Initial implementation of APKINDEX, fetching, reading, parsing, & merging

Sources/apk/Index/ApkRawIndex.swift

@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: Apache-2.0
+
+import Foundation
+
+struct ApkRawIndex {
+  let packages: [ApkRawIndexEntry]
+
+  init(lines: any Sequence<String>) throws {
+    var packages = [ApkRawIndexEntry]()
+
+    var recordLines = [String]()
+    recordLines.reserveCapacity(15)
+
+    for line in lines {
+      if line.trimmingCharacters(in: .whitespaces).isEmpty {
+        if !recordLines.isEmpty {
+          packages.append(try .init(parsingEntryLines: recordLines))
+          recordLines.removeAll(keepingCapacity: true)
+        }
+      } else {
+        recordLines.append(line)
+      }
+    }
+    if !recordLines.isEmpty {
+      packages.append(try .init(parsingEntryLines: recordLines))
+    }
+
+    self.packages = packages
+  }
+}
+
+struct ApkRawIndexEntry {
+  let fields: [Record]
+
+  struct Record {
+    let key: Character
+    let value: String
+  }
+}
+
+extension ApkRawIndexEntry {
+  init(parsingEntryLines lines: any Sequence<String>) throws {
+    self.fields = try lines.map { line in
+      guard let splitIdx = line.firstIndex(of: ":"),
+          line.distance(from: line.startIndex, to: splitIdx) == 1 else {
+        throw ApkRawIndexError.badPair
+      }
+      return Record(
+        key:   line.first!,
+        value: String(line[line.index(after: splitIdx)...]))
+    }
+  }
+
+  func toMap() -> [Character: String] {
+    Dictionary(uniqueKeysWithValues: self.fields.map { $0.pair })
+  }
+
+  func lookup(_ key: Character) -> String? {
+    fields.first(where: { $0.key == key })?.value
+  }
+}
+
+extension ApkRawIndexEntry.Record {
+  var pair: (Character, String) {
+    (self.key, self.value)
+  }
+}
+
+enum ApkRawIndexError: Error, LocalizedError {
+  case badPair
+
+  var errorDescription: String? {
+    switch self {
+    case .badPair: "Malformed raw key-value pair"
+    }
+  }
+}