use std::{
  cell::RefCell, collections::{HashMap, VecDeque}, fmt::Display, ops::{BitAnd, BitAndAssign, BitOr, BitOrAssign, Deref}, str::FromStr, time::Duration
};

use nix::unistd::{gethostname, getppid, User};

use crate::{
  exec_input,
  jobs::JobTab,
  libsh::{
    error::{ShErr, ShErrKind, ShResult},
    utils::VecDequeExt,
  },
  parse::{ConjunctNode, NdRule, Node, ParsedSrc},
  prelude::*,
  shopt::ShOpts,
};

pub struct Fern {
	pub jobs: RefCell<JobTab>,
	pub var_scopes: RefCell<ScopeStack>,
	pub meta: RefCell<MetaTab>,
	pub logic: RefCell<LogTab>,
	pub shopts: RefCell<ShOpts>,
}

impl Fern {
	pub fn new() -> Self {
		Self {
			jobs: RefCell::new(JobTab::new()),
			var_scopes: RefCell::new(ScopeStack::new()),
			meta: RefCell::new(MetaTab::new()),
			logic: RefCell::new(LogTab::new()),
			shopts: RefCell::new(ShOpts::default()),
		}
	}
}

impl Default for Fern {
	fn default() -> Self {
		Self::new()
	}
}

#[derive(Hash, Eq, PartialEq, Debug, Clone, Copy)]
pub enum ShellParam {
	// Global
	Status,
	ShPid,
	LastJob,
	ShellName,

	// Local
	Pos(usize),
	AllArgs,
	AllArgsStr,
	ArgCount
}

impl ShellParam {
	pub fn is_global(&self) -> bool {
		matches!(
			self,
			Self::Status | Self::ShPid | Self::LastJob | Self::ShellName
		)
	}
}

impl Display for ShellParam {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	  match self {
			Self::Status => write!(f, "?"),
			Self::ShPid => write!(f, "$"),
			Self::LastJob => write!(f, "!"),
			Self::ShellName => write!(f, "0"),
			Self::Pos(n) => write!(f, "{}", n),
			Self::AllArgs => write!(f, "@"),
			Self::AllArgsStr => write!(f, "*"),
			Self::ArgCount => write!(f, "#"),
		}
	}
}

impl FromStr for ShellParam {
	type Err = ShErr;
	fn from_str(s: &str) -> Result<Self, Self::Err> {
		match s {
			"?" => Ok(Self::Status),
			"$" => Ok(Self::ShPid),
			"!" => Ok(Self::LastJob),
			"0" => Ok(Self::ShellName),
			"@" => Ok(Self::AllArgs),
			"*" => Ok(Self::AllArgsStr),
			"#" => Ok(Self::ArgCount),
			n if n.parse::<usize>().is_ok() => {
				let idx = n.parse::<usize>().unwrap();
				Ok(Self::Pos(idx))
			}
			_ => Err(ShErr::simple(
				ShErrKind::InternalErr,
				format!("Invalid shell parameter: {}", s),
			)),
		}
	}
}

#[derive(Clone, Default, Debug)]
pub struct ScopeStack {
	// ALWAYS keep one scope.
	// The bottom scope is the global variable space.
	// Scopes that come after that are pushed in functions,
	// and only contain variables that are defined using `local`.
	scopes: Vec<VarTab>,
	depth: u32,

	// Global parameters such as $?, $!, $$, etc
	global_params: HashMap<String, String>,
}

