package pipeline

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"

	"textmachine/backend/internal/config"
	"textmachine/backend/internal/membank"
	"textmachine/backend/internal/seed"
	"textmachine/backend/internal/store"
	"textmachine/backend/internal/text"
)

// bankdecisions.go: the WIRING of the bank-decisions door — the lock, the reads, the writes and the
// report. The decision logic itself is pure and lives in membank/decisions.go.
//
// It is a package-level function and not a Runner method on purpose. A Runner is the composite root of a
// RUN: it loads the pipeline and model configs, resolves prompts, builds provider clients. This verb
// spends nothing and calls nobody, and making it depend on a valid models.yaml would mean a book could
// stop being decidable because of a file its decisions have nothing to do with.

// BankDecisionsReport is what the verb prints — the whole of its answer, on stdout, in every outcome
// that has one. A caller that is told "no" has to be told what to change.
//
// ITS FIELDS ARE OF TWO NATURES, and the split is the report's own law (the single-commit-point rule):
//
//   - THE VERDICT — what was accepted, what was rejected and why, what pre-existing faults the files
//     carry, indexes, `replaced`, `depth`, `files`. A fact about the decisions against the state
//     BEFORE the call; it is not on disk and never will be, which is why the verb composes it at all.
//     Built once, by decisionVerdict, before the outcome exists.
//   - THE OUTCOME — mode, `changed`, the re-render warnings, `written_*`, `signature`. A fact about
//     the world AFTER. Filled in exactly one place, finishReport, by a switch over the explicit
//     outcome of the effect phase — so a new exit branch has nowhere to forget a field.
type BankDecisionsReport struct {
	Version string `json:"report_version"`
	BookID  string `json:"book_id"`
	// Mode names the outcome: `apply` (the write completed, or a byte-no-op — `changed` tells the two
	// apart) · `projection` (the 17-seam-inbound-law п.7 preview; a report printed by the same call
	// that already wrote is not a projection) · `refused` (the document was declined whole; the reasons
	// are in `rejected`) · `stopped` (a stop signal arrived before the first byte) · `write_incomplete`
	// (the document was accepted and the write did not complete; `written_*` says which file landed).
	Mode string `json:"mode"`
	// Depth says how far an accepted decision reaches — see membank.DecisionDepth. A caller renders its
	// own words from it; what it must not do is assume the corrected term re-forms the draft.
	Depth string `json:"depth"`
	// Changed reports whether THIS call moved a file on disk (in projection: whether it would). False on
	// a byte-no-op — then nothing is written AT ALL, not even identical bytes, so a retrying worker
	// cannot move a file's mtime, let alone its content.
	Changed bool             `json:"changed"`
	Files   BankDecisionPath `json:"files"`
	// WrittenDelta / WrittenRejects are the per-file truth of the write phase: true means THIS call
	// replaced that file on disk. They are what tells «nothing landed» from «half landed» under
	// mode `write_incomplete` — the class is one, the report carries the difference.
	WrittenDelta   bool `json:"written_delta"`
	WrittenRejects bool `json:"written_rejects"`
	// CanonicalRewrite warns that a file this call would WRITE is not in the form the engine writes, so
	// applying will re-render it: its comments and its key order will not survive. Visible BEFORE the
	// mutation, which is the only moment at which it is actionable.
	//
	// It is the OR of the two fields below and it is kept because a consumer that only wants to raise a
	// dialog has one thing to read. The two are what it must render: the OR alone named a RISK without
	// naming the FILE at risk, and since a call routinely touches one document and not the other, it
	// warned about a file the call would never open — an operator's comments in the reject list raised
	// it for a set of pure approvals.
	CanonicalRewrite bool `json:"canonical_rewrite"`
	// CanonicalRewriteDelta / CanonicalRewriteRejects are the same warning per file, and each is false
	// for a document this call does not touch.
	CanonicalRewriteDelta   bool `json:"canonical_rewrite_delta"`
	CanonicalRewriteRejects bool `json:"canonical_rewrite_rejects"`
	// PreexistingProblems are faults the two files ALREADY have — a delta that would not load, a
	// collision with the signed seed — that this call neither caused nor refuses over. They are here
	// because the alternative is a verb that answers "applied, exit 0" about a book whose next run is
	// already going to die at the bank boundary, and nothing else on this surface would say so.
	// ⚠ On a CAP refusal the list is empty because nothing below the verdict was measured, not because
	// the book is clean — signature.unreadable is the report's «unmeasured» flag for that state.
	PreexistingProblems []string                   `json:"preexisting_problems"`
	Accepted            []membank.AcceptedDecision `json:"accepted"`
	Rejected            []membank.RejectedDecision `json:"rejected"`
	// Signature is the one thing this call can honestly say about the bank-mining STOP.
	Signature SignatureState `json:"signature"`
}

