// Package notes implements a data structure for reasoning about and rendering
// markdown notes
package notes

import (
	"bufio"
	"bytes"
	"crypto/rand"
	"errors"
	"fmt"
	"html/template"
	"log"
	"os"
	"path/filepath"
	"strings"
	"time"

	"forgejo.gwairfelin.com/max/gonotes/internal/conf"
	markdown "github.com/teekennedy/goldmark-markdown"
	"github.com/yuin/goldmark"
	meta "github.com/yuin/goldmark-meta"
	"github.com/yuin/goldmark/ast"
	"github.com/yuin/goldmark/extension"
	astext "github.com/yuin/goldmark/extension/ast"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/text"
	"github.com/yuin/goldmark/util"
	"gopkg.in/yaml.v2"
)

// Note is the central data structure.  It can be Saved, Rendered and Loaded
// using the Save, Render and LoadNote functions.
type Note struct {
	Title        string
	BodyRendered template.HTML
	Body         []byte
	Owner        string
	Viewers      map[string]struct{}
	Uid          string
	LastModified time.Time
	Tags         []string
}

type noteSet map[*Note]bool

type NoteStore struct {
	notes map[string]noteSet
}

var (
	Notes NoteStore
	md    goldmark.Markdown
)

func Init() error {
	Notes = NoteStore{
		notes: make(map[string]noteSet),
	}

	md = goldmark.New(
		goldmark.WithExtensions(
			extension.TaskList, meta.Meta,
		),
	)

	notesDir := conf.Conf.NotesDir

	files, err := os.ReadDir(notesDir)
	if err != nil {
		if os.IsNotExist(err) {
			os.MkdirAll(notesDir, os.FileMode(0o750))
		} else {
			log.Print(err.Error())
			return err
		}
	}
	log.Printf("Looking in %s", notesDir)
	for _, f := range files {
		if !f.IsDir() {
			uid := strings.TrimSuffix(f.Name(), filepath.Ext(f.Name()))
			note, err := loadNote(uid)
			if err != nil {
				return err
			}

			title := note.Title

			log.Printf("Found note %s (title '%s', owner %s)", uid, title, note.Owner)

			Notes.Add(note, note.Owner)

			for viewer := range note.Viewers {
				Notes.Add(note, viewer)
			}
		}
	}

	return nil
}

func (ns *NoteStore) Get(owner string) noteSet {
	return ns.notes[owner]
}

func (ns *NoteStore) GetOne(owner string, uid string) (*Note, bool) {
	notes := ns.Get(owner)

	for note, _ := range notes {
		if note.Uid == uid {
			log.Printf("Found single note during GetOne %s", note.Title)
			return note, true
		}
	}
	return nil, false
}

func (ns *NoteStore) Add(note *Note, user string) {
	if ns.notes[user] == nil {
		ns.notes[user] = make(noteSet)
	}
	ns.notes[user][note] = true
}

func (ns *NoteStore) Del(note *Note, user string) {
	delete(ns.notes[user], note)
}

func (ns *NoteStore) UserTags(user string) []string {
	tagSet := make(map[string]bool)

	notes, ok := ns.notes[user]

	if !ok {
		return make([]string, 0)
	}

	log.Printf("Got notes for user %v", notes)

	for note := range notes {
		log.Printf("considering note %s (%s)", note.Title, note.Tags)
		for _, tag := range note.Tags {
			tagSet[tag] = true
		}
	}

	log.Printf("Tagset is %v", tagSet)

	tags := make([]string, len(tagSet))
	i := 0
	for tag := range tagSet {
		tags[i] = tag
		i++
	}
	return tags
}

func fmtPath(path string) string {
	return fmt.Sprintf("%s.%s", path, conf.Conf.Extension)
}

func (n *Note) marshalFrontmatter() ([]byte, error) {
	viewers := make([]string, 0, len(n.Viewers))

	for viewer := range n.Viewers {
		viewers = append(viewers, viewer)
	}
	frontmatter := make(map[string]any)
	frontmatter["owner"] = n.Owner
	frontmatter["viewers"] = viewers
	frontmatter["title"] = n.Title
	frontmatter["tags"] = n.Tags

	marshaled, err := yaml.Marshal(&frontmatter)
	return marshaled, err
}

func (n *Note) ViewersAsList() []string {
	keys := make([]string, 0, len(n.Viewers))
	for key := range n.Viewers {
		keys = append(keys, key)
	}
	return keys
}

func NewNoteNoSave(title string, owner string) *Note {
	note := &Note{Title: title, Owner: owner}
	note.Viewers = make(map[string]struct{})
	note.Tags = make([]string, 0, 5)
	return note
}

func NewNote(title string, owner string) *Note {
	note := NewNoteNoSave(title, owner)
	note.Uid = rand.Text()
	note.Save()
	Notes.Add(note, note.Owner)
	return note
}

// Save a note to a path derived from the title
func (n *Note) Save() error {
	frontmatter, err := n.marshalFrontmatter()
	if err != nil {
		return err
	}

	filename := filepath.Join(conf.Conf.NotesDir, fmtPath(n.Uid))
	return os.WriteFile(
		filename,
		[]byte(fmt.Sprintf("---\n%s---\n%s", frontmatter, n.Body)),
		0o600,
	)
}