impl ScopeStack {
	pub fn new() -> Self {
		let mut new = Self::default();
		new.scopes.push(VarTab::new());
		new
	}
	pub fn descend(&mut self, argv: Option<Vec<String>>) {
		let mut new_vars = VarTab::new();
		if let Some(argv) = argv {
			for arg in argv {
				new_vars.bpush_arg(arg);
			}
		}
		self.scopes.push(new_vars);
		self.depth += 1;
	}
	pub fn ascend(&mut self) {
		if self.depth >= 1 {
			self.scopes.pop();
			self.depth -= 1;
		}
	}
	pub fn cur_scope(&self) -> &VarTab {
		self.scopes.last().unwrap()
	}
	pub fn cur_scope_mut(&mut self) -> &mut VarTab {
		self.scopes.last_mut().unwrap()
	}
	pub fn unset_var(&mut self, var_name: &str) {
		for scope in self.scopes.iter_mut().rev() {
			if scope.var_exists(var_name) {
				scope.unset_var(var_name);
				return;
			}
		}
	}
	pub fn export_var(&mut self, var_name: &str) {
		for scope in self.scopes.iter_mut().rev() {
			if scope.var_exists(var_name) {
				scope.export_var(var_name);
				return;
			}
		}
	}
	pub fn var_exists(&self, var_name: &str) -> bool {
		for scope in self.scopes.iter().rev() {
			if scope.var_exists(var_name) {
				return true;
			}
		}
		if let Ok(param) = var_name.parse::<ShellParam>() {
			return self.global_params.contains_key(&param.to_string());
		}
		false
	}
	pub fn flatten_vars(&self) -> HashMap<String, Var> {
		let mut flat_vars = HashMap::new();
		for scope in self.scopes.iter() {
			for (var_name, var) in scope.vars() {
				flat_vars.insert(var_name.clone(), var.clone());
			}
		}
		flat_vars
	}
	pub fn set_var(&mut self, var_name: &str, val: &str, flags: VarFlags) {
		if flags.contains(VarFlags::LOCAL) {
			self.set_var_local(var_name, val, flags);
		} else {
			self.set_var_global(var_name, val, flags);
		}
	}
	fn set_var_global(&mut self, var_name: &str, val: &str, flags: VarFlags) {
		if let Some(scope) = self.scopes.first_mut() {
			scope.set_var(var_name, val, flags);
		}
	}
	fn set_var_local(&mut self, var_name: &str, val: &str, flags: VarFlags) {
		if let Some(scope) = self.scopes.last_mut() {
			scope.set_var(var_name, val, flags);
		}
	}
	pub fn get_var(&self, var_name: &str) -> String {
		if let Ok(param) = var_name.parse::<ShellParam>() {
			return self.get_param(param);
		}
		for scope in self.scopes.iter().rev() {
			if scope.var_exists(var_name) {
				return scope.get_var(var_name);
			}
		}
		// Fallback to env var
		std::env::var(var_name).unwrap_or_default()
	}
	pub fn get_param(&self, param: ShellParam) -> String {
		if param.is_global() && let Some(val) = self.global_params.get(&param.to_string()) {
			return val.clone();
		}
		for scope in self.scopes.iter().rev() {
			let val = scope.get_param(param);
			if !val.is_empty() {
				return val;
			}
		}
		// Fallback to empty string
		"".into()
	}
	/// Set a shell parameter
	/// Therefore, these are global state and we use the global scope
	pub fn set_param(&mut self, param: ShellParam, val: &str) {
		match param {
			ShellParam::ShPid |
			ShellParam::Status |
			ShellParam::LastJob |
			ShellParam::ShellName => {
				self.global_params.insert(param.to_string(), val.to_string());
			}
			ShellParam::Pos(_) |
			ShellParam::AllArgs |
			ShellParam::AllArgsStr |
			ShellParam::ArgCount => {
				if let Some(scope) = self.scopes.first_mut() {
					scope.set_param(param, val);
				}
			}
		}
	}
}

thread_local! {
	pub static FERN: Fern = Fern::new();
}

/// A shell function
///
/// Consists of the BraceGrp Node and the stored ParsedSrc that the node refers
/// to The Node must be stored with the ParsedSrc because the tokens of the node
/// contain an Arc<String> Which refers to the String held in ParsedSrc
///
/// Can be dereferenced to pull out the wrapped Node
#[derive(Clone, Debug)]
pub struct ShFunc(Node);

impl ShFunc {
  pub fn new(mut src: ParsedSrc) -> Self {
    let body = Self::extract_brc_grp_hack(src.extract_nodes());
    Self(body)
  }
  fn extract_brc_grp_hack(mut tree: Vec<Node>) -> Node {
    // FIXME: find a better way to do this
    let conjunction = tree.pop().unwrap();
    let NdRule::Conjunction { mut elements } = conjunction.class else {
      unreachable!()
    };
    let conjunct_node = elements.pop().unwrap();
    let ConjunctNode { cmd, operator: _ } = conjunct_node;
    *cmd
  }
}

impl Deref for ShFunc {
  type Target = Node;
  fn deref(&self) -> &Self::Target {
    &self.0
  }
}

