package bnwasm

import (
	"context"

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

// Pool implements plugin.Pool (the pgx-flavored interface plugins bind their
// sqlc DBTX to) over the db.* host calls. It is also itself a valid DBTX: its
// Exec/Query/QueryRow run in autocommit (tx_handle 0), so a plugin can pass the
// Pool directly to sqlc's New(db) for non-transactional queries, exactly as it
// passes a *pgxpool.Pool today.
type Pool struct {
	t Transport
}

// NewPool returns a Pool bound to transport t. A nil t (native build / DESCRIBE
// probe) yields a Pool whose every operation fails cleanly with errNoHost.
func NewPool(t Transport) *Pool { return &Pool{t: t} }

// Begin opens a host-side transaction and returns a pgx.Tx bound to its handle.
func (p *Pool) Begin(ctx context.Context) (pgx.Tx, error) {
	handle, err := p.t.txBegin(ctx)
	if err != nil {
		return nil, err
	}
	return &Tx{t: p.t, handle: handle}, nil
}

// Exec runs a statement in autocommit and returns its command tag.
func (p *Pool) Exec(ctx context.Context, sql string, args ...any) (pgconn.CommandTag, error) {
	return p.t.exec(ctx, sql, 0, args)
}

// Query runs a rows-returning statement in autocommit.
func (p *Pool) Query(ctx context.Context, sql string, args ...any) (pgx.Rows, error) {
	resp, err := p.t.query(ctx, sql, 0, args)
	if err != nil {
		return errRows(err), err
	}
	return newPgxRows(resp), nil
}

// QueryRow runs a rows-returning statement in autocommit and returns the first
// row; any error is deferred to Row.Scan, matching pgx.
func (p *Pool) QueryRow(ctx context.Context, sql string, args ...any) pgx.Row {
	resp, err := p.t.query(ctx, sql, 0, args)
	if err != nil {
		return &pgxRow{err: err}
	}
	return &pgxRow{rows: newPgxRows(resp)}
}

// errRows is a closed, empty pgx.Rows carrying err, so a Query caller that
// ignores the returned error and iterates still terminates and reports it.
func errRows(err error) *pgxRows {
	return &pgxRows{idx: -1, err: err, closed: true}
}