Local collection trait and beets implementation (#9)

Closes #4

Reviewed-on: https://git.wojciechkozlowski.eu/wojtek/musichoard/pulls/9

src/database/json.rs

@@ -1,3 +1,5 @@
+//! Module for storing MusicHoard data in a JSON file database.
+
 use std::fs::File;
 use std::io::{Read, Write};
 use std::path::Path;
@@ -5,7 +7,7 @@ use std::path::Path;
 use serde::de::DeserializeOwned;
 use serde::Serialize;
 
-use crate::database::{DatabaseRead, DatabaseWrite};
+use super::{DatabaseRead, DatabaseWrite};
 
 /// A JSON file database.
 pub struct DatabaseJson {
@@ -59,84 +61,49 @@ impl DatabaseWrite for DatabaseJson {
 mod tests {
     use std::path::Path;
     use tempfile::NamedTempFile;
-    use uuid::uuid;
 
     use super::*;
 
-    use crate::{Artist, Release, ReleaseGroup, ReleaseGroupType, Track};
+    use crate::{Album, AlbumId, Track};
 
     const TEST_FILENAME: &str = "tests/files/database_json_test.json";
 
-    fn test_data() -> Vec<ReleaseGroup> {
+    fn test_data() -> Vec<Album> {
         vec![
-            ReleaseGroup {
-                r#type: ReleaseGroupType::Album,
-                title: String::from("Release group A"),
-                artist: vec![Artist {
-                    name: String::from("Artist A"),
-                    mbid: Some(uuid!("f7769831-746b-4a12-8124-0123d7fe17c9")),
-                }],
-                year: 1998,
-                mbid: Some(uuid!("89efbf43-3395-4f6e-ac11-32c1ce514bb0")),
-                releases: vec![Release {
-                    tracks: vec![
-                        Track {
-                            number: 1,
-                            title: String::from("Track A.1"),
-                            artist: vec![Artist {
-                                name: String::from("Artist A.A"),
-                                mbid: Some(uuid!("b7f7163d-61d5-4c96-b305-005df54fb999")),
-                            }],
-                            mbid: None,
-                        },
-                        Track {
-                            number: 2,
-                            title: String::from("Track A.2"),
-                            artist: vec![Artist {
-                                name: String::from("Artist A.A"),
-                                mbid: Some(uuid!("b7f7163d-61d5-4c96-b305-005df54fb999")),
-                            }],
-                            mbid: None,
-                        },
-                        Track {
-                            number: 3,
-                            title: String::from("Track A.3"),
-                            artist: vec![
-                                Artist {
-                                    name: String::from("Artist A.A"),
-                                    mbid: Some(uuid!("b7f7163d-61d5-4c96-b305-005df54fb999")),
-                                },
-                                Artist {
-                                    name: String::from("Artist A.B"),
-                                    mbid: Some(uuid!("6f6b46f2-4bb5-47e7-a8c8-03ebde30164f")),
-                                },
-                            ],
-                            mbid: None,
-                        },
-                    ],
-                    mbid: None,
-                }],
-            },
-            ReleaseGroup {
-                r#type: ReleaseGroupType::Single,
-                title: String::from("Release group B"),
-                artist: vec![Artist {
-                    name: String::from("Artist B"),
-                    mbid: None,
-                }],
-                year: 2008,
-                mbid: None,
-                releases: vec![Release {
-                    tracks: vec![Track {
+            Album {
+                id: AlbumId {
+                    artist: String::from("Artist A"),
+                    year: 1998,
+                    title: String::from("Release group A"),
+                },
+                tracks: vec![
+                    Track {
                         number: 1,
-                        title: String::from("Track B.1"),
-                        artist: vec![Artist {
-                            name: String::from("Artist B.A"),
-                            mbid: Some(uuid!("d927e216-2e63-415c-acec-bf9f1abd3e3c")),
-                        }],
-                        mbid: Some(uuid!("dacc9ce4-118c-4c92-aed7-1ebe4c7543b5")),
-                    }],
-                    mbid: Some(uuid!("ac7b642d-8b71-4588-a694-e5ae43fac873")),
+                        title: String::from("Track A.1"),
+                        artist: vec![String::from("Artist A.A")],
+                    },
+                    Track {
+                        number: 2,
+                        title: String::from("Track A.2"),
+                        artist: vec![String::from("Artist A.A")],
+                    },
+                    Track {
+                        number: 3,
+                        title: String::from("Track A.3"),
+                        artist: vec![String::from("Artist A.A"), String::from("Artist A.B")],
+                    },
+                ],
+            },
+            Album {
+                id: AlbumId {
+                    artist: String::from("Artist B"),
+                    year: 2008,
+                    title: String::from("Release group B"),
+                },
+                tracks: vec![Track {
+                    number: 1,
+                    title: String::from("Track B.1"),
+                    artist: vec![String::from("Artist B.A")],
                 }],
             },
         ]
@@ -168,7 +135,7 @@ mod tests {
 
