package pipeline

import (
	"fmt"
	"sort"
	"strings"
	"unicode"
)

// cheapgates.go: four cheap, deterministic post-check flaggers on the FINAL chunk text (04-unhappy
// §6/§9, план v3). They are OBSERVABILITY, never hard gates (like the glossary post-check's default
// flagger mode): a hit is recorded in the retrieval-state and surfaced in the report / chapter
// passport, but it never changes a chunk disposition or costs an LLM call. All four are pure and
// deterministic (no time/rand, sorted detail) so a resume re-derives identical counts.
//
//   1. dialogue-dash linter (Rosenthal §47–52): direct speech marked with straight quotes or a
//      hyphen/en-dash instead of the em-dash on a new line, or a chunk mixing the two styles.
//   2. yofikator: inconsistent ё — the SAME word spelled both with ё and with е (Пётр/Петр), or a
//      brief ё-policy (all-ё / all-е) violated.
//   3. translit-interjection blocklist: untranslated JP/EN fillers («ара-ара», «маа», «хмф»,
//      «нани», «ауч», «упс») left in the Russian output (04-unhappy §9); per-project allowlist.
//   4. 万/億 magnitude gate: a CJK myriad/hundred-million magnitude in the source whose order is not
//      represented on the Russian side (三万 → «три миллиона» is a 100× error, 04-unhappy §9).
//
// FALSE POSITIVES are the main risk (quotations, stylization, homographs), so each rule is tuned
// for PRECISION over recall: it fires only on a high-confidence signal and stays silent on the
// ambiguous middle. The unit tests assert both firing AND non-firing.

// cheapGateVersion versions the rules above. It is folded into the job snapshot (like
// classifierVersion): editing any rule is a loud --resnapshot, so the reported style-flag counts
// never shift silently between runs under the same snapshot. [D15.2 note: this is a VERDICT
// version — once content-addressed resume lands it moves to verdictSnapshotID and a rule edit
// re-classifies free instead of re-paying the book.]
//
// v2 (D20.4, пакет №3) closes three adversarial-review false positives, so the bump is LOUD by
// design (counts shift): (1) a chevron CITATION at line start no longer counts as dialogue-style
// mixing — only the «…», — attribution shape does; (2) a source 万/億 magnitude is no longer
// false-flagged against a STRAY output integer (a year, a count) — only a mismatching magnitude
// WORD triggers, bare integers can merely confirm; (3) same mechanism covers a 万-in-a-name +
// unrelated output number. No live book has run under v1 (D18 acceptance pending), so the re-pin is free.
//
// v3 (WS5, R4) adds the defect-class checkers DC1 (时辰 double-hour units), DC2 (千万/数十万 magnitude
// scale) and DC6 (register negative-list — the zh-ru pack, checkers_zh_ru.go). They are observability
// (never a disposition), tuned precision-over-recall; the bump is a loud --resnapshot as the discipline
// requires (a rule/pack edit shifts recorded counts). They fire 0 on a non-zh source / non-register text.
const cheapGateVersion = "cheapgate-v3-dc-checkers"

// cheapGateConfig carries the brief-derived knobs: the ё-policy and the per-project allowlist of
// surfaces that look like a blocklisted interjection but are legitimate here (e.g. a character
// named «Ара»). Both come from book.yaml.
type cheapGateConfig struct {
	yoPolicy  string          // "auto" (inconsistency only) | "all-yo" | "all-e"
	allowlist map[string]bool // lower-cased surfaces exempt from the interjection blocklist
	// regressionEnabled turns on the post-reflow regression guard (D38, regressionguard.go): an
	// OPT-IN observability flagger (draft→final length collapse + number drift) folded into this
	// result. Off → the two regression fields stay 0 and the output is byte-identical to before.
	regressionEnabled bool
}

