package web

import (
	"context"
	"embed"
	"errors"
	"fmt"
	"html/template"
	"io/fs"
	"log/slog"
	"net/http"
	"sort"
	"strings"

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

//go:embed templates/*.tmpl
var templatesFS embed.FS

//go:embed static/*
var staticFS embed.FS

// Server bundles handlers, templates, and the store.
type Server struct {
	Store  *store.Store
	pages  map[string]*template.Template
	Logger *slog.Logger
	Auth   *AuthConfig // nil → no auth (local dev / tests)
	CalDAV *CalDAVDeps // nil → CalDAV integration disabled
	Gitea  *GiteaDeps  // nil → Gitea integration disabled
}

// New builds a Server. Each page is parsed alongside the layout into its own
// Template so per-page `define "content"` blocks don't shadow each other. The
// login page is intentionally NOT wrapped in the regular layout (chrome would
// imply you're already inside the app).
func New(s *store.Store, logger *slog.Logger) (*Server, error) {
	if logger == nil {
		logger = slog.Default()
	}
	funcs := template.FuncMap{
		"deref": func(p *string) string {
			if p == nil {
				return ""
			}
			return *p
		},
		"join": func(sep string, parts []string) string { return strings.Join(parts, sep) },
		"contains": func(haystack []string, needle string) bool {
			for _, h := range haystack {
				if h == needle {
					return true
				}
			}
			return false
		},
		"tagToggleURL": func(active []string, tag string, isActive bool) string {
			next := []string{}
			if isActive {
				for _, t := range active {
					if t != tag {
						next = append(next, t)
					}
				}
			} else {
				next = append(next, active...)
				next = append(next, tag)
			}
			if len(next) == 0 {
				return "/"
			}
			return "/?tag=" + strings.Join(next, ",")
		},
	}
	pages := map[string]*template.Template{}
	for _, name := range []string{"tree", "new", "classify", "caldav_admin", "caldav_disabled", "error"} {
		t, err := template.New(name).Funcs(funcs).ParseFS(templatesFS,
			"templates/layout.tmpl",
			"templates/"+name+".tmpl",
		)
		if err != nil {
			return nil, fmt.Errorf("parse %s: %w", name, err)
		}
		pages[name] = t
	}
	// detail bundles the shared tasks-section + issues-section partials so
	// HTMX swaps and the initial page render hit the same template definitions.
	detailTmpl, err := template.New("detail").Funcs(funcs).ParseFS(templatesFS,
		"templates/layout.tmpl",
		"templates/detail.tmpl",
		"templates/tasks_section.tmpl",
		"templates/issues_section.tmpl",
	)
	if err != nil {
		return nil, fmt.Errorf("parse detail: %w", err)
	}
	pages["detail"] = detailTmpl
	// Standalone tasks-section template for HTMX fragment responses.
	tasksFragment, err := template.New("tasks_section").Funcs(funcs).ParseFS(templatesFS, "templates/tasks_section.tmpl")
	if err != nil {
		return nil, fmt.Errorf("parse tasks_section: %w", err)
	}
	pages["tasks_section"] = tasksFragment
	loginTmpl, err := template.New("login").Funcs(funcs).ParseFS(templatesFS, "templates/login.tmpl")
	if err != nil {
		return nil, fmt.Errorf("parse login: %w", err)
	}
	pages["login"] = loginTmpl
	return &Server{Store: s, pages: pages, Logger: logger}, nil
}

// Routes wires every URL to a handler and returns the mux.
func (s *Server) Routes() http.Handler {
	mux := http.NewServeMux()

	mux.HandleFunc("GET /", s.handleTree)
	mux.HandleFunc("GET /i/", s.handleDetail)
	mux.HandleFunc("POST /i/", s.handleDetailWrite)
	mux.HandleFunc("GET /new", s.handleNewForm)
	mux.HandleFunc("POST /new", s.handleNewSubmit)
	mux.HandleFunc("GET /admin/classify", s.handleClassify)
	mux.HandleFunc("GET /admin/caldav", s.handleCalDAVAdmin)
	mux.HandleFunc("POST /admin/caldav/link", s.handleCalDAVLink)
	mux.HandleFunc("POST /admin/caldav/unlink", s.handleCalDAVUnlink)
	mux.HandleFunc("GET /login", s.handleLoginForm)
	mux.HandleFunc("POST /login", s.handleLoginSubmit)
	mux.HandleFunc("POST /logout", s.handleLogout)
	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, r *http.Request) {
		if err := s.Store.Pool.Ping(r.Context()); err != nil {
			http.Error(w, err.Error(), http.StatusServiceUnavailable)
			return
		}
		fmt.Fprintln(w, "ok")
	})

	static, _ := fs.Sub(staticFS, "static")
	mux.Handle("GET /static/", http.StripPrefix("/static/", http.FileServer(http.FS(static))))

	var h http.Handler = mux
	if s.Auth != nil {
		h = authMiddleware(*s.Auth, s.Logger, h)
	}
	return logging(s.Logger, h)
}

