"======================================================================
 Class: Book
 ======================================================================"
Object subclass: Book [
    | title author isBorrowed |

    "クラスメソッド: インスタンス生成用"
    Book class >> title: aTitle author: anAuthor [
        ^self new setTitle: aTitle author: anAuthor
    ]

    setTitle: aTitle author: anAuthor [
        title := aTitle.
        author := anAuthor.
        isBorrowed := false.
    ]

    "ゲッター / セッター"
    title [ ^title ]
    author [ ^author ]
    isBorrowed [ ^isBorrowed ]
    isBorrowed: aBoolean [ isBorrowed := aBoolean ]

    "文字列表現"
    asString [
        ^title , ' (by ' , author , ')' , (isBorrowed ifTrue: [ ' [貸出中]' ] ifFalse: [ ' [貸出可能]' ])
    ]
]

"======================================================================
 Class: User
 ======================================================================"
Object subclass: User [
    | name borrowedBooks maxBooks |

    "クラスメソッド: インスタンス生成用"
    User class >> name: aName maxBooks: aLimit [
        ^self new setName: aName maxBooks: aLimit
    ]

    setName: aName maxBooks: aLimit [
        name := aName.
        maxBooks := aLimit.
        borrowedBooks := OrderedCollection new.
    ]

    "ゲッター"
    name [ ^name ]
    borrowedBooks [ ^borrowedBooks ]

    "ビジネスロジック: まだ借りられるか判定"
    canBorrowMore [
        ^borrowedBooks size < maxBooks
    ]

    borrowBook: aBook [
        borrowedBooks add: aBook.
    ]

    returnBook: aBook [
        borrowedBooks remove: aBook ifAbsent: [].
    ]
]

"======================================================================
 Class: Library
 ======================================================================"
Object subclass: Library [
    | books users |

    "クラスメソッド: 初期化を伴うインスタンス作成"
    Library class >> new [
        ^super new initialize
    ]

    initialize [
        books := OrderedCollection new.
        users := OrderedCollection new.
    ]

    "管理リストへの追加"
    addBook: aBook [ books add: aBook ]
    addUser: aUser [ users add: aUser ]

    "貸出メソッド"
    checkoutBook: aBook forUser: aUser [
        "バリデーション"
        (books includes: aBook) ifFalse: [
            '【エラー】この本は図書館に登録されていません。' printNl. ^false
        ].
        (users includes: aUser) ifFalse: [
            '【エラー】この利用者は登録されていません。' printNl. ^false
        ].
        aBook isBorrowed ifTrue: [
            ('【エラー】「' , aBook title , '」はすでに貸出中です。') printNl. ^false
        ].
        aUser canBorrowMore ifFalse: [
            ('【エラー】' , aUser name , ' 様は貸出上限（制限数に達しています）を超えています。') printNl. ^false
        ].

        "貸出の実行（状態変更）"
        aBook isBorrowed: true.
        aUser borrowBook: aBook.
        (aUser name , ' 様が「' , aBook title , '」を借りました。') printNl.
        ^true
    ]

    "返却メソッド"
    returnBook: aBook fromUser: aUser [
        (aUser borrowedBooks includes: aBook) ifFalse: [
            ('【エラー】' , aUser name , ' 様はこの本を借りていません。') printNl. ^false
        ].

        "返却の実行（状態変更）"
        aBook isBorrowed: false.
        aUser returnBook: aBook.
        (aUser name , ' 様が「' , aBook title , '」を返却しました。') printNl.
        ^true
    ]

    "現在のステータス表示"
    printStatus [
        '---------------------------------------' printNl.
        '【図書館ステータス】' printNl.
        '■ 蔵書一覧:' printNl.
        books do: [ :each | ('  - ' , each asString) printNl ].
        '■ 利用者一覧:' printNl.
        users do: [ :each |
            ('  - ' , each name , ' (貸出中: ' , each borrowedBooks size printString , '冊)') printNl.
        ].
        '---------------------------------------' printNl.
    ]
]

"======================================================================
 テストスクリプトの実行（メインルーチン）
 ======================================================================"
| myLibrary book1 book2 book3 student prof |

"1. 図書館の作成"
myLibrary := Library new.

"2. 本の登録"
book1 := Book title: 'Smalltalk-80 Blue Book' author: 'Adele Goldberg'.
book2 := Book title: 'Design Patterns' author: 'GoF'.
book3 := Book title: 'Squeak by Example' author: 'Stephane Ducasse'.

myLibrary addBook: book1; addBook: book2; addBook: book3.

"3. ユーザーの登録（学生は上限2冊、教授は上限5冊）"
student := User name: '山田太郎(学生)' maxBooks: 2.
prof := User name: 'スミス教授' maxBooks: 5.

myLibrary addUser: student; addUser: prof.

"--- 初期状態の出力 ---"
myLibrary printStatus.

"--- 貸出シミュレーション ---"
'>>> シナリオ1: 山田さんが2冊借りる' printNl.
myLibrary checkoutBook: book1 forUser: student.
myLibrary checkoutBook: book2 forUser: student.

'>>> シナリオ2: 山田さんが3冊目を借りようとする（上限エラーになるはず）' printNl.
myLibrary checkoutBook: book3 forUser: student.

'>>> シナリオ3: スミス教授が山田さんの借りている本を借りようとする（貸出中エラーになるはず）' printNl.
myLibrary checkoutBook: book1 forUser: prof.

'>>> シナリオ4: スミス教授が空いている本を借りる（成功するはず）' printNl.
myLibrary checkoutBook: book3 forUser: prof.

myLibrary printStatus.

'>>> シナリオ5: 山田さんが1冊返却し、再度別の人に貸し出せるようにする' printNl.
myLibrary returnBook: book1 fromUser: student.

myLibrary printStatus.