package agent

import (
	"regexp"
	"strings"

	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
)

// finalOutput selects the user-facing answer when the loop reaches a clean
// terminal turn (one with no tool calls).
//
// Normally that terminal turn's text IS the answer: well-behaved models defer
// their answer to the final, tool-free turn. But some models — notably several
// open-weight ones — "front-load" their full answer into an earlier turn that
// ALSO calls a tool (e.g. answer text alongside a citation call), then close
// with a degenerate terminal turn that is not itself the answer. Three shapes
// are recovered from the transcript (zero extra model calls):
//
//   - a trivial back-reference ("(Already answered above.)", "see above", …):
//     the real answer sits earlier, so recover it and DISCARD the worthless
//     closer.
//   - a sources/citations-only addendum ("Sources: [x](…), [y](…)"): the model
//     front-loaded the prose answer and closed with just its citations (the
//     glm-5.2 "cite" pattern behind mort issue #1418). The citations are real,
//     useful content — unlike a back-reference — so recover the prior answer and
//     KEEP the citations, appended below it.
//   - a deferring closer ("Citations are logged. Short version: …", "Done —
//     that's the full chain above. Short version: …"): the model points at the
//     answer it had already written and compresses it into a one-liner (mort
//     run b3cb9ee9 — a 2,089-char answer shrank to a 153-byte closer; mort
//     issue #1611 — a 2,245-char analysis shrank to 220 bytes). The
//     compression is strictly poorer than the front-loaded answer, so recover
//     the prior turn and DISCARD the closer — but only when the prior turn
//     clearly dwarfs it, because unlike a bare back-reference this closer DOES
//     carry answer content (see modeSummary).
//
// The last two shapes share one signal — the terminal DEFERS: it tells us the
// answer is somewhere the user cannot see (pointsAbove, or the bookkeeping
// ack). They differ only in whether the terminal also carries content of its
// own, so a new deferral phrasing added to pointsAbove is covered in both the
// bare and the "+ compression" variant at once.
//
// A citations addendum is tested first and wins over the other two (a short
// terminal can match more than one shape), so its links are never discarded.
// The back-reference test wins over the summary-closer test: a terminal
// matching both ("Citations are logged. As I said above…") carries no answer
// content of its own, so the looser back-ref recovery bar — not the summary
// closer's dwarf ratio — is the right one. When the terminal text stands
// on its own it is returned unchanged; when it is degenerate but nothing
// better can be recovered, it is returned as-is (a compressed answer still
// beats nothing).
//
// msgs must already include the terminal assistant message as its last element
// (the loop appends it before calling this); terminal is that message's text.
func finalOutput(msgs []llm.Message, terminal string) string {
	mode := modeBackRef
	switch {
	case isCitationsOnly(terminal):
		mode = modeCitations
	case isWeakFinal(terminal):
		mode = modeBackRef
	case isSummaryCloser(terminal):
		mode = modeSummary
	default:
		return terminal
	}
	rec, ok := lastSubstantiveAssistantText(msgs, terminal, mode)
	if !ok {
		return terminal
	}
	if mode == modeCitations {
		// Preserve the citations addendum below the recovered answer, unless the
		// recovered turn already carries it (guards against a duplicate sources
		// block when the front-loaded turn included its own citations). The
		// containment test ignores <url> angle-bracket wrappers so a turn that
		// listed the same sources unwrapped still suppresses the duplicate.
		if tail := strings.TrimSpace(terminal); !strings.Contains(stripURLAngles(rec), stripURLAngles(tail)) {
			return rec + "\n\n" + tail
		}
	}
	return rec
}

// stripURLAngles removes the <…> wrappers Discord uses to suppress link embeds,
// so the citations dedup compares URLs regardless of that formatting delta.
func stripURLAngles(s string) string {
	if !strings.ContainsAny(s, "<>") {
		return s
	}
	return strings.NewReplacer("<", "", ">", "").Replace(s)
}

