package cal

import (
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"
	_ "time/tzdata" // TZID= resolution; 9front has no zoneinfo

	"github.com/emersion/go-ical"
	"github.com/teambition/rrule-go"
)

// Event is one VEVENT, with its recurrence set resolved but not expanded.
type Event struct {
	UID         string
	Summary     string
	Location    string
	Description string
	Start       time.Time
	End         time.Time
	AllDay      bool
	RRule       string
	Alarms      []time.Duration // relative to start; negative means before
	Raw         string
	RecurID     time.Time // set when this event overrides one instance
	Cancelled   bool
	Organizer   string
	Attendees   []Attendee
	master      *Event           // set on an override: the series it belongs to
	set         *rrule.Set       // nil when the event does not recur
	overrides   map[int64]*Event // by RECURRENCE-ID, unix seconds
}

// Attendee is one ATTENDEE line, reduced to what a person wants to see.
type Attendee struct {
	Name     string // CN
	Email    string // the mailto: value, stripped
	Partstat string // NEEDS-ACTION, ACCEPTED, DECLINED, TENTATIVE
	Role     string
}

// Instance is one occurrence of an Event at a concrete time.
type Instance struct {
	Ev    *Event
	Start time.Time
	End   time.Time
}

// Duration of a single occurrence.
func (e *Event) dur() time.Duration {
	if e.End.IsZero() || !e.End.After(e.Start) {
		return time.Hour
	}
	return e.End.Sub(e.Start)
}

// Instances returns every occurrence starting within [t0, t1).
//
// An overridden occurrence is emitted from the override, not from the
// recurrence rule, because the override may have moved it into or out of
// the window, or cancelled it outright.
func (e *Event) Instances(t0, t1 time.Time) []Instance {
	var out []Instance
	in := func(t time.Time) bool { return !t.Before(t0) && t.Before(t1) }

	if e.set == nil {
		if in(e.Start) {
			out = append(out, Instance{e, e.Start, e.Start.Add(e.dur())})
		}
	} else {
		for _, t := range e.set.Between(t0, t1, true) {
			if _, ok := e.overrides[t.Unix()]; ok {
				continue // the override speaks for this occurrence
			}
			out = append(out, Instance{e, t, t.Add(e.dur())})
		}
	}
	for _, ov := range e.overrides {
		if ov.Cancelled || !in(ov.Start) {
			continue
		}
		out = append(out, Instance{ov, ov.Start, ov.Start.Add(ov.dur())})
	}
	return out
}

// loadDir reads every .ics file in dir and returns the events it contains.
// LoadDir reads every .ics file in dir.
func LoadDir(dir string) ([]*Event, error) {
	names, err := filepath.Glob(filepath.Join(dir, "*.ics"))
	if err != nil {
		return nil, err
	}
	sort.Strings(names)
	var evs []*Event
	for _, name := range names {
		f, err := os.Open(name)
		if err != nil {
			Warnf("%s: %v", name, err)
			continue
		}
		cal, err := ical.NewDecoder(f).Decode()
		f.Close()
		if err != nil {
			Warnf("%s: %v", name, err)
			continue
		}
		for _, c := range cal.Events() {
			ev, err := newEvent(&c)
			if err != nil {
				Warnf("%s: %v", name, err)
				continue
			}
			evs = append(evs, ev)
		}
	}
	return link(evs), nil
}

// link attaches RECURRENCE-ID events to the series they override.
// An override with no matching series is kept as an event of its own.
func link(evs []*Event) []*Event {
	masters := make(map[string]*Event, len(evs))
	for _, e := range evs {
		if e.RecurID.IsZero() {
			masters[e.UID] = e
		}
	}
	out := make([]*Event, 0, len(masters))
	for _, e := range evs {
		if e.RecurID.IsZero() {
			out = append(out, e)
			continue
		}
		m, ok := masters[e.UID]
		if !ok {
			out = append(out, e) // orphan; stands alone
			continue
		}
		e.master = m
		if m.overrides == nil {
			m.overrides = make(map[int64]*Event)
		}
		m.overrides[e.RecurID.Unix()] = e
	}
	return out
}

func newEvent(ev *ical.Event) (*Event, error) {
	e := &Event{}
	e.UID, _ = ev.Props.Text(ical.PropUID)
	if e.UID == "" {
		return nil, fmt.Errorf("event with no UID")
	}
	e.Summary, _ = ev.Props.Text(ical.PropSummary)
	e.Location, _ = ev.Props.Text(ical.PropLocation)
	e.Description, _ = ev.Props.Text(ical.PropDescription)