// SignatureState measures the last-written signature map against the book's decisions. INFORMATIONAL,
// exactly as D39.144 demoted it — it counts, it does not gate.
//
// ⚠ IT DOES NOT ANSWER «погаснет ли стоп», in either direction, and a consumer must not read it as if
// it did. The stop is the flag model's (mining.go): a run with `--verify-bank` stops only when its OWN
// freshly-mined map holds a cluster outside the presented memory. This field cannot compute that from
// either end — the next run's mined set does not exist yet (computing it means re-ingesting and
// re-chunking the whole book, which is what makes `status` expensive and is not what a $0 decision verb
// does), and the presented memory would not close the gap (memory without the next map still decides
// nothing) — so the door does not open the database for it at all, and `undecided: 0` promises nothing
// about the next run's behaviour. Deciding surfaces is the owner's RIGHT, not the stop's demand.
//
// What the numbers ARE for: a signing screen. «Of the surfaces the last stop offered, how many has the
// owner not yet spoken about» — counted by the SAME rule the run uses to fold decisions into the bank
// (ownerHandled over unsignedEngineSurfaces), so the count agrees with what the next run will treat as
// decided content.
type SignatureState struct {
	// Map is the signature map's path, or empty when the book has none — no run has reached the bank
	// boundary yet, and there is nothing to count against.
	Map string `json:"map"`
	// Surfaces is how many surfaces that map asks about; Undecided how many of them are still neither
	// approved in the delta nor declined in the rejects AFTER this call.
	Surfaces  int `json:"surfaces"`
	Undecided int `json:"undecided"`
	// Unreadable says the two numbers mean NOTHING for this call — the map or the delta could not be
	// parsed, or the call was refused before it could measure them (a cap refusal never opens the
	// book). Without it a state this door could not measure was byte-identical to the state it most
	// wants to report, «nothing left undecided».
	Unreadable bool `json:"unreadable"`
}

// BankDecisionPath names the two files the verb owns. The paths are ABSOLUTE: the engine resolves them
// against the book's directory, and a consumer reading this report runs in a different working directory
// (the platform's own process), where a relative path resolves to something else entirely.
type BankDecisionPath struct {
	MinedDelta   string `json:"mined_delta"`
	MinedRejects string `json:"mined_rejects"`
}

// ErrDecisionsRefused is "the document was read as a decisions document and this engine will not apply
// it" — the carrier of RefusalDecisionsRejected, whose own comment says why that is a class of its own
// rather than the config one. A document that never parsed as a decisions document at all is the CONFIG
// class instead (see the top of ApplyBankDecisions): the caller's wiring is what is wrong there.
//
// The per-decision reasons ride the report, which is printed either way.
var ErrDecisionsRefused = errors.New("the decision document was refused; nothing was written")

// ApplyBankDecisions applies one decision document to a book's memory-bank decision files.
//
// $0 by construction: it opens no provider client, reads the bank read-only and writes two YAML files.
//
// THE PROJECTION TOUCHES NO DECISION FILE, and that is the whole of what it promises. It does create
// `<project_db>.lock` in the book's directory when none is there, because the lock is the arbiter below
// and a projection computed without it is a projection of nothing. "Changes nothing" is about the two
// documents and the bank; it was never true of the lock file, and the difference matters to anyone
// diffing a book directory after a preview.
//
// ⚠ THE ARBITER COVERS THE PROJECT, AND SINCE FIX-PACK-2 THAT IS ALMOST ENOUGH. The flock is on
// `<project_db>.lock`, and the two files written are pure functions of the book's directory and its
// book_id (config.Book.MinedDelta — the path keys are retired): two DIFFERENT books can no longer
// share a decision file, which retires the original cross-book race (two configs declaring ONE delta,
// one side's approvals lost with exit 0 — the ⛔ ping the previous pack left open). What REMAINS is the
// same-book spelling: `project_db` is still declarable, so two configs in ONE directory with ONE
// book_id but different project_db values write the same pair of files under two different locks —
// including past the flock of a live run (reproduced by the fix2 review workflow: a second config with
// a scratch project_db applied decisions while the real project's lock was held). That is an operator
// keeping a second config of the same book, not an ordinary deployment; closing it means a second
// arbiter or a refusal at load, which touches 17-seam-inbound-law п.2 and stays a ping, not this
// door's own decision.
//
// THE LOCK IS THE ARBITER, and it is the project's own flock — the one a run holds for its whole life.
// Taken non-blocking, and a busy one refuses with RefusalProjectLocked (exit 12), never with the config
// class: the engine RE-READS the seed in the middle of a run (mining.go), so a write that landed under a
// live run would enter its snapshot non-deterministically. The projection mode takes it too — a
// projection computed against state another process is rewriting is not a projection of anything.
func ApplyBankDecisions(ctx context.Context, cfgPath, decisionsPath string, dryRun bool) (BankDecisionsReport, error) {
	book, doc, err := openDecisionRequest(cfgPath, decisionsPath)
	if err != nil {
		// The DECISIONS class prints a report in EVERY spelling, the two caps included: an all-or-nothing
		// verb's report of reasons IS its product, and the contract used to have two carriers that
		// disagreed (the class promised a report, the cap path printed a stderr line). Config-class
		// failures before the lock still speak on stderr alone — there the wiring itself is broken and a
		// report about a book this call never opened would say nothing.
		var refusal *Refusal
		if book != nil && errors.As(err, &refusal) && refusal.Class == RefusalDecisionsRejected {
			return capRefusalReport(book, err), err
		}
		return BankDecisionsReport{}, err
	}

	lock, err := store.LockProject(book.ProjectDB)
	if err != nil {
		return BankDecisionsReport{}, RefuseStoreOpen(err)
	}
	defer lock.Release()

	st, err := readBookState(book)
	if err != nil {
		return BankDecisionsReport{}, err
	}
	if err := ctx.Err(); err != nil {
		return BankDecisionsReport{}, err
	}
	res := membank.ApplyDecisions(membank.ApplyInput{
		Bank: st.bank, Seed: st.seed.Terms, Voices: st.seed.Voices, Pairs: st.seed.Pairs, Ruby: st.ruby,
		Delta: st.delta, Rejects: st.rejects, Decisions: doc.Decisions,
	})

