package storage

import (
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/sandrodach/mindsift/internal/collab"
	"github.com/sandrodach/mindsift/internal/domain"
)

// Restructuring notes: turn a bullet with its children into a note of its own, and merge one note into
// another. Both change the affected notes through the normal operation log, so open editors follow
// live, and nothing is lost: an extracted branch lives on in the new note, a merged note goes to the
// trash and the merge can be undone.

var (
	ErrBlockNotFound = errors.New("Punkt nicht gefunden")
	ErrBranchLocked  = errors.New("Jemand anderes bearbeitet gerade einen Punkt in diesem Ast. Bitte kurz warten.")
	ErrMergeSelf     = errors.New("Eine Notiz kann nicht mit sich selbst zusammengeführt werden")
	ErrMergeNotOwner = errors.New("Zusammenführen geht nur mit eigenen Notizen als Quelle")
)

// readCollabDoc loads the current state of a note outside of a change.
func (s *Store) readCollabDoc(docID string) (*collab.Doc, error) {
	tx, err := s.db.Begin()
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()
	doc, _, err := loadCollabDoc(tx, docID)
	return doc, err
}

var (
	titlePrefixRe = regexp.MustCompile(`^(\s*(-|\*|#{1,6}|\[[ xX]?\])\s+)+`)
	titleTagRe    = regexp.MustCompile(`(^|\s)#[\p{L}0-9_-]+`)
)

// branchTitle makes a note title from a bullet's text (without hashtags) and returns the hashtags,
// which stay next to the link in the original bullet.
func branchTitle(content string) (string, string) {
	first := titlePrefixRe.ReplaceAllString(strings.SplitN(content, "\n", 2)[0], "")
	var tags []string
	for _, m := range titleTagRe.FindAllString(first, -1) {
		tags = append(tags, strings.TrimSpace(m))
	}
	t := strings.TrimSpace(titleTagRe.ReplaceAllString(first, ""))
	t = strings.NewReplacer("[[", "", "]]", "").Replace(t)
	if r := []rune(t); len(r) > 120 {
		t = strings.TrimSpace(string(r[:119])) + "…"
	}
	if t == "" {
		t = "Unbenannte Notiz"
	}
	return t, strings.Join(tags, " ")
}

// uniqueTitle appends " (2)", " (3)" … when the user already has a note of that name, so the wiki link
// points to exactly one note.
func (s *Store) uniqueTitle(userID, title string) string {
	docs, _ := s.GetDocuments(userID)
	taken := map[string]bool{}
	for _, d := range docs {
		taken[strings.ToLower(d.Title)] = true
	}
	candidate := title
	for n := 2; taken[strings.ToLower(candidate)]; n++ {
		candidate = fmt.Sprintf("%s (%d)", title, n)
	}
	return candidate
}

func toDocumentBlock(b collab.FlatBlock, level int, pos int) domain.DocumentBlock {
	return domain.DocumentBlock{
		ID: domain.NewID("blk"), Type: b.Type, Content: b.Content, Level: level, Position: float64(pos + 1),
		Checked: b.Props.Checked, Collapsed: b.Props.Collapsed, Lang: b.Props.Lang,
	}
}

func foreignLeaseIn(ids []string, a collab.Actor, leases collab.LeaseView) bool {
	if leases == nil {
		return false
	}
	for _, id := range ids {
		if holder, ok := leases.HolderOf(id); ok && holder != a.ClientID {
			return true
		}
	}
	return false
}

// ExtractBranch creates a new note from a bullet's children, named after the bullet, in the same folder
// and shared like the original. The original note is not changed here: the editor replaces the branch
// by the returned link itself, as an ordinary own edit (no clash with unsent typing, undo works).
func (s *Store) ExtractBranch(userID, docID, blockID string, a collab.Actor, leases collab.LeaseView) (*domain.Document, string, error) {
	source, err := s.GetDocumentByID(userID, docID)
	if err != nil {
		return nil, "", err
	}
	state, err := s.readCollabDoc(docID)
	if err != nil {
		return nil, "", err
	}
	flat := state.Flatten()
	start := -1
	for i, b := range flat {
		if b.ID == blockID {
			start = i
			break
		}
	}
	if start < 0 {
		return nil, "", ErrBlockNotFound
	}
	root := flat[start]
	var children []domain.DocumentBlock
	ids := []string{root.ID}
	for i := start + 1; i < len(flat) && flat[i].Level > root.Level; i++ {
		children = append(children, toDocumentBlock(flat[i], flat[i].Level-root.Level-1, len(children)))
		ids = append(ids, flat[i].ID)
	}
	if foreignLeaseIn(ids, a, leases) {
		return nil, "", ErrBranchLocked
	}

	base, tags := branchTitle(root.Content)
	title := s.uniqueTitle(userID, base)
	created, err := s.CreateDocument(userID, "", title, "📄", source.FolderPath, children, nil, false)
	if err != nil {
		return nil, "", err
	}
	s.copyShares(userID, source, created.ID)
	link := "[[" + title + "]]"
	if tags != "" {
		link += " " + tags
	}
	return created, link, nil
}