// cheapGateResult is the per-chunk outcome: a count per flagger plus human-readable detail lines
// (deterministic order) for the report. total() is what the passport surfaces.
type cheapGateResult struct {
	DialogueDash    int `json:"dialogue_dash,omitempty"`
	YoInconsistent  int `json:"yo,omitempty"`
	TranslitInterj  int `json:"translit_interj,omitempty"`
	NumberMagnitude int `json:"number_magnitude,omitempty"`
	// LengthCollapse / NumberDrift are the opt-in post-reflow regression guard (D38,
	// regressionguard.go), folded into this observability result. They stay 0 unless
	// cfg.regressionEnabled, so a book that does not enable the guard serialises identically.
	LengthCollapse int `json:"length_collapse,omitempty"`
	NumberDrift    int `json:"number_drift,omitempty"`
	// DC1TimeUnits / DC2Magnitude / DC6Register are the WS5 defect-class checkers (checkers_zh_ru.go),
	// observability like the others. Zero on a non-zh source / non-register final (the golden fixture).
	DC1TimeUnits int      `json:"dc1_time_units,omitempty"`
	DC2Magnitude int      `json:"dc2_magnitude,omitempty"`
	DC6Register  int      `json:"dc6_register,omitempty"`
	Detail       []string `json:"detail,omitempty"`
}

func (c cheapGateResult) total() int {
	return c.DialogueDash + c.YoInconsistent + c.TranslitInterj + c.NumberMagnitude + c.LengthCollapse + c.NumberDrift +
		c.DC1TimeUnits + c.DC2Magnitude + c.DC6Register
}

// runCheapGates runs the four always-on style flaggers over one chunk's source and FINAL text, plus
// (opt-in) the draft→final regression guard. `draft` is the first-stage translator output (== final
// when there is no distinct reflow stage, so the guard then trivially never fires).
func runCheapGates(source, draft, final string, cfg cheapGateConfig) cheapGateResult {
	var r cheapGateResult
	n, det := lintDialogueDash(final)
	r.DialogueDash, r.Detail = n, append(r.Detail, det...)
	n, det = lintYofikation(final, cfg.yoPolicy)
	r.YoInconsistent = n
	r.Detail = append(r.Detail, det...)
	n, det = lintTranslitInterjections(final, cfg.allowlist)
	r.TranslitInterj = n
	r.Detail = append(r.Detail, det...)
	n, det = lintNumberMagnitude(source, final)
	r.NumberMagnitude = n
	r.Detail = append(r.Detail, det...)
	// WS5 defect-class checkers (DC1/DC2/DC6, checkers_zh_ru.go) — src↔target observability flaggers.
	n, det = lintTimeUnits(source, final)
	r.DC1TimeUnits = n
	r.Detail = append(r.Detail, det...)
	n, det = lintMagnitudeScale(source, final)
	r.DC2Magnitude = n
	r.Detail = append(r.Detail, det...)
	n, det = lintRegisterLexicon(final)
	r.DC6Register = n
	r.Detail = append(r.Detail, det...)
	if cfg.regressionEnabled {
		rg := runRegressionGuard(draft, final)
		r.LengthCollapse = rg.LengthCollapse
		r.NumberDrift = rg.NumberDrift
		r.Detail = append(r.Detail, rg.Detail...)
	}
	return r
}

// --- 1. dialogue-dash linter ----------------------------------------------------

