//! Module defining the core shell structure and behavior.

use std::borrow::Cow;
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::Arc;

use tokio::sync::Mutex;

use crate::{
    ExecutionControlFlow, ExecutionResult, builtins, env::ShellEnvironment, error, extensions,
    functions, interfaces, jobs, keywords, openfiles, options::RuntimeOptions, pathcache,
    wellknownvars,
};

/// Type for storing a key bindings helper.
pub type KeyBindingsHelper = Arc<Mutex<dyn interfaces::KeyBindings>>;

/// Type alias for shell file descriptors.
pub type ShellFd = i32;

// NOTE: The submodule files below (e.g., `shell/traps.rs`, `shell/callstack.rs`) contain
// `impl Shell<SE>` blocks that provide methods coordinating with types defined in the
// corresponding top-level modules (e.g., `traps.rs`, `callstack.rs`). This is an intentional
// layered architecture: top-level modules define domain types and data structures, while
// shell/ submodules implement Shell methods that operate on those types.

mod builder;
mod builtin_registry;
mod callstack;
mod completion;
mod env;
mod execution;
mod expansion;
mod fs;
mod funcs;
mod history;
mod initscripts;
mod io;
mod job_control;
mod parsing;
mod prompts;
mod readline;
mod state;
mod traps;

pub use builder::{CreateOptions, ShellBuilder, ShellBuilderState};
pub use initscripts::{ProfileLoadBehavior, RcLoadBehavior};
pub use state::ShellState;

/// Represents an instance of a shell.
///
/// # Type Parameters
///
/// * `SE` - The shell extensions implementation to use. These extensions are statically injected
///   into the shell at compile time to provide custom behavior. When unspecified, defaults to
///   `DefaultShellExtensions`, which provide standard behavior.
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct Shell<SE: extensions::ShellExtensions = extensions::DefaultShellExtensions> {
    /// Injected error behavior.
    #[cfg_attr(feature = "serde", serde(skip, default = "default_error_formatter"))]
    error_formatter: SE::ErrorFormatter,

    /// Injected process launcher.
    #[cfg_attr(feature = "serde", serde(skip, default = "default_process_launcher"))]
    process_launcher: SE::ProcessLauncher,

    /// Injected task spawner.
    #[cfg_attr(feature = "serde", serde(skip, default = "default_task_spawner"))]
    task_spawner: SE::TaskSpawner,

    /// The builtins' state; see [`crate::ExecutionContext::state_mut`].
    #[cfg_attr(feature = "serde", serde(skip, default))]
    builtin_states: builtins::BuiltinStates,

    /// Trap handler configuration for the shell.
    traps: crate::traps::TrapHandlerConfig,

    /// Manages files opened and accessible via redirection operators.
    open_files: openfiles::OpenFiles,

    /// The current working directory.
    working_dir: PathBuf,

    /// The shell environment, containing shell variables.
    env: ShellEnvironment,

    /// Shell function definitions.
    funcs: functions::FunctionEnv,

    /// Runtime shell options.
    options: RuntimeOptions,

    /// State of managed jobs.
    /// TODO(serde): Need to warn somehow that jobs cannot be serialized.
    #[cfg_attr(feature = "serde", serde(skip))]
    jobs: jobs::JobManager,

    /// Shell aliases.
    aliases: HashMap<String, String>,

    /// The status of the last completed command.
    last_exit_status: u8,

    /// Tracks changes to `last_exit_status`. Assignment-only commands observe it
    /// to tell whether an expansion set a status (see `interp.rs`), so code that
    /// rolls back `$?` must roll this back too.
    last_exit_status_change_count: usize,

    /// The status of each of the commands in the last pipeline.
    last_pipeline_statuses: Vec<u8>,

    /// Clone depth from the original ancestor shell.
    depth: usize,

    /// The number the `\#` prompt escape shows: 1, plus one for each command the
    /// interactive loop has run.
    command_number: usize,

    /// Shell name
    name: Option<String>,

    /// Positional shell arguments (not including shell name).
    args: Vec<String>,

