package classes

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"reflect"
	"sort"
	"strconv"
	"strings"
	"time"

	"git.golem15.com/golem15/sm-seo-plugin/models"
	"git.golem15.com/golem15/summercms/modules/bouncer"
	"git.golem15.com/golem15/summercms/modules/pact"
	"gorm.io/gorm"
)

// The undo refusals (D-13, T-32-27).
const (
	UndoStale       = "undo_stale"
	UndoLoop        = "undo_loop"
	UndoGone        = "undo_gone"
	UndoDone        = "already_undone"
	UndoUnsupported = "undo_unsupported"
)

// UndoRefusal refuses an undo: Code is one of the Undo* constants, Key the
// phrase key of its message and Params the message's parameters. Nothing
// was undone.
type UndoRefusal struct {
	Code   string
	Key    string
	Params map[string]string
}

func (e *UndoRefusal) Error() string { return "golem15.seo: " + e.Code }

// LoadRevision returns history entry id; ErrNoRecord when there is none.
func LoadRevision(db *gorm.DB, id uint) (models.Revision, error) {
	var rows []models.Revision
	if err := db.Where("id = ?", id).Limit(1).Find(&rows).Error; err != nil {
		return models.Revision{}, err
	}
	if len(rows) == 0 {
		return models.Revision{}, ErrNoRecord
	}
	return rows[0], nil
}

// Undoable reports whether a history entry can be offered an undo: not
// undone yet and of a kind undo restores.
func Undoable(r models.Revision) bool {
	if r.UndoneAt != nil {
		return false
	}
	switch r.SubjectKind {
	case models.SubjectEntry, models.SubjectRule, models.SubjectRedirect, models.SubjectRobots, models.SubjectSettings, models.SubjectNotFound:
		return true
	}
	return false
}

// Undo restores the values before history entry id inside tx (D-13): the
// undo is itself recorded (via undo) and the entry is marked undone. It
// is refused with an *UndoRefusal when the entry is undone already, when a
// later change touched the same values (undo_stale, naming who and when),
// when the restore would create a redirect loop (undo_loop) or when the
// record it belongs to is gone (undo_gone).
func (s *Service) Undo(ctx context.Context, tx *gorm.DB, id uint) ([]uint, error) {
	rev, err := LoadRevision(tx, id)
	if err != nil {
		return nil, err
	}
	if rev.UndoneAt != nil {
		return nil, &UndoRefusal{Code: UndoDone, Key: "golem15.seo::lang.history.undo_done"}
	}
	if err := s.undoOne(WithVia(ctx, models.ViaUndo), tx, rev); err != nil {
		return nil, err
	}
	return []uint{rev.ID}, nil
}

// UndoBatch undoes every change of batch that is not undone yet, newest
// first, inside tx: all of them or none (D-13). ErrNoRecord when the batch
// has nothing left to undo.
func (s *Service) UndoBatch(ctx context.Context, tx *gorm.DB, batch string) ([]uint, error) {
	var revs []models.Revision
	if err := tx.Where("batch_id = ? AND undone_at IS NULL", batch).Order("id DESC").Find(&revs).Error; err != nil {
		return nil, err
	}
	if len(revs) == 0 {
		return nil, ErrNoRecord
	}
	ctx = WithVia(ctx, models.ViaUndo)
	ids := make([]uint, 0, len(revs))
	for _, rev := range revs {
		if err := s.undoOne(ctx, tx, rev); err != nil {
			return nil, err
		}
		ids = append(ids, rev.ID)
	}
	return ids, nil
}

// BatchSize counts the changes of batch that are not undone yet.
func BatchSize(db *gorm.DB, batch string) (int64, error) {
	var n int64
	err := db.Model(&models.Revision{}).Where("batch_id = ? AND undone_at IS NULL", batch).Count(&n).Error
	return n, err
}

// jsonNorm brings a value to its JSON form, so a stored history value
// and a current one compare equal when they encode the same.
func jsonNorm(v any) any {
	raw, err := json.Marshal(plainValue(v))
	if err != nil {
		return fmt.Sprint(v)
	}
	var out any
	if json.Unmarshal(raw, &out) != nil {
		return string(raw)
	}
	if s, ok := out.(string); ok {
		return strings.TrimSpace(s)
	}
	return out
}

// sameValue reports whether two values encode the same; nil and "" are
// the same empty value.
func sameValue(a, b any) bool {
	na, nb := jsonNorm(a), jsonNorm(b)
	if na == nil {
		na = ""
	}
	if nb == nil {
		nb = ""
	}
	return reflect.DeepEqual(na, nb)
}