// --- handlers ---

type treeNode struct {
	Item     *store.Item
	Children []*treeNode
}

func (s *Server) handleTree(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path != "/" {
		http.NotFound(w, r)
		return
	}
	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
	}
	activeTags := parseCSV(r.URL.Query().Get("tag"))
	roots, orphans, total, orphanN := buildForest(items, activeTags)
	s.render(w, "tree", map[string]any{
		"Title":      "tree",
		"Roots":      roots,
		"Orphans":    orphans,
		"Total":      total,
		"OrphanN":    orphanN,
		"AllTags":    tags,
		"ActiveTags": activeTags,
	})
}

func (s *Server) handleDetail(w http.ResponseWriter, r *http.Request) {
	path := strings.TrimPrefix(r.URL.Path, "/i/")
	if path == "" {
		http.NotFound(w, r)
		return
	}
	it, err := s.Store.GetByPath(r.Context(), path)
	if err != nil {
		s.fail(w, r, err)
		return
	}
	parents, err := s.parentOptions(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	tasks, err := s.detailTodos(r.Context(), it)
	if err != nil {
		s.Logger.Warn("detail tasks", "path", it.PrimaryPath(), "err", err)
	}
	issues, err := s.detailIssues(r.Context(), it)
	if err != nil {
		s.Logger.Warn("detail issues", "path", it.PrimaryPath(), "err", err)
	}
	openTotal := 0
	for _, ri := range issues {
		openTotal += ri.OpenCount
	}
	s.render(w, "detail", map[string]any{
		"Title":            it.Title,
		"Item":             it,
		"ParentOptions":    parents,
		"StatusOptions":    []string{"active", "done", "archived"},
		"Tasks":            tasks,
		"CalDAVOn":         s.CalDAV != nil,
		"Issues":           issues,
		"IssuesOpenTotal":  openTotal,
		"GiteaOn":          s.Gitea != nil,
	})
}

func (s *Server) handleDetailWrite(w http.ResponseWriter, r *http.Request) {
	path := strings.TrimPrefix(r.URL.Path, "/i/")
	if base, ok := strings.CutSuffix(path, "/reparent"); ok {
		s.handleReparent(w, r, base)
		return
	}
	if base, ok := strings.CutSuffix(path, "/caldav/create"); ok {
		s.handleCalDAVCreate(w, r, base)
		return
	}
	for _, action := range []string{"complete", "reopen", "edit", "delete", "todo-create"} {
		if base, ok := strings.CutSuffix(path, "/caldav/todo/"+action); ok {
			s.handleCalDAVTodoAction(w, r, base, action)
			return
		}
	}
	it, err := s.Store.GetByPath(r.Context(), path)
	if err != nil {
		s.fail(w, r, err)
		return
	}
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, err)
		return
	}
	parentIDs := r.Form["parent_ids"]
	if len(parentIDs) == 0 {
		// Legacy single-value field for the classify HTMX action.
		if v := strings.TrimSpace(r.FormValue("parent_id")); v != "" {
			parentIDs = []string{v}
		}
	}
	parentIDs = dedupeStrings(parentIDs)
	in := store.UpdateInput{
		Title:      strings.TrimSpace(r.FormValue("title")),
		Slug:       strings.TrimSpace(r.FormValue("slug")),
		ParentIDs:  parentIDs,
		ContentMD:  r.FormValue("content_md"),
		Status:     strings.TrimSpace(r.FormValue("status")),
		Pinned:     r.FormValue("pinned") == "1",
		Archived:   r.FormValue("archived") == "1",
		Tags:       parseCSV(r.FormValue("tags")),
		Management: parseCSV(r.FormValue("management")),
	}
	updated, err := s.Store.Update(r.Context(), it.ID, in)
	if err != nil {
		s.fail(w, r, err)
		return
	}
	http.Redirect(w, r, "/i/"+updated.PrimaryPath(), http.StatusSeeOther)
}

