aug = nil,
  gen = 0, -- session generation id

  -- async jobs
  job_files = nil,
  job_rg = nil,

  -- UI
  win_inp = nil,
  buf_inp = nil,
  win_res = nil,
  buf_res = nil,

  -- Data
  query = '',
  items = {}, -- full set (files or grep lines)
  filtered = {}, -- current view
  positions = {}, -- positions[i] = { {scol, ecol}, ... } for filtered[i]
  select = 1, -- absolute index in filtered (1-based)
  scroll = 0, -- top index (0-based)
}

---------------------------------------------------------------------
-- Utils
---------------------------------------------------------------------
local function L(msg, data)
  if not M.config.debug then
    return
  end
  local s = '[finder] ' .. msg
  if data ~= nil then
    s = s .. ' ' .. vim.inspect(data)
  end
  vim.schedule(function()
    vim.notify(s)
  end)
end

local function now_sec()
  return vim.loop.now() / 1000
end
local function clamp(v, lo, hi)
  return (v < lo) and lo or ((v > hi) and hi or v)
end
local function cmd_exists(bin)
  return vim.fn.executable(bin) == 1
end

local function debounce(fn, ms)
  if S.timer then
    S.timer:stop()
    S.timer:close()
    S.timer = nil
  end
  S.timer = vim.loop.new_timer()
  S.timer:start(ms, 0, function()
    if S.timer then
      S.timer:stop()
      S.timer:close()
      S.timer = nil
    end
    vim.schedule(fn)
  end)
end

local function is_windows()
  local sys = vim.loop.os_uname().sysname
  return sys == 'Windows_NT'
end

local function is_abs_path(p)
  if is_windows() then
    -- C:\... or \\server\share...
    return p:match('^%a:[/\\]') or p:match('^[/\\][/\\]')
  else
    return p:sub(1, 1) == '/'
  end
end

local function joinpath(a, b)
  return vim.fs.normalize(vim.fs.joinpath(a, b))
end

local function to_abs_in_root(root, p)
  if is_abs_path(p) then
    return p
  end
  local joined = joinpath(root, p)
  local rp = vim.loop.fs_realpath(joined)
  return rp or joined
end

local function project_root()
  local obj = vim.system({ 'git', 'rev-parse', '--show-toplevel' }, { text = true }):wait()
  if obj.code == 0 and obj.stdout and obj.stdout ~= '' then
    S.is_git = true
    return vim.trim(obj.stdout)
  end
  S.is_git = false
  -- Respect Neovim cwd, not process cwd
  return vim.fn.getcwd(0, 0)
end

local function resolve_file_cmd()
  if M.config.file_cmd then
    return M.config.file_cmd
  end
  if cmd_exists('fd') then
    return 'fd'
  end
  if cmd_exists('fdfind') then
    return 'fdfind'
  end
  return nil
end

local function page_rows()
  if S.win_res and vim.api.nvim_win_is_valid(S.win_res) then
    local h = vim.api.nvim_win_get_height(S.win_res)
    return math.max(1, h)
  end
  return math.max(1, math.min(M.config.page_size, vim.o.lines))
end

---------------------------------------------------------------------
-- Render helpers
---------------------------------------------------------------------
local function ensure_visible()
  local page = page_rows()
  local sel = clamp(S.select, 1, #S.filtered)
  local top = S.scroll + 1
  local bot = S.scroll + page
  if sel < top then
    S.scroll = sel - 1
  elseif sel > bot then
    S.scroll = sel - page
  end
  S.scroll = clamp(S.scroll, 0, math.max(#S.filtered - page, 0))
end

---------------------------------------------------------------------
-- Render
---------------------------------------------------------------------
local function render()
  if not (S.active and S.buf_res and vim.api.nvim_buf_is_valid(S.buf_res)) then
    return
  end

  ensure_visible()

  local total = #S.filtered
  local view = {}
  if total == 0 then
    view = { '-- no matches --' }
  else
    local start_idx = S.scroll + 1
    local end_idx = math.min(start_idx + page_rows() - 1, total)
    for i = start_idx, end_idx do
      view[#view + 1] = S.filtered[i]
    end
  end

  for i = 1, #view do
    if type(view[i]) ~= 'string' then
      view[i] = tostring(view[i] or '')
    end
  end

  vim.bo[S.buf_res].modifiable = true
  vim.bo[S.buf_res].readonly = false
  vim.api.nvim_buf_set_lines(S.buf_res, 0, -1, false, view)
  vim.api.nvim_buf_clear_namespace(S.buf_res, S.ns, 0, -1)

