package matching

import (
	"context"

	"github.com/jackc/pgx/v5"
	"github.com/shopspring/decimal"

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

// rerankModelKey is the champion display order re ranker read at slate generation to order the members. It is
// the same model_key the MAG trainer (cmd/train-model -kind reranker) fits and the evaluator promotes.
const rerankModelKey = "slate_display_order"

// championRerankWeights reads the champion display order re ranker's utility weights keyed by feature name plus
// its version, from the global MAG coefficient store on the caller's tx. It is BEST EFFORT: on any absence or
// error it returns nil weights and version 0, and the caller keeps the frozen engine order (the re ranker only
// ever permutes an already scored slate, never blocks generating it). The prior only champion (version 1) holds
// the engine component weights, so the order is unchanged until a LEARNED challenger is promoted; generateSlate
// therefore applies the reorder only for a learned champion (version above 1), keeping the prior only order byte
// identical to the engine order.
func championRerankWeights(ctx context.Context, tx pgx.Tx) (map[string]float64, int) {
	rows, err := tx.Query(ctx, `
		SELECT c.feature_name, c.coefficient::float8, m.version
		FROM aedt_learned_models m
		JOIN aedt_model_coefficients c ON c.model_key = m.model_key AND c.version = m.version
		WHERE m.model_key = $1 AND m.champion = true AND m.output_kind = 'display_order'`, rerankModelKey)
	if err != nil {
		return nil, 0
	}
	defer rows.Close()
	weights := map[string]float64{}
	version := 0
	for rows.Next() {
		var name string
		var coef float64
		var v int
		if err := rows.Scan(&name, &coef, &v); err != nil {
			return nil, 0
		}
		weights[name] = coef
		version = v
	}
	if rows.Err() != nil || len(weights) == 0 {
		return nil, 0
	}
	return weights, version
}

// rerankUtility is a candidate's display utility under the re ranker weights: the learned weight on each frozen
// engine sub score. The display order is this utility descending. It is NEVER a candidate score; it only orders
// an already scored slate, and the frozen engine Total remains the score shown. The feature names match the
// trainer's RerankFeatureOrder and map one to one onto the engine MatchResult sub scores.
func rerankUtility(weights map[string]float64, res engine.MatchResult) float64 {
	term := func(name string, d decimal.Decimal) float64 {
		v, _ := d.Float64()
		return weights[name] * v
	}
	return term("clearance_score", res.Clearance) +
		term("skills_score", res.Skills) +
		term("certs_score", res.Certifications) +
		term("customer_score", res.CustomerExperience) +
		term("experience_score", res.Experience) +
		term("location_score", res.Location)
}