v4.7.0: Add domain-vs-domain comparison

- DiffService.compare(domainA:domainB:) reuses the existing section-diff
  builders to compare two distinct domains' latest reports, returning a new
  DomainComparisonResult (parallel to the time-based DomainDiff).
- DomainCompareView: pick two tracked domains and render the comparison with
  the existing DomainDiffView section renderer.
- Entry point: "Compare Domains" in the Watchlist toolbar menu, shown once at
  least two domains are tracked.

1 files changed, 51 insertions, 0 deletions

diff --git a/DomainDig/DiffService.swift b/DomainDig/DiffService.swift
index 211a16e..cf25b6f 100644
--- a/DomainDig/DiffService.swift
+++ b/DomainDig/DiffService.swift
@@ -105,6 +105,32 @@ struct DomainDiff: Identifiable, Equatable, Codable {
 typealias DomainDiffItem = DiffItem
 typealias DomainDiffSection = DiffSection
 
+/// Result of comparing two distinct domains' latest reports side by side, as
+/// opposed to `DomainDiff`, which compares the same domain across time.
+struct DomainComparisonResult: Identifiable, Equatable {
+    let domainA: String
+    let domainB: String
+    let generatedAt: Date
+    let sections: [DiffSection]
+    let contextNote: String?
+
+    var id: String {
+        "\(domainA)-\(domainB)-\(generatedAt.timeIntervalSince1970)"
+    }
+
+    var changedSections: [DiffSection] {
+        sections.filter(\.hasChanges)
+    }
+
+    var changeCount: Int {
+        sections.reduce(0) { $0 + $1.changeCount }
+    }
+
+    var severity: ChangeSeverity {
+        sections.map(\.severity).max() ?? .low
+    }
+}
+
 enum DiffService {
     static func compare(from oldReport: DomainReport, to newReport: DomainReport) -> DomainDiff {
         let sections = [
@@ -181,6 +207,31 @@ enum DiffService {
         )
     }
 
+    /// Compares two distinct domains' reports section by section. Reuses the same
+    /// field-level diff logic as time-based comparison; the two reports are simply
+    /// unrelated domains rather than the same domain at different times.
+    static func compare(domainA: DomainReport, domainB: DomainReport) -> DomainComparisonResult {
+        let sections = [
+            availabilitySection(from: domainA, to: domainB),
+            ownershipSection(from: domainA, to: domainB),
+            dnsSection(from: domainA, to: domainB),
+            webSection(from: domainA, to: domainB),
+            emailSection(from: domainA, to: domainB),
+            networkSection(from: domainA, to: domainB),
+            subdomainsSection(from: domainA, to: domainB),
+            intelligenceSection(from: domainA, to: domainB),
+            riskSection(from: domainA, to: domainB)
+        ]
+
+        return DomainComparisonResult(
+            domainA: domainA.domain,
+            domainB: domainB.domain,
+            generatedAt: Date(),
+            sections: sections,
+            contextNote: comparisonContextNote(from: domainA, to: domainB)
+        )
+    }
+
     static func comparisonContextNote(from oldReport: DomainReport, to newReport: DomainReport) -> String? {
         var notes: [String] = []
         if oldReport.resolverURLString != newReport.resolverURLString {