import Foundation
import Testing
@testable import Music

// Verifies the pure single/multi-track edit logic: extraction, change detection,
// shared-vs-mixed across many tracks, and applying only edited fields.
struct EditableTrackFieldsTests {
    @Test func initCopiesEditableValues() {
        // Step 1: build fields from a fixture track.
        let t = Track.fixture(title: "A", artist: "B", album: "C", year: 2001, rating: 3)
        let f = EditableTrackFields(from: t)
        // Step 2: editable values match.
        #expect(f.title == "A"); #expect(f.artist == "B")
        #expect(f.album == "C"); #expect(f.year == 2001); #expect(f.rating == 3)
    }

    @Test func changedFieldsDetectsOnlyDifferences() {
        // Step 1: two field sets differing only in genre + bpm.
        let a = EditableTrackFields(from: .fixture(genre: "Rock", bpm: 120))
        var b = a; b.genre = "Jazz"; b.bpm = 90
        // Step 2: change set is exactly {genre, bpm}.
        #expect(a.changedFields(to: b) == [.genre, .bpm])
    }

    @Test func sharedMarksDifferingFieldsMixed() {
        // Step 1: two tracks share artist but differ in genre.
        let t1 = Track.fixture(artist: "Same", genre: "Rock")
        let t2 = Track.fixture(artist: "Same", genre: "Pop")
        // Step 2: shared() returns common artist and flags genre as mixed.
        let (values, mixed) = EditableTrackFields.shared(across: [t1, t2])
        #expect(values.artist == "Same")
        #expect(mixed.contains(.genre))
        #expect(!mixed.contains(.artist))
    }

    @Test func sharedAcrossThreeTracksAccumulatesMixed() {
        // Step 1: three tracks all share the same album, but title differs on the
        //         third track and genre differs on the second — so both title and
        //         genre must end up "mixed", while album stays shared.
        let t1 = Track.fixture(title: "Same", album: "One Album", genre: "Rock")
        let t2 = Track.fixture(title: "Same", album: "One Album", genre: "Pop")
        let t3 = Track.fixture(title: "Different", album: "One Album", genre: "Rock")
        // Step 2: shared() over all three.
        let (values, mixed) = EditableTrackFields.shared(across: [t1, t2, t3])
        // Step 3: album is shared (not mixed); title + genre are mixed.
        #expect(values.album == "One Album")
        #expect(!mixed.contains(.album))
        #expect(mixed.contains(.title))
        #expect(mixed.contains(.genre))
    }

    @Test func applyOnlyWritesEditedFields() {
        // Step 1: a track and a fields object that changes album only.
        let t = Track.fixture(album: "Old", genre: "Rock")
        var f = EditableTrackFields(from: t); f.album = "New"; f.genre = "IGNORED"
        // Step 2: applying with editing={.album} changes album, leaves genre.
        let out = f.apply(editing: [.album], to: t)
        #expect(out.album == "New")
        #expect(out.genre == "Rock")
    }

    @Test func applyEmptyEditSetReturnsUnchanged() {
        let t = Track.fixture(title: "Keep")
        let f = EditableTrackFields(from: t)
        #expect(f.apply(editing: [], to: t) == t)
    }
}