package pipeline

import (
	"errors"

	"textmachine/backend/internal/store"
)

// refusal.go: the shell contract's REFUSAL classes (row 165 / PD-196 of the platform).
//
// The defect this closes was not cosmetic. `tmctl` mapped every failure it did not recognise onto exit
// 1, so "this source is unreadable", "this config is broken" and "another process holds the project"
// arrived at an automated caller as one number — and the platform's intake, which retries a book five
// times and then rejects it as `source_unreadable`, came within one step of deleting a user's upload
// because an operator mistyped a key in a hand-written book.yaml.
//
// The form is a CLASS carried by a typed error, mapped to an exit code by cmd/tmctl. It is a class and
// not a code here on purpose: the engine owns the vocabulary, the shell contract owns the numbers, and a
// class this build of a reader has never heard of still lands inside the reserved band and reads as
// "refused" rather than as "failed" — which is the difference between waiting and destroying data.
//
// THE BAND HAS TWO TIERS, and the letter of each matters:
//
//   - The FLOOR — what membership in [10,19] alone guarantees — is «no work needs rolling back, and a
//     retry is SAFE». Safe means "will not harm", never "will help": retrying a broken config forever
//     helps nobody, but it destroys nothing either.
//   - EACH CLASS declares its own, stronger invariant on top of the floor, in its own comment. The five
//     original classes (config, source, lock, schema, decisions) all keep «nothing of the book's state
//     changed» (bank, decisions, database) — as a clause of the CLASS, not of the band. Stated that
//     narrowly on purpose: the translate path writes its pre-flight BACKUP before the store open can
//     refuse 12/13, so «nothing happened at all» is not true of the process even there — a backup is
//     additive and rotationless, which is what keeps the floor's «no rollback needed» intact.
//
// GUARDRAIL, now letter rather than habit: a consumer keys a DESTRUCTIVE action (deleting an upload,
// dropping a book, rewriting state) on a specific CLASS it knows, never on band membership. Band
// membership licenses waiting and retrying, nothing more — a class weaker than «nothing happened» (see
// RefusalWriteIncomplete) can join the band without any consumer becoming wrong.

// RefusalClass names WHY an invocation was turned down. Values are stable strings: a new class is a new
// value here and a new number in cmd/tmctl's table, never a new branch in a consumer.
type RefusalClass string

const (
	// RefusalBadConfig is a configuration this engine will not run: unreadable, unparseable, or invalid.
	// The operator's file is the thing to fix; the book's source is untouched and blameless.
	RefusalBadConfig RefusalClass = "config_invalid"
	// RefusalSourceUnreadable is a book whose SOURCE cannot be read or decoded. This is the one class
	// that says something about the user's text rather than about the operator's config.
	RefusalSourceUnreadable RefusalClass = "source_unreadable"
	// RefusalProjectLocked is another tmctl process owning the project. Nothing is wrong with anything —
	// the answer is to come back later.
	RefusalProjectLocked RefusalClass = "project_locked"
	// RefusalSchemaMismatch is a project database whose schema version is not this binary's. Nothing is
	// wrong with the book either: the answer is `tmctl migrate` (or, in the other direction, a newer
	// binary), and the two numbers a caller needs to tell those apart ride the message as the stable
	// token `schema_mismatch found=<N> expected=<M>` (store.SchemaMismatchError).
	//
	// It is its own class because read-only opens never migrate, so an engine upgrade refuses every
	// existing book until a write command touches it — and the platform's own pre-spawn call is one of
	// those read-only opens, so that write command never came (the deploy deadlock, backlog row 174).
	// A caller that can SEE this class self-heals ("caught it → migrate → retry") where it used to stop
	// the world over what looked like a broken project.
	RefusalSchemaMismatch RefusalClass = "schema_mismatch"
	// RefusalDecisionsRejected is a decision document that WAS read as one and that this engine will not
	// apply: it conflicts with the signed seed, it decides a term twice, it approves a term with no
	// rendering. Nothing about the deployment is wrong and nothing about the book is wrong.
	//
	// It is its own class and not the config one, on the axis that decides what a caller DOES with the
	// number. Both mean "a human acts", but not the same human: 10 means the OPERATOR fixes a
	// deployment — the platform's own reader treats it that way mechanically, exempting the failure
	// from a book's attempt budget as "a condition every book on the host shares"
	// (platform/internal/ingest/exit.go DeploymentFault) — while this one means the END USER re-decides,
	// about one document, on one book, with retry futile until they do. Filing it as a deployment fault
	// would hide a user's own mistake behind an outage that is not happening.
	//
	// Safe to add by construction, which is the whole point of a BAND: a reader that has never heard of
	// the number still sees it inside [10,19] and reads "refused, retry is safe" rather than "failed"
	// (ingest.Refused → OutcomeRefused), and new flags and codes travel engine-first.
	RefusalDecisionsRejected RefusalClass = "decisions_rejected"
	// RefusalWriteIncomplete is a decision document the engine ACCEPTED whose write did not complete —
	// covering both «nothing landed» (an environment failure met while both documents were still staged
	// under temp names) and «half landed» (a failure between the two renames). ONE class for both on
	// purpose: a consumer acts identically — nothing to roll back, re-send the same document — and the
	// difference rides the report's per-file truth (written_delta / written_rejects), not the number.
	//
	// Its invariant is the band FLOOR and deliberately nothing more: this is the one class that CANNOT
	// promise «nothing happened», which is why the floor is worded as «no rollback needed, retry safe»
	// rather than as innocence. The retry converges because the call is all-or-nothing and recomputed
	// from scratch — a landed half reports `already_applied`, an unlanded half is applied (proven by the
	// acceptance's half-write probe). It is NOT the config class: the deployment is fine and the
	// document is fine — the disk, at that moment, was not.
	RefusalWriteIncomplete RefusalClass = "write_incomplete"
	// RefusalBookIncomplete is a book file `tmctl build` will not write: the book has a HOLE — a unit not
	// yet translated, a unit whose text was withheld (a substantive flag, D2), a unit missing a member's
	// worth of text, or translated text the current cut of the book cannot place (ghost rows) — and the
	// caller did not say `--partial`. The default is the refusal because a reader-facing copy is
	// fail-closed (D29.1(б)): a file that is silently short of the book is the worst outcome the writer
	// can produce. The refusal lists every hole (chapter, unit, reason), and `--partial` writes the same
	// book with the notice on its first page and a mark at every hole (bookbuild.go).
	//
	// Nothing was written and nothing of the book's state changed — the class keeps the full «nothing
	// happened» clause. It is its own class, not the config one: the deployment is fine and the book is
	// fine; the book is simply not finished, and the caller decides whether an unfinished copy is wanted.
	RefusalBookIncomplete RefusalClass = "book_incomplete"
)

