local buffer = require('pending.buffer')
local diff = require('pending.diff')
local parse = require('pending.parse')
local store = require('pending.store')

---@class pending.init
local M = {}

---@type pending.Task[][]
local _undo_states = {}
local UNDO_MAX = 20

---@return integer bufnr
function M.open()
  local bufnr = buffer.open()
  M._setup_autocmds(bufnr)
  M._setup_buf_mappings(bufnr)
  return bufnr
end

---@param bufnr integer
function M._setup_autocmds(bufnr)
  local group = vim.api.nvim_create_augroup('PendingBuffer', { clear = true })
  vim.api.nvim_create_autocmd('BufWriteCmd', {
    group = group,
    buffer = bufnr,
    callback = function()
      M._on_write(bufnr)
    end,
  })
  vim.api.nvim_create_autocmd('BufEnter', {
    group = group,
    buffer = bufnr,
    callback = function()
      if not vim.bo[bufnr].modified then
        store.load()
        buffer.render(bufnr)
      end
    end,
  })
end

---@param bufnr integer
function M._setup_buf_mappings(bufnr)
  local opts = { buffer = bufnr, silent = true }
  vim.keymap.set('n', '<CR>', function()
    M.toggle_complete()
  end, opts)
  vim.keymap.set('n', '<Tab>', function()
    buffer.toggle_view()
  end, opts)
  vim.keymap.set('n', 'g?', function()
    M.show_help()
  end, opts)
  vim.keymap.set('n', '!', function()
    M.toggle_priority()
  end, opts)
  vim.keymap.set('n', 'D', function()
    M.prompt_date()
  end, opts)
  vim.keymap.set('n', 'U', function()
    M.undo_write()
  end, opts)
end

---@param bufnr integer
function M._on_write(bufnr)
  local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
  local snapshot = store.snapshot()
  table.insert(_undo_states, snapshot)
  if #_undo_states > UNDO_MAX then
    table.remove(_undo_states, 1)
  end
  diff.apply(lines)
  buffer.render(bufnr)
end

function M.undo_write()
  if #_undo_states == 0 then
    vim.notify('Nothing to undo.', vim.log.levels.WARN)
    return
  end
  local state = table.remove(_undo_states)
  store.replace_tasks(state)
  store.save()
  buffer.render(buffer.bufnr())
end

function M.toggle_complete()
  local bufnr = buffer.bufnr()
  if not bufnr then
    return
  end
  local row = vim.api.nvim_win_get_cursor(0)[1]
  local meta = buffer.meta()
  if not meta[row] or meta[row].type ~= 'task' then
    return
  end
  local id = meta[row].id
  if not id then
    return
  end
  local task = store.get(id)
  if not task then
    return
  end
  if task.status == 'done' then
    store.update(id, { status = 'pending', ['end'] = vim.NIL })
  else
    store.update(id, { status = 'done' })
  end
  store.save()
  buffer.render(bufnr)
end

function M.toggle_priority()
  local bufnr = buffer.bufnr()
  if not bufnr then
    return
  end
  local row = vim.api.nvim_win_get_cursor(0)[1]
  local meta = buffer.meta()
  if not meta[row] or meta[row].type ~= 'task' then
    return
  end
  local id = meta[row].id
  if not id then
    return
  end
  local task = store.get(id)
  if not task then
    return
  end
  local new_priority = task.priority == 1 and 0 or 1
  store.update(id, { priority = new_priority })
  store.save()
  buffer.render(bufnr)
end

function M.prompt_date()
  local bufnr = buffer.bufnr()
  if not bufnr then
    return
  end
  local row = vim.api.nvim_win_get_cursor(0)[1]
  local meta = buffer.meta()
  if not meta[row] or meta[row].type ~= 'task' then
    return
  end
  local id = meta[row].id
  if not id then
    return
  end
  vim.ui.input({ prompt = 'Due date (YYYY-MM-DD): ' }, function(input)
    if not input then
      return
    end
    local due = input ~= '' and input or nil
    if due then
      local resolved = parse.resolve_date(due)
      if resolved then
        due = resolved
      elseif not due:match('^%d%d%d%d%-%d%d%-%d%d$') then
        vim.notify('Invalid date format. Use YYYY-MM-DD.', vim.log.levels.ERROR)
        return
      end
    end
    store.update(id, { due = due })
    store.save()
    buffer.render(bufnr)
  end)
end

---@param text string
function M.add(text)
  if not text or text == '' then
    vim.notify('Usage: :Pending add <description>', vim.log.levels.ERROR)
    return
  end
  store.load()
  local description, metadata = parse.command_add(text)
  if not description or description == '' then
    vim.notify('Pending must have a description.', vim.log.levels.ERROR)
    return
  end
  store.add({
    description = description,
    category = metadata.cat,
    due = metadata.due,
  })
  store.save()
  local bufnr = buffer.bufnr()
  if bufnr and vim.api.nvim_buf_is_valid(bufnr) then
    buffer.render(bufnr)
  end
  vim.notify('Pending added: ' .. description)
end

function M.sync()
  local ok, gcal = pcall(require, 'pending.sync.gcal')
  if not ok then
    vim.notify('Google Calendar sync module not available.', vim.log.levels.ERROR)
    return
  end
  gcal.sync()
end

