package classes

import (
	"context"
	"errors"
	"net/url"
	"strings"
	"sync"
	"time"

	"git.golem15.com/golem15/sm-seo-plugin/models"
	"gorm.io/gorm"
	"gorm.io/gorm/clause"
)

// Config keys of the 404 log (P-22).
const (
	// NotFoundTokenConfigKey is the shared secret the frontend server
	// sends as "Authorization: Bearer <token>" with each 404 report. Empty
	// turns the report endpoint off (it answers 404).
	NotFoundTokenConfigKey = "golem15.seo.notfound_token"
	// NotFoundMaxRowsConfigKey caps the 404 log; new addresses beyond it
	// are dropped (default DefaultNotFoundMaxRows).
	NotFoundMaxRowsConfigKey = "golem15.seo.notfound_max_rows"
)

// The 404 report limits (P-22).
const (
	DefaultNotFoundMaxRows = 10000
	MaxNotFoundURLBytes    = 2048
	MaxRefererBytes        = 1024
)

// ErrNotFoundURL refuses a reported address that is not a path or an
// http(s) URL, or is longer than MaxNotFoundURLBytes.
var ErrNotFoundURL = errors.New("golem15.seo: url must be a path or an absolute http(s) URL of at most 2048 bytes")

// NotFoundToken is the configured report token, "" when unset.
func (s *Service) NotFoundToken() string {
	cfg := s.Config()
	if cfg == nil {
		return ""
	}
	return strings.TrimSpace(cfg.String(NotFoundTokenConfigKey))
}

// NotFoundMaxRows is the configured row cap of the 404 log.
func (s *Service) NotFoundMaxRows() int64 {
	if cfg := s.Config(); cfg != nil {
		if n := cfg.Int(NotFoundMaxRowsConfigKey); n > 0 {
			return int64(n)
		}
	}
	return DefaultNotFoundMaxRows
}

// NotFoundPath turns a reported address into the logged one: the path
// with its query; an absolute URL loses its scheme and host.
func NotFoundPath(raw string) (string, error) {
	raw = strings.TrimSpace(raw)
	if raw == "" || len(raw) > MaxNotFoundURLBytes {
		return "", ErrNotFoundURL
	}
	u, err := url.Parse(raw)
	if err != nil {
		return "", ErrNotFoundURL
	}
	if u.IsAbs() {
		if u.Scheme != "http" && u.Scheme != "https" {
			return "", ErrNotFoundURL
		}
	} else if !strings.HasPrefix(raw, "/") || strings.HasPrefix(raw, "//") {
		return "", ErrNotFoundURL
	}
	p := u.Path
	if p == "" {
		p = "/"
	}
	return joinQuery(p, u.RawQuery), nil
}

// capWarned keeps when the row-cap warning was last logged.
var capWarned struct {
	sync.Mutex
	at time.Time
}

// ReportNotFound records one 404 of rawURL (D-20, P-22): a known address
// gets one more hit, its last hit time and, when given, the referer; a new
// one is added unless the log holds NotFoundMaxRows rows, which is logged
// at most once an hour.
func (s *Service) ReportNotFound(ctx context.Context, rawURL, referer string) error {
	path, err := NotFoundPath(rawURL)
	if err != nil {
		return err
	}
	referer = strings.TrimSpace(referer)
	if len(referer) > MaxRefererBytes {
		referer = referer[:MaxRefererBytes]
		for len(referer) > 0 && !utf8ValidTail(referer) {
			referer = referer[:len(referer)-1]
		}
	}
	db, err := s.DB(ctx)
	if err != nil {
		return err
	}
	now := time.Now().UTC()
	updates := map[string]any{"hits": gorm.Expr("hits + 1"), "last_hit": now}
	if referer != "" {
		updates["referer"] = referer
	}
	res := db.Model(&models.NotFound{}).Where("url = ?", path).Updates(updates)
	if res.Error != nil || res.RowsAffected > 0 {
		return res.Error
	}
	var count int64
	if err := db.Model(&models.NotFound{}).Count(&count).Error; err != nil {
		return err
	}
	if count >= s.NotFoundMaxRows() {
		capWarned.Lock()
		if time.Since(capWarned.at) >= time.Hour {
			capWarned.at = time.Now()
			log.Warn("golem15.seo: the 404 log is full, new addresses are dropped", "max_rows", s.NotFoundMaxRows(), "url", path)
		}
		capWarned.Unlock()
		return nil
	}
	row := models.NotFound{URL: path, Hits: 1, FirstSeen: &now, LastHit: &now, Referer: referer}
	return db.Clauses(clause.OnConflict{
		Columns:   []clause.Column{{Name: "url"}},
		DoUpdates: clause.Assignments(map[string]any{"hits": gorm.Expr("golem15_seo_notfound.hits + 1"), "last_hit": now}),
	}).Create(&row).Error
}

// utf8ValidTail reports whether s does not end inside a UTF-8 sequence.
func utf8ValidTail(s string) bool {
	return strings.ToValidUTF8(s, "�") == s
}

// NotFoundCover returns the rule that answers url now (a redirect or a
// 410), nil when the address still answers 404: the Resolved state.
func NotFoundCover(set *RedirectSet, url string) (*models.Redirect, error) {
	return CoveringRedirect(set, url)
}

// NotFoundHasRuleError refuses a 404 action on an address a rule already
// answers.
type NotFoundHasRuleError struct{ URL string }

func (e *NotFoundHasRuleError) Error() string {
	return "golem15.seo: a redirect for " + e.URL + " already exists"
}

// ResolveNotFound creates the rule of a 404 log action inside tx (D-20): a
// 301 to target when target is set, else a 410, with origin notfound. It
// refuses an address a rule already answers (*NotFoundHasRuleError), and
// the redirect's own refusals (*ProblemsError, *LoopError).
func (s *Service) ResolveNotFound(ctx context.Context, tx *gorm.DB, entry models.NotFound, target string) (models.Redirect, error) {
	set, err := LoadRedirectSet(tx)
	if err != nil {
		return models.Redirect{}, err
	}
	if rule, err := NotFoundCover(set, entry.URL); err != nil {
		return models.Redirect{}, err
	} else if rule != nil {
		return models.Redirect{}, &NotFoundHasRuleError{URL: entry.URL}
	}
	r := models.NewRedirect()
	r.Source, r.Origin = entry.URL, models.OriginNotFound
	if strings.TrimSpace(target) == "" {
		r.Status = models.Status410
	} else {
		r.Target = strings.TrimSpace(target)
	}
	if _, err := s.SaveRedirect(ctx, tx, &r); err != nil {
		return r, err
	}
	return r, nil
}