// Package claim is the customer-claim password-code engine (v0.50.0, closes DRILL-day0-vm F-4).
// The hub generates a one-time claim code, emails it (Hungarian) to the REGISTERED customer
// address, and stores only bcrypt(code) — the plaintext exists solely inside the email send
// (the retrieval-passphrase custody rule). The controller receives the hash (+ generation)
// baked into controller.yaml at Day-0 and via the report ACK for live boxes, and gates its
// dashboard until the customer claims it by setting their own password. Reset rides the same
// engine: a rotation bumps the generation (single active code) and NEVER clears claimed_at.
package claim

import (
	"fmt"
	"log"

	"gitea.dooplex.hu/admin/felhom-hub/internal/configgen"
	"gitea.dooplex.hu/admin/felhom-hub/internal/store"
	"golang.org/x/crypto/bcrypt"
)

// codeWords is the claim/reset code length: 3 Hungarian words (~44 bits with the ~29K list) —
// dictatable over the phone, and the controller's 5-attempt/15-min lockout makes online guessing
// infeasible.
const codeWords = 3

// maxResetPerDay is the hub-side cap on controller-forwarded reset requests (per customer).
const maxResetPerDay = 3

// EmailKind selects the Hungarian template for a code delivery.
type EmailKind string

const (
	EmailClaim   EmailKind = "claim"   // first setup: "Elindult a Felhom szervered"
	EmailReset   EmailKind = "reset"   // forgotten password
	EmailClaimed EmailKind = "claimed" // confirmation after a successful claim (carries no code)
)

// Mailer delivers a claim-arc email. The code is passed through and MUST NOT be persisted or
// logged by implementations (empty for EmailClaimed). kind is one of the EmailKind constants
// (plain string in the signature so implementations need no import of this package).
type Mailer interface {
	SendClaimEmail(kind, customerID, email, domain, code string) error
}

// Engine composes the store, the code generator and the mailer. All methods are idempotent or
// explicitly rotating; none ever stores or logs a plaintext code.
type Engine struct {
	Store  *store.Store
	Mailer Mailer
	Logger *log.Logger
}

func (e *Engine) logf(f string, a ...any) {
	if e.Logger != nil {
		e.Logger.Printf(f, a...)
	}
}

// newCode generates a fresh code and its bcrypt hash.
func newCode() (code, hash string, err error) {
	code, err = configgen.RandomPassphrase(codeWords)
	if err != nil {
		return "", "", fmt.Errorf("claim: generating code: %w", err)
	}
	h, err := bcrypt.GenerateFromPassword([]byte(code), 10)
	if err != nil {
		return "", "", fmt.Errorf("claim: hashing code: %w", err)
	}
	return code, string(h), nil
}

// rotateAndSend rotates the code (generation+1 / create) and emails it. The email failure path
// keeps the rotated hash (the gate stays armed) and is LOUD: the operator sees emailed_at unset
// on the customer page and can resend. Returns the new generation.
func (e *Engine) rotateAndSend(cc *store.CustomerConfig, kind EmailKind) (int, error) {
	code, hash, err := newCode()
	if err != nil {
		return 0, err
	}
	gen, err := e.Store.RotateClaimCode(cc.CustomerID, hash)
	if err != nil {
		return 0, fmt.Errorf("claim: storing code hash: %w", err)
	}
	if cc.Email == "" {
		e.logf("[ERROR] [claim] %s code generated (gen %d) but customer %s has NO registered email — deliver via resend after setting one", kind, gen, cc.CustomerID)
		return gen, fmt.Errorf("claim: customer %s has no registered email", cc.CustomerID)
	}
	if err := e.Mailer.SendClaimEmail(string(kind), cc.CustomerID, cc.Email, cc.Domain, code); err != nil {
		e.logf("[ERROR] [claim] %s code email to customer %s FAILED (gate stays armed; resend from the customer page): %v", kind, cc.CustomerID, err)
		return gen, fmt.Errorf("claim: sending %s email: %w", kind, err)
	}
	if err := e.Store.MarkClaimEmailed(cc.CustomerID); err != nil {
		e.logf("[WARN] [claim] %s code sent to customer %s but emailed_at not recorded: %v", kind, cc.CustomerID, err)
	}
	e.logf("[INFO] [claim] %s code (gen %d) emailed to the registered address of %s", kind, gen, cc.CustomerID)
	return gen, nil
}

