package recsettings

import (
	"testing"
	"time"

	"git.fabledsword.com/bvandeusen/minstrel/internal/recommendation"
)

// The bug, reproduced as a ranking: a track that sounds nothing like the seed
// but which the user liked and has not played lately used to OUTRANK a perfect
// similarity match. Operator, 2026-09-10: "I was getting a seeming wide variety
// of music from each one when I was hoping to stay in a certain neighborhood."
//
// This is the whole point of the songs_like profile, so it is asserted as
// BEHAVIOUR — two candidates, which one wins — rather than by checking the
// weight numbers. Numbers get retuned; this property must survive that.
//
// It also pins the contrast: daily_mix is EXPECTED to fail this. If both
// profiles started ranking the same way, the split would have quietly become
// pointless and nothing else would notice.
func TestSongsLikeWeights_SimilarityBeatsAnUnrelatedLikedTrack(t *testing.T) {
	now := time.Now().UTC()
	stale := now.Add(-365 * 24 * time.Hour)

	// A perfect similarity match the user has never liked and played recently.
	// Everything except similarity is working against it.
	perfectMatch := recommendation.ScoringInputs{
		SimilarityScore: 1.0,
		IsGeneralLiked:  false,
		LastPlayedAt:    &now,
	}
	// Nothing to do with the seed, but liked and long unplayed — every
	// seed-independent term in its favour.
	unrelatedFavourite := recommendation.ScoringInputs{
		SimilarityScore: 0.0,
		IsGeneralLiked:  true,
		LastPlayedAt:    &stale,
		TasteMatchScore: 1.0,
	}

	// Jitter fixed at its midpoint so the comparison is about the weights.
	noJitter := func() float64 { return 0.5 }

	songsLike := ShippedSongsLikeWeights()
	matchScore := recommendation.Score(perfectMatch, songsLike, now, noJitter)
	favScore := recommendation.Score(unrelatedFavourite, songsLike, now, noJitter)
	if matchScore <= favScore {
		t.Errorf("songs_like ranks an unrelated liked track (%.3f) at or above a "+
			"perfect similarity match (%.3f) — the mix will wander", favScore, matchScore)
	}

	// The contrast that makes the split worth having. If this ever passes,
	// daily_mix has been tightened into songs_like and one of them is redundant.
	daily := ShippedDailyMixWeights()
	dMatch := recommendation.Score(perfectMatch, daily, now, noJitter)
	dFav := recommendation.Score(unrelatedFavourite, daily, now, noJitter)
	if dMatch > dFav {
		t.Errorf("daily_mix now also puts similarity first (%.3f vs %.3f); the two "+
			"profiles no longer differ, so songs_like is buying nothing", dMatch, dFav)
	}
}

// The property the songs_like numbers encode, stated independently of them:
// the similarity term's range must exceed the combined range of every
// seed-INDEPENDENT differentiator, so a closer match cannot be beaten on
// likes, freshness and taste alone.
//
// BaseWeight is excluded deliberately — it is identical for every candidate
// and so differentiates nothing. SkipPenalty is excluded because it only ever
// pushes a candidate DOWN, and a skipped track should lose however similar.
func TestSongsLikeWeights_SimilarityOutrangesEverySeedIndependentTerm(t *testing.T) {
	w := ShippedSongsLikeWeights()

	// TasteMatchScore and ContextAffinityScore are in [-1,+1]; recencyDecay is
	// in [0,1]; LikeBoost is all-or-nothing.
	seedIndependent := w.LikeBoost + w.RecencyWeight + w.TasteWeight +
		w.ContextTimeWeight + w.JitterMagnitude

	if w.SimilarityWeight <= seedIndependent {
		t.Errorf("SimilarityWeight %.2f does not outrange the seed-independent "+
			"terms (%.2f) — likes/recency/taste can outvote sounding like the seed",
			w.SimilarityWeight, seedIndependent)
	}
}

// A scope that is seedable but not resettable is the half-wired shape this
// guards: the profile appears in the admin card, the operator turns a knob,
// and Reset then 404s on a scope the rest of the service knows about.
func TestShippedWeightsFor_CoversEveryWeightProfile(t *testing.T) {
	for _, scope := range []string{ScopeRadio, ScopeDailyMix, ScopeSongsLike} {
		if _, ok := shippedWeightsFor(scope); !ok {
			t.Errorf("scope %q has no shipped defaults; it cannot be seeded or reset", scope)
		}
	}
	// Non-weight scopes must NOT resolve here, or Reset would treat the taste
	// singleton as a weight profile and write nonsense.
	for _, scope := range []string{ScopeTaste, ScopeDiscover, "nonsense"} {
		if _, ok := shippedWeightsFor(scope); ok {
			t.Errorf("scope %q resolved as a weight profile and is not one", scope)
		}
	}
}

// Guards the sync the comment in playlists/system.go asks for: the pre-push
// literal there must match the shipped defaults here, or a build that has not
// yet been reconciled ranks differently from one that has.
func TestShippedSongsLikeWeights_AreDominatedBySimilarity(t *testing.T) {
	w := ShippedSongsLikeWeights()
	daily := ShippedDailyMixWeights()

	if w.SimilarityWeight <= daily.SimilarityWeight {
		t.Errorf("songs_like SimilarityWeight %.2f is not above daily_mix's %.2f",
			w.SimilarityWeight, daily.SimilarityWeight)
	}
	for _, tc := range []struct {
		name       string
		songs, day float64
	}{
		{"LikeBoost", w.LikeBoost, daily.LikeBoost},
		{"TasteWeight", w.TasteWeight, daily.TasteWeight},
		{"RecencyWeight", w.RecencyWeight, daily.RecencyWeight},
	} {
		if tc.songs >= tc.day {
			t.Errorf("songs_like %s (%.2f) is not demoted below daily_mix (%.2f); "+
				"these are the seed-independent terms that made the mix wander",
				tc.name, tc.songs, tc.day)
		}
	}
}