Added code for backend glue

backend/internal/db/repo.go

@@ -0,0 +1,88 @@
+package db
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+
+	"mind/internal/models"
+)
+
+type Repo struct { db *sql.DB }
+
+func NewRepo(db *sql.DB) *Repo { return &Repo{db: db} }
+
+// Conversations
+func (r *Repo) CreateConversation(ctx context.Context, ownerID int64, title string) (int64, error) {
+	res, err := r.db.ExecContext(ctx, `INSERT INTO conversations(owner_id,title) VALUES(?,?)`, ownerID, title)
+	if err != nil { return 0, err }
+	return res.LastInsertId()
+}
+
+func (r *Repo) ListConversations(ctx context.Context, ownerID int64) ([]models.Conversation, error) {
+	rows, err := r.db.QueryContext(ctx, `SELECT id, owner_id, title, created_at FROM conversations WHERE owner_id=? ORDER BY id DESC`, ownerID)
+	if err != nil { return nil, err }
+	defer rows.Close()
+	var out []models.Conversation
+	for rows.Next() {
+		var c models.Conversation
+		if err := rows.Scan(&c.ID, &c.OwnerID, &c.Title, &c.Created); err != nil { return nil, err }
+		out = append(out, c)
+	}
+	return out, nil
+}
+
+// Nodes & Edges
+func (r *Repo) CreateNode(ctx context.Context, convID int64, authorKind, content string) (int64, error) {
+	res, err := r.db.ExecContext(ctx, `INSERT INTO nodes(conversation_id,author_kind,content) VALUES(?,?,?)`, convID, authorKind, content)
+	if err != nil { return 0, err }
+	return res.LastInsertId()
+}
+
+func (r *Repo) Link(ctx context.Context, parentID, childID int64) error {
+	_, err := r.db.ExecContext(ctx, `INSERT INTO edges(parent_id,child_id) VALUES(?,?)`, parentID, childID)
+	return err
+}
+
+func (r *Repo) GetNode(ctx context.Context, id int64) (models.Node, error) {
+	var n models.Node
+	err := r.db.QueryRowContext(ctx, `SELECT id,conversation_id,author_kind,content,created_at FROM nodes WHERE id=?`, id).
+		Scan(&n.ID, &n.ConversationID, &n.AuthorKind, &n.Content, &n.Created)
+	return n, err
+}
+
+// Branches
+func (r *Repo) CreateOrGetBranch(ctx context.Context, convID int64, name string, headNodeID int64) (models.Branch, error) {
+	// Try insert
+	_, _ = r.db.ExecContext(ctx, `INSERT INTO branches(conversation_id,name,head_node_id) VALUES(?,?,?)`, convID, name, headNodeID)
+	return r.GetBranch(ctx, convID, name)
+}
+
+func (r *Repo) GetBranch(ctx context.Context, convID int64, name string) (models.Branch, error) {
+	var b models.Branch
+	err := r.db.QueryRowContext(ctx, `SELECT id,conversation_id,name,head_node_id FROM branches WHERE conversation_id=? AND name=?`, convID, name).
+		Scan(&b.ID, &b.ConversationID, &b.Name, &b.HeadNodeID)
+	return b, err
+}
+
+func (r *Repo) MoveBranchHead(ctx context.Context, branchID, newHeadID int64) error {
+	_, err := r.db.ExecContext(ctx, `UPDATE branches SET head_node_id=? WHERE id=?`, newHeadID, branchID)
+	return err
+}
+
+// Latest-parent walk for linearize
+func (r *Repo) LatestParent(ctx context.Context, childID int64) (models.Node, bool, error) {
+	row := r.db.QueryRowContext(ctx, `
+		SELECT n.id,n.conversation_id,n.author_kind,n.content,n.created_at
+		FROM edges e
+		JOIN nodes n ON n.id=e.parent_id
+		WHERE e.child_id=?
+		ORDER BY n.created_at DESC
+		LIMIT 1`, childID)
+	var n models.Node
+	if err := row.Scan(&n.ID, &n.ConversationID, &n.AuthorKind, &n.Content, &n.Created); err != nil {
+		if errors.Is(err, sql.ErrNoRows) { return models.Node{}, false, nil }
+		return models.Node{}, false, err
+	}
+	return n, true, nil
+}