    /// Shell version
    version: Option<String>,

    /// Detailed display string for the shell
    product_display_str: Option<String>,

    /// Function/script call stack.
    call_stack: crate::callstack::CallStack,

    /// Directory stack used by pushd et al.
    directory_stack: Vec<PathBuf>,

    /// Programmable completion state.
    completion: crate::completion::State,

    /// Shell built-in commands.
    #[cfg_attr(feature = "serde", serde(skip))]
    builtins: builtins::Registry<SE>,

    /// Shell program location cache.
    program_location_cache: pathcache::PathCache,

    /// Last "SECONDS" captured time.
    last_stopwatch_time: std::time::SystemTime,

    /// Last "SECONDS" offset requested.
    last_stopwatch_offset: u32,

    /// Parser implementation to use.
    #[cfg_attr(feature = "serde", serde(skip))]
    parser_impl: crate::parser::ParserImpl,

    /// Key bindings for the shell, optionally implemented by an interactive shell.
    #[cfg_attr(feature = "serde", serde(skip))]
    key_bindings: Option<KeyBindingsHelper>,

    /// History of commands executed in the shell.
    history: Option<crate::history::History>,
}

impl<SE: extensions::ShellExtensions> Clone for Shell<SE> {
    fn clone(&self) -> Self {
        Self {
            error_formatter: self.error_formatter.clone(),
            process_launcher: self.process_launcher.clone(),
            task_spawner: self.task_spawner.clone(),
            builtin_states: self.builtin_states.clone(),
            traps: self.traps.clone(),
            open_files: self.open_files.clone(),
            working_dir: self.working_dir.clone(),
            env: self.env.clone(),
            funcs: self.funcs.clone(),
            options: self.options.clone(),
            jobs: jobs::JobManager::new(),
            aliases: self.aliases.clone(),
            last_exit_status: self.last_exit_status,
            last_exit_status_change_count: self.last_exit_status_change_count,
            last_pipeline_statuses: self.last_pipeline_statuses.clone(),
            name: self.name.clone(),
            args: self.args.clone(),
            version: self.version.clone(),
            product_display_str: self.product_display_str.clone(),
            call_stack: {
                // Subshells must not inherit the parent's "currently handling signal X"
                // state; otherwise a trap handler that spawns a subshell would see itself
                // as already inside that handler and skip re-entrant delivery.
                let mut cs = self.call_stack.clone();
                cs.clear_active_trap_signals();
                cs
            },
            directory_stack: self.directory_stack.clone(),
            // A subshell of a completion function (e.g. `$(compgen ...)`) is in that
            // completion too. Like a forked subshell in bash, it changes only its own copy
            // (e.g. with `compopt`), which its parent doesn't see.
            completion: self.completion.clone(),
            builtins: self.builtins.clone(),
            program_location_cache: self.program_location_cache.clone(),
            last_stopwatch_time: self.last_stopwatch_time,
            last_stopwatch_offset: self.last_stopwatch_offset,
            parser_impl: self.parser_impl,
            key_bindings: self.key_bindings.clone(),
            history: self.history.clone(),
            depth: self.depth + 1,
            command_number: self.command_number,
        }
    }
}

impl<SE: extensions::ShellExtensions> AsRef<Self> for Shell<SE> {
    fn as_ref(&self) -> &Self {
        self
    }
}

impl<SE: extensions::ShellExtensions> AsMut<Self> for Shell<SE> {
    fn as_mut(&mut self) -> &mut Self {
        self
    }
}

impl<SE: extensions::ShellExtensions> Shell<SE> {
    /// Returns a new shell instance created with the given options.
    /// Does *not* load any configuration files (e.g., bashrc).
    ///
    /// # Arguments
    ///
    /// * `options` - The options to use when creating the shell.
    pub(crate) fn new(options: CreateOptions<SE>) -> Result<Self, error::Error> {
        // Compute runtime options before moving fields out of `options`.
        let runtime_options = RuntimeOptions::defaults_from(&options);