  -- match highlights (visible window only)
  vim.api.nvim_set_hl(0, 'FinderMatch', { link = 'Search', default = true })
  for i = 1, #view do
    local idx = S.scroll + i
    local spans = S.positions[idx]
    if spans then
      for _, se in ipairs(spans) do
        local scol, ecol = se[1], se[2]
        if ecol > scol then
          vim.api.nvim_buf_set_extmark(S.buf_res, S.ns, i - 1, scol, {
            end_col = ecol,
            hl_group = 'FinderMatch',
          })
        end
      end
    end
  end

  -- selection highlight
  if total > 0 and #view > 0 then
    vim.api.nvim_set_hl(0, 'FinderSelection', { link = 'CursorLine', default = true })
    local rel = clamp(S.select - S.scroll, 1, #view)
    vim.api.nvim_buf_set_extmark(S.buf_res, S.ns, rel - 1, 0, {
      end_line = rel,
      hl_group = 'FinderSelection',
      hl_eol = true,
    })
  end

  vim.bo[S.buf_res].modifiable = false
  L('render', { select = S.select, scroll = S.scroll, total = total, lines = #view })
end

---------------------------------------------------------------------
-- Querying / Filtering
---------------------------------------------------------------------
local function compute_positions_files(items, q)
  local ok, res = pcall(vim.fn.matchfuzzypos, items, q)
  if not ok or type(res) ~= 'table' then
    return {}, {}
  end
  local out_items = res[1] or {}
  local pos = res[2] or {}

  local filtered, positions = {}, {}
  for i, v in ipairs(out_items) do
    filtered[i] = (type(v) == 'string') and v or tostring(v or '')
    local cols = pos[i] or {}
    local spans = {}
    for _, c in ipairs(cols) do
      local start0 = (c > 0) and (c - 1) or 0
      spans[#spans + 1] = { start0, start0 + 1 }
    end
    positions[i] = spans
  end
  return filtered, positions
end

local function compute_positions_grep(lines, q)
  if q == '' then
    return lines, {}
  end
  local pat = vim.pesc(q)
  local positions = {}
  for i, line in ipairs(lines) do
    local sidx = 1
    local spans = {}
    if type(line) ~= 'string' then
      line = tostring(line or '')
    end
    while true do
      local s, e = string.find(line, pat, sidx, true)
      if not s then
        break
      end
      spans[#spans + 1] = { s - 1, e } -- 0-based start, exclusive end
      sidx = e + 1
      if #spans > 64 then
        break
      end
    end
    positions[i] = (#spans > 0) and spans or nil
  end
  return lines, positions
end

---------------------------------------------------------------------
-- set_items
---------------------------------------------------------------------
local function set_items(list)
  list = list or {}
  if #list > M.config.max_items then
    local tmp = {}
    for i = 1, M.config.max_items do
      tmp[i] = list[i]
    end
    list = tmp
  end
  for i, v in ipairs(list) do
    if type(v) ~= 'string' then
      list[i] = tostring(v or '')
    end
  end

  S.items = list
  S.filtered = list
  S.positions = {}
  S.select = 1
  S.scroll = 0
  render()
end

---------------------------------------------------------------------
-- set_query
---------------------------------------------------------------------
local function set_query(q)
  local prev_val = S.filtered[S.select]
  S.query = q

  if S.mode == 'grep' then
    local filtered, pos = compute_positions_grep(S.items, q)
    S.filtered, S.positions = filtered, pos
  else
    if q == '' then
      S.filtered = S.items
      S.positions = {}
    else
      local filtered, pos = compute_positions_files(S.items, q)
      S.filtered, S.positions = filtered, pos
    end
  end

  for i, v in ipairs(S.filtered) do
    if type(v) ~= 'string' then
      S.filtered[i] = tostring(v or '')
    end
  end

  -- preserve previous pick if still present
  local idx = 1
  if prev_val then
    for i, v in ipairs(S.filtered) do
      if v == prev_val then
        idx = i
        break
      end
    end
  end
  S.select = clamp(idx, 1, #S.filtered)
  ensure_visible()
  render()
  L('set_query', { query = q, filtered = #S.filtered })
end