     #[test]
     fn read() {
-        let mut read_data: Vec<ReleaseGroup> = vec![];
+        let mut read_data: Vec<Album> = vec![];
         DatabaseJson::reader(Path::new(TEST_FILENAME))
             .unwrap()
             .read(&mut read_data)
@@ -179,7 +146,7 @@ mod tests {
     #[test]
     fn reverse() {
         let write_data = test_data();
-        let mut read_data: Vec<ReleaseGroup> = vec![];
+        let mut read_data: Vec<Album> = vec![];
 
         let temp_file = NamedTempFile::new().unwrap();
 

src/database/mod.rs

@@ -1,3 +1,5 @@
+//! Module for storing MusicHoard data in a database.
+
 use serde::de::DeserializeOwned;
 use serde::Serialize;
 
@@ -5,6 +7,7 @@ pub mod json;
 
 /// Trait for database reads.
 pub trait DatabaseRead {
+    /// Read collection from the database.
     fn read<D>(&mut self, collection: &mut D) -> Result<(), std::io::Error>
     where
         D: DeserializeOwned;
@@ -12,6 +15,7 @@ pub trait DatabaseRead {
 
 /// Trait for database writes.
 pub trait DatabaseWrite {
+    /// Write collection to the database.
     fn write<S>(&mut self, collection: &S) -> Result<(), std::io::Error>
     where
         S: Serialize;

src/lib.rs

@@ -4,49 +4,30 @@ use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
 pub mod database;
+pub mod library;
 
 /// [MusicBrainz Identifier](https://musicbrainz.org/doc/MusicBrainz_Identifier) (MBID).
 pub type Mbid = Uuid;
 
-/// [Artist](https://musicbrainz.org/doc/Artist).
-#[derive(Debug, Deserialize, Serialize, PartialEq)]
-pub struct Artist {
-    pub name: String,
-    pub mbid: Option<Mbid>,
-}
-
-/// [Track](https://musicbrainz.org/doc/Track).
-#[derive(Debug, Deserialize, Serialize, PartialEq)]
+/// A single track on an album.
+#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
 pub struct Track {
     pub number: u32,
     pub title: String,
-    pub artist: Vec<Artist>,
-    pub mbid: Option<Mbid>,
+    pub artist: Vec<String>,
 }
 
-/// [Release](https://musicbrainz.org/doc/Release).
-#[derive(Debug, Deserialize, Serialize, PartialEq)]
-pub struct Release {
-    pub tracks: Vec<Track>,
-    pub mbid: Option<Mbid>,
-}
-
-/// [Release group primary type](https://musicbrainz.org/doc/Release_Group/Type).
-#[derive(Debug, Deserialize, Serialize, PartialEq)]
-pub enum ReleaseGroupType {
-    Album,
-    Ep,
-    Single,
-    Other,
-}
-
-/// [Release group](https://musicbrainz.org/doc/Release_Group).
-#[derive(Debug, Deserialize, Serialize, PartialEq)]
-pub struct ReleaseGroup {
-    pub r#type: ReleaseGroupType,
-    pub title: String,
-    pub artist: Vec<Artist>,
+/// The album identifier.
+#[derive(Debug, Deserialize, Serialize, PartialEq, Eq, Clone, Hash)]
+pub struct AlbumId {
+    pub artist: String,
     pub year: u32,
-    pub mbid: Option<Mbid>,
-    pub releases: Vec<Release>,
+    pub title: String,
+}
+
+/// An album is a collection of tracks that were released together.
+#[derive(Debug, Deserialize, Serialize, PartialEq, Eq)]
+pub struct Album {
+    pub id: AlbumId,
+    pub tracks: Vec<Track>,
 }