// handleReparent replaces parent_ids. /admin/classify uses this to move
// a root mai-managed item under a chosen parent without touching other fields.
// HTMX-friendly: returns a fragment when HX-Request is set.
func (s *Server) handleReparent(w http.ResponseWriter, r *http.Request, path string) {
	it, err := s.Store.GetByPath(r.Context(), path)
	if err != nil {
		s.fail(w, r, err)
		return
	}
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, err)
		return
	}
	parentIDs := r.Form["parent_ids"]
	if len(parentIDs) == 0 {
		if v := strings.TrimSpace(r.FormValue("parent_id")); v != "" {
			parentIDs = []string{v}
		}
	}
	parentIDs = dedupeStrings(parentIDs)
	if len(parentIDs) == 0 {
		http.Error(w, "reparent: parent_ids required", http.StatusBadRequest)
		return
	}
	moved, err := s.Store.Reparent(r.Context(), it.ID, parentIDs)
	if err != nil {
		s.fail(w, r, err)
		return
	}
	if r.Header.Get("HX-Request") == "true" {
		fmt.Fprintf(w, `<tr class="classified"><td colspan="5">Moved to <a href="/i/%s">%s</a></td></tr>`,
			template.HTMLEscapeString(moved.PrimaryPath()), template.HTMLEscapeString(moved.PrimaryPath()))
		return
	}
	http.Redirect(w, r, "/i/"+moved.PrimaryPath(), http.StatusSeeOther)
}

// dedupeStrings preserves order, drops empties.
func dedupeStrings(in []string) []string {
	seen := map[string]struct{}{}
	out := make([]string, 0, len(in))
	for _, s := range in {
		s = strings.TrimSpace(s)
		if s == "" {
			continue
		}
		if _, ok := seen[s]; ok {
			continue
		}
		seen[s] = struct{}{}
		out = append(out, s)
	}
	return out
}

// parseCSV splits a comma/space-delimited chip input into a deduplicated,
// trimmed lowercase string slice. Empty input → []string{} (nil avoided so
// JSON/SQL writes get an explicit empty array).
func parseCSV(raw string) []string {
	if strings.TrimSpace(raw) == "" {
		return []string{}
	}
	seen := map[string]struct{}{}
	out := []string{}
	for _, part := range strings.FieldsFunc(raw, func(r rune) bool {
		return r == ',' || r == ' ' || r == '\t' || r == '\n'
	}) {
		t := strings.ToLower(strings.TrimSpace(part))
		if t == "" {
			continue
		}
		if _, ok := seen[t]; ok {
			continue
		}
		seen[t] = struct{}{}
		out = append(out, t)
	}
	return out
}

func (s *Server) handleNewForm(w http.ResponseWriter, r *http.Request) {
	parentPath := r.URL.Query().Get("parent")
	var parent *store.Item
	if parentPath != "" {
		p, err := s.Store.GetByPath(r.Context(), parentPath)
		if err != nil {
			s.fail(w, r, err)
			return
		}
		parent = p
	}
	s.render(w, "new", map[string]any{
		"Title":         "new",
		"Parent":        parent,
		"StatusOptions": []string{"active", "done", "archived"},
	})
}

func (s *Server) handleNewSubmit(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		s.fail(w, r, err)
		return
	}
	kind := strings.TrimSpace(r.FormValue("kind"))
	if kind == "" {
		kind = "project"
	}
	parentIDs := r.Form["parent_ids"]
	if len(parentIDs) == 0 {
		if v := strings.TrimSpace(r.FormValue("parent_id")); v != "" {
			parentIDs = []string{v}
		}
	}
	parentIDs = dedupeStrings(parentIDs)
	in := store.CreateInput{
		Kind:       []string{kind},
		Title:      strings.TrimSpace(r.FormValue("title")),
		Slug:       strings.TrimSpace(r.FormValue("slug")),
		ParentIDs:  parentIDs,
		ContentMD:  r.FormValue("content_md"),
		Status:     strings.TrimSpace(r.FormValue("status")),
		Tags:       parseCSV(r.FormValue("tags")),
		Management: parseCSV(r.FormValue("management")),
	}
	it, err := s.Store.Create(r.Context(), in)
	if err != nil {
		s.fail(w, r, err)
		return
	}
	http.Redirect(w, r, "/i/"+it.PrimaryPath(), http.StatusSeeOther)
}

func (s *Server) handleClassify(w http.ResponseWriter, r *http.Request) {
	orphans, err := s.Store.MaiOrphans(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	parents, err := s.parentOptions(r.Context())
	if err != nil {
		s.fail(w, r, err)
		return
	}
	s.render(w, "classify", map[string]any{
		"Title":         "classify",
		"Orphans":       orphans,
		"ParentOptions": parents,
	})
}