// subjectState is the current values of a history subject; exists is
// false when the object is gone.
type subjectState struct {
	values map[string]any
	exists bool
	// recordGone is true for an entry whose record no longer exists.
	recordGone bool
	typ        pact.MenuItemType
	model      string
	recordID   string
	locale     string
}

// currentState reads the current values of rev's subject.
func (s *Service) currentState(ctx context.Context, tx *gorm.DB, rev models.Revision) (subjectState, error) {
	var st subjectState
	switch rev.SubjectKind {
	case models.SubjectEntry:
		parts := strings.SplitN(rev.SubjectID, "|", 3)
		if len(parts) != 3 {
			return st, &UndoRefusal{Code: UndoUnsupported, Key: "golem15.seo::lang.history.undo_unsupported"}
		}
		st.model, st.recordID, st.locale = parts[0], parts[1], parts[2]
		reg := s.Registry()
		typ, ok := pact.MenuItemType{}, false
		if reg != nil {
			typ, ok = reg.ContentTypeForModel(st.model)
		}
		if !ok || typ.Content == nil {
			st.recordGone = true
			return st, nil
		}
		st.typ = typ
		rec, err := reg.Describe(ctx, typ.Key, st.recordID, s.UnprefixedLocale())
		if err != nil {
			return st, err
		}
		if rec == nil {
			st.recordGone = true
			return st, nil
		}
		e, found, err := LoadEntry(tx, st.model, st.recordID, st.locale)
		if err != nil {
			return st, err
		}
		st.exists = true
		st.values = map[string]any{}
		for _, c := range EntryColumns {
			v := ""
			if found {
				v = EntryValue(e, c)
			}
			st.values[c] = v
		}
	case models.SubjectRule:
		id, _ := strconv.ParseUint(rev.SubjectID, 10, 64)
		r, err := LoadRule(tx, uint(id))
		if errors.Is(err, ErrNoRecord) {
			return st, nil
		}
		if err != nil {
			return st, err
		}
		st.exists, st.values = true, RuleValues(r)
	case models.SubjectRedirect:
		id, _ := strconv.ParseUint(rev.SubjectID, 10, 64)
		r, err := LoadRedirect(tx, uint(id))
		if errors.Is(err, ErrNoRecord) {
			return st, nil
		}
		if err != nil {
			return st, err
		}
		st.exists, st.values = true, RedirectValues(r)
	case models.SubjectRobots:
		r, err := LoadRobots(tx)
		if err != nil {
			return st, err
		}
		st.exists, st.values = true, RobotsValues(r)
	case models.SubjectSettings:
		if key, ok := strings.CutPrefix(rev.SubjectID, "type:"); ok {
			ts, err := LoadTypeSetting(tx, key)
			if err != nil {
				return st, err
			}
			st.exists, st.values = true, TypeSettingValues(ts)
		} else {
			row, err := LoadSettings(tx)
			if err != nil {
				return st, err
			}
			st.exists, st.values = true, SettingsValues(row)
		}
	case models.SubjectNotFound:
		id, _ := strconv.ParseUint(rev.SubjectID, 10, 64)
		n, err := LoadNotFound(tx, uint(id))
		if errors.Is(err, ErrNoRecord) {
			return st, nil
		}
		if err != nil {
			return st, err
		}
		st.exists, st.values = true, NotFoundValues(n)
	default:
		return st, &UndoRefusal{Code: UndoUnsupported, Key: "golem15.seo::lang.history.undo_unsupported"}
	}
	return st, nil
}

// staleRefusal names the newest later change of field on rev's subject.
func (s *Service) staleRefusal(ctx context.Context, tx *gorm.DB, rev models.Revision, field string) error {
	author, when := "—", ""
	var later []models.Revision
	if err := tx.Where("subject_kind = ? AND subject_id = ? AND id > ?", rev.SubjectKind, rev.SubjectID, rev.ID).Order("id DESC").Find(&later).Error; err != nil {
		return err
	}
	for _, l := range later {
		if _, ok := l.After[field]; ok || len(l.After) == 0 {
			if l.AuthorLabel != "" {
				author = l.AuthorLabel
			}
			when = l.CreatedAt.UTC().Format("2006-01-02 15:04")
			break
		}
	}
	return &UndoRefusal{Code: UndoStale, Key: "golem15.seo::lang.history.undo_stale", Params: map[string]string{
		"field": s.fieldLabel(ctx, field), "author": author, "time": when,
	}}
}