        // Instantiate the shell with some defaults.
        let mut shell = Self {
            error_formatter: options.error_formatter,
            process_launcher: options.process_launcher,
            task_spawner: options.task_spawner,
            builtin_states: builtins::BuiltinStates::default(),
            open_files: openfiles::OpenFiles::new(),
            options: runtime_options,
            name: options.shell_name,
            args: options.shell_args.unwrap_or_default(),
            version: options.shell_version,
            product_display_str: options.shell_product_display_str,
            working_dir: options.working_dir.map_or_else(std::env::current_dir, Ok)?,
            builtins: options.builtins,
            parser_impl: options.parser,
            key_bindings: options.key_bindings,
            ..Self::default()
        };

        // Add in any open files provided.
        shell.open_files.update_from(options.fds.into_iter());

        // TODO(patterns): Without this a script that sets extglob will fail because we
        // parse the entire script with the same settings.
        shell.options.extended_globbing = true;

        // If requested, seed parameters from environment.
        if !options.do_not_inherit_env {
            wellknownvars::inherit_env_vars(&mut shell)?;
        }

        // If requested, set well-known variables.
        if !options.skip_well_known_vars {
            wellknownvars::init_well_known_vars(&mut shell)?;
        }

        // Set any provided variables.
        for (var_name, var_value) in options.vars {
            shell.env.set_global(var_name, var_value)?;
        }

        // Set up history, if relevant. The history file itself is loaded later, once startup
        // files have run, since they may change HISTFILE.
        if shell.options.enable_command_history {
            shell.history = Some(crate::history::History::default());
        }

        Ok(shell)
    }
}

impl<SE: extensions::ShellExtensions> Shell<SE> {
    /// Increments the interactive line offset in the shell by the indicated number
    /// of lines. The interactive loop calls this once after each command it runs, so
    /// it also advances the command number that the `\#` prompt escape shows.
    ///
    /// # Arguments
    ///
    /// * `delta` - The number of lines to increment the current line offset by.
    pub fn increment_interactive_line_offset(&mut self, delta: usize) {
        self.call_stack.increment_current_line_offset(delta);
        // shortcut: counts every line the loop runs, which bash doesn't for blank, comment-only
        // or unparsable ones or for a bound key; count where the reader loop parses, once it's
        // in core.
        self.command_number += 1;
    }

    /// Updates the currently executing command in the shell.
    pub fn set_current_cmd(&mut self, cmd: &impl brush_parser::ast::Node) {
        self.call_stack
            .set_current_pos(cmd.location().map(|span| span.start));
    }

    /// Updates the `$_` shell variable (last-argument of the previous simple
    /// command).
    ///
    /// Passes `Some(last_arg)` to record the last argument of the just-executed
    /// command, or `None` to clear `$_` (used for assignment-only statements,
    /// which bash treats as having no "last argument").
    ///
    /// The update is applied in-place so that attributes on `_` (notably
    /// `readonly`) are preserved: attempting to update a readonly `_` is a
    /// silent no-op, matching bash's observable stdout behavior.
    pub(crate) fn update_last_arg_variable(&mut self, last_arg: Option<String>) {
        // Bash refuses to update a readonly `_`, emitting an error to stderr
        // on each attempt. We silently skip the update here — the observable
        // stdout effect ($_ stays unchanged) matches bash; the missing stderr
        // diagnostics are harmless.
        if self
            .env
            .get_using_policy("_", crate::env::EnvironmentLookup::Anywhere)
            .is_some_and(|v| v.is_readonly())
        {
            return;
        }

        // Replace the variable entirely (fresh, non-exported). This matches
        // bash, which never exports `_` — even under `set -a` — and always
        // clears any previously-set attributes (except readonly, handled
        // above).
        let value = last_arg.unwrap_or_default();
        let _ = self
            .env
            .set_global("_", crate::variables::ShellVariable::new(value));
    }

