// samsa — a privacy-respecting metasearch engine
// Copyright (C) 2026-present metamorphosis-dev
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

package httpclient

import (
	"net/http"
	"sync"
	"time"
)

var (
	defaultTransport http.RoundTripper
	once             sync.Once
)

// Default returns a shared, pre-configured http.RoundTripper suitable for
// outgoing engine requests. It is safe for concurrent use across goroutines.
// All fields are tuned for a meta-search engine that makes many concurrent
// requests to a fixed set of upstream hosts:
//
//   - MaxIdleConnsPerHost = 20  (vs default of 2; keeps more warm connections
//     to each host, avoiding repeated TCP+TLS handshakes)
//   - MaxIdleConns = 100         (total idle connection ceiling)
//   - IdleConnTimeout = 90s      (prunes connections before they go stale)
//   - DialContext timeout = 5s   (fails fast on DNS/connect rather than
//     holding a goroutine indefinitely)
func Default() http.RoundTripper {
	once.Do(func() {
		defaultTransport = &http.Transport{
			MaxIdleConnsPerHost: 20,
			MaxIdleConns:        100,
			IdleConnTimeout:     90 * time.Second,
			DialContext: dialWithTimeout(5 * time.Second),
		}
	})
	return defaultTransport
}

// NewClient returns an http.Client that uses DefaultTransport and the given
// request timeout. The returned client reuses the shared connection pool,
// so all clients created via this function share the same warm connections.
func NewClient(timeout time.Duration) *http.Client {
	return &http.Client{
		Transport: Default(),
		Timeout:   timeout,
	}
}