package main

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io"
	"log"
	"math"
	"net/http"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync"
)

// Canvases are JSON Canvas 1.0 files (https://jsoncanvas.org) stored as
// <name>.canvas inside a page's folder, so a page can hold any number of them.
//
//	GET  /Page/Board.canvas          the canvas view (canvas/main.html)
//	GET  /Page/Board.canvas?raw      the file itself
//	POST /Page/Board.canvas?save     the whole document (autosave, canvas.js)
//	POST /Page/Board.canvas?render   one node → its rendered element
//	POST /Page/?canvas               create a canvas (dialog "canvas")
//
// The canvas URL sits next to the page, so relative links and embeds in text
// nodes resolve against the page folder exactly like they do in index.md.
//
// The server only reads the fields it renders. Saves write the client's JSON
// back as sent (reindented), so fields this code does not know survive.

const canvasExt = ".canvas"

var canvasTmpl = template.Must(template.New("canvas").Funcs(tmplFuncs).ParseFS(assets,
	"assets/layout.html", "assets/editor/toolbar.html", "assets/canvas/main.html", "assets/canvas/node.html"))

func isCanvasFile(name string) bool {
	return strings.EqualFold(path.Ext(name), canvasExt)
}

type canvasNode struct {
	ID              string  `json:"id"`
	Type            string  `json:"type"`
	X               float64 `json:"x"`
	Y               float64 `json:"y"`
	Width           float64 `json:"width"`
	Height          float64 `json:"height"`
	Color           string  `json:"color,omitempty"`
	Text            string  `json:"text,omitempty"`
	File            string  `json:"file,omitempty"`
	Subpath         string  `json:"subpath,omitempty"`
	URL             string  `json:"url,omitempty"`
	Label           string  `json:"label,omitempty"`
	Background      string  `json:"background,omitempty"`
	BackgroundStyle string  `json:"backgroundStyle,omitempty"`
}

type canvasEdge struct {
	ID       string `json:"id"`
	FromNode string `json:"fromNode"`
	FromSide string `json:"fromSide,omitempty"`
	FromEnd  string `json:"fromEnd,omitempty"`
	ToNode   string `json:"toNode"`
	ToSide   string `json:"toSide,omitempty"`
	ToEnd    string `json:"toEnd,omitempty"`
	Color    string `json:"color,omitempty"`
	Label    string `json:"label,omitempty"`
}

type canvasDoc struct {
	Nodes []canvasNode `json:"nodes"`
	Edges []canvasEdge `json:"edges"`
}

// emptyCanvas is what a new canvas file holds, and what an empty file reads as.
var emptyCanvas = []byte("{\n\t\"nodes\": [],\n\t\"edges\": []\n}\n")

// parseCanvas decodes and validates a canvas document. An empty file is an
// empty canvas.
func parseCanvas(raw []byte) (canvasDoc, error) {
	var doc canvasDoc
	if len(bytes.TrimSpace(raw)) == 0 {
		return doc, nil
	}
	// The top level must be an object; Unmarshal into a struct would accept
	// `null` silently.
	var top map[string]json.RawMessage
	if err := json.Unmarshal(raw, &top); err != nil {
		return doc, fmt.Errorf("not a JSON Canvas object: %v", err)
	}
	if err := json.Unmarshal(raw, &doc); err != nil {
		return doc, fmt.Errorf("invalid canvas: %v", err)
	}
	return doc, validateCanvas(doc)
}

var canvasHexColorRe = regexp.MustCompile(`^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$`)

// canvasColor splits a canvas color into a preset ("1"–"6") or a hex value.
// Anything else is no color.
func canvasColor(c string) (preset string, hex template.CSS) {
	if len(c) == 1 && c[0] >= '1' && c[0] <= '6' {
		return c, ""
	}
	if canvasHexColorRe.MatchString(c) {
		return "", template.CSS(c)
	}
	return "", ""
}

func validCanvasColor(c string) bool {
	p, h := canvasColor(c)
	return c == "" || p != "" || h != ""
}

func validCanvasSide(s string) bool {
	switch s {
	case "", "top", "right", "bottom", "left":
		return true
	}
	return false
}

func validCanvasEnd(s string) bool {
	return s == "" || s == "none" || s == "arrow"
}