	// ONE verdict, ONE commit point. The verdict half is composed here and never patched again; every
	// exit below names its outcome and finishReport fills the outcome half — a new branch cannot forget
	// a field, because no branch owns any.
	verdict := decisionVerdict(book, res)
	if len(res.Rejected) > 0 {
		return finishReport(verdict, outcomeRefused, book, st, res, writtenFiles{}),
			refuse(RefusalDecisionsRejected, ErrDecisionsRefused)
	}
	deltaChanged, rejectsChanged := changedFiles(st, res)
	if dryRun {
		return finishReport(verdict, outcomeProjection, book, st, res, writtenFiles{delta: deltaChanged, rejects: rejectsChanged}), nil
	}
	if !deltaChanged && !rejectsChanged {
		// The byte-no-op still RE-PROVES DURABILITY. The write-incomplete contract says «re-send the same
		// document», and when the original failure was the directory sync the retry converges exactly
		// here, with the bytes already on disk — without this call the one thing that exit 15 warned
		// about would never be re-proven, and the retry would answer 0 (review-workflow finding). A
		// directory that cannot be flushed keeps refusing with the same class until it heals; an
		// ordinary no-op pays one fsync.
		if err := syncDir(filepath.Dir(book.MinedDelta)); err != nil {
			return finishReport(verdict, outcomeWriteFailed, book, st, res, writtenFiles{}),
				refuse(RefusalWriteIncomplete, fmt.Errorf("nothing was written by this call, but the directory holding the decision files still cannot be flushed — their durability is unproven: %w", err))
		}
		return finishReport(verdict, outcomeNoop, book, st, res, writtenFiles{}), nil
	}
	// SIGTERM means STOP, and for an all-or-nothing $0 verb the answer is the whole of it: drop the work
	// and release the lock, having written nothing. There is no partial result worth finishing — the law
	// gives SIGTERM the sense «finish the chunk you are PAYING for and let go» (17-seam-inbound-law п.2),
	// and this verb pays for nothing. Checked at the last moment before the first byte, which is the only
	// place where the difference between «stopped» and «applied» is still available.
	//
	// The context is cancelled by signal.NotifyContext in main and by nothing else, so a cancelled one is
	// somebody asking this process to stop; tmctl maps it to exit 5 (graceful stop). ⚠ What the PLATFORM
	// records for 5 is `stopped` — and only when it has a stop request on file: without one the case
	// falls through to `failed` (platform/internal/runs/reconcile.go:700-712 and :756, read not edited).
	// It is NOT `paused`; that is exit 4, the resumable ceiling verdict, and PD-113 forbids reusing it.
	//
	// The longest stretch this cannot interrupt is one membank.ApplyDecisions, which is pure and takes no
	// context by charter — maxDecisions bounds it at ~11 s in the worst measured shape. But the reason
	// that stretch is SAFE is not its length: the writes are last and each is atomic, so a process killed
	// anywhere before this line has written nothing, and one killed between the two renames leaves one
	// proven file and a retry that converges.
	if err := ctx.Err(); err != nil {
		return finishReport(verdict, outcomeStopped, book, st, res, writtenFiles{}), err
	}
	wrote, werr := writeDecisionFiles(book, res, deltaChanged, rejectsChanged)
	if werr != nil {
		return finishReport(verdict, outcomeWriteFailed, book, st, res, wrote),
			refuse(RefusalWriteIncomplete, werr)
	}
	return finishReport(verdict, outcomeWritten, book, st, res, wrote), nil
}

// openDecisionRequest loads the book and the request, and refuses everything that can be judged before
// the project is locked — so a malformed call never takes the lock a run might be waiting for. The book
// is returned WITH a refusal once it has loaded, because a cap refusal owes the caller a report and the
// report needs the book's identity and paths.
func openDecisionRequest(cfgPath, decisionsPath string) (*config.Book, membank.DecisionsDoc, error) {
	book, err := config.LoadBook(cfgPath)
	if err != nil {
		return nil, membank.DecisionsDoc{}, RefuseConfig(err)
	}
	raw, err := readDecisions(decisionsPath)
	if err != nil {
		return book, membank.DecisionsDoc{}, err
	}
	doc, err := membank.DecodeDecisions(raw)
	if err != nil {
		return book, membank.DecisionsDoc{}, RefuseConfig(err)
	}
	if doc.BookID != book.BookID {
		return book, membank.DecisionsDoc{}, RefuseConfig(fmt.Errorf("pipeline: the decisions are for book %q and this configuration is book %q", doc.BookID, book.BookID))
	}
	// The bound that actually holds the call inside a caller's timeout — see maxDecisions. Checked after
	// the decode, because it is a fact about the REQUEST and not about the file.
	if n := len(doc.Decisions); n > maxDecisions {
		return book, membank.DecisionsDoc{}, refuse(RefusalDecisionsRejected, fmt.Errorf(
			"pipeline: the document carries %d decisions and this engine applies at most %d in one act (beyond that the call stops fitting the caller's timeout and is killed on every retry) — split it",
			n, maxDecisions))
	}
	return book, doc, nil
}

