// maubot - A plugin-based Matrix bot system written in Go.
// Copyright (C) 2018 Tulir Asokan
//
// 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 <https://www.gnu.org/licenses/>.

package matrix

import (
	"fmt"
	"regexp"
	"strings"

	log "maunium.net/go/maulogger"

	"maubot.xyz"
)

type ParsedCommand struct {
	Name         string
	StartsWith   string
	Matches      *regexp.Regexp
	MatchAgainst string
	MatchesEvent *maubot.Event
}

func (pc *ParsedCommand) parseCommandSyntax(command maubot.Command) error {
	regexBuilder := &strings.Builder{}
	swBuilder := &strings.Builder{}
	argumentEncountered := false

	regexBuilder.WriteRune('^')
	words := strings.Split(command.Syntax, " ")
	for i, word := range words {
		argument, ok := command.Arguments[word]
		if ok {
			argumentEncountered = true
			regex := argument.Matches
			if argument.Required {
				regex = fmt.Sprintf("(?:%s)?", regex)
			}
			regexBuilder.WriteString(regex)
		} else {
			if !argumentEncountered {
				swBuilder.WriteString(word)
			}
			regexBuilder.WriteString(regexp.QuoteMeta(word))
		}

		if i < len(words) - 1 {
			if !argumentEncountered {
				swBuilder.WriteRune(' ')
			}
			regexBuilder.WriteRune(' ')
		}
	}
	regexBuilder.WriteRune('$')

	var err error
	pc.StartsWith = swBuilder.String()
	// Trim the extra space at the end added in the parse loop
	pc.StartsWith = pc.StartsWith[:len(pc.StartsWith)-1]
	pc.Matches, err = regexp.Compile(regexBuilder.String())
	pc.MatchAgainst = "body"
	return err
}

func (pc *ParsedCommand) parsePassiveCommandSyntax(command maubot.PassiveCommand) error {
	pc.MatchAgainst = command.MatchAgainst
	var err error
	pc.Matches, err = regexp.Compile(command.Matches)
	pc.MatchesEvent = command.MatchEvent
	return err
}

func ParseSpec(spec *maubot.CommandSpec) (commands []*ParsedCommand) {
	for _, command := range spec.Commands {
		parsing := &ParsedCommand{
			Name: command.Syntax,
		}
		err := parsing.parseCommandSyntax(command)
		if err != nil {
			log.Warnf("Failed to parse regex of command %s: %v\n", command.Syntax, err)
			continue
		}
		commands = append(commands, parsing)
	}
	for _, command := range spec.PassiveCommands {
		parsing := &ParsedCommand{
			Name: command.Name,
		}
		err := parsing.parsePassiveCommandSyntax(command)
		if err != nil {
			log.Warnf("Failed to parse regex of passive command %s: %v\n", command.Name, err)
			continue
		}
		commands = append(commands, parsing)
	}
	return commands
}

func deepGet(from map[string]interface{}, path string) interface{} {
	for {
		dotIndex := strings.IndexRune(path, '.')
		if dotIndex == -1 {
			return from[path]
		}

		var key string
		key, path = path[:dotIndex], path[dotIndex+1:]
		var ok bool
		from, ok = from[key].(map[string]interface{})
		if !ok {
			return nil
		}
	}
}

func (pc *ParsedCommand) Match(evt *maubot.Event) bool {
	matchAgainst, ok := deepGet(evt.Content.Raw, pc.MatchAgainst).(string)
	if !ok {
		matchAgainst = evt.Content.Body
	}

	return strings.HasPrefix(matchAgainst, pc.StartsWith) &&
		pc.Matches.MatchString(matchAgainst) &&
		(pc.MatchesEvent == nil || pc.MatchesEvent.Equals(evt))
}