// recoveryMode selects the bar a prior assistant turn must clear to replace
// the terminal turn (see isSubstantiveAnswer) and what finalOutput does with
// the terminal once recovery succeeds.
type recoveryMode int

const (
	// modeBackRef: the terminal is empty or a pure back-reference — worthless
	// on its own, so any real prior answer replaces it and it is discarded.
	modeBackRef recoveryMode = iota
	// modeCitations: the terminal is a sources-only addendum — not a rival
	// answer, so the dwarf ratio is skipped and the addendum is kept, appended
	// below the recovered answer.
	modeCitations
	// modeSummary: the terminal acknowledges the citation round and may carry
	// a short compression of the front-loaded answer. Unlike a back-reference
	// it DOES contain answer content, so it is only replaced when a prior turn
	// clearly dwarfs it — the ratio is mandatory at every length, the recovery
	// scan stops at the most recent user message (a compression can only be of
	// THIS turn's answer; never resurrect one from an earlier question), and
	// the closer is discarded (its content is a strict subset of what it
	// replaced).
	modeSummary
)

// backRefRe matches a terminal turn that merely points back to an earlier
// message instead of stating the answer ("(Already answered above.)",
// "see above", "as I said", ...). It is a list of fixed phrasings; aboveRefRe
// covers the open-ended half of the same family.
var backRefRe = regexp.MustCompile(`(?i)(already answered|see above|as (i )?(said|mentioned|stated|noted)|answered (that )?above|per my (previous|earlier))`)

// aboveRefRe matches a DEICTIC "above" — one pointing at earlier text rather
// than serving as a preposition. What follows the word separates the two uses:
// the deictic use ends its clause ("that's the full chain above.", "as shown
// above,", a line that simply ends in "above"), while the preposition always
// continues into a noun phrase ("above 100°C", "above the fold", "above all,
// the ..."). Only the clause-final form matches, so the open-ended half of the
// back-reference family is covered without enumerating every phrasing a model
// might invent — backRefRe's fixed list kept missing new ones (mort issue
// #1611: "Done — that's the full chain above.").
//
// The terminator set deliberately excludes the ASCII hyphen. `\b` holds
// between "above" and "-", so a literal '-' in the class made every
// hyphenated compound — "above-average", "above-board", "above-ground" —
// read as a clause-final deictic and put a legitimate short answer at risk of
// being discarded. The em dash stays: a model writes "…above — see the
// links", never "above-" as a separator. CR is listed alongside LF so a
// CRLF transcript does not quietly lose every line-final "above".
var aboveRefRe = regexp.MustCompile(`(?i)\babove\b[ \t]*([.,;:!?)\]"'’”—]|\r|\n|$)`)

// pointsAbove reports whether a deictic "above" appears in the terminal's
// OPENING. The offset bound is what makes a bare "above" safe to key on: with
// almost no text before it in THIS message, the reference cannot be pointing
// at the message's own content, so it must point at a turn the user never saw
// (the harness delivers only the final turn).
//
// This is the DEFERRAL SIGNAL SHARED by both recovery shapes — isWeakFinal and
// isSummaryCloser both call it, so a widening here reaches the bare closer and
// the "+ compression" closer at once. Its sibling backRefRe is deliberately
// NOT shared: those fixed phrases are matched anywhere in the text, which is
// only safe under isWeakFinal's 120-byte cap. Folding the two into one
// predicate for tidiness would hand isSummaryCloser an unanchored match across
// 300 bytes — widening the gate, not deduplicating it.
func pointsAbove(t string) bool {
	loc := aboveRefRe.FindStringIndex(t)
	return loc != nil && loc[0] <= backRefHeadChars
}

