/internal/search/rerank/query_kind.go

package rerank

import (
	"strings"
	"unicode"
)

// QueryClass is the detected shape of a search query. The class tunes
// the bm25 ↔ semantic blend in two places: the per-signal weight
// scaling inside Pipeline.Rerank, and the α value of the hybrid
// alpha-fusion path in internal/search/hybrid.go. Identifier and path
// queries lean on exact-token (BM25) evidence; natural-language
// queries give the semantic channel its full weight.
type QueryClass int

const (
	// QueryClassUnknown is the zero value — "not yet classified". A
	// caller that leaves it unset lets Pipeline.Rerank auto-detect.
	QueryClassUnknown QueryClass = iota
	// QueryClassSymbol is a single identifier-shaped token: a symbol
	// or API name (validateToken, HTTPServer, pkg.Type). Exact-token
	// BM25 evidence dominates.
	QueryClassSymbol
	// QueryClassConcept is a natural-language description of intent
	// ("how does auth refresh", "validate user token"). The semantic
	// channel earns its keep here. This is the neutral baseline class.
	QueryClassConcept
	// QueryClassPath is a file-path-shaped query (internal/auth/token.go,
	// auth/handler). Path components are exact tokens and the semantic
	// channel is near-useless, so BM25 leans hardest of all classes.
	QueryClassPath
	// QueryClassSignature is a type- or function-signature fragment
	// ("func(ctx) error", "(string) bool"). Structural keywords carry
	// the signal: BM25-leaning but less extreme than a bare path.
	QueryClassSignature
	// QueryClassKeywordSoup is a degenerate boolean / OR-soup query
	// ("A OR B OR 'no access'") -- a list of disjuncts rather than a
	// description of intent. It defeats ordinary retrieval, so the
	// search handler treats it specially: LLM expansion is suppressed
	// and the soup is split into per-disjunct BM25 fetches. Detected
	// by LooksLikeKeywordSoup; a caller may also pin it via the
	// search_symbols query_class argument.
	QueryClassKeywordSoup
)

// String returns the lowercase class name used by the search_symbols
// query_class argument and surfaced back on the response.
func (q QueryClass) String() string {
	switch q {
	case QueryClassSymbol:
		return "symbol"
	case QueryClassConcept:
		return "concept"
	case QueryClassPath:
		return "path"
	case QueryClassSignature:
		return "signature"
	case QueryClassKeywordSoup:
		return "keyword_soup"
	default:
		return "unknown"
	}
}

// ParseQueryClass maps the search_symbols query_class argument to a
// QueryClass. "" and "auto" map to QueryClassUnknown — the signal to
// auto-detect. The bool is false for an unrecognised value so the
// caller can reject it with a clear error.
func ParseQueryClass(s string) (QueryClass, bool) {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case "", "auto":
		return QueryClassUnknown, true
	case "symbol":
		return QueryClassSymbol, true
	case "concept":
		return QueryClassConcept, true
	case "path":
		return QueryClassPath, true
	case "signature":
		return QueryClassSignature, true
	case "keyword_soup", "soup":
		return QueryClassKeywordSoup, true
	default:
		return QueryClassUnknown, false
	}
}

// Hybrid retrieval blend weights for the BM25 ↔ semantic mix used by
// the alpha-fusion path in internal/search/hybrid.go. Lower α leans
// toward BM25 (identifier-style queries where exact tokens dominate);
// higher α gives semantic search more weight (natural-language
// concept queries where wording varies).
//
// The values mirror the empirical sweet spot found by hybrid-search
// benchmarks (HyDE / RAGAS papers): symbol queries benefit from a
// strong BM25 prior; NL queries benefit from a near-balanced blend.
const (
	// AlphaSymbol weights BM25 vs semantic for identifier-shaped
	// queries (CamelCase, snake_case, namespaced, all-caps). The
	// blend favors BM25 because exact-token matches are the most
	// reliable signal for code identifiers.
	AlphaSymbol = 0.3
	// AlphaNL weights BM25 vs semantic for natural-language queries
	// ("validate user token", "auth middleware"). Both channels
	// contribute roughly equally — semantic catches synonymous
	// wording, BM25 catches literal keywords.
	AlphaNL = 0.5
	// AlphaPath weights BM25 vs semantic for file-path queries. The
	// most BM25-heavy blend: path components are exact tokens and the
	// semantic channel mostly contributes noise.
	AlphaPath = 0.15
	// AlphaSignature weights BM25 vs semantic for type/function-
	// signature fragments. BM25-leaning — structural keywords are
	// literal — but less extreme than a bare path.
	AlphaSignature = 0.35
)

