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

---@class pending.Counts
---@field overdue integer
---@field today integer
---@field pending integer
---@field priority integer
---@field next_due? string

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

local UNDO_MAX = 20

---@type pending.Counts?
local _counts = nil

---@return nil
function M._recompute_counts()
  local cfg = require('pending.config').get()
  local someday = cfg.someday_date
  local overdue = 0
  local today = 0
  local pending = 0
  local priority = 0
  local next_due = nil ---@type string?
  local today_str = os.date('%Y-%m-%d') --[[@as string]]

  for _, task in ipairs(store.active_tasks()) do
    if task.status == 'pending' then
      pending = pending + 1
      if task.priority > 0 then
        priority = priority + 1
      end
      if task.due and task.due ~= someday then
        if parse.is_overdue(task.due) then
          overdue = overdue + 1
        elseif parse.is_today(task.due) then
          today = today + 1
        end
        local date_part = task.due:match('^(%d%d%d%d%-%d%d%-%d%d)') or task.due
        if date_part >= today_str and (not next_due or task.due < next_due) then
          next_due = task.due
        end
      end
    end
  end

  _counts = {
    overdue = overdue,
    today = today,
    pending = pending,
    priority = priority,
    next_due = next_due,
  }

  vim.api.nvim_exec_autocmds('User', { pattern = 'PendingStatusChanged' })
end

---@return nil
local function _save_and_notify()
  store.save()
  M._recompute_counts()
end

---@return pending.Counts
function M.counts()
  if not _counts then
    store.load()
    M._recompute_counts()
  end
  return _counts --[[@as pending.Counts]]
end

---@return string
function M.statusline()
  local c = M.counts()
  if c.overdue > 0 and c.today > 0 then
    return c.overdue .. ' overdue, ' .. c.today .. ' today'
  elseif c.overdue > 0 then
    return c.overdue .. ' overdue'
  elseif c.today > 0 then
    return c.today .. ' today'
  end
  return ''
end

---@return boolean
function M.has_due()
  local c = M.counts()
  return c.overdue > 0 or c.today > 0
end

---@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
---@return nil
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,
  })
  vim.api.nvim_create_autocmd('WinClosed', {
    group = group,
    callback = function(ev)
      if tonumber(ev.match) == buffer.winid() then
        buffer.clear_winid()
      end
    end,
  })
end

---@param bufnr integer
---@return nil
function M._setup_buf_mappings(bufnr)
  local cfg = require('pending.config').get()
  local km = cfg.keymaps
  local opts = { buffer = bufnr, silent = true }

  ---@type table<string, fun()>
  local actions = {
    close = function()
      buffer.close()
    end,
    toggle = function()
      M.toggle_complete()
    end,
    view = function()
      buffer.toggle_view()
    end,
    priority = function()
      M.toggle_priority()
    end,
    date = function()
      M.prompt_date()
    end,
    undo = function()
      M.undo_write()
    end,
    open_line = function()
      buffer.open_line(false)
    end,
    open_line_above = function()
      buffer.open_line(true)
    end,
  }

  for name, fn in pairs(actions) do
    local key = km[name]
    if key and key ~= false then
      vim.keymap.set('n', key --[[@as string]], fn, opts)
    end
  end

  local textobj = require('pending.textobj')

  ---@type table<string, { modes: string[], fn: fun(count: integer), visual_fn?: fun(count: integer) }>
  local textobjs = {
    a_task = {
      modes = { 'o', 'x' },
      fn = textobj.a_task,
      visual_fn = textobj.a_task_visual,
    },
    i_task = {
      modes = { 'o', 'x' },
      fn = textobj.i_task,
      visual_fn = textobj.i_task_visual,
    },
    a_category = {
      modes = { 'o', 'x' },
      fn = textobj.a_category,
      visual_fn = textobj.a_category_visual,
    },
    i_category = {
      modes = { 'o', 'x' },
      fn = textobj.i_category,
      visual_fn = textobj.i_category_visual,
    },
  }

  for name, spec in pairs(textobjs) do
    local key = km[name]
    if key and key ~= false then
      for _, mode in ipairs(spec.modes) do
        if mode == 'x' and spec.visual_fn then
          vim.keymap.set(mode, key --[[@as string]], function()
            spec.visual_fn(vim.v.count1)
          end, opts)
        else
          vim.keymap.set(mode, key --[[@as string]], function()
            spec.fn(vim.v.count1)
          end, opts)
        end
      end
    end
  end