// validateCanvas checks what the renderer and editor rely on: unique ids,
// known node types with their required field, finite geometry, and edges
// between existing nodes.
func validateCanvas(doc canvasDoc) error {
	ids := map[string]bool{}
	for i, n := range doc.Nodes {
		if n.ID == "" {
			return fmt.Errorf("node %d has no id", i)
		}
		if ids[n.ID] {
			return fmt.Errorf("duplicate id %q", n.ID)
		}
		ids[n.ID] = true
		for _, v := range []float64{n.X, n.Y, n.Width, n.Height} {
			if math.IsNaN(v) || math.IsInf(v, 0) {
				return fmt.Errorf("node %q has invalid geometry", n.ID)
			}
		}
		switch n.Type {
		case "text", "group":
		case "file":
			if n.File == "" {
				return fmt.Errorf("file node %q has no file", n.ID)
			}
		case "link":
			if n.URL == "" {
				return fmt.Errorf("link node %q has no url", n.ID)
			}
		default:
			return fmt.Errorf("node %q has unknown type %q", n.ID, n.Type)
		}
		if !validCanvasColor(n.Color) {
			return fmt.Errorf("node %q has invalid color %q", n.ID, n.Color)
		}
	}
	edgeIDs := map[string]bool{}
	for i, e := range doc.Edges {
		if e.ID == "" {
			return fmt.Errorf("edge %d has no id", i)
		}
		if edgeIDs[e.ID] {
			return fmt.Errorf("duplicate edge id %q", e.ID)
		}
		edgeIDs[e.ID] = true
		if !ids[e.FromNode] || !ids[e.ToNode] {
			return fmt.Errorf("edge %q connects a missing node", e.ID)
		}
		if !validCanvasSide(e.FromSide) || !validCanvasSide(e.ToSide) {
			return fmt.Errorf("edge %q has an invalid side", e.ID)
		}
		if !validCanvasEnd(e.FromEnd) || !validCanvasEnd(e.ToEnd) {
			return fmt.Errorf("edge %q has an invalid end", e.ID)
		}
		if !validCanvasColor(e.Color) {
			return fmt.Errorf("edge %q has invalid color %q", e.ID, e.Color)
		}
	}
	return nil
}

// canvasVersion identifies one exact file content. Saves carry the version
// they were based on; a mismatch means someone else changed the file.
func canvasVersion(raw []byte) string {
	sum := sha256.Sum256(raw)
	return hex.EncodeToString(sum[:8])
}

// canvasMu serializes the version check and write of canvas saves.
var canvasMu sync.Mutex

// === Rendering ===

// canvasNodeView is one node element (canvas/node.html). Geometry is in
// canvas units; the client positions the world, not the nodes.
type canvasNodeView struct {
	ID, Type   string
	X, Y, W, H int
	Preset     string
	Hex        template.CSS
	Label      string
	LabelURL   string
	Markdown   bool // body is rendered markdown (.content styling)
	Body       template.HTML
}

// canvasBody* feed the node body templates in canvas/node.html.
type canvasMediaBody struct {
	URL, Thumb, Kind string
}

type canvasCardBody struct {
	Icon      template.HTML
	Name, URL string
	Host      string
	Label     string // a link's display text, shown instead of its URL
}

