add untested ringMerge function

geom/ring.go

@@ -0,0 +1,93 @@
+package geom
+
+import (
+	"goposm/element"
+)
+
+type Ring struct {
+	ways  []*element.Way
+	refs  []int64
+	nodes []*element.Node
+}
+
+func reverseRefs(refs []int64) {
+	for i, j := 0, len(refs)-1; i < j; i, j = i+1, j-1 {
+		refs[i], refs[j] = refs[j], refs[i]
+	}
+}
+
+func reverseNodes(nodes []*element.Node) {
+	for i, j := 0, len(nodes)-1; i < j; i, j = i+1, j-1 {
+		nodes[i], nodes[j] = nodes[j], nodes[i]
+	}
+}
+
+func mergeRings(rings []*Ring) []*Ring {
+	endpoints := make(map[int64]*Ring)
+	for _, ring := range rings {
+		left := ring.refs[0]
+		right := ring.refs[len(ring.refs)-1]
+		if origRing, ok := endpoints[left]; ok {
+			delete(endpoints, left)
+			if left == origRing.refs[len(origRing.refs)-1] {
+				origRing.refs = append(origRing.refs, ring.refs[1:]...)
+				origRing.nodes = append(origRing.nodes, ring.nodes[1:]...)
+			} else {
+				reverseRefs(origRing.refs)
+				origRing.refs = append(origRing.refs, ring.refs[1:]...)
+				reverseNodes(origRing.nodes)
+				origRing.nodes = append(origRing.nodes, ring.nodes[1:]...)
+			}
+			origRing.ways = append(origRing.ways, ring.ways...)
+			// TODO tags
+
+			if rightRing, ok := endpoints[right]; ok && rightRing != origRing {
+				// close gap
+				delete(endpoints, right)
+				if right == ring.refs[0] {
+					origRing.refs = append(origRing.refs, ring.refs[1:]...)
+					origRing.nodes = append(origRing.nodes, ring.nodes[1:]...)
+				} else {
+
+					reverseRefs(ring.refs)
+					origRing.refs = append(origRing.refs[:len(origRing.refs)-2], ring.refs...)
+					reverseNodes(ring.nodes)
+					origRing.nodes = append(origRing.nodes[:len(origRing.nodes)-2], ring.nodes...)
+				}
+
+				origRing.ways = append(origRing.ways, ring.ways...)
+				right := origRing.refs[len(origRing.refs)-1]
+				endpoints[right] = origRing
+
+			} else {
+				endpoints[right] = origRing
+			}
+		} else if origRing, ok := endpoints[right]; ok {
+			delete(endpoints, right)
+			if right == origRing.refs[0] {
+				origRing.refs = append(ring.refs[:len(ring.refs)-1], origRing.refs...)
+				origRing.nodes = append(ring.nodes[:len(ring.nodes)-1], origRing.nodes...)
+			} else {
+				reverseRefs(ring.refs)
+				origRing.refs = append(origRing.refs[:len(origRing.refs)-2], ring.refs...)
+				reverseNodes(ring.nodes)
+				origRing.nodes = append(origRing.nodes[:len(origRing.nodes)-2], ring.nodes...)
+			}
+			origRing.ways = append(origRing.ways, ring.ways...)
+			// TODO tags
+			endpoints[left] = origRing
+		} else {
+			endpoints[left] = ring
+			endpoints[right] = ring
+		}
+	}
+	uniqueRings := make(map[*Ring]bool)
+	for _, ring := range endpoints {
+		uniqueRings[ring] = true
+	}
+	result := make([]*Ring, len(uniqueRings))
+	for ring, _ := range uniqueRings {
+		result = append(result, ring)
+	}
+	return result
+}