package storage

import (
	"context"
	"fmt"

	"git.obamna.ru/erius/ozon-task/graph/model"
)

type InMemory struct {
	postId    uint
	commentId uint
	posts     []*model.Post
	comments  []*model.Comment
}

func InitInMemory() *InMemory {
	return &InMemory{
		postId:    0,
		commentId: 0,
		posts:     make([]*model.Post, 0),
		comments:  make([]*model.Comment, 0),
	}
}

func (s *InMemory) AddPost(input *model.PostInput) (*model.AddResult, error) {
	post := model.PostFromInput(input)
	s.insertPost(post)
	return &model.AddResult{ItemID: &post.ID}, nil
}

func (s *InMemory) AddReplyToComment(input *model.CommentInput) (*model.AddResult, error) {
	if !s.commentExists(*input.ParentCommentID) {
		return nil, &IDNotFoundError{objName: "comment", id: *input.ParentCommentID}
	}
	comment, parent := model.CommentFromInput(input), s.comments[*input.ParentCommentID]
	s.insertComment(comment)
	parent.Replies = append(parent.Replies, comment)
	return &model.AddResult{ItemID: &comment.ID}, nil
}

func (s *InMemory) AddCommentToPost(input *model.CommentInput) (*model.AddResult, error) {
	if !s.postExists(*input.ParentPostID) {
		return nil, &IDNotFoundError{objName: "post", id: *input.ParentPostID}
	}
	parent := s.posts[*input.ParentPostID]
	if !parent.AllowComments {
		return nil, fmt.Errorf("author disabled comments for this post")
	}
	comment := model.CommentFromInput(input)
	comment.RootComment = true
	s.insertComment(comment)
	parent.Comments = append(parent.Comments, comment)
	return &model.AddResult{ItemID: &comment.ID}, nil
}

func (s *InMemory) GetPost(id uint, ctx context.Context) (*model.Post, error) {
	if !s.postExists(id) {
		return nil, &IDNotFoundError{objName: "post", id: id}
	}
	return s.posts[id], nil
}

func (s *InMemory) GetComment(id uint, ctx context.Context) (*model.Comment, error) {
	if !s.commentExists(id) {
		return nil, &IDNotFoundError{objName: "comment", id: id}
	}
	return s.comments[id], nil
}

func (s *InMemory) GetPosts(first uint, cursor *uint, ctx context.Context) (*model.PostsConnection, error) {
	start := uint(0)
	if cursor != nil {
		start = *cursor + 1
	}
	if !s.postExists(start) {
		return &model.EmptyPostsConnections, nil
	}
	nextPage, until := true, start+first
	if !s.postExists(until) {
		nextPage = false
		until = uint(len(s.posts))
	}
	info, edges := &model.PageInfo{
		StartCursor: start,
		EndCursor:   until - 1,
		HasNextPage: nextPage,
	}, make([]*model.PostsEdge, until-start)
	for i, p := range s.posts[start:until] {
		edges[i] = &model.PostsEdge{
			Cursor: p.ID,
			Node:   p,
		}
	}
	return &model.PostsConnection{
		Edges:    edges,
		PageInfo: info,
	}, nil
}

func (s *InMemory) GetComments(post *model.Post, first uint, cursor *uint, ctx context.Context) (*model.CommentsConnection, error) {
	return getCommentsFrom(post.Comments, first, cursor), nil
}

func (s *InMemory) GetReplies(comment *model.Comment, first uint, cursor *uint, ctx context.Context) (*model.CommentsConnection, error) {
	return getCommentsFrom(comment.Replies, first, cursor), nil
}

func getCommentsFrom(source []*model.Comment, first uint, cursor *uint) *model.CommentsConnection {
	start := uint(0)
	if cursor != nil {
		start = *cursor + 1
	}
	if start >= uint(len(source)) {
		return &model.EmptyCommentsConnection
	}
	nextPage, until := true, start+first
	if until >= uint(len(source)) {
		nextPage = false
		until = uint(len(source))
	}
	info, edges := &model.PageInfo{
		StartCursor: start,
		EndCursor:   until - 1,
		HasNextPage: nextPage,
	}, make([]*model.CommentsEdge, until-start)
	for i, c := range source[start:until] {
		edges[i] = &model.CommentsEdge{
			Cursor: c.ID,
			Node:   c,
		}
	}
	return &model.CommentsConnection{
		Edges:    edges,
		PageInfo: info,
	}
}

func (s *InMemory) postExists(id uint) bool {
	return id < uint(len(s.posts))
}

func (s *InMemory) commentExists(id uint) bool {
	return id < uint(len(s.comments))
}

func (s *InMemory) insertComment(comment *model.Comment) {
	comment.ID = s.commentId
	s.comments = append(s.comments, comment)
	s.commentId++
}

func (s *InMemory) insertPost(post *model.Post) {
	post.ID = s.postId
	s.posts = append(s.posts, post)
	s.postId++
}