---------------------------------------------------------------------
-- Move / Accept
---------------------------------------------------------------------
local function move_down()
  if #S.filtered == 0 then
    return
  end
  S.select = clamp(S.select + 1, 1, #S.filtered)
  ensure_visible()
  render()
end

local function move_up()
  if #S.filtered == 0 then
    return
  end
  S.select = clamp(S.select - 1, 1, #S.filtered)
  ensure_visible()
  render()
end

local function accept_selection_files()
  local pick = S.filtered[S.select]
  if not pick then
    return
  end
  local file = to_abs_in_root(S.root, pick)
  local edit_cb = function()
    vim.cmd.edit(vim.fn.fnameescape(file))
  end
  M.close()
  vim.schedule(edit_cb)
end

local function parse_vimgrep(line)
  -- Robust against Windows drive letters and extra colons in path.
  -- Greedy file capture up to last ":<lnum>:"
  local file, lnum = line:match('^(.*):(%d+):')
  if not file then
    return nil
  end
  return file, tonumber(lnum) or 1
end

local function accept_selection_grep()
  local pick = S.filtered[S.select]
  if not pick then
    return
  end
  local file, lnum = parse_vimgrep(pick)
  if not file then
    return
  end
  file = to_abs_in_root(S.root, file)
  lnum = tonumber(lnum) or 1
  local edit_cb = function()
    vim.cmd.edit(vim.fn.fnameescape(file))
    if vim.api.nvim_get_current_buf() > 0 then
      pcall(vim.api.nvim_win_set_cursor, 0, { lnum, 0 })
    end
  end
  M.close()
  vim.schedule(edit_cb)
end

---------------------------------------------------------------------
-- Backends
---------------------------------------------------------------------
local function cancel_job(j)
  if not j then
    return
  end
  pcall(function()
    j:kill(15)
  end) -- SIGTERM if available
end

local function collect_files_async(cb)
  local gen = S.gen
  local root = S.root
  local c = S.cache[root]
  if c and c.files and now_sec() - c.files.at < M.config.cache_ttl_sec then
    cb(c.files.list)
    return
  end

  -- Prefer fd/fdfind, then git ls-files, then blocking glob fallback.
  local file_cmd = resolve_file_cmd()
  if file_cmd then
    local args =
      { file_cmd, '--type', 'f', '--hidden', '--follow', '--color', 'never', '--exclude', '.git' }
    if file_cmd == 'fd' or file_cmd == 'fdfind' then
      table.insert(args, '--strip-cwd-prefix')
    end
    cancel_job(S.job_files)
    S.job_files = vim.system(args, { text = true, cwd = root }, function(obj)
      if not (S.active and gen == S.gen) then
        return
      end
      local list
      if obj.code == 0 and obj.stdout then
        local raw = vim.split(obj.stdout, '\n', { trimempty = true })
        list = {}
        for i = 1, #raw do
          list[i] = to_abs_in_root(root, raw[i])
        end
      else
        list = {}
      end
      if #list == 0 and S.is_git and cmd_exists('git') then
        -- fallback to git ls-files, still async
        local gargs = { 'git', 'ls-files', '-co', '--exclude-standard', '-z' }
        cancel_job(S.job_files)
        S.job_files = vim.system(gargs, { text = true, cwd = root }, function(o2)
          if not (S.active and gen == S.gen) then
            return
          end
          local glist = {}
          if o2.code == 0 and o2.stdout then
            for p in o2.stdout:gmatch('([^%z]+)') do
              glist[#glist + 1] = to_abs_in_root(root, p)
            end
          end
          if #glist > M.config.max_items then
            local tmp = {}
            for i = 1, M.config.max_items do
              tmp[i] = glist[i]
            end
            glist = tmp
          end
          S.cache[root] = S.cache[root] or {}
          S.cache[root].files = { list = glist, at = now_sec() }
          vim.schedule(function()
            if S.active and gen == S.gen then
              cb(glist)
            end
          end)
        end)
        return
      end
      if #list > M.config.max_items then
        local tmp = {}
        for i = 1, M.config.max_items do
          tmp[i] = list[i]
        end
        list = tmp
      end
      S.cache[root] = S.cache[root] or {}
      S.cache[root].files = { list = list, at = now_sec() }
      vim.schedule(function()
        if S.active and gen == S.gen then
          cb(list)
        end
      end)
    end)
    return
  end