// IsSymbolQuery returns true when the query looks like a code
// identifier rather than a natural-language description. The
// classification drives:
//
//   - the definition-keyword bias signal (only fires for symbol
//     queries — boosting `class Foo` for the query "Foo")
//   - the auto-adaptive α blend in hybrid retrieval (symbol queries
//     get AlphaSymbol, NL queries get AlphaNL)
//
// Heuristic: the query is a single token (no whitespace) that carries
// at least one structural marker — CamelCase, snake_case, dotted /
// double-colon / slash namespace qualifier, or an all-uppercase
// shape. A multi-word query (containing spaces) is always treated as
// NL even if individual tokens look identifier-shaped — the user is
// describing intent, not naming a symbol. Empty or whitespace-only
// queries return false.
func IsSymbolQuery(query string) bool {
	q := strings.TrimSpace(query)
	if q == "" {
		return false
	}
	// Multi-token queries are natural-language.
	for _, r := range q {
		if unicode.IsSpace(r) {
			return false
		}
	}
	// Namespace qualifiers: pkg.Type, Module::Symbol, dir/file::Sym,
	// path/to/foo.go. Any of these is a strong symbol indicator.
	for _, sep := range []string{"::", ".", "/", "\\"} {
		if strings.Contains(q, sep) && hasIdentifierChar(q) {
			return true
		}
	}
	// Snake-case identifier: at least one underscore between letters
	// or digits and no whitespace already established above.
	if strings.Contains(q, "_") && hasIdentifierChar(q) {
		return true
	}
	// CamelCase / PascalCase: lowercase→uppercase transition or
	// uppercase→lowercase after another uppercase (e.g. HTTPServer).
	var prev rune
	for i, r := range q {
		if i > 0 {
			if unicode.IsUpper(r) && unicode.IsLower(prev) {
				return true
			}
			if unicode.IsLower(r) && unicode.IsUpper(prev) {
				return true
			}
		}
		prev = r
	}
	// All-uppercase token of length >= 2 (e.g. URL, JWT, API). Single
	// uppercase letter is too ambiguous to flag.
	if len(q) >= 2 {
		allUpper := true
		hasLetter := false
		for _, r := range q {
			if unicode.IsLetter(r) {
				hasLetter = true
				if !unicode.IsUpper(r) {
					allUpper = false
					break
				}
			}
		}
		if hasLetter && allUpper {
			return true
		}
	}
	return false
}

// hasIdentifierChar reports whether the string contains at least one
// letter or digit. Used by IsSymbolQuery to avoid classifying punct-
// only strings ("::", ".", "/") as symbol queries.
func hasIdentifierChar(s string) bool {
	for _, r := range s {
		if unicode.IsLetter(r) || unicode.IsDigit(r) {
			return true
		}
	}
	return false
}

