// Package store keeps notes as plain markdown files, one per note, so they stay readable and
// portable with or without Basking. An in-memory index makes listing and searching quick.
package store

import (
	"archive/zip"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"sync"
	"time"
)

// MaxBody is the longest note, in bytes.
const MaxBody = 256 << 10

var (
	ErrNotFound = errors.New("note not found")
	ErrBadID    = errors.New("bad note id")
	ErrEmpty    = errors.New("a note needs some text")
	ErrTooLong  = errors.New("that note is too long")
	ErrConflict = errors.New("this note changed somewhere else")
	ErrBadDate  = errors.New("the date must look like 2026-10-31")
	ErrNotTrash = errors.New("only a note in the trash can be deleted for good")
)

type Note struct {
	ID      string    `json:"id"`
	Created time.Time `json:"created"`
	Updated time.Time `json:"updated"`
	Pinned  bool      `json:"pinned"`
	Daily   string    `json:"daily,omitempty"` // the date, for a daily note
	Trashed bool      `json:"trashed,omitempty"`
	Body    string    `json:"body"`
	Tags    []string  `json:"tags"`

	lower string // lower-cased body, for searching
}

type Store struct {
	dir string
	mu  sync.RWMutex
	by  map[string]*Note
}

var idRe = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{0,63}$`)

// ValidID says whether s can be used as a note id (and so as a file name).
func ValidID(s string) bool { return idRe.MatchString(s) }

// Open reads every note under dir, creating the folders if needed.
func Open(dir string) (*Store, error) {
	s := &Store{dir: dir, by: map[string]*Note{}}
	for _, sub := range []string{"notes", "trash"} {
		if err := os.MkdirAll(filepath.Join(dir, sub), 0o755); err != nil {
			return nil, err
		}
		entries, err := os.ReadDir(filepath.Join(dir, sub))
		if err != nil {
			return nil, err
		}
		for _, e := range entries {
			id := strings.TrimSuffix(e.Name(), ".md")
			if e.IsDir() || id == e.Name() || !ValidID(id) {
				continue
			}
			path := filepath.Join(dir, sub, e.Name())
			b, err := os.ReadFile(path)
			if err != nil {
				return nil, err
			}
			info, err := e.Info()
			if err != nil {
				return nil, err
			}
			n := parse(id, string(b), info.ModTime())
			n.Trashed = sub == "trash"
			s.by[id] = n
		}
	}
	return s, nil
}

func (s *Store) path(n *Note) string {
	sub := "notes"
	if n.Trashed {
		sub = "trash"
	}
	return filepath.Join(s.dir, sub, n.ID+".md")
}

// ---- file format ----
//
//	---
//	created: 2026-10-31T14:32:05.123Z
//	updated: 2026-10-31T14:35:00.456Z
//	pinned: true
//	daily: 2026-10-31
//	---
//
//	the note, in markdown

func format(n *Note) []byte {
	var b strings.Builder
	b.WriteString("---\n")
	fmt.Fprintf(&b, "created: %s\n", n.Created.UTC().Format(time.RFC3339Nano))
	fmt.Fprintf(&b, "updated: %s\n", n.Updated.UTC().Format(time.RFC3339Nano))
	if n.Pinned {
		b.WriteString("pinned: true\n")
	}
	if n.Daily != "" {
		fmt.Fprintf(&b, "daily: %s\n", n.Daily)
	}
	b.WriteString("---\n\n")
	b.WriteString(n.Body)
	b.WriteString("\n")
	return []byte(b.String())
}

// parse reads a note file. A file with no header is still a note: it takes its time from the file.
func parse(id, text string, mod time.Time) *Note {
	text = strings.ReplaceAll(text, "\r\n", "\n")
	n := &Note{ID: id, Created: mod.UTC(), Updated: mod.UTC()}
	if rest, ok := strings.CutPrefix(text, "---\n"); ok {
		if head, body, ok := strings.Cut(rest, "\n---\n"); ok || strings.HasSuffix(rest, "\n---") {
			if !ok {
				head, body = strings.TrimSuffix(rest, "\n---"), ""
			}
			for _, line := range strings.Split(head, "\n") {
				k, v, _ := strings.Cut(line, ":")
				v = strings.TrimSpace(v)
				switch strings.TrimSpace(k) {
				case "created":
					if t, err := time.Parse(time.RFC3339Nano, v); err == nil {
						n.Created = t.UTC()
					}
				case "updated":
					if t, err := time.Parse(time.RFC3339Nano, v); err == nil {
						n.Updated = t.UTC()
					}
				case "pinned":
					n.Pinned = v == "true"
				case "daily":
					if _, err := time.Parse("2006-01-02", v); err == nil {
						n.Daily = v
					}
				}
			}
			text = strings.TrimPrefix(body, "\n")
		}
	}
	n.set(text)
	return n
}