// Refusal is an invocation the engine turned down: nothing reached a provider, nothing was spent, no
// work needs rolling back and a retry is safe (the band floor). How much MORE than that holds — for
// every class but RefusalWriteIncomplete, «nothing of the book's state changed» — is each class's own
// clause, stated with the classes. It says nothing about whether the BOOK is untouched by history: a
// resumed run refused at ingest has been paid for before.
type Refusal struct {
	Class RefusalClass
	err   error
}

func (e *Refusal) Error() string { return e.err.Error() }
func (e *Refusal) Unwrap() error { return e.err }

// refuse wraps err as a refusal of class c. A nil err is nil: the wrapper never invents a failure.
func refuse(c RefusalClass, err error) error {
	if err == nil {
		return nil
	}
	return &Refusal{Class: c, err: err}
}

// RefuseConfig classifies a config-load failure for a caller OUTSIDE this package. The pre-flight backup
// guard is one: it loads book.yaml before the runner exists, so it — not openRunner — is what a broken
// config meets first on the `translate` path, and an unclassified error there would put every refusal
// back on exit 1 no matter how carefully the runner classifies its own.
func RefuseConfig(err error) error {
	return refuse(RefusalBadConfig, err)
}

// RefuseStoreOpen classifies a store-open failure. It is exported and it is the ONE place the mapping
// lives, because two callers open a project store: openRunner below, and `tmctl migrate`, which opens
// one with no runner at all. A second copy of this switch is how "another process holds it" and "this
// binary does not match the schema" drift back into a single exit 1 on one of the two paths.
//
// An unrecognised failure is returned UNCHANGED rather than swept into the band: the band means "turned
// down before doing any work", and a caller destroys or waits on data because of it.
func RefuseStoreOpen(err error) error {
	var mismatch *store.SchemaMismatchError
	switch {
	case err == nil:
		return nil
	case errors.Is(err, store.ErrLocked):
		return refuse(RefusalProjectLocked, err)
	case errors.As(err, &mismatch):
		return refuse(RefusalSchemaMismatch, err)
	default:
		return err
	}
}

// refuseSource classifies a failure to obtain the book's text, and it classifies almost all of them as a
// CONFIG fault. That is deliberate, and it is the most consequential decision in this file.
//
// RefusalSourceUnreadable is the verdict an automated intake acts on by DELETING the user's upload. So
// it may only be returned for something no configuration knob can explain — and a read failure is not
// that: a path that is not there, a permission, an I/O error, a vanished mount all say something about
// the deployment (a template naming a filename the upload route did not use, a chown bug) and nothing
// about the text. Neither is a DECODE failure, which was the first answer here and is wrong for the same
// reason: decoding is driven by the book's declared `encoding` and `source_lang`, so "these bytes are
// not text" and "you told me the wrong way to read them" are the same error. Two independent reviews
// arrived at that case from opposite directions.
//
// What is left, and the only thing the engine can assert about the TEXT with no config in the way, is
// sourceHasNoContent below: the bytes were read and cut, and there is no book in them.
func refuseSource(err error) error {
	return refuse(RefusalBadConfig, err)
}

// sourceHasNoContent is the one refusal that IS about the user's text: reading and cutting the source
// succeeded and produced nothing to translate. No `encoding`, `source_lang` or path setting explains an
// empty result from a successful read, which is what makes it safe to act on.
func sourceHasNoContent(err error) error {
	return refuse(RefusalSourceUnreadable, err)
}