[smartpl] update readme for smart playlists

README.md

@@ -269,7 +269,8 @@ Support for iTunes Music Library XML format is available as a compile-time
 option. By default, metadata from our parsers is preferred over what's in
 the iTunes DB; use itunes_overrides = true if you prefer iTunes' metadata.
 
-Smart playlists are not supported at the moment.
+forked-daapd has support for smart playlists. How to create a smart playlist is
+documented in [README_SMARTPL.md](README_SMARTPL.md).
 
 
 ## Artwork

README_SMARTPL.md

@@ -0,0 +1,165 @@
+# forked-daapd smart playlists
+
+
+To add a smart playlist to forked-daapd, create a new text file with a filename ending with .smartpl; 
+the filename doesn't matter, only the .smartpl ending does. The file must be placed somewhere in your
+library folder.
+
+
+## Syntax
+
+The contents of a smart playlist must follow the syntax:
+
+```
+"Playlist Name" { expression }
+```
+
+There is exactly one smart playlist allowed for a .smartpl file.
+
+
+An expression consists of:
+
+```
+field-name operator operand
+```
+
+Where valid field-names (with there types) are:
+* artist (string)
+* album_artist (string)
+* album (string)
+* title (string)
+* genre (string)
+* composer (string)
+* path (string)
+* type (string)
+* data_kind (enumeration)
+* media_kind (enumeration)
+* play_count (integer)
+* rating (integer)
+* year (integer)
+* compilation (integer)
+* time_added (date)
+* time_played (date)
+
+Valid operators include:
+* is, includes (string)
+* >, <, <=, >=, = (int)
+* after, before (date)
+* is (enumeration)
+
+The "is" operator must exactly match the field value, while the "includes" operator matches a substring.
+Both matches are case-insensitive.
+
+Valid operands include:
+* "string value" (string)
+* integer (int)
+
+Valid operands for the enumeration "data_kind" are:
+* file
+* url
+* spotify
+* pipe
+
+Valid operands for the enumeration "media_kind" are:
+* music
+* movie
+* podcast
+* audiobook
+* tvshow
+
+
+Multiple expressions can be anded or ored together, using the keywords OR and AND. The unary not operator is also supported using the keyword NOT.
+
+Example:
+
+```
+"techno" {
+   genre includes "techno"
+   and artist includes "zombie"
+}
+```
+
+This would match songs by "Rob Zombie" or "White Zombie", as well as those with a genre of "Techno-Industrial" or
+"Trance/Techno", for example.
+
+```
+"techno 2015" {
+   genre includes "techno"
+   and artist includes "zombie"
+   and not genre includes "industrial"
+}
+```
+
+This would exclude e. g. songs with the genre "Techno-Industrial".
+
+```
+"Local music" {
+  data_kind is file
+  and media_kind is music
+}
+```
+
+This would match all songs added as files to the library that are not placed under the folders for podcasts, audiobooks.
+
+```
+"Unplayed podcasts and audiobooks" {
+  play_count = 0
+  and (media_kind is podcast or media_kind is audiobook)
+}
+```
+
+This would match any podcast and audiobook file that was never played with forked-daapd.
+
+
+## Date oprand syntax
+
+One example of a valid date is a date in yyyy-mm-dd format:
+
+```
+"Files added after January 1, 2004" {
+  time_added after 2004-01-01
+}
+```
+
+There are also some special date keywords:
+* "today", "yesterday", "last week", "last month", "last year"
+
+A valid date can also be made by appling an interval to a date. Intervals can be defined as "days", "weeks", "months", "years".
+As an example, a valid date might be:
+
+```3 weeks before today``` or ```3 weeks ago```
+
+
+Examples:
+
+```
+"Recently Added" {
+    time_added after 2 weeks ago
+}
+```
+
+This matches all songs added in the last 2 weeks.
+
+```
+"Recently played audiobooks" {
+    time_played after last week
+    and media_kind is audiobook
+}
+```
+
+This matches all audiobooks played in the last week.
+
+
+## Differences to mt-daapd smart playlists
+
+The syntax is really close to the mt-daapd smart playlist syntax (see
+http://sourceforge.net/p/mt-daapd/code/HEAD/tree/tags/release-0.2.4.2/contrib/mt-daapd.playlist).
+
+Even this documentation is based on the file linked above.
+
+Some differences are:
+* only one smart playlist per file
+* the not operator must be placed before an expression and not before the operator
+* "||", "&&", "!" are not supported (use "or", "and", "not")
+* comments are not supported
+