package main

import (
	"encoding/json"
	"flag"
	"io/ioutil"
	"log"
	"sort"
)

/*************************** meeting.go ***************************/
type Invitee struct {
	Id   int `json:"id"`
	Rank int `json:"rank"`
}

type Meeting struct {
	MeetingId   int        `json:"meeting_id"`
	OrganiserId int        `json:"organiser_id"`
	Rank        int        `json:"rank"`
	BeginTime   int64      `json:"begin_time"`
	EndTime     int64      `json:"end_time"`
	Invitees    []*Invitee `json:"invitees"`
}

func (m *Meeting) AverageInviteeRank() float64 {
	sum := 0
	for _, i := range m.Invitees {
		sum += i.Rank
	}

	return float64(sum) / float64(len(m.Invitees))
}

func IsConflicting(m1, m2 *Meeting) bool {
	if m1.BeginTime < m2.BeginTime {
		return m1.EndTime > m2.BeginTime
	} else {
		return m2.EndTime > m1.BeginTime
	}
}

// for sorting based on meeting begin time
type MeetingSlice []*Meeting

func (ms MeetingSlice) Len() int {
	return len(ms)
}

func (ms MeetingSlice) Swap(i, j int) {
	ms[i], ms[j] = ms[j], ms[i]
}

func (ms MeetingSlice) Less(i, j int) bool {
	return ms[i].BeginTime < ms[j].BeginTime
}

// for sorting based on meeting priority
type MeetingPrioritySlice struct {
	Meetings []*Meeting
	CRE      ConflictResolutionEngine
	OwnerId  int
}

func (mps MeetingPrioritySlice) Len() int {
	return len(mps.Meetings)
}

func (mps MeetingPrioritySlice) Swap(i, j int) {
	mps.Meetings[i], mps.Meetings[j] = mps.Meetings[j], mps.Meetings[i]
}

func (mps MeetingPrioritySlice) Less(i, j int) bool {
	return mps.CRE.Less(mps.OwnerId, mps.Meetings[i], mps.Meetings[j])
}

/*************************** calendar.go ***************************/
type Calendar struct {
	OwnerId  int        `json:"owner_id"`
	Meetings []*Meeting `json:"meetings`
}

type EmptySlot struct {
	BeginTime int64 `json:"begin_time"`
	EndTime   int64 `json:"end_time"`
}

func (c *Calendar) findConflicts() [][]*Meeting {
	conflicts := make([][]*Meeting, 0)
	for i := 0; i < len(c.Meetings); i++ {
		for j := i + 1; j < len(c.Meetings); j++ {
			if IsConflicting(c.Meetings[i], c.Meetings[j]) {
				conflicts = append(conflicts, []*Meeting{c.Meetings[i], c.Meetings[j]})
			}
		}
	}

	return conflicts
}

// TODO: we currently modify the list of meetings in a
// calendar to the resolved list of meetings
func (c *Calendar) resolveConflicts(cre ConflictResolutionEngine) []*Meeting {
	mps := MeetingPrioritySlice{
		Meetings: c.Meetings,
		CRE:      cre,
		OwnerId:  c.OwnerId,
	}
	sort.Sort(mps)

	for i := 0; i < len(c.Meetings); i++ {
		if c.Meetings[i] == nil {
			continue
		}

		for j := i + 1; j < len(c.Meetings); j++ {
			if c.Meetings[j] == nil {
				continue
			}

			if IsConflicting(c.Meetings[i], c.Meetings[j]) {
				c.Meetings[j] = nil
			}
		}
	}

	resolved_meetings := make([]*Meeting, 0)
	for i := 0; i < len(c.Meetings); i++ {
		if c.Meetings[i] != nil {
			// TODO: pointer copy only!
			resolved_meetings = append(resolved_meetings, c.Meetings[i])
		}
	}

	c.Meetings = resolved_meetings
	return c.Meetings
}

func (c *Calendar) FindFreeSlots() []*EmptySlot {
	sort.Sort(MeetingSlice(c.Meetings))

	empty_slots := make([]*EmptySlot, 0)
	for i := 1; i < len(c.Meetings); i++ {
		if c.Meetings[i-1].EndTime != c.Meetings[i].BeginTime {
			empty_slots = append(empty_slots, &EmptySlot{
				BeginTime: c.Meetings[i-1].EndTime,
				EndTime:   c.Meetings[i].BeginTime,
			})
		}
	}

	return empty_slots
}

/*************************** engines.go ***************************/
// return -1, 0, 1
type Rule func(int, *Meeting, *Meeting) int
type ConflictResolutionEngine []Rule