type canvasGroupBody struct {
	URL   string
	Style string
}

func (h *handler) renderCanvasNode(n canvasNode) canvasNodeView {
	v := canvasNodeView{
		ID:   n.ID,
		Type: n.Type,
		X:    int(math.Round(n.X)),
		Y:    int(math.Round(n.Y)),
		W:    int(math.Round(n.Width)),
		H:    int(math.Round(n.Height)),
	}
	v.Preset, v.Hex = canvasColor(n.Color)
	switch n.Type {
	case "text":
		v.Markdown = true
		v.Body = template.HTML(canvasTaskCheckboxes(convertMarkdown([]byte(n.Text), "")))
	case "file":
		h.renderCanvasFile(&v, n)
	case "link":
		host := n.URL
		if u, err := url.Parse(n.URL); err == nil && u.Host != "" {
			host = u.Host
		}
		v.Body = execNodeTemplate("canvas-link", canvasCardBody{Name: n.URL, URL: n.URL, Host: host, Label: strings.TrimSpace(n.Label)})
	case "group":
		v.Label = n.Label
		if n.Background != "" {
			if rel, _, ok := h.canvasFilePath(n.Background); ok {
				style := n.BackgroundStyle
				if style != "ratio" && style != "repeat" {
					style = "cover"
				}
				v.Body = execNodeTemplate("canvas-group-bg", canvasGroupBody{URL: fileURL(rel), Style: style})
			}
		}
	}
	return v
}

// canvasFilePath resolves a file node's path. Paths are relative to the wiki
// root (the spec's "vault"); a leading slash is accepted. Dot segments are
// refused like everywhere else.
func (h *handler) canvasFilePath(p string) (rel, fsPath string, ok bool) {
	rel = strings.Trim(path.Clean("/"+strings.ReplaceAll(p, "\\", "/")), "/")
	if hasDotSegment(rel) {
		return "", "", false
	}
	return rel, filepath.Join(h.root, filepath.FromSlash(rel)), true
}

func (h *handler) renderCanvasFile(v *canvasNodeView, n canvasNode) {
	rel, fsPath, ok := h.canvasFilePath(n.File)
	v.Label = path.Base("/" + rel)
	info, err := os.Stat(fsPath)
	if !ok || err != nil {
		v.Body = execNodeTemplate("canvas-missing", n.File)
		return
	}
	if info.IsDir() {
		// A folder is a page: show its index.md.
		v.LabelURL = pageURL(rel)
		raw, _ := os.ReadFile(filepath.Join(fsPath, "index.md"))
		if heading := extractFirstHeading(raw); heading != "" {
			v.Label = heading
		}
		v.Markdown = true
		v.Body = template.HTML(convertMarkdown(canvasSubpath(raw, n.Subpath), dirBase(rel)))
		return
	}
	u := fileURL(rel)
	v.LabelURL = u
	name := info.Name()
	ext := strings.ToLower(path.Ext(name))
	switch {
	case ext == ".md":
		raw, _ := os.ReadFile(fsPath)
		v.Markdown = true
		v.Body = template.HTML(convertMarkdown(canvasSubpath(raw, n.Subpath), dirBase(path.Dir("/"+rel))))
	case isImageFile(name) || ext == ".svg" || ext == ".webp":
		thumb := u
		if hasThumbnail(name) {
			thumb = u + "?w=800"
		}
		v.Body = execNodeTemplate("canvas-media", canvasMediaBody{URL: u, Thumb: thumb, Kind: "image"})
	case isVideoFile(name):
		v.Body = execNodeTemplate("canvas-media", canvasMediaBody{URL: u, Kind: "video"})
	case ext == ".mp3" || ext == ".flac" || ext == ".ogg" || ext == ".wav":
		v.Body = execNodeTemplate("canvas-media", canvasMediaBody{URL: u, Kind: "audio"})
	default:
		v.Body = execNodeTemplate("canvas-file", canvasCardBody{Icon: fileIcon(name), Name: name, URL: u})
	}
}

// dirBase is the base URL path for markdown that lives in the folder rel
// (wiki-relative, "" or "/" for the root).
func dirBase(rel string) string {
	rel = strings.Trim(rel, "/")
	if rel == "" {
		return "/"
	}
	return "/" + rel + "/"
}

// canvasSubpath narrows markdown to a file node's "#Heading" subpath: that
// heading's section including its subsections. Unknown subpaths (or block
// references, "#^id") show the whole file.
func canvasSubpath(raw []byte, subpath string) []byte {
	want := strings.TrimSpace(strings.TrimPrefix(subpath, "#"))
	if want == "" || strings.HasPrefix(want, "^") {
		return raw
	}
	sections := splitSections(raw)
	for i, s := range sections {
		if _, text := sectionHeading(s); i > 0 && strings.EqualFold(text, want) {
			return joinSections(sections[i:secionSpanEnd(sections, i)])
		}
	}
	return raw
}

