package payments

import (
	"context"
	"errors"
	"log"
	"net/http"
	"os"
	"strings"

	"crussell/db"
	"crussell/internal/twofa"
	"crussell/mw"

	"github.com/jackc/pgx/v5"
)

// require2FADisabled reports whether REQUIRE_2FA explicitly disables 2FA
// enforcement. The parse is case-insensitive and alias-tolerant (false/0/off/no),
// so a value like "False", "OFF" or "off" never silently leaves the gate ON.
// Any other value — including empty or unknown — keeps enforcement ON
// (fail-closed).
func require2FADisabled() bool {
	switch strings.ToLower(strings.TrimSpace(os.Getenv("REQUIRE_2FA"))) {
	case "false", "0", "off", "no":
		return true
	default:
		return false
	}
}

// twoFactorEnforced reports whether 2FA is required for online card payments.
// It is fail-closed: enforcement is ON unless 2FA has been explicitly disabled
// (REQUIRE_2FA=false/0/off/no, case-insensitive — see require2FADisabled) or
// SQUARE_ENVIRONMENT explicitly selects the dev/mock stack
// (mock/dev/development/test — see IsExplicitDevOrMockEnv in
// idempotency_helpers.go). Empty or unknown SQUARE_ENVIRONMENT values are
// treated as production-enforced, so a mistyped env var can never silently
// disarm the gate — main.go logs a startup warning for that misconfiguration.
func twoFactorEnforced() bool {
	return !require2FADisabled() && !IsExplicitDevOrMockEnv()
}

// TwoFactorEnforced is the exported form of twoFactorEnforced, so the user
// package (settings endpoints) and the profile handler can report whether 2FA
// is currently required without re-implementing the env logic.
func (s *PaymentService) TwoFactorEnforced() bool {
	return twoFactorEnforced()
}

// UserTwoFactorEnabled reports whether the user has completed 2FA setup
// (users.two_factor_enabled). It is the source of truth for the card-access
// gate: an enforced environment blocks online card access for users who have
// not enabled 2FA.
func (s *PaymentService) UserTwoFactorEnabled(ctx context.Context, userID string) (bool, error) {
	var enabled bool
	err := db.Conn.QueryRow(ctx, `SELECT two_factor_enabled FROM users WHERE id = $1`, userID).Scan(&enabled)
	if err != nil {
		return false, err
	}
	return enabled, nil
}

// Single source of truth for 2FA verification: crussell/internal/twofa owns
// the code hashing (HMAC-SHA256 keyed by TWO_FACTOR_PEPPER, legacy SHA-256
// fallback), the constant-time compare, the code-lifetime check, and the
// per-user brute-force lockout. The user package's interactive endpoints
// (setup/verify/disable) and this saved-card gate all share it; nothing is
// re-implemented locally here. Two agents once shipped a drift-risk duplicate
// of the hash+verify in this file (hashTwoFAVerificationCode +
// verifyPendingTwoFactorCode) — that copy is gone, and any future change to
// the hashing or lockout rules must land in internal/twofa only.

// verifyPendingTwoFactorCode verifies the submitted code against the user's
// stored pending 2FA code. It is a thin delegation shim over
// twofa.VerifyForUser — the single source of truth for the verification core
// (per-user brute-force lockout, constant-time compare, legacy pre-pepper
// hash fallback, code lifetime). consume=true makes a verified code SINGLE-USE
// immediately (the pending code is NULLed on success); consume=false verifies
// WITHOUT consuming (MEDIUM-2 — the saved-card CHARGE gates pass false and
// defer consumption to the completed-charge transaction via
// twofa.ConsumePendingCode, so a failed Square charge does not burn the code;
// the save-card SAVE gate passes true because saving a card is a terminal
// operation with no downstream charge to attach consumption to). It returns nil
// on a valid code, or a classified twofa.ErrIncorrect / twofa.ErrLockedOut /
// twofa.ErrMissingOrExpired (or a wrapped DB error) for the caller to map to
// the correct HTTP status.
func verifyPendingTwoFactorCode(ctx context.Context, userID, code string, consume bool) error {
	return twofa.VerifyForUser(ctx, userID, code, consume)
}

// twoFactorFallbackEnabled reports whether the homegrown 2FA may act as a
// BACKUP authorization for a saved-card charge when SCA is unavailable (the
// charge carries no Square verification_token). The parse is case-insensitive
// and alias-tolerant (false/0/off/no) — a value like "False" or "OFF" never
// silently leaves the fallback ON. Any other value — including empty and
// unknown — keeps the fallback enabled (the shipped default). It is the
// TWO_FACTOR_FALLBACK policy switch read at startup by main.go and exposed via
// PaymentService.TwoFactorFallbackEnabled.
func twoFactorFallbackEnabled() bool {
	switch strings.ToLower(strings.TrimSpace(os.Getenv("TWO_FACTOR_FALLBACK"))) {
	case "false", "0", "off", "no":
		return false
	default:
		return true
	}
}

// TwoFactorFallbackEnabled is the exported form of twoFactorFallbackEnabled, so
// main.go can log the SCA-primary/2FA-backup posture at startup without
// re-implementing the env logic.
func (s *PaymentService) TwoFactorFallbackEnabled() bool {
	return twoFactorFallbackEnabled()
}