// bookState is everything the decision pass reads about a book, plus the BYTES the two decision files
// hold right now — which is what the write gates compare against.
type bookState struct {
	bank       []store.GlossaryEntry
	ruby       []store.RubyReading
	seed       membank.BankSeed
	delta      seed.File
	deltaRaw   []byte
	rejects    seed.RejectFile
	rejectsRaw []byte
}

// readBookState reads all of it under the lock, in one place, so no caller can accidentally judge a
// decision against half a book.
func readBookState(book *config.Book) (bookState, error) {
	var st bookState
	var err error
	if st.bank, st.ruby, err = bankRows(book); err != nil {
		return st, err
	}
	// The WHOLE seed, not only its terms: its voice/address rows are what make some decisions unsafe
	// (see membank.inspectDocuments), and reading half of it would hide that.
	if book.GlossarySeed != "" {
		if st.seed, err = membank.LoadBankSeed(book.GlossarySeed); err != nil {
			return st, RefuseConfig(err)
		}
	}
	if st.delta, st.deltaRaw, err = readDelta(book); err != nil {
		return st, RefuseConfig(err)
	}
	if st.rejects, st.rejectsRaw, err = readRejects(book); err != nil {
		return st, RefuseConfig(err)
	}
	return st, nil
}

// applyOutcome is what the effect phase actually did — the value the ONE outcome constructor switches
// over. Every exit of ApplyBankDecisions names exactly one of these.
type applyOutcome int

const (
	outcomeProjection  applyOutcome = iota // --dry-run: measured, nothing touched
	outcomeRefused                         // the document was declined whole; nothing touched
	outcomeNoop                            // every decision already in the files; nothing touched, by design
	outcomeStopped                         // a stop signal arrived before the first byte; nothing touched
	outcomeWritten                         // the write completed
	outcomeWriteFailed                     // the write did not complete; writtenFiles says how far it got
)

// writtenFiles is the write phase's per-file truth. For the projection outcome it carries "would write".
type writtenFiles struct{ delta, rejects bool }

// decisionVerdict builds the VERDICT half of the report — the fact about the decisions against the
// state before the call (see BankDecisionsReport). Nothing here may depend on how the call ends.
func decisionVerdict(book *config.Book, res membank.ApplyResult) BankDecisionsReport {
	return BankDecisionsReport{
		Version: membank.DecisionsReportVersion, BookID: book.BookID,
		Depth:    membank.DecisionDepth,
		Files:    BankDecisionPath{MinedDelta: absPath(book.MinedDelta), MinedRejects: absPath(book.MinedRejects)},
		Accepted: orEmpty(res.Accepted), Rejected: orEmpty(res.Rejected),
		PreexistingProblems: orEmpty(res.Preexisting),
	}
}

// finishReport fills the OUTCOME half — mode, changed, the re-render warnings, written_*, signature —
// by a switch over the explicit outcome. It is the report's single commit point: four review rounds
// each found one more exit branch hand-patching its own subset of these fields, and the only fix that
// closes the class is a constructor with no subsets to choose from.
func finishReport(rep BankDecisionsReport, o applyOutcome, book *config.Book, st bookState, res membank.ApplyResult, files writtenFiles) BankDecisionsReport {
	// "Would applying re-render a file the engine did not write?" — asked against the CURRENT documents
	// re-rendered unchanged, so it reports the file's form and not the decisions' effect. Per file, and
	// only for the file this call would actually touch: a warning about a document the call does not
	// open is a warning about nothing (a reject list full of an operator's comments used to raise it for
	// a call that only approves).
	warn := func() {
		rep.CanonicalRewriteDelta = res.DeltaTouched && notCanonical(st.deltaRaw, st.delta)
		rep.CanonicalRewriteRejects = res.RejectsTouched && notCanonicalRejects(st.rejectsRaw, st.rejects)
		rep.CanonicalRewrite = rep.CanonicalRewriteDelta || rep.CanonicalRewriteRejects
	}
	switch o {
	case outcomeProjection:
		rep.Mode, rep.Changed = "projection", files.delta || files.rejects
		warn()
		rep.Signature = signatureState(book, st.seed.Terms, docsFromResult(st, res))
	case outcomeRefused:
		// A REFUSED call writes nothing: no re-render to warn about (a destructive-action dialog raised
		// for a call that wrote nothing is how a real warning gets trained out of an operator — the pure
		// layer rolls the documents back but leaves *Touched standing as a record of what the fold did),
		// no accepted work to list (the pure layer already returns none), and the measured state is the
		// disk's, not the refused result's.
		rep.Mode, rep.Changed = "refused", false
		rep.Signature = signatureState(book, st.seed.Terms, docsFromDisk(st))
	case outcomeNoop:
		rep.Mode, rep.Changed = "apply", false
		warn() // false in practice: a byte-no-op's documents are already in the engine's own form
		rep.Signature = signatureState(book, st.seed.Terms, docsFromResult(st, res))
	case outcomeStopped:
		// Accepted is cleared like on the refused path: a list of decisions each stamped `state: applied`
		// is a claim about work, and this call did none — the accepted list is what a consumer iterates.
		rep.Mode, rep.Changed, rep.Accepted = "stopped", false, []membank.AcceptedDecision{}
		rep.Signature = signatureState(book, st.seed.Terms, docsFromDisk(st))
	case outcomeWritten:
		rep.Mode, rep.Changed = "apply", true
		rep.WrittenDelta, rep.WrittenRejects = files.delta, files.rejects
		warn()
		rep.Signature = signatureState(book, st.seed.Terms, docsReRead(book))
	case outcomeWriteFailed:
		// Accepted is cleared HERE too, and for the harder reason: with one file landed the list would be
		// half true, and a consumer recording deliveries from it cannot know which half. The retry
		// re-sends the same document and converges — the landed half comes back `already_applied`.
		rep.Mode, rep.Changed = "write_incomplete", files.delta || files.rejects
		rep.WrittenDelta, rep.WrittenRejects = files.delta, files.rejects
		rep.Accepted = []membank.AcceptedDecision{}
		warn()
		// The POST-state, re-read from disk: for an outcome that touched the world the report describes
		// the files as they now are, never the bytes the call intended.
		rep.Signature = signatureState(book, st.seed.Terms, docsReRead(book))
	}
	return rep
}

