package openstack

import (
	"context"
	"errors"
	"io"
	"net"
	"strings"
	"time"
)

// DefaultListPageSize is the page size used when the caller passes a
// non-positive one.
const DefaultListPageSize = 200

// DefaultListPageRetries is how many times a single failed page request is
// retried (so up to DefaultListPageRetries+1 attempts in total).
const DefaultListPageRetries = 5

// pageFetcher fetches one page of floating IPs: at most limit entries that
// follow the entry with ID marker ("" = from the start), in a stable server
// order. A page shorter than limit is the last one.
type pageFetcher func(ctx context.Context, marker string, limit int) ([]FloatingIP, error)

// pageRetry configures per-page retries. The zero value retries nothing.
type pageRetry struct {
	// Retries is the number of retries after the first failed attempt.
	Retries int
	// Sleep waits for d or until ctx is done; nil uses a real timer. Tests
	// inject a fake to avoid real backoff delays.
	Sleep func(ctx context.Context, d time.Duration) error
}

// retryBackoff is the delay before retry number attempt (1-based):
// 1s, 2s, 4s, 8s, 16s, then capped at 30s.
func retryBackoff(attempt int) time.Duration {
	if attempt < 1 {
		attempt = 1
	}
	d := time.Second << uint(attempt-1)
	if d > 30*time.Second || d <= 0 {
		d = 30 * time.Second
	}
	return d
}

func sleepCtx(ctx context.Context, d time.Duration) error {
	t := time.NewTimer(d)
	defer t.Stop()
	select {
	case <-ctx.Done():
		return ctx.Err()
	case <-t.C:
		return nil
	}
}

// statusCoder is implemented by gophercloud.ErrUnexpectedResponseCode (and
// anything wrapping it): it carries the HTTP status of a failed request.
type statusCoder interface{ GetStatusCode() int }

// IsRetryableListError reports whether a failed page request is worth
// repeating: transport-level failures (timeouts, resets, EOF /
// RemoteDisconnected), HTTP 429 and HTTP 5xx. Any other 4xx, context
// cancellation and unknown errors are not retried.
func IsRetryableListError(err error) bool {
	if err == nil {
		return false
	}
	if errors.Is(err, context.Canceled) {
		return false
	}
	var sc statusCoder
	if errors.As(err, &sc) {
		code := sc.GetStatusCode()
		return code == 429 || code >= 500
	}
	if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
		return true
	}
	// A deadline is retryable only when it is a per-request network timeout
	// (net.Error), which is checked below; the caller's own ctx deadline is
	// filtered out by the paginator via ctx.Err().
	var ne net.Error
	if errors.As(err, &ne) {
		return true
	}
	msg := strings.ToLower(err.Error())
	for _, s := range []string{
		"remotedisconnected", "remote end closed connection",
		"connection reset", "connection refused", "broken pipe",
		"unexpected eof", "eof", "timeout", "tls handshake",
	} {
		if strings.Contains(msg, s) {
			return true
		}
	}
	return false
}

// paginate walks all pages with marker-based pagination, retrying each failed
// page per rp, and hands every non-empty page to onPage in server order. It
// returns the number of non-empty pages delivered. An error from onPage, a
// non-retryable error, exhausted retries or ctx cancellation stop the walk.
func paginate(ctx context.Context, pageSize int, rp pageRetry, fetch pageFetcher, onPage func([]FloatingIP) error) (int, error) {
	if pageSize <= 0 {
		pageSize = DefaultListPageSize
	}
	sleep := rp.Sleep
	if sleep == nil {
		sleep = sleepCtx
	}
	marker := ""
	pages := 0
	for {
		if err := ctx.Err(); err != nil {
			return pages, err
		}
		var page []FloatingIP
		var err error
		for attempt := 0; ; attempt++ {
			page, err = fetch(ctx, marker, pageSize)
			if err == nil {
				break
			}
			if ctx.Err() != nil {
				return pages, ctx.Err()
			}
			if attempt >= rp.Retries || !IsRetryableListError(err) {
				return pages, err
			}
			if serr := sleep(ctx, retryBackoff(attempt+1)); serr != nil {
				return pages, serr
			}
		}
		if len(page) == 0 {
			return pages, nil
		}
		pages++
		if err := onPage(page); err != nil {
			return pages, err
		}
		if len(page) < pageSize {
			return pages, nil
		}
		marker = page[len(page)-1].ID
	}
}