package staffing

import "github.com/shopspring/decimal"

// Confidence is a DETERMINISTIC transparency aid in [0,1], never a probability and never an input to a
// decision. It blends three observable, explainable factors:
//
//	confidence = wFit * (total / 100) + wProvenance * provenanceScore + wCompleteness * completeness
//
// fit is how far the engine score is above zero, provenanceScore reflects how the clearance was
// established (a self reported clearance is weaker evidence than continuous vetting), and completeness is
// the fraction of profile sections present. All three are bounded in [0,1] and the weights sum to 1, so
// the result is bounded in [0,1]. It is computed with decimal, never float, and rounded to 4 places to
// match the numeric(5,4) column.
func Confidence(cfg Config, c ScoredCandidate) decimal.Decimal {
	fit := c.Total.Div(decimal.NewFromInt(100))
	prov, ok := provenanceScore[c.Provenance]
	if !ok {
		prov = unknownProvenanceScore // an unknown or absent provenance is the conservative floor
	}
	comp := clamp01(c.Completeness)
	score := cfg.ConfidenceFitWeight.Mul(clamp01(fit)).
		Add(cfg.ConfidenceProvenanceWeight.Mul(prov)).
		Add(cfg.ConfidenceCompletenessWeight.Mul(comp))
	return clamp01(score).Round(4)
}

// provenanceScore maps a clearance provenance code to its evidence strength. The codes are the
// candidates.clearance_provenance domain. Higher is stronger evidence the clearance is real and current.
var provenanceScore = map[string]decimal.Decimal{
	"self_reported":      decimal.RequireFromString("0.40"),
	"document":           decimal.RequireFromString("0.60"),
	"sponsor_verified":   decimal.RequireFromString("0.90"),
	"continuous_vetting": decimal.NewFromInt(1),
}

var unknownProvenanceScore = decimal.RequireFromString("0.30")

func clamp01(d decimal.Decimal) decimal.Decimal {
	if d.LessThan(decimal.Zero) {
		return decimal.Zero
	}
	if d.GreaterThan(decimal.NewFromInt(1)) {
		return decimal.NewFromInt(1)
	}
	return d
}