package engine

import (
	"testing"
)

// L1186 测试: FileHistoryView 窄接口契约
//
// 验证:
//   1. *FileHistory 通过结构化 typing 实现 FileHistoryView (编译期保证)
//   2. 从 Engine.FileHistoryView() 拿到的值在无快照时返回合理默认
//   3. 接口类型可以被 mock 替换 (用于测试消费者代码)

// mockFileHistoryView 是纯 mock 实现, 证明接口可被任意类型实现.
// 消费者测试代码可以用类似的 mock 隔离 engine 依赖.
type mockFileHistoryView struct {
	canRollbackResult bool
	canRollbackFiles  []string
	snapshotCount     int
	canRollbackCalls  []string
}

func (m *mockFileHistoryView) CanRollback(messageID string) (bool, []string) {
	m.canRollbackCalls = append(m.canRollbackCalls, messageID)
	return m.canRollbackResult, m.canRollbackFiles
}

func (m *mockFileHistoryView) SnapshotCount() int {
	return m.snapshotCount
}

// TestFileHistoryView_StructuralTyping 验证 *FileHistory 满足 FileHistoryView.
// 这是编译期断言, 如果接口 / 实现不匹配编译就会失败.
func TestFileHistoryView_StructuralTyping(t *testing.T) {
	var _ FileHistoryView = (*FileHistory)(nil) // compile-time assertion
}

// TestFileHistoryView_MockImplementation 验证消费者可以用 mock 替换接口.
// 这是 L1186 抽象的核心价值: 消费者的代码不需要真实 FileHistory 也能跑测试.
func TestFileHistoryView_MockImplementation(t *testing.T) {
	m := &mockFileHistoryView{
		canRollbackResult: true,
		canRollbackFiles:  []string{"/tmp/a.txt", "/tmp/b.txt"},
		snapshotCount:     42,
	}

	// consumer 代码接受 FileHistoryView 接口, 而非 *FileHistory 具体类型
	var view FileHistoryView = m

	if count := view.SnapshotCount(); count != 42 {
		t.Errorf("SnapshotCount() = %d, want 42", count)
	}

	can, files := view.CanRollback("msg-X")
	if !can {
		t.Errorf("CanRollback = false, want true")
	}
	if len(files) != 2 || files[0] != "/tmp/a.txt" || files[1] != "/tmp/b.txt" {
		t.Errorf("CanRollback files = %v, want [/tmp/a.txt /tmp/b.txt]", files)
	}

	// 验证 mock 记录了调用
	if len(m.canRollbackCalls) != 1 || m.canRollbackCalls[0] != "msg-X" {
		t.Errorf("CanRollback calls = %v, want [msg-X]", m.canRollbackCalls)
	}
}

// TestFileHistoryView_RealImplementation 验证 FileHistory 真实行为通过窄接口仍然正确.
func TestFileHistoryView_RealImplementation(t *testing.T) {
	baseDir := t.TempDir()
	fh := NewFileHistoryWithDir(baseDir, nil)

	// 通过接口调用, 而非具体类型
	var view FileHistoryView = fh

	if count := view.SnapshotCount(); count != 0 {
		t.Errorf("SnapshotCount() on fresh history = %d, want 0", count)
	}

	can, files := view.CanRollback("nonexistent")
	if can {
		t.Errorf("CanRollback('nonexistent') = true, want false")
	}
	if len(files) != 0 {
		t.Errorf("CanRollback files = %v, want empty", files)
	}
}