// bareAbovePointer reports whether the terminal is a deictic back-reference and
// essentially NOTHING ELSE — the form isWeakFinal may discard outright.
//
// pointsAbove alone is not enough for that, because a pointer can share a short
// terminal with the answer: "That's the chain above. Ship Tuesday." is 37 bytes
// and the decision is the four words the pointer is not. Discarding it in
// favour of an earlier turn throws away the only thing the user needed. Same
// shape as the summary-closer fix — a pointer says where the detail is, it does
// not say the text beside it is disposable.
//
// So the reference's own clause is cut out and whatever remains must be filler:
// nothing, punctuation, or a throat-clearing "Done —". Cutting the CLAUSE (from
// the end of the previous sentence through the reference) rather than testing
// position is also what makes a mixed terminal safe — "Anything above 100
// boils. See the note above." keeps its first sentence and is correctly not
// bare, and a comparative "above," with an interjection after it keeps the rest
// of its own sentence for the same reason.
func bareAbovePointer(t string) bool {
	loc := aboveRefRe.FindStringIndex(t)
	if loc == nil || loc[0] > backRefHeadChars {
		return false
	}
	start := 0
	if k := strings.LastIndexAny(t[:loc[0]], ".!?\n"); k >= 0 {
		start = k + 1
	}
	rest := strings.TrimSpace(t[:start]) + " " + strings.TrimSpace(t[loc[1]:])
	return bareRemainderRe.MatchString(strings.Trim(rest, pointerResidueCutset))
}

// pointerResidueCutset is trimmed from both ends of what survives cutting the
// pointer's clause — the brackets, quotes, and punctuation a model wraps a
// back-reference in ("(Already answered above.)").
const pointerResidueCutset = " \t\r\n.,;:!?()[]{}\"'“”‘’*_-—"

// bareRemainderRe matches a remainder that carries no answer: empty, or only
// the filler a closer opens with. Shares fillerWords with summaryPreface so the
// two lists cannot drift.
var bareRemainderRe = regexp.MustCompile(`(?i)^(` + fillerWords + `[\s,.!:—-]*)*$`)

// compressionMarkerRe matches a model announcing that what follows is the
// short form of something longer ("Short version: …", "TL;DR: …", "In short,
// …"). It is the second half of the deictic summary-closer test: the pointer
// says the full answer is elsewhere, and this says the text beside it is a
// condensation rather than new reasoning.
//
// Both halves are required, because a deictic pointer alone does not mean the
// terminal is disposable. "Given the analysis above, I recommend option B
// because X" opens with a pointer and then states a CONCLUSION the earlier
// turn never contained — discarding it in favour of that turn would throw away
// the answer. A compression marker is the model telling us the opposite.
//
// A marker WITHOUT a pointer stays out of scope, as summaryCloserRe's own
// comment explains: a user who asked for brevity is answered with exactly that
// shape.
// The marker must OPEN a sentence. Mid-sentence the same words are ordinary
// prose carrying new content — "Given the analysis above, the bottom line is
// that we need a different vendor" states a conclusion, it does not announce a
// condensation — and treating that as disposable is the very failure the
// two-part test exists to prevent.
var compressionMarkerRe = regexp.MustCompile(`(?i)(^|[.!?:;—]\s*|\n\s*)(short version|shorter version|short answer|tl;?dr|in short|in brief|in summary|in sum|bottom line|net[- ]net|the gist)\b`)

