snapshot of https://github.com/cortezaproject/corteza.git (2024.9.x, 2026-09-18; blobs > 131072B omitted)

server/pkg/dal/iterator.go

@@ -0,0 +1,119 @@
+package dal
+
+import (
+	"context"
+	"encoding/json"
+	"io"
+
+	"github.com/cortezaproject/corteza/server/pkg/filter"
+)
+
+type (
+	// Iterator provides an interface for loading data from the underlying store
+	Iterator interface {
+		Next(ctx context.Context) bool
+		More(uint, ValueGetter) error
+		Err() error
+		Scan(ValueSetter) error
+		Close() error
+
+		BackCursor(ValueGetter) (*filter.PagingCursor, error)
+		ForwardCursor(ValueGetter) (*filter.PagingCursor, error)
+
+		// // -1 means unknown
+		// Total() int
+		// Cursor() any
+		// // ... do we need anything else here?
+	}
+
+	iterator interface {
+		Preload(context.Context, uint, *filter.PagingCursor) error
+		Sorting() filter.SortExprSet
+	}
+)
+
+// IteratorEncodeJSON helper function that encodes each item from the iterator as JSON
+// and writes it to th given io.Writer.
+//
+// target initialization function is intentionally used to avoid use of reflection
+func IteratorEncodeJSON(ctx context.Context, w io.Writer, iter Iterator, initTarget func() ValueSetter) (err error) {
+	var (
+		target   ValueSetter
+		firstOut = false
+	)
+
+	for iter.Next(ctx) {
+		if err = iter.Err(); err != nil {
+			return
+		}
+
+		if firstOut {
+			if _, err = w.Write([]byte(`,`)); err != nil {
+				return
+			}
+		}
+
+		firstOut = true
+
+		target = initTarget()
+
+		if err = iter.Scan(target); err != nil {
+			return
+		}
+
+		err = json.NewEncoder(w).Encode(target)
+		if err != nil {
+			return
+		}
+	}
+
+	return
+}
+
+// PreLoadCursor into iterator and check it exist then return the cursor
+// @todo this should be move to the Iterator
+func PreLoadCursor(ctx context.Context, iter Iterator, limit uint, reverse bool, r ValueGetter, fx func(Iterator) (bool, error)) (out *filter.PagingCursor, err error) {
+	makeCursor := func() (*filter.PagingCursor, error) {
+		if reverse {
+			return iter.BackCursor(r)
+		} else {
+			return iter.ForwardCursor(r)
+		}
+	}
+
+	out, err = makeCursor()
+	if err != nil {
+		return
+	}
+
+	err = iter.(iterator).Preload(ctx, limit, out)
+	if err != nil {
+		return nil, nil
+	}
+
+	for {
+		if !iter.Next(ctx) {
+			out = nil
+			return
+		}
+
+		ok, err := fx(iter)
+		if err != nil {
+			return nil, err
+		}
+
+		if ok {
+			return out, err
+
+			// // @todo Skip the things we don't have access to; could cause some edge cases so probably not
+			// // It adds some performance since we skip unneeded stuff but could some records change in the mean time?
+			// // return makeCursor()
+		}
+	}
+}
+
+// IteratorSorting return iterator sorting
+// @todo this should be move to the Iterator
+func IteratorSorting(iter Iterator) filter.SortExprSet {
+	return iter.(iterator).Sorting()
+}