local ZK = {}

local zettel_extension, anchor_separator

local api
if vim ~= nil then
  api = vim.api
  anchor_separator = vim.g["zettel_anchor_separator"] or vim.b["zettel_anchor_separator"] or "_"
  zettel_extension = vim.g["zettel_extension"] or vim.b["zettel_extension"] or ".md"
end
package.loaded['zettelkasten'] = nil

local anchor_separator = "_"

function ZK.init(vimapi)
  vim = vimapi or vim
  anchor_separator = vim.g["zettel_anchor_separator"] or vim.b["zettel_anchor_separator"] or "_"
  zettel_extension = vim.g["zettel_extension"] or vim.b["zettel_extension"] or ".md"
  zettel_root = vim.g["zettel_extension"] or vim.b["zettel_extension"] or ".md"
end

-- entrypoint for pressing the zettel key when the cursor
-- is either on an existing link  (it will then
-- follow it) or over text (it will then turn it into a
-- zettel link)
function ZK.follow_link()
  assert(false, "NOT IMPLEMENTED")
  return ''
end

-- Return a valid zettelkasten anchor,
-- composed of yymmddHHMM.
--
-- date can be passed in as a table containing a year, a month, a day, an hour,
-- and a minute key. Returns nil if the date passed in is invalid.
-- If no date is passed in, returns Zettel anchor for current moment.
function ZK.create_anchor(date)
  local timestamp
  if pcall(function() timestamp=os.time(date) end) then
    return os.date('%y%m%d%H%M', timestamp)
  else
    return nil
  end
end

-- Returns a link to a markdown file with the date replaced with a zettel anchor,
-- and the text cleaned up to be useful in a link.
function ZK.create_link(text, date)
  text = text or ""
  if text == "" then
    text = "" .. ZK.create_anchor(date)
  else
    text = text:lower():gsub(" ", "-")
    text = "" .. ZK.create_anchor(date) .. anchor_separator .. text
  end
  return text .. (zettel_extension or ".md")
end

function ZK._get_anchors_and_paths(path, recursive)
  -- TODO check for duplicates and warn user
  local zettel = {}
  local anchorreg = '^.*/?([%d][%d][%d][%d][%d][%d][%d][%d][%d][%d])[^/]*.md$'

  local handle = vim.loop.fs_scandir(path)
  while handle do
    local name, ftype = vim.loop.fs_scandir_next(handle)
    if not name then break end

    if ftype == 'directory' and recursive then
      local subdir = ZK._get_anchors_and_paths(path .. "/" .. name, true)
      for k, v in pairs(subdir) do
        zettel[tostring(k)] = v
      end
    end

    local anchor = string.match(name, anchorreg)
    if anchor then
      zettel[tostring(anchor)] = name
    end
  end
  return zettel
end

-- Returns all zettel in path as a
-- { "anchor" = "path/to/zettel/anchor filename.md" }
-- table.
-- Recurses into subdirectories if recursive argument is true.
function ZK.get_zettel_list(path, recursive)
  -- TODO transform paths:
  --    * to absolute value (e.g. ~ to home, scandir needs absolute)
  --    * to ensure / at the end (or no /) gets taken into account
  return ZK._get_anchors_and_paths(path, recursive or false)
end

return {
  init = ZK.init,
  zettel_link_create = ZK.zettel_link_create,
  create_anchor = ZK.create_anchor,
  create_link = ZK.create_link,
  get_zettel_list = ZK.get_zettel_list,
}