package main

import (
	"bytes"
	"html/template"
	"log"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
)

var treeTmpl = template.Must(template.New("tree").ParseFS(assets, "assets/tree.html"))

// treeOpts selects what a folder tree renders. The same markup serves the
// sidebar (links) and the tree picker (radio inputs named "pick").
type treeOpts struct {
	Files  bool   // list files, not just folders
	Pick   string // "" renders links; "folder", "file" or "any" renders a picker for that kind
	Active string // wiki path of the current page, highlighted (sidebar)
	Select string // wiki path of the initially checked row (picker)
}

// query returns the ?tree query that lazy-loads a folder's children with the
// same options.
func (o treeOpts) query() string {
	q := "?tree"
	if o.Files {
		q += "&files=1"
	}
	if o.Pick != "" {
		q += "&pick=" + o.Pick
	}
	return q
}

type treeEntry struct {
	Name string
	Kind string // "folder" or "file"
	// HasChildren reports whether a folder has any visible entries (under the
	// same files filter), so empty folders render without a chevron.
	HasChildren bool
}

// treeRow is one rendered row. Folders with children are expandable: either
// pre-expanded (Children set, along the requested path) or lazy-loaded from
// ChildrenURL when first opened.
type treeRow struct {
	Name, Path, Kind string
	URL              string // page URL (sidebar links)
	Link             bool   // render the name as a link
	Selectable       bool   // render a picker radio
	Active, Checked  bool
	Expandable       bool
	Children         []treeRow
	ChildrenURL      string
}

// handleTree responds with the rendered rows of the folder at fsPath:
//
//	?tree                   sidebar rows (folders only, links)
//	&files=1                include files
//	&pick=folder|file|any   picker rows selecting that kind
//	&expandTo=/a/b          pre-expand the chain down to /a/b
//	&select=/a/b            check that row
//	&root=1                 lead with a row for "/" itself (picker)
func (h *handler) handleTree(w http.ResponseWriter, r *http.Request, urlPath, fsPath string) {
	info, err := os.Stat(fsPath)
	if err != nil {
		if os.IsNotExist(err) {
			http.NotFound(w, r)
			return
		}
		http.Error(w, "stat failed", http.StatusInternalServerError)
		return
	}
	if !info.IsDir() {
		http.Error(w, "not a folder", http.StatusBadRequest)
		return
	}

	q := r.URL.Query()
	o := treeOpts{Files: q.Has("files"), Select: q.Get("select")}
	switch p := q.Get("pick"); p {
	case "", "folder", "file", "any":
		o.Pick = p
	default:
		http.Error(w, "bad pick mode", http.StatusBadRequest)
		return
	}

	dir := normalizeMovePath(urlPath)
	var expand []string
	if segs, base := treePathSegments(q.Get("expandTo")), treePathSegments(dir); len(segs) >= len(base) &&
		strings.Join(segs[:len(base)], "/") == strings.Join(base, "/") {
		expand = segs[len(base):]
	}
	rows, err := buildTreeRows(fsPath, dir, expand, o)
	if err != nil {
		http.Error(w, "read failed", http.StatusInternalServerError)
		return
	}
	if dir == "/" && q.Has("root") && o.Pick != "" {
		root := newTreeRow(treeEntry{Name: "/", Kind: "folder"}, "/", o)
		rows = append([]treeRow{root}, rows...)
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := treeTmpl.ExecuteTemplate(w, "rows", rows); err != nil {
		log.Printf("tree template error: %v", err)
	}
}

// sidebarTree renders the navigation tree for the page at urlPath: the root
// listing with the chain down to the page expanded and the page highlighted.
// The tree is part of the page itself, so the rail never paints empty.
func sidebarTree(root, urlPath string) template.HTML {
	page := normalizeMovePath(urlPath)
	rows, err := buildTreeRows(root, "/", treePathSegments(page), treeOpts{Active: page})
	if err != nil {
		return ""
	}
	var buf bytes.Buffer
	if err := treeTmpl.ExecuteTemplate(&buf, "rows", rows); err != nil {
		log.Printf("tree template error: %v", err)
		return ""
	}
	return template.HTML(buf.String())
}

