package engine

import (
	"fmt"

	"github.com/shopspring/decimal"
)

// GlobalDefaultProfileVersion names the weight set every tenant scores on until the Adaptive
// Intelligence Optimization Engine has produced a tenant profile. It is stamped into results and
// audit rows so a served score always names the exact weights that produced it.
const GlobalDefaultProfileVersion = "global.default"

// Weights carries the six dimension weights the scorer applies. The engine stays pure and
// deterministic: weights are an INPUT, injected by the caller, decimal end to end. The fixed
// package constants (WeightClearance and friends) remain the frozen global default; a tenant
// profile from the AIOE layer arrives here already validated and clamped.
type Weights struct {
	Clearance          decimal.Decimal
	Skills             decimal.Decimal
	Certifications     decimal.Decimal
	CustomerExperience decimal.Decimal
	Experience         decimal.Decimal
	Location           decimal.Decimal
}

// DefaultWeights returns the frozen global default weight set (CLAUDE.md fixed weights). Scoring
// with DefaultWeights is byte identical to the historical ScoreCandidate behavior; the frozen
// golden tests prove it.
func DefaultWeights() Weights {
	return Weights{
		Clearance:          WeightClearance,
		Skills:             WeightSkills,
		Certifications:     WeightCerts,
		CustomerExperience: WeightCustomer,
		Experience:         WeightExperience,
		Location:           WeightLocation,
	}
}

// Sum returns the exact decimal sum of the six weights.
func (w Weights) Sum() decimal.Decimal {
	return w.Clearance.Add(w.Skills).Add(w.Certifications).
		Add(w.CustomerExperience).Add(w.Experience).Add(w.Location)
}

// Validate rejects any weight set that is not a well formed probability style allocation: every
// dimension strictly positive, none above one, and the total exactly 1 at four decimal places.
// The scorer refuses an invalid set and falls back to the global default, so a corrupt profile
// can degrade a tenant to defaults but can never distort a score.
func (w Weights) Validate() error {
	one := decimal.NewFromInt(1)
	for name, v := range map[string]decimal.Decimal{
		"clearance":           w.Clearance,
		"skills":              w.Skills,
		"certifications":      w.Certifications,
		"customer_experience": w.CustomerExperience,
		"experience":          w.Experience,
		"location":            w.Location,
	} {
		if !v.IsPositive() || v.GreaterThan(one) {
			return fmt.Errorf("engine: weight %s out of range: %s", name, v.String())
		}
	}
	if !w.Sum().Round(4).Equal(one) {
		return fmt.Errorf("engine: weights sum to %s, not 1", w.Sum().String())
	}
	return nil
}