package history

import (
	"context"
	"strings"
	"testing"
)

// sessionOf returns the SessionMeta of one session from ListSessions, failing the test
// when the session is absent.
func sessionOf(t *testing.T, st *Store, id string) SessionMeta {
	t.Helper()
	sessions, err := st.ListSessions(context.Background())
	if err != nil {
		t.Fatalf("list sessions: %v", err)
	}
	for _, m := range sessions {
		if m.ID == id {
			return m
		}
	}
	t.Fatalf("session %q not found in %+v", id, sessions)
	return SessionMeta{}
}

func TestListSessionsLastMessagePreview(t *testing.T) {
	t.Parallel()
	st := newStore(t)
	ctx := context.Background()

	// The empty main session has no preview.
	if got := sessionOf(t, st, MainSessionID); got.LastMessage != nil {
		t.Fatalf("empty main LastMessage = %+v, want nil", got.LastMessage)
	}

	sub, err := st.NewSubSession(ctx, "owner")
	if err != nil {
		t.Fatalf("new sub: %v", err)
	}
	if err := st.Append(ctx, Message{SessionID: MainSessionID, Role: RoleUser, Content: "first", CreatedAt: 1000}); err != nil {
		t.Fatalf("append main user: %v", err)
	}
	if err := st.Append(ctx, Message{SessionID: MainSessionID, Role: RoleAssistant, Content: "latest reply", CreatedAt: 2000}); err != nil {
		t.Fatalf("append main assistant: %v", err)
	}
	if err := st.Append(ctx, Message{SessionID: sub, Role: RoleUser, Content: "sub question", CreatedAt: 1500}); err != nil {
		t.Fatalf("append sub: %v", err)
	}

	// Main stays first and carries its newest message, not the first one.
	sessions, err := st.ListSessions(ctx)
	if err != nil {
		t.Fatalf("list sessions: %v", err)
	}
	if len(sessions) != 2 || sessions[0].ID != MainSessionID {
		t.Fatalf("sessions = %+v, want main first", sessions)
	}
	main := sessions[0].LastMessage
	if main == nil || main.Role != RoleAssistant || main.Content != "latest reply" || main.CreatedAt != 2000 {
		t.Fatalf("main LastMessage = %+v, want assistant/latest reply/2000", main)
	}
	subPreview := sessions[1].LastMessage
	if subPreview == nil || subPreview.Role != RoleUser || subPreview.Content != "sub question" || subPreview.CreatedAt != 1500 {
		t.Fatalf("sub LastMessage = %+v, want user/sub question/1500", subPreview)
	}

	// A sub session created after the main one but never written has no preview.
	empty, err := st.NewSubSession(ctx, "owner")
	if err != nil {
		t.Fatalf("new empty sub: %v", err)
	}
	if got := sessionOf(t, st, empty); got.LastMessage != nil {
		t.Fatalf("empty sub LastMessage = %+v, want nil", got.LastMessage)
	}
}

func TestListSessionsLastMessageTruncatesAndCollapses(t *testing.T) {
	t.Parallel()
	st := newStore(t)
	ctx := context.Background()

	long := strings.Repeat("字", lastMessagePreviewRunes+10) + "\n\n尾部"
	if err := st.Append(ctx, Message{SessionID: MainSessionID, Role: RoleUser, Content: long, CreatedAt: 1000}); err != nil {
		t.Fatalf("append long: %v", err)
	}
	want := strings.Repeat("字", lastMessagePreviewRunes) + "…"
	if got := sessionOf(t, st, MainSessionID).LastMessage; got == nil || got.Content != want {
		t.Fatalf("truncated preview = %+v, want %q", got, want)
	}

	// Whitespace runs (including newlines) collapse to single spaces, and a short
	// message is returned whole.
	sub, err := st.NewSubSession(ctx, "owner")
	if err != nil {
		t.Fatalf("new sub: %v", err)
	}
	if err := st.Append(ctx, Message{SessionID: sub, Role: RoleUser, Content: "  你好\n\t世界  ", CreatedAt: 1000}); err != nil {
		t.Fatalf("append spaced: %v", err)
	}
	if got := sessionOf(t, st, sub).LastMessage; got == nil || got.Content != "你好 世界" {
		t.Fatalf("collapsed preview = %+v, want %q", got, "你好 世界")
	}
}

func TestListSessionsLastMessageTieBreaksByInsertion(t *testing.T) {
	t.Parallel()
	st := newStore(t)
	ctx := context.Background()

	// Two messages sharing a millisecond timestamp: the later insert is the newest.
	for _, content := range []string{"older", "newer"} {
		if err := st.Append(ctx, Message{SessionID: MainSessionID, Role: RoleAssistant, Content: content, CreatedAt: 5000}); err != nil {
			t.Fatalf("append %s: %v", content, err)
		}
	}
	if got := sessionOf(t, st, MainSessionID).LastMessage; got == nil || got.Content != "newer" {
		t.Fatalf("tie-break preview = %+v, want newer", got)
	}
}

func TestPreviewContentBounds(t *testing.T) {
	t.Parallel()
	if got := previewContent(""); got != "" {
		t.Fatalf("empty preview = %q, want empty", got)
	}
	exact := strings.Repeat("a", lastMessagePreviewRunes)
	if got := previewContent(exact); got != exact {
		t.Fatalf("exact-length preview changed: %q", got)
	}
	over := strings.Repeat("a", lastMessagePreviewRunes+1)
	if got := previewContent(over); got != exact+"…" {
		t.Fatalf("over-length preview = %q, want ellipsis", got)
	}
}