// buildTreeRows lists the folder fsPath (wiki path dir) and expands the
// folder named by expand[0], recursing down the chain. The walk stops at the
// deepest segment that still exists. Segments only ever match real directory
// names from listTreeEntries, so this cannot traverse outside the tree.
func buildTreeRows(fsPath, dir string, expand []string, o treeOpts) ([]treeRow, error) {
	entries, err := listTreeEntries(fsPath, !o.Files)
	if err != nil {
		return nil, err
	}
	rows := make([]treeRow, len(entries))
	for i, e := range entries {
		p := path.Join(dir, e.Name)
		rows[i] = newTreeRow(e, p, o)
		if len(expand) > 0 && e.Kind == "folder" && e.Name == expand[0] && e.HasChildren {
			kids, err := buildTreeRows(filepath.Join(fsPath, e.Name), p, expand[1:], o)
			if err == nil {
				rows[i].Children = kids
			}
		}
	}
	return rows, nil
}

func newTreeRow(e treeEntry, p string, o treeOpts) treeRow {
	row := treeRow{
		Name:       e.Name,
		Path:       p,
		Kind:       e.Kind,
		URL:        pageURL(p),
		Link:       o.Pick == "",
		Active:     o.Pick == "" && p == o.Active,
		Expandable: e.HasChildren,
	}
	if e.Kind == "file" {
		row.URL = fileURL(strings.TrimPrefix(p, "/"))
	}
	if o.Pick != "" {
		row.Selectable = o.Pick == "any" || o.Pick == e.Kind
		row.Checked = row.Selectable && p == o.Select
	}
	if row.Expandable {
		row.ChildrenURL = row.URL + o.query()
	}
	return row
}

// listTreeEntries returns the immediate children of fsPath, filtering hidden
// entries and index.md. Folders are listed before files; both groups are
// sorted alphabetically. foldersOnly will not list any individual files at all.
func listTreeEntries(fsPath string, foldersOnly bool) ([]treeEntry, error) {
	raw, err := os.ReadDir(fsPath)
	if err != nil {
		return nil, err
	}
	var folders, files []treeEntry
	for _, e := range raw {
		name := e.Name()
		if strings.HasPrefix(name, ".") {
			continue
		}
		if e.IsDir() {
			folders = append(folders, treeEntry{
				Name:        name,
				Kind:        "folder",
				HasChildren: folderHasChildren(filepath.Join(fsPath, name), foldersOnly),
			})
		} else {
			if foldersOnly || name == "index.md" {
				continue
			}
			files = append(files, treeEntry{Name: name, Kind: "file"})
		}
	}
	sort.Slice(folders, func(i, j int) bool { return folders[i].Name < folders[j].Name })
	sort.Slice(files, func(i, j int) bool { return files[i].Name < files[j].Name })
	return append(folders, files...), nil
}

// folderHasChildren reports whether fsPath contains at least one entry that
// listTreeEntries would list. It reads the directory in small batches and
// stops at the first match, so large folders stay cheap. Unreadable folders
// report false.
func folderHasChildren(fsPath string, foldersOnly bool) bool {
	f, err := os.Open(fsPath)
	if err != nil {
		return false
	}
	defer f.Close()
	for {
		batch, err := f.ReadDir(32)
		for _, e := range batch {
			name := e.Name()
			if strings.HasPrefix(name, ".") {
				continue
			}
			if e.IsDir() || (!foldersOnly && name != "index.md") {
				return true
			}
		}
		if err != nil {
			return false
		}
	}
}

// treePathSegments splits a wiki path into its non-empty segments.
func treePathSegments(p string) []string {
	var segs []string
	for _, s := range strings.Split(p, "/") {
		if s != "" {
			segs = append(segs, s)
		}
	}
	return segs
}