package web

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"

	"github.com/m/projax/store"
)

// Phase 5j paliad-shape views handlers. Slice B introduces the route
// family; slices C–G evolve the render, editor, system-views, sidebar,
// and polish layers.
//
// Route table:
//   GET  /views                  → handleViewsLanding   (MRU 302 or shell)
//   GET  /views/{slug}           → handleViewRender     (saved or system)
//   GET  /views/new              → handleViewEditor     (blank)
//   GET  /views/{slug}/edit      → handleViewEditor     (existing)
//   POST /views                  → handleViewCreate
//   POST /views/{slug}           → handleViewUpdate
//   POST /views/{slug}/delete    → handleViewDelete
//   POST /views/reorder          → handleViewReorder    (slice G — wired now,
//                                                        used in v2)

// handleViewsLanding implements m's Q5 pick: 302 to the most-recently-used
// view if any, else render the onboarding shell listing every saved view.
func (s *Server) handleViewsLanding(w http.ResponseWriter, r *http.Request) {
	if r.URL.Query().Get("nodefault") != "1" {
		mr, err := s.Store.MostRecentView(r.Context())
		if err != nil {
			s.Logger.Warn("views landing: mru", "err", err)
		} else if mr != nil {
			http.Redirect(w, r, "/views/"+mr.Slug, http.StatusFound)
			return
		}
	}
	views, err := s.Store.ListViews(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	s.render(w, r, "views_landing", map[string]any{
		"Title": "views",
		"Views": views,
	})
}

// handleViewRender resolves a slug into either a user view (Slice A
// schema) or a system view (Slice C), then renders the appropriate
// template. The render path also fire-and-forgets a TouchView so the
// view climbs the MRU ladder for the next /views landing redirect.
//
// Slice B implementation: only user views are wired; system views
// resolve via LookupSystemView (added in Slice C) and 404 in this slice
// when the slug is unknown.
func (s *Server) handleViewRender(w http.ResponseWriter, r *http.Request) {
	slug := r.PathValue("slug")
	if slug == "" {
		http.NotFound(w, r)
		return
	}
	v, err := s.Store.GetView(r.Context(), slug)
	if errors.Is(err, store.ErrViewNotFound) {
		http.NotFound(w, r)
		return
	}
	if err != nil {
		s.fail(w, r, err)
		return
	}
	if err := s.Store.TouchView(r.Context(), slug); err != nil {
		s.Logger.Warn("touch view", "slug", slug, "err", err)
	}

	// Parse the saved spec.
	filter, viewType, groupBy := decodeViewSpec(v.FilterJSON)
	// Allow URL chip overlay so chip clicks inside a saved view narrow
	// further. The page chip URLs round-trip ?view= via the URL anchor
	// added in slice E's sidebar wiring; here we just respect anything
	// the user typed in the query.
	urlFilter := ParseTreeFilter(r.URL.Query())
	overlayURLOntoSavedFilter(&filter, urlFilter, r.URL.Query())
	if raw := strings.TrimSpace(r.URL.Query().Get("view_type")); raw != "" {
		viewType = raw
	}
	if raw := strings.TrimSpace(r.URL.Query().Get("group_by")); raw != "" {
		groupBy = raw
	}

