package recruitmatch

import "github.com/shopspring/decimal"

var hundred = decimal.NewFromInt(100)

// pct returns num over den as a percentage rounded to two places.
//
// A zero or negative denominator yields exactly zero rather than NaN or a panic. That is the zero data
// organization case, which is the first thing every new client sees, so it is the default path and not
// an edge case.
//
// The operand order matches internal/modules/commandcenter.pct deliberately. Dividing first and
// multiplying second is equivalent to multiplying first at this precision: with
// decimal.DivisionPrecision at 16, an exhaustive sweep of every num and den pair for den from 1 to 400
// produced zero divergence after Round(2). Keeping one formula across both dashboards means the two
// screens can never disagree about the same ratio.
func pct(num, den int64) decimal.Decimal {
	if den <= 0 {
		return decimal.Zero
	}
	return decimal.NewFromInt(num).Div(decimal.NewFromInt(den)).Mul(hundred).Round(2)
}

// funnelStages is the fixed, ordered pipeline. It is a package level definition rather than a literal
// inside buildFunnel so the key set is a single source of truth for the tests and the frontend.
var funnelStages = []struct{ key, label string }{
	{"identified", "Identified"},
	{"screened", "Screened"},
	{"submitted", "Submitted"},
	{"approved", "Approved"},
}

// buildFunnel renders the pipeline overview from four counts of DISTINCT people.
//
// The caller must pass counts drawn from the same live candidate set, which service_queries guarantees
// by deriving every stage from rm_cand. Under that guarantee the sequence is non increasing, so no
// stage can exceed 100 percent and the funnel never renders an impossible width.
//
// buildFunnel does not enforce monotonicity, it relies on it. Enforcing here by clamping would hide a
// query bug behind a plausible looking chart, which is worse than rendering the anomaly. The invariant
// is asserted in the tests and in the integration test against a real database.
func buildFunnel(identified, screened, submitted, approved int64) []FunnelStage {
	counts := []int64{identified, screened, submitted, approved}
	out := make([]FunnelStage, 0, len(funnelStages))
	for i, s := range funnelStages {
		out = append(out, FunnelStage{
			Key:   s.key,
			Label: s.label,
			Count: counts[i],
			Pct:   pct(counts[i], identified).StringFixed(2),
		})
	}
	return out
}

// buildDecisions totals slate membership decisions and the approve rate over decided members only.
// Pending members are excluded from the rate denominator because an undecided member is not evidence
// either way; including them would make the rate drift purely from review backlog.
func buildDecisions(approved, rejected, pending int64) Decisions {
	decided := approved + rejected
	return Decisions{
		Approved:    approved,
		Rejected:    rejected,
		Pending:     pending,
		Total:       decided + pending,
		ApproveRate: pct(approved, decided).StringFixed(2),
	}
}

// notTracked is the fixed set of panels the product shows as explicitly untracked, with the reason each
// one is blank. Keeping it in one place means the UI never has to guess and never invents a number.
func notTracked() []EmptyPanel {
	return []EmptyPanel{
		{Key: "interviews", Title: "Interviews", Reason: "Interview scheduling is not tracked in missionMATCH yet."},
		{Key: "offers", Title: "Offers", Reason: "Offers are not tracked in missionMATCH yet."},
		{Key: "placements", Title: "Placements", Reason: "Placements are not tracked in missionMATCH yet."},
		{Key: "revenue", Title: "Revenue", Reason: "Bill rates and revenue are not tracked in missionMATCH yet."},
		{Key: "time_to_fill", Title: "Average time to fill", Reason: "Requirements do not record a fill date yet."},
		{Key: "source_mix", Title: "Candidate source", Reason: "Candidate source records seed or external only, so job board attribution is not available."},
	}
}