// Package account owns durable internal accounts and their platform/email
// identities. First contact from a platform auto-provisions an account bound to
// that identity. An ephemeral guest is also a durable account row (the sessions
// and game_players foreign keys both require one) but carries no identity and is
// flagged is_guest, which excludes it from statistics, friends and history.
package account

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

	"github.com/go-jet/jet/v2/postgres"
	"github.com/go-jet/jet/v2/qrm"
	"github.com/google/uuid"
	"github.com/jackc/pgx/v5/pgconn"

	"scrabble/backend/internal/postgres/jet/backend/model"
	"scrabble/backend/internal/postgres/jet/backend/table"
)

// Identity kinds recognised by the backend. Email is modelled as an identity
// alongside platform identities; its confirmed flag is driven by the email
// confirm-code flow in a later stage. Robot is a synthetic kind: each pooled
// robot opponent is a durable account bound to one robot identity (Stage 5).
const (
	KindTelegram = "telegram"
	KindEmail    = "email"
	KindRobot    = "robot"
)

// uniqueViolation is the PostgreSQL SQLSTATE for a unique-constraint violation.
const uniqueViolation = "23505"

// ErrNotFound is returned when no account matches the lookup.
var ErrNotFound = errors.New("account: not found")

// Account is a durable internal account. AwayStart and AwayEnd bound the daily
// local-time window (in TimeZone) during which the player is asleep, so the
// turn-timeout sweeper does not auto-resign them inside it. (The robot opponent's
// own sleep is anchored to its human opponent's timezone with a per-game drift,
// computed in internal/robot, not from a robot account's away window.) HintBalance
// is the player's wallet of purchasable hints, spent after a game's per-seat
// allowance.
type Account struct {
	ID                  uuid.UUID
	DisplayName         string
	PreferredLanguage   string
	TimeZone            string
	AwayStart           time.Time
	AwayEnd             time.Time
	HintBalance         int
	BlockChat           bool
	BlockFriendRequests bool
	// IsGuest marks an ephemeral guest account: a durable row with no identity,
	// excluded from statistics, friends and history.
	IsGuest   bool
	CreatedAt time.Time
	UpdatedAt time.Time
}

// Store is the Postgres-backed query surface for accounts and identities.
type Store struct {
	db *sql.DB
}

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

// ProvisionByIdentity returns the account bound to (kind, externalID), creating
// a fresh durable account and identity when none exists yet. It is safe under
// concurrent callers: a losing race on the identity's unique constraint is
// resolved by re-reading the winner's account. A platform identity is recorded
// as confirmed; an email identity starts unconfirmed.
func (s *Store) ProvisionByIdentity(ctx context.Context, kind, externalID string) (Account, error) {
	acc, err := s.findByIdentity(ctx, kind, externalID)
	if err == nil {
		return acc, nil
	}
	if !errors.Is(err, ErrNotFound) {
		return Account{}, err
	}

	acc, err = s.create(ctx, kind, externalID)
	if err != nil {
		if isUniqueViolation(err) {
			// A concurrent caller created the identity first; return theirs.
			return s.findByIdentity(ctx, kind, externalID)
		}
		return Account{}, err
	}
	return acc, nil
}

// GetByID loads the account identified by id, or ErrNotFound when it is absent.
func (s *Store) GetByID(ctx context.Context, id uuid.UUID) (Account, error) {
	stmt := postgres.SELECT(table.Accounts.AllColumns).
		FROM(table.Accounts).
		WHERE(table.Accounts.AccountID.EQ(postgres.UUID(id))).
		LIMIT(1)

	var row model.Accounts
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Account{}, ErrNotFound
		}
		return Account{}, fmt.Errorf("account: get by id %s: %w", id, err)
	}
	return modelToAccount(row), nil
}

// findByIdentity joins identities to accounts and returns the matching account,
// or ErrNotFound.
func (s *Store) findByIdentity(ctx context.Context, kind, externalID string) (Account, error) {
	stmt := postgres.SELECT(table.Accounts.AllColumns).
		FROM(table.Accounts.INNER_JOIN(
			table.Identities,
			table.Identities.AccountID.EQ(table.Accounts.AccountID),
		)).
		WHERE(
			table.Identities.Kind.EQ(postgres.String(kind)).
				AND(table.Identities.ExternalID.EQ(postgres.String(externalID))),
		).
		LIMIT(1)

	var row model.Accounts
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Account{}, ErrNotFound
		}
		return Account{}, fmt.Errorf("account: find by identity (%s, %s): %w", kind, externalID, err)
	}
	return modelToAccount(row), nil
}