/// The logic table for the shell
///
/// Contains aliases and functions
#[derive(Default, Clone, Debug)]
pub struct LogTab {
  functions: HashMap<String, ShFunc>,
  aliases: HashMap<String, String>,
}

impl LogTab {
  pub fn new() -> Self {
    Self::default()
  }
  pub fn insert_func(&mut self, name: &str, src: ShFunc) {
    self.functions.insert(name.into(), src);
  }
  pub fn get_func(&self, name: &str) -> Option<ShFunc> {
    self.functions.get(name).cloned()
  }
  pub fn funcs(&self) -> &HashMap<String, ShFunc> {
    &self.functions
  }
  pub fn aliases(&self) -> &HashMap<String, String> {
    &self.aliases
  }
  pub fn insert_alias(&mut self, name: &str, body: &str) {
    self.aliases.insert(name.into(), body.into());
  }
  pub fn get_alias(&self, name: &str) -> Option<String> {
    self.aliases.get(name).cloned()
  }
  pub fn remove_alias(&mut self, name: &str) {
    flog!(DEBUG, self.aliases);
    flog!(DEBUG, name);
    self.aliases.remove(name);
    flog!(DEBUG, self.aliases);
  }
  pub fn clear_aliases(&mut self) {
    self.aliases.clear()
  }
  pub fn clear_functions(&mut self) {
    self.functions.clear()
  }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq, PartialOrd, Ord)]
pub struct VarFlags(u8);

impl VarFlags {
	pub const NONE : Self = Self(0);
	pub const EXPORT : Self = Self(1 << 0);
	pub const LOCAL	: Self = Self(1 << 1);
	pub const READONLY : Self = Self(1 << 2);
}

impl BitOr for VarFlags {
	type Output = Self;
	fn bitor(self, rhs: Self) -> Self::Output {
		Self(self.0 | rhs.0)
	}
}

impl BitOrAssign for VarFlags {
	fn bitor_assign(&mut self, rhs: Self) {
		self.0 |= rhs.0;
	}
}

impl BitAnd for VarFlags {
	type Output = Self;
	fn bitand(self, rhs: Self) -> Self::Output {
		Self(self.0 & rhs.0)
	}
}

impl BitAndAssign for VarFlags {
	fn bitand_assign(&mut self, rhs: Self) {
		self.0 &= rhs.0;
	}
}

impl VarFlags {
	pub fn contains(&self, flag: Self) -> bool {
		(self.0 & flag.0) == flag.0
	}
	pub fn intersects(&self, flag: Self) -> bool {
		(self.0 & flag.0) != 0
	}
	pub fn is_empty(&self) -> bool {
		self.0 == 0
	}

	pub fn insert(&mut self, flag: Self) {
		self.0 |= flag.0;
	}
	pub fn remove(&mut self, flag: Self) {
		self.0 &= !flag.0;
	}
	pub fn toggle(&mut self, flag: Self) {
		self.0 ^= flag.0;
	}
	pub fn set(&mut self, flag: Self, value: bool) {
		if value {
			self.insert(flag);
		} else {
			self.remove(flag);
		}
	}
}

#[derive(Clone, Debug)]
pub enum VarKind {
	Str(String),
	Int(i32),
	Arr(Vec<String>),
	AssocArr(Vec<(String, String)>),
}

impl Display for VarKind {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		match self {
			VarKind::Str(s) => write!(f, "{s}"),
			VarKind::Int(i) => write!(f, "{i}"),
			VarKind::Arr(items) => {
				let mut item_iter = items.iter().peekable();
				while let Some(item) = item_iter.next() {
					write!(f, "{item}")?;
					if item_iter.peek().is_some() {
						write!(f, " ")?;
					}
				}
				Ok(())
			}
			VarKind::AssocArr(items) => {
				let mut item_iter = items.iter().peekable();
				while let Some(item) = item_iter.next() {
					let (k,v) = item;
					write!(f, "{k}={v}")?;
					if item_iter.peek().is_some() {
						write!(f, " ")?;
					}
				}
				Ok(())
			}
		}
	}
}