// ClassifyQuery detects the QueryClass of a query with cheap
// structural heuristics — no LLM, no graph walk. Checks run in
// precedence order: signature markers (parentheses, arrows) are the
// most distinctive, then a path-separated single token, then the
// identifier-shape rubric IsSymbolQuery uses, and finally the
// natural-language default. An empty query classifies as concept.
func ClassifyQuery(query string) QueryClass {
	q := strings.TrimSpace(query)
	if q == "" {
		return QueryClassConcept
	}
	// Keyword-soup detection runs first: a degenerate boolean OR-list
	// is its own class regardless of what its disjuncts look like.
	if soup, _ := LooksLikeKeywordSoup(q); soup {
		return QueryClassKeywordSoup
	}
	if looksLikeSignature(q) {
		return QueryClassSignature
	}
	if looksLikePath(q) {
		return QueryClassPath
	}
	if IsSymbolQuery(q) {
		return QueryClassSymbol
	}
	return QueryClassConcept
}

// looksLikeSignature reports whether the query carries an unambiguous
// type/function-signature marker — a parenthesis or a Go/JS-style
// return or lambda arrow. Natural-language queries virtually never do.
func looksLikeSignature(q string) bool {
	if strings.ContainsAny(q, "()") {
		return true
	}
	return strings.Contains(q, "->") || strings.Contains(q, "=>")
}

// looksLikePath reports whether the query is a single whitespace-free
// token carrying a directory separator — "internal/auth/token.go",
// "auth/handler". A "::" or bare "." qualifier is NOT a path: those
// stay in the symbol class.
func looksLikePath(q string) bool {
	if strings.ContainsAny(q, " \t\n") {
		return false
	}
	if !strings.ContainsAny(q, "/\\") {
		return false
	}
	return hasIdentifierChar(q)
}

// AlphaFor returns the recommended α blend value for the query. It
// scores the query shape on a continuous identifier↔natural-language
// axis (see AlphaForContinuous) rather than snapping to a discrete
// class bucket, so a half-identifier query like "validateToken
// handler" lands between AlphaSymbol and AlphaNL instead of jumping a
// whole tier. The discrete AlphaForClass remains for callers that
// have already classified.
func AlphaFor(query string) float64 {
	return AlphaForContinuous(query)
}

// queryStopwords are the relationship / question words that mark a
// query as natural-language intent rather than an identifier list.
// Deliberately excludes code-ish verbs (get/set/find/parse) which are
// real symbol-name fragments. Kept local to rerank so the package
// stays free of an internal/search import cycle.
var queryStopwords = map[string]struct{}{
	"how": {}, "does": {}, "do": {}, "the": {}, "a": {}, "an": {}, "of": {},
	"to": {}, "is": {}, "are": {}, "in": {}, "on": {}, "for": {}, "and": {},
	"or": {}, "with": {}, "where": {}, "what": {}, "when": {}, "why": {},
	"which": {}, "this": {}, "that": {}, "from": {}, "by": {}, "as": {},
	"about": {}, "into": {}, "via": {},
}

// AlphaForContinuous returns a continuous α blend in [AlphaPath,
// AlphaNL] derived from the query's shape rather than a discrete
// class. Hard structural shapes (signature, path, keyword-soup) still
// pin to their class α — they are unambiguous and the discrete value
// is already correct, and keyword-soup carries non-α side effects
// (LLM suppression, per-disjunct fetch) that must stay class-based.
// Everything else interpolates between AlphaSymbol (a single
// identifier-shaped token) and AlphaNL (multi-word prose) by how
// identifier-like the query reads.
//
// The extreme points match the discrete table — AlphaForContinuous of
// a bare CamelCase token equals AlphaSymbol and of a prose phrase
// equals AlphaNL — so it is a strict refinement, not a re-tuning.
func AlphaForContinuous(query string) float64 {
	q := strings.TrimSpace(query)
	if q == "" {
		return AlphaNL
	}
	if soup, _ := LooksLikeKeywordSoup(q); soup {
		return AlphaForClass(QueryClassKeywordSoup)
	}
	if looksLikeSignature(q) {
		return AlphaSignature
	}
	if looksLikePath(q) {
		return AlphaPath
	}
	// score in [0,1]: 1 == fully identifier-shaped, 0 == prose.
	score := identifierScore(q)
	// AlphaSymbol < AlphaNL, so a higher identifier score pulls α down
	// toward the BM25-leaning end.
	return AlphaNL + score*(AlphaSymbol-AlphaNL)
}

