use std::cell::{Cell, RefCell};
use std::collections::HashMap;
use std::env;
use std::fmt;
use std::fs::{metadata, File};
use std::io::{BufRead, BufReader};
use std::path::Path;
use std::rc::Rc;
use std::time::SystemTime;

use lazy_static::lazy_static;
use regex::Regex;

use crate::args::Args;

mod token;

use token::{tokenize, Token, TokenString};

#[derive(PartialEq, Eq, Clone, Debug)]
pub struct InferenceRule {
    /// POSIX calls this ".s1" but that's not useful.
    product: String,
    /// POSIX calls this ".s2" but that's not useful.
    prereq: String,
    commands: Vec<CommandLine>,
}

impl fmt::Display for InferenceRule {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "{}{}:", &self.prereq, &self.product)?;
        for command in &self.commands {
            writeln!(f, "\t{}", command)?;
        }
        Ok(())
    }
}

#[derive(PartialEq, Eq, Clone, Debug)]
pub struct Target {
    name: String,
    prerequisites: Vec<String>,
    commands: Vec<CommandLine>,
    already_updated: Cell<bool>,
}

impl Target {
    fn modified_time(&self) -> Option<SystemTime> {
        metadata(&self.name)
            .and_then(|metadata| metadata.modified())
            .ok()
    }

    fn newer_than(&self, other: &Target) -> Option<bool> {
        let self_updated = self.already_updated.get();
        let other_updated = other.already_updated.get();
        Some(match (self.modified_time(), other.modified_time()) {
            (Some(self_mtime), Some(other_mtime)) => self_mtime >= other_mtime,
            // per POSIX: "If the target does not exist after the target has been
            // successfully made up-to-date, the target shall be treated as being
            // newer than any target for which it is a prerequisite."
            (None, _) if self_updated && other.prerequisites.contains(&self.name) => true,
            (_, None) if other_updated && self.prerequisites.contains(&other.name) => false,
            _ => return None,
        })
    }

    fn is_up_to_date(&self, file: &Makefile) -> bool {
        if self.already_updated.get() {
            return true;
        }
        let exists = metadata(&self.name).is_ok();
        let newer_than_all_dependencies = self.prerequisites.iter().all(|t| {
            self.newer_than(&file.get_target(t).borrow())
                .unwrap_or(false)
        });
        exists && newer_than_all_dependencies
    }

    pub fn update(&self, file: &Makefile) {
        for prereq in &self.prerequisites {
            file.update_target(prereq);
        }
        if !self.is_up_to_date(file) {
            self.execute_commands(file);
        }
        self.already_updated.set(true);
    }

    fn execute_commands(&self, file: &Makefile) {
        for command in &self.commands {
            command.execute(file, self);
        }
    }
}

impl fmt::Display for Target {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let prereqs = self.prerequisites.join(" ");
        writeln!(f, "{}: {}", &self.name, prereqs)?;
        for command in &self.commands {
            writeln!(f, "\t{}", command)?;
        }
        Ok(())
    }
}

#[derive(PartialEq, Eq, Clone, Debug)]
pub struct CommandLine {
    /// If the command prefix contains a <hyphen-minus>, or the -i option is present, or
    /// the special target .IGNORE has either the current target as a prerequisite or has
    /// no prerequisites, any error found while executing the command shall be ignored.
    ignore_errors: bool,
    /// If the command prefix contains an at-sign and the make utility command line -n
    /// option is not specified, or the -s option is present, or the special target
    /// .SILENT has either the current target as a prerequisite or has no prerequisites,
    /// the command shall not be written to standard output before it is executed.
    silent: bool,
    /// If the command prefix contains a <plus-sign>, this indicates a makefile command
    /// line that shall be executed even if -n, -q, or -t is specified.
    always_execute: bool,
    execution_line: TokenString,
}

impl CommandLine {
    fn from(mut line: TokenString) -> Self {
        let mut ignore_errors = false;
        let mut silent = false;
        let mut always_execute = false;

        if let Token::Text(text) = line.first_token_mut() {
            let mut text_chars = text.chars().peekable();
            while let Some(x) = text_chars.next_if(|x| matches!(x, '-' | '@' | '+')) {
                match x {
                    '-' => ignore_errors = true,
                    '@' => silent = true,
                    '+' => always_execute = true,
                    _ => unreachable!(),
                }
            }
            *text = text_chars.collect();
        }

