package main

import (
	"fmt"
	"testing"
	"time"

	"github.com/mattermost/mattermost/server/public/model"
	"github.com/stretchr/testify/require"
)

type mockPostService struct {
	postsByChannel map[string][]*model.Post
	deleted        []string
	failDeleteIDs  map[string]bool
}

func newMockPostService() *mockPostService {
	return &mockPostService{
		postsByChannel: make(map[string][]*model.Post),
		failDeleteIDs:  make(map[string]bool),
	}
}

func (m *mockPostService) addPost(channelID, postID string, createAt int64) {
	m.postsByChannel[channelID] = append(m.postsByChannel[channelID], &model.Post{
		Id:        postID,
		ChannelId: channelID,
		CreateAt:  createAt,
	})
}

func (m *mockPostService) GetPostsForChannel(channelID string, page, perPage int) (*model.PostList, error) {
	posts := m.postsByChannel[channelID]
	start := page * perPage
	if start >= len(posts) {
		return &model.PostList{Order: []string{}, Posts: map[string]*model.Post{}}, nil
	}

	end := min(start+perPage, len(posts))

	pagePosts := posts[start:end]
	order := make([]string, len(pagePosts))
	postMap := make(map[string]*model.Post, len(pagePosts))
	for i, post := range pagePosts {
		order[i] = post.Id
		postMap[post.Id] = post
	}

	return &model.PostList{Order: order, Posts: postMap}, nil
}

func (m *mockPostService) DeletePost(postID string) error {
	if m.failDeleteIDs[postID] {
		return fmt.Errorf("delete failed for %s", postID)
	}

	for channelID, posts := range m.postsByChannel {
		for i, post := range posts {
			if post.Id == postID {
				m.deleted = append(m.deleted, postID)
				m.postsByChannel[channelID] = append(posts[:i], posts[i+1:]...)
				return nil
			}
		}
	}
	return nil
}

type mockErrorLogger struct {
	messages []string
}

func (l *mockErrorLogger) Error(message string, _ ...any) {
	l.messages = append(l.messages, message)
}

func TestDeleteChannelPostsDeletesAllWhenNoCutoff(t *testing.T) {
	postSvc := newMockPostService()
	postSvc.addPost("channel-a", "post-1", time.Now().UnixMilli())
	postSvc.addPost("channel-a", "post-2", time.Now().Add(-48*time.Hour).UnixMilli())

	deleted, err := deleteChannelPosts(postSvc, "channel-a", 0, nil)
	require.NoError(t, err)
	require.Equal(t, 2, deleted)
	require.ElementsMatch(t, []string{"post-1", "post-2"}, postSvc.deleted)
}

func TestDeleteChannelPostsRespectsAgeThreshold(t *testing.T) {
	now := time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC)
	cutoff := cutoffMillis(30, now)

	postSvc := newMockPostService()
	postSvc.addPost("channel-a", "old-post", now.Add(-31*24*time.Hour).UnixMilli())
	postSvc.addPost("channel-a", "recent-post", now.Add(-5*24*time.Hour).UnixMilli())

	deleted, err := deleteChannelPosts(postSvc, "channel-a", cutoff, nil)
	require.NoError(t, err)
	require.Equal(t, 1, deleted)
	require.Equal(t, []string{"old-post"}, postSvc.deleted)
}

func TestDeleteChannelPostsDoesNotTouchOtherChannels(t *testing.T) {
	postSvc := newMockPostService()
	postSvc.addPost("channel-a", "a-post", time.Now().Add(-60*24*time.Hour).UnixMilli())
	postSvc.addPost("channel-b", "b-post", time.Now().Add(-60*24*time.Hour).UnixMilli())

	cutoff := cutoffMillis(30, time.Now())
	deleted, err := deleteChannelPosts(postSvc, "channel-a", cutoff, nil)
	require.NoError(t, err)
	require.Equal(t, 1, deleted)
	require.Equal(t, []string{"a-post"}, postSvc.deleted)
	require.Len(t, postSvc.postsByChannel["channel-b"], 1)
}

func TestDeleteChannelPostsDeletesNothingWhenAllRecent(t *testing.T) {
	now := time.Now()
	cutoff := cutoffMillis(30, now)

	postSvc := newMockPostService()
	postSvc.addPost("channel-a", "recent-1", now.Add(-1*24*time.Hour).UnixMilli())
	postSvc.addPost("channel-a", "recent-2", now.Add(-2*24*time.Hour).UnixMilli())

	deleted, err := deleteChannelPosts(postSvc, "channel-a", cutoff, nil)
	require.NoError(t, err)
	require.Equal(t, 0, deleted)
	require.Empty(t, postSvc.deleted)
}

func TestDeleteChannelPostsEmptyChannel(t *testing.T) {
	postSvc := newMockPostService()

	deleted, err := deleteChannelPosts(postSvc, "empty-channel", cutoffMillis(30, time.Now()), nil)
	require.NoError(t, err)
	require.Equal(t, 0, deleted)
}

func TestDeleteChannelPostsDeletesAcrossMultiplePages(t *testing.T) {
	postSvc := newMockPostService()
	total := postsPerPage + 50
	for i := range total {
		postSvc.addPost("channel-a", fmt.Sprintf("post-%d", i), time.Now().UnixMilli())
	}

	deleted, err := deleteChannelPosts(postSvc, "channel-a", 0, nil)
	require.NoError(t, err)
	require.Equal(t, total, deleted)
	require.Len(t, postSvc.deleted, total)
	require.Empty(t, postSvc.postsByChannel["channel-a"])
}

func TestDeleteChannelPostsAgeThresholdAcrossPagesWithRecentPosts(t *testing.T) {
	now := time.Date(2026, 7, 28, 12, 0, 0, 0, time.UTC)
	cutoff := cutoffMillis(30, now)

	postSvc := newMockPostService()
	// Newest-first style: recent posts first, then old ones beyond one page.
	for i := range postsPerPage {
		postSvc.addPost("channel-a", fmt.Sprintf("recent-%d", i), now.Add(-5*24*time.Hour).UnixMilli())
	}
	oldCount := 75
	for i := range oldCount {
		postSvc.addPost("channel-a", fmt.Sprintf("old-%d", i), now.Add(-60*24*time.Hour).UnixMilli())
	}

	deleted, err := deleteChannelPosts(postSvc, "channel-a", cutoff, nil)
	require.NoError(t, err)
	require.Equal(t, oldCount, deleted)
	require.Len(t, postSvc.postsByChannel["channel-a"], postsPerPage)
}

func TestDeleteChannelPostsLogsDeleteFailures(t *testing.T) {
	postSvc := newMockPostService()
	postSvc.addPost("channel-a", "ok-post", time.Now().UnixMilli())
	postSvc.addPost("channel-a", "bad-post", time.Now().UnixMilli())
	postSvc.failDeleteIDs["bad-post"] = true

	logger := &mockErrorLogger{}
	deleted, err := deleteChannelPosts(postSvc, "channel-a", 0, logger)
	require.NoError(t, err)
	require.Equal(t, 1, deleted)
	require.Equal(t, []string{"ok-post"}, postSvc.deleted)
	require.NotEmpty(t, logger.messages)
	require.Contains(t, logger.messages[0], "Failed to delete post")
	require.Len(t, postSvc.postsByChannel["channel-a"], 1)
}

func TestCutoffMillis(t *testing.T) {
	now := time.Date(2026, 7, 28, 0, 0, 0, 0, time.UTC)
	expected := time.Date(2026, 6, 28, 0, 0, 0, 0, time.UTC).UnixMilli()
	require.Equal(t, expected, cutoffMillis(30, now))
}