//! Implementation of const-evaluation
//!
//! This enables you to assign `const`-constants and execute parse-time code dependent on this.
//! e.g. `source $my_const`
use crate::{
    ast::{Assignment, Block, Call, Expr, Expression, ExternalArgument},
    debugger::{DebugContext, WithoutDebug},
    engine::{EngineState, StateWorkingSet},
    eval_base::Eval,
    record, BlockId, Config, HistoryFileFormat, PipelineData, Record, ShellError, Span, Value,
    VarId,
};
use nu_system::os_info::{get_kernel_version, get_os_arch, get_os_family, get_os_name};
use std::{
    path::{Path, PathBuf},
    sync::Arc,
};

/// Create a Value for `$nu`.
pub(crate) fn create_nu_constant(engine_state: &EngineState, span: Span) -> Value {
    fn canonicalize_path(engine_state: &EngineState, path: &Path) -> PathBuf {
        #[allow(deprecated)]
        let cwd = engine_state.current_work_dir();

        if path.exists() {
            match nu_path::canonicalize_with(path, cwd) {
                Ok(canon_path) => canon_path,
                Err(_) => path.to_owned(),
            }
        } else {
            path.to_owned()
        }
    }

    let mut record = Record::new();

    let config_path = match nu_path::nu_config_dir() {
        Some(path) => Ok(canonicalize_path(engine_state, path.as_ref())),
        None => Err(Value::error(
            ShellError::ConfigDirNotFound { span: Some(span) },
            span,
        )),
    };

    record.push(
        "default-config-dir",
        config_path.as_ref().map_or_else(
            |e| e.clone(),
            |path| Value::string(path.to_string_lossy(), span),
        ),
    );

    record.push(
        "config-path",
        if let Some(path) = engine_state.get_config_path("config-path") {
            let canon_config_path = canonicalize_path(engine_state, path);
            Value::string(canon_config_path.to_string_lossy(), span)
        } else {
            config_path.clone().map_or_else(
                |e| e,
                |mut path| {
                    path.push("config.nu");
                    let canon_config_path = canonicalize_path(engine_state, &path);
                    Value::string(canon_config_path.to_string_lossy(), span)
                },
            )
        },
    );

    record.push(
        "env-path",
        if let Some(path) = engine_state.get_config_path("env-path") {
            let canon_env_path = canonicalize_path(engine_state, path);
            Value::string(canon_env_path.to_string_lossy(), span)
        } else {
            config_path.clone().map_or_else(
                |e| e,
                |mut path| {
                    path.push("env.nu");
                    let canon_env_path = canonicalize_path(engine_state, &path);
                    Value::string(canon_env_path.to_string_lossy(), span)
                },
            )
        },
    );

    record.push(
        "history-path",
        config_path.clone().map_or_else(
            |e| e,
            |mut path| {
                match engine_state.config.history.file_format {
                    HistoryFileFormat::Sqlite => {
                        path.push("history.sqlite3");
                    }
                    HistoryFileFormat::Plaintext => {
                        path.push("history.txt");
                    }
                }
                let canon_hist_path = canonicalize_path(engine_state, &path);
                Value::string(canon_hist_path.to_string_lossy(), span)
            },
        ),
    );

    record.push(
        "loginshell-path",
        config_path.clone().map_or_else(
            |e| e,
            |mut path| {
                path.push("login.nu");
                let canon_login_path = canonicalize_path(engine_state, &path);
                Value::string(canon_login_path.to_string_lossy(), span)
            },
        ),
    );

