package store

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"sort"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5/pgconn"

	"plumber/internal/pacific"
	"plumber/internal/store/sqlc"
)

var (
	ErrInvalidPost    = errors.New("invalid post")
	ErrPostNotVotable = errors.New("post not votable")
)

type PostState string

const (
	PostStateVisible PostState = "visible"
	PostStateHidden  PostState = "hidden"
	PostStateLocked  PostState = "locked"
)

// Post is either a root question (ParentID nil) or a reply to another post.
type Post struct {
	ID         string
	ParentID   *string
	AuthorID   string
	AuthorName string
	AuthorRole Role
	Title      string
	Body       string
	City       string
	PostDate   string
	PostState  PostState
	CreatedAt  string
	UpdatedAt  string
	Score      int
	Answered   bool
	UserVote   int
	Replies    []*Post
	db         *sql.DB
}

// NewPost returns a post bound to db.
func NewPost(db *sql.DB) *Post {
	return &Post{db: db}
}

// Create inserts a root post or reply according to ParentID.
func (p *Post) Create(ctx context.Context) error {
	if p == nil || p.db == nil {
		return fmt.Errorf("post: no database")
	}
	if err := preparePost(p); err != nil {
		return err
	}
	err := sqlc.New(p.db).CreatePost(ctx, sqlc.CreatePostParams{
		ID:        p.ID,
		ParentID:  nullableParentID(p.ParentID),
		AuthorID:  p.AuthorID,
		Title:     p.Title,
		Body:      p.Body,
		City:      p.City,
		PostDate:  p.PostDate,
		PostState: string(p.PostState),
		CreatedAt: p.CreatedAt,
		UpdatedAt: p.UpdatedAt,
	})
	return mapPostCreateError(err)
}

// Update changes only the post body and update timestamp.
func (p *Post) Update(ctx context.Context) error {
	if p == nil || p.db == nil {
		return fmt.Errorf("post: no database")
	}
	p.Body = strings.TrimSpace(p.Body)
	if p.Body == "" {
		return fmt.Errorf("%w: body is required", ErrInvalidPost)
	}
	p.UpdatedAt = time.Now().UTC().Format(time.RFC3339Nano)
	n, err := sqlc.New(p.db).UpdatePost(ctx, sqlc.UpdatePostParams{
		ID:        p.ID,
		Body:      p.Body,
		UpdatedAt: p.UpdatedAt,
	})
	if err != nil {
		return err
	}
	if n == 0 {
		return sql.ErrNoRows
	}
	return nil
}

func preparePost(p *Post) error {
	p.ID = strings.TrimSpace(p.ID)
	p.AuthorID = strings.TrimSpace(p.AuthorID)
	p.Title = strings.TrimSpace(p.Title)
	p.Body = strings.TrimSpace(p.Body)
	p.City = strings.TrimSpace(p.City)
	p.PostDate = strings.TrimSpace(p.PostDate)
	if p.PostState == "" {
		p.PostState = PostStateVisible
	}
	switch p.PostState {
	case PostStateVisible, PostStateHidden, PostStateLocked:
	default:
		return fmt.Errorf("%w: invalid post state", ErrInvalidPost)
	}
	if p.AuthorID == "" {
		return fmt.Errorf("%w: author is required", ErrInvalidPost)
	}
	if p.Body == "" {
		return fmt.Errorf("%w: body is required", ErrInvalidPost)
	}
	if p.ParentID == nil {
		if p.Title == "" {
			return fmt.Errorf("%w: root title is required", ErrInvalidPost)
		}
		if p.PostDate == "" {
			p.PostDate = pacific.Today()
		}
	} else {
		parentID := strings.TrimSpace(*p.ParentID)
		if parentID == "" {
			return fmt.Errorf("%w: parent is required", ErrInvalidPost)
		}
		p.ParentID = &parentID
		if p.Title != "" || p.City != "" || p.PostDate != "" || p.PostState != PostStateVisible {
			return fmt.Errorf("%w: reply contains root-only fields", ErrInvalidPost)
		}
	}
	if p.ID == "" {
		p.ID = uuid.NewString()
	}
	now := time.Now().UTC().Format(time.RFC3339Nano)
	if p.CreatedAt == "" {
		p.CreatedAt = now
	}
	if p.UpdatedAt == "" {
		p.UpdatedAt = p.CreatedAt
	}
	return nil
}

func nullableParentID(parentID *string) sql.NullString {
	if parentID == nil {
		return sql.NullString{}
	}
	return sql.NullString{String: *parentID, Valid: true}
}

func parentIDFromNull(parentID sql.NullString) *string {
	if !parentID.Valid {
		return nil
	}
	id := parentID.String
	return &id
}

func mapPostCreateError(err error) error {
	if err == nil {
		return nil
	}
	var pgErr *pgconn.PgError
	if errors.As(err, &pgErr) {
		switch pgErr.Code {
		case "23503", "23505", "23514":
			return fmt.Errorf("%w: %v", ErrInvalidPost, err)
		}
	}
	return err
}

func postFromValues(
	db *sql.DB,
	id string,
	parentID sql.NullString,
	authorID, authorName, authorRole, title, body, city, postDate string,
	postState string,
	createdAt, updatedAt string,
) Post {
	return Post{
		ID:         id,
		ParentID:   parentIDFromNull(parentID),
		AuthorID:   authorID,
		AuthorName: authorName,
		AuthorRole: Role(authorRole),
		Title:      title,
		Body:       body,
		City:       city,
		PostDate:   postDate,
		PostState:  PostState(postState),
		CreatedAt:  createdAt,
		UpdatedAt:  updatedAt,
		db:         db,
	}
}