// lower the value, higher the priority
func (cre ConflictResolutionEngine) Less(owner_id int, m1, m2 *Meeting) bool {
	for _, rule := range cre {
		ret := rule(owner_id, m1, m2)
		if ret == 1 {
			return true
		} else if ret == -1 {
			return false
		}
	}

	// if no decision yet, simply return true
	return true
}

func Rule1(owner_id int, m1, m2 *Meeting) int {
	if m1.OrganiserId == m2.OrganiserId {
		return 0
	} else {
		if m1.OrganiserId == owner_id {
			return 1
		} else if m2.OrganiserId == owner_id {
			return -1
		} else {
			return 0
		}
	}
}

func Rule2(owner_id int, m1, m2 *Meeting) int {
	if m1.Rank == m2.Rank {
		return 0
	} else if m1.Rank < m2.Rank {
		return 1
	} else {
		return -1
	}
}

func Rule3(owner_id int, m1, m2 *Meeting) int {
	if len(m1.Invitees) == len(m2.Invitees) {
		return 0
	} else if len(m1.Invitees) > len(m2.Invitees) {
		return 1
	} else {
		return -1
	}
}

func Rule4(owner_id int, m1, m2 *Meeting) int {
	m1_avg_rank := m1.AverageInviteeRank()
	m2_avg_rank := m2.AverageInviteeRank()
	if m1_avg_rank == m2_avg_rank {
		return 0
	} else if m1_avg_rank < m2_avg_rank {
		return 1
	} else {
		return -1
	}
}

/*************************** input.json ***************************/
// {
// 	"cmd": 1,
// 	"engine": "simple",
// 	"calendars": [
// 		{
// 			"owner_id": 1,
// 			"meetings": [
// 				{
// 					"meeting_id": 1,
// 					"organiser_id": 1,
// 					"rank": 1,
// 					"begin_time": 23,
// 					"end_time": 34,
// 					"invitees": [
// 						{
// 							"id": 1,
// 							"rank": 1
// 						}
// 					]
// 				},
// 				{
// 					"meeting_id": 2,
// 					"organiser_id": 1,
// 					"rank": 1,
// 					"begin_time": 26,
// 					"end_time": 35,
// 					"invitees": [
// 						{
// 							"id": 1,
// 							"rank": 1
// 						}
// 					]
// 				}
// 			]
// 		}
// 	]
// }

/************************** main.go **************************/
type Command struct {
	Cmd       int         `json:"cmd"`
	Engine    string      `json:"engine"`
	Calendars []*Calendar `json:"calendars"`
}

func main() {
	output_file := flag.String("o", "output.json", "output file to dump data into")
	input_file := flag.String("i", "input.json", "input file to read json data from")
	flag.Parse()

	jdata, err := ioutil.ReadFile(*input_file)
	if err != nil {
		log.Println(err)
		log.Fatalf("[ERROR] unable to read input file %s", *input_file)
	}

	var command Command
	err = json.Unmarshal(jdata, &command)
	if err != nil {
		log.Println(err)
		log.Fatal("[ERROR] unable to parse input file")
	}

	// define engines
	SimpleEngine := ConflictResolutionEngine([]Rule{Rule1, Rule2, Rule3})
	ComplexEngine := ConflictResolutionEngine([]Rule{Rule1, Rule2, Rule3, Rule4})
	var cre ConflictResolutionEngine
	if command.Engine == "simple" {
		cre = SimpleEngine
	} else if command.Engine == "complex" {
		cre = ComplexEngine
	} else {
		log.Fatal("[ERROR] unknown conflict resolution engine!")
	}

	switch command.Cmd {
	case 1:
		// find list of conflicting meetings, given a calendar
		calendar := command.Calendars[0]
		data, err := json.MarshalIndent(calendar.findConflicts(), "", "  ")
		if err != nil {
			log.Println(err)
			log.Fatal("[ERROR] error in marshaling the conflicting meetings")
		}
		ioutil.WriteFile(*output_file, data, 0644)

	case 2:
		// find resolved calendar, given a calendar
		calendar := command.Calendars[0]
		data, err := json.MarshalIndent(calendar.resolveConflicts(cre), "", "  ")
		if err != nil {
			log.Println(err)
			log.Fatal("[ERROR] error in marshaling the resolved calendar")
		}
		ioutil.WriteFile(*output_file, data, 0644)

	case 3:
		// find free slots in a calendar
		calendar := command.Calendars[0]
		calendar.resolveConflicts(cre)

		data, err := json.MarshalIndent(calendar.FindFreeSlots(), "", "  ")
		if err != nil {
			log.Println(err)
			log.Fatal("[ERROR] error in marshaling free meeting slots")
		}
		ioutil.WriteFile(*output_file, data, 0644)
	case 4:
		// find common free slot of given time in 2 given calendar
	}

	log.Println("[_INFO] stored output in", *output_file)
}