package main

import (
	"regexp"
	"strconv"
	"strings"
)

// latestChapter is the newest chapter a series page advertises.
type latestChapter struct {
	Num   float64
	Label string
}

// asuraSlugRe pulls the series slug out of a stored series_url.
// Shape verified live 2026-07-26: https://asurascans.com/comics/<slug>, where
// the slug carries a trailing hash-like suffix (e.g. "-f886a8af").
var asuraSlugRe = regexp.MustCompile(`/comics/([^/?#]+)`)

// demonicChapterRe matches the pre-redirect anchors demonic series pages link
// through. Both the raw "&" and the HTML-escaped "&amp;" forms occur.
var demonicChapterRe = regexp.MustCompile(`chaptered\.php\?manga=\d+&(?:amp;)?chapter=([0-9.]+)`)

// latestChapterFrom returns the highest chapter number body advertises for this
// series. ok is false when the body yields nothing usable — an unknown site, an
// empty body, a Cloudflare challenge page, and a site redesign all land here,
// and the caller treats all four identically.
//
// Ported from the userscript's latestChapterFromAnchors (asura L123-133,
// demonic L183-193), including its reason for taking a maximum rather than a
// first or last: neither site lists chapters in a dependable order.
//
// The userscript's asura rule additionally requires the anchor text to match
// /Chapter\s+[\d.]+/i. That check exists only to skip the "First Chapter"
// shortcut, which points at chapter/1 and therefore can never win a maximum, so
// it is redundant here. For asura, scoping the pattern to this series' own slug
// replaces it with a stronger guarantee: a chapter link belonging to some other
// series cannot contribute even if the page starts carrying them. demonic has no
// such guarantee — demonicChapterRe matches any chaptered.php?manga=<id> anchor
// with no per-series scoping, because the stored series_id for demonic is a
// slug, not the numeric id the URL carries, so it cannot easily be scoped.
func latestChapterFrom(site, seriesURL, body string) (latestChapter, bool) {
	var re *regexp.Regexp
	switch site {
	case "asura":
		m := asuraSlugRe.FindStringSubmatch(seriesURL)
		if m == nil {
			return latestChapter{}, false
		}
		// Compiled per call rather than cached: this runs once per fetch, which
		// is at most a few times a minute, and the slug varies per series.
		re = regexp.MustCompile(`/comics/` + regexp.QuoteMeta(m[1]) + `/chapter/([0-9.]+)`)
	case "demonic":
		re = demonicChapterRe
	default:
		return latestChapter{}, false
	}

	var best latestChapter
	found := false
	for _, m := range re.FindAllStringSubmatch(body, -1) {
		// [0-9.]+ can swallow a trailing separator, e.g. "chapter/12." in a
		// sentence; ParseFloat would reject the whole match.
		raw := strings.Trim(m[1], ".")
		num, err := strconv.ParseFloat(raw, 64)
		if err != nil {
			continue
		}
		if !found || num > best.Num {
			best = latestChapter{Num: num, Label: "Chapter " + raw}
			found = true
		}
	}
	return best, found
}