Intermediate Decoding reference

exampleAlbum.json

{
  "artist" : "Weezer",
  "coverArt" : [ {
    "url" : "https://lastfm-img2.akamaized.net/i/u/174s/1918fe81bb68441d96b2247682bfda21.png"
  } ],
  "genres" : [ "Alternative" ],
  "id" : "5E58FA0F-7DBD-4F1D-956F-89756CF1EB22",
  "name" : "Weezer (The Blue Album)",
  "songs" : [ {
    "duration" : {
      "duration" : "3:25"
    },
    "id" : "82BDE132-E492-4FED-9A77-B49CADBC2BFD",
    "name" : {
      "title" : "My Name Is Jonas"
    }
  }, {
    "duration" : {
      "duration" : "3:05"
    },
    "id" : "6E8AC92B-ABB4-4303-89CC-51020CEBB557",
    "name" : {
      "title" : "No One Else"
    }
  }, {
    "duration" : {
      "duration" : "4:19"
    },
    "id" : "0A856A54-2E15-4D4A-9B4B-1870F7783EBE",
    "name" : {
      "title" : "The World Has Turned And Left Me Here"
    }
  }, {
    "duration" : {
      "duration" : "2:39"
    },
    "id" : "7119F603-B37E-40B5-968D-E0091A610765",
    "name" : {
      "title" : "Buddy Holly"
    }
  }, {
    "duration" : {
      "duration" : "5:06"
    },
    "id" : "DDECE717-E075-4A64-9A9F-68CB2A5A58B6",
    "name" : {
      "title" : "Undone (The Sweater Song)"
    }
  }, {
    "duration" : {
      "duration" : "3:06"
    },
    "id" : "3FD6E647-4DF1-48CF-8E76-B932DF773ED3",
    "name" : {
      "title" : "Surf Wax America"
    }
  }, {
    "duration" : {
      "duration" : "4:17"
    },
    "id" : "214FB379-4032-4310-8B7C-C69BA21C4394",
    "name" : {
      "title" : "Say It Ain’t So"
    }
  }, {
    "duration" : {
      "duration" : "3:56"
    },
    "id" : "E4ECC640-120D-4A35-8938-3D83DE031430",
    "name" : {
      "title" : "In The Garage"
    }
  }, {
    "duration" : {
      "duration" : "3:25"
    },
    "id" : "34C44D53-6B14-40F7-8438-F147BD2B321D",
    "name" : {
      "title" : "Holiday"
    }
  }, {
    "duration" : {
      "duration" : "7:59"
    },
    "id" : "BA71E72D-E148-4D81-9A11-D7EA048F2949",
    "name" : {
      "title" : "Only In Dreams"
    }
  } ]
}

IntermediateDecoding.swift

import Foundation

struct Album: Decodable {
    
    let artist: String
    let coverArt: [URL]
    let genres: [String]
    let id: UUID
    let name: String
    let songs: [Song]
    
    enum AlbumKeys: String, CodingKey {
        case artist
        case coverArt
        case genres
        case id
        case name
        case songs
    }
    
    enum CoverArtKey: String, CodingKey {
        case url
    }
    
    init(from decoder: Decoder) throws {
        do {
            let albumContainer = try decoder.container(keyedBy: AlbumKeys.self)
            artist = try albumContainer.decode(String.self, forKey: .artist)
            
            var coverArtContainer = try albumContainer.nestedUnkeyedContainer(forKey: .coverArt)
            var coverArtUrls = [URL]()
            let urlContainer = try coverArtContainer.nestedContainer(keyedBy: CoverArtKey.self)
            while !coverArtContainer.isAtEnd {
                coverArtUrls.append(try urlContainer.decode(URL.self, forKey: .url))
            }
            coverArt = coverArtUrls
            
            genres = try albumContainer.decode([String].self, forKey: .genres)
            id = try albumContainer.decode(UUID.self, forKey: .id)
            name = try albumContainer.decode(String.self, forKey: .name)
            songs = try albumContainer.decode([Song].self, forKey: .songs)
            
        } catch {
            throw error
        }
        
    }
    
    
    
    struct Song: Decodable {
        let duration: String
        let id: UUID
        let title: String
        
        enum SongKeys: String, CodingKey {
            case id
            case title = "name"
            case duration
        }
        
        enum TitleKey: String, CodingKey {
            case title
        }
        
        enum DurationKeys: String, CodingKey {
            case duration
        }
        
        init(from decoder: Decoder) throws {
            let songContainer = try decoder.container(keyedBy: SongKeys.self)
            do {
                let titleContainer = try songContainer.nestedContainer(keyedBy: TitleKey.self, forKey: .title)
                title = try titleContainer.decode(String.self, forKey: .title)
                id = try songContainer.decode(UUID.self, forKey: .id)
                
                let durationContainer = try songContainer.nestedContainer(keyedBy: DurationKeys.self, forKey: .duration)
                duration = try durationContainer.decode(String.self, forKey: .duration)
            } catch {
                throw error
            }
        }
    }
}