    /// Captures the state the last command left behind; see [`SavedCommandStatus`].
    pub fn save_command_status(&self) -> SavedCommandStatus {
        SavedCommandStatus {
            exit_status: self.last_exit_status,
            exit_status_change_count: self.last_exit_status_change_count,
            pipeline_statuses: self.last_pipeline_statuses.clone(),
            last_arg: self.env_str("_").map(|value| value.into_owned()),
        }
    }

    /// Reapplies a snapshot, exit-status change counter included. Consumes it; `clone` it to
    /// put the same one back more than once, e.g. between successive hook functions.
    ///
    /// # Arguments
    ///
    /// * `saved` - The snapshot to restore.
    pub fn restore_command_status(&mut self, saved: SavedCommandStatus) {
        self.last_pipeline_statuses = saved.pipeline_statuses;
        // Assigned directly rather than through `set_last_exit_status`, which would bump
        // the change counter we're about to put back.
        self.last_exit_status = saved.exit_status;
        self.last_exit_status_change_count = saved.exit_status_change_count;
        match saved.last_arg {
            Some(last_arg) => self.update_last_arg_variable(Some(last_arg)),
            // `_` was unset when the snapshot was taken, so put it back that way. Unsetting
            // a readonly `_` fails; ignore that, as `update_last_arg_variable` does.
            None => _ = self.env.unset("_"),
        }
    }

    /// Applies errexit semantics to a result if enabled and appropriate.
    /// This should be called at "statement boundaries" where errexit should be checked.
    ///
    /// # Arguments
    ///
    /// * `result` - The execution result to potentially modify.
    pub const fn apply_errexit_if_enabled(&self, result: &mut ExecutionResult) {
        if self.options.exit_on_nonzero_command_exit
            && !result.is_success()
            && result.is_normal_flow()
        {
            result.next_control_flow = ExecutionControlFlow::ExitShell;
        }
    }

    /// Returns the keywords that are reserved by the shell, in the order bash lists them.
    pub(crate) fn get_keywords(&self) -> impl IntoIterator<Item = &'static str> {
        keywords::keywords(self.options.sh_mode)
    }

    /// Returns the launcher that starts the processes the shell runs.
    pub const fn process_launcher(&self) -> &SE::ProcessLauncher {
        &self.process_launcher
    }

    /// Returns the spawner that starts the tasks the shell runs concurrently with
    /// itself.
    pub const fn task_spawner(&self) -> &SE::TaskSpawner {
        &self.task_spawner
    }

    /// Checks if the given string is a keyword reserved in this shell.
    ///
    /// # Arguments
    ///
    /// * `s` - The string to check.
    pub fn is_keyword(&self, s: &str) -> bool {
        keywords::keywords(self.options.sh_mode).any(|keyword| keyword == s)
    }

    pub(crate) const fn last_exit_status_change_count(&self) -> usize {
        self.last_exit_status_change_count
    }

    pub(crate) const fn command_number(&self) -> usize {
        self.command_number
    }
}

/// Snapshot of the state the last command left behind: `$?`, `PIPESTATUS`, and `$_`.
///
/// Take one with [`Shell::save_command_status`] and put it back with
/// [`Shell::restore_command_status`] around anything the user didn't type -- a shell hook,
/// `PROMPT_COMMAND`, prompt expansion -- so it stays invisible to the next command.
#[derive(Clone, Debug)]
pub struct SavedCommandStatus {
    exit_status: u8,
    exit_status_change_count: usize,
    pipeline_statuses: Vec<u8>,
    last_arg: Option<String>,
}

#[inherent::inherent]
impl<SE: extensions::ShellExtensions> ShellState for Shell<SE> {
    /// Returns whether or not this shell is a subshell.
    pub fn is_subshell(&self) -> bool {
        self.depth > 0
    }

    /// Returns the last "SECONDS" captured time.
    pub fn last_stopwatch_time(&self) -> std::time::SystemTime {
        self.last_stopwatch_time
    }

    /// Returns the last "SECONDS" offset requested.
    pub fn last_stopwatch_offset(&self) -> u32 {
        self.last_stopwatch_offset
    }

