package notificationservice

import (
	"encoding/json"
	"strconv"
	"strings"
)

// normalizeFCMCredentialsJSON returns credential bytes valid for encoding/json and
// Firebase's credentials parser. Repairs the common mistake of pasting PEM with
// literal newlines inside the JSON "private_key" string (.env multiline breakage).
func normalizeFCMCredentialsJSON(raw string) ([]byte, error) {
	s := strings.TrimSpace(strings.TrimPrefix(raw, "\ufeff"))
	if json.Valid([]byte(s)) {
		return []byte(s), nil
	}
	if fixed := tryRepairFirebasePrivateKeyNewlines(s); fixed != "" && fixed != s {
		b := []byte(fixed)
		if json.Valid(b) {
			return b, nil
		}
	}
	var m map[string]any
	err := json.Unmarshal([]byte(strings.TrimSpace(s)), &m)
	return nil, err
}

// tryRepairFirebasePrivateKeyNewlines rewrites `"private_key": "...(PEM with real newlines)..."`
// using strconv.Quote for the inner PEM. Empty string means no rewrite applied.
func tryRepairFirebasePrivateKeyNewlines(s string) string {
	const beginRSA = "-----BEGIN RSA PRIVATE KEY-----"
	const endRSA = "-----END RSA PRIVATE KEY-----"
	const beginPK = "-----BEGIN PRIVATE KEY-----"
	const endPK = "-----END PRIVATE KEY-----"

	beginIdx := strings.Index(s, beginRSA)
	endMarker := endRSA
	endIdx := strings.Index(s, endMarker)
	if beginIdx < 0 {
		beginIdx = strings.Index(s, beginPK)
		endMarker = endPK
		endIdx = strings.Index(s, endMarker)
	}
	if beginIdx < 0 || endIdx < beginIdx {
		return ""
	}
	endInclusive := endIdx + len(endMarker)

	const pkAttr = `"private_key"`
	pkIdx := strings.Index(s, pkAttr)
	if pkIdx < 0 || pkIdx > beginIdx {
		return ""
	}

	restAfterKey := s[pkIdx+len(pkAttr):]
	colonRel := strings.Index(restAfterKey, ":")
	if colonRel < 0 {
		return ""
	}
	searchFrom := pkIdx + len(pkAttr) + colonRel + 1

	openQuote := -1
	for i := searchFrom; i < beginIdx; i++ {
		c := s[i]
		if c == '"' {
			openQuote = i
			break
		}
		if c != ' ' && c != '\t' && c != '\n' && c != '\r' {
			return ""
		}
	}
	if openQuote < 0 {
		return ""
	}

	closeQuote := -1
	for i := endInclusive; i < len(s); i++ {
		c := s[i]
		if c == '"' {
			closeQuote = i
			break
		}
		if c != ' ' && c != '\t' && c != '\n' && c != '\r' {
			return ""
		}
	}
	if closeQuote < 0 || closeQuote <= openQuote {
		return ""
	}

	inner := s[openQuote+1 : closeQuote]
	quoted := strconv.Quote(inner)
	return s[:openQuote] + quoted + s[closeQuote+1:]
}