package db

import (
	"context"
	"regexp"

	"emperror.dev/errors"
	"github.com/bwmarrin/discordgo"
	"github.com/georgysavva/scany/pgxscan"
	"github.com/jackc/pgconn"
	"github.com/jackc/pgx/v4"
	"github.com/rs/xid"
)

type User struct {
	ID          xid.ID
	Username    string
	DisplayName *string
	Bio         *string

	AvatarURLs []string `db:"avatar_urls"`
	Links      []string

	Discord         *string
	DiscordUsername *string

	MaxInvites int
}

// usernames must match this regex
var usernameRegex = regexp.MustCompile(`^[\w-.]{2,40}$`)

const (
	ErrUserNotFound = errors.Sentinel("user not found")

	ErrUsernameTaken    = errors.Sentinel("username is already taken")
	ErrInvalidUsername  = errors.Sentinel("username contains invalid characters")
	ErrUsernameTooShort = errors.Sentinel("username is too short")
	ErrUsernameTooLong  = errors.Sentinel("username is too long")
)

const (
	MaxUsernameLength    = 40
	MaxDisplayNameLength = 100
	MaxUserBioLength     = 1000
	MaxUserLinksLength   = 25
	MaxLinkLength        = 256
)

// CreateUser creates a user with the given username.
func (db *DB) CreateUser(ctx context.Context, tx pgx.Tx, username string) (u User, err error) {
	// check if the username is valid
	// if not, return an error depending on what failed
	if !usernameRegex.MatchString(username) {
		if len(username) < 2 {
			return u, ErrUsernameTooShort
		} else if len(username) > 40 {
			return u, ErrUsernameTooLong
		}

		return u, ErrInvalidUsername
	}

	sql, args, err := sq.Insert("users").Columns("id", "username").Values(xid.New(), username).Suffix("RETURNING *").ToSql()
	if err != nil {
		return u, errors.Wrap(err, "building sql")
	}

	err = pgxscan.Get(ctx, tx, &u, sql, args...)
	if err != nil {
		if v, ok := errors.Cause(err).(*pgconn.PgError); ok {
			if v.Code == "23505" { // unique constraint violation
				return u, ErrUsernameTaken
			}
		}

		return u, errors.Cause(err)
	}

	return u, nil
}

// DiscordUser fetches a user by Discord user ID.
func (db *DB) DiscordUser(ctx context.Context, discordID string) (u User, err error) {
	sql, args, err := sq.Select("*").From("users").Where("discord = ?", discordID).ToSql()
	if err != nil {
		return u, errors.Wrap(err, "building sql")
	}

	err = pgxscan.Get(ctx, db, &u, sql, args...)
	if err != nil {
		if errors.Cause(err) == pgx.ErrNoRows {
			return u, ErrUserNotFound
		}
		return u, errors.Cause(err)
	}

	return u, nil
}

func (u *User) UpdateFromDiscord(ctx context.Context, db pgxscan.Querier, du *discordgo.User) error {
	builder := sq.Update("users").
		Set("discord", du.ID).
		Set("discord_username", du.String()).
		Where("id = ?", u.ID).
		Suffix("RETURNING *")

	sql, args, err := builder.ToSql()
	if err != nil {
		return errors.Wrap(err, "building sql")
	}

	return pgxscan.Get(ctx, db, u, sql, args...)
}

func (db *DB) getUser(ctx context.Context, q pgxscan.Querier, id xid.ID) (u User, err error) {
	err = pgxscan.Get(ctx, q, &u, "select * from users where id = $1", id)
	if err != nil {
		if errors.Cause(err) == pgx.ErrNoRows {
			return u, ErrUserNotFound
		}

		return u, errors.Cause(err)
	}

	return u, nil
}

// User gets a user by ID.
func (db *DB) User(ctx context.Context, id xid.ID) (u User, err error) {
	return db.getUser(ctx, db, id)
}

// Username gets a user by username.
func (db *DB) Username(ctx context.Context, name string) (u User, err error) {
	err = pgxscan.Get(ctx, db, &u, "select * from users where username = $1", name)
	if err != nil {
		if errors.Cause(err) == pgx.ErrNoRows {
			return u, ErrUserNotFound
		}

		return u, errors.Cause(err)
	}

	return u, nil
}

// UsernameTaken checks if the given username is already taken.
func (db *DB) UsernameTaken(ctx context.Context, username string) (valid, taken bool, err error) {
	if !usernameRegex.MatchString(username) {
		return false, false, nil
	}

	err = db.QueryRow(ctx, "select exists (select id from users where username = $1)", username).Scan(&taken)
	return true, taken, err
}

// UpdateUsername validates the given username, then updates the given user's name to it if valid.
func (db *DB) UpdateUsername(ctx context.Context, tx pgx.Tx, id xid.ID, newName string) error {
	if !usernameRegex.MatchString(newName) {
		return ErrInvalidUsername
	}

	sql, args, err := sq.Update("users").Set("username", newName).Where("id = ?", id).ToSql()
	if err != nil {
		return errors.Wrap(err, "building sql")
	}

	_, err = db.Exec(ctx, sql, args...)
	if err != nil {
		pge := &pgconn.PgError{}
		if errors.As(err, &pge) {
			// unique constraint violation
			if pge.Code == "23505" {
				return ErrUsernameTaken
			}
		}

		return errors.Wrap(err, "executing query")
	}
	return nil
}

func (db *DB) UpdateUser(
	ctx context.Context,
	tx pgx.Tx, id xid.ID,
	displayName, bio *string,
	links *[]string,
	avatarURLs []string,
) (u User, err error) {
	if displayName == nil && bio == nil && links == nil && avatarURLs == nil {
		return db.getUser(ctx, tx, id)
	}

	builder := sq.Update("users").Where("id = ?", id)
	if displayName != nil {
		if *displayName == "" {
			builder = builder.Set("display_name", nil)
		} else {
			builder = builder.Set("display_name", *displayName)
		}
	}
	if bio != nil {
		if *bio == "" {
			builder = builder.Set("bio", nil)
		} else {
			builder = builder.Set("bio", *bio)
		}
	}
	if links != nil {
		if len(*links) == 0 {
			builder = builder.Set("links", nil)
		} else {
			builder = builder.Set("links", *links)
		}
	}

	if avatarURLs != nil {
		if len(avatarURLs) == 0 {
			builder = builder.Set("avatar_urls", nil)
		} else {
			builder = builder.Set("avatar_urls", avatarURLs)
		}
	}

	sql, args, err := builder.Suffix("RETURNING *").ToSql()
	if err != nil {
		return u, errors.Wrap(err, "building sql")
	}

	err = pgxscan.Get(ctx, tx, &u, sql, args...)
	if err != nil {
		return u, errors.Wrap(err, "executing sql")
	}

	return u, nil
}