src/library/beets.rs

@@ -0,0 +1,432 @@
+//! Module for interacting with the music library via
+//! [beets](https://beets.readthedocs.io/en/stable/).
+
+use std::{collections::HashSet, fmt::Display, process::Command};
+
+use crate::{Album, AlbumId, Track};
+
+use super::{Error, Library, Query, QueryOption};
+
+trait QueryOptionArgBeets {
+    fn to_arg(&self, option_name: &str) -> Option<String>;
+}
+
+trait QueryArgsBeets {
+    fn to_args(&self) -> Vec<String>;
+}
+
+trait SimpleOption {}
+impl SimpleOption for String {}
+impl SimpleOption for u32 {}
+
+impl<T: SimpleOption + Display> QueryOptionArgBeets for QueryOption<T> {
+    fn to_arg(&self, option_name: &str) -> Option<String> {
+        let (negate, value) = match self {
+            Self::Include(value) => ("", value),
+            Self::Exclude(value) => ("^", value),
+            Self::None => return None,
+        };
+        Some(format!("{}{}{}", negate, option_name, value))
+    }
+}
+
+impl QueryOptionArgBeets for QueryOption<Vec<String>> {
+    fn to_arg(&self, option_name: &str) -> Option<String> {
+        let (negate, vec) = match self {
+            Self::Include(value) => ("", value),
+            Self::Exclude(value) => ("^", value),
+            Self::None => return None,
+        };
+        Some(format!("{}{}{}", negate, option_name, vec.join("; ")))
+    }
+}
+
+impl QueryArgsBeets for Query {
+    fn to_args(&self) -> Vec<String> {
+        let mut arguments: Vec<String> = vec![];
+
+        if let Some(album_artist) = self.album_artist.to_arg("albumartist:") {
+            arguments.push(album_artist);
+        };
+
+        if let Some(album_year) = self.album_year.to_arg("year:") {
+            arguments.push(album_year);
+        };
+
+        if let Some(album_title) = self.album_title.to_arg("album:") {
+            arguments.push(album_title);
+        };
+
+        if let Some(track_number) = self.track_number.to_arg("track:") {
+            arguments.push(track_number);
+        };
+
+        if let Some(track_title) = self.track_title.to_arg("title:") {
+            arguments.push(track_title);
+        };
+
+        if let Some(track_artist) = self.track_artist.to_arg("artist:") {
+            arguments.push(track_artist);
+        };
+
+        if let Some(all) = self.all.to_arg("") {
+            arguments.push(all);
+        }
+
+        arguments
+    }
+}
+
+/// Trait for invoking beets commands.
+pub trait BeetsExecutor {
+    /// Invoke beets with the provided arguments.
+    fn exec(&mut self, arguments: Vec<String>) -> Result<Vec<String>, Error>;
+}
+
+/// Struct for interacting with the music library via beets.
+pub struct Beets {
+    executor: Box<dyn BeetsExecutor>,
+}
+
+trait LibraryPrivate {
+    const CMD_LIST: &'static str;
+    const LIST_FORMAT_SEPARATOR: &'static str;
+    const LIST_FORMAT_ARG: &'static str;
+
+    fn list_cmd_and_args(query: &Query) -> Vec<String>;
+    fn list_to_albums(list_output: Vec<String>) -> Result<Vec<Album>, Error>;
+}
+
+impl Beets {
+    pub fn new(executor: Box<dyn BeetsExecutor>) -> Beets {
+        Beets { executor }
+    }
+}
+
+impl Library for Beets {
+    fn list(&mut self, query: &Query) -> Result<Vec<Album>, Error> {
+        let cmd = Self::list_cmd_and_args(query);
+        let output = self.executor.exec(cmd)?;
+        Self::list_to_albums(output)
+    }
+}
+
+macro_rules! list_format_separator {
+    () => {
+        "-*^-"
+    };
+}
+
+impl LibraryPrivate for Beets {
+    const CMD_LIST: &'static str = "ls";
+    const LIST_FORMAT_SEPARATOR: &'static str = list_format_separator!();
+    const LIST_FORMAT_ARG: &'static str = concat!(
+        "--format=",
+        "$albumartist",
+        list_format_separator!(),
+        "$year",
+        list_format_separator!(),
+        "$album",
+        list_format_separator!(),
+        "$track",
+        list_format_separator!(),
+        "$title",
+        list_format_separator!(),
+        "$artist"
+    );
+
+    fn list_cmd_and_args(query: &Query) -> Vec<String> {
+        let mut cmd: Vec<String> = vec![String::from(Self::CMD_LIST)];
+        cmd.push(Self::LIST_FORMAT_ARG.to_string());
+        cmd.append(&mut query.to_args());
+        cmd
+    }
+
+    fn list_to_albums(list_output: Vec<String>) -> Result<Vec<Album>, Error> {
+        let mut albums: Vec<Album> = vec![];
+        let mut album_ids = HashSet::<AlbumId>::new();
+
+        for line in list_output.iter() {
+            let split: Vec<&str> = line.split(Self::LIST_FORMAT_SEPARATOR).collect();
+
+            if split.len() != 6 {
+                return Err(Error::InvalidData(line.to_string()));