// lintDialogueDash flags direct-speech lines opened with the wrong marker. Russian direct speech
// takes an EM-dash «—» at the line start; MTL output leaves a straight ASCII quote or a plain
// hyphen/en-dash. It fires per offending line, and additionally when a chunk MIXES em-dash speech
// with chevron-quote «…» speech (a within-chapter style clash). Precision guards: a hyphen only
// counts as a mis-set dash when followed by a space and a letter (so a hyphenated word wrap or a
// «- 1» list item does not fire); chevron lines count only under mixing (a chunk that uses «…» for
// speech throughout may be a deliberate style, but mixing it with dashes is an inconsistency).
func lintDialogueDash(text string) (int, []string) {
	var emDash, hyphenLike, chevronSpeech int
	var detail []string
	for _, line := range strings.Split(text, "\n") {
		t := strings.TrimLeft(line, " \t ")
		rs := []rune(t)
		if len(rs) == 0 {
			continue
		}
		switch rs[0] {
		case '—': // em-dash: the correct Russian dialogue marker — count only true speech shape
			if dialogueShape(rs[1:]) { // «— 15 минут спустя» (dash+space+digit, a scene break) is NOT dialogue (self-review)
				emDash++
			}
		case '"': // straight ASCII quote leading a line → Russian typography never uses these → MTL artifact
			if quoteShape(rs[1:]) {
				detail = append(detail, "прямая речь открыта прямой кавычкой \" вместо тире: "+preview(t))
				hyphenLike++ // counted in the offending total
			}
		case '-', '–': // hyphen / en-dash where an em-dash belongs
			if dialogueShape(rs[1:]) {
				detail = append(detail, "реплика через дефис/короткое тире вместо длинного «—»: "+preview(t))
				hyphenLike++
			}
		case '«': // chevron-led line counts toward mixing ONLY as chevron DIALOGUE (not a citation/title)
			if chevronSpeechShape(rs) { // D20.4 FP: «-цитата в начале строки больше не считается смешением
				chevronSpeech++
			}
		}
	}
	n := hyphenLike
	if emDash > 0 && chevronSpeech > 0 {
		n += chevronSpeech
		detail = append(detail, fmt.Sprintf("смешение стилей прямой речи в чанке: %d реплик через «—» и %d через «…»", emDash, chevronSpeech))
	}
	return n, detail
}

// chevronSpeechShape reports whether a chevron-led line is a chevron DIALOGUE turn rather than a
// citation, title or quoted term (which also open with «). The high-precision signal is the Russian
// dialogue-attribution join: a closing » directly followed by a comma, then (spaces) an em/en/hyphen
// dash — «Реплика», — сказал он. A quotation/definition uses «X» — … (a dash WITHOUT the comma) or
// ends mid-sentence, so it does NOT match, which kills the D20.4 false positive «-цитата с начала
// строки как «смешение стилей». It deliberately MISSES exclamatory «Реплика!» — and unattributed
// «Реплика.» chevron dialogue (precision over recall — the gate header's stated bias).
func chevronSpeechShape(rs []rune) bool {
	i := 1 // rs[0] is '«'
	for i < len(rs) && (rs[i] == ' ' || rs[i] == ' ') {
		i++
	}
	if i >= len(rs) || !unicode.IsLetter(rs[i]) {
		return false // «» empty or «123…» — not spoken content
	}
	for ; i < len(rs); i++ {
		if rs[i] != '»' {
			continue
		}
		j := i + 1
		if j >= len(rs) || rs[j] != ',' { // the attribution comma must sit right after the closing »
			continue
		}
		j++
		for j < len(rs) && (rs[j] == ' ' || rs[j] == ' ') {
			j++
		}
		if j < len(rs) && (rs[j] == '—' || rs[j] == '–' || rs[j] == '-') {
			return true
		}
	}
	return false
}

// dialogueShape reports whether the runes after a leading marker look like spoken text: an optional
// space then a letter. It filters out non-dialogue leading dashes (word wraps, «-1», bare marks).
func dialogueShape(after []rune) bool {
	i := 0
	for i < len(after) && (after[i] == ' ' || after[i] == ' ') {
		i++
	}
	if i == 0 {
		return false // a marker glued to the next glyph (a hyphenated fragment), not «— реплика»
	}
	return i < len(after) && unicode.IsLetter(after[i])
}

// quoteShape reports whether the runes after a leading quote look like spoken text: an OPTIONAL
// space then a letter («"Привет»). Unlike a dash, a quote sits directly on the first word, so no
// space is required.
func quoteShape(after []rune) bool {
	i := 0
	for i < len(after) && (after[i] == ' ' || after[i] == ' ') {
		i++
	}
	return i < len(after) && unicode.IsLetter(after[i])
}

