local oauth = require('pending.sync.oauth')
local config = require('pending.config')

local M = {}

M.name = 'gcal'

local BASE_URL = 'https://www.googleapis.com/calendar/v3'
local SCOPE = 'https://www.googleapis.com/auth/calendar'

local client = oauth.new({
  name = 'gcal',
  scope = SCOPE,
  port = 18392,
  config_key = 'gcal',
})

---@return string? calendar_id
---@return string? err
local function find_or_create_calendar(access_token)
  local cfg = config.get()
  local gc = (cfg.sync and cfg.sync.gcal) or {}
  local cal_name = gc.calendar or 'Pendings'

  local data, err =
    oauth.curl_request('GET', BASE_URL .. '/users/me/calendarList', oauth.auth_headers(access_token))
  if err then
    return nil, err
  end

  for _, item in ipairs(data and data.items or {}) do
    if item.summary == cal_name then
      return item.id, nil
    end
  end

  local body = vim.json.encode({ summary = cal_name })
  local created, create_err =
    oauth.curl_request('POST', BASE_URL .. '/calendars', oauth.auth_headers(access_token), body)
  if create_err then
    return nil, create_err
  end

  return created and created.id, nil
end

---@param date_str string
---@return string
local function next_day(date_str)
  local y, m, d = date_str:match('^(%d%d%d%d)-(%d%d)-(%d%d)$')
  local t = os.time({ year = tonumber(y) or 0, month = tonumber(m) or 0, day = tonumber(d) or 0 })
    + 86400
  return os.date('%Y-%m-%d', t) --[[@as string]]
end

---@param access_token string
---@param calendar_id string
---@param task pending.Task
---@return string? event_id
---@return string? err
local function create_event(access_token, calendar_id, task)
  local event = {
    summary = task.description,
    start = { date = task.due },
    ['end'] = { date = next_day(task.due or '') },
    transparency = 'transparent',
    extendedProperties = {
      private = { taskId = tostring(task.id) },
    },
  }
  local data, err = oauth.curl_request(
    'POST',
    BASE_URL .. '/calendars/' .. oauth.url_encode(calendar_id) .. '/events',
    oauth.auth_headers(access_token),
    vim.json.encode(event)
  )
  if err then
    return nil, err
  end
  return data and data.id, nil
end

---@param access_token string
---@param calendar_id string
---@param event_id string
---@param task pending.Task
---@return string? err
local function update_event(access_token, calendar_id, event_id, task)
  local event = {
    summary = task.description,
    start = { date = task.due },
    ['end'] = { date = next_day(task.due or '') },
  }
  local _, err = oauth.curl_request(
    'PATCH',
    BASE_URL
      .. '/calendars/'
      .. oauth.url_encode(calendar_id)
      .. '/events/'
      .. oauth.url_encode(event_id),
    oauth.auth_headers(access_token),
    vim.json.encode(event)
  )
  return err
end

---@param access_token string
---@param calendar_id string
---@param event_id string
---@return string? err
local function delete_event(access_token, calendar_id, event_id)
  local _, err = oauth.curl_request(
    'DELETE',
    BASE_URL
      .. '/calendars/'
      .. oauth.url_encode(calendar_id)
      .. '/events/'
      .. oauth.url_encode(event_id),
    oauth.auth_headers(access_token)
  )
  return err
end

function M.auth()
  client:auth()
end

function M.sync()
  local access_token = client:get_access_token()
  if not access_token then
    return
  end

  local calendar_id, err = find_or_create_calendar(access_token)
  if err or not calendar_id then
    vim.notify('pending.nvim: ' .. (err or 'calendar not found'), vim.log.levels.ERROR)
    return
  end

  local tasks = require('pending').store():tasks()
  local created, updated, deleted = 0, 0, 0

  for _, task in ipairs(tasks) do
    local extra = task._extra or {}
    local event_id = extra['_gcal_event_id'] --[[@as string?]]

    local should_delete = event_id ~= nil
      and (
        task.status == 'done'
        or task.status == 'deleted'
        or (task.status == 'pending' and not task.due)
      )

    if should_delete and event_id then
      local del_err = delete_event(access_token, calendar_id, event_id) --[[@as string]]
      if not del_err then
        extra['_gcal_event_id'] = nil
        if next(extra) == nil then
          task._extra = nil
        else
          task._extra = extra
        end
        task.modified = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
        deleted = deleted + 1
      end
    elseif task.status == 'pending' and task.due then
      if event_id then
        local upd_err = update_event(access_token, calendar_id, event_id, task)
        if not upd_err then
          updated = updated + 1
        end
      else
        local new_id, create_err = create_event(access_token, calendar_id, task)
        if not create_err and new_id then
          if not task._extra then
            task._extra = {}
          end
          task._extra['_gcal_event_id'] = new_id
          task.modified = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
          created = created + 1
        end
      end
    end
  end

  require('pending').store():save()
  require('pending')._recompute_counts()
  vim.notify(
    string.format(
      'pending.nvim: Synced to Google Calendar (created: %d, updated: %d, deleted: %d)',
      created,
      updated,
      deleted
    )
  )
end

---@return nil
function M.health()
  oauth.health(M.name)
end

return M