    /// Returns the shell environment containing variables.
    pub fn env(&self) -> &ShellEnvironment {
        &self.env
    }

    /// Returns a mutable reference to the shell environment.
    pub fn env_mut(&mut self) -> &mut ShellEnvironment {
        &mut self.env
    }

    /// Returns the shell's runtime options.
    pub fn options(&self) -> &RuntimeOptions {
        &self.options
    }

    /// Returns a mutable reference to the shell's runtime options.
    pub fn options_mut(&mut self) -> &mut RuntimeOptions {
        &mut self.options
    }

    /// Returns the shell's aliases.
    pub fn aliases(&self) -> &HashMap<String, String> {
        &self.aliases
    }

    /// Returns a mutable reference to the shell's aliases.
    pub fn aliases_mut(&mut self) -> &mut HashMap<String, String> {
        &mut self.aliases
    }

    /// Returns the shell's job manager.
    pub fn jobs(&self) -> &jobs::JobManager {
        &self.jobs
    }

    /// Returns a mutable reference to the shell's job manager.
    pub fn jobs_mut(&mut self) -> &mut jobs::JobManager {
        &mut self.jobs
    }

    /// Returns the shell's trap handler configuration.
    pub fn traps(&self) -> &crate::traps::TrapHandlerConfig {
        &self.traps
    }

    /// Returns a mutable reference to the shell's trap handler configuration.
    pub fn traps_mut(&mut self) -> &mut crate::traps::TrapHandlerConfig {
        &mut self.traps
    }

    /// Returns the shell's directory stack.
    pub fn directory_stack(&self) -> &[PathBuf] {
        &self.directory_stack
    }

    /// Returns a mutable reference to the shell's directory stack.
    pub fn directory_stack_mut(&mut self) -> &mut Vec<PathBuf> {
        &mut self.directory_stack
    }

    /// Returns the statuses of commands in the last pipeline.
    pub fn last_pipeline_statuses(&self) -> &[u8] {
        &self.last_pipeline_statuses
    }

    /// Returns a mutable reference to the statuses of commands in the last pipeline.
    pub fn last_pipeline_statuses_mut(&mut self) -> &mut Vec<u8> {
        &mut self.last_pipeline_statuses
    }

    /// Returns the shell's program location cache.
    pub fn program_location_cache(&self) -> &pathcache::PathCache {
        &self.program_location_cache
    }

    /// Returns a mutable reference to the shell's program location cache.
    pub fn program_location_cache_mut(&mut self) -> &mut pathcache::PathCache {
        &mut self.program_location_cache
    }

    /// Returns the shell's completion configuration.
    pub fn completion_config(&self) -> &crate::completion::Config {
        &self.completion.config
    }

    /// Returns a mutable reference to the shell's completion configuration.
    pub fn completion_config_mut(&mut self) -> &mut crate::completion::Config {
        &mut self.completion.config
    }

    /// Returns the shell's open files.
    pub fn open_files(&self) -> &openfiles::OpenFiles {
        &self.open_files
    }

    /// Returns a mutable reference to the shell's open files.
    pub fn open_files_mut(&mut self) -> &mut openfiles::OpenFiles {
        &mut self.open_files
    }

    /// Returns the *current* name of the shell ($0).
    /// Influenced by the current call stack.
    pub fn current_shell_name(&self) -> Option<Cow<'_, str>> {
        for frame in self.call_stack.iter() {
            // Executed scripts shadow the shell name.
            if frame.frame_type.is_run_script() {
                return Some(frame.frame_type.name());
            }
        }

        self.name.as_deref().map(|name| name.into())
    }

    /// Returns the current subshell depth; 0 is returned if this shell is not a subshell.
    pub fn depth(&self) -> usize {
        self.depth
    }

    /// Returns the call stack for the shell.
    pub fn call_stack(&self) -> &crate::callstack::CallStack {
        &self.call_stack
    }

    /// Returns the shell's history, if it exists.
    pub fn history(&self) -> Option<&crate::history::History> {
        self.history.as_ref()
    }