        CommandLine {
            ignore_errors,
            silent,
            always_execute,
            execution_line: line,
        }
    }

    fn execute(&self, file: &Makefile, target: &Target) {
        let ignore_error = self.ignore_errors
            || file.args.ignore_errors
            || file.special_target_has_prereq(".IGNORE", &target.name);
        let silent = (self.silent && !file.args.dry_run)
            || file.args.silent
            || file.special_target_has_prereq(".SILENT", &target.name);

        let execution_line = file.expand_macros(&self.execution_line, Some(target));

        if !silent {
            println!("{}", execution_line);
        }

        let should_execute =
            self.always_execute || !(file.args.dry_run || file.args.question || file.args.touch);
        if !should_execute {
            return;
        }

        // TODO don't fuck this up
        let execution_line = ::std::ffi::CString::new(execution_line.as_bytes())
            .expect("execution line shouldn't have a null in the middle");
        // TODO pass shell "-e" if errors are not ignored
        let return_value = unsafe { libc::system(execution_line.as_ptr()) };
        if return_value != 0 {
            // apparently there was an error. do we care?
            if !ignore_error {
                // TODO handle this error gracefully
                panic!("error from command execution!");
            }
        }
    }
}

impl fmt::Display for CommandLine {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        if self.ignore_errors {
            write!(f, "-")?;
        }
        if self.silent {
            write!(f, "@")?;
        }
        if self.always_execute {
            write!(f, "+")?;
        }
        let execution_line = format!("{}", &self.execution_line);
        let execution_line = execution_line.replace("\n", "↵\n");
        write!(f, "{}", execution_line)?;
        Ok(())
    }
}

enum MacroSource {
    File,
    CommandLineOrMAKEFLAGS,
    Environment,
    Builtin,
}

pub struct Makefile {
    inference_rules: Vec<InferenceRule>,
    macros: HashMap<String, (MacroSource, TokenString)>,
    targets: RefCell<HashMap<String, Rc<RefCell<Target>>>>,
    pub first_non_special_target: Option<String>,
    args: Args,
    // TODO borrow warnings from Python version
}

impl Makefile {
    pub fn new(args: Args) -> Makefile {
        let mut inference_rules = vec![];
        let mut macros = HashMap::new();
        let mut targets = HashMap::new();
        let first_non_special_target = None;

        if !args.no_builtin_rules {
            inference_rules.extend(builtin_inference_rules());
            for (k, v) in builtin_macros() {
                macros.insert(k.into(), (MacroSource::Builtin, v));
            }
            targets.extend(
                builtin_targets()
                    .into_iter()
                    .map(|t| (t.name.clone(), Rc::new(RefCell::new(t)))),
            );
        }

        for (k, v) in env::vars() {
            if k != "MAKEFLAGS" && k != "SHELL" {
                macros.insert(k, (MacroSource::Environment, TokenString::text(v)));
            }
        }

        for r#macro in args.macros() {
            if let [name, value] = *r#macro.splitn(2, '=').collect::<Vec<_>>() {
                macros.insert(
                    name.into(),
                    (
                        MacroSource::CommandLineOrMAKEFLAGS,
                        TokenString::text(value),
                    ),
                );
            }
        }

