{-# LANGUAGE OverloadedRecordDot #-}

-- |
-- Module      : Zettel.Links
-- Description : Calculate the backlinks and forward links for each Zettel
-- Copyright   : (c) 2023, Yann Herklotz
-- License     : GPL-3.0-only
-- Maintainer  : git [at] yannherklotz [dot] com
-- Stability   : experimental
-- Portability : POSIX
module Zettel.Links where

import Data.List (nub)
import qualified Data.Map.Strict as Map
import qualified Data.Text as T
import Text.Pandoc.Definition (Inline (..))
import Text.Pandoc.Shared (stringify)
import Text.Pandoc.Walk (query, walk)
import Zettel.Common
import Zettel.Types

gatherForwardIds :: Inline -> [ZettelId]
gatherForwardIds (Link _ i _)
  | T.null ident = []
  | otherwise = [ZettelId ident]
  where
    ident = parseIds $ stringify i
gatherForwardIds (RawInline t v)
  | t == "markdown" && not (T.null parsed) = [ZettelId parsed]
  | otherwise = []
  where
    parsed = T.takeWhile (/= '"') . T.drop 1 $ T.dropWhile (/= '"') v
gatherForwardIds _ = []

addIdPresent :: ZettelGraph -> Maybe ZettelId -> [ZettelId]
addIdPresent zg (Just ident) =
  [ident | ident `elem` Map.keys (unZettelGraph zg)]
addIdPresent _ Nothing = []

forwardLinkNode :: ZettelGraph -> ZettelId -> Zettel -> Zettel
forwardLinkNode zg ident zn =
  zn
    { zettelNext =
        nub
          ( query gatherForwardIds zn.zettelBody
              <> addIdPresent zg (defNextId ident)
              <> addIdPresent zg (defBranchId ident)
          )
    }

forwardLink :: ZettelGraph -> ZettelGraph
forwardLink zg =
  ZettelGraph
    (Map.mapWithKey (forwardLinkNode zg) $ unZettelGraph zg)
    zg.zettelGraphBib

backwardLinkNode :: ZettelGraph -> ZettelId -> Zettel -> Zettel
backwardLinkNode graph ident node = Map.foldlWithKey' f node (unZettelGraph graph)
  where
    f :: Zettel -> ZettelId -> Zettel -> Zettel
    f l ident' zg
      | ident `elem` zg.zettelNext =
          l {zettelPrev = ident' : l.zettelPrev}
      | otherwise = l

backwardLink :: ZettelGraph -> ZettelGraph
backwardLink zg =
  ZettelGraph
    (Map.mapWithKey (backwardLinkNode zg) $ unZettelGraph zg)
    zg.zettelGraphBib

updatePandocLinksInline :: Inline -> Inline
updatePandocLinksInline l@(Link a i (_, t))
  | not $ T.null ids = Link a i ("/zettel/" <> ids, t)
  | otherwise = l
  where
    ids = parseIds $ stringify i
updatePandocLinksInline i = i

updatePandocLinks :: ZettelGraph -> ZettelGraph
updatePandocLinks = walk updatePandocLinksInline

linkAll :: ZettelGraph -> ZettelGraph
linkAll = refreshPandocMeta . backwardLink . forwardLink . updatePandocLinks