---@param days? integer
function M.archive(days)
  days = days or 30
  local cutoff = os.time() - (days * 86400)
  local tasks = store.tasks()
  local archived = 0
  local kept = {}
  for _, task in ipairs(tasks) do
    if (task.status == 'done' or task.status == 'deleted') and task['end'] then
      local y, mo, d, h, mi, s = task['end']:match('^(%d+)-(%d+)-(%d+)T(%d+):(%d+):(%d+)Z$')
      if y then
        local t = os.time({
          year = tonumber(y) --[[@as integer]],
          month = tonumber(mo) --[[@as integer]],
          day = tonumber(d) --[[@as integer]],
          hour = tonumber(h) --[[@as integer]],
          min = tonumber(mi) --[[@as integer]],
          sec = tonumber(s) --[[@as integer]],
        })
        if t < cutoff then
          archived = archived + 1
          goto skip
        end
      end
    end
    table.insert(kept, task)
    ::skip::
  end
  store.replace_tasks(kept)
  store.save()
  vim.notify('Archived ' .. archived .. ' tasks.')
  local bufnr = buffer.bufnr()
  if bufnr and vim.api.nvim_buf_is_valid(bufnr) then
    buffer.render(bufnr)
  end
end

function M.due()
  local today = os.date('%Y-%m-%d') --[[@as string]]
  local bufnr = buffer.bufnr()
  local is_valid = bufnr ~= nil and vim.api.nvim_buf_is_valid(bufnr)
  local meta = is_valid and buffer.meta() or nil
  local qf_items = {}

  if meta and bufnr then
    for lnum, m in ipairs(meta) do
      if m.type == 'task' and m.raw_due and m.status ~= 'done' and m.raw_due <= today then
        local task = store.get(m.id or 0)
        local label = m.raw_due < today and '[OVERDUE] ' or '[DUE] '
        table.insert(qf_items, {
          bufnr = bufnr,
          lnum = lnum,
          col = 1,
          text = label .. (task and task.description or ''),
        })
      end
    end
  else
    store.load()
    for _, task in ipairs(store.active_tasks()) do
      if task.status == 'pending' and task.due and task.due <= today then
        local label = task.due < today and '[OVERDUE] ' or '[DUE] '
        local text = label .. task.description
        if task.category then
          text = text .. ' [' .. task.category .. ']'
        end
        table.insert(qf_items, { text = text })
      end
    end
  end

  if #qf_items == 0 then
    vim.notify('No due or overdue tasks.')
    return
  end

  vim.fn.setqflist(qf_items, 'r')
  vim.cmd('copen')
end

function M.show_help()
  local cfg = require('pending.config').get()
  local dk = cfg.date_syntax or 'due'
  local lines = {
    'pending.nvim keybindings',
    '',
    '<CR>     Toggle complete/uncomplete',
    '<Tab>    Switch category/priority view',
    '!        Toggle priority',
    'D        Set due date',
    'U        Undo last write',
    'o / O    Add new task line',
    'dd       Delete task line (on :w)',
    'p / P    Paste (duplicates get new IDs)',
    'zc / zo  Fold/unfold category (category view)',
    ':w       Save all changes',
    '',
    ':Pending add <text>          Quick-add task',
    ':Pending add Cat: <text>     Quick-add with category',
    ':Pending due                 Show overdue/due qflist',
    ':Pending sync                Push to Google Calendar',
    ':Pending archive [days]      Purge old done tasks',
    ':Pending undo                Undo last write',
    '',
    'Inline metadata (on new lines before :w):',
    '  ' .. dk .. ':YYYY-MM-DD    Set due date',
    '  cat:Name          Set category',
    '',
    'Due date input:',
    '  today, tomorrow, +Nd, mon-sun',
    '  Empty input clears due date',
    '',
    'Highlights:',
    '  PendingOverdue  overdue tasks (red)',
    '',
    'Press q or <Esc> to close',
  }
  local buf = vim.api.nvim_create_buf(false, true)
  vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
  vim.bo[buf].modifiable = false
  vim.bo[buf].bufhidden = 'wipe'
  local width = 54
  local height = #lines
  local win = vim.api.nvim_open_win(buf, true, {
    relative = 'editor',
    width = width,
    height = height,
    col = math.floor((vim.o.columns - width) / 2),
    row = math.floor((vim.o.lines - height) / 2),
    style = 'minimal',
    border = 'rounded',
  })
  vim.keymap.set('n', 'q', function()
    vim.api.nvim_win_close(win, true)
  end, { buffer = buf, silent = true })
  vim.keymap.set('n', '<Esc>', function()
    vim.api.nvim_win_close(win, true)
  end, { buffer = buf, silent = true })
end

---@param args string
function M.command(args)
  if not args or args == '' then
    M.open()
    return
  end
  local cmd, rest = args:match('^(%S+)%s*(.*)')
  if cmd == 'add' then
    M.add(rest)
  elseif cmd == 'sync' then
    M.sync()
  elseif cmd == 'archive' then
    local d = rest ~= '' and tonumber(rest) or nil
    M.archive(d)
  elseif cmd == 'due' then
    M.due()
  elseif cmd == 'undo' then
    M.undo_write()
  else
    vim.notify('Unknown Pending subcommand: ' .. cmd, vim.log.levels.ERROR)
  end
end

return M