	start, err := ev.DateTimeStart(time.Local)
	if err != nil {
		return nil, fmt.Errorf("%s: bad DTSTART: %v", e.UID, err)
	}
	e.Start = start
	if end, err := ev.DateTimeEnd(time.Local); err == nil {
		e.End = end
	}
	if p := ev.Props.Get(ical.PropDateTimeStart); p != nil {
		e.AllDay = p.ValueType() == ical.ValueDate
	}
	if p := ev.Props.Get(ical.PropRecurrenceRule); p != nil {
		e.RRule = p.Value
	}
	if p := ev.Props.Get(ical.PropRecurrenceID); p != nil {
		if t, err := parseICSTime(p.Value, time.Local); err == nil {
			e.RecurID = t
		} else if t, err := ev.Props.DateTime(ical.PropRecurrenceID, time.Local); err == nil {
			e.RecurID = t
		}
	}
	if st, err := ev.Props.Text(ical.PropStatus); err == nil {
		e.Cancelled = strings.EqualFold(st, "CANCELLED")
	}
	if p := ev.Props.Get(ical.PropOrganizer); p != nil {
		e.Organizer = person(p)
	}
	for _, p := range ev.Props.Values(ical.PropAttendee) {
		e.Attendees = append(e.Attendees, Attendee{
			Name:     p.Params.Get(ical.ParamCommonName),
			Email:    strings.TrimPrefix(p.Value, "mailto:"),
			Partstat: p.Params.Get(ical.ParamParticipationStatus),
			Role:     p.Params.Get(ical.ParamRole),
		})
	}
	e.Raw = rawOf(ev.Component)
	e.Alarms = alarmsOf(ev.Component)

	if err := e.buildSet(ev); err != nil {
		Warnf("%s: %v", e.UID, err)
	}
	return e, nil
}

// buildSet assembles the recurrence set from RRULE, EXDATE and RDATE.
func (e *Event) buildSet(ev *ical.Event) error {
	opt, err := ev.Props.RecurrenceRule()
	if err != nil {
		return fmt.Errorf("bad RRULE: %v", err)
	}
	exd := ev.Props.Values(ical.PropExceptionDates)
	rdt := ev.Props.Values(ical.PropRecurrenceDates)
	if opt == nil && len(exd) == 0 && len(rdt) == 0 {
		return nil
	}
	set := &rrule.Set{}
	set.DTStart(e.Start)
	if opt != nil {
		opt.Dtstart = e.Start
		r, err := rrule.NewRRule(*opt)
		if err != nil {
			return fmt.Errorf("bad RRULE: %v", err)
		}
		set.RRule(r)
	}
	for _, p := range exd {
		for _, t := range dateList(p, e.Start.Location()) {
			set.ExDate(t)
		}
	}
	for _, p := range rdt {
		for _, t := range dateList(p, e.Start.Location()) {
			set.RDate(t)
		}
	}
	e.set = set
	return nil
}

// dateList parses the comma-separated date list in EXDATE/RDATE.
func dateList(p ical.Prop, loc *time.Location) []time.Time {
	var out []time.Time
	for _, s := range strings.Split(p.Value, ",") {
		s = strings.TrimSpace(s)
		if s == "" {
			continue
		}
		t, err := parseICSTime(s, loc)
		if err != nil {
			Warnf("bad %s %q: %v", p.Name, s, err)
			continue
		}
		out = append(out, t)
	}
	return out
}

func parseICSTime(s string, loc *time.Location) (time.Time, error) {
	for _, f := range []string{"20060102T150405Z", "20060102T150405", "20060102"} {
		l := loc
		if strings.HasSuffix(f, "Z") {
			l = time.UTC
		}
		if t, err := time.ParseInLocation(f, s, l); err == nil {
			return t, nil
		}
	}
	return time.Time{}, fmt.Errorf("unrecognised time")
}

// alarmsOf returns the relative triggers of every VALARM child.
// Absolute triggers are ignored for now; see doc/design.md.
func alarmsOf(c *ical.Component) []time.Duration {
	var out []time.Duration
	for _, child := range c.Children {
		if child.Name != ical.CompAlarm {
			continue
		}
		p := child.Props.Get(ical.PropTrigger)
		if p == nil {
			continue
		}
		d, err := parseDuration(p.Value)
		if err != nil {
			continue
		}
		out = append(out, d)
	}
	return out
}

func rawOf(c *ical.Component) string {
	var b strings.Builder
	fmt.Fprintf(&b, "BEGIN:%s\n", c.Name)
	var names []string
	for name := range c.Props {
		names = append(names, name)
	}
	sort.Strings(names)
	for _, name := range names {
		for _, p := range c.Props[name] {
			fmt.Fprintf(&b, "%s:%s\n", p.Name, p.Value)
		}
	}
	fmt.Fprintf(&b, "END:%s\n", c.Name)
	return b.String()
}

// person renders ORGANIZER as a name, falling back to the address.
func person(p *ical.Prop) string {
	addr := strings.TrimPrefix(p.Value, "mailto:")
	if cn := p.Params.Get(ical.ParamCommonName); cn != "" && cn != addr {
		return cn + " <" + addr + ">"
	}
	return addr
}