// summaryCloserRe matches a terminal turn that OPENS with a bookkeeping
// acknowledgment of the citation round — "Citations are logged.", "Sources
// cited.", "Logged the citations." — the shape a model produces when it
// front-loaded its answer into an earlier cite-call turn and closes by
// acknowledging the tool results, often followed by a "Short version: …"
// compression of the answer it already wrote. The ack clause must end at a
// sentence terminator ([.!]) DIRECTLY after the verb: "The citations are
// recorded in the court transcript…" is a real answer about citations, not
// bookkeeping, and must never match. A compression marker without the ack
// ("Short version: no.") is deliberately out of scope — a user who asked for
// brevity would be answered with exactly that shape, and misclassifying it
// would hijack a legitimate answer; an unmatched closer merely keeps today's
// behavior (fail closed). Assembled from named fragments so the alternations
// stay legible and extendable.
const (
	// fillerWords are the throat-clearing tokens a closer opens with. Shared
	// with bareRemainderRe, which has to recognise exactly the same set as
	// "not answer content".
	fillerWords    = `(done|all set|ok(ay)?)`
	summaryPreface = `(` + fillerWords + `[\s,.!:—-]+)?` // optional "Done —" style opener
	summaryNouns   = `(citations?|sources?|references?|claims?)`
	// "all" appears here AND in summaryArticle on purpose: as a quantifier
	// between noun and verb ("Citations all logged.") and as a determiner
	// before the noun ("All claims cited.", "Logged all the citations.").
	summaryCopulas = `((are|were|have\s+been|all)\s+)*`
	summaryVerbs   = `(logged|recorded|cited|saved|noted|captured|filed)`
	summaryArticle = `((all|the)\s+)*` // star, not ?: "Logged all the citations."
)

var summaryCloserRe = regexp.MustCompile(`(?i)^` + leadingMarkers + summaryPreface +
	`(` + summaryArticle + summaryNouns + `\s+` + summaryCopulas + summaryVerbs +
	`|logged\s+` + summaryArticle + summaryNouns + `)[.!]`)

// preambleRe matches intent-announcing prefixes ("Let me search...", "I'll
// check...") so a preamble is never mistaken for the answer during recovery.
var preambleRe = regexp.MustCompile(`(?i)^(let me|let'?s|i'?ll|i will|first[, ]|sure[,. ]|okay[,. ]|on it|checking)`)

// citationLabelRe matches a terminal turn that OPENS with a sources/citations
// heading — the shape a model produces when it front-loads its answer into an
// earlier tool-call turn and closes with only its sources. Leading markdown
// emphasis (*, _), list (-, +, *), block-quote (>), and ATX-heading (#) markers
// — with their whitespace, since \s is in the class — are tolerated before the
// label, as is closing emphasis (** / __) plus whitespace between the label and
// the colon/dash separator. Anchored at ^ so a normal answer that merely
// mentions "sources" mid-sentence, or ends with a "Sources:" section AFTER its
// prose, is never matched.
var citationLabelRe = regexp.MustCompile(`(?i)^` + leadingMarkers +
	`(sources?|references?|citations?|works cited|further reading)\b[\s*_]*[:：\-—]`)

// leadingMarkers tolerates markdown noise before a label: emphasis (*, _),
// list (-, +, *), block-quote (>), and ATX-heading (#) markers, with their
// whitespace. Shared by citationLabelRe and summaryCloserRe so the two
// classifiers cannot drift apart (the first draft of the summary class
// dropped '+' by hand-copying this set).
const leadingMarkers = `[\s>#*_+-]*`

// linkRe matches a whole markdown link "[label](url)" or a bare URL. Used both
// to require that a citations terminal carries at least one link and to strip
// links out when measuring how citation-dominated the terminal is.
var linkRe = regexp.MustCompile(`\[[^\]]*\]\([^)]*\)|https?://\S+`)

// citationResidueCutset is trimmed from the ends of a citations terminal's
// non-link remainder before measuring it — list bullets, separators, and the
// short per-source annotations models add in parentheses.
const citationResidueCutset = " \t\r\n,;.:|·•*_()[]—-"