// --- 2. yofikator ---------------------------------------------------------------

// yoHomographEForms are е-spellings that are DISTINCT words from their ё-counterpart (все≠всё,
// небо≠нёбо, берет≠берёт, осел≠осёл, …). The inconsistency rule below would otherwise false-flag
// «все»+«всё» as one word spelled two ways. Expanded (self-review major) to cover the frequent
// distinct-word pairs and their common inflections; still not exhaustive — full disambiguation
// needs a ё-dictionary (deferred, B-tier). Names — the primary target (Пётр/Петр) — are never
// homographs, so they are always caught regardless.
var yoHomographEForms = map[string]bool{
	"все": true, "всех": true, "всем": true, "всеми": true,
	"небо": true, "небом": true,
	"узнаем": true, "узнаете": true, "узнает": true,
	"падеж": true, "падежа": true,
	"совершенный": true, "совершенное": true, "совершенная": true, "совершенно": true, "совершенны": true,
	"чем": true, "тем": true, "тема": true, "теме": true, "темы": true,
	"берет": true, "берете": true, "берета": true,
	"осел": true, "осла": true, "ослы": true, "ослов": true,
	"мел": true, "мела": true,
	"лен": true, "лена": true,
	"нес": true, "несем": true, "несет": true,
	"вел": true, "ведет": true, "ведем": true,
}

// lintYofikation flags inconsistent ё. Default ("auto"): the same word appears BOTH with ё and, as
// a separate token, with its exact ё→е form (Пётр/Петр) — excluding the homograph traps above.
// Policy "all-e": any ё present is a violation (the project wants no ё). Policy "all-yo": an е-form
// of a word that ALSO appears somewhere with ё is flagged (the partial-ёфикация case), same signal
// as auto — full "every word that SHOULD have ё" enforcement needs a ё-dictionary (deferred, B-tier).
func lintYofikation(text, policy string) (int, []string) {
	words := tokenizeCyrillic(text)
	if policy == "all-e" {
		seen := map[string]bool{}
		var det []string
		n := 0
		for _, w := range words {
			if strings.ContainsRune(w, 'ё') && !seen[w] {
				seen[w] = true
				n++
				det = append(det, "ё при политике all-e: "+w)
			}
		}
		sort.Strings(det)
		return n, det
	}
	// auto / all-yo: detect a word present in BOTH its ё-form and its е-form.
	present := map[string]bool{}
	for _, w := range words {
		present[w] = true
	}
	seenPair := map[string]bool{}
	var det []string
	n := 0
	for _, w := range words {
		if !strings.ContainsRune(w, 'ё') {
			continue
		}
		eForm := strings.ReplaceAll(w, "ё", "е")
		if eForm == w || yoHomographEForms[eForm] {
			continue // no ё, or a distinct-word homograph (все/всё) — not an inconsistency
		}
		if present[eForm] && !seenPair[w] {
			seenPair[w] = true
			n++
			det = append(det, fmt.Sprintf("непоследовательная ё: %q и %q", w, eForm))
		}
	}
	sort.Strings(det)
	return n, det
}

// tokenizeCyrillic lower-cases and splits text into Cyrillic word tokens (ё kept distinct from е).
func tokenizeCyrillic(text string) []string {
	var words []string
	var b strings.Builder
	flush := func() {
		if b.Len() > 0 {
			words = append(words, b.String())
			b.Reset()
		}
	}
	for _, r := range strings.ToLower(text) {
		if unicode.Is(unicode.Cyrillic, r) {
			b.WriteRune(r)
		} else {
			flush()
		}
	}
	flush()
	return words
}

// --- 3. translit-interjection blocklist -----------------------------------------

