package owliver

import (
	"sort"

	"github.com/krow/krow-backend/go-api/internal/domain"
)

// Context is the state of one organization's hiring, as counts.
//
// It is the answer to "what is actually going on here right now", read from
// PostgreSQL by service.SuggestionsService and handed to Highlights. Nothing in
// this package fetches it: the ranking stays a pure function of its inputs, and
// the one place that touches a database stays in the service layer where every
// other query lives.
//
// Counts rather than records, deliberately. A suggestion is a question, and
// deciding whether a question is worth asking needs to know that eleven
// candidates are waiting on a decision — never who they are. Nothing here can
// leak a name, and a zero-valued Context is a valid one: it means the reading
// has nothing to report, and Highlights answers with nothing rather than with a
// question about an empty set.
type Context struct {
	// Positions.
	ActivePositions   int // status = 'active'
	DraftPositions    int // status = 'draft'
	StarvedPositions  int // active postings nobody has applied to
	UnderfilledActive int // active postings with fewer hires than headcount

	// Candidates, by where they are in the funnel.
	Applications int
	Unscreened   int // status = 'applied' — nobody has scored them
	Shortlisted  int
	Interviewing int
	Hired        int
	FlaggedRisks int // interviews carrying at least one ai_flag

	// Supply and the record behind it.
	Staff              int
	Profiles           int
	UnverifiedProfiles int // profiles with no evidence filed
	Courses            int
	ActivityEvents     int
}

// Empty reports that nothing in this organization is worth remarking on.
//
// Used to tell "the database says there is nothing here" apart from "the
// database was not consulted": both produce no highlights, but only the second
// is a reason to fall back to anything.
func (c Context) Empty() bool { return c == Context{} }

/* ── Highlights ─────────────────────────────────────────────────────────── */

// Highlights is what is worth asking on this page given the state of the data.
//
// The counterpart to Suggest, and deliberately a separate function rather than
// a mode of it. Suggest answers "the user typed this, what did they mean" and
// is a pure string match; this answers "the user typed nothing, what should
// they know" and is a pure read of the organization. Merging them would make
// every keystroke pay for a database round trip in order to serve the one
// request per page that has nothing typed.
//
// The stages are the same and in the same order: page context, then permission,
// then relevance, then the cap. An intent the caller may not perform is never
// scored, so no ordering bug can surface one; an intent whose signal is zero is
// dropped rather than padded in, so a quiet workspace is offered nothing rather
// than three questions about empty sets.
func Highlights(page string, ctx Context, role domain.Role) []Suggestion {
	out := []Suggestion{}

	// Deny by default, exactly as Suggest does. An intent that reads nothing is
	// permitted to every role, so without this an unparseable role would be
	// offered the account readings.
	if _, known := domain.ParseRole(string(role)); !known {
		return out
	}

	intents, ok := catalogue[page]
	if !ok {
		return out
	}

	candidates := make([]scored, 0, len(intents))
	for order, intent := range intents {
		if !intent.permitted(role) {
			continue
		}
		if intent.Signal == nil {
			continue
		}
		signal := intent.Signal(ctx)
		if signal <= 0 {
			continue
		}
		candidates = append(candidates, scored{
			suggestion: Suggestion{Text: intent.Text, Intent: intent.ID},
			score:      signal,
			order:      order,
			onTopic:    true,
		})
	}

	// Strongest signal first; declaration order breaks every tie, so the same
	// database state always produces the same three in the same sequence.
	sort.SliceStable(candidates, func(a, b int) bool {
		if candidates[a].score != candidates[b].score {
			return candidates[a].score > candidates[b].score
		}
		return candidates[a].order < candidates[b].order
	})

	seenIntent := make(map[string]bool, MaxSuggestions)
	for _, c := range candidates {
		if len(out) == MaxSuggestions {
			break
		}
		if seenIntent[c.suggestion.Intent] {
			continue
		}
		seenIntent[c.suggestion.Intent] = true
		out = append(out, c.suggestion)
	}
	return out
}

/* ── Signal helpers ─────────────────────────────────────────────────────── */

// maxTiebreak bounds the count half of a signal, so a very large organization
// cannot let a tie-break spill into the tier above it.
const maxTiebreak = 999

// when scores a reading as "how much does this matter when it is happening at
// all", with the count breaking ties inside a tier.
//
// The obvious formulation — weight × count — is wrong here, and wrong in a way
// that gets worse as an organization grows: a workspace with forty applications
// and one role nobody has applied to would be asked about the forty, because
// forty of anything outscores one of anything else. But the single starved role
// is the finding. Nobody needs to be told there are applications.
//
// So the tier dominates and the count only orders readings within it. `tier` is
// a judgement about the SUBJECT, made once where the intent is declared:
//
//	9  something is at risk and nobody is on it — a role with no applicants,
//	   an interview carrying a flag
//	7  work is queued on a person's decision — unscored candidates, unfinished
//	   drafts, unverified profiles
//	5  a state worth reviewing — a shortlist waiting, a role under-filled,
//	   recent hires
//	3  what exists, as a figure — headcounts, comparisons, trends
//
// A count of zero scores zero whatever the tier, which is what stops a page
// being asked an urgent-sounding question about an empty set.
func when(count, tier int) int {
	if count <= 0 {
		return 0
	}
	if count > maxTiebreak {
		count = maxTiebreak
	}
	return tier*(maxTiebreak+1) + count
}

// atLeastTwo is the count, or zero below two.
//
// A comparison needs something to compare. "Which position has the strongest
// pipeline?" is not a question about a workspace holding one position, and
// "how is each department performing?" is not a question about one department —
// both would answer with a table of a single row, which is the padding
// Highlights exists to refuse.
func atLeastTwo(n int) int {
	if n < 2 {
		return 0
	}
	return n
}