// fieldLabel is the label of a history field in the request locale.
func (s *Service) fieldLabel(ctx context.Context, key string) string {
	base, locale, _ := strings.Cut(key, ".")
	for _, p := range models.RuleProperties {
		if p.Column == base {
			label := s.PhraseCtx(ctx, p.Label, nil)
			if locale != "" {
				label += " (" + locale + ")"
			}
			return label
		}
	}
	return key
}

// undoOne restores the values before rev and marks rev undone.
func (s *Service) undoOne(ctx context.Context, tx *gorm.DB, rev models.Revision) error {
	st, err := s.currentState(ctx, tx, rev)
	if err != nil {
		return err
	}
	if rev.SubjectKind == models.SubjectEntry && st.recordGone {
		label := s.PhraseCtx(ctx, "golem15.seo::lang.history.record", nil)
		if st.typ.Label != "" {
			label = s.PhraseCtx(ctx, st.typ.Label, nil)
		}
		return &UndoRefusal{Code: UndoGone, Key: "golem15.seo::lang.history.undo_gone", Params: map[string]string{"type": label}}
	}
	created := len(rev.Before) == 0 && len(rev.After) > 0
	deleted := len(rev.After) == 0 && len(rev.Before) > 0
	if deleted {
		if st.exists && rev.SubjectKind != models.SubjectEntry {
			return s.staleRefusal(ctx, tx, rev, firstKey(rev.Before))
		}
	} else {
		if !st.exists {
			return &UndoRefusal{Code: UndoGone, Key: "golem15.seo::lang.history.undo_gone", Params: map[string]string{"type": s.PhraseCtx(ctx, kindLabels[rev.SubjectKind], nil)}}
		}
		keys := make([]string, 0, len(rev.After))
		for k := range rev.After {
			keys = append(keys, k)
		}
		sort.Strings(keys)
		for _, k := range keys {
			cur, ok := st.values[k]
			if !ok {
				return &UndoRefusal{Code: UndoUnsupported, Key: "golem15.seo::lang.history.undo_unsupported"}
			}
			if !sameValue(cur, rev.After[k]) {
				return s.staleRefusal(ctx, tx, rev, k)
			}
		}
	}
	if err := s.restore(ctx, tx, rev, st, created, deleted); err != nil {
		var loop *LoopError
		if errors.As(err, &loop) {
			return &UndoRefusal{Code: UndoLoop, Key: "golem15.seo::lang.history.undo_loop", Params: map[string]string{"path": loop.Check.PathText()}}
		}
		return err
	}
	now := time.Now().UTC()
	updates := map[string]any{"undone_at": now}
	if p, ok := bouncer.User(ctx); ok && p.ID != 0 {
		updates["undone_by_id"] = p.ID
	} else if p, ok := mcpPrincipal(ctx); ok && p.ID != 0 {
		updates["undone_by_id"] = p.ID
	}
	return tx.Model(&models.Revision{}).Where("id = ?", rev.ID).Updates(updates).Error
}

// kindLabels are the phrase keys of the history subjects in the undo_gone
// refusal.
var kindLabels = map[string]string{
	models.SubjectEntry:    "golem15.seo::lang.history.record",
	models.SubjectRule:     "golem15.seo::lang.history.kind_rule",
	models.SubjectRedirect: "golem15.seo::lang.history.kind_redirect",
	models.SubjectRobots:   "golem15.seo::lang.history.kind_robots",
	models.SubjectSettings: "golem15.seo::lang.history.kind_settings",
	models.SubjectNotFound: "golem15.seo::lang.history.kind_notfound",
}

// firstKey is the first key of m in order, "" for none.
func firstKey(m map[string]any) string {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	if len(keys) == 0 {
		return ""
	}
	return keys[0]
}

// text reads a history value as text.
func text(v any) string {
	switch t := v.(type) {
	case nil:
		return ""
	case string:
		return t
	case float64:
		return strconv.FormatFloat(t, 'f', -1, 64)
	case bool:
		return strconv.FormatBool(t)
	}
	return fmt.Sprint(v)
}

