// Package httpclient provides shared HTTP clients and retry helpers for outbound calls.
package httpclient

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"time"

	"evobgp/internal/observability"
)

const DefaultTimeout = 45 * time.Second

// New returns an HTTP client with timeout and tuned idle connection pooling.
// Standard proxy env (HTTP_PROXY / HTTPS_PROXY / NO_PROXY) is honored via the cloned DefaultTransport.
func New(timeout time.Duration) *http.Client {
	if timeout <= 0 {
		timeout = DefaultTimeout
	}
	tr := http.DefaultTransport.(*http.Transport).Clone()
	tr.MaxIdleConns = 100
	tr.MaxIdleConnsPerHost = 10
	return &http.Client{Timeout: timeout, Transport: tr}
}

// DoWithRetry executes hc.Do(req) up to maxAttempts times with linear backoff.
func DoWithRetry(ctx context.Context, hc *http.Client, req *http.Request, maxAttempts int) (*http.Response, error) {
	if maxAttempts <= 0 {
		maxAttempts = 3
	}
	var lastErr error
	for attempt := 0; attempt < maxAttempts; attempt++ {
		if attempt > 0 {
			wait := time.Duration(attempt) * 2 * time.Second
			select {
			case <-ctx.Done():
				return nil, ctx.Err()
			case <-time.After(wait):
			}
			if req.GetBody != nil {
				body, err := req.GetBody()
				if err != nil {
					return nil, err
				}
				req.Body = body
			}
		}
		reqClone := req.Clone(ctx)
		resp, err := hc.Do(reqClone)
		if err != nil {
			lastErr = err
			continue
		}
		if resp.StatusCode >= 500 {
			_, _ = io.Copy(io.Discard, resp.Body)
			_ = resp.Body.Close()
			lastErr = fmt.Errorf("httpclient: upstream %s", resp.Status)
			continue
		}
		return resp, nil
	}
	if lastErr != nil {
		return nil, lastErr
	}
	return nil, fmt.Errorf("httpclient: request failed after %d attempts", maxAttempts)
}

// DoWithBreaker applies per-host circuit breaking then retries transient failures.
func DoWithBreaker(ctx context.Context, hc *http.Client, req *http.Request, maxAttempts int) (*http.Response, error) {
	if req == nil || req.URL == nil {
		return nil, fmt.Errorf("httpclient: nil request")
	}
	host := req.URL.Hostname()
	br := breakerForHost(host)
	if !br.allow() {
		observability.SetUpstreamBreakerOpen(host, true)
		return nil, fmt.Errorf("httpclient: circuit open for %s", host)
	}
	resp, err := DoWithRetry(ctx, hc, req, maxAttempts)
	if err != nil {
		br.recordFailure()
		observability.SetUpstreamBreakerOpen(host, !br.allow())
		return nil, err
	}
	if resp.StatusCode >= 500 {
		br.recordFailure()
		observability.SetUpstreamBreakerOpen(host, !br.allow())
		return resp, nil
	}
	br.recordSuccess()
	observability.SetUpstreamBreakerOpen(host, false)
	return resp, nil
}