// set stores the body (without trailing blank space) and works out the tags.
func (n *Note) set(body string) {
	n.Body = strings.TrimRight(strings.ReplaceAll(body, "\r\n", "\n"), " \t\n")
	n.lower = strings.ToLower(n.Body)
	n.Tags = Tags(n.Body)
}

var (
	tagRe        = regexp.MustCompile(`(?:^|[\s(])#([\p{L}\p{N}_][\p{L}\p{N}_/-]*)`)
	inlineCodeRe = regexp.MustCompile("`[^`\n]*`")
)

// Tags returns the #tags in a note, lower-cased and without repeats. Code is skipped, and so are
// numbers such as #12.
func Tags(body string) []string {
	var lines []string
	fence := false
	for _, l := range strings.Split(body, "\n") {
		if strings.HasPrefix(strings.TrimSpace(l), "```") {
			fence = !fence
			continue
		}
		if !fence {
			lines = append(lines, inlineCodeRe.ReplaceAllString(l, ""))
		}
	}
	seen := map[string]bool{}
	out := []string{}
	for _, m := range tagRe.FindAllStringSubmatch(strings.Join(lines, "\n"), -1) {
		t := strings.ToLower(strings.TrimRight(m[1], "/-"))
		if t == "" || len(t) > 40 || isNumber(t) || seen[t] {
			continue
		}
		seen[t] = true
		out = append(out, t)
	}
	return out
}

func isNumber(s string) bool {
	for _, r := range s {
		if r < '0' || r > '9' {
			return false
		}
	}
	return true
}

func (s *Store) write(n *Note) error {
	path := s.path(n)
	tmp := filepath.Join(filepath.Dir(path), "."+n.ID+".tmp")
	if err := os.WriteFile(tmp, format(n), 0o644); err != nil {
		return err
	}
	return os.Rename(tmp, path)
}

func newID(t time.Time) string {
	b := make([]byte, 3)
	rand.Read(b)
	return t.UTC().Format("20060102-150405") + "-" + hex.EncodeToString(b)
}

func (n *Note) copy() Note {
	c := *n
	c.Tags = append([]string{}, n.Tags...)
	return c
}

func checkBody(body string) error {
	if len(body) > MaxBody {
		return ErrTooLong
	}
	return nil
}

// ---- changes ----

// Create saves a new note.
func (s *Store) Create(body string) (Note, error) {
	if err := checkBody(body); err != nil {
		return Note{}, err
	}
	if strings.TrimSpace(body) == "" {
		return Note{}, ErrEmpty
	}
	now := time.Now().UTC()
	n := &Note{ID: newID(now), Created: now, Updated: now}
	n.set(body)
	s.mu.Lock()
	defer s.mu.Unlock()
	if err := s.write(n); err != nil {
		return Note{}, err
	}
	s.by[n.ID] = n
	return n.copy(), nil
}

// Daily returns the note for a date (like 2026-10-31), making it if it is not there yet.
func (s *Store) Daily(date string) (Note, error) {
	if _, err := time.Parse("2006-01-02", date); err != nil {
		return Note{}, ErrBadDate
	}
	id := "daily-" + date
	s.mu.Lock()
	defer s.mu.Unlock()
	if n, ok := s.by[id]; ok {
		if n.Trashed { // asking for the day brings it back
			old := s.path(n)
			n.Trashed = false
			if err := os.Rename(old, s.path(n)); err != nil {
				n.Trashed = true
				return Note{}, err
			}
		}
		return n.copy(), nil
	}
	now := time.Now().UTC()
	n := &Note{ID: id, Created: now, Updated: now, Daily: date}
	if err := s.write(n); err != nil {
		return Note{}, err
	}
	s.by[id] = n
	return n.copy(), nil
}

func (s *Store) Get(id string) (Note, error) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	n, ok := s.by[id]
	if !ok {
		return Note{}, ErrNotFound
	}
	return n.copy(), nil
}

// Update changes the text and/or the pin. When base is given, the text is only replaced if the
// note has not been changed since then; otherwise the current note comes back with ErrConflict.
func (s *Store) Update(id string, body *string, pinned *bool, base time.Time) (Note, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	n, ok := s.by[id]
	if !ok {
		return Note{}, ErrNotFound
	}
	if body != nil {
		if err := checkBody(*body); err != nil {
			return Note{}, err
		}
		if !base.IsZero() && !n.Updated.Equal(base) {
			return n.copy(), ErrConflict
		}
	}
	next := n.copy()
	if body != nil {
		next.set(*body)
		next.Updated = time.Now().UTC()
		if !next.Updated.After(n.Updated) { // keep updated moving forward, so a stale tab is always noticed
			next.Updated = n.Updated.Add(time.Microsecond)
		}
	}
	if pinned != nil {
		next.Pinned = *pinned
	}
	if err := s.write(&next); err != nil {
		return Note{}, err
	}
	*n = next
	return n.copy(), nil
}

func (s *Store) move(id string, toTrash bool) (Note, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	n, ok := s.by[id]
	if !ok {
		return Note{}, ErrNotFound
	}
	if n.Trashed == toTrash {
		return n.copy(), nil
	}
	old := s.path(n)
	n.Trashed = toTrash
	if err := os.Rename(old, s.path(n)); err != nil {
		n.Trashed = !toTrash
		return Note{}, err
	}
	return n.copy(), nil
}