// translitInterjections is the starter blocklist (04-unhappy §9): JP/EN fillers that must be
// translated/adapted, not transliterated. Only surfaces that are NOT ordinary Russian words are
// listed (self-review majors): «ара» (a macaw, also a name) and «уму» (dative of «ум») were removed
// as high-false-positive collisions; «ара-ара» (the reduplicated JP filler) stays. A residual name
// collision is handled by the per-project allowlist. Lower-cased.
//
// NOTE (D20.4): only the EXACT hyphenated reduplications enumerated here fire. Other reduplicated
// fillers a translit-leak might emit («уху-уху», «эхе-хе», «ня-ня», «фу-фу») are NOT caught — a
// generic «X-X»-reduplication rule was rejected as too false-positive-prone (legitimate Russian
// reduplications: «еле-еле», «чуть-чуть», «крепко-накрепко»). Extend this list per corpus finding
// rather than by heuristic; the residual leak is an accepted recall gap (precision over recall).
var translitInterjections = []string{
	"ара-ара", "маа", "хмф", "нани", "ауч", "упс", "кья", "десу",
}

// lintTranslitInterjections counts whole-word (letter-bounded, case-insensitive) occurrences of a
// blocklisted interjection in the output, minus any surface on the per-project allowlist. Whole-word
// matching keeps «ара» from firing inside «характер»; the allowlist exempts legitimate uses.
func lintTranslitInterjections(text string, allowlist map[string]bool) (int, []string) {
	low := []rune(strings.ToLower(text))
	counts := map[string]int{}
	for _, interj := range translitInterjections {
		if allowlist[interj] {
			continue
		}
		f := []rune(interj)
		for i := 0; i+len(f) <= len(low); i++ {
			if !runesEqual(low[i:i+len(f)], f) {
				continue
			}
			if (i == 0 || !isWordRune(low[i-1])) && (i+len(f) == len(low) || !isWordRune(low[i+len(f)])) {
				counts[interj]++
			}
		}
	}
	n := 0
	surfaces := make([]string, 0, len(counts))
	for k, c := range counts {
		n += c
		surfaces = append(surfaces, k)
	}
	sort.Strings(surfaces)
	var det []string
	for _, s := range surfaces {
		det = append(det, fmt.Sprintf("непереведённое междометие %q ×%d", s, counts[s]))
	}
	return n, det
}

// isWordRune reports whether r is part of a word for boundary checks (letter or a hyphen inside a
// compound interjection like «ара-ара»). The hyphen inclusion means «ара-ара» matches as one unit
// and its inner «ара» does not double-count against a hyphen boundary.
func isWordRune(r rune) bool {
	return unicode.IsLetter(r) || r == '-'
}

// --- 4. 万/億 magnitude gate -----------------------------------------------------

// lintNumberMagnitude flags a source CJK myriad/hundred-million magnitude whose ORDER of magnitude
// is not represented on the Russian side (04-unhappy §9: 三万 → «три миллиона» is a 100× error). It
// parses each CJK numeral RUN that carries a big marker (万/萬/億/亿/兆) into an order of magnitude,
// then checks the output's magnitude coverage (Russian magnitude words expanded to a [base,base+2]
// range for their possible multiplier, plus Arabic-number orders). It fires only when the source's
// TOP order is outside every output range — a conservative, multiplier-tolerant signal that leaves
// 三億→«триста миллионов» (8 within миллион's [6,8]) silent while catching 三万→«три миллиона».
func lintNumberMagnitude(source, final string) (int, []string) {
	srcOrders := cjkMagnitudeOrders(source)
	if len(srcOrders) == 0 {
		return 0, nil
	}
	maxSrc := 0
	for _, o := range srcOrders {
		if o > maxSrc {
			maxSrc = o
		}
	}
	if maxSrc < 4 { // only gate on 万+ magnitudes (the 万/億 concern)
		return 0, nil
	}
	// A bare output integer (a year, a count, a page number) may CONFIRM the magnitude but must never
	// TRIGGER a flag: an unrelated number of a different order is not evidence the 万/億 was
	// mistranslated (D20.4 FPs: «万 в составе имени + постороннее число в выводе», «перефраз магнитуды +
	// год»). So an Arabic figure of the RIGHT order suppresses; a mismatching one is ignored.
	for _, o := range arabicNumberOrders(final) {
		if o == maxSrc {
			return 0, nil // an Arabic figure of the source order confirms coverage (30000 for 三万)
		}
	}
	wordRanges := magnitudeWordRanges(final)
	for _, rg := range wordRanges {
		if maxSrc >= rg[0] && maxSrc <= rg[1] {
			return 0, nil // a magnitude WORD covers the source order (三万 → «тридцать тысяч»)
		}
	}
	// Only a mismatching magnitude WORD is evidence of a разряд error (三万 → «три миллиона»). Absent
	// any magnitude word, stay silent: the magnitude was rephrased as prose, or the number in the
	// output is unrelated (the two D20.4 FPs above). Accepted recall cost: a dropped-magnitude error
	// rendered as a BARE integer of a smaller order (三万 → «300») is now also silent — indistinguishable
	// offline from an unrelated stray integer without number alignment (Ф2). Precision over recall.
	if len(wordRanges) == 0 {
		return 0, nil
	}
	return 1, []string{fmt.Sprintf("разряд источника 10^%d (万/億) не отражён в порядках величин перевода — возможна ошибка разряда (напр. 三万→«три миллиона»)", maxSrc)}
}