	s.renderViewPage(w, r, v, filter, viewType, groupBy)
}

// renderViewPage runs the shared render path for a resolved view (user
// view or future system view). Slice B reuses the tree handler's
// rendering pieces — list / card / kanban share the tree-section
// dispatch shape. Calendar / timeline view_types fall back to list in
// slice B; slice D wires their dedicated templates.
func (s *Server) renderViewPage(w http.ResponseWriter, r *http.Request, v *store.View, filter TreeFilter, viewType, groupBy string) {
	items, err := s.Store.ListAll(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	tags, err := s.Store.AllTags(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	linkKinds, err := s.linkKindsByItem(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	viewSet := PageViewTypes("/")
	if viewType == "" {
		viewType = viewSet.Default
	}
	viewType = viewSet.Resolve(viewType)
	roots, orphans, total, orphanN, matched := applyTreeFilter(items, filter, linkKinds)
	base := "/views/" + v.Slug
	counts := computeChipCounts(items, filter, linkKinds, tags, base)
	cardItems := flatMatchedItems(items, filter, linkKinds)
	if groupBy == "" {
		groupBy = ParseGroupBy(r.URL.Query())
	}
	kanban := BuildKanbanBoard(cardItems, groupBy)
	groupByChips := GroupByChips(base, filter, groupBy)
	data := map[string]any{
		"Title":             v.Name,
		"View":              v,
		"Roots":             roots,
		"Orphans":           orphans,
		"Total":             total,
		"OrphanN":           orphanN,
		"Matched":           matched,
		"AllTags":           tags,
		"Filter":            filter,
		"Counts":            counts,
		"Projects":          parentOptionsFromItems(items),
		"BasePath":          base,
		"ProjectChipTarget": "#tree-section",
		"ViewType":          viewType,
		"ViewTypeChips":     ViewTypeChips(base, filter, viewType),
		"CardItems":         cardItems,
		"Kanban":            kanban,
		"GroupBy":           groupBy,
		"GroupByChips":      groupByChips,
		"ActiveTags":        filter.Tags,
	}
	if r.Header.Get("HX-Request") == "true" {
		s.render(w, r, "tree_section", data)
		return
	}
	s.render(w, r, "view_render", data)
}

// handleViewEditor renders the create / edit form. Slice B ships a
// minimal placeholder; Slice D rebuilds the form with the chip strip
// + slug derivation + icon picker.
func (s *Server) handleViewEditor(w http.ResponseWriter, r *http.Request) {
	slug := r.PathValue("slug")
	var (
		view  *store.View
		err   error
		title = "new view"
	)
	if slug != "" {
		view, err = s.Store.GetView(r.Context(), slug)
		if errors.Is(err, store.ErrViewNotFound) {
			http.NotFound(w, r)
			return
		}
		if err != nil {
			s.fail(w, r, err)
			return
		}
		title = "edit " + view.Name
	}
	filterQuery := ""
	currentViewType := "list"
	if view != nil {
		f, vt, _ := decodeViewSpec(view.FilterJSON)
		filterQuery = f.QueryString()
		if vt != "" {
			currentViewType = vt
		}
	}
	s.render(w, r, "view_editor", map[string]any{
		"Title":          title,
		"View":           view,
		"FilterQuery":    filterQuery,
		"ViewTypes":      []string{ViewTypeList, ViewTypeCard, ViewTypeKanban},
		"CurrentVT":      currentViewType,
		"GroupByOptions": []string{"", "status", "area", "tag", "management"},
		"SortDirOptions": []string{"", "asc", "desc"},
		"IconKeys":       IconRegistryKeys(),
	})
}

// handleViewCreate accepts the create form POST.
func (s *Server) handleViewCreate(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, err)
		return
	}
	in, err := viewInputFromForm(r.PostForm)
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	v, err := s.Store.CreateView(r.Context(), in)
	if err != nil {
		s.writeViewError(w, err)
		return
	}
	http.Redirect(w, r, "/views/"+v.Slug, http.StatusSeeOther)
}

// handleViewUpdate accepts the edit form POST.
func (s *Server) handleViewUpdate(w http.ResponseWriter, r *http.Request) {
	slug := r.PathValue("slug")
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, err)
		return
	}
	in, err := viewInputFromForm(r.PostForm)
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	v, err := s.Store.UpdateView(r.Context(), slug, in)
	if err != nil {
		if errors.Is(err, store.ErrViewNotFound) {
			http.NotFound(w, r)
			return
		}
		s.writeViewError(w, err)
		return
	}
	http.Redirect(w, r, "/views/"+v.Slug, http.StatusSeeOther)
}

