/*
   GoToSocial
   Copyright (C) 2021 GoToSocial Authors admin@gotosocial.org

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU Affero General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Affero General Public License for more details.

   You should have received a copy of the GNU Affero General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package util

import (
	"fmt"
	"regexp"
	"strings"
)

// To play around with these regexes, see: https://regex101.com/r/2km2EK/1
var (
	// mention regex can be played around with here: https://regex101.com/r/2km2EK/1
	hostnameRegexString = `(?:(?:[a-zA-Z]{1})|(?:[a-zA-Z]{1}[a-zA-Z]{1})|(?:[a-zA-Z]{1}[0-9]{1})|(?:[0-9]{1}[a-zA-Z]{1})|(?:[a-zA-Z0-9][a-zA-Z0-9-_]{1,61}[a-zA-Z0-9]))\.(?:[a-zA-Z]{2,6}|[a-zA-Z0-9-]{2,30}\.[a-zA-Z]{2,5}))`
	mentionRegexString  = fmt.Sprintf(`(?: |^|\W)(@[a-zA-Z0-9_]+@%s(?: |\n)`, hostnameRegexString)
	mentionRegex        = regexp.MustCompile(mentionRegexString)
	// hashtag regex can be played with here: https://regex101.com/r/Vhy8pg/1
	hashtagRegexString = `(?: |^|\W)?#([a-zA-Z0-9]{1,30})(?:\b|\r)`
	hashtagRegex = regexp.MustCompile(hashtagRegexString)
	// emoji regex can be played with here: https://regex101.com/r/478XGM/1
	emojiRegexString = `(?: |^|\W)?:([a-zA-Z0-9_]{2,30}):(?:\b|\r)?`
	emojiRegex = regexp.MustCompile(emojiRegexString)
)

// DeriveMentions takes a plaintext (ie., not html-formatted) status,
// and applies a regex to it to return a deduplicated list of accounts
// mentioned in that status.
//
// It will look for fully-qualified account names in the form "@user@example.org".
// Mentions that are just in the form "@username" will not be detected.
// The case of the returned mentions will be lowered, for consistency.
func DeriveMentions(status string) []string {
	mentionedAccounts := []string{}
	for _, m := range mentionRegex.FindAllStringSubmatch(status, -1) {
		mentionedAccounts = append(mentionedAccounts, m[1])
	}
	return Lower(Unique(mentionedAccounts))
}

// DeriveHashtags takes a plaintext (ie., not html-formatted) status,
// and applies a regex to it to return a deduplicated list of hashtags
// used in that status, without the leading #. The case of the returned
// tags will be lowered, for consistency.
func DeriveHashtags(status string) []string {
	tags := []string{}
	for _, m := range hashtagRegex.FindAllStringSubmatch(status, -1) {
		tags = append(tags, m[1])
	}
	return Lower(Unique(tags))
}

// DeriveEmojis takes a plaintext (ie., not html-formatted) status,
// and applies a regex to it to return a deduplicated list of emojis
// used in that status, without the surround ::. The case of the returned
// emojis will be lowered, for consistency.
func DeriveEmojis(status string) []string {
	emojis := []string{}
	for _, m := range emojiRegex.FindAllStringSubmatch(status, -1) {
		emojis = append(emojis, m[1])
	}
	return Lower(Unique(emojis))
}

// Unique returns a deduplicated version of a given string slice.
func Unique(s []string) []string {
	keys := make(map[string]bool)
	list := []string{}
	for _, entry := range s {
		if _, value := keys[entry]; !value {
			keys[entry] = true
			list = append(list, entry)
		}
	}
	return list
}

// Lower lowercases all strings in a given string slice
func Lower(s []string) []string {
	new := []string{}
	for _, i := range s {
		new = append(new, strings.ToLower(i))
	}
	return new
}

// HTMLFormat takes a plaintext formatted status string, and converts it into
// a nice HTML-formatted string.
//
// This includes:
// - Replacing line-breaks with <p>
// - Replacing URLs with hrefs.
// - Replacing mentions with links to that account's URL as stored in the database.
func HTMLFormat(status string) string {
	// TODO: write proper HTML formatting logic for a status
	return status
}