  -- Last-resort blocking fallback (no fd, not git, or git failed)
  local list = vim.fn.globpath(root, '**/*', false, true)
  list = vim.tbl_filter(function(p)
    return vim.fn.isdirectory(p) == 0
  end, list)
  if #list > M.config.max_items then
    local tmp = {}
    for i = 1, M.config.max_items do
      tmp[i] = list[i]
    end
    list = tmp
  end
  S.cache[root] = S.cache[root] or {}
  S.cache[root].files = { list = list, at = now_sec() }
  cb(list)
end

local function grep_async(query, cb)
  local gen = S.gen
  if query == '' then
    cb({})
    return
  end
  local rg = M.config.grep_cmd
  if rg ~= 'rg' and not cmd_exists(rg) then
    rg = 'rg'
  end
  if not cmd_exists(rg) then
    cb({})
    return
  end
  local args = {
    rg,
    '--vimgrep',
    '--hidden',
    '--smart-case',
    '--no-heading',
    '--no-config',
    '--color',
    'never',
    '--path-separator',
    '/',
    '--',
    query,
  }
  cancel_job(S.job_rg)
  S.job_rg = vim.system(args, { text = true, cwd = S.root }, function(obj)
    if not (S.active and gen == S.gen) then
      return
    end
    local list = {}
    if obj.code == 0 and obj.stdout then
      list = vim.split(obj.stdout, '\n', { trimempty = true })
    end
    if #list > M.config.max_items then
      local tmp = {}
      for i = 1, M.config.max_items do
        tmp[i] = list[i]
      end
      list = tmp
    end
    vim.schedule(function()
      if S.active and gen == S.gen then
        cb(list)
      end
    end)
  end)
end

---------------------------------------------------------------------
-- Layout
---------------------------------------------------------------------
local function open_layout(prompt)
  S.buf_inp = vim.api.nvim_create_buf(false, true)
  S.buf_res = vim.api.nvim_create_buf(false, true)

  for _, b in ipairs({ S.buf_inp, S.buf_res }) do
    vim.bo[b].buflisted = false
    vim.bo[b].bufhidden = 'wipe'
    vim.bo[b].swapfile = false
  end
  vim.bo[S.buf_inp].buftype = 'prompt'
  vim.bo[S.buf_res].buftype = 'nofile'
  vim.bo[S.buf_res].modifiable = false
  vim.bo[S.buf_res].readonly = false

  local width = math.floor(vim.o.columns * 0.8)
  local height = math.min(math.floor(vim.o.lines * 0.5), M.config.page_size + 2)
  local col = math.floor((vim.o.columns - width) / 2)
  local row = math.floor((vim.o.lines - height) * 0.7)

  S.win_inp = vim.api.nvim_open_win(S.buf_inp, true, {
    relative = 'editor',
    style = 'minimal',
    border = 'rounded',
    width = width,
    height = 1,
    col = col,
    row = row,
    focusable = true,
    zindex = 200,
  })
  vim.fn.prompt_setprompt(S.buf_inp, prompt)

  S.win_res = vim.api.nvim_open_win(S.buf_res, false, {
    relative = 'editor',
    style = 'minimal',
    border = 'single',
    width = width,
    height = math.max(1, height - 2),
    col = col,
    row = row + 2,
    focusable = false,
    zindex = 199,
  })
  vim.wo[S.win_res].cursorline = false
  vim.wo[S.win_res].cursorlineopt = 'line'

  if S.aug then
    pcall(vim.api.nvim_del_augroup_by_id, S.aug)
  end
  S.aug = vim.api.nvim_create_augroup('finder_session', { clear = true })

  vim.api.nvim_create_autocmd('WinEnter', {
    group = S.aug,
    callback = function()
      if not S.active then
        return
      end
      local w = vim.api.nvim_get_current_win()
      if w == S.win_inp or w == S.win_res then
        return
      end
      local cfg = vim.api.nvim_win_get_config(w)
      if cfg and cfg.relative == '' then
        M.close()
      end
    end,
  })

  vim.api.nvim_create_autocmd({ 'BufHidden', 'BufLeave' }, {
    group = S.aug,
    buffer = S.buf_inp,
    callback = function()
      if S.active then
        M.close()
      end
    end,
  })

