// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0

// Package identifiers validates the scholarly identifiers a post or an
// account can carry: a DOI names the work, an ORCID names an author. It
// is a leaf so the configuration, the domain object, the payload
// builders and the admin share one rule without importing one another.
//
// The rules are syntactic on purpose. A DOI resolves through doi.org and
// an ORCID through orcid.org, and both publish registries; asking those
// services here would tie a save to the network, leak who is writing to
// a third party, and make the offline binary wait on someone else's
// uptime. Syntax plus the ORCID check digit catches every realistic
// typo; resolution stays the consumer's job.
package identifiers

import (
	"regexp"
	"strings"
)

var doiRe = regexp.MustCompile(`\A10\.[0-9]{4,9}/\S+\z`)

// orcidRe is the display form: four groups of four digits, the last
// character a digit or the uppercase X that stands for a checksum of 10.
var orcidRe = regexp.MustCompile(`\A[0-9]{4}-[0-9]{4}-[0-9]{4}-[0-9]{3}[0-9X]\z`)

// NormalizeDOI accepts the bare form, a doi: scheme and a doi.org URL,
// and returns the bare identifier; an empty result means the input
// carries no DOI at all.
func NormalizeDOI(text string) string {
	text = strings.TrimSpace(text)
	for _, prefix := range []string{
		"https://doi.org/", "http://doi.org/", "doi.org/", "doi:",
	} {
		if len(text) > len(prefix) && strings.EqualFold(text[:len(prefix)], prefix) {
			text = strings.TrimSpace(text[len(prefix):])
			break
		}
	}
	return text
}

// ValidDOI reports whether text is a syntactically valid bare DOI: the
// 10. prefix, a registrant needle of four to nine digits, a slash, and
// a non-empty suffix without spaces.
func ValidDOI(text string) bool {
	return doiRe.MatchString(NormalizeDOI(text))
}

// NormalizeORCID trims and lower-cases to upper; it fixes no body.
func NormalizeORCID(text string) string {
	return strings.ToUpper(strings.TrimSpace(text))
}

// ValidORCID reports whether text is an ORCID iD in display form with a
// correct ISO 7064 (MOD 11-2) check digit.
func ValidORCID(text string) bool {
	id := NormalizeORCID(text)
	if !orcidRe.MatchString(id) {
		return false
	}
	digits := strings.ReplaceAll(id, "-", "")
	total := 0
	for _, r := range digits[:15] {
		total = (total + int(r-'0')) * 2
	}
	remainder := (12 - total%11) % 11
	want := byte('0' + remainder)
	if remainder == 10 {
		want = 'X'
	}
	return digits[15] == want
}

// DOIURL names the resolver for a bare or already-prefixed DOI; an
// invalid input yields "".
func DOIURL(text string) string {
	doi := NormalizeDOI(text)
	if !doiRe.MatchString(doi) {
		return ""
	}
	return "https://doi.org/" + doi
}

// ORCIDURL names the public record for a valid iD; an invalid input
// yields "".
func ORCIDURL(text string) string {
	id := NormalizeORCID(text)
	if !ValidORCID(id) {
		return ""
	}
	return "https://orcid.org/" + id
}