// handleViewDelete soft-… nope. New schema is hard-delete (no
// deleted_at). One POST removes the row.
func (s *Server) handleViewDelete(w http.ResponseWriter, r *http.Request) {
	slug := r.PathValue("slug")
	if err := s.Store.DeleteView(r.Context(), slug); err != nil {
		if errors.Is(err, store.ErrViewNotFound) {
			http.NotFound(w, r)
			return
		}
		s.fail(w, r, err)
		return
	}
	http.Redirect(w, r, "/views", http.StatusSeeOther)
}

// handleViewReorder takes a comma-separated slug list and applies new
// sort_order values. Wired now so slice G's drag UI has a target.
func (s *Server) handleViewReorder(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, err)
		return
	}
	raw := strings.TrimSpace(r.PostForm.Get("slugs"))
	if raw == "" {
		http.Error(w, "slugs is required", http.StatusBadRequest)
		return
	}
	slugs := strings.Split(raw, ",")
	for i, slug := range slugs {
		slugs[i] = strings.TrimSpace(slug)
	}
	if err := s.Store.ReorderViews(r.Context(), slugs); err != nil {
		s.fail(w, r, err)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// writeViewError maps the typed store errors to friendly HTTP status +
// banner copy. Falls back to 400 for anything else.
func (s *Server) writeViewError(w http.ResponseWriter, err error) {
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	switch {
	case errors.Is(err, store.ErrViewSlugFormat):
		http.Error(w, "slug must match ^[a-z0-9][a-z0-9-]{0,62}$ (lowercase, no underscores, no leading dash)", http.StatusBadRequest)
	case errors.Is(err, store.ErrViewSlugReserved):
		http.Error(w, "slug is reserved (system views and top-level routes shadow it)", http.StatusBadRequest)
	case errors.Is(err, store.ErrViewSlugTaken):
		http.Error(w, "slug already exists — pick a different one", http.StatusConflict)
	default:
		http.Error(w, err.Error(), http.StatusBadRequest)
	}
}

// viewInputFromForm decodes the create/edit form. Slug + name are
// required; the rest defaults sensibly. filter_query is optional and
// canonicalises into filter_json on save (URL-query form is what the
// editor's chip strip emits in slice D).
func viewInputFromForm(form url.Values) (store.ViewInput, error) {
	in := store.ViewInput{
		Slug:      strings.TrimSpace(form.Get("slug")),
		Name:      strings.TrimSpace(form.Get("name")),
		SortField: strings.TrimSpace(form.Get("sort_field")),
		SortDir:   strings.TrimSpace(form.Get("sort_dir")),
		GroupBy:   strings.TrimSpace(form.Get("group_by")),
		ShowCount: form.Get("show_count") == "1",
	}
	if iconRaw := strings.TrimSpace(form.Get("icon")); iconRaw != "" {
		in.Icon = &iconRaw
	}
	viewType := strings.TrimSpace(form.Get("view_type"))
	if viewType == "" {
		viewType = ViewTypeList
	}
	fq := strings.TrimSpace(form.Get("filter_query"))
	filterJSON, err := encodeFilterToJSON(fq, viewType)
	if err != nil {
		return in, fmt.Errorf("filter_query: %w", err)
	}
	in.FilterJSON = filterJSON
	return in, nil
}