+            }
+
+            let album_artist = split[0].to_string();
+            let album_year = split[1].parse::<u32>()?;
+            let album_title = split[2].to_string();
+            let track_number = split[3].parse::<u32>()?;
+            let track_title = split[4].to_string();
+            let track_artist = split[5].to_string();
+
+            let aid = AlbumId {
+                artist: album_artist,
+                year: album_year,
+                title: album_title,
+            };
+
+            let track = Track {
+                number: track_number,
+                title: track_title,
+                artist: track_artist.split("; ").map(|s| s.to_owned()).collect(),
+            };
+
+            if album_ids.contains(&aid) {
+                // Beets returns results in order so we look from the back.
+                let album = albums.iter_mut().rev().find(|a| a.id == aid).unwrap();
+                album.tracks.push(track);
+            } else {
+                album_ids.insert(aid.clone());
+                albums.push(Album {
+                    id: aid,
+                    tracks: vec![track],
+                });
+            }
+        }
+
+        Ok(albums)
+    }
+}
+
+/// Executor for executing beets commands on the local system.
+pub struct SystemExecutor {
+    bin: String,
+}
+
+impl SystemExecutor {
+    pub fn new(bin: &str) -> SystemExecutor {
+        SystemExecutor {
+            bin: bin.to_string(),
+        }
+    }
+}
+
+impl Default for SystemExecutor {
+    fn default() -> Self {
+        SystemExecutor::new("beet")
+    }
+}
+
+impl BeetsExecutor for SystemExecutor {
+    fn exec(&mut self, arguments: Vec<String>) -> Result<Vec<String>, Error> {
+        let output = Command::new(&self.bin).args(arguments).output()?;
+        let output = std::str::from_utf8(&output.stdout)?;
+        Ok(output.split('\n').map(|s| s.to_string()).collect())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    struct TestExecutor {
+        arguments: Option<Vec<String>>,
+        output: Option<Result<Vec<String>, Error>>,
+    }
+
+    impl BeetsExecutor for TestExecutor {
+        fn exec(&mut self, arguments: Vec<String>) -> Result<Vec<String>, Error> {
+            if self.arguments.is_some() {
+                assert_eq!(self.arguments.take().unwrap(), arguments);
+            }
+            self.output.take().unwrap()
+        }
+    }
+
+    fn test_data() -> Vec<Album> {
+        vec![
+            Album {
+                id: AlbumId {
+                    artist: "album_artist.a".to_string(),
+                    year: 1998,
+                    title: "album_title.a".to_string(),
+                },
+                tracks: vec![
+                    Track {
+                        number: 1,
+                        title: "track.a.1".to_string(),
+                        artist: vec!["artist.a.1".to_string()],
+                    },
+                    Track {
+                        number: 2,
+                        title: "track.a.2".to_string(),
+                        artist: vec!["artist.a.2.1".to_string(), "artist.a.2.2".to_string()],
+                    },
+                    Track {
+                        number: 3,
+                        title: "track.a.3".to_string(),
+                        artist: vec!["artist.a.3".to_string()],
+                    },
+                ],
+            },
+            Album {
+                id: AlbumId {
+                    artist: "album_artist.b".to_string(),
+                    year: 2003,
+                    title: "album_title.b".to_string(),
+                },
+                tracks: vec![
+                    Track {
+                        number: 1,
+                        title: "track.b.1".to_string(),
+                        artist: vec!["artist.b.1".to_string()],
+                    },
+                    Track {
+                        number: 2,
+                        title: "track.b.2".to_string(),
+                        artist: vec!["artist.b.2.1".to_string(), "artist.b.2.2".to_string()],
+                    },
+                ],
+            },
+        ]
+    }
+
+    fn album_to_beets_string(album: &Album) -> Vec<String> {
+        let album_artist = &album.id.artist;
+        let album_year = &album.id.year;
+        let album_title = &album.id.title;
+
+        let mut strings = vec![];
+        for track in album.tracks.iter() {
+            let track_number = &track.number;
+            let track_title = &track.title;
+            let track_artist = &track.artist.join("; ");