        Makefile {
            inference_rules,
            macros,
            targets: RefCell::new(targets),
            first_non_special_target,
            args,
        }
    }

    pub fn and_read_file(&mut self, path: impl AsRef<Path>) -> &mut Makefile {
        let file = File::open(path);
        // TODO handle errors
        let file = file.expect("couldn't open makefile!");
        let file_reader = BufReader::new(file);
        self.and_read(file_reader)
    }

    pub fn and_read(&mut self, source: impl BufRead) -> &mut Makefile {
        let mut lines_iter = source.lines().enumerate().peekable();
        while let Some((line_number, line)) = lines_iter.next() {
            // TODO handle I/O errors at all
            let mut line = line.expect("failed to read line of makefile!");

            // handle escaped newlines
            while line.ends_with('\\') {
                line.pop();
                line.push(' ');
                if let Some((_, x)) = lines_iter.next() {
                    line.push_str(x.expect("failed to read line of makefile!").trim_start())
                }
            }

            // handle comments
            lazy_static! {
                static ref COMMENT: Regex = Regex::new("#.*$").unwrap();
            }
            let line = COMMENT.replace(&line, "").into_owned();

            // handle include lines
            if let Some(line) = line.strip_prefix("include ") {
                // remove extra leading space
                let line = line.trim_start();
                let line = self.expand_macros(&tokenize(line), None);
                let fields = line.split_whitespace();
                // POSIX says we only have to handle a single filename, but GNU make
                // handles arbitrarily many filenames, and it's not like that's more work
                for field in fields {
                    self.and_read_file(field);
                }
            } else if line.trim().is_empty() {
                // handle blank lines
                continue;
            } else {
                // unfortunately, rules vs macros can't be determined until after
                // macro tokenizing. so that's suboptimal.
                // TODO errors
                let line_tokens: TokenString = line.parse().unwrap();

                enum LineType {
                    Rule,
                    Macro,
                    Unknown,
                }

                fn get_line_type(line_tokens: &TokenString) -> LineType {
                    for token in line_tokens.tokens() {
                        if let Token::Text(text) = token {
                            let colon_idx = text.find(':');
                            let equals_idx = text.find('=');
                            match (colon_idx, equals_idx) {
                                (Some(_), None) => {
                                    return LineType::Rule;
                                }
                                (Some(c), Some(e)) if c < e => {
                                    return LineType::Rule;
                                }
                                (None, Some(_)) => {
                                    return LineType::Macro;
                                }
                                (Some(c), Some(e)) if e < c => {
                                    return LineType::Macro;
                                }
                                _ => {}
                            }
                        }
                    }
                    LineType::Unknown
                }

                let line_type = get_line_type(&line_tokens);

                match line_type {
                    LineType::Rule => {
                        let (targets, not_targets) = line_tokens.split_once(':').unwrap();
                        let targets = self.expand_macros(&targets, None);
                        let targets = targets
                            .split_whitespace()
                            .map(Into::into)
                            .collect::<Vec<String>>();
                        let (prerequisites, mut commands) = match not_targets.split_once(';') {
                            Some((prerequisites, mut command)) => {
                                while command.ends_with("\\") && lines_iter.peek().is_some() {
                                    command.strip_suffix("\\");
                                    command
                                        .extend(tokenize(&lines_iter.next().unwrap().1.unwrap()));
                                }
                                (prerequisites, vec![command])
                            }
                            None => (not_targets, vec![]),
                        };
                        let prerequisites = self.expand_macros(&prerequisites, None);
                        let prerequisites = prerequisites
                            .split_whitespace()
                            .map(|x| x.into())
                            .collect::<Vec<String>>();

                        while let Some((_, x)) = lines_iter.next_if(|(_, x)| {
                            x.as_ref()
                                .ok()
                                .map_or(false, |line| line.starts_with('\t') || line.is_empty())
                        }) {
                            let mut line = x.unwrap();
                            if !line.is_empty() {
                                line.remove(0);
                            }
                            if line.is_empty() {
                                continue;
                            }
                            while line.ends_with('\\') {
                                match lines_iter.next() {
                                    Some((_, Ok(next_line))) => {
                                        let next_line =
                                            next_line.strip_prefix("\t").unwrap_or(&next_line);
                                        line.push('\n');
                                        line.push_str(next_line);
                                    }
                                    _ => break,
                                }
                            }
                            commands.push(line.parse().unwrap());
                        }

