Add current conditions condition code consensus helper

internal/adapters/outbound/postgres/conditions_codes.go

@@ -0,0 +1,107 @@
+// conditions_codes.go selects current-conditions WMO codes from source candidates.
+// Layer: adapters/outbound/postgres conditions feature.
+package postgres
+
+import "gitea.maximumdirect.net/ejr/weatherfeeder/model"
+
+type currentConditionsConditionCodeCandidate struct {
+	EventSource   string
+	ConditionCode model.WMOCode
+}
+
+type conditionCodeFamily int
+
+const (
+	conditionCodeFamilyUnknown conditionCodeFamily = iota
+	conditionCodeFamilyClearOrCloud
+	conditionCodeFamilyFog
+	conditionCodeFamilyDrizzle
+	conditionCodeFamilyRain
+	conditionCodeFamilySnow
+	conditionCodeFamilyThunderstorm
+)
+
+var currentConditionsConditionCodeRankings = map[conditionCodeFamily][]model.WMOCode{
+	conditionCodeFamilyClearOrCloud: {0, 1, 2, 3},
+	conditionCodeFamilyFog:          {45, 48},
+	conditionCodeFamilyDrizzle:      {51, 53, 55, 56, 57},
+	conditionCodeFamilyRain:         {61, 63, 65, 80, 81, 82, 66, 67},
+	conditionCodeFamilySnow:         {71, 73, 75, 85, 86, 77},
+	conditionCodeFamilyThunderstorm: {95, 96, 99},
+}
+
+var currentConditionsConditionCodeFamilies = buildCurrentConditionsConditionCodeFamilies()
+
+func buildCurrentConditionsConditionCodeFamilies() map[model.WMOCode]conditionCodeFamily {
+	families := make(map[model.WMOCode]conditionCodeFamily)
+	for family, ranking := range currentConditionsConditionCodeRankings {
+		for _, code := range ranking {
+			families[code] = family
+		}
+	}
+	return families
+}
+
+func selectCurrentConditionsConditionCode(candidates []currentConditionsConditionCodeCandidate) model.WMOCode {
+	seenSources := make(map[string]struct{})
+	familyCounts := make(map[conditionCodeFamily]int)
+	codeCounts := make(map[model.WMOCode]int)
+
+	for _, candidate := range candidates {
+		if _, seen := seenSources[candidate.EventSource]; seen {
+			continue
+		}
+		seenSources[candidate.EventSource] = struct{}{}
+
+		family, ok := currentConditionsConditionCodeFamilies[candidate.ConditionCode]
+		if !ok {
+			continue
+		}
+		familyCounts[family]++
+		codeCounts[candidate.ConditionCode]++
+	}
+
+	winningFamily, ok := currentConditionsWinningConditionCodeFamily(familyCounts)
+	if !ok {
+		return model.WMOUnknown
+	}
+
+	return currentConditionsWinningConditionCode(winningFamily, codeCounts)
+}
+
+func currentConditionsWinningConditionCodeFamily(counts map[conditionCodeFamily]int) (conditionCodeFamily, bool) {
+	winningFamily := conditionCodeFamilyUnknown
+	winningCount := 0
+	tied := false
+
+	for family, count := range counts {
+		if count > winningCount {
+			winningFamily = family
+			winningCount = count
+			tied = false
+			continue
+		}
+		if count == winningCount {
+			tied = true
+		}
+	}
+
+	if winningCount == 0 || tied {
+		return conditionCodeFamilyUnknown, false
+	}
+	return winningFamily, true
+}
+
+func currentConditionsWinningConditionCode(family conditionCodeFamily, counts map[model.WMOCode]int) model.WMOCode {
+	winningCode := model.WMOUnknown
+	winningCount := 0
+
+	for _, code := range currentConditionsConditionCodeRankings[family] {
+		if counts[code] > winningCount {
+			winningCode = code
+			winningCount = counts[code]
+		}
+	}
+
+	return winningCode
+}

internal/adapters/outbound/postgres/conditions_codes_test.go

@@ -0,0 +1,116 @@
+// conditions_codes_test.go tests current-conditions WMO code selection.
+// Layer: adapters/outbound/postgres conditions feature.
+package postgres
+
+import (
+	"testing"
+
+	"gitea.maximumdirect.net/ejr/weatherfeeder/model"
+)
+
+func TestSelectCurrentConditionsConditionCode(t *testing.T) {
+	tests := []struct {
+		name       string
+		candidates []currentConditionsConditionCodeCandidate
+		want       model.WMOCode
+	}{
+		{
+			name: "clear cloud ranking breaks exact tie",
+			candidates: conditionCodeCandidates(
+				0,
+				1,
+				2,
+			),
+			want: 0,
+		},
+		{
+			name: "clear cloud family wins over thunderstorm",
+			candidates: conditionCodeCandidates(
+				1,
+				2,
+				95,
+			),
+			want: 1,
+		},
+		{
+			name: "tied families return unknown",
+			candidates: conditionCodeCandidates(
+				0,
+				95,
+			),
+			want: model.WMOUnknown,
+		},
+		{
+			name: "rain ranking breaks exact tie",
+			candidates: conditionCodeCandidates(
+				61,
+				63,
+				80,
+			),
+			want: 61,
+		},
+		{
+			name: "three tied families return unknown",
+			candidates: conditionCodeCandidates(
+				61,
+				95,
+				0,
+			),
+			want: model.WMOUnknown,
+		},
+		{
+			name: "single thunderstorm code wins",
+			candidates: conditionCodeCandidates(
+				95,
+			),
+			want: 95,
+		},
+		{
+			name: "unrecognized only returns unknown",
+			candidates: conditionCodeCandidates(
+				4,
+				100,
+			),
+			want: model.WMOUnknown,
+		},
+		{
+			name: "duplicate source only votes once",
+			candidates: []currentConditionsConditionCodeCandidate{
+				{EventSource: "source-1", ConditionCode: 95},
+				{EventSource: "source-1", ConditionCode: 95},
+				{EventSource: "source-2", ConditionCode: 0},
+				{EventSource: "source-3", ConditionCode: 0},
+			},
+			want: 0,
+		},
+		{
+			name: "exact code frequency wins before ranking",
+			candidates: []currentConditionsConditionCodeCandidate{
+				{EventSource: "source-1", ConditionCode: 61},
+				{EventSource: "source-2", ConditionCode: 63},
+				{EventSource: "source-3", ConditionCode: 63},
+			},
+			want: 63,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := selectCurrentConditionsConditionCode(tt.candidates)
+			if got != tt.want {
+				t.Fatalf("expected condition code %d, got %d", tt.want, got)
+			}
+		})
+	}
+}
+
+func conditionCodeCandidates(codes ...model.WMOCode) []currentConditionsConditionCodeCandidate {
+	candidates := make([]currentConditionsConditionCodeCandidate, 0, len(codes))
+	for i, code := range codes {
+		candidates = append(candidates, currentConditionsConditionCodeCandidate{
+			EventSource:   string(rune('a' + i)),
+			ConditionCode: code,
+		})
+	}
+	return candidates
+}