const (
	// weakFinalMaxChars bounds how long a back-reference closer can be. A
	// genuine final answer that merely contains "as I said" mid-sentence is
	// longer than this, so it is never treated as weak.
	weakFinalMaxChars = 120
	// backRefHeadChars bounds how far into the terminal a deictic "above" may
	// sit and still read as pointing OUTSIDE this message (see pointsAbove).
	// It IS weakFinalMaxChars — the same guard ("there is not enough text
	// before the reference for it to be pointing at content inside this
	// turn"), expressed as an offset because a summary closer carries a
	// compression AFTER the pointer and so is not itself short. Defined by
	// reference, not by repeating the literal: tuning the weak cap without the
	// offset following it would split one rule into two.
	backRefHeadChars = weakFinalMaxChars
	// recoverMinChars: a prior assistant turn this long is treated as a real
	// answer regardless of how it opens (the preamble filter is not applied at
	// this length — see isSubstantiveAnswer).
	recoverMinChars = 200
	// recoverFloorChars / recoverRatio gate the borderline band: a shorter
	// prior turn must clear the floor and — unless the terminal is a citations
	// addendum, which is not a rival answer — also clearly dwarf the (very
	// short) terminal. See isSubstantiveAnswer.
	recoverFloorChars = 80
	recoverRatio      = 3
	// citationDominatedDivisor: a citations terminal's non-link remainder must
	// be at most len/N of the whole, so a prose answer that merely opens with
	// "Source:" and cites a URL mid-sentence is not mistaken for a bare list.
	citationDominatedDivisor = 3
	// summaryCloserMaxChars bounds a summary closer: room for the ack sentence
	// plus a couple of compression sentences (the b3cb9ee9 closer was 153
	// bytes — Go len(), which is what every threshold here compares). Beyond
	// this the "short version" is substantial enough that replacing it risks
	// losing content the front-loaded turn never had.
	summaryCloserMaxChars = 300
)

// isWeakFinal reports whether a terminal turn's text fails to stand on its own
// as the answer: empty/whitespace, or a short pure back-reference. The length
// cap is what keeps a genuine answer that merely contains a back-reference
// phrase mid-sentence out of the class; past the cap a deferring terminal is
// isSummaryCloser's business, under the stricter dwarf bar.
//
// The deictic half additionally demands that the pointer be the WHOLE message
// (bareAbovePointer), not merely present in it. Both classes now enforce the
// same rule from opposite ends: a terminal is only disposable when it carries
// no answer of its own — proved here by there being nothing beside the pointer,
// and in isSummaryCloser by the model declaring what is beside it a
// compression.
func isWeakFinal(s string) bool {
	t := strings.TrimSpace(s)
	if t == "" {
		return true
	}
	return len(t) <= weakFinalMaxChars && (backRefRe.MatchString(t) || bareAbovePointer(t))
}

// isCitationsOnly reports whether a terminal turn is essentially just a
// sources/citations addendum: it OPENS with a citations heading, carries at
// least one link, and — once the heading and links are removed — is dominated
// by that citation structure (only list punctuation and short per-source
// annotations remain). The dominance check is what separates a bare sources
// list (recover the front-loaded answer, keep the links) from a real prose
// answer that merely opens with "Source:" and references a URL mid-sentence
// (leave it as the answer). Unlike a back-reference closer the links are worth
// keeping, so finalOutput appends them to the recovered answer.
//
// A citations terminal whose sources are bare domains (no scheme, no markdown
// link) is intentionally out of scope — there is no reliable link signal, so it
// is left as-is rather than risk misclassifying prose.
func isCitationsOnly(s string) bool {
	t := strings.TrimSpace(s)
	if !citationLabelRe.MatchString(t) {
		return false
	}
	body := citationLabelRe.ReplaceAllString(t, "")
	if !linkRe.MatchString(body) {
		return false
	}
	residue := strings.Trim(linkRe.ReplaceAllString(body, ""), citationResidueCutset)
	return len(residue) <= len(t)/citationDominatedDivisor
}