  ---@type table<string, fun(count: integer)>
  local motions = {
    next_header = textobj.next_header,
    prev_header = textobj.prev_header,
    next_task = textobj.next_task,
    prev_task = textobj.prev_task,
  }

  for name, fn in pairs(motions) do
    local key = km[name]
    if cfg.debug then
      vim.notify(
        ('[pending] mapping motion %s → %s (buf=%d)'):format(name, key or 'nil', bufnr),
        vim.log.levels.INFO
      )
    end
    if key and key ~= false then
      vim.keymap.set({ 'n', 'x', 'o' }, key --[[@as string]], function()
        fn(vim.v.count1)
      end, opts)
    end
  end
end

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

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

---@return nil
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
    if task.recur and task.due then
      local recur = require('pending.recur')
      local mode = task.recur_mode or 'scheduled'
      local next_date = recur.next_due(task.due, task.recur, mode)
      store.add({
        description = task.description,
        category = task.category,
        priority = task.priority,
        due = next_date,
        recur = task.recur,
        recur_mode = task.recur_mode,
      })
    end
    store.update(id, { status = 'done' })
  end
  _save_and_notify()
  buffer.render(bufnr)
  for lnum, m in ipairs(buffer.meta()) do
    if m.id == id then
      vim.api.nvim_win_set_cursor(0, { lnum, 0 })
      break
    end
  end
end

---@return nil
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 > 0 and 0 or 1
  store.update(id, { priority = new_priority })
  _save_and_notify()
  buffer.render(bufnr)
  for lnum, m in ipairs(buffer.meta()) do
    if m.id == id then
      vim.api.nvim_win_set_cursor(0, { lnum, 0 })
      break
    end
  end
end

---@return nil
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 (today, +3d, fri@2pm, etc.): ' }, 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$')
        and not due:match('^%d%d%d%d%-%d%d%-%d%dT%d%d:%d%d$')
      then
        vim.notify('Invalid date format. Use YYYY-MM-DD or YYYY-MM-DDThh:mm.', vim.log.levels.ERROR)
        return
      end
    end
    store.update(id, { due = due })
    _save_and_notify()
    buffer.render(bufnr)
  end)
end

---@param text string
---@return nil
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,
    recur = metadata.rec,
    recur_mode = metadata.rec_mode,
  })
  _save_and_notify()
  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

---@param backend_name string
---@param action? string
---@return nil
function M.sync(backend_name, action)
  if not backend_name or backend_name == '' then
    vim.notify('Usage: :Pending sync <backend> [action]', vim.log.levels.ERROR)
    return
  end
  action = (action and action ~= '') and action or 'sync'
  local ok, backend = pcall(require, 'pending.sync.' .. backend_name)
  if not ok then
    vim.notify('Unknown sync backend: ' .. backend_name, vim.log.levels.ERROR)
    return
  end
  if type(backend[action]) ~= 'function' then
    vim.notify(backend_name .. " backend has no '" .. action .. "' action", vim.log.levels.ERROR)
    return
  end
  backend[action]()
end

---@param days? integer
---@return nil
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)
  _save_and_notify()
  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

---@return nil
function M.due()
  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 (parse.is_overdue(m.raw_due) or parse.is_today(m.raw_due))
      then
        local task = store.get(m.id or 0)
        local label = parse.is_overdue(m.raw_due) 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 (parse.is_overdue(task.due) or parse.is_today(task.due))
      then
        local label = parse.is_overdue(task.due) 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

---@param token string
---@return string|nil field
---@return any value
---@return string|nil err
local function parse_edit_token(token)
  local recur = require('pending.recur')
  local cfg = require('pending.config').get()
  local dk = cfg.date_syntax or 'due'
  local rk = cfg.recur_syntax or 'rec'

  if token == '+!' then
    return 'priority', 1, nil
  end
  if token == '-!' then
    return 'priority', 0, nil
  end
  if token == '-due' or token == '-' .. dk then
    return 'due', vim.NIL, nil
  end
  if token == '-cat' then
    return 'category', vim.NIL, nil
  end
  if token == '-rec' or token == '-' .. rk then
    return 'recur', vim.NIL, nil
  end