// changedFiles opens or closes the write gate for each document. TWO gates PER FILE, and both have to
// open before a byte of it is written.
//
// The first is whether a decision actually changed THAT document. Per-file and not per-call: a decline
// changes the reject list, and re-rendering the delta beside it would destroy an operator's formatting
// of a file the call had no opinion about. A call whose every decision was already applied opens neither
// gate and writes nothing at all.
//
// The second is the bytes themselves, which is what makes the no-op a BYTE no-op rather than a rewrite
// that happens to produce the same content. The bytes are the ones the pure layer already PROVED
// readable (membank.ApplyResult.DeltaBytes); rendering them again here would be a second renderer of the
// same document, and the one thing this door must never do is write bytes that nothing checked.
//
// ⚠ NIL BYTES ARE NEVER WRITTEN, and that guard is the difference between a report and a data loss. A
// document that could not be RENDERED yields nil bytes, and when that failure is PRE-EXISTING the pure
// layer reports it instead of refusing (which is right — a book whose files are already broken must stay
// repairable). Without the nil check this saw `DeltaTouched && changedDoc(raw, nil, …)` → true and wrote
// a ZERO-BYTE file over every approval the owner had made.
func changedFiles(st bookState, res membank.ApplyResult) (delta, rejects bool) {
	delta = res.DeltaBytes != nil && res.DeltaTouched &&
		changedDoc(st.deltaRaw, res.DeltaBytes, emptyDelta(res.Delta))
	rejects = res.RejectBytes != nil && res.RejectsTouched &&
		changedDoc(st.rejectsRaw, res.RejectBytes, len(res.Rejects.Rejects) == 0)
	return delta, rejects
}

// writeDecisionFiles performs the mutation: BOTH documents are staged completely — written, synced,
// chmodded under temp names — before either rename, so the whole class of environment failures (a full
// disk, a permission, an I/O error) is met before a single byte of either document has moved, and a call
// it strikes reports «nothing landed», having changed nothing.
//
// What this is NOT: atomicity of the PAIR against a dying process. The window between the two renames
// remains, and closing it needs a journal across two files — a mechanism this door has not earned. The
// residue is covered by convergence: the call is all-or-nothing and recomputed from scratch, so a retry
// of the same document converges from either half-state, and a killed process prints no report.
// ⚠ What a half-state leaves is stated precisely, because the older wording ("every half-state leaves
// the term UNDECIDED rather than wrongly decided") stopped being true when the order changed: under
// rejects-first an interrupted DECLINE leaves the decision RECORDED while the delta row is still on
// disk. That is not "wrongly decided" — it is decided correctly and half-written — and it is only safe
// because the bank loader drops a delta row whose surface is on the reject list (mining.go
// loadMinedDelta). Without that filter this order would have bought recoverability with a window in
// which a paid run injects a term the owner declined. The RENAME ORDER is what makes
// that true, and it is REJECTS FIRST. It used to be delta-first with a comment calling the order
// arbitrary — "the mirror order swaps which verb loses, and convergence is what actually carries both".
// The second half of that sentence was the load-bearing one and it was false for a decline: dropping the
// delta row is exactly what makes refuseSeedConflicts fire on the re-send, so delta-first did not swap
// which verb loses, it chose the verb that CANNOT recover. The order below is argued in place.
//
// The per-file return is the report's: which file this call replaced on disk, however far it got.
func writeDecisionFiles(book *config.Book, res membank.ApplyResult, deltaChanged, rejectsChanged bool) (writtenFiles, error) {
	var wrote writtenFiles
	var deltaStage, rejectsStage *stagedFile
	var err error
	if deltaChanged {
		if deltaStage, err = stageFileAtomic(book.MinedDelta, res.DeltaBytes); err != nil {
			return wrote, err
		}
	}
	if rejectsChanged {
		if rejectsStage, err = stageFileAtomic(book.MinedRejects, res.RejectBytes); err != nil {
			if deltaStage != nil {
				deltaStage.abort()
			}
			return wrote, err
		}
	}
	// REJECTS FIRST, and the order is NOT arbitrary — see the header. Whichever document lands
	// alone, the re-send has to converge, and only this order lets it for BOTH verbs:
	//
	//	rejects-first, decline killed between the renames → the reject is recorded and the delta
	//	  STILL HOLDS the row, so refuseSeedConflicts stays silent (its own precondition holds) and
	//	  the re-send drops the row and no-ops the reject: converged.
	//	rejects-first, approve killed between → the reject is withdrawn and the delta lacks the row,
	//	  so the re-send merges the row and no-ops the withdrawal: converged.
	//	delta-first, decline killed between → the row is GONE and no reject was recorded, and the two
	//	  files are then byte-for-byte the state in which declining that surface is genuinely inert.
	//	  No predicate over them can tell the half-state from the inert one, so the re-send is refused
	//	  and the term is stranded neither approved nor declined, with no channel forward.
	//
	// That last line is why this is a swap and not a preference: the delta is the document the
	// seed-conflict refusal READS, so the document that decides must not be the one that lands first.
	if rejectsStage != nil {
		if err := rejectsStage.commit(); err != nil {
			if deltaStage != nil {
				deltaStage.abort()
			}
			return wrote, err
		}
		wrote.rejects = true
	}
	if deltaStage != nil {
		if err := deltaStage.commit(); err != nil {
			return wrote, err
		}
		wrote.delta = true
	}
	// The decision files are the USER's words, so their durability is not left to the kernel's leisure:
	// the renames' directory entries are flushed here (both files live in the book's directory — the
	// paths are conventional). A failure is the write-incomplete class like any other write failure —
	// the renames are visible but not proven durable, and the report's per-file truth still names what
	// landed.
	if err := syncDir(filepath.Dir(book.MinedDelta)); err != nil {
		return wrote, fmt.Errorf("the files are renamed but their directory entries are not proven durable (a host crash could still lose them): %w", err)
	}
	return wrote, nil
}

