package matching

import (
	"context"

	"github.com/shopspring/decimal"

	"github.com/missionworkforce/missionmatch/internal/modules/matching/engine"
	"github.com/missionworkforce/missionmatch/internal/platform/embeddings"
)

// EmbeddingSkillMatcher implements engine.SkillMatcher using the embedding provider: it embeds the
// required skill name and each candidate skill name and picks the best cosine match at/above the
// engine's threshold. Vectors from the provider are L2-normalized, so cosine == dot product.
//
// This is the semantic ("synonyms / adjacent skills") layer the engine defers to AFTER exact match.
// With the deterministic offline embedder, unrelated skills score near zero, so it never invents a
// false semantic match — exact matching still dominates. Determinism follows from the embedder's.
type EmbeddingSkillMatcher struct {
	embedder embeddings.Embedder
	ctx      context.Context
}

// NewEmbeddingSkillMatcher wraps an embedder as an engine.SkillMatcher.
func NewEmbeddingSkillMatcher(e embeddings.Embedder) *EmbeddingSkillMatcher {
	return &EmbeddingSkillMatcher{embedder: e, ctx: context.Background()}
}

// Match satisfies engine.SkillMatcher. It returns the candidate skill side and the similarity; the
// engine owns the required-side identity and the match flags.
func (m *EmbeddingSkillMatcher) Match(required engine.RequiredSkill, cands []engine.CandidateSkill, threshold decimal.Decimal) (engine.SkillMatch, bool) {
	if m == nil || m.embedder == nil || len(cands) == 0 {
		return engine.SkillMatch{}, false
	}
	rv, err := m.embedder.Embed(m.ctx, required.Name)
	if err != nil {
		return engine.SkillMatch{}, false
	}
	thr, _ := threshold.Float64()

	bestSim := -2.0
	var best engine.CandidateSkill
	found := false
	for _, cs := range cands {
		cv, err := m.embedder.Embed(m.ctx, cs.Name)
		if err != nil || len(cv) != len(rv) {
			continue
		}
		if sim := dot(rv, cv); sim > bestSim {
			bestSim, best, found = sim, cs, true
		}
	}
	if !found || bestSim < thr {
		return engine.SkillMatch{}, false
	}
	return engine.SkillMatch{
		CandidateSkillID: best.SkillID,
		CandidateName:    best.Name,
		Similarity:       decimal.NewFromFloat(bestSim).Round(4),
		Matched:          true,
	}, true
}

func dot(a, b []float32) float64 {
	var s float64
	for i := range a {
		s += float64(a[i]) * float64(b[i])
	}
	return s
}