+
+            strings.push(format!(
+                "{album_artist}{0}{album_year}{0}{album_title}{0}\
+                 {track_number}{0}{track_title}{0}{track_artist}",
+                Beets::LIST_FORMAT_SEPARATOR,
+            ));
+        }
+
+        strings
+    }
+
+    #[test]
+    fn test_query() {
+        let query = Query::new()
+            .album_title(QueryOption::Exclude(String::from("some.album")))
+            .track_number(QueryOption::Include(5))
+            .track_artist(QueryOption::Include(vec![
+                String::from("some.artist.1"),
+                String::from("some.artist.2"),
+            ]))
+            .all(QueryOption::Exclude(String::from("some.all")));
+
+        assert_eq!(
+            query.to_args(),
+            vec![
+                String::from("^album:some.album"),
+                String::from("track:5"),
+                String::from("artist:some.artist.1; some.artist.2"),
+                String::from("^some.all"),
+            ]
+        );
+    }
+
+    #[test]
+    fn test_list_empty() {
+        let executor = TestExecutor {
+            arguments: Some(vec!["ls".to_string(), Beets::LIST_FORMAT_ARG.to_string()]),
+            output: Some(Ok(vec![])),
+        };
+        let mut beets = Beets::new(Box::new(executor));
+        let output = beets.list(&Query::default()).unwrap();
+
+        let expected: Vec<Album> = vec![];
+        assert_eq!(output, expected);
+    }
+
+    #[test]
+    fn test_list_ordered() {
+        let expected = test_data();
+        let mut output = vec![];
+        for album in expected.iter() {
+            output.append(&mut album_to_beets_string(album));
+        }
+
+        let executor = TestExecutor {
+            arguments: Some(vec!["ls".to_string(), Beets::LIST_FORMAT_ARG.to_string()]),
+            output: Some(Ok(output)),
+        };
+        let mut beets = Beets::new(Box::new(executor));
+        let output = beets.list(&Query::default()).unwrap();
+
+        assert_eq!(output, expected);
+    }
+
+    #[test]
+    fn test_list_unordered() {
+        let mut expected = test_data();
+        let mut output = vec![];
+        for album in expected.iter() {
+            output.append(&mut album_to_beets_string(album));
+        }
+        let last = output.len() - 1;
+        output.swap(0, last);
+
+        // Putting the last track first will make its entire album come first in the output.
+        expected.rotate_right(1);
+
+        // Same applies to that album's tracks.
+        expected[0].tracks.rotate_right(1);
+
+        // And the (now) second album's tracks first track comes last.
+        expected[1].tracks.rotate_left(1);
+
+        let executor = TestExecutor {
+            arguments: Some(vec!["ls".to_string(), Beets::LIST_FORMAT_ARG.to_string()]),
+            output: Some(Ok(output)),
+        };
+        let mut beets = Beets::new(Box::new(executor));
+        let output = beets.list(&Query::default()).unwrap();
+
+        assert_eq!(output, expected);
+    }
+
+    #[test]
+    fn test_list_album_title_year_clash() {
+        let mut expected = test_data();
+        expected[1].id.year = expected[0].id.year;
+        expected[1].id.title = expected[0].id.title.clone();
+
+        let mut output = vec![];
+        for album in expected.iter() {
+            output.append(&mut album_to_beets_string(album));
+        }
+
+        let executor = TestExecutor {
+            arguments: Some(vec!["ls".to_string(), Beets::LIST_FORMAT_ARG.to_string()]),
+            output: Some(Ok(output)),
+        };
+        let mut beets = Beets::new(Box::new(executor));
+        let output = beets.list(&Query::default()).unwrap();
+
+        assert_eq!(output, expected);
+    }
+
+    #[test]
+    fn test_list_query() {
+        let query = Query::new()
+            .album_title(QueryOption::Exclude(String::from("some.album")))
+            .track_number(QueryOption::Include(5))
+            .track_artist(QueryOption::Include(vec![String::from("some.artist")]));
+
+        let executor = TestExecutor {
+            arguments: Some(vec![
+                "ls".to_string(),
+                Beets::LIST_FORMAT_ARG.to_string(),
+                String::from("^album:some.album"),
+                String::from("track:5"),
+                String::from("artist:some.artist"),
+            ]),
+            output: Some(Ok(vec![])),
+        };
+        let mut beets = Beets::new(Box::new(executor));
+        let output = beets.list(&query).unwrap();
+
+        let expected: Vec<Album> = vec![];
+        assert_eq!(output, expected);
+    }
+}