// decidedDocs is the pair of decision documents signatureState measures the map against, and whether
// they could be obtained at all. Three sources, one per kind of outcome: the would-be result, the disk
// as read under the lock, and the disk re-read after a write.
type decidedDocs struct {
	delta   []byte
	rejects map[string]bool
	broken  bool // the documents could not be read or parsed — the numbers cannot be measured
}

// docsFromResult is the state the call intends: the proven bytes it would write (falling back to the
// disk for a document it does not touch) and the result's reject set.
func docsFromResult(st bookState, res membank.ApplyResult) decidedDocs {
	delta := res.DeltaBytes
	if delta == nil {
		delta = st.deltaRaw
	}
	return decidedDocs{delta: delta, rejects: rejectSurfaces(res.Rejects)}
}

// docsFromDisk is the state as it was read under the lock — what an outcome that touched nothing
// measures against (the refused result's own documents are not the world's).
func docsFromDisk(st bookState) decidedDocs {
	return decidedDocs{delta: st.deltaRaw, rejects: rejectSurfaces(st.rejects)}
}

// docsReRead is the POST-state: the two files re-read from disk after the write phase, however far it
// got. A file that cannot be re-read or re-parsed marks the pair broken — «could not measure», never
// zeroes.
func docsReRead(book *config.Book) decidedDocs {
	var out decidedDocs
	raw, err := os.ReadFile(book.MinedDelta)
	switch {
	case err == nil:
		out.delta = raw
	case errors.Is(err, fs.ErrNotExist):
		// absent = no decisions, the same standing readDelta gives it
	default:
		out.broken = true
		return out
	}
	rejRaw, err := os.ReadFile(book.MinedRejects)
	switch {
	case err == nil:
		f, perr := seed.DecodeRejects(rejRaw)
		if perr != nil {
			out.broken = true
			return out
		}
		out.rejects = rejectSurfaces(f)
	case errors.Is(err, fs.ErrNotExist):
	default:
		out.broken = true
	}
	return out
}

