package auth

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"time"

	"galaxy/backend/internal/postgres/jet/backend/model"
	"galaxy/backend/internal/postgres/jet/backend/table"

	"github.com/go-jet/jet/v2/postgres"
	"github.com/go-jet/jet/v2/qrm"
	"github.com/google/uuid"
)

// Challenge mirrors a row in `backend.auth_challenges` enriched with the
// PreferredLanguage column added by migration 00002. The CodeHash slice
// is the raw bcrypt hash; verifyCode wraps the comparison.
type Challenge struct {
	ChallengeID uuid.UUID
	Email string
	CodeHash []byte
	Attempts int32
	CreatedAt time.Time
	ExpiresAt time.Time
	ConsumedAt *time.Time
	PreferredLanguage string
}

// Session mirrors a row in `backend.device_sessions`. The
// ClientPublicKey slice is the raw 32-byte Ed25519 key; the handler
// layer is responsible for base64 encoding/decoding on the wire.
type Session struct {
	DeviceSessionID uuid.UUID
	UserID uuid.UUID
	Status string
	ClientPublicKey []byte
	CreatedAt time.Time
	RevokedAt *time.Time
	LastSeenAt *time.Time
}

// SessionStatusActive and SessionStatusRevoked enumerate the values
// auth writes. The CHECK constraint on `device_sessions.status` also
// allows 'blocked', which the user package emits when applying a
// `permanent_block` sanction.
const (
	SessionStatusActive = "active"
	SessionStatusRevoked = "revoked"
)

// Store is the Postgres-backed query surface for `backend.auth_challenges`,
// `backend.device_sessions` and the read-side `backend.accounts` lookup
// auth needs to detect permanently-blocked emails.
type Store struct {
	db *sql.DB
}

// NewStore constructs a Store wrapping db.
func NewStore(db *sql.DB) *Store {
	return &Store{db: db}
}

// challengeColumns lists the projection used by every read of
// `auth_challenges`. The order matches model.AuthChallenges field order
// inside QueryContext destination scans.
func challengeColumns() postgres.ColumnList {
	return postgres.ColumnList{
		table.AuthChallenges.ChallengeID,
		table.AuthChallenges.Email,
		table.AuthChallenges.CodeHash,
		table.AuthChallenges.Attempts,
		table.AuthChallenges.CreatedAt,
		table.AuthChallenges.ExpiresAt,
		table.AuthChallenges.ConsumedAt,
		table.AuthChallenges.PreferredLanguage,
	}
}

// sessionColumns lists the projection used by every read of
// `device_sessions`.
func sessionColumns() postgres.ColumnList {
	return postgres.ColumnList{
		table.DeviceSessions.DeviceSessionID,
		table.DeviceSessions.UserID,
		table.DeviceSessions.ClientPublicKey,
		table.DeviceSessions.Status,
		table.DeviceSessions.CreatedAt,
		table.DeviceSessions.RevokedAt,
		table.DeviceSessions.LastSeenAt,
	}
}

// IsEmailPermanentlyBlocked reports whether email maps to a live
// `accounts` row whose permanent_block column is true. The lookup is
// case-sensitive: callers are expected to pass an already-normalised
// (lowercase, trimmed) email.
//
// A non-existent account returns (false, nil) — the auth flow treats
// such emails as eligible for fresh registration.
func (s *Store) IsEmailPermanentlyBlocked(ctx context.Context, email string) (bool, error) {
	stmt := postgres.SELECT(table.Accounts.PermanentBlock).
		FROM(table.Accounts).
		WHERE(
			table.Accounts.Email.EQ(postgres.String(email)).
				AND(table.Accounts.DeletedAt.IS_NULL()),
		).
		LIMIT(1)

	var row model.Accounts
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return false, nil
		}
		return false, fmt.Errorf("auth store: query permanent_block for %q: %w", email, err)
	}
	return row.PermanentBlock, nil
}