// isSummaryCloser reports whether a terminal turn defers to an earlier answer
// and is short enough that whatever follows the deferral can only be a
// compression of it. Two openers qualify:
//
//   - a complete bookkeeping ack sentence — "Citations are logged." — which is
//     summaryCloserRe, and carries no answer content of its own;
//   - a deictic back-reference in the opening PLUS a compression marker —
//     mort issue #1611's "Done — that's the full chain above. Short version:
//     …" — which the ack shape alone did not cover.
//
// The second opener needs both halves. A pointer on its own does not make a
// terminal disposable: "Given the analysis above, I recommend option B because
// X" points backwards and then states a conclusion the earlier turn never
// contained, and replacing it with that turn would discard the answer. The
// compression marker is the model saying the opposite — that what follows is
// the short form of something it already wrote.
//
// Whether the fuller answer actually exists is modeSummary's job — the dwarf
// ratio in isSubstantiveAnswer keeps a matching closer in place when nothing
// earlier clearly outweighs it.
//
// pointsAbove is used here; its sibling backRefRe is NOT. Those fixed phrases
// are matched anywhere in the text, and a 300-byte closer has room for a real
// answer that merely mentions "as I said" mid-sentence. pointsAbove is
// offset-bounded, so it stays anchored to the opening.
func isSummaryCloser(s string) bool {
	t := strings.TrimSpace(s)
	if t == "" || len(t) > summaryCloserMaxChars {
		return false
	}
	return summaryCloserRe.MatchString(t) ||
		(pointsAbove(t) && compressionMarkerRe.MatchString(t))
}

// lastSubstantiveAssistantText scans msgs newest→oldest (skipping the terminal
// turn and empty tool-only turns) for the most recent assistant turn whose text
// reads like a real answer. mode selects the recovery bar (see
// isSubstantiveAnswer). Returns ("", false) when nothing qualifies.
func lastSubstantiveAssistantText(msgs []llm.Message, terminal string, mode recoveryMode) (string, bool) {
	tt := strings.TrimSpace(terminal)
	for i := len(msgs) - 1; i >= 0; i-- {
		m := msgs[i]
		if mode == modeSummary && m.Role == llm.RoleUser {
			// A summary closer compresses THIS turn's front-loaded answer, so
			// the scan must not cross into an earlier question: once the dwarf
			// ratio has rejected the current turn's text, walking further back
			// would resurrect a stale answer to a DIFFERENT question — strictly
			// worse than keeping the closer. (A mid-run steer message is also a
			// user-role boundary; recovery then fails closed, which is fine.)
			// The other modes keep their historical unbounded scan.
			break
		}
		if m.Role != llm.RoleAssistant {
			continue
		}
		txt := strings.TrimSpace(m.Text())
		if txt == "" || txt == tt {
			continue // the terminal turn itself, or an empty tool-only turn
		}
		if isSubstantiveAnswer(txt, tt, mode) {
			return txt, true
		}
	}
	return "", false
}

// isSubstantiveAnswer reports whether txt (a prior assistant turn) reads like a
// real answer rather than a preamble, relative to the terminal text.
//
// modeSummary demands the dwarf ratio FIRST, at every length: a summary closer
// carries a real (compressed) answer, so replacing it is only justified when
// the prior turn is clearly the fuller original it was compressed from.
//
// A sufficiently long turn (>= recoverMinChars) is otherwise accepted
// unconditionally: a multi-hundred-char turn is an answer even when it opens
// conversationally ("Sure, here's…", "Let me explain: …"), so the preamble
// filter is NOT applied to it — applying it there would drop a legitimate long
// front-loaded answer. Only in the borderline band does a turn have to clear a
// floor, not read like a short planning preamble ("Let me look that up…"),
// and — for modeBackRef only — also clearly dwarf the terminal (a citations
// addendum is not a rival answer, so its length is irrelevant; a summary
// closer already proved the ratio above).
func isSubstantiveAnswer(txt, terminal string, mode recoveryMode) bool {
	dwarfs := len(txt) >= recoverRatio*len(terminal)
	if mode == modeSummary && !dwarfs {
		return false
	}
	if len(txt) >= recoverMinChars {
		return true
	}
	if len(txt) < recoverFloorChars || preambleRe.MatchString(txt) {
		return false
	}
	return mode != modeBackRef || dwarfs
}