#[derive(Clone, Debug)]
pub struct Var {
  flags: VarFlags,
  kind: VarKind,
}

impl Var {
  pub fn new(kind: VarKind, flags: VarFlags) -> Self {
    Self {
      flags,
      kind
    }
  }
	pub fn kind(&self) -> &VarKind {
		&self.kind
	}
	pub fn kind_mut(&mut self) -> &mut VarKind {
		&mut self.kind
	}
  pub fn mark_for_export(&mut self) {
    self.flags.set(VarFlags::EXPORT, true);
  }
}

impl Display for Var {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		self.kind.fmt(f)
	}
}

#[derive(Default, Clone, Debug)]
pub struct VarTab {
  vars: HashMap<String, Var>,
  params: HashMap<ShellParam, String>,
  sh_argv: VecDeque<String>, /* Using a VecDeque makes the implementation of `shift`
                              * straightforward */
}

impl VarTab {
  pub fn new() -> Self {
    let vars = HashMap::new();
    let params = Self::init_params();
    Self::init_env();
    let mut var_tab = Self {
      vars,
      params,
      sh_argv: VecDeque::new(),
    };
    var_tab.init_sh_argv();
    var_tab
  }
  fn init_params() -> HashMap<ShellParam, String> {
    let mut params = HashMap::new();
    params.insert(ShellParam::ArgCount, "0".into()); // Number of positional parameters
    params.insert(
      ShellParam::Pos(0),
      std::env::current_exe()
        .unwrap()
        .to_str()
        .unwrap()
        .to_string(),
    ); // Name of the shell
    params.insert(ShellParam::ShPid, Pid::this().to_string()); // PID of the shell
    params.insert(ShellParam::LastJob, "".into()); // PID of the last background job (if any)
    params
  }
  fn init_env() {
    let pathbuf_to_string =
      |pb: Result<PathBuf, std::io::Error>| pb.unwrap_or_default().to_string_lossy().to_string();
    // First, inherit any env vars from the parent process
    let term = {
      if isatty(1).unwrap() {
        if let Ok(term) = std::env::var("TERM") {
          term
        } else {
          "linux".to_string()
        }
      } else {
        "xterm-256color".to_string()
      }
    };
    let home;
    let username;
    let uid;
    if let Some(user) = User::from_uid(nix::unistd::Uid::current()).ok().flatten() {
      home = user.dir;
      username = user.name;
      uid = user.uid;
    } else {
      home = PathBuf::new();
      username = "unknown".into();
      uid = 0.into();
    }
    let home = pathbuf_to_string(Ok(home));
    let hostname = gethostname()
      .map(|hname| hname.to_string_lossy().to_string())
      .unwrap_or_default();