// --- helpers ---

// ParentOption is a flat option for the parent <select>.
type ParentOption struct {
	ID   string
	Path string
}

func (s *Server) parentOptions(ctx context.Context) ([]ParentOption, error) {
	items, err := s.Store.ListAll(ctx)
	if err != nil {
		return nil, err
	}
	var out []ParentOption
	for _, it := range items {
		// Surface every primary path as a candidate parent — multi-parent
		// items appear once per parent option using their primary path so the
		// UI stays unambiguous.
		out = append(out, ParentOption{ID: it.ID, Path: it.PrimaryPath()})
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Path < out[j].Path })
	return out, nil
}

// buildForest groups items_unified rows by parent into a sortable tree. A
// multi-parent item appears under EACH of its parents (duplicated nodes in
// distinct branches). When activeTags is non-empty, a branch is kept only
// when it (or any descendant) matches every active tag. orphans lists
// mai-managed root items so /admin/classify and the tree page can surface
// them.
func buildForest(items []*store.Item, activeTags []string) (roots []*treeNode, orphans []*store.Item, total, orphanN int) {
	for _, it := range items {
		total++
		if len(it.ParentIDs) == 0 && it.HasManagement("mai") {
			orphans = append(orphans, it)
			orphanN++
		}
	}
	// Build a forest where every parent relationship creates a node — so
	// multi-parent items are rendered under each parent. Root items get
	// one node total.
	nodeFor := func(it *store.Item) *treeNode { return &treeNode{Item: it} }
	rootNodes := []*treeNode{}
	childByParent := make(map[string][]*treeNode, len(items))
	for _, it := range items {
		if len(it.ParentIDs) == 0 {
			rootNodes = append(rootNodes, nodeFor(it))
			continue
		}
		for _, pid := range it.ParentIDs {
			childByParent[pid] = append(childByParent[pid], nodeFor(it))
		}
	}
	var attach func(n *treeNode)
	attach = func(n *treeNode) {
		n.Children = childByParent[n.Item.ID]
		for _, c := range n.Children {
			attach(c)
		}
	}
	for _, r := range rootNodes {
		attach(r)
	}
	roots = rootNodes
	if len(activeTags) > 0 {
		var keep func(n *treeNode) bool
		keep = func(n *treeNode) bool {
			filtered := n.Children[:0]
			for _, c := range n.Children {
				if keep(c) {
					filtered = append(filtered, c)
				}
			}
			n.Children = filtered
			if nodeHasAllTags(n.Item, activeTags) {
				return true
			}
			return len(n.Children) > 0
		}
		filtered := roots[:0]
		for _, n := range roots {
			if keep(n) {
				filtered = append(filtered, n)
			}
		}
		roots = filtered
	}
	sort.Slice(roots, func(i, j int) bool { return roots[i].Item.Slug < roots[j].Item.Slug })
	sort.Slice(orphans, func(i, j int) bool { return orphans[i].Slug < orphans[j].Slug })
	var sortChildren func(n *treeNode)
	sortChildren = func(n *treeNode) {
		sort.Slice(n.Children, func(i, j int) bool { return n.Children[i].Item.Slug < n.Children[j].Item.Slug })
		for _, c := range n.Children {
			sortChildren(c)
		}
	}
	for _, r := range roots {
		sortChildren(r)
	}
	return
}

func nodeHasAllTags(it *store.Item, want []string) bool {
	for _, t := range want {
		if !it.HasTag(t) {
			return false
		}
	}
	return true
}

func (s *Server) render(w http.ResponseWriter, name string, data map[string]any) {
	t, ok := s.pages[name]
	if !ok {
		http.Error(w, "unknown page: "+name, http.StatusInternalServerError)
		return
	}
	entry := "layout"
	switch name {
	case "login":
		// Login page is intentionally standalone — no nav chrome.
		entry = "login"
	case "tasks_section":
		// HTMX fragment — no layout chrome.
		entry = "tasks-section"
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := t.ExecuteTemplate(w, entry, data); err != nil {
		s.Logger.Error("render", "page", name, "err", err)
	}
}

func (s *Server) fail(w http.ResponseWriter, r *http.Request, err error) {
	status := http.StatusInternalServerError
	if errors.Is(err, store.ErrNotFound) {
		status = http.StatusNotFound
	}
	w.WriteHeader(status)
	s.render(w, "error", map[string]any{
		"Title":   "error",
		"Message": err.Error(),
	})
	s.Logger.Error("handler", "path", r.URL.Path, "err", err)
}

// logging wraps the mux with a tiny access log.
func logging(logger *slog.Logger, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		next.ServeHTTP(w, r)
		logger.Info("req", "method", r.Method, "path", r.URL.Path, "remote", r.RemoteAddr)
	})
}