    #[cfg(feature = "plugin")]
    {
        record.push(
            "plugin-path",
            if let Some(path) = &engine_state.plugin_path {
                let canon_plugin_path = canonicalize_path(engine_state, path);
                Value::string(canon_plugin_path.to_string_lossy(), span)
            } else {
                // If there are no signatures, we should still populate the plugin path
                config_path.clone().map_or_else(
                    |e| e,
                    |mut path| {
                        path.push("plugin.msgpackz");
                        let canonical_plugin_path = canonicalize_path(engine_state, &path);
                        Value::string(canonical_plugin_path.to_string_lossy(), span)
                    },
                )
            },
        );
    }

    record.push(
        "home-path",
        if let Some(path) = nu_path::home_dir() {
            let canon_home_path = canonicalize_path(engine_state, path.as_ref());
            Value::string(canon_home_path.to_string_lossy(), span)
        } else {
            Value::error(
                ShellError::IOError {
                    msg: "Could not get home path".into(),
                },
                span,
            )
        },
    );

    record.push(
        "data-dir",
        if let Some(path) = nu_path::data_dir() {
            let mut canon_data_path = canonicalize_path(engine_state, path.as_ref());
            canon_data_path.push("nushell");
            Value::string(canon_data_path.to_string_lossy(), span)
        } else {
            Value::error(
                ShellError::IOError {
                    msg: "Could not get data path".into(),
                },
                span,
            )
        },
    );

    record.push(
        "cache-dir",
        if let Some(path) = nu_path::cache_dir() {
            let mut canon_cache_path = canonicalize_path(engine_state, path.as_ref());
            canon_cache_path.push("nushell");
            Value::string(canon_cache_path.to_string_lossy(), span)
        } else {
            Value::error(
                ShellError::IOError {
                    msg: "Could not get cache path".into(),
                },
                span,
            )
        },
    );

    record.push(
        "vendor-autoload-dirs",
        Value::list(
            get_vendor_autoload_dirs(engine_state)
                .iter()
                .map(|path| Value::string(path.to_string_lossy(), span))
                .collect(),
            span,
        ),
    );

    record.push("temp-path", {
        let canon_temp_path = canonicalize_path(engine_state, &std::env::temp_dir());
        Value::string(canon_temp_path.to_string_lossy(), span)
    });

    record.push("pid", Value::int(std::process::id().into(), span));

    record.push("os-info", {
        let ver = get_kernel_version();
        Value::record(
            record! {
                "name" => Value::string(get_os_name(), span),
                "arch" => Value::string(get_os_arch(), span),
                "family" => Value::string(get_os_family(), span),
                "kernel_version" => Value::string(ver, span),
            },
            span,
        )
    });

    record.push(
        "startup-time",
        Value::duration(engine_state.get_startup_time(), span),
    );

    record.push(
        "is-interactive",
        Value::bool(engine_state.is_interactive, span),
    );

    record.push("is-login", Value::bool(engine_state.is_login, span));

    record.push(
        "history-enabled",
        Value::bool(engine_state.history_enabled, span),
    );

    record.push(
        "current-exe",
        if let Ok(current_exe) = std::env::current_exe() {
            Value::string(current_exe.to_string_lossy(), span)
        } else {
            Value::error(
                ShellError::IOError {
                    msg: "Could not get current executable path".to_string(),
                },
                span,
            )
        },
    );

    Value::record(record, span)
}

pub fn get_vendor_autoload_dirs(_engine_state: &EngineState) -> Vec<PathBuf> {
    // load order for autoload dirs
    // /Library/Application Support/nushell/vendor/autoload on macOS
    // <dir>/nushell/vendor/autoload for every dir in XDG_DATA_DIRS in reverse order on platforms other than windows. If XDG_DATA_DIRS is not set, it falls back to <PREFIX>/share if PREFIX ends in local, or <PREFIX>/local/share:<PREFIX>/share otherwise. If PREFIX is not set, fall back to /usr/local/share:/usr/share.
    // %ProgramData%\nushell\vendor\autoload on windows
    // NU_VENDOR_AUTOLOAD_DIR from compile time, if env var is set at compile time
    // if on macOS, additionally check XDG_DATA_HOME, which `dirs` is only doing on Linux
    // <data_dir>/nushell/vendor/autoload of the current user according to the `dirs` crate
    // NU_VENDOR_AUTOLOAD_DIR at runtime, if env var is set

    let into_autoload_path_fn = |mut path: PathBuf| {
        path.push("nushell");
        path.push("vendor");
        path.push("autoload");
        path
    };

    let mut dirs = Vec::new();

    let mut append_fn = |path: PathBuf| {
        if !dirs.contains(&path) {
            dirs.push(path)
        }
    };