// requireTwoFactorForCardAccess gates the saved-card online payment paths under
// the SCA-primary / 2FA-backup decision model. It returns (allowed, fallbackUsed):
// allowed is true when the request may proceed; fallbackUsed is true when the
// authorization was granted by the homegrown 2FA BACKUP (SCA was unavailable and
// the customer's 2FA code verified) — the caller must then write a strict
// insertTwoFAFallbackAudit row for the charge.
//
// The decision model, in order:
//
//   - 2FA is not enforced (dev/mock) → allowed, no fallback.
//
//   - The request carries a Square verification_token (SCA performed — the
//     issuer has already authenticated the buyer): SKIP the 2FA gate entirely.
//     SCA is PRIMARY; the issuer did the job, so the homegrown gate is never
//     consulted (fallbackUsed=false). A charge that carries a token passes even
//     for a user who has not enabled 2FA.
//
//   - Otherwise the gate is the FALLBACK authorization for a ccof charge with
//     no verification token. It only runs when the fallback is permitted:
//
//     (a) TWO_FACTOR_FALLBACK is enabled (see twoFactorFallbackEnabled) — when
//     the deployment opts out, a token-less charge is denied 402
//     verification_required: the frontend shows the SCA challenge, and if the
//     bank cannot do SCA the payment cannot proceed (security-first); and
//
//     (b) a 2FA code delivery channel exists (twoFADeliveryAvailable, build-
//     dependent like the user package's) — a code the customer can never
//     receive would silently lock the gate, so it is denied 503
//     ("2FA requires an email or SMS delivery channel").
//
//   - The user has completed 2FA setup (two_factor_enabled) AND the request
//     carries a verification_code matching the user's stored pending code.
//
// B10: the setup flag alone must NOT unlock saved-card charges — an enforced
// environment requires an actual one-time code challenge at charge time, so
// merely enabling 2FA (a setup flag) can never unlock saved-card access with
// no challenge. The code is the customer's current pending 2FA code, which an
// operator relays (delivery is the user package's build-dependent [2FA] log /
// email-SMS channel).
//
// consume controls whether a verified code is NULLed immediately (consume=true
// — the save-card SAVE gate) or left intact for the caller to consume when its
// operation reaches a terminal success state (consume=false — the saved-card
// CHARGE gates; see verifyPendingTwoFactorCode / twofa.ConsumePendingCode,
// MEDIUM-2). In every case the 5-attempt lockout and the
// code-destroy-on-lockout semantics are unchanged (twofa.Check).
//
// The code check is delegated to crussell/internal/twofa via
// verifyPendingTwoFactorCode, so this gate participates in the SAME per-user
// brute-force lockout (5 failed attempts invalidate the pending code) as the
// user package's setup/verify/disable flows. Classified errors map to the HTTP
// statuses the frontend expects: incorrect → 400, locked out → 429, missing or
// expired → 400, DB failure → 500.
//
// On any denial an error JSON is written (parseable by the frontend via
// extractErrorMessage) and allowed=false is returned — the caller must abort
// the charge.
func requireTwoFactorForCardAccess(w http.ResponseWriter, r *http.Request, service *PaymentService, userID, verificationCode, verificationToken string, consume bool) (allowed, fallbackUsed bool) {
	if !twoFactorEnforced() {
		return true, false
	}
	if service == nil {
		service = &PaymentService{}
	}
	// SCA-primary: a Square verification_token means the issuer already
	// completed Strong Customer Authentication — the 2FA gate is skipped and no
	// fallback audit applies.
	if verificationToken != "" {
		return true, false
	}
	// 2FA is now the BACKUP authorization for a token-less ccof charge. Fail
	// closed when the deployment disabled the fallback (TWO_FACTOR_FALLBACK) or
	// has no delivery channel for its codes (twoFADeliveryAvailable).
	if !twoFactorFallbackEnabled() {
		writeVerificationRequiredResponse(w)
		return false, false
	}
	if !twoFADeliveryAvailable() {
		mw.RespondError(w, http.StatusServiceUnavailable, "2FA requires an email or SMS delivery channel; contact the salon")
		return false, false
	}
	enabled, err := service.UserTwoFactorEnabled(r.Context(), userID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			mw.RespondError(w, http.StatusForbidden, "Two-factor authentication is required to use online card payments. Enable it in your account settings.")
			return false, false
		}
		log.Printf("failed to check two-factor status for user %s: %v", userID, err)
		mw.RespondError(w, http.StatusInternalServerError, "failed to check two-factor status")
		return false, false
	}
	if !enabled {
		mw.RespondError(w, http.StatusForbidden, "Two-factor authentication is required to use online card payments. Enable it in your account settings.")
		return false, false
	}
	// B10: an enforced charge of a saved card needs a live one-time code, not
	// just the enabled setup flag.
	if verificationCode == "" {
		mw.RespondError(w, http.StatusForbidden, "A two-factor verification code is required to use this saved card. Ask the customer for their current code.")
		return false, false
	}
	switch err := verifyPendingTwoFactorCode(r.Context(), userID, verificationCode, consume); {
	case err == nil:
		// The 2FA BACKUP authorized this token-less saved-card charge. The
		// caller writes the strict fallback audit row on the charge's success.
		return true, true
	case errors.Is(err, twofa.ErrIncorrect):
		mw.RespondError(w, http.StatusBadRequest, "Invalid verification code")
		return false, false
	case errors.Is(err, twofa.ErrLockedOut):
		mw.RespondError(w, http.StatusTooManyRequests, "Too many attempts")
		return false, false
	case errors.Is(err, twofa.ErrMissingOrExpired):
		mw.RespondError(w, http.StatusBadRequest, "Verification code expired — request a new one")
		return false, false
	default:
		log.Printf("failed to check two-factor verification code for user %s: %v", userID, err)
		mw.RespondError(w, http.StatusInternalServerError, "failed to check two-factor verification code")
		return false, false
	}
}