package cart

import (
	"context"
	"testing"
	"time"

	cart_messages "git.k6n.net/mats/go-cart-actor/proto/cart"
)

// Item identity is the catalog item id, not the (reference-only) SKU: two adds
// with the same ItemId but different SKU strings must merge into one line.
func TestAddItem_MergesByItemIdNotSku(t *testing.T) {
	reg := NewCartMultationRegistry(NewCartMutationContext(nil))
	g := NewCartGrain(1, time.Now())
	ctx := context.Background()

	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 144047, Sku: "A0162590", Quantity: 1, Price: 1000}); err != nil {
		t.Fatalf("first add: %v", err)
	}
	// Same id, different (reference) sku string -> should merge, not create a line.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 144047, Sku: "STALE-REF", Quantity: 2, Price: 1000}); err != nil {
		t.Fatalf("second add: %v", err)
	}

	if len(g.Items) != 1 {
		t.Fatalf("items = %d, want 1 (merged by id)", len(g.Items))
	}
	if g.Items[0].Quantity != 3 {
		t.Errorf("quantity = %d, want 3", g.Items[0].Quantity)
	}

	// A different id is a distinct line.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 170852, Sku: "A0190103", Quantity: 1, Price: 500}); err != nil {
		t.Fatalf("third add: %v", err)
	}
	if len(g.Items) != 2 {
		t.Fatalf("items = %d, want 2", len(g.Items))
	}
}

// Re-adding the same parent (same ItemId + StoreId, no ParentId on the
// re-add itself) merges the quantity, and the proportional cascade resizes
// every direct child to match the new parent qty so a "+1 drill" leaves
// the bundle internally consistent.
func TestAddItem_MergeCascadesToChildren(t *testing.T) {
	reg := NewCartMultationRegistry(NewCartMutationContext(nil))
	g := NewCartGrain(1, time.Now())
	ctx := context.Background()

	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 100, Sku: "P", Quantity: 1, Price: 1000}); err != nil {
		t.Fatalf("add parent: %v", err)
	}
	parentLine := g.Items[0].Id
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 101, Sku: "C1", Quantity: 1, Price: 100, ParentId: &parentLine}); err != nil {
		t.Fatalf("add child: %v", err)
	}

	// Re-add the same parent — same ItemId, no ParentId on the re-add itself.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 100, Sku: "P", Quantity: 1, Price: 1000}); err != nil {
		t.Fatalf("re-add parent: %v", err)
	}

	// Parent qty 1 -> 2; child qty 1 -> 2 via cascade.
	for _, it := range g.Items {
		if it.Quantity != 2 {
			t.Errorf("line %s qty = %d, want 2 (merge cascade)", it.Sku, it.Quantity)
		}
	}
}

// Item identity for merge purposes includes ParentId: a standalone root
// line (ParentId == nil) and a child line (ParentId == &someParentLine) that
// happen to share an ItemId are different roles and MUST stay as distinct
// lines. Merging would silently turn an accessory into a +N on the root
// (or vice versa), corrupting the parent-child link.
func TestAddItem_DoesNotMergeWhenParentIdDiffers(t *testing.T) {
	reg := NewCartMultationRegistry(NewCartMutationContext(nil))
	g := NewCartGrain(1, time.Now())
	ctx := context.Background()

	// Standalone root (no ParentId).
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 100, Sku: "P", Quantity: 1, Price: 1000}); err != nil {
		t.Fatalf("add standalone: %v", err)
	}
	parentLine := g.Items[0].Id