		unsafe {
			env::set_var("IFS", " \t\n");
			env::set_var("HOST", hostname.clone());
			env::set_var("UID", uid.to_string());
			env::set_var("PPID", getppid().to_string());
			env::set_var("TMPDIR", "/tmp");
			env::set_var("TERM", term);
			env::set_var("LANG", "en_US.UTF-8");
			env::set_var("USER", username.clone());
			env::set_var("LOGNAME", username);
			env::set_var("PWD", pathbuf_to_string(std::env::current_dir()));
			env::set_var("OLDPWD", pathbuf_to_string(std::env::current_dir()));
			env::set_var("HOME", home.clone());
			env::set_var("SHELL", pathbuf_to_string(std::env::current_exe()));
			env::set_var("FERN_HIST", format!("{}/.fernhist", home));
			env::set_var("FERN_RC", format!("{}/.fernrc", home));
		}
  }
  pub fn init_sh_argv(&mut self) {
    for arg in env::args() {
      self.bpush_arg(arg);
    }
  }
  pub fn update_exports(&mut self) {
    for var_name in self.vars.keys() {
      let var = self.vars.get(var_name).unwrap();
      if var.flags.contains(VarFlags::EXPORT) {
        unsafe { env::set_var(var_name, var.to_string()) };
      } else {
        unsafe { env::set_var(var_name, "") };
      }
    }
  }
  pub fn sh_argv(&self) -> &VecDeque<String> {
    &self.sh_argv
  }
  pub fn sh_argv_mut(&mut self) -> &mut VecDeque<String> {
    &mut self.sh_argv
  }
  pub fn clear_args(&mut self) {
    self.sh_argv.clear();
    // Push the current exe again
    // This makes sure that $0 is always the current shell, no matter what
    // It also updates the arg parameters '@' and '#' as well
    self.bpush_arg(env::current_exe().unwrap().to_str().unwrap().to_string());
  }
  fn update_arg_params(&mut self) {
    self.set_param(ShellParam::AllArgs, &self.sh_argv.clone().to_vec()[1..].join(" "));
    self.set_param(ShellParam::ArgCount, &(self.sh_argv.len() - 1).to_string());
  }
  /// Push an arg to the front of the arg deque
  pub fn fpush_arg(&mut self, arg: String) {
    self.sh_argv.push_front(arg);
    self.update_arg_params();
  }
  /// Push an arg to the back of the arg deque
  pub fn bpush_arg(&mut self, arg: String) {
    self.sh_argv.push_back(arg);
    self.update_arg_params();
  }
  /// Pop an arg from the front of the arg deque
  pub fn fpop_arg(&mut self) -> Option<String> {
    let arg = self.sh_argv.pop_front();
    self.update_arg_params();
    arg
  }
  /// Pop an arg from the back of the arg deque
  pub fn bpop_arg(&mut self) -> Option<String> {
    let arg = self.sh_argv.pop_back();
    self.update_arg_params();
    arg
  }
  pub fn vars(&self) -> &HashMap<String, Var> {
    &self.vars
  }
  pub fn vars_mut(&mut self) -> &mut HashMap<String, Var> {
    &mut self.vars
  }
  pub fn params(&self) -> &HashMap<ShellParam, String> {
    &self.params
  }
  pub fn params_mut(&mut self) -> &mut HashMap<ShellParam, String> {
    &mut self.params
  }
  pub fn export_var(&mut self, var_name: &str) {
    if let Some(var) = self.vars.get_mut(var_name) {
      var.mark_for_export();
      unsafe { env::set_var(var_name, var.to_string()) };
    }
  }
  pub fn get_var(&self, var: &str) -> String {
		if let Ok(param) = var.parse::<ShellParam>() {
      let param = self.get_param(param);
      if !param.is_empty() {
        return param;
      }
		}
    if let Some(var) = self.vars.get(var).map(|s| s.to_string()) {
      var
    } else {
      std::env::var(var).unwrap_or_default()
    }
  }
	pub fn unset_var(&mut self, var_name: &str) {
		self.vars.remove(var_name);
		unsafe { env::remove_var(var_name) };
	}
  pub fn set_var(&mut self, var_name: &str, val: &str, flags: VarFlags) {
    if let Some(var) = self.vars.get_mut(var_name) {
      var.kind = VarKind::Str(val.to_string());
      if var.flags.contains(VarFlags::EXPORT) || flags.contains(VarFlags::EXPORT) {
				if flags.contains(VarFlags::EXPORT) && !var.flags.contains(VarFlags::EXPORT) {
					var.mark_for_export();
				}
        unsafe { env::set_var(var_name, val) };
      }
    } else {
      let mut var = Var::new(VarKind::Str(val.to_string()), VarFlags::NONE);
      if flags.contains(VarFlags::EXPORT) {
        var.mark_for_export();
        unsafe { env::set_var(var_name, var.to_string()) };
      }
      self.vars.insert(var_name.to_string(), var);
    }
  }
  pub fn var_exists(&self, var_name: &str) -> bool {
		flog!(DEBUG, "checking existence of {}",var_name);
    if let Ok(param) = var_name.parse::<ShellParam>() {
      return self.params.contains_key(&param);
    }
    self.vars.contains_key(var_name)
  }
  pub fn set_param(&mut self, param: ShellParam, val: &str) {
    self.params.insert(param, val.to_string());
  }
  pub fn get_param(&self, param: ShellParam) -> String {
		match param {
			ShellParam::Pos(n) => {
				self
					.sh_argv()
					.get(n)
					.map(|s| s.to_string())
					.unwrap_or_default()
			}
			ShellParam::Status => {
				self
					.params
					.get(&ShellParam::Status)
					.map(|s| s.to_string())
					.unwrap_or("0".into())
			}
			_ => self
				.params
				.get(&param)
				.map(|s| s.to_string())
				.unwrap_or_default(),
		}
  }
}