  local due_val = token:match('^' .. vim.pesc(dk) .. ':(.+)$')
  if due_val then
    local resolved = parse.resolve_date(due_val)
    if resolved then
      return 'due', resolved, nil
    end
    if
      due_val:match('^%d%d%d%d%-%d%d%-%d%d$') or due_val:match('^%d%d%d%d%-%d%d%-%d%dT%d%d:%d%d$')
    then
      return 'due', due_val, nil
    end
    return nil,
      nil,
      'Invalid date: ' .. due_val .. '. Use YYYY-MM-DD, today, tomorrow, +Nd, weekday names, etc.'
  end

  local cat_val = token:match('^cat:(.+)$')
  if cat_val then
    return 'category', cat_val, nil
  end

  local rec_val = token:match('^' .. vim.pesc(rk) .. ':(.+)$')
  if rec_val then
    local raw_spec = rec_val
    local rec_mode = nil
    if raw_spec:sub(1, 1) == '!' then
      rec_mode = 'completion'
      raw_spec = raw_spec:sub(2)
    end
    if not recur.validate(raw_spec) then
      return nil, nil, 'Invalid recurrence pattern: ' .. rec_val
    end
    return 'recur', { spec = raw_spec, mode = rec_mode }, nil
  end

  return nil,
    nil,
    'Unknown operation: '
      .. token
      .. '. Valid: '
      .. dk
      .. ':<date>, cat:<name>, '
      .. rk
      .. ':<pattern>, +!, -!, -'
      .. dk
      .. ', -cat, -'
      .. rk
end

---@param id_str string
---@param rest string
---@return nil
function M.edit(id_str, rest)
  if not id_str or id_str == '' then
    vim.notify(
      'Usage: :Pending edit <id> [due:<date>] [cat:<name>] [rec:<pattern>] [+!] [-!] [-due] [-cat] [-rec]',
      vim.log.levels.ERROR
    )
    return
  end

  local id = tonumber(id_str)
  if not id then
    vim.notify('Invalid task ID: ' .. id_str, vim.log.levels.ERROR)
    return
  end

  store.load()
  local task = store.get(id)
  if not task then
    vim.notify('No task with ID ' .. id .. '.', vim.log.levels.ERROR)
    return
  end

  if not rest or rest == '' then
    vim.notify(
      'Usage: :Pending edit <id> [due:<date>] [cat:<name>] [rec:<pattern>] [+!] [-!] [-due] [-cat] [-rec]',
      vim.log.levels.ERROR
    )
    return
  end

  local tokens = {}
  for tok in rest:gmatch('%S+') do
    table.insert(tokens, tok)
  end

  local updates = {}
  local feedback = {}

  for _, tok in ipairs(tokens) do
    local field, value, err = parse_edit_token(tok)
    if err then
      vim.notify(err, vim.log.levels.ERROR)
      return
    end
    if field == 'recur' then
      if value == vim.NIL then
        updates.recur = vim.NIL
        updates.recur_mode = vim.NIL
        table.insert(feedback, 'recurrence removed')
      else
        updates.recur = value.spec
        updates.recur_mode = value.mode
        table.insert(feedback, 'recurrence set to ' .. value.spec)
      end
    elseif field == 'due' then
      if value == vim.NIL then
        updates.due = vim.NIL
        table.insert(feedback, 'due date removed')
      else
        updates.due = value
        table.insert(feedback, 'due date set to ' .. tostring(value))
      end
    elseif field == 'category' then
      if value == vim.NIL then
        updates.category = vim.NIL
        table.insert(feedback, 'category removed')
      else
        updates.category = value
        table.insert(feedback, 'category set to ' .. tostring(value))
      end
    elseif field == 'priority' then
      updates.priority = value
      table.insert(feedback, value == 1 and 'priority added' or 'priority removed')
    end
  end

  local snapshot = store.snapshot()
  local stack = store.undo_stack()
  table.insert(stack, snapshot)
  if #stack > UNDO_MAX then
    table.remove(stack, 1)
  end

  store.update(id, updates)
  store.save()

  local bufnr = buffer.bufnr()
  if bufnr and vim.api.nvim_buf_is_valid(bufnr) then
    buffer.render(bufnr)
  end

  vim.notify('Task #' .. id .. ' updated: ' .. table.concat(feedback, ', '))
end

---@param args string
---@return nil
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 == 'edit' then
    local id_str, edit_rest = rest:match('^(%S+)%s*(.*)')
    M.edit(id_str, edit_rest)
  elseif cmd == 'sync' then
    local backend, action = rest:match('^(%S+)%s*(.*)')
    M.sync(backend, action)
  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