// cjkNumeralRunes are the characters that can form a CJK numeral expression (digits, small units,
// big markers). A maximal run of these is one candidate number.
var cjkNumeralRunes = map[rune]bool{}

func init() {
	for _, r := range "0123456789〇零一二三四五六七八九十百千两兩万萬億亿兆" {
		cjkNumeralRunes[r] = true
	}
}

// cjkMagnitudeOrders returns the base-10 order of every CJK numeral run in text that contains a big
// marker (万/億/兆). Runs without a big marker are ignored (the gate is about myriad-scale разряды).
func cjkMagnitudeOrders(text string) []int {
	var orders []int
	rs := []rune(text)
	for i := 0; i < len(rs); {
		if !cjkNumeralRunes[rs[i]] {
			i++
			continue
		}
		j := i
		for j < len(rs) && cjkNumeralRunes[rs[j]] {
			j++
		}
		run := string(rs[i:j])
		// A run counts only when it carries a big marker AND has an explicit DIGIT coefficient before
		// it (self-review major): this excludes the common web-novel IDIOMS that are not magnitudes —
		// 万一 (in case), 万分 (extremely), 万物 (all things), 千万 (by all means), 亿万 (myriads) — where 万/億
		// is not preceded by a digit. It also drops bare-unit magnitudes (十万/百万) — an accepted recall
		// trade for not false-flagging the far more frequent idioms.
		if strings.ContainsAny(run, "万萬億亿兆") && hasDigitBeforeBigMarker(run) {
			if v, ok := parseCJKNumber(run); ok && v > 0 {
				orders = append(orders, orderOf(v))
			}
		}
		i = j
	}
	return orders
}

// hasDigitBeforeBigMarker reports whether a digit (一-九 / 两 / 0-9) appears before the FIRST big
// marker (万/億/兆) in the run — the signature of a real magnitude expression (三万) vs an idiom (万一).
func hasDigitBeforeBigMarker(run string) bool {
	for _, r := range run {
		if strings.ContainsRune("万萬億亿兆", r) {
			return false // hit a big marker with no digit before it → idiom / bare unit
		}
		if (r >= '0' && r <= '9') || strings.ContainsRune("一二三四五六七八九两兩", r) {
			return true
		}
	}
	return false
}