// signatureState measures how much of the last run's signature map the given documents leave undecided.
// See SignatureState for what the number does and does not mean.
//
// The delta bytes go through the real loader, so "approved" here means what it means to the run —
// including the loader's default for a row that states no status at all.
//
// Every failure on this path is silent and leaves the state marked unreadable. It is a report field
// about another artifact: a book whose signature map is missing or malformed still has decisions to
// apply, and refusing them over a sidecar would be the door failing at its own job for a footnote.
func signatureState(book *config.Book, seedRows []store.GlossaryEntry, docs decidedDocs) SignatureState {
	path := signatureMapPath(book.ProjectDB)
	raw, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return SignatureState{} // no run has reached the bank boundary: nothing to count against
		}
		// Anything ELSE — a permission, an EIO, a vanished mount, a raced unlink — is a state this door
		// could not measure, and it must not come back as {surfaces:0, undecided:0}, which is what
		// «everything is decided» looks like. Same reason as the parse branch below.
		return SignatureState{Map: absPath(path), Unreadable: true}
	}
	if docs.broken {
		return SignatureState{Map: absPath(path), Unreadable: true}
	}
	sig, err := seed.DecodeSignatureMap(raw)
	if err != nil {
		// A map that will not parse must NOT come back as {surfaces:0, undecided:0} — byte-identical to
		// «everything is decided», which is the one answer this field must never give by accident.
		return SignatureState{Map: absPath(path), Unreadable: true}
	}
	var minedRows []store.GlossaryEntry
	if len(docs.delta) > 0 {
		bs, perr := membank.ParseEngineBankSeed("mined-delta", docs.delta)
		if perr != nil {
			return SignatureState{Map: absPath(path), Unreadable: true}
		}
		minedRows = bs.Terms
		for i := range minedRows {
			minedRows[i].Source = "mined" // as loadMinedDelta stamps them, so unsignedEngineSurfaces judges them
		}
	}
	// The SAME entry set the run judges: the signed seed AND the delta, filtered by the run's own
	// "does this row count as banked" rule. A surface the owner has since written into glossary_seed by
	// hand is handled there, and counting it as undecided here would be a warning about nothing.
	all := make([]store.GlossaryEntry, 0, len(seedRows)+len(minedRows))
	all = append(append(all, seedRows...), minedRows...)
	handled := ownerHandled(unsignedEngineSurfaces(all), docs.rejects)
	st := SignatureState{Map: absPath(path)}
	for _, t := range sig.Terms {
		nk := text.NormalizeSourceKey(t.Src)
		if nk == "" {
			continue
		}
		st.Surfaces++
		if !handled[nk] {
			st.Undecided++
		}
	}
	return st
}

// capRefusalReport is the report of a document refused at one of the two caps — before the lock, before
// any read of the book. Everything below the verdict is unmeasured and says so: the signature block is
// marked unreadable when a map exists, never zeroed into «everything is decided».
func capRefusalReport(book *config.Book, err error) BankDecisionsReport {
	rep := decisionVerdict(book, membank.ApplyResult{})
	rep.Mode = "refused"
	rep.Rejected = []membank.RejectedDecision{{Index: -1, Reason: err.Error()}}
	mapPath := signatureMapPath(book.ProjectDB)
	if _, statErr := os.Stat(mapPath); statErr == nil || !errors.Is(statErr, fs.ErrNotExist) {
		rep.Signature = SignatureState{Map: absPath(mapPath), Unreadable: true}
	}
	return rep
}

// TWO caps, because ONE of them cannot bound what matters. The decision document is the only input to
// this engine whose size a USER chooses, and the engine had no bound on it at all.
//
// Why a bound is not optional: the engine's answer to running out of memory is `fatal error: out of
// memory` and exit 2, and the platform reads 2 as «the command DID its work, some units need a human»
// (platform/internal/ingest/exit.go) — the death of the engine reads as a successful run. That mis-read
// is a general engine class and is pinged, not fixed here; these bounds keep this verb from being the
// one that reaches it.
//
// ⚠ THE BYTE CAP DOES NOT BOUND TIME, and a first version of this comment claimed it did. Measured
// (`/usr/bin/time -f '%M %e'`, this machine, idle), the cost per decision depends on the SHAPE of the
// document, and the cheapest shape is the one a byte cap admits most of — `{"action":"decline",
// "src":"t1"}` is ~35 bytes against ~85 for an approval with a note:
//
//	approvals with a note:  1 000 → 0.6 s ·  5 000 → 5.2 s · 10 000 → 15.7 s · 20 000 → 50 s
//	minimal declines:       5 000 → 11.3 s · 12 000 → 58.0 s · 20 000 → 153 s · 28 900 → 308 s
//
// 28 900 minimal declines are 1 029 369 bytes — UNDER a 1 MiB cap — and take five minutes. The
// platform's budget for one engine call is 60 seconds (platform/internal/runs/reconcile.go), so such a
// document is killed on every attempt, forever, and the refusal that would have told the caller to split
// it never fires — which is why the bound that matters is the COUNT and not the bytes.
const (
	// maxDecisionsBytes bounds what is READ, before anything is parsed: a pre-parse guard against a file
	// that is not a decision document at all. Generous on purpose — it is not the interesting bound.
	maxDecisionsBytes = 1 << 20
	// maxDecisions bounds what is APPLIED, and it is the one chosen from time. 5 000 is ~11 s in the
	// worst shape measured above — five times inside the platform's budget, so a host half this speed
	// still fits. For scale it is twenty-five signing acts (the miner proposes at most 200 surfaces per
	// act) and eighty-six times the stand book's whole seed.
	//
	// It is low because the pass is Θ(N²) by construction — every per-decision helper scans the whole
	// document — and raising it means indexing those scans first. That is a ping, not this pack's work.
	maxDecisions = 5000
)