// LatestUnconsumedChallenge returns the most recently issued
// un-consumed, non-expired challenge for email created at or after
// since. Returns sql.ErrNoRows when no such challenge exists. The
// throttle path uses this method to reuse the existing challenge_id
// rather than emit a fresh row.
func (s *Store) LatestUnconsumedChallenge(ctx context.Context, email string, since time.Time) (Challenge, error) {
	stmt := postgres.SELECT(challengeColumns()).
		FROM(table.AuthChallenges).
		WHERE(
			table.AuthChallenges.Email.EQ(postgres.String(email)).
				AND(table.AuthChallenges.ConsumedAt.IS_NULL()).
				AND(table.AuthChallenges.ExpiresAt.GT(postgres.NOW())).
				AND(table.AuthChallenges.CreatedAt.GT_EQ(postgres.TimestampzT(since))),
		).
		ORDER_BY(table.AuthChallenges.CreatedAt.DESC()).
		LIMIT(1)

	var row model.AuthChallenges
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Challenge{}, sql.ErrNoRows
		}
		return Challenge{}, err
	}
	return modelToChallenge(row), nil
}

// CountRecentChallenges returns the number of un-consumed, non-expired
// challenges issued for email at or after since. Used by the throttle
// gate in SendEmailCode.
func (s *Store) CountRecentChallenges(ctx context.Context, email string, since time.Time) (int, error) {
	stmt := postgres.SELECT(postgres.COUNT(postgres.STAR).AS("count")).
		FROM(table.AuthChallenges).
		WHERE(
			table.AuthChallenges.Email.EQ(postgres.String(email)).
				AND(table.AuthChallenges.ConsumedAt.IS_NULL()).
				AND(table.AuthChallenges.ExpiresAt.GT(postgres.NOW())).
				AND(table.AuthChallenges.CreatedAt.GT_EQ(postgres.TimestampzT(since))),
		)

	var dest struct {
		Count int64 `alias:"count"`
	}
	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
		return 0, fmt.Errorf("auth store: count recent challenges: %w", err)
	}
	return int(dest.Count), nil
}

// InsertChallenge persists a fresh `auth_challenges` row. The caller
// owns the primary-key, the bcrypt hash, the expires_at timestamp and
// the captured locale. created_at and attempts default at the schema
// level.
func (s *Store) InsertChallenge(ctx context.Context, c Challenge) error {
	stmt := table.AuthChallenges.INSERT(
		table.AuthChallenges.ChallengeID,
		table.AuthChallenges.Email,
		table.AuthChallenges.CodeHash,
		table.AuthChallenges.ExpiresAt,
		table.AuthChallenges.PreferredLanguage,
	).VALUES(c.ChallengeID, c.Email, c.CodeHash, c.ExpiresAt, c.PreferredLanguage)

	if _, err := stmt.ExecContext(ctx, s.db); err != nil {
		return fmt.Errorf("auth store: insert challenge: %w", err)
	}
	return nil
}

// LoadAndIncrementChallenge atomically locks the challenge row,
// validates that it is still un-consumed and non-expired, and increments
// its `attempts` counter. The returned Challenge carries the
// post-increment counter so the caller can compare it against the
// configured ceiling without a second query.
//
// Returns ErrChallengeNotFound when the row does not exist, has been
// consumed, or has expired. Any other error is wrapped with the auth
// store prefix.
func (s *Store) LoadAndIncrementChallenge(ctx context.Context, challengeID uuid.UUID) (Challenge, error) {
	var loaded Challenge
	err := withTx(ctx, s.db, func(tx *sql.Tx) error {
		selectStmt := postgres.SELECT(challengeColumns()).
			FROM(table.AuthChallenges).
			WHERE(table.AuthChallenges.ChallengeID.EQ(postgres.UUID(challengeID))).
			FOR(postgres.UPDATE())

		var row model.AuthChallenges
		if err := selectStmt.QueryContext(ctx, tx, &row); err != nil {
			if errors.Is(err, qrm.ErrNoRows) {
				return ErrChallengeNotFound
			}
			return err
		}
		loaded = modelToChallenge(row)
		if loaded.ConsumedAt != nil {
			return ErrChallengeNotFound
		}
		if !loaded.ExpiresAt.After(time.Now()) {
			return ErrChallengeNotFound
		}
		updateStmt := table.AuthChallenges.
			UPDATE(table.AuthChallenges.Attempts).
			SET(table.AuthChallenges.Attempts.ADD(postgres.Int(1))).
			WHERE(table.AuthChallenges.ChallengeID.EQ(postgres.UUID(challengeID)))
		if _, err := updateStmt.ExecContext(ctx, tx); err != nil {
			return err
		}
		loaded.Attempts++
		return nil
	})
	if err != nil {
		if errors.Is(err, ErrChallengeNotFound) {
			return Challenge{}, err
		}
		return Challenge{}, fmt.Errorf("auth store: load and increment challenge: %w", err)
	}
	return loaded, nil
}

