// 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 lives in the ENGINE, not here: a context with no identity
// simply declares nothing, and any RLS-governed statement (media_items)
// then raises on the unset GUC — while ungoverned tables (auth lookups,
// settings, sessions) keep working, as they have no policy. That is the
// plan-C property: the database is the one door everything crosses; the
// decorator is only the identity declarer.
//
// 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/pgtype"
	"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. Fallback (test harness ONLY —
// see NewSeedDB) supplies an identity when the context carries none.
type ScopedDB struct {
	Pool     *pgxpool.Pool
	Fallback *pgtype.UUID
}

// 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}
}

// NewSeedDB returns a ScopedDB for TEST-HARNESS seeding/verification:
// when the context carries no identity it falls back to
// rls.SeedIdentity, so direct media reads/writes from helpers work
// without impersonating a real user. Never use in product wiring.
func NewSeedDB(pool *pgxpool.Pool) *ScopedDB {
	seed := rls.SeedIdentity
	return &ScopedDB{Pool: pool, Fallback: &seed}
}

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

// begin opens the per-statement transaction. If the context carries a
// user identity, the GUC is declared (LOCAL); if not, NOTHING is
// declared and the ENGINE decides: RLS-governed tables (media_items)
// raise on the unset GUC — fail-loud at the database, the layer plan C
// exists to enforce at — while RLS-ungoverned tables (users, settings,
// sessions, auth lookups pre-bridge) simply work, as they have no
// policy to evaluate. The decorator therefore never refuses: refusing
// here would re-create a convention gate in code, one more door future
// paths could forget — the engine is the one door everything crosses.
func (s *ScopedDB) begin(ctx context.Context) (pgx.Tx, error) {
	tx, err := s.Pool.Begin(ctx)
	if err != nil {
		return nil, err
	}
	uid, ok := rls.FromContext(ctx)
	if (!ok || !uid.Valid || uid.String() == zeroUUID) && s.Fallback != nil {
		uid, ok = *s.Fallback, true
	}
	if ok && uid.Valid && uid.String() != zeroUUID {
		if err := rls.DeclareUser(ctx, tx, uid); err != nil {
			_ = tx.Rollback(ctx)
			return nil, fmt.Errorf("rls: declare user: %w", err)
		}
	}
	return tx, nil
}

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}
}