// readDecisions reads the decision document under the cap.
//
// Read through a limit rather than stat-then-read: a stat is a fact about the file a moment ago, and the
// path may not be a regular file at all (a fifo or a /proc entry stats as zero bytes and then delivers
// whatever it likes). Reading one byte past the cap is what tells the two apart.
//
// Over the cap is the DECISIONS class, not the config one: the document is well-formed and the
// deployment is fine — the caller asked for more than this engine will do in one act, and the answer is
// to split it. That is a fact about the request, which is what class 14 says.
func readDecisions(path string) ([]byte, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, RefuseConfig(fmt.Errorf("pipeline: read decisions %s: %w", path, err))
	}
	defer f.Close()
	raw, err := io.ReadAll(io.LimitReader(f, maxDecisionsBytes+1))
	if err != nil {
		return nil, RefuseConfig(fmt.Errorf("pipeline: read decisions %s: %w", path, err))
	}
	if len(raw) > maxDecisionsBytes {
		return nil, refuse(RefusalDecisionsRejected, fmt.Errorf(
			"pipeline: the decision document %s is over %d bytes — more than this engine reads in one act; split it",
			path, maxDecisionsBytes))
	}
	return raw, nil
}

// bankRows reads the book's bank AND its captured ruby readings — one open for both, because they are
// two halves of the same question ("what does the run see?") and a second open is a second lock dance.
//
// A project that has never been opened has no database and therefore neither — an ordinary state, and
// the same one an absent decision file means: nothing has been decided yet. A term can still be ADDED by
// its full tuple; only an `id` has nothing to resolve against.
func bankRows(book *config.Book) ([]store.GlossaryEntry, []store.RubyReading, error) {
	if _, err := os.Stat(book.ProjectDB); errors.Is(err, fs.ErrNotExist) {
		return nil, nil, nil
	}
	s, err := store.OpenReadOnly(book.ProjectDB)
	if err != nil {
		return nil, nil, RefuseStoreOpen(err)
	}
	defer s.Close()
	rows, err := s.GlossaryForBook(book.BookID)
	if err != nil {
		return nil, nil, fmt.Errorf("pipeline: read the bank of %s: %w", book.BookID, err)
	}
	ruby, err := s.RubyReadingsForBook(book.BookID)
	if err != nil {
		return nil, nil, fmt.Errorf("pipeline: read the ruby readings of %s: %w", book.BookID, err)
	}
	return rows, ruby, nil
}

// readDelta returns the mined delta as a document and as the bytes on disk. An absent CONVENTIONAL file
// is the empty document with nil bytes — "no decisions yet" — while an absent DECLARED one is an error,
// the same rule the run path follows (decisionFilePresent).
func readDelta(book *config.Book) (seed.File, []byte, error) {
	present, err := decisionFilePresent(book.MinedDelta)
	if err != nil || !present {
		return seed.File{}, nil, err
	}
	raw, err := os.ReadFile(book.MinedDelta)
	if err != nil {
		return seed.File{}, nil, fmt.Errorf("pipeline: read mined-delta %s: %w", book.MinedDelta, err)
	}
	f, err := seed.DecodeFile(raw)
	if err != nil {
		return seed.File{}, nil, fmt.Errorf("pipeline: parse mined-delta %s: %w", book.MinedDelta, err)
	}
	return f, raw, nil
}

func readRejects(book *config.Book) (seed.RejectFile, []byte, error) {
	present, err := decisionFilePresent(book.MinedRejects)
	if err != nil || !present {
		return seed.RejectFile{}, nil, err
	}
	raw, err := os.ReadFile(book.MinedRejects)
	if err != nil {
		return seed.RejectFile{}, nil, fmt.Errorf("pipeline: read mined-rejects %s: %w", book.MinedRejects, err)
	}
	f, err := seed.DecodeRejects(raw)
	if err != nil {
		return seed.RejectFile{}, nil, fmt.Errorf("pipeline: parse mined-rejects %s: %w", book.MinedRejects, err)
	}
	return f, raw, nil
}

// notCanonical reports whether the file on disk differs from what the engine would write for the SAME
// content — an operator's hand-formatting, comments, a different key order.
func notCanonical(raw []byte, current seed.File) bool {
	if raw == nil {
		return false
	}
	rendered, err := membank.RenderSeedFile(current)
	return err != nil || !bytes.Equal(raw, rendered)
}

func notCanonicalRejects(raw []byte, current seed.RejectFile) bool {
	if raw == nil {
		return false
	}
	rendered, err := membank.RenderRejectFile(current)
	return err != nil || !bytes.Equal(raw, rendered)
}

// changedDoc reports whether the document on disk has to be replaced. An ABSENT file (raw == nil) is
// replaced only by a document that says something: creating an empty one where "nobody has decided
// anything" was the state is exactly the file-in-advance this door exists to abolish.
func changedDoc(raw, next []byte, resultEmpty bool) bool {
	if raw == nil {
		return !resultEmpty
	}
	return !bytes.Equal(raw, next)
}

// emptyDelta reports a seed document with nothing in any of its sections.
func emptyDelta(f seed.File) bool {
	return len(f.Terms) == 0 && len(f.Voices) == 0 && len(f.Addresses) == 0
}

// orEmpty renders a nil slice as an empty one, so every list in the report serializes as `[]` and never
// as `null`: a consumer iterating it has one shape to handle, and "nothing was refused" is a value
// rather than an absence (the discipline BookExport.Chunks already keeps).
func orEmpty[T any](v []T) []T {
	if v == nil {
		return []T{}
	}
	return v
}

// absPath makes a path readable by a consumer running elsewhere. A failure to resolve leaves the path as
// the engine holds it, which is still the truth about where the engine looks.
func absPath(p string) string {
	if abs, err := filepath.Abs(p); err == nil {
		return abs
	}
	return p
}