package api

import (
	"context"
	"reflect"
	"sort"
	"strconv"
	"time"

	"git.golem15.com/golem15/sm-journal-plugin/models"
	translate "git.golem15.com/golem15/sm-translate-plugin/classes"
	"git.golem15.com/golem15/summercms/modules/pact"
	"git.golem15.com/golem15/summercms/modules/towel"
	"gorm.io/gorm"
)

// postEventColumns are the post columns a record event reports, in order.
var postEventColumns = []struct {
	name  string
	value func(p *models.Post) any
}{
	{"user_id", func(p *models.Post) any { return derefValue(p.UserID) }},
	{"redactor_id", func(p *models.Post) any { return derefValue(p.RedactorID) }},
	{"title", func(p *models.Post) any { return p.Title }},
	{"slug", func(p *models.Post) any { return p.Slug }},
	{"excerpt", func(p *models.Post) any { return p.Excerpt }},
	{"content", func(p *models.Post) any { return p.Content }},
	{"content_html", func(p *models.Post) any { return p.ContentHTML }},
	{"published_at", func(p *models.Post) any { return derefValue(p.PublishedAt) }},
	{"published", func(p *models.Post) any { return p.Published }},
	{"is_pinned", func(p *models.Post) any { return p.IsPinned }},
	{"metadata", func(p *models.Post) any { return derefValue(p.Metadata) }},
	{"sources", func(p *models.Post) any { return derefValue(p.Sources) }},
}

// translatedEventFields are the translated fields a write may submit under
// "translations" (syncTranslations).
var translatedEventFields = []string{"title", "slug", "content", "content_html", "excerpt", "metadata"}

// postSnapshot is a post's values before an API write: its columns and the
// stored translations of the fields the request submits per locale.
type postSnapshot struct {
	columns      map[string]any
	translations map[string]map[string]any // locale -> field -> old (nil when missing)
}

// snapshotPost takes the values an update may change, before it changes
// them. A translation read error leaves that value out (reported as new).
func snapshotPost(ctx context.Context, db *gorm.DB, post *models.Post, body map[string]any) *postSnapshot {
	snap := &postSnapshot{columns: map[string]any{}, translations: map[string]map[string]any{}}
	for _, col := range postEventColumns {
		snap.columns[col.name] = col.value(post)
	}
	for locale, fields := range submittedTranslations(body) {
		snap.translations[locale] = map[string]any{}
		for _, field := range fields {
			text, ok, err := translate.TranslatedExact(ctx, db, post, field, locale)
			if err == nil && ok {
				snap.translations[locale][field] = text
			} else {
				snap.translations[locale][field] = nil
			}
		}
	}
	return snap
}

// postSavedEvent is the RecordSaved of an API write, which the handler
// fires with cabana.EmitRecordSaved once the write is committed (the API
// writes run outside a transaction, so at once). before is nil on create:
// every column with a value and every submitted translation is then
// reported with a nil Old. Controller is "": the write did not go through an
// admin form.
func postSavedEvent(ctx context.Context, db *gorm.DB, before *postSnapshot, post *models.Post, body map[string]any) pact.RecordSaved {
	changes := []pact.RecordChange{}
	for _, col := range postEventColumns {
		next := col.value(post)
		if before == nil {
			if next == nil || reflect.ValueOf(next).IsZero() {
				continue
			}
			changes = append(changes, pact.RecordChange{Attribute: col.name, New: next})
			continue
		}
		prev := before.columns[col.name]
		if sameEventValue(prev, next) {
			continue
		}
		changes = append(changes, pact.RecordChange{Attribute: col.name, Old: prev, New: next})
	}
	submitted := submittedTranslations(body)
	locales := make([]string, 0, len(submitted))
	for locale := range submitted {
		locales = append(locales, locale)
	}
	sort.Strings(locales)
	for _, locale := range locales {
		for _, field := range submitted[locale] {
			text, ok, err := translate.TranslatedExact(ctx, db, post, field, locale)
			if err != nil || !ok {
				continue
			}
			var prev any
			if before != nil {
				prev = before.translations[locale][field]
			}
			if old, _ := prev.(string); old == text {
				continue
			}
			changes = append(changes, pact.RecordChange{Attribute: field, Locale: locale, Old: prev, New: text})
		}
	}
	locale, _ := towel.Locale(ctx)
	return pact.RecordSaved{
		Model:   post.MorphName(),
		ID:      strconv.FormatUint(uint64(post.ID), 10),
		Locale:  locale,
		Created: before == nil,
		Changes: changes,
	}
}

// submittedTranslations lists, per locale, the translated fields a request
// body submits with a value, in translatedEventFields order.
func submittedTranslations(body map[string]any) map[string][]string {
	out := map[string][]string{}
	m, ok := body["translations"].(map[string]any)
	if !ok {
		return out
	}
	for locale, raw := range m {
		attrs, ok := raw.(map[string]any)
		if !ok {
			continue
		}
		for _, field := range translatedEventFields {
			if v, has := attrs[field]; has && v != nil {
				out[locale] = append(out[locale], field)
			}
		}
	}
	return out
}

// derefValue is a pointer column's value, nil for a nil pointer.
func derefValue[T any](p *T) any {
	if p == nil {
		return nil
	}
	return *p
}

// sameEventValue compares two column values; times compare as instants.
func sameEventValue(a, b any) bool {
	ta, okA := a.(time.Time)
	tb, okB := b.(time.Time)
	if okA && okB {
		return ta.Equal(tb)
	}
	return reflect.DeepEqual(a, b)
}