// Package dedup provides deterministic normalization helpers for detecting
// duplicate stories across feeds.
package dedup

import (
	"net/url"
	"strings"
	"unicode"
)

// trackingParams are query-string keys stripped during URL canonicalization.
// Anything starting with "utm_" is also stripped.
var trackingParams = map[string]struct{}{
	"fbclid":      {},
	"gclid":       {},
	"mc_cid":      {},
	"mc_eid":      {},
	"ref":         {},
	"ref_src":     {},
	"ref_url":     {},
	"share":       {},
	"shared":      {},
	"cmpid":       {},
	"cmp":         {},
	"icid":        {},
	"ito":         {},
	"yclid":       {},
	"_ga":         {},
	"igshid":      {},
	"feature":     {},
	"si":          {},
	"smid":        {},
	"twclid":      {},
	"mibextid":    {},
	"src":         {},
}

// CanonicalURL returns a stable form of a story URL suitable for dedup.
// It lowercases the scheme/host, drops fragments and common tracking params,
// and trims trailing slashes. If parsing fails, the input is returned unchanged.
func CanonicalURL(raw string) string {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return ""
	}
	u, err := url.Parse(raw)
	if err != nil || u.Host == "" {
		return raw
	}

	u.Scheme = strings.ToLower(u.Scheme)
	u.Host = strings.ToLower(u.Host)
	u.Host = strings.TrimPrefix(u.Host, "www.")
	u.Host = strings.TrimPrefix(u.Host, "m.")
	u.Host = strings.TrimPrefix(u.Host, "amp.")
	u.Fragment = ""

	if q := u.Query(); len(q) > 0 {
		for k := range q {
			lk := strings.ToLower(k)
			if strings.HasPrefix(lk, "utm_") {
				q.Del(k)
				continue
			}
			if _, drop := trackingParams[lk]; drop {
				q.Del(k)
			}
		}
		u.RawQuery = q.Encode()
	}

	u.Path = strings.TrimRight(u.Path, "/")
	if u.Path == "" {
		u.Path = "/"
	}
	return u.String()
}

// NormalizeHeadline returns a comparable form of a headline: lowercase,
// punctuation stripped, whitespace collapsed. Empty input returns "".
func NormalizeHeadline(h string) string {
	if h == "" {
		return ""
	}
	var b strings.Builder
	b.Grow(len(h))
	prevSpace := true
	for _, r := range h {
		switch {
		case unicode.IsLetter(r) || unicode.IsDigit(r):
			b.WriteRune(unicode.ToLower(r))
			prevSpace = false
		case unicode.IsSpace(r) || unicode.IsPunct(r) || unicode.IsSymbol(r):
			if !prevSpace {
				b.WriteByte(' ')
				prevSpace = true
			}
		}
	}
	return strings.TrimSpace(b.String())
}