TODO

Design decisions:
  - Photo library has to reside in a single director, but no specific folder structure inside is imposed
    Reasons:
      - easy to access photos even without the software
      - easy to move library to a different location
      - "importing" is as easy as copying the files to the correct location
  - Arbitrary kinds of tags (e.g. people, places, but really anything user-defined), arbitrary tag values per kind
    - values of tags are defined dynamically by assigning them for the first time
  - Keep reference to raw file around
  - Allow multiple versions of the same picture (original, post-processed), grouped together
  - Fast and efficient to use

Main features:
  Foto store:
    ✔ decide on a on-disk format @done
    ✔ enumerate all photos in store on startup @done
    ✔ read metadata
      ☐ EXIF @started
      ☐ XMP (?)
    ☐ write metadata (e.g. changed EXIF tags)
    ☐ search for duplicates (how to deal with duplicates?)
    ☐ allow moving photos around
    ☐ support RAW files
    ☐ link between images

  Gallery-Widget:
    ✔ display photos fast @done
    ✔ nice scrolling @done
    ☐ manage selection of photos
    ☐ display extra information about photos (file path, etc.)
      ☐ as tooltip
      ☐ as overlay
    ☐ allow grouping of images (based on linking above)
      - groups take one tile, can scroll through them
    ☐ show aggregate information
      ☐ time range of photos in view
      ☐ number of photos in current gallery

  Slideshow:
    ✔ basic slideshow of photos in current gallery view @done(19-10-19 21:27)
    ☐ zoom/pan
    ☐ animated transitions

  Explorer-widget:
    Displays the various categories for filtering the photo library.
    ☐ list of current filters
    ☐ list of tag kinds
    ☐ list of tags of a tag kind
    ☐ group into albums
      Difference to searching with filters is that albums are a static set of photos
    ☐ save tag filters (dynamic albums)

  Albums:
    ☐ data structure for albums
      - `PRAGMA foreign_keys = ON;`
      - `CREATE TABLE albums (id INTEGER PRIMARY KEY, name TEXT NOT NULL, description TEXT NOT NULL)`
      - `CREATE TABLE albums_x_photos (photo_id INTEGER NOT NULL, album_id INTEGER NOT NULL, PRIMARY KEY (photo_id, album_id), order INTEGER NOT NULL, FOREIGN KEY(photo_id) REFERENCES photos(id) ON DELETE CASCADE, FOREIGN KEY(album_id) REFERENCES albums(id) ON DELETE CASCADE)`

  Metadata:
    ☐ read all EXIF things, cache in DB
    ☐ free-text comment for photos
      - `ALTER TABLE photos ADD COLUMN comment TEXT`

  Tagging:
    ☐ data structure for tags
      - `PRAGMA foreign_keys = ON;`
      - `CREATE TABLE tag_kinds (id INTEGER PRIMARY KEY, name TEXT NOT NULL)`
      - `CREATE TABLE tags (id INTEGER PRIMARY KEY, name TEXT NOT NULL, kind INTEGER NOT NULL, FOREIGN KEY(kind) REFERENCES tag_kinds(id) ON DELETE CASCADE)`
      - `CREATE TABLE tags_x_photos (photo_id INTEGER NOT NULL, tag_id INTEGER NOT NULL, PRIMARY KEY (photo_id, tag_id), FOREIGN KEY(photo_id) REFERENCES photos(id) ON DELETE CASCADE, FOREIGN KEY(tag_id) REFERENCES tags(id) ON DELETE CASCADE)`
    ☐ default tag kinds: people, location
    ☐ manage tag kinds
    ☐ allow assigning tags to pictures (auto-completion of existing values for the current tag kind)
    ☐ allow easy (from the usability perspective) and efficient (from the implementation perspective) renaming of tag kinds and values

  Discovering:
    A single text box input (but maybe more structured) with auto-completion
    ☐ search by tag
    ☐ search by time of day
    ☐ search by month/season
    ☐ search by absolute date
    ☐ search by geo-location (need to read this from EXIF)
      ☐ get database of geographic entities
      ☐ use spatial extension of sqlite