src/library/mod.rs

@@ -0,0 +1,133 @@
+//! Module for interacting with the music library.
+
+use std::{num::ParseIntError, str::Utf8Error};
+
+use crate::Album;
+
+pub mod beets;
+
+/// A single query option.
+pub enum QueryOption<T> {
+    /// Inclusive query.
+    Include(T),
+    /// Exclusive query.
+    Exclude(T),
+    /// No query.
+    None,
+}
+
+impl<T> QueryOption<T> {
+    /// Return `true` if [QueryOption] is not [QueryOption::None].
+    pub fn is_some(&self) -> bool {
+        !matches!(self, QueryOption::None)
+    }
+
+    /// Return `true` if [QueryOption] is [QueryOption::None].
+    pub fn is_none(&self) -> bool {
+        matches!(self, QueryOption::None)
+    }
+}
+
+impl<T> Default for QueryOption<T> {
+    fn default() -> Self {
+        Self::None
+    }
+}
+
+/// Options for refining library queries.
+#[derive(Default)]
+pub struct Query {
+    album_artist: QueryOption<String>,
+    album_year: QueryOption<u32>,
+    album_title: QueryOption<String>,
+    track_number: QueryOption<u32>,
+    track_title: QueryOption<String>,
+    track_artist: QueryOption<Vec<String>>,
+    all: QueryOption<String>,
+}
+
+impl Query {
+    /// Create an empty query.
+    pub fn new() -> Self {
+        Query::default()
+    }
+
+    /// Refine the query to a specific album artist.
+    pub fn album_artist(mut self, album_artist: QueryOption<String>) -> Self {
+        self.album_artist = album_artist;
+        self
+    }
+
+    /// Refine the query to a specific album year.
+    pub fn album_year(mut self, album_year: QueryOption<u32>) -> Self {
+        self.album_year = album_year;
+        self
+    }
+
+    /// Refine the query to a specific album title.
+    pub fn album_title(mut self, album_title: QueryOption<String>) -> Self {
+        self.album_title = album_title;
+        self
+    }
+
+    /// Refine the query to a specific track number.
+    pub fn track_number(mut self, track_number: QueryOption<u32>) -> Self {
+        self.track_number = track_number;
+        self
+    }
+
+    /// Refine the query to a specific track title.
+    pub fn track_title(mut self, track_title: QueryOption<String>) -> Self {
+        self.track_title = track_title;
+        self
+    }
+
+    /// Refine the query to a specific set of track artists.
+    pub fn track_artist(mut self, track_artist: QueryOption<Vec<String>>) -> Self {
+        self.track_artist = track_artist;
+        self
+    }
+
+    /// Refine the query for all fields.
+    pub fn all(mut self, all: QueryOption<String>) -> Self {