// canvasTaskCheckboxes makes a text node's task checkboxes clickable. The
// canvas editor (canvas.js) flips the Nth task line of the node's text and
// saves the whole canvas, so they carry only their index.
func canvasTaskCheckboxes(in []byte) []byte {
	idx := 0
	return taskCheckboxRe.ReplaceAllFunc(in, func(match []byte) []byte {
		out := `<input type="checkbox" class="task-checkbox" data-task="` + strconv.Itoa(idx) + `"`
		if bytes.Contains(match, []byte("checked")) {
			out += ` checked=""`
		}
		idx++
		return []byte(out + ">")
	})
}

func execNodeTemplate(name string, data any) template.HTML {
	var buf bytes.Buffer
	if err := canvasTmpl.ExecuteTemplate(&buf, name, data); err != nil {
		log.Printf("canvas template %s: %v", name, err)
	}
	return template.HTML(buf.String())
}

// === Handlers ===

type canvasPageData struct {
	Title    string
	EditMode bool
	CanEdit  bool
	IsRoot   bool
	PageURL  string // the page the canvas belongs to
	RawURL   string
	Name     string
	Nodes    []canvasNodeView
	Doc      json.RawMessage
	Version  string
	Error    string
	renderTimer
}

// serveCanvas handles every request to an existing .canvas file.
func (h *handler) serveCanvas(w http.ResponseWriter, r *http.Request, urlPath, fsPath string) {
	q := r.URL.Query()
	switch {
	case r.Method == http.MethodGet && q.Has("raw"):
		w.Header().Set("Content-Type", "application/json; charset=utf-8")
		http.ServeFile(w, r, fsPath)
	case r.Method == http.MethodGet:
		h.serveCanvasPage(w, r, urlPath, fsPath)
	case r.Method == http.MethodPost && q.Has("save"):
		h.handleCanvasSave(w, r, fsPath)
	case r.Method == http.MethodPost && q.Has("render"):
		h.handleCanvasRender(w, r)
	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

func (h *handler) serveCanvasPage(w http.ResponseWriter, r *http.Request, urlPath, fsPath string) {
	raw, err := os.ReadFile(fsPath)
	if err != nil {
		http.Error(w, "read failed: "+err.Error(), http.StatusInternalServerError)
		return
	}
	name := path.Base(urlPath)
	data := canvasPageData{
		Title:   strings.TrimSuffix(name, path.Ext(name)),
		CanEdit: true,
		PageURL: pageURL(path.Dir(urlPath)),
		RawURL:  fileURL(strings.TrimPrefix(urlPath, "/")) + "?raw",
		Name:    name,
		Version: canvasVersion(raw),
		Doc:     json.RawMessage(emptyCanvas),
	}
	doc, err := parseCanvas(raw)
	if err != nil {
		data.Error = err.Error()
	} else {
		if len(bytes.TrimSpace(raw)) > 0 {
			data.Doc = json.RawMessage(raw)
		}
		for _, n := range doc.Nodes {
			data.Nodes = append(data.Nodes, h.renderCanvasNode(n))
		}
	}
	data.renderTimer = renderTimer{requestStart(r)}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := canvasTmpl.ExecuteTemplate(w, "layout", data); err != nil {
		log.Printf("canvas template error: %v", err)
	}
}

// maxCanvasBytes caps a saved canvas; text nodes hold markdown, not files.
const maxCanvasBytes = 10 << 20