  vim.api.nvim_create_autocmd('VimResized', {
    group = S.aug,
    callback = function()
      if S.active then
        render()
      end
    end,
  })

  vim.cmd.startinsert()
  L('open_layout', { win_inp = S.win_inp, win_res = S.win_res })
end

local function close_layout()
  for _, win in ipairs({ S.win_inp, S.win_res }) do
    if win and vim.api.nvim_win_is_valid(win) then
      pcall(vim.api.nvim_win_close, win, true)
    end
  end
  for _, buf in ipairs({ S.buf_inp, S.buf_res }) do
    if buf and vim.api.nvim_buf_is_valid(buf) then
      pcall(vim.api.nvim_buf_delete, buf, { force = true })
    end
  end
  if S.aug then
    pcall(vim.api.nvim_del_augroup_by_id, S.aug)
    S.aug = nil
  end
  L('close_layout')
end

---------------------------------------------------------------------
-- Input handlers
---------------------------------------------------------------------
local function attach_handlers()
  local opts = { buffer = S.buf_inp, nowait = true, silent = true, noremap = true }
  vim.keymap.set('i', '<C-n>', move_down, opts)
  vim.keymap.set('i', '<C-p>', move_up, opts)
  vim.keymap.set('i', '<Down>', move_down, opts)
  vim.keymap.set('i', '<Up>', move_up, opts)
  vim.keymap.set('i', '<CR>', function()
    if S.mode == 'grep' then
      accept_selection_grep()
    else
      accept_selection_files()
    end
  end, opts)
  vim.keymap.set('i', '<Esc>', function()
    M.close()
  end, opts)
  vim.keymap.set('i', '<C-c>', function()
    M.close()
  end, opts)

  vim.api.nvim_create_autocmd({ 'TextChangedI', 'TextChangedP' }, {
    group = S.aug,
    buffer = S.buf_inp,
    callback = function()
      debounce(function()
        if not (S.active and vim.api.nvim_buf_is_valid(S.buf_inp)) then
          return
        end
        -- Prompt buffers usually return only the user input, but strip prompt defensively.
        local raw = vim.fn.getline('.')
        local prompt = (S.mode == 'files') and '^Search:%s*' or '^Grep:%s*'
        local q = raw:gsub(prompt, '')
        if S.mode == 'grep' then
          grep_async(q, function(list)
            if not S.active then
              return
            end
            S.items = list
            set_query(q)
          end)
        else
          set_query(q)
        end
      end, M.config.debounce_ms)
    end,
  })

  L('keymaps attached', opts)
end

---------------------------------------------------------------------
-- Public
---------------------------------------------------------------------
function M.files()
  if S.active then
    M.close()
  end
  S.active = true
  S.gen = S.gen + 1
  S.mode = 'files'
  S.root = project_root()
  open_layout('Search: ')
  attach_handlers()
  collect_files_async(function(list)
    if not S.active then
      return
    end
    set_items(list)
  end)
end

function M.grep()
  if S.active then
    M.close()
  end
  S.active = true
  S.gen = S.gen + 1
  S.mode = 'grep'
  S.root = project_root()
  open_layout('Grep: ')
  attach_handlers()
  S.items = {}
  set_query('')
end

function M.close()
  if not S.active then
    return
  end
  -- stop timers and jobs first
  if S.timer then
    S.timer:stop()
    S.timer:close()
    S.timer = nil
  end
  cancel_job(S.job_rg)
  S.job_rg = nil
  cancel_job(S.job_files)
  S.job_files = nil

  close_layout()
  S.active = false
  S.mode, S.root = nil, nil
  S.items, S.filtered, S.positions = {}, {}, {}
  S.query, S.select, S.scroll = '', 1, 0
  L('session closed')
end

function M.setup(opts)
  M.config = vim.tbl_deep_extend('force', M.config, opts or {})
  if M.config.file_cmd and not cmd_exists(M.config.file_cmd) then
    vim.notify(("finder: file_cmd '%s' not found"):format(M.config.file_cmd), vim.log.levels.WARN)
  end
  if M.config.grep_cmd and not cmd_exists(M.config.grep_cmd) then
    vim.notify(
      ("finder: grep_cmd '%s' not found, will try 'rg'"):format(M.config.grep_cmd),
      vim.log.levels.WARN
    )
  end
  L('setup', M.config)
end

return M