// identifierScore rates how identifier-like a (non-path, non-signature)
// query is, in [0,1]. A single CamelCase/snake/dotted token scores 1;
// a single plain word or any stopword-heavy phrase scores 0; a mixed
// multi-word query interpolates by the fraction of identifier-shaped
// tokens, discounted by stopword density and a gentle length penalty
// (longer queries read more like prose).
func identifierScore(q string) float64 {
	tokens := strings.Fields(q)
	n := len(tokens)
	if n == 0 {
		return 0
	}
	if n == 1 {
		if IsSymbolQuery(tokens[0]) {
			return 1.0
		}
		return 0
	}
	idCount, stopCount := 0, 0
	for _, t := range tokens {
		if IsSymbolQuery(t) {
			idCount++
		}
		if _, ok := queryStopwords[strings.ToLower(t)]; ok {
			stopCount++
		}
	}
	idFrac := float64(idCount) / float64(n)
	stopFrac := float64(stopCount) / float64(n)
	lengthPenalty := 0.12 * float64(n-2)
	score := idFrac - stopFrac - lengthPenalty
	if score < 0 {
		return 0
	}
	if score > 1 {
		return 1
	}
	return score
}

// AlphaForClass returns the α blend for a known class. The α-fusion
// formula in hybrid.go is `final = (1-α)·text_rrf + α·vector_rrf`, so
// a smaller α leans toward BM25. QueryClassUnknown falls back to the
// natural-language blend.
func AlphaForClass(c QueryClass) float64 {
	switch c {
	case QueryClassSymbol:
		return AlphaSymbol
	case QueryClassPath:
		return AlphaPath
	case QueryClassSignature:
		return AlphaSignature
	case QueryClassKeywordSoup:
		// Soup is split into per-disjunct BM25 fetches and the LLM
		// channel is suppressed -- lean hard on exact-token evidence.
		return AlphaSymbol
	default: // QueryClassConcept, QueryClassUnknown
		return AlphaNL
	}
}

// classWeights holds the per-class scaling applied to the bm25 and
// semantic rerank signals. Every other signal scales by 1.0 — the
// per-class lever tunes only the text-vs-semantic balance and leaves
// the structural and session signals untouched.
type classWeights struct {
	bm25     float64
	semantic float64
	// proximity scales the RWR/PPR centrality signal per class.
	// Concept (natural-language) queries lean hardest on graph
	// proximity — the user is describing intent, so "what is this code
	// structurally about" is the strongest discriminator. Exact
	// identifier / path queries dampen it so a central-but-wrong symbol
	// can't unseat the literal match the user named.
	proximity float64
}

// classWeightTable is the tuned per-class multiplier set. Concept is
// the neutral 1.0/1.0 baseline, so natural-language queries score
// exactly as they did before per-class weighting existed; the
// identifier, path, and signature classes push BM25 up and the
// semantic channel down by amounts that grow with how literal the
// query is.
var classWeightTable = map[QueryClass]classWeights{
	QueryClassConcept:     {bm25: 1.00, semantic: 1.00, proximity: 1.30},
	QueryClassSymbol:      {bm25: 1.20, semantic: 0.65, proximity: 0.55},
	QueryClassPath:        {bm25: 1.25, semantic: 0.45, proximity: 0.40},
	QueryClassSignature:   {bm25: 1.10, semantic: 0.80, proximity: 0.75},
	QueryClassKeywordSoup: {bm25: 1.20, semantic: 0.50, proximity: 0.60},
}