// create inserts a new account and its first identity inside one transaction
// and returns the persisted account row.
func (s *Store) create(ctx context.Context, kind, externalID string) (Account, error) {
	accountID, err := uuid.NewV7()
	if err != nil {
		return Account{}, fmt.Errorf("account: new account id: %w", err)
	}
	identityID, err := uuid.NewV7()
	if err != nil {
		return Account{}, fmt.Errorf("account: new identity id: %w", err)
	}

	var created Account
	err = withTx(ctx, s.db, func(tx *sql.Tx) error {
		insertAccount := table.Accounts.
			INSERT(table.Accounts.AccountID).
			VALUES(accountID).
			RETURNING(table.Accounts.AllColumns)

		var row model.Accounts
		if err := insertAccount.QueryContext(ctx, tx, &row); err != nil {
			return err
		}

		insertIdentity := table.Identities.INSERT(
			table.Identities.IdentityID,
			table.Identities.AccountID,
			table.Identities.Kind,
			table.Identities.ExternalID,
			table.Identities.Confirmed,
		).VALUES(identityID, accountID, kind, externalID, kind == KindTelegram)
		if _, err := insertIdentity.ExecContext(ctx, tx); err != nil {
			return err
		}

		created = modelToAccount(row)
		return nil
	})
	if err != nil {
		return Account{}, fmt.Errorf("account: create for identity (%s, %s): %w", kind, externalID, err)
	}
	return created, nil
}

// guestDisplayName is the display name stamped on a freshly provisioned guest.
const guestDisplayName = "Guest"

// ProvisionGuest creates a fresh ephemeral guest account: a durable row carrying
// no identity, flagged is_guest, so it can hold a session and a game seat (both
// foreign-key the accounts table) while being excluded from statistics, friends
// and history. Guests are not reused — each bootstrap mints a new account.
func (s *Store) ProvisionGuest(ctx context.Context) (Account, error) {
	accountID, err := uuid.NewV7()
	if err != nil {
		return Account{}, fmt.Errorf("account: new guest id: %w", err)
	}
	stmt := table.Accounts.
		INSERT(table.Accounts.AccountID, table.Accounts.DisplayName, table.Accounts.IsGuest).
		VALUES(accountID, guestDisplayName, true).
		RETURNING(table.Accounts.AllColumns)

	var row model.Accounts
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		return Account{}, fmt.Errorf("account: provision guest: %w", err)
	}
	return modelToAccount(row), nil
}

// SpendHint atomically decrements the account's hint wallet by one, returning
// true when a hint was spent and false when the balance was already empty. The
// guarded UPDATE keeps it safe under concurrent spends across the player's games.
func (s *Store) SpendHint(ctx context.Context, id uuid.UUID) (bool, error) {
	stmt := table.Accounts.
		UPDATE(table.Accounts.HintBalance, table.Accounts.UpdatedAt).
		SET(table.Accounts.HintBalance.SUB(postgres.Int(1)), postgres.TimestampzT(time.Now().UTC())).
		WHERE(
			table.Accounts.AccountID.EQ(postgres.UUID(id)).
				AND(table.Accounts.HintBalance.GT(postgres.Int(0))),
		)
	res, err := stmt.ExecContext(ctx, s.db)
	if err != nil {
		return false, fmt.Errorf("account: spend hint %s: %w", id, err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return false, fmt.Errorf("account: spend hint rows %s: %w", id, err)
	}
	return n > 0, nil
}

// modelToAccount projects a generated model row into the public Account struct.
func modelToAccount(row model.Accounts) Account {
	return Account{
		ID:                  row.AccountID,
		DisplayName:         row.DisplayName,
		PreferredLanguage:   row.PreferredLanguage,
		TimeZone:            row.TimeZone,
		AwayStart:           row.AwayStart,
		AwayEnd:             row.AwayEnd,
		HintBalance:         int(row.HintBalance),
		BlockChat:           row.BlockChat,
		BlockFriendRequests: row.BlockFriendRequests,
		IsGuest:             row.IsGuest,
		CreatedAt:           row.CreatedAt,
		UpdatedAt:           row.UpdatedAt,
	}
}

// isUniqueViolation reports whether err is a PostgreSQL unique-constraint
// violation, used to collapse a concurrent-provision race into a re-read.
func isUniqueViolation(err error) bool {
	var pgErr *pgconn.PgError
	return errors.As(err, &pgErr) && pgErr.Code == uniqueViolation
}

// withTx wraps fn in a transaction, committing on nil and rolling back on error.
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("begin tx: %w", err)
	}
	if err := fn(tx); err != nil {
		_ = tx.Rollback()
		return err
	}
	if err := tx.Commit(); err != nil {
		return fmt.Errorf("commit tx: %w", err)
	}
	return nil
}