// GetPost returns one post without loading its replies.
func GetPost(ctx context.Context, db *sql.DB, id string) (*Post, error) {
	r, err := sqlc.New(db).GetPost(ctx, id)
	if err != nil {
		return nil, err
	}
	p := postFromValues(
		db,
		r.ID,
		r.ParentID,
		r.AuthorID,
		r.AuthorName,
		r.AuthorRole,
		r.Title,
		r.Body,
		r.City,
		r.PostDate,
		r.PostState,
		r.CreatedAt,
		r.UpdatedAt,
	)
	return &p, nil
}

// GetPostThread returns a root post with all descendants nested under Replies.
func GetPostThread(ctx context.Context, db *sql.DB, rootID string) (*Post, error) {
	rows, err := sqlc.New(db).ListPostThread(ctx, rootID)
	if err != nil {
		return nil, err
	}
	posts := make([]Post, 0, len(rows))
	for _, r := range rows {
		posts = append(posts, postFromValues(
			db,
			r.ID,
			r.ParentID,
			r.AuthorID,
			r.AuthorName,
			r.AuthorRole,
			r.Title,
			r.Body,
			r.City,
			r.PostDate,
			r.PostState,
			r.CreatedAt,
			r.UpdatedAt,
		))
	}
	return buildPostTree(posts, rootID)
}

func buildPostTree(posts []Post, rootID string) (*Post, error) {
	byID := make(map[string]*Post, len(posts))
	for i := range posts {
		posts[i].Replies = nil
		byID[posts[i].ID] = &posts[i]
	}
	root, ok := byID[rootID]
	if !ok || root.ParentID != nil {
		return nil, sql.ErrNoRows
	}
	for i := range posts {
		post := &posts[i]
		if post.ID == rootID {
			continue
		}
		if post.ParentID == nil {
			return nil, fmt.Errorf("post %s is not in thread %s", post.ID, rootID)
		}
		parent, ok := byID[*post.ParentID]
		if !ok {
			return nil, fmt.Errorf("post %s has missing parent %s", post.ID, *post.ParentID)
		}
		parent.Replies = append(parent.Replies, post)
	}
	var sortReplies func(*Post)
	sortReplies = func(post *Post) {
		sort.Slice(post.Replies, func(i, j int) bool {
			if post.Replies[i].CreatedAt != post.Replies[j].CreatedAt {
				return post.Replies[i].CreatedAt < post.Replies[j].CreatedAt
			}
			return post.Replies[i].ID < post.Replies[j].ID
		})
		for _, reply := range post.Replies {
			sortReplies(reply)
		}
	}
	sortReplies(root)
	return root, nil
}

// ListRootPosts returns visible root posts for a post date.
func ListRootPosts(ctx context.Context, db *sql.DB, postDate, viewerID string) ([]Post, error) {
	rows, err := sqlc.New(db).ListRootPosts(ctx, sqlc.ListRootPostsParams{
		ViewerID:    viewerID,
		RowLimit:    HuntListLimit,
		PostDate:    postDate,
		HiddenState: string(PostStateHidden),
	})
	if err != nil {
		return nil, err
	}
	posts := make([]Post, 0, len(rows))
	for _, r := range rows {
		post := postFromValues(
			db,
			r.ID,
			r.ParentID,
			r.AuthorID,
			r.AuthorName,
			r.AuthorRole,
			r.Title,
			r.Body,
			r.City,
			r.PostDate,
			r.PostState,
			r.CreatedAt,
			r.UpdatedAt,
		)
		post.Score = int(r.Score)
		post.Answered = r.Answered
		post.UserVote = int(r.UserVote)
		posts = append(posts, post)
	}
	return posts, nil
}

// SetPostVote sets value to 1, -1, or 0 on a visible root post.
func SetPostVote(ctx context.Context, db *sql.DB, userID, postID string, value int) error {
	if value != 1 && value != -1 && value != 0 {
		return fmt.Errorf("invalid vote")
	}
	q := sqlc.New(db)
	if value == 0 {
		visible, err := q.PostIsVisibleRoot(ctx, sqlc.PostIsVisibleRootParams{
			ID:          postID,
			HiddenState: string(PostStateHidden),
		})
		if err != nil {
			return err
		}
		if !visible {
			return ErrPostNotVotable
		}
		return q.DeletePostVote(ctx, sqlc.DeletePostVoteParams{
			UserID: userID,
			PostID: postID,
		})
	}
	n, err := q.UpsertPostVoteOnVisibleRoot(ctx, sqlc.UpsertPostVoteOnVisibleRootParams{
		UserID:      userID,
		PostID:      postID,
		Value:       int32(value),
		HiddenState: string(PostStateHidden),
	})
	if err != nil {
		return err
	}
	if n == 0 {
		return ErrPostNotVotable
	}
	return nil
}