// ClassWeightMultiplier returns the factor applied to a signal's
// configured weight for a given query class. Only the bm25 and
// semantic signals are class-sensitive; every other signal — and an
// unknown class — returns 1.0.
func ClassWeightMultiplier(c QueryClass, signal string) float64 {
	cw, ok := classWeightTable[c]
	if !ok {
		return 1.0
	}
	switch signal {
	case SignalBM25:
		return cw.bm25
	case SignalSemantic, SignalSemanticCosine:
		return cw.semantic
	case SignalProximity:
		if cw.proximity == 0 {
			return 1.0
		}
		return cw.proximity
	default:
		return 1.0
	}
}

// proseWeightTable is the per-signal multiplier applied on top of the
// class / α weighting when Context.ProseMode is set — a documentation
// (prose-section) query. It mirrors the shape of classWeightTable /
// ClassWeightMultiplier but lives on its own lever, independent of
// Alpha, so a docs query gets BOTH its query-shape blend and this
// prose profile.
//
// The profile lifts the two signals that actually discriminate prose
// (bm25 and semantic — a prose section has body text and an embedding,
// little else) and zeroes the code-structural signals that are
// meaningless for a KindDoc node: api_signature and type_signature
// (a prose section has no signature) and definition_bias (no
// definition keyword to match). A signal absent from the table keeps
// its weight unchanged (multiplier 1.0), so the structural / session
// signals that still make sense for prose (recency, feedback,
// file_coherence) are untouched.
var proseWeightTable = map[string]float64{
	SignalBM25:           1.25,
	SignalSemantic:       1.30,
	SignalSemanticCosine: 1.30,
	SignalAPISignature:   0.0,
	SignalTypeSignature:  0.0,
	SignalDefinitionBias: 0.0,
}

// proseWeightMultiplier returns the prose-profile multiplier for a
// signal. Signals not in proseWeightTable return 1.0 (unchanged).
// Applied by Pipeline.Rerank only when Context.ProseMode is set, and
// composed multiplicatively with the class / α multiplier so the two
// levers stay independent.
func proseWeightMultiplier(signal string) float64 {
	if m, ok := proseWeightTable[signal]; ok {
		return m
	}
	return 1.0
}

// continuousClassMultiplier is the continuous analogue of
// ClassWeightMultiplier: it maps a continuous α (as produced by
// AlphaForContinuous) onto the bm25 / semantic weight multipliers,
// interpolating smoothly between the natural-language anchor
// (α=AlphaNL → 1.0/1.0, the neutral baseline) and the most
// BM25-leaning anchor (α=AlphaPath → the path class's 1.25/0.45).
// The endpoints reproduce the discrete classWeightTable exactly, so a
// query that snaps to a class scores as it always did and only the
// in-between queries see the interpolation. Pipeline.Rerank uses this
// in place of ClassWeightMultiplier when Context.Alpha is set.
func continuousClassMultiplier(alpha float64, signal string) float64 {
	a := alpha
	if a < AlphaPath {
		a = AlphaPath
	}
	if a > AlphaNL {
		a = AlphaNL
	}
	// frac: 0 at the NL anchor, 1 at the most BM25-leaning anchor.
	frac := (AlphaNL - a) / (AlphaNL - AlphaPath)
	// The BM25-leaning anchor's multipliers come from the path class,
	// the most exact-token-reliant of the discrete buckets.
	maxBM25 := classWeightTable[QueryClassPath].bm25
	minSem := classWeightTable[QueryClassPath].semantic
	switch signal {
	case SignalBM25:
		return 1.0 + frac*(maxBM25-1.0)
	case SignalSemantic, SignalSemanticCosine:
		return 1.0 - frac*(1.0-minSem)
	case SignalProximity:
		// Interpolate proximity from the concept (NL) anchor down to
		// the path anchor, the mirror of how bm25/semantic move: a
		// natural-language query leans hardest on graph centrality,
		// an exact path/identifier query least.
		nlProx := classWeightTable[QueryClassConcept].proximity
		pathProx := classWeightTable[QueryClassPath].proximity
		return nlProx + frac*(pathProx-nlProx)
	default:
		return 1.0
	}
}