    /// Returns a mutable reference to the shell's history, if it exists.
    pub fn history_mut(&mut self) -> Option<&mut crate::history::History> {
        self.history.as_mut()
    }

    /// Returns the shell's official version string (if available).
    pub fn version(&self) -> Option<&str> {
        self.version.as_deref()
    }

    /// Returns the exit status of the last command executed in this shell.
    pub fn last_exit_status(&self) -> u8 {
        self.last_exit_status
    }

    /// Updates the last exit status, bumping `last_exit_status_change_count`. To *restore* a
    /// status rather than set one, use [`Self::restore_command_status`], which puts the
    /// counter back too.
    pub fn set_last_exit_status(&mut self, status: u8) {
        self.last_exit_status = status;
        self.last_exit_status_change_count += 1;
    }

    /// Returns the key bindings helper for the shell.
    pub fn key_bindings(&self) -> Option<&KeyBindingsHelper> {
        self.key_bindings.as_ref()
    }

    /// Sets the key bindings helper for the shell.
    pub fn set_key_bindings(&mut self, key_bindings: Option<KeyBindingsHelper>) {
        self.key_bindings = key_bindings;
    }

    /// Returns the shell's current working directory.
    pub fn working_dir(&self) -> &Path {
        &self.working_dir
    }

    /// Returns a mutable reference to the shell's current working directory.
    /// This is only accessible within the crate.
    pub(crate) fn working_dir_mut(&mut self) -> &mut PathBuf {
        &mut self.working_dir
    }

    /// Returns the product display name for this shell.
    pub fn product_display_str(&self) -> Option<&str> {
        self.product_display_str.as_deref()
    }
}

#[cfg(feature = "serde")]
fn default_error_formatter<EF: extensions::ErrorFormatter>() -> EF {
    EF::default()
}

#[cfg(feature = "serde")]
fn default_process_launcher<PL: extensions::ProcessLauncher>() -> PL {
    PL::default()
}

#[cfg(feature = "serde")]
fn default_task_spawner<TS: extensions::TaskSpawner>() -> TS {
    TS::default()
}

#[cfg(test)]
#[allow(clippy::panic_in_result_fn, reason = "assertions in a fallible test")]
mod tests {
    use super::*;

    /// `$_` round-trips through a snapshot, unset included, so an embedder that saves before
    /// running commands of its own gets back exactly what was there -- not an empty string.
    /// (The interactive loop can't reach the unset case: every command resets `$_`.)
    #[tokio::test]
    async fn saved_command_status_round_trips_last_arg() -> Result<(), error::Error> {
        let mut shell = Shell::builder()
            .profile(ProfileLoadBehavior::Skip)
            .rc(RcLoadBehavior::Skip)
            .build()
            .await?;

        shell.update_last_arg_variable(Some(String::from("saved")));
        let with_value = shell.save_command_status();

        shell.env.unset("_")?;
        let while_unset = shell.save_command_status();

        shell.restore_command_status(with_value);
        assert_eq!(shell.env_str("_").as_deref(), Some("saved"));

        shell.restore_command_status(while_unset);
        assert_eq!(shell.env_str("_"), None);

        Ok(())
    }

    #[tokio::test]
    async fn unset_env_str_contract_is_independent_of_ifs_default() -> Result<(), error::Error> {
        let mut shell = Shell::builder()
            .profile(ProfileLoadBehavior::Skip)
            .rc(RcLoadBehavior::Skip)
            .build()
            .await?;

        shell.env.set_global(
            "IFS",
            crate::ShellVariable::new(crate::ShellValue::Unset(
                crate::variables::ShellValueUnsetType::Untyped,
            )),
        )?;
        assert_eq!(shell.env_str("IFS").as_deref(), Some(""));
        assert_eq!(shell.ifs(), " \t\n");

        shell.env.set_global("IFS", crate::ShellVariable::new(""))?;
        assert_eq!(shell.env_str("IFS").as_deref(), Some(""));
        assert_eq!(shell.ifs(), "");

        Ok(())
    }
}