    #[cfg(target_os = "macos")]
    std::iter::once("/Library/Application Support")
        .map(PathBuf::from)
        .map(into_autoload_path_fn)
        .for_each(&mut append_fn);
    #[cfg(unix)]
    {
        use std::os::unix::ffi::OsStrExt;

        std::env::var_os("XDG_DATA_DIRS")
            .or_else(|| {
                option_env!("PREFIX").map(|prefix| {
                    if prefix.ends_with("local") {
                        std::ffi::OsString::from(format!("{prefix}/share"))
                    } else {
                        std::ffi::OsString::from(format!("{prefix}/local/share:{prefix}/share"))
                    }
                })
            })
            .unwrap_or_else(|| std::ffi::OsString::from("/usr/local/share/:/usr/share/"))
            .as_encoded_bytes()
            .split(|b| *b == b':')
            .map(|split| into_autoload_path_fn(PathBuf::from(std::ffi::OsStr::from_bytes(split))))
            .rev()
            .for_each(&mut append_fn);
    }

    #[cfg(target_os = "windows")]
    dirs_sys::known_folder(windows_sys::Win32::UI::Shell::FOLDERID_ProgramData)
        .into_iter()
        .map(into_autoload_path_fn)
        .for_each(&mut append_fn);

    option_env!("NU_VENDOR_AUTOLOAD_DIR")
        .into_iter()
        .map(PathBuf::from)
        .for_each(&mut append_fn);

    #[cfg(target_os = "macos")]
    std::env::var("XDG_DATA_HOME")
        .ok()
        .map(PathBuf::from)
        .or_else(|| {
            dirs::home_dir().map(|mut home| {
                home.push(".local");
                home.push("share");
                home
            })
        })
        .map(into_autoload_path_fn)
        .into_iter()
        .for_each(&mut append_fn);

    dirs::data_dir()
        .into_iter()
        .map(into_autoload_path_fn)
        .for_each(&mut append_fn);

    std::env::var_os("NU_VENDOR_AUTOLOAD_DIR")
        .into_iter()
        .map(PathBuf::from)
        .for_each(&mut append_fn);

    dirs
}

fn eval_const_call(
    working_set: &StateWorkingSet,
    call: &Call,
    input: PipelineData,
) -> Result<PipelineData, ShellError> {
    let decl = working_set.get_decl(call.decl_id);

    if !decl.is_const() {
        return Err(ShellError::NotAConstCommand { span: call.head });
    }

    if !decl.is_known_external() && call.named_iter().any(|(flag, _, _)| flag.item == "help") {
        // It would require re-implementing get_full_help() for const evaluation. Assuming that
        // getting help messages at parse-time is rare enough, we can simply disallow it.
        return Err(ShellError::NotAConstHelp { span: call.head });
    }

    decl.run_const(working_set, &call.into(), input)
}

pub fn eval_const_subexpression(
    working_set: &StateWorkingSet,
    block: &Block,
    mut input: PipelineData,
    span: Span,
) -> Result<PipelineData, ShellError> {
    for pipeline in block.pipelines.iter() {
        for element in pipeline.elements.iter() {
            if element.redirection.is_some() {
                return Err(ShellError::NotAConstant { span });
            }

            input = eval_constant_with_input(working_set, &element.expr, input)?
        }
    }

    Ok(input)
}

pub fn eval_constant_with_input(
    working_set: &StateWorkingSet,
    expr: &Expression,
    input: PipelineData,
) -> Result<PipelineData, ShellError> {
    match &expr.expr {
        Expr::Call(call) => eval_const_call(working_set, call, input),
        Expr::Subexpression(block_id) => {
            let block = working_set.get_block(*block_id);
            eval_const_subexpression(working_set, block, input, expr.span(&working_set))
        }
        _ => eval_constant(working_set, expr).map(|v| PipelineData::Value(v, None)),
    }
}