// MarkConsumedAndInsertSession atomically:
//
// 1. Locks the challenge row.
// 2. Validates that it is still un-consumed and non-expired.
// 3. Sets consumed_at = now().
// 4. Inserts the supplied Session into device_sessions with status =
// 'active'.
//
// The two writes are committed together so a single challenge yields at
// most one device session even under concurrent confirm-email-code
// callers.
//
// Returns ErrChallengeNotFound when the challenge has been consumed (by
// a concurrent caller) or has expired in the gap between the
// LoadAndIncrementChallenge call and this one.
func (s *Store) MarkConsumedAndInsertSession(ctx context.Context, challengeID uuid.UUID, session Session) error {
	err := withTx(ctx, s.db, func(tx *sql.Tx) error {
		lockStmt := postgres.SELECT(table.AuthChallenges.ConsumedAt, table.AuthChallenges.ExpiresAt).
			FROM(table.AuthChallenges).
			WHERE(table.AuthChallenges.ChallengeID.EQ(postgres.UUID(challengeID))).
			FOR(postgres.UPDATE())

		var locked model.AuthChallenges
		if err := lockStmt.QueryContext(ctx, tx, &locked); err != nil {
			if errors.Is(err, qrm.ErrNoRows) {
				return ErrChallengeNotFound
			}
			return err
		}
		if locked.ConsumedAt != nil || !locked.ExpiresAt.After(time.Now()) {
			return ErrChallengeNotFound
		}
		consumeStmt := table.AuthChallenges.
			UPDATE(table.AuthChallenges.ConsumedAt).
			SET(postgres.NOW()).
			WHERE(table.AuthChallenges.ChallengeID.EQ(postgres.UUID(challengeID)))
		if _, err := consumeStmt.ExecContext(ctx, tx); err != nil {
			return err
		}
		insertStmt := table.DeviceSessions.INSERT(
			table.DeviceSessions.DeviceSessionID,
			table.DeviceSessions.UserID,
			table.DeviceSessions.ClientPublicKey,
			table.DeviceSessions.Status,
		).VALUES(session.DeviceSessionID, session.UserID, session.ClientPublicKey, SessionStatusActive)
		if _, err := insertStmt.ExecContext(ctx, tx); err != nil {
			return err
		}
		return nil
	})
	if err != nil {
		if errors.Is(err, ErrChallengeNotFound) {
			return err
		}
		return fmt.Errorf("auth store: mark consumed and insert session: %w", err)
	}
	return nil
}

// ListActiveSessions loads every row from device_sessions whose status
// is 'active'. Cache.Warm calls this at process boot.
func (s *Store) ListActiveSessions(ctx context.Context) ([]Session, error) {
	stmt := postgres.SELECT(sessionColumns()).
		FROM(table.DeviceSessions).
		WHERE(table.DeviceSessions.Status.EQ(postgres.String(SessionStatusActive)))

	var rows []model.DeviceSessions
	if err := stmt.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("auth store: list active sessions: %w", err)
	}
	out := make([]Session, 0, len(rows))
	for _, row := range rows {
		out = append(out, modelToSession(row))
	}
	return out, nil
}

// LoadSession returns the row for deviceSessionID regardless of status.
// Returns ErrSessionNotFound on missing row.
func (s *Store) LoadSession(ctx context.Context, deviceSessionID uuid.UUID) (Session, error) {
	stmt := postgres.SELECT(sessionColumns()).
		FROM(table.DeviceSessions).
		WHERE(table.DeviceSessions.DeviceSessionID.EQ(postgres.UUID(deviceSessionID))).
		LIMIT(1)

	var row model.DeviceSessions
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Session{}, ErrSessionNotFound
		}
		return Session{}, fmt.Errorf("auth store: load session %s: %w", deviceSessionID, err)
	}
	return modelToSession(row), nil
}