// EnsureIssued guarantees a claim row exists for the customer, issuing + emailing the first code
// when absent. An existing row (any state) is returned untouched — repeated config pulls and
// reports never rotate or re-send. This is the Day-0 entry point (API config retrieve) and the
// live-box entry point (first report of an upgrading fleet).
func (e *Engine) EnsureIssued(cc *store.CustomerConfig) (*store.ClaimState, error) {
	cs, err := e.Store.GetClaim(cc.CustomerID)
	if err != nil {
		return nil, fmt.Errorf("claim: reading state: %w", err)
	}
	if cs != nil {
		return cs, nil
	}
	if _, err := e.rotateAndSend(cc, EmailClaim); err != nil {
		// The hash (if stored) still arms the gate; surface the error for the caller's log.
		cs, gerr := e.Store.GetClaim(cc.CustomerID)
		if gerr == nil && cs != nil {
			return cs, err
		}
		return nil, err
	}
	return e.Store.GetClaim(cc.CustomerID)
}

// Resend rotates the code and re-sends it — the operator "Kód újraküldése" button. An unclaimed
// customer gets the claim template; a claimed one gets the reset template (the only code a
// claimed box can consume is a reset).
func (e *Engine) Resend(cc *store.CustomerConfig) error {
	cs, err := e.Store.GetClaim(cc.CustomerID)
	if err != nil {
		return fmt.Errorf("claim: reading state: %w", err)
	}
	kind := EmailClaim
	if cs.Claimed() {
		kind = EmailReset
	}
	_, err = e.rotateAndSend(cc, kind)
	return err
}

// RequestReset handles a controller-forwarded "Elfelejtett jelszó": rate-limited hub-side
// (maxResetPerDay per customer), then rotates + emails a reset code. The neutral customer-facing
// response ("ha az e-mail cím regisztrálva van…") is the CALLER's job — this returns real errors
// for the operator log.
func (e *Engine) RequestReset(cc *store.CustomerConfig) error {
	cs, err := e.Store.GetClaim(cc.CustomerID)
	if err != nil {
		return fmt.Errorf("claim: reading state: %w", err)
	}
	if cs == nil {
		// No claim row yet (pre-arc box asking for a reset): issue the first code instead.
		_, err := e.EnsureIssued(cc)
		return err
	}
	count, err := e.Store.BumpResetCount(cc.CustomerID)
	if err != nil {
		return fmt.Errorf("claim: reset limiter: %w", err)
	}
	if count > maxResetPerDay {
		e.logf("[WARN] [claim] reset request for %s REFUSED: daily cap reached (%d/%d)", cc.CustomerID, count, maxResetPerDay)
		return fmt.Errorf("claim: reset cap reached for %s (%d/day)", cc.CustomerID, maxResetPerDay)
	}
	_, err = e.rotateAndSend(cc, EmailReset)
	return err
}

// MarkClaimed records a controller-reported successful claim and sends the one-time confirmation
// email on the unclaimed→claimed transition (idempotent — repeated reports are no-ops).
func (e *Engine) MarkClaimed(cc *store.CustomerConfig) error {
	transitioned, err := e.Store.MarkClaimed(cc.CustomerID)
	if err != nil {
		return fmt.Errorf("claim: marking claimed: %w", err)
	}
	if !transitioned {
		return nil
	}
	e.logf("[INFO] [claim] customer %s CLAIMED its dashboard (password set by the customer)", cc.CustomerID)
	if cc.Email != "" {
		if err := e.Mailer.SendClaimEmail(string(EmailClaimed), cc.CustomerID, cc.Email, cc.Domain, ""); err != nil {
			e.logf("[WARN] [claim] claimed-confirmation email to %s failed: %v", cc.CustomerID, err)
		}
	}
	return nil
}