func provideMappings()

in Sources/XCRemoteCache/Dependencies/OverlayReader.swift [88:131]
42 lines of code
10 McCabe index (conditional complexity)

    func provideMappings() throws -> [OverlayMapping] {
        guard let jsonContent = try fileReader.contents(atPath: json.path) else {
            switch mode {
            case .strict:
                throw JsonOverlayReaderError.missingSourceFile(json)
            case .bestEffort:
                debugLog("overlay mapping file \(json) doesn't exist. Skipping overlay for the best-effort mode.")
                return []
            }
        }
        do {
        let overlay: Overlay = try jsonDecoder.decode(Overlay.self, from: jsonContent)
            let mappings: [OverlayMapping] = try overlay.roots.reduce([]) { prev, root in
                switch root.type {
                case .directory:
                    // iterate all contents
                    let dir = URL(fileURLWithPath: root.name)
                    let mappings: [OverlayMapping] = try root.contents.map { content in
                        switch content.type {
                        case .file:
                            let virtual = dir.appendingPathComponent(content.name)
                            let local = URL(fileURLWithPath: content.externalContents)
                            return .init(virtual: virtual, local: local)
                        case .directory:
                            throw JsonOverlayReaderError.unsupportedFormat
                        }

                    }
                    return prev + mappings
                case .file:
                    throw JsonOverlayReaderError.unsupportedFormat
                }
            }
            return mappings
        } catch {
            switch mode {
            case .strict:
                throw error
            case .bestEffort:
                errorLog("Overlay reader has failed with an error \(error). Best-effort mode - skipping an overlay.")
                return []
            }
        }
    }