// UndoExtract puts a note created by ExtractBranch into the trash (only its creator may).
func (s *Store) UndoExtract(userID, docID string) error {
	doc, err := s.GetDocumentByID(userID, docID)
	if err != nil {
		return err
	}
	if !doc.IsOwner {
		return ErrMergeNotOwner
	}
	if doc.IsArchived {
		return nil
	}
	return s.trashDocument(userID, docID)
}

// copyShares gives the new note the direct and team shares of the source; when someone else owns the
// source, that owner may edit the new note as well (the branch was theirs to read before).
func (s *Store) copyShares(userID string, source *domain.Document, newDocID string) {
	shares, _ := s.GetDocShares(source.ID)
	for _, sh := range shares {
		switch {
		case sh.TargetType == "team":
			_, _ = s.CreateDocTeamShare(userID, newDocID, sh.TargetID, sh.Permission)
		case sh.UserID != "" && sh.UserID != userID:
			_, _ = s.CreateDocShare(userID, newDocID, sh.UserID, sh.Permission)
		}
	}
	if source.UserID != "" && source.UserID != userID {
		_, _ = s.CreateDocShare(userID, newDocID, source.UserID, "write")
	}
}

// MergeResult tells the client what to undo.
type MergeResult struct {
	TargetID    string `json:"targetId"`
	SourceID    string `json:"sourceId"`
	SourceTitle string `json:"sourceTitle"`
	HeadingID   string `json:"headingId"`
}

// MergeDocuments appends the source note to the end of the target: a heading with the source's title,
// its blocks below it. The source goes to the trash (it must belong to the user; the caller checks
// write access to the target).
func (s *Store) MergeDocuments(userID, sourceID, targetID string, a collab.Actor, leases collab.LeaseView) (*MergeResult, error) {
	if sourceID == targetID {
		return nil, ErrMergeSelf
	}
	source, err := s.GetDocumentByID(userID, sourceID)
	if err != nil {
		return nil, err
	}
	if !source.IsOwner {
		return nil, ErrMergeNotOwner
	}
	if source.IsArchived {
		return nil, ErrDocInTrash
	}
	state, err := s.readCollabDoc(sourceID)
	if err != nil {
		return nil, err
	}
	flat := state.Flatten()

	headingID := domain.NewID("blk")
	heading := strings.TrimSpace(source.Icon + " " + source.Title)
	if heading == "" {
		heading = "Zusammengeführte Notiz"
	}
	heading += " (" + time.Now().Format("02.01.2006") + ")"

	_, _, err = s.applyDocChange(targetID, a, leases, func(d *collab.Doc) []collab.Op {
		// After the last top-level block, deleted ones included, so keys never collide
		last := ""
		for _, b := range d.Blocks {
			if b.ParentID == "" && b.OrderKey > last {
				last = b.OrderKey
			}
		}
		key, err := collab.KeyBetween(last, "")
		if err != nil {
			return nil
		}
		root := ""
		ops := []collab.Op{{OpID: domain.NewID("op"), Kind: collab.OpInsert, BlockID: headingID, ParentID: &root, OrderKey: key, Type: "h2", Content: &heading}}
		// Parents by level: the heading holds the source's top level
		parents := []string{headingID}
		lastKey := map[string]string{}
		for _, b := range flat {
			if b.Level+1 > len(parents) {
				continue // cannot happen with a flattened tree; guards against gaps
			}
			parents = parents[:b.Level+1]
			parent := parents[b.Level]
			k, err := collab.KeyBetween(lastKey[parent], "")
			if err != nil {
				return nil
			}
			lastKey[parent] = k
			id := domain.NewID("blk")
			content := b.Content
			props := collab.Props{Checked: b.Props.Checked, Collapsed: b.Props.Collapsed, Lang: b.Props.Lang}
			p := parent
			ops = append(ops, collab.Op{OpID: domain.NewID("op"), Kind: collab.OpInsert, BlockID: id, ParentID: &p, OrderKey: k, Type: b.Type, Content: &content, Props: &props})
			parents = append(parents, id)
		}
		return ops
	})
	if err != nil {
		return nil, err
	}
	if err := s.trashDocument(userID, sourceID); err != nil {
		return nil, err
	}
	return &MergeResult{TargetID: targetID, SourceID: sourceID, SourceTitle: source.Title, HeadingID: headingID}, nil
}

// UndoMerge removes the appended section from the target and brings the source back from the trash.
func (s *Store) UndoMerge(userID string, m MergeResult, a collab.Actor, leases collab.LeaseView) error {
	if err := s.RestoreDocument(userID, m.SourceID); err != nil {
		return err
	}
	_, _, err := s.applyDocChange(m.TargetID, a, leases, func(d *collab.Doc) []collab.Op {
		if b, ok := d.Blocks[m.HeadingID]; !ok || b.Deleted {
			return nil
		}
		return []collab.Op{{OpID: domain.NewID("op"), Kind: collab.OpDelete, BlockID: m.HeadingID}}
	})
	return err
}

// DocHead is the newest log position of a note (to tell open editors to sync).
func (s *Store) DocHead(docID string) int64 {
	var head int64
	_ = s.db.QueryRow(`SELECT head_seq FROM documents WHERE id = ?`, docID).Scan(&head)
	return head
}