package ticket

import (
	"fmt"
	"sort"
	"strings"
	"time"
)

// GroupBy selects how Aggregate buckets time entries.
type GroupBy string

const (
	GroupByProject GroupBy = "project"
	GroupByStatus  GroupBy = "status"
	GroupByTicket  GroupBy = "ticket"
	GroupByDay     GroupBy = "day"
)

// AllGroupBys is the ordered list of report grouping options.
var AllGroupBys = []GroupBy{
	GroupByProject,
	GroupByStatus,
	GroupByTicket,
	GroupByDay,
}

// Label returns a human-readable name for the grouping.
func (g GroupBy) Label() string {
	switch g {
	case GroupByProject:
		return "Project"
	case GroupByStatus:
		return "Status"
	case GroupByTicket:
		return "Ticket"
	case GroupByDay:
		return "Day"
	default:
		return string(g)
	}
}

// Shortcut returns the jump letter for the grouping picker.
func (g GroupBy) Shortcut() rune {
	switch g {
	case GroupByProject:
		return 'p'
	case GroupByStatus:
		return 's'
	case GroupByTicket:
		return 't'
	case GroupByDay:
		return 'd'
	default:
		return 0
	}
}

// Index returns the position in AllGroupBys, or 0 if unknown.
func (g GroupBy) Index() int {
	for i, x := range AllGroupBys {
		if x == g {
			return i
		}
	}
	return 0
}

// GroupRow is one aggregated bucket in a time report.
type GroupRow struct {
	Key      string
	Label    string
	Duration time.Duration
}

// Aggregate sums entry durations grouped by groupBy.
// ticketsByID is used for status/ticket labels; missing tickets fall back to IDs.
func Aggregate(entries []TimeEntry, ticketsByID map[string]Ticket, groupBy GroupBy) []GroupRow {
	sums := map[string]time.Duration{}
	labels := map[string]string{}

	for _, e := range entries {
		key, label := groupKeyLabel(e, ticketsByID, groupBy)
		sums[key] += e.Duration
		if _, ok := labels[key]; !ok {
			labels[key] = label
		}
	}

	rows := make([]GroupRow, 0, len(sums))
	for key, d := range sums {
		rows = append(rows, GroupRow{Key: key, Label: labels[key], Duration: d})
	}
	sort.Slice(rows, func(i, j int) bool {
		if groupBy == GroupByDay {
			return rows[i].Key > rows[j].Key // newest day first
		}
		if rows[i].Duration != rows[j].Duration {
			return rows[i].Duration > rows[j].Duration
		}
		return rows[i].Label < rows[j].Label
	})
	return rows
}

func groupKeyLabel(e TimeEntry, ticketsByID map[string]Ticket, groupBy GroupBy) (key, label string) {
	t, ok := ticketsByID[e.TicketID]
	switch groupBy {
	case GroupByProject:
		key = e.ProjectID
		if key == "" && ok {
			key = t.ProjectID
		}
		if key == "" {
			key = "(none)"
		}
		return key, key
	case GroupByStatus:
		if ok {
			key = string(t.Status)
		} else {
			key = "(unknown)"
		}
		return key, key
	case GroupByTicket:
		key = e.TicketID
		if ok && t.Title != "" {
			return key, t.Title
		}
		if key == "" {
			return "(none)", "(none)"
		}
		return key, key
	case GroupByDay:
		start := e.Start
		if start.IsZero() {
			start = e.End
		}
		if start.IsZero() {
			return "(unknown)", "(unknown)"
		}
		local := start.Local()
		key = local.Format("2006-01-02")
		return key, key
	default:
		return fmt.Sprintf("%v", groupBy), string(groupBy)
	}
}

// TotalDuration sums all entry durations.
func TotalDuration(entries []TimeEntry) time.Duration {
	var sum time.Duration
	for _, e := range entries {
		sum += e.Duration
	}
	return sum
}

// TimeFilter selects which time entries belong in a report.
// From/To are inclusive bounds on the entry's work instant (Start, else End).
// Zero times mean no bound on that side.
type TimeFilter struct {
	From     time.Time
	To       time.Time
	TicketID string
}

// FilterEntries returns entries matching f. The input slice is not modified.
func FilterEntries(entries []TimeEntry, f TimeFilter) []TimeEntry {
	if f.From.IsZero() && f.To.IsZero() && f.TicketID == "" {
		out := make([]TimeEntry, len(entries))
		copy(out, entries)
		return out
	}
	out := make([]TimeEntry, 0, len(entries))
	for _, e := range entries {
		if f.TicketID != "" && e.TicketID != f.TicketID {
			continue
		}
		when := e.Start
		if when.IsZero() {
			when = e.End
		}
		if !f.From.IsZero() && (when.IsZero() || when.Before(f.From)) {
			continue
		}
		if !f.To.IsZero() && (when.IsZero() || when.After(f.To)) {
			continue
		}
		out = append(out, e)
	}
	return out
}

// ParseReportDay parses YYYY-MM-DD as local midnight. Empty returns zero time.
func ParseReportDay(s string) (time.Time, error) {
	s = strings.TrimSpace(s)
	if s == "" {
		return time.Time{}, nil
	}
	t, err := time.ParseInLocation("2006-01-02", s, time.Local)
	if err != nil {
		return time.Time{}, fmt.Errorf("invalid date %q", s)
	}
	return t, nil
}

// EndOfReportDay returns the last instant of the calendar day of t in local time.
func EndOfReportDay(t time.Time) time.Time {
	if t.IsZero() {
		return t
	}
	local := t.In(time.Local)
	y, m, d := local.Date()
	return time.Date(y, m, d, 23, 59, 59, 999999999, time.Local)
}