+        self.all = all;
+        self
+    }
+}
+
+/// Error type for library calls.
+#[derive(Debug)]
+pub enum Error {
+    /// The underlying library returned invalid data.
+    InvalidData(String),
+    /// The underlying library experienced an I/O error.
+    IoError(String),
+    /// The underlying library failed to parse an integer.
+    ParseIntError(String),
+    /// The underlying library failed to parse a UTF-8 string.
+    Utf8Error(String),
+}
+
+impl From<std::io::Error> for Error {
+    fn from(err: std::io::Error) -> Error {
+        Error::IoError(err.to_string())
+    }
+}
+
+impl From<ParseIntError> for Error {
+    fn from(err: ParseIntError) -> Error {
+        Error::ParseIntError(err.to_string())
+    }
+}
+
+impl From<Utf8Error> for Error {
+    fn from(err: Utf8Error) -> Error {
+        Error::Utf8Error(err.to_string())
+    }
+}
+
+/// Trait for interacting with the music library.
+pub trait Library {
+    /// List lirbary items that match the a specific query.
+    fn list(&mut self, query: &Query) -> Result<Vec<Album>, Error>;
+}

tests/files/database_json_test.json

@@ -1 +1 @@
-[{"type":"Album","title":"Release group A","artist":[{"name":"Artist A","mbid":"f7769831-746b-4a12-8124-0123d7fe17c9"}],"year":1998,"mbid":"89efbf43-3395-4f6e-ac11-32c1ce514bb0","releases":[{"tracks":[{"number":1,"title":"Track A.1","artist":[{"name":"Artist A.A","mbid":"b7f7163d-61d5-4c96-b305-005df54fb999"}],"mbid":null},{"number":2,"title":"Track A.2","artist":[{"name":"Artist A.A","mbid":"b7f7163d-61d5-4c96-b305-005df54fb999"}],"mbid":null},{"number":3,"title":"Track A.3","artist":[{"name":"Artist A.A","mbid":"b7f7163d-61d5-4c96-b305-005df54fb999"},{"name":"Artist A.B","mbid":"6f6b46f2-4bb5-47e7-a8c8-03ebde30164f"}],"mbid":null}],"mbid":null}]},{"type":"Single","title":"Release group B","artist":[{"name":"Artist B","mbid":null}],"year":2008,"mbid":null,"releases":[{"tracks":[{"number":1,"title":"Track B.1","artist":[{"name":"Artist B.A","mbid":"d927e216-2e63-415c-acec-bf9f1abd3e3c"}],"mbid":"dacc9ce4-118c-4c92-aed7-1ebe4c7543b5"}],"mbid":"ac7b642d-8b71-4588-a694-e5ae43fac873"}]}]
+[{"id":{"artist":"Artist A","year":1998,"title":"Release group A"},"tracks":[{"number":1,"title":"Track A.1","artist":["Artist A.A"]},{"number":2,"title":"Track A.2","artist":["Artist A.A"]},{"number":3,"title":"Track A.3","artist":["Artist A.A","Artist A.B"]}]},{"id":{"artist":"Artist B","year":2008,"title":"Release group B"},"tracks":[{"number":1,"title":"Track B.1","artist":["Artist B.A"]}]}]