// handleCanvasSave replaces the canvas with the posted document. The client
// sends the version it last loaded or saved (X-Canvas-Version); when the file
// has changed since, the save is refused with 409 so nothing is overwritten.
func (h *handler) handleCanvasSave(w http.ResponseWriter, r *http.Request, fsPath string) {
	body, err := io.ReadAll(http.MaxBytesReader(w, r.Body, maxCanvasBytes))
	if err != nil {
		http.Error(w, "canvas too large", http.StatusRequestEntityTooLarge)
		return
	}
	if len(bytes.TrimSpace(body)) == 0 {
		http.Error(w, "refusing to save an empty canvas body", http.StatusBadRequest)
		return
	}
	if _, err := parseCanvas(body); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	var out bytes.Buffer
	if err := json.Indent(&out, body, "", "\t"); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	out.WriteByte('\n')

	canvasMu.Lock()
	defer canvasMu.Unlock()
	current, err := os.ReadFile(fsPath)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			http.Error(w, "this canvas no longer exists", http.StatusNotFound)
			return
		}
		http.Error(w, "read failed: "+err.Error(), http.StatusInternalServerError)
		return
	}
	if r.Header.Get("X-Canvas-Version") != canvasVersion(current) {
		http.Error(w, "the canvas changed since it was opened — reload to see the current version", http.StatusConflict)
		return
	}
	if err := writeFileAtomic(fsPath, out.Bytes(), 0644); err != nil {
		http.Error(w, "write failed: "+err.Error(), http.StatusInternalServerError)
		return
	}
	w.Header().Set("X-Canvas-Version", canvasVersion(out.Bytes()))
	w.WriteHeader(http.StatusNoContent)
}

// handleCanvasRender renders one posted node as its element, so the editor
// shows nodes exactly as the server renders them on load.
func (h *handler) handleCanvasRender(w http.ResponseWriter, r *http.Request) {
	var n canvasNode
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, maxCanvasBytes)).Decode(&n); err != nil {
		http.Error(w, "bad node: "+err.Error(), http.StatusBadRequest)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if err := canvasTmpl.ExecuteTemplate(w, "canvas-node", h.renderCanvasNode(n)); err != nil {
		log.Printf("canvas template error: %v", err)
	}
}

// canvasFileName validates a new canvas's name from the create dialog and
// returns the file name, with the extension added when missing.
func canvasFileName(raw string) (string, error) {
	name := strings.TrimSpace(raw)
	if isCanvasFile(name) {
		name = strings.TrimSpace(name[:len(name)-len(canvasExt)])
	}
	if name == "" {
		return "", fmt.Errorf("name is empty")
	}
	if strings.HasPrefix(name, ".") || strings.ContainsAny(name, "/\\\x00") {
		return "", fmt.Errorf("name must not start with a dot or contain slashes")
	}
	return name + canvasExt, nil
}

// handleCanvasCreate creates an empty canvas in the page's folder (creating
// the folder for a page that does not exist yet) and opens it.
func (h *handler) handleCanvasCreate(w http.ResponseWriter, r *http.Request, urlPath, fsPath string) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "bad request", http.StatusBadRequest)
		return
	}
	name, err := canvasFileName(r.FormValue("name"))
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	_, statErr := os.Stat(fsPath)
	newlyCreated := os.IsNotExist(statErr)
	if err := os.MkdirAll(fsPath, 0755); err != nil {
		http.Error(w, "mkdir failed: "+err.Error(), http.StatusInternalServerError)
		return
	}
	f, err := os.OpenFile(filepath.Join(fsPath, name), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0644)
	if err != nil {
		if errors.Is(err, os.ErrExist) {
			http.Error(w, name+" already exists", http.StatusConflict)
			return
		}
		http.Error(w, "create failed: "+err.Error(), http.StatusInternalServerError)
		return
	}
	_, werr := f.Write(emptyCanvas)
	if cerr := f.Close(); werr == nil {
		werr = cerr
	}
	if werr != nil {
		http.Error(w, "write failed: "+werr.Error(), http.StatusInternalServerError)
		return
	}
	if newlyCreated {
		if rel, err := filepath.Rel(h.root, fsPath); err == nil {
			folderIndexAdd(filepath.ToSlash(rel))
		}
	}
	rel := strings.Trim(urlPath, "/")
	if rel != "" {
		rel += "/"
	}
	redirectAfter(w, r, fileURL(rel+name))
}