// restore writes the values before rev through the service, so the undo
// is checked (loops) and recorded like any write.
func (s *Service) restore(ctx context.Context, tx *gorm.DB, rev models.Revision, st subjectState, created, deleted bool) error {
	switch rev.SubjectKind {
	case models.SubjectEntry:
		values := RecordValues{}
		for k := range rev.After {
			values[k] = map[string]string{st.locale: text(rev.Before[k])}
		}
		if deleted {
			for k, v := range rev.Before {
				values[k] = map[string]string{st.locale: text(v)}
			}
		}
		_, _, err := s.SaveRecord(ctx, tx, RecordWrite{Type: st.typ, ID: st.recordID, Values: values})
		return err
	case models.SubjectRule:
		id, _ := strconv.ParseUint(rev.SubjectID, 10, 64)
		switch {
		case created:
			r, err := LoadRule(tx, uint(id))
			if err != nil {
				return err
			}
			return s.DeleteRule(ctx, tx, r)
		case deleted:
			r := models.Rule{}
			for k, v := range rev.Before {
				SetRuleValue(&r, k, text(v))
			}
			return s.SaveRule(ctx, tx, &r)
		}
		r, err := LoadRule(tx, uint(id))
		if err != nil {
			return err
		}
		for k := range rev.After {
			SetRuleValue(&r, k, text(rev.Before[k]))
		}
		return s.SaveRule(ctx, tx, &r)
	case models.SubjectRedirect:
		id, _ := strconv.ParseUint(rev.SubjectID, 10, 64)
		switch {
		case created:
			r, err := LoadRedirect(tx, uint(id))
			if err != nil {
				return err
			}
			return s.DeleteRedirect(ctx, tx, r)
		case deleted:
			r := models.NewRedirect()
			for k, v := range rev.Before {
				setRedirectValue(&r, k, v)
			}
			_, err := s.SaveRedirect(ctx, tx, &r)
			return err
		}
		r, err := LoadRedirect(tx, uint(id))
		if err != nil {
			return err
		}
		for k := range rev.After {
			setRedirectValue(&r, k, rev.Before[k])
		}
		_, err = s.SaveRedirect(ctx, tx, &r)
		return err
	case models.SubjectRobots:
		var w RobotsWrite
		if v, ok := rev.Before["content"]; ok {
			content := text(v)
			w.Content = &content
		}
		if bots, ok := rev.Before["bots"].(map[string]any); ok {
			w.Bots = map[string]bool{}
			for token, on := range bots {
				b, _ := on.(bool)
				w.Bots[token] = b
			}
		}
		_, _, err := s.SaveRobots(ctx, tx, w)
		return err
	case models.SubjectSettings:
		if key, ok := strings.CutPrefix(rev.SubjectID, "type:"); ok {
			w := TypeSettingWrite{}
			for k := range rev.After {
				v := rev.Before[k]
				switch k {
				case "inject":
					b, _ := v.(bool)
					w.Inject = &b
				case "title_template":
					t := text(v)
					w.TitleTemplate = &t
				case "description_template":
					t := text(v)
					w.DescriptionTemplate = &t
				case "robots":
					t := text(v)
					w.Robots = &t
				}
			}
			_, err := s.SaveSettings(ctx, tx, SettingsWrite{Types: map[string]TypeSettingWrite{key: w}})
			return err
		}
		values := map[string]any{}
		for k := range rev.After {
			values[k] = rev.Before[k]
		}
		_, err := s.SaveSettings(ctx, tx, SettingsWrite{Values: values})
		return err
	case models.SubjectNotFound:
		if !deleted {
			return &UndoRefusal{Code: UndoUnsupported, Key: "golem15.seo::lang.history.undo_unsupported"}
		}
		now := time.Now().UTC()
		row := models.NotFound{URL: text(rev.Before["url"]), Referer: text(rev.Before["referer"]), FirstSeen: &now, LastHit: &now}
		if h, ok := rev.Before["hits"].(float64); ok {
			row.Hits = int64(h)
		}
		if err := tx.Create(&row).Error; err != nil {
			return err
		}
		return s.Record(ctx, tx, Change{
			Kind:      models.SubjectNotFound,
			SubjectID: strconv.FormatUint(uint64(row.ID), 10),
			What:      s.Phrase("golem15.seo::lang.history.what_notfound", map[string]string{"url": row.URL}),
			After:     NotFoundValues(row),
		})
	}
	return &UndoRefusal{Code: UndoUnsupported, Key: "golem15.seo::lang.history.undo_unsupported"}
}

// setRedirectValue writes one history value onto a redirect.
func setRedirectValue(r *models.Redirect, key string, v any) {
	switch key {
	case "source":
		r.Source = text(v)
	case "match":
		r.Match = text(v)
	case "target":
		r.Target = text(v)
	case "status":
		if n, err := strconv.Atoi(text(v)); err == nil {
			r.Status = models.RedirectStatus(n)
		}
	case "query":
		r.Query = text(v)
	case "ignore_case":
		r.IgnoreCase, _ = v.(bool)
	case "trailing_slash":
		r.TrailingSlash, _ = v.(bool)
	case "origin":
		r.Origin = text(v)
	case "note":
		r.Note = text(v)
	}
}