// parseCJKNumber parses a CJK numeral expression (mixed with Arabic digits) into its integer value.
// Standard section algorithm: small units (十百千) scale the pending coefficient into the current
// <10^4 section; big units (万億兆) flush the section times the big unit into the total. Returns
// ok=false on a shape it cannot parse (conservative — an unparseable run does not flag).
func parseCJKNumber(s string) (int64, bool) {
	var total, section, cur int64
	sawBig := false
	for _, r := range s {
		switch {
		case r >= '0' && r <= '9':
			cur = cur*10 + int64(r-'0')
		case r == '〇' || r == '零':
			cur = cur * 10
		default:
			if d, ok := cjkDigit(r); ok {
				cur = cur*10 + d // positional accumulation (一二→12), matching the Arabic-digit branch (self-review)
				continue
			}
			if u, ok := cjkSmallUnit(r); ok {
				if cur == 0 {
					cur = 1
				}
				section += cur * u
				cur = 0
				continue
			}
			if u, ok := cjkBigUnit(r); ok {
				sawBig = true
				section += cur
				if section == 0 {
					section = 1
				}
				total += section * u
				section = 0
				cur = 0
				continue
			}
			return 0, false // an unexpected rune
		}
	}
	if !sawBig {
		return 0, false // no 万/億/兆 → not a magnitude expression this gate cares about
	}
	return total + section + cur, true
}

func cjkDigit(r rune) (int64, bool) {
	switch r {
	case '一':
		return 1, true
	case '二', '两', '兩':
		return 2, true
	case '三':
		return 3, true
	case '四':
		return 4, true
	case '五':
		return 5, true
	case '六':
		return 6, true
	case '七':
		return 7, true
	case '八':
		return 8, true
	case '九':
		return 9, true
	}
	return 0, false
}

func cjkSmallUnit(r rune) (int64, bool) {
	switch r {
	case '十':
		return 10, true
	case '百':
		return 100, true
	case '千':
		return 1000, true
	}
	return 0, false
}

func cjkBigUnit(r rune) (int64, bool) {
	switch r {
	case '万', '萬':
		return 10000, true
	case '億', '亿':
		return 100000000, true
	case '兆':
		return 1000000000000, true
	}
	return 0, false
}

func orderOf(v int64) int {
	o := 0
	for v >= 10 {
		v /= 10
		o++
	}
	return o
}

// magnitudeWordRanges returns the covered [minOrder,maxOrder] ranges implied by Russian magnitude
// WORDS in the output. A word covers [base, base+2] because an unseen multiplier can lift it up to
// two orders (триста миллионов = 3·10^8, base 6 → order 8). Arabic integers are handled separately
// by the caller (they may only CONFIRM coverage, never trigger a mismatch — D20.4), so they are NOT
// folded in here.
func magnitudeWordRanges(text string) [][2]int {
	low := strings.ToLower(text)
	var ranges [][2]int
	for stem, base := range map[string]int{"тысяч": 3, "миллион": 6, "миллиард": 9, "триллион": 12} {
		if strings.Contains(low, stem) {
			ranges = append(ranges, [2]int{base, base + 2})
		}
	}
	return ranges
}

// arabicNumberOrders returns the order of each Arabic integer in text, stitching grouping
// separators (space / NBSP / comma) between runs of exactly three digits so "30 000" reads as one
// 5-digit number, not "30" and "000".
func arabicNumberOrders(text string) []int {
	rs := []rune(text)
	var orders []int
	for i := 0; i < len(rs); {
		if !isASCIIDigit(rs[i]) {
			i++
			continue
		}
		// Leading group.
		j := i
		for j < len(rs) && isASCIIDigit(rs[j]) {
			j++
		}
		digits := j - i
		// Stitch " ddd" / ",ddd" groups.
		for j < len(rs) {
			if (rs[j] == ' ' || rs[j] == ' ' || rs[j] == ',') && j+3 < len(rs)+1 {
				k := j + 1
				g := 0
				for k < len(rs) && isASCIIDigit(rs[k]) {
					k++
					g++
				}
				if g == 3 {
					digits += 3
					j = k
					continue
				}
			}
			break
		}
		orders = append(orders, digits-1)
		i = j
	}
	return orders
}

func isASCIIDigit(r rune) bool { return r >= '0' && r <= '9' }

// preview trims a long line for the human detail (deterministic).
func preview(s string) string {
	rs := []rune(s)
	if len(rs) > 48 {
		return string(rs[:48]) + "…"
	}
	return s
}