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
+}