// Trash moves a note to the trash. Restore brings it back.
func (s *Store) Trash(id string) (Note, error)   { return s.move(id, true) }
func (s *Store) Restore(id string) (Note, error) { return s.move(id, false) }

// Purge deletes a note that is already in the trash, for good.
func (s *Store) Purge(id string) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	n, ok := s.by[id]
	if !ok {
		return ErrNotFound
	}
	if !n.Trashed {
		return ErrNotTrash
	}
	if err := os.Remove(s.path(n)); err != nil && !errors.Is(err, os.ErrNotExist) {
		return err
	}
	delete(s.by, id)
	return nil
}

// EmptyTrash deletes everything in the trash for good and says how many notes that was.
func (s *Store) EmptyTrash() (int, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	count := 0
	for id, n := range s.by {
		if !n.Trashed {
			continue
		}
		if err := os.Remove(s.path(n)); err != nil && !errors.Is(err, os.ErrNotExist) {
			return count, err
		}
		delete(s.by, id)
		count++
	}
	return count, nil
}

// ---- reading ----

type Query struct {
	Text   string // words that must all appear; #tag words must be tags
	Tag    string
	View   string // "" or "all", "pinned", "daily", "trash"
	Offset int
	Limit  int
}

// List returns one page of matching notes, newest first, and how many matched in all.
func (s *Store) List(q Query) ([]Note, int) {
	var words, tags []string
	for _, w := range strings.Fields(strings.ToLower(q.Text)) {
		if t := strings.TrimPrefix(w, "#"); t != w && t != "" {
			tags = append(tags, t)
		} else {
			words = append(words, w)
		}
	}
	if t := strings.ToLower(strings.TrimPrefix(q.Tag, "#")); t != "" {
		tags = append(tags, t)
	}

	s.mu.RLock()
	var hits []*Note
	for _, n := range s.by {
		if n.Trashed != (q.View == "trash") || (q.View == "pinned" && !n.Pinned) || (q.View == "daily" && n.Daily == "") {
			continue
		}
		if matches(n, words, tags) {
			hits = append(hits, n)
		}
	}
	sort.Slice(hits, func(i, j int) bool {
		a, b := hits[i], hits[j]
		if q.View == "daily" && a.Daily != b.Daily {
			return a.Daily > b.Daily
		}
		if !a.Created.Equal(b.Created) {
			return a.Created.After(b.Created)
		}
		return a.ID > b.ID
	})
	total := len(hits)
	if q.Offset > 0 {
		hits = hits[min(q.Offset, len(hits)):]
	}
	if q.Limit > 0 && len(hits) > q.Limit {
		hits = hits[:q.Limit]
	}
	out := make([]Note, len(hits))
	for i, n := range hits {
		out[i] = n.copy()
	}
	s.mu.RUnlock()
	return out, total
}

func matches(n *Note, words, tags []string) bool {
	for _, w := range words {
		if !strings.Contains(n.lower, w) {
			return false
		}
	}
	for _, want := range tags {
		found := false
		for _, have := range n.Tags {
			if have == want || strings.HasPrefix(have, want+"/") {
				found = true
				break
			}
		}
		if !found {
			return false
		}
	}
	return true
}

type TagCount struct {
	Tag   string `json:"tag"`
	Count int    `json:"count"`
}

type Counts struct {
	All    int `json:"all"`
	Pinned int `json:"pinned"`
	Daily  int `json:"daily"`
	Trash  int `json:"trash"`
}

// Summary counts the notes and the tags in use (trashed notes do not count towards tags).
func (s *Store) Summary() (Counts, []TagCount) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	var c Counts
	per := map[string]int{}
	for _, n := range s.by {
		if n.Trashed {
			c.Trash++
			continue
		}
		c.All++
		if n.Pinned {
			c.Pinned++
		}
		if n.Daily != "" {
			c.Daily++
		}
		for _, t := range n.Tags {
			per[t]++
		}
	}
	tags := make([]TagCount, 0, len(per))
	for t, k := range per {
		tags = append(tags, TagCount{t, k})
	}
	sort.Slice(tags, func(i, j int) bool {
		if tags[i].Count != tags[j].Count {
			return tags[i].Count > tags[j].Count
		}
		return tags[i].Tag < tags[j].Tag
	})
	return c, tags
}

// WriteZip writes every note that is not in the trash as a .md file in a zip archive.
func (s *Store) WriteZip(w io.Writer) error {
	s.mu.RLock()
	defer s.mu.RUnlock()
	ids := make([]string, 0, len(s.by))
	for id, n := range s.by {
		if !n.Trashed {
			ids = append(ids, id)
		}
	}
	sort.Strings(ids)
	zw := zip.NewWriter(w)
	for _, id := range ids {
		n := s.by[id]
		f, err := zw.CreateHeader(&zip.FileHeader{Name: "basking/" + id + ".md", Method: zip.Deflate, Modified: n.Updated})
		if err != nil {
			return err
		}
		if _, err := f.Write(format(n)); err != nil {
			return err
		}
	}
	return zw.Close()
}