// ScopedDB wraps a pgx pool so every sqlc statement runs inside a
// transaction that declares the acting user via the LOCAL
// `app.user_id` GUC — the one thing the RLS policies
// (database/schema/schema.sql) need to filter media rows per user.
//
// Fail-loud, twice: a query whose context carries neither a user
// identity nor the internal marker is refused HERE, and the policies
// themselves raise on an unset/empty GUC. The internal marker
// (rls.WithInternal) declares "not a user" — it sets NO GUC, so
// policy'd tables (media_items) still raise at the engine; only
// RLS-ungoverned tables (system_settings, users counts) work, which
// user-less startup paths need. A code path that forgets the auth
// middleware bridge breaks visibly; it never silently sees all rows.
//
// SEMANTICS PRESERVED: every sqlc call was already a single
// auto-committed statement; one transaction per call keeps per-call
// atomicity identical. pgx v5 rows are bound to their transaction, so
// the transaction ends when the ROWS end: commit-on-Close for :many
// results, commit-on-Scan for :one results, plain commit for Exec.
//
// Rollout plan: ~/.opencode/plan/server-rls-library-visibility.md.
package database

import (
	"context"
	"fmt"
	"log"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgconn"
	"github.com/jackc/pgx/v5/pgxpool"

	"bookhoard/internal/rls"
)

// Compile-pin: ScopedDB is a drop-in DBTX for database.New.
var _ DBTX = (*ScopedDB)(nil)

// ScopedDB implements DBTX over a pool, declaring the acting user for
// the RLS policies on every statement.
type ScopedDB struct {
	Pool *pgxpool.Pool
}

// NewScopedDB is the constructor used at the single Queries
// construction site (cmd/server/main.go).
func NewScopedDB(pool *pgxpool.Pool) *ScopedDB {
	return &ScopedDB{Pool: pool}
}

const zeroUUID = "00000000-0000-0000-0000-000000000000"

// begin opens the per-statement transaction. Identity semantics:
//   - user context  → declares app.user_id (LOCAL) — RLS filters rows
//   - internal ctx  → NO GUC declared. Grants nothing: policy'd tables
//     still raise at the engine (FORCE applies to the owner); only
//     RLS-ungoverned tables (system_settings, users, …) are workable —
//     which is exactly what user-less startup paths need.
//   - neither       → refused HERE (fail-loud before SQL is even sent)
func (s *ScopedDB) begin(ctx context.Context) (pgx.Tx, error) {
	if !rls.IsInternal(ctx) {
		uid, ok := rls.FromContext(ctx)
		if !ok || !uid.Valid || uid.String() == zeroUUID {
			return nil, fmt.Errorf("rls: no authenticated user in context — query refused " +
				"(route through the auth middleware bridge, or declare an internal " +
				"identity via rls.WithUser; see the RLS plan §5–6)")
		}
		tx, err := s.Pool.Begin(ctx)
		if err != nil {
			return nil, err
		}
		if err := rls.DeclareUser(ctx, tx, uid); err != nil {
			_ = tx.Rollback(ctx)
			return nil, fmt.Errorf("rls: declare user: %w", err)
		}
		return tx, nil
	}
	return s.Pool.Begin(ctx)
}

func (s *ScopedDB) Exec(ctx context.Context, sql string, args ...any) (pgconn.CommandTag, error) {
	tx, err := s.begin(ctx)
	if err != nil {
		return pgconn.CommandTag{}, err
	}
	// Rollback after a successful Commit is a no-op (ErrTxClosed ignored):
	// this defer only acts on the error paths.
	defer func() { _ = tx.Rollback(ctx) }()
	tag, err := tx.Exec(ctx, sql, args...)
	if err != nil {
		return pgconn.CommandTag{}, err
	}
	return tag, tx.Commit(ctx)
}

func (s *ScopedDB) Query(ctx context.Context, sql string, args ...any) (pgx.Rows, error) {
	tx, err := s.begin(ctx)
	if err != nil {
		return nil, err
	}
	rows, err := tx.Query(ctx, sql, args...)
	if err != nil {
		_ = tx.Rollback(ctx)
		return nil, err
	}
	return &scopedRows{Rows: rows, tx: tx, ctx: ctx}, nil
}

// scopedRows commits the transaction when the rows close — committing
// earlier would kill the rows mid-read. sqlc's :many path fully
// consumes rows then Close()s. pgx v5 Rows.Close returns nothing, so a
// commit error is logged, not propagated (a commit failure on a
// read-only transaction is log-worthy only).
type scopedRows struct {
	pgx.Rows
	tx  pgx.Tx
	ctx context.Context
}

func (r *scopedRows) Close() {
	r.Rows.Close()
	if err := r.tx.Commit(r.ctx); err != nil {
		log.Printf("rls: tx commit after rows: %v", err)
	}
}

// scopedRow terminates the transaction on EVERY Scan path for sqlc's
// :one results (pgx.Row is just { Scan(dest ...) error }).
type scopedRow struct {
	row pgx.Row
	tx  pgx.Tx
	ctx context.Context
}

func (r scopedRow) Scan(dest ...any) error {
	err := r.row.Scan(dest...)
	if err == nil {
		return r.tx.Commit(r.ctx)
	}
	_ = r.tx.Rollback(r.ctx) // best effort; the tx ends either way
	return err
}

type errRow struct{ err error }

func (r errRow) Scan(_ ...any) error { return r.err }

func (s *ScopedDB) QueryRow(ctx context.Context, sql string, args ...any) pgx.Row {
	tx, err := s.begin(ctx)
	if err != nil {
		return errRow{err}
	}
	return scopedRow{row: tx.QueryRow(ctx, sql, args...), tx: tx, ctx: ctx}
}