// RevokeSession transitions an active row to status='revoked' and
// returns the row as it stands after the update. The boolean reports
// whether the UPDATE actually changed a row — false means the row was
// already revoked or did not exist; the auth Service then falls back to
// LoadSession for idempotent-revoke responses.
func (s *Store) RevokeSession(ctx context.Context, deviceSessionID uuid.UUID) (Session, bool, error) {
	stmt := table.DeviceSessions.
		UPDATE(table.DeviceSessions.Status, table.DeviceSessions.RevokedAt).
		SET(postgres.String(SessionStatusRevoked), postgres.NOW()).
		WHERE(
			table.DeviceSessions.DeviceSessionID.EQ(postgres.UUID(deviceSessionID)).
				AND(table.DeviceSessions.Status.EQ(postgres.String(SessionStatusActive))),
		).
		RETURNING(sessionColumns())

	var row model.DeviceSessions
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Session{}, false, nil
		}
		return Session{}, false, fmt.Errorf("auth store: revoke session %s: %w", deviceSessionID, err)
	}
	return modelToSession(row), true, nil
}

// RevokeAllForUser transitions every active row for userID to
// status='revoked' and returns the rows as they stand after the update.
// An empty slice with a nil error is returned when the user owned no
// active sessions; the caller must treat that as a successful idempotent
// revoke (the API surface returns revoked_count=0 in that case).
func (s *Store) RevokeAllForUser(ctx context.Context, userID uuid.UUID) ([]Session, error) {
	stmt := table.DeviceSessions.
		UPDATE(table.DeviceSessions.Status, table.DeviceSessions.RevokedAt).
		SET(postgres.String(SessionStatusRevoked), postgres.NOW()).
		WHERE(
			table.DeviceSessions.UserID.EQ(postgres.UUID(userID)).
				AND(table.DeviceSessions.Status.EQ(postgres.String(SessionStatusActive))),
		).
		RETURNING(sessionColumns())

	var rows []model.DeviceSessions
	if err := stmt.QueryContext(ctx, s.db, &rows); err != nil {
		return nil, fmt.Errorf("auth store: revoke all for user %s: %w", userID, err)
	}
	out := make([]Session, 0, len(rows))
	for _, row := range rows {
		out = append(out, modelToSession(row))
	}
	return out, nil
}

// modelToChallenge projects a generated model row into the public
// Challenge struct. Pointer fields are copied so callers cannot mutate
// the underlying scan buffer.
func modelToChallenge(row model.AuthChallenges) Challenge {
	c := Challenge{
		ChallengeID: row.ChallengeID,
		Email: row.Email,
		CodeHash: row.CodeHash,
		Attempts: row.Attempts,
		CreatedAt: row.CreatedAt,
		ExpiresAt: row.ExpiresAt,
		PreferredLanguage: row.PreferredLanguage,
	}
	if row.ConsumedAt != nil {
		t := *row.ConsumedAt
		c.ConsumedAt = &t
	}
	return c
}

// modelToSession projects a generated model row into the public Session
// struct.
func modelToSession(row model.DeviceSessions) Session {
	s := Session{
		DeviceSessionID: row.DeviceSessionID,
		UserID: row.UserID,
		Status: row.Status,
		ClientPublicKey: row.ClientPublicKey,
		CreatedAt: row.CreatedAt,
	}
	if row.RevokedAt != nil {
		t := *row.RevokedAt
		s.RevokedAt = &t
	}
	if row.LastSeenAt != nil {
		t := *row.LastSeenAt
		s.LastSeenAt = &t
	}
	return s
}

// withTx wraps fn in a Postgres transaction. fn's return value
// determines commit (nil) vs rollback (non-nil). Rollback errors are
// swallowed when fn already returned an error, since the latter is more
// actionable.
func withTx(ctx context.Context, db *sql.DB, fn func(tx *sql.Tx) error) error {
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("auth store: begin tx: %w", err)
	}
	if err := fn(tx); err != nil {
		_ = tx.Rollback()
		return err
	}
	if err := tx.Commit(); err != nil {
		return fmt.Errorf("auth store: commit tx: %w", err)
	}
	return nil
}