/// Evaluate a constant value at parse time
pub fn eval_constant(
    working_set: &StateWorkingSet,
    expr: &Expression,
) -> Result<Value, ShellError> {
    // TODO: Allow debugging const eval
    <EvalConst as Eval>::eval::<WithoutDebug>(working_set, &mut (), expr)
}

struct EvalConst;

impl Eval for EvalConst {
    type State<'a> = &'a StateWorkingSet<'a>;

    type MutState = ();

    fn get_config(state: Self::State<'_>, _: &mut ()) -> Arc<Config> {
        state.get_config().clone()
    }

    fn eval_filepath(
        _: &StateWorkingSet,
        _: &mut (),
        path: String,
        _: bool,
        span: Span,
    ) -> Result<Value, ShellError> {
        Ok(Value::string(path, span))
    }

    fn eval_directory(
        _: &StateWorkingSet,
        _: &mut (),
        _: String,
        _: bool,
        span: Span,
    ) -> Result<Value, ShellError> {
        Err(ShellError::NotAConstant { span })
    }

    fn eval_var(
        working_set: &StateWorkingSet,
        _: &mut (),
        var_id: VarId,
        span: Span,
    ) -> Result<Value, ShellError> {
        match working_set.get_variable(var_id).const_val.as_ref() {
            Some(val) => Ok(val.clone()),
            None => Err(ShellError::NotAConstant { span }),
        }
    }

    fn eval_call<D: DebugContext>(
        working_set: &StateWorkingSet,
        _: &mut (),
        call: &Call,
        span: Span,
    ) -> Result<Value, ShellError> {
        // TODO: Allow debugging const eval
        // TODO: eval.rs uses call.head for the span rather than expr.span
        eval_const_call(working_set, call, PipelineData::empty())?.into_value(span)
    }

    fn eval_external_call(
        _: &StateWorkingSet,
        _: &mut (),
        _: &Expression,
        _: &[ExternalArgument],
        span: Span,
    ) -> Result<Value, ShellError> {
        // TODO: It may be more helpful to give not_a_const_command error
        Err(ShellError::NotAConstant { span })
    }

    fn eval_collect<D: DebugContext>(
        _: &StateWorkingSet,
        _: &mut (),
        _var_id: VarId,
        expr: &Expression,
    ) -> Result<Value, ShellError> {
        Err(ShellError::NotAConstant { span: expr.span })
    }

    fn eval_subexpression<D: DebugContext>(
        working_set: &StateWorkingSet,
        _: &mut (),
        block_id: BlockId,
        span: Span,
    ) -> Result<Value, ShellError> {
        // TODO: Allow debugging const eval
        let block = working_set.get_block(block_id);
        eval_const_subexpression(working_set, block, PipelineData::empty(), span)?.into_value(span)
    }

    fn regex_match(
        _: &StateWorkingSet,
        _op_span: Span,
        _: &Value,
        _: &Value,
        _: bool,
        expr_span: Span,
    ) -> Result<Value, ShellError> {
        Err(ShellError::NotAConstant { span: expr_span })
    }

    fn eval_assignment<D: DebugContext>(
        _: &StateWorkingSet,
        _: &mut (),
        _: &Expression,
        _: &Expression,
        _: Assignment,
        _op_span: Span,
        expr_span: Span,
    ) -> Result<Value, ShellError> {
        // TODO: Allow debugging const eval
        Err(ShellError::NotAConstant { span: expr_span })
    }

    fn eval_row_condition_or_closure(
        _: &StateWorkingSet,
        _: &mut (),
        _: BlockId,
        span: Span,
    ) -> Result<Value, ShellError> {
        Err(ShellError::NotAConstant { span })
    }

    fn eval_overlay(_: &StateWorkingSet, span: Span) -> Result<Value, ShellError> {
        Err(ShellError::NotAConstant { span })
    }

    fn unreachable(working_set: &StateWorkingSet, expr: &Expression) -> Result<Value, ShellError> {
        Err(ShellError::NotAConstant {
            span: expr.span(&working_set),
        })
    }
}