// encodeFilterToJSON turns a URL-query-form filter + view_type into the
// canonical filter_json shape stored on the view. view_type lives inside
// the JSON per m's Q2 pick.
func encodeFilterToJSON(query, viewType string) ([]byte, error) {
	q, err := url.ParseQuery(strings.TrimPrefix(query, "?"))
	if err != nil {
		return nil, err
	}
	f := ParseTreeFilter(q)
	payload := map[string]any{
		"view_type": viewType,
	}
	if f.Q != "" {
		payload["q"] = f.Q
	}
	if len(f.Tags) > 0 {
		payload["tags"] = f.Tags
	}
	if len(f.Management) > 0 {
		payload["management"] = f.Management
	}
	if !(len(f.Status) == 1 && f.Status[0] == "active") {
		payload["status"] = f.Status
	}
	if len(f.HasLinks) > 0 {
		payload["has_links"] = f.HasLinks
	}
	if f.Public != nil {
		payload["public"] = *f.Public
	}
	if f.ShowArchived {
		payload["show_archived"] = true
	}
	if f.ProjectPath != "" {
		payload["project_path"] = f.ProjectPath
		if !f.IncludeDescendants {
			payload["include_descendants"] = false
		}
	}
	return json.Marshal(payload)
}

// decodeViewSpec parses filter_json into a TreeFilter + view_type +
// group_by. Inverse of encodeFilterToJSON.
func decodeViewSpec(filterJSON []byte) (TreeFilter, string, string) {
	f := TreeFilter{
		Status:             []string{"active"},
		IncludeDescendants: true,
	}
	viewType := ""
	groupBy := ""
	if len(filterJSON) == 0 {
		return f, viewType, groupBy
	}
	payload := map[string]any{}
	if err := json.Unmarshal(filterJSON, &payload); err != nil {
		return f, viewType, groupBy
	}
	if v, ok := payload["view_type"].(string); ok {
		viewType = v
	}
	if v, ok := payload["group_by"].(string); ok {
		groupBy = v
	}
	if v, ok := payload["q"].(string); ok {
		f.Q = v
	}
	if v, ok := payload["tags"].([]any); ok {
		f.Tags = anySliceToStrings(v)
	}
	if v, ok := payload["management"].([]any); ok {
		f.Management = anySliceToStrings(v)
	}
	if v, ok := payload["status"].([]any); ok {
		f.Status = anySliceToStrings(v)
		if len(f.Status) == 0 {
			f.Status = []string{"active"}
		}
	}
	if v, ok := payload["has_links"].([]any); ok {
		f.HasLinks = anySliceToStrings(v)
	}
	if v, ok := payload["public"].(bool); ok {
		f.Public = &v
	}
	if v, ok := payload["show_archived"].(bool); ok && v {
		f.ShowArchived = true
	}
	if v, ok := payload["project_path"].(string); ok {
		f.ProjectPath = v
	}
	if v, ok := payload["include_descendants"].(bool); ok {
		f.IncludeDescendants = v
	}
	return f, viewType, groupBy
}

// overlayURLOntoSavedFilter applies URL-query chip values on top of the
// saved-view baseline. Same pattern the 5i fix-shift had (URL overrides
// saved); slice B reintroduces it here on the /views/{slug} render path.
func overlayURLOntoSavedFilter(base *TreeFilter, urlFilter TreeFilter, q url.Values) {
	if q.Get("q") != "" {
		base.Q = urlFilter.Q
	}
	if _, ok := q["tag"]; ok {
		base.Tags = urlFilter.Tags
	}
	if _, ok := q["mgmt"]; ok {
		base.Management = urlFilter.Management
	}
	if _, ok := q["status"]; ok {
		base.Status = urlFilter.Status
	}
	if _, ok := q["has"]; ok {
		base.HasLinks = urlFilter.HasLinks
	}
	if q.Get("show-archived") != "" {
		base.ShowArchived = urlFilter.ShowArchived
	}
	if q.Get("public") != "" {
		base.Public = urlFilter.Public
	}
	if q.Get("project") != "" {
		base.ProjectPath = urlFilter.ProjectPath
	}
	if q.Get("project_descendants") != "" {
		base.IncludeDescendants = urlFilter.IncludeDescendants
	}
}

func anySliceToStrings(in []any) []string {
	out := make([]string, 0, len(in))
	for _, v := range in {
		if s, ok := v.(string); ok {
			out = append(out, s)
		}
	}
	return out
}