// Render the markdown content of the note to HTML
func (n *Note) Render() {
	var buf bytes.Buffer

	err := md.Convert(n.Body, &buf)
	if err != nil {
		log.Fatal(err)
	}

	n.BodyRendered = template.HTML(buf.String())
}

// loadNote from the disk. The path is derived from the uid
func loadNote(uid string) (*Note, error) {
	filename := filepath.Join(conf.Conf.NotesDir, fmtPath(uid))
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	stat, err := os.Stat(filename)
	if err != nil {
		return nil, err
	}

	bodyScanner := bufio.NewScanner(f)
	body := make([]byte, 0, 10)
	fullBody := make([]byte, 0, 10)

	inFrontmatter := false
	for bodyScanner.Scan() {
		fullBody = append(fullBody, bodyScanner.Bytes()...)
		fullBody = append(fullBody, '\n')

		text := bodyScanner.Text()
		if text == "---" {
			if !inFrontmatter {
				inFrontmatter = true
			} else {
				inFrontmatter = false
				break
			}
		}
	}

	for bodyScanner.Scan() {
		body = append(body, bodyScanner.Bytes()...)
		body = append(body, '\n')
	}

	var buf bytes.Buffer
	context := parser.NewContext()
	if err := md.Convert([]byte(fullBody), &buf, parser.WithContext(context)); err != nil {
		return nil, err
	}
	metaData := meta.Get(context)

	log.Printf("note has frontmatter %+v", metaData)
	owner, ok := metaData["owner"].(string)
	if !ok {
		return nil, errors.New("invalid note, missing 'owner' in frontmatter")
	}

	title, ok := metaData["title"].(string)
	if !ok {
		return nil, errors.New("invalid note, missing 'title' in frontmatter")
	}

	note := NewNoteNoSave(title, owner)
	note.Uid = uid
	note.Body = body
	note.LastModified = stat.ModTime()

	viewers := metaData["viewers"].([]any)

	for _, viewer := range viewers {
		v, ok := viewer.(string)
		if !ok {
			return nil, errors.New("invalid note, non string type in 'viewers' in frontmatter")
		}

		if v == "" {
			continue
		}

		note.AddViewer(v)
	}
	log.Printf("Note %s shared with %v", note.Title, note.Viewers)

	tags, ok := metaData["tags"]

	if ok {
		tags := tags.([]any)

		for _, tag := range tags {
			t, ok := tag.(string)
			if !ok {
				return nil, errors.New("invalid note, non string type in 'tags' in frontmatter")
			}

			if t == "" {
				continue
			}
			note.Tags = append(note.Tags, t)
		}
	}

	return note, nil
}

func (n *Note) AddViewer(viewer string) {
	n.Viewers[viewer] = struct{}{}
}

func (n *Note) DelViewer(viewer string) {
	delete(n.Viewers, viewer)
}

func DeleteNote(uid string) error {
	filename := filepath.Join(conf.Conf.NotesDir, fmtPath(uid))
	return os.Remove(filename)
}

type toggleCheckboxTransformer struct{ nthBox int }

func (t *toggleCheckboxTransformer) Transform(node *ast.Document, reader text.Reader, pc parser.Context) {
	boxesFound := 0

	// Walk to find checkbox, toggle checked status
	ast.Walk(node, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
		if !entering {
			return ast.WalkContinue, nil
		}

		box, ok := n.(*astext.TaskCheckBox)
		if !ok {
			return ast.WalkContinue, nil
		}

		if boxesFound < t.nthBox {
			boxesFound += 1
			return ast.WalkContinue, nil
		}

		box.IsChecked = !box.IsChecked
		return ast.WalkStop, nil
	})
}

func renderTaskCheckBox(writer util.BufWriter, source []byte, node ast.Node, entering bool) (ast.WalkStatus, error) {
	var err error
	var _ int
	n, ok := node.(*astext.TaskCheckBox)
	if !ok {
		return ast.WalkContinue, errors.New("not a TaskCheckBox")
	}
	if entering {
		// Render a box if necessary
		if n.IsChecked {
			_, err = writer.Write([]byte("[x] "))
		} else {
			_, err = writer.Write([]byte("[ ] "))
		}
	}
	return ast.WalkContinue, err
}

func (n *Note) ToggleBox(nthBox int) {
	checkboxTransformer := toggleCheckboxTransformer{nthBox: nthBox}
	transformer := util.Prioritized(&checkboxTransformer, 0)

	renderer := markdown.NewRenderer()
	renderer.Register(astext.KindTaskCheckBox, renderTaskCheckBox)

	var buf bytes.Buffer
	md := goldmark.New(goldmark.WithRenderer(renderer))

	md.Parser().AddOptions(parser.WithInlineParsers(
		util.Prioritized(extension.NewTaskCheckBoxParser(), 0),
	), parser.WithASTTransformers(transformer))

	md.Convert(n.Body, &buf)
	n.Body = buf.Bytes()
	n.Save()
}

func (n *Note) HasTag(tag string) bool {
	for _, tag_ := range n.Tags {
		if tag_ == tag {
			return true
		}
	}
	return false
}