package parse

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

// This file parses the per-child day widget that Compass renders on a child's
// own pages ("/Records/User.aspx?userId=..." and the Learning Tasks page). The
// widget is labelled "Today" and its events are that child's own periods:
//
//	8:55: 1 - 7SCF - H14LAB - KNI
//
// The week calendar is school-wide (it carries the eldest child's lesson grid),
// so it must never be the source of a child's timetable (AGENTS.md §4 FR-16).
// This is the per-child source.

// dayWidgetBaseHour is unused: the widget's grid start moves with the day's
// first event (a page whose first event is 7:45 starts at 07:00, one whose
// first event is 8:55 starts at 06:00), so the printed clock is the reliable
// source and the grid offset is not.

// parseDayWidget returns the periods in one child's day widget. found reports
// whether the page carried a day widget at all.
func parseDayWidget(child string, page Page, loc *time.Location, ref time.Time) (items []Item, found bool, err error) {
	root := parseHTML(page.HTML)
	events := findAll(root, func(n *node) bool {
		return n.Tag == "div" && n.hasClassPart("day-bd-evt-") && n.hasClassPart("calendardaywidget-")
	})
	if len(events) == 0 {
		return nil, false, nil
	}

	day := ref.In(loc)
	if day.IsZero() {
		day = time.Now().In(loc)
	}
	date := time.Date(day.Year(), day.Month(), day.Day(), 0, 0, 0, 0, loc)

	for _, ev := range events {
		labelSpan := find(ev, func(n *node) bool { return n.hasClass("ext-evt-bd") })
		if labelSpan == nil {
			continue
		}
		label := collapse(labelSpan.Text())
		if label == "" {
			continue
		}
		cm := clockPrefix.FindStringSubmatch(label)
		if cm == nil {
			return nil, true, fmt.Errorf("parse: %s: day-widget event %q has no start time", page.Slug, label)
		}
		at, err := dayWidgetTime(cm, date)
		if err != nil {
			return nil, true, fmt.Errorf("parse: %s: day-widget event %q: %w", page.Slug, label, err)
		}
		title := strings.TrimSpace(cm[3])
		if title == "" {
			title = label
		}

		subject, teacher, body := splitEvent(label, title)
		url := page.URL
		if url == "" {
			url = compassHost + "/Organise/Calendar/"
		}

		items = append(items, Item{
			Child:       child,
			Source:      SourceCompass,
			Type:        TypeEvent,
			Subject:     subject,
			Teacher:     teacher,
			Title:       title,
			Body:        body,
			DueAt:       &at,
			URL:         url,
			SourcePage:  page.Slug,
			ExternalRef: dedupeKey("day-period", at.Format(time.RFC3339), title),
			Importance:  importanceNormal,
		})
	}
	return items, true, nil
}

// dayWidgetTime reads an event's start from the printed clock. Compass prints a
// 12-hour clock with no AM/PM marker ("1:26" is the afternoon period), so the
// school-day convention applies: 1-6 are PM, 7-11 are AM, 12 is noon.
func dayWidgetTime(clock []string, date time.Time) (time.Time, error) {
	hour, minute := atoiSafe(clock[1]), atoiSafe(clock[2])
	if hour < 0 || hour > 23 || minute < 0 || minute > 59 {
		return time.Time{}, fmt.Errorf("bad time %02d:%02d", hour, minute)
	}
	if hour >= 1 && hour <= 6 { // 1:26 means 1:26 PM in the Compass day grid
		hour += 12
	}
	return date.Add(time.Duration(hour)*time.Hour + time.Duration(minute)*time.Minute), nil
}

// atoiSafe parses a small decimal number, returning -1 when it is not one.
func atoiSafe(s string) int {
	n := 0
	if s == "" {
		return -1
	}
	for _, r := range s {
		if r < '0' || r > '9' {
			return -1
		}
		n = n*10 + int(r-'0')
	}
	return n
}