package store

import (
	"crypto/sha256"
	"encoding/hex"
	"sort"
)

// PrefixSnapshotHash is the content key of prefix_snapshot.
// It fingerprints prefix rows only. Peer configuration stays on
// config_revision.content_hash so a peer-only change can reuse the snapshot.
// The result is 64 lowercase hex characters. Row order does not affect the hash.
func PrefixSnapshotHash(rows []PrefixRow) string {
	cp := append([]PrefixRow(nil), rows...)
	sortPrefixRows(cp)
	h := sha256.New()
	for _, row := range cp {
		_, _ = h.Write([]byte(row.Prefix))
		_, _ = h.Write([]byte{1})
		if row.CommunityID == nil {
			_, _ = h.Write([]byte{0})
		} else {
			_, _ = h.Write([]byte{1})
			_, _ = h.Write([]byte(*row.CommunityID))
		}
		_, _ = h.Write([]byte{1})
		_, _ = h.Write([]byte(row.Source))
		_, _ = h.Write([]byte{0})
	}
	sum := h.Sum(nil)
	return hex.EncodeToString(sum)
}

func sortPrefixRows(rows []PrefixRow) {
	sort.Slice(rows, func(i, j int) bool {
		if rows[i].Prefix != rows[j].Prefix {
			return rows[i].Prefix < rows[j].Prefix
		}
		ni, vi := communitySortKey(rows[i].CommunityID)
		nj, vj := communitySortKey(rows[j].CommunityID)
		if ni != nj {
			return ni
		}
		if vi != vj {
			return vi < vj
		}
		return rows[i].Source < rows[j].Source
	})
}

func communitySortKey(id *string) (isNil bool, val string) {
	if id == nil {
		return true, ""
	}
	return false, *id
}

func samePrefixRow(a, b PrefixRow) bool {
	if a.Prefix != b.Prefix || a.Source != b.Source {
		return false
	}
	if (a.CommunityID == nil) != (b.CommunityID == nil) {
		return false
	}
	if a.CommunityID != nil && *a.CommunityID != *b.CommunityID {
		return false
	}
	return true
}