	// Same ItemId+StoreId but with ParentId set — must create a NEW line,
	// not bump the standalone's qty.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 100, Sku: "P", Quantity: 1, Price: 1000, ParentId: &parentLine}); err != nil {
		t.Fatalf("add child-form: %v", err)
	}

	if len(g.Items) != 2 {
		t.Fatalf("items = %d, want 2 (different ParentId => distinct lines)", len(g.Items))
	}
	// Standalone untouched at qty 1; child-form is its own line at qty 1.
	for _, it := range g.Items {
		if it.Quantity != 1 {
			t.Errorf("line %d (parentId=%v) qty = %d, want 1 (no merge)", it.Id, it.ParentId, it.Quantity)
		}
		// One of them has nil ParentId and the other has &parentLine — guard
		// against an accidental merge ever flipping both to non-nil.
	}
	var seenNil, seenSet bool
	for _, it := range g.Items {
		if it.ParentId == nil {
			seenNil = true
		} else if *it.ParentId == parentLine {
			seenSet = true
		}
	}
	if !seenNil || !seenSet {
		t.Errorf("expected one line with nil ParentId and one with &parentLine; got nil=%v set=%v", seenNil, seenSet)
	}
}

// Positive control: when BOTH sides have ParentId set to the SAME parent
// line, the merge proceeds (this guards the new sameParent guard against
// accidentally rejecting a legitimate "re-add same child of same parent"
// case — e.g. an idempotent retry from a flaky request).
func TestAddItem_MergesWhenBothParentIdMatch(t *testing.T) {
	reg := NewCartMultationRegistry(NewCartMutationContext(nil))
	g := NewCartGrain(1, time.Now())
	ctx := context.Background()

	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 100, Sku: "P", Quantity: 1, Price: 1000}); err != nil {
		t.Fatalf("add parent: %v", err)
	}
	parentLine := g.Items[0].Id

	// First child: ItemId 200 under parent.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 200, Sku: "C", Quantity: 1, Price: 100, ParentId: &parentLine}); err != nil {
		t.Fatalf("add child: %v", err)
	}
	// Re-add the SAME child (same ItemId+StoreId+ParentId) — must merge into
	// qty 2, not create a second accessory line.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 200, Sku: "C", Quantity: 1, Price: 100, ParentId: &parentLine}); err != nil {
		t.Fatalf("re-add child: %v", err)
	}

	if len(g.Items) != 2 {
		t.Fatalf("items = %d, want 2 (parent + merged child)", len(g.Items))
	}
	for _, it := range g.Items {
		switch it.Id {
		case parentLine:
			if it.Quantity != 1 {
				t.Errorf("parent qty = %d, want 1 (untouched)", it.Quantity)
			}
		default:
			if it.Quantity != 2 {
				t.Errorf("child qty = %d, want 2 (merged on same-PARENT re-add)", it.Quantity)
			}
		}
	}
}

// Same ItemId+StoreId+both with ParentId set to *different* parent lines
// must also stay distinct — children belong to their own parent.
func TestAddItem_DoesNotMergeAcrossDifferentParentLines(t *testing.T) {
	reg := NewCartMultationRegistry(NewCartMutationContext(nil))
	g := NewCartGrain(1, time.Now())
	ctx := context.Background()

	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 100, Sku: "P1", Quantity: 1, Price: 500}); err != nil {
		t.Fatalf("add parent A: %v", err)
	}
	parentA := g.Items[0].Id
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 200, Sku: "P2", Quantity: 1, Price: 500}); err != nil {
		t.Fatalf("add parent B: %v", err)
	}
	parentB := g.Items[1].Id

	// Two children of different parents sharing an ItemId — distinct lines.
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 999, Sku: "C", Quantity: 1, Price: 100, ParentId: &parentA}); err != nil {
		t.Fatalf("add child of A: %v", err)
	}
	if _, err := reg.Apply(ctx, g, &cart_messages.AddItem{ItemId: 999, Sku: "C", Quantity: 1, Price: 100, ParentId: &parentB}); err != nil {
		t.Fatalf("add child of B: %v", err)
	}

	// 2 parent lines + 2 child lines = 4 total; no merges across.
	if len(g.Items) != 4 {
		t.Errorf("items = %d, want 4 (parents A,B + their distinct children)", len(g.Items))
	}
	for _, it := range g.Items {
		if it.Quantity != 1 {
			t.Errorf("line %d qty = %d, want 1 (no accidental merge)", it.Id, it.Quantity)
		}
	}
}