sequenceDiagram
    actor User
    participant Shell
    participant Fnmbin as fnm_binary
    participant EnvCmd as Env_command
    participant UseCmd as Use_command
    participant OS as OS_environment

    User->>Shell: evaluate env setup (fnm env --use-on-cd --shell <shell>)
    Shell->>Fnmbin: invoke Env subcommand
    Fnmbin->>EnvCmd: run Env.apply(config)

    EnvCmd->>OS: compute multishell_path
    EnvCmd->>OS: set_path_for_multishell(multishell_path)
    OS-->>EnvCmd: PATH updated to include multishell bin

    EnvCmd->>EnvCmd: config_with_multishell = config.with_multishell_path(multishell_path)
    EnvCmd->>UseCmd: construct Use_command(info_to_stderr = true, install_if_missing = false, silent_if_unchanged = true)

    EnvCmd->>OS: check NO_COLOR, stdout, stderr
    alt should_force_stderr_color
        EnvCmd->>OS: enable colored override
    end

    EnvCmd->>UseCmd: Use.apply(config_with_multishell)
    UseCmd->>OS: read version file and select Node version
    UseCmd->>OS: update PATH for selected Node version
    UseCmd-->>EnvCmd: result (errors ignored)

    alt should_force_stderr_color
        EnvCmd->>OS: disable colored override
    end

    EnvCmd->>Shell: print shell hook script (shell.use_on_cd(config))
    Shell-->>User: hook installed without extra fnm use subprocess on first cd

classDiagram
    class FnmConfig {
        <<clap::Parser, Clone>>
        +mirror Url
        +arch Arch
        +multishell_path Option~PathBuf~
        +with_base_dir(base_dir Option~PathBuf~) FnmConfig
        +with_multishell_path(multishell_path PathBuf) FnmConfig
    }

    class Directories {
        <<Clone>>
        +base BaseStrategy
        +new() Directories
        +cache_dir() PathBuf
    }

    class Use {
        +version Option~UserVersion~
        +install_if_missing bool
        +silent_if_unchanged bool
        +info_to_stderr bool
        +apply(config &FnmConfig) Result~(), Error~
    }

    class Arch {
        <<enum>>
        X86
        X64
        X64Musl
        X64Glibc217
        Arm64
        Armv7l
        Ppc64le
        Arm64Musl
        +to_string() &str
        +from_str(s &str) Result~Arch, Error~
    }

    class EnvCommand {
        +use_on_cd bool
        +apply(config &FnmConfig) Result~(), Error~
        -set_path_for_multishell(multishell_path &Path)
    }

    class Shell {
        <<trait>>
        +env(config &FnmConfig) String
        +use_on_cd(config &FnmConfig) Result~String, Error~
        +rehash() Option~String~
    }

    class Zsh {
        +use_on_cd(config &FnmConfig) Result~String, Error~
        -add_zsh_hook_remove_existing()
    }

    class Bash {
        +use_on_cd(config &FnmConfig) Result~String, Error~
    }

    class Fish {
        +use_on_cd(config &FnmConfig) Result~String, Error~
    }

    class PowerShell {
        +use_on_cd(config &FnmConfig) Result~String, Error~
    }

    class WindowsCmd {
        +use_on_cd(config &FnmConfig) Result~String, Error~
        +create_cd_file_at(path &Path) Result~(), IoError~
    }

    FnmConfig *-- Directories
    FnmConfig o-- Arch
    EnvCommand ..> Use : constructs
    EnvCommand ..> FnmConfig : reads and clones
    Use ..> FnmConfig : uses
    Zsh ..|> Shell
    Bash ..|> Shell
    Fish ..|> Shell
    PowerShell ..|> Shell
    WindowsCmd ..|> Shell