/// A table of metadata for the shell
#[derive(Default, Debug)]
pub struct MetaTab {
  runtime_start: Option<Instant>,
	runtime_stop: Option<Instant>,
}

impl MetaTab {
  pub fn new() -> Self {
    Self::default()
  }
  pub fn start_timer(&mut self) {
    self.runtime_start = Some(Instant::now());
  }
  pub fn stop_timer(&mut self) {
    self.runtime_stop = Some(Instant::now());
  }
	pub fn get_time(&self) -> Option<Duration> {
		if let (Some(start), Some(stop)) = (self.runtime_start, self.runtime_stop) {
			Some(stop.duration_since(start))
		} else {
			None
		}
	}
}

/// Read from the job table
pub fn read_jobs<T, F: FnOnce(&JobTab) -> T>(f: F) -> T {
	FERN.with(|fern| f(&fern.jobs.borrow()))
}

/// Write to the job table
pub fn write_jobs<T, F: FnOnce(&mut JobTab) -> T>(f: F) -> T {
	FERN.with(|fern| f(&mut fern.jobs.borrow_mut()))
}

/// Read from the var scope stack
pub fn read_vars<T, F: FnOnce(&ScopeStack) -> T>(f: F) -> T {
	FERN.with(|fern| f(&fern.var_scopes.borrow()))
}

/// Write to the variable table
pub fn write_vars<T, F: FnOnce(&mut ScopeStack) -> T>(f: F) -> T {
	FERN.with(|fern| f(&mut fern.var_scopes.borrow_mut()))
}

pub fn read_meta<T, F: FnOnce(&MetaTab) -> T>(f: F) -> T {
	FERN.with(|fern| f(&fern.meta.borrow()))
}

/// Write to the meta table
pub fn write_meta<T, F: FnOnce(&mut MetaTab) -> T>(f: F) -> T {
	FERN.with(|fern| f(&mut fern.meta.borrow_mut()))
}

/// Read from the logic table
pub fn read_logic<T, F: FnOnce(&LogTab) -> T>(f: F) -> T {
	FERN.with(|fern| f(&fern.logic.borrow()))
}

/// Write to the logic table
pub fn write_logic<T, F: FnOnce(&mut LogTab) -> T>(f: F) -> T {
	FERN.with(|fern| f(&mut fern.logic.borrow_mut()))
}

pub fn read_shopts<T, F: FnOnce(&ShOpts) -> T>(f: F) -> T {
	FERN.with(|fern| f(&fern.shopts.borrow()))
}

pub fn write_shopts<T, F: FnOnce(&mut ShOpts) -> T>(f: F) -> T {
	FERN.with(|fern| f(&mut fern.shopts.borrow_mut()))
}

pub fn descend_scope(argv: Option<Vec<String>>) {
	write_vars(|v| v.descend(argv));
}
pub fn ascend_scope() {
	write_vars(|v| v.ascend());
}

/// This function is used internally and ideally never sees user input
///
/// It will panic if you give it an invalid path.
pub fn get_shopt(path: &str) -> String {
  read_shopts(|s| s.get(path)).unwrap().unwrap()
}

pub fn get_status() -> i32 {
  read_vars(|v| v.get_param(ShellParam::Status)).parse::<i32>().unwrap()
}
#[track_caller]
pub fn set_status(code: i32) {
  write_vars(|v| v.set_param(ShellParam::Status, &code.to_string()))
}

pub fn source_rc() -> ShResult<()> {
  let path = if let Ok(path) = env::var("FERN_RC") {
    PathBuf::from(&path)
  } else {
    let home = env::var("HOME").unwrap();
    PathBuf::from(format!("{home}/.fernrc"))
  };
  if !path.exists() {
    return Err(ShErr::simple(ShErrKind::InternalErr, ".fernrc not found"));
  }
  source_file(path)
}

pub fn source_file(path: PathBuf) -> ShResult<()> {
  let mut file = OpenOptions::new().read(true).open(path)?;

  let mut buf = String::new();
  file.read_to_string(&mut buf)?;
  exec_input(buf, None)?;
  Ok(())
}