                        let commands = commands
                            .into_iter()
                            .map(CommandLine::from)
                            .collect::<Vec<_>>();

                        if targets.is_empty() {
                            continue;
                        }

                        // we don't know yet if it's a target rule or an inference rule
                        lazy_static! {
                            static ref INFERENCE_RULE: Regex =
                                Regex::new(r"^(?P<s2>(\.[^/.]+)?)(?P<s1>\.[^/.]+)$").unwrap();
                            static ref SPECIAL_TARGET: Regex = Regex::new(r"^\.[A-Z]+$").unwrap();
                        }

                        let inference_match = INFERENCE_RULE.captures(&targets[0]);
                        let special_target_match = SPECIAL_TARGET.captures(&targets[0]);

                        let inference_rule = targets.len() == 1
                            && prerequisites.is_empty()
                            && inference_match.is_some()
                            && special_target_match.is_none();
                        if inference_rule {
                            let inference_match = inference_match.unwrap();
                            let new_rule = InferenceRule {
                                product: inference_match.name("s1").unwrap().as_str().to_string(),
                                prereq: inference_match.name("s2").unwrap().as_str().to_string(),
                                commands,
                            };

                            self.inference_rules.retain(|existing_rule| {
                                (&existing_rule.prereq, &existing_rule.product)
                                    != (&new_rule.prereq, &new_rule.product)
                            });
                            self.inference_rules.push(new_rule);
                        } else {
                            for target in targets {
                                if self.first_non_special_target.is_none()
                                    && !target.starts_with('.')
                                {
                                    self.first_non_special_target = Some(target.clone());
                                }
                                let mut targets = self.targets.borrow_mut();
                                match targets.get_mut(&target) {
                                    Some(old_target)
                                        if commands.is_empty()
                                            && !(target == ".SUFIXES"
                                                && prerequisites.is_empty()) =>
                                    {
                                        let mut old_target = old_target.borrow_mut();
                                        let new_prerequisites = prerequisites
                                            .iter()
                                            .filter(|x| !old_target.prerequisites.contains(x))
                                            .cloned()
                                            .collect::<Vec<_>>();
                                        old_target.prerequisites.extend(new_prerequisites);
                                    }
                                    _ => {
                                        let new_target = Target {
                                            name: target.clone(),
                                            prerequisites: prerequisites.clone(),
                                            commands: commands.clone(),
                                            already_updated: Cell::new(false),
                                        };
                                        targets.insert(
                                            target.clone(),
                                            Rc::new(RefCell::new(new_target)),
                                        );
                                    }
                                }
                            }
                        }
                    }
                    LineType::Macro => {
                        let (name, mut value) = line_tokens.split_once('=').unwrap();
                        let name = self.expand_macros(&name, None);
                        // GNUisms are annoying, but popular
                        let mut expand_value = false;
                        let mut skip_if_defined = false;
                        let mut append = false;
                        let name = if let Some(real_name) = name.strip_suffix("::") {
                            expand_value = true;
                            real_name
                        } else if let Some(real_name) = name.strip_suffix(":") {
                            expand_value = true;
                            real_name
                        } else if let Some(real_name) = name.strip_suffix("?") {
                            skip_if_defined = true;
                            real_name
                        } else if let Some(real_name) = name.strip_suffix("+") {
                            append = true;
                            real_name
                        } else {
                            &name
                        };

                        let name = name.trim_end();
                        value.trim_start();

                        let value = if expand_value {
                            TokenString::text(self.expand_macros(&value, None))
                        } else {
                            value
                        };

                        match self.macros.get(name) {
                            // We always let command line or MAKEFLAGS macros override macros from the file.
                            Some((MacroSource::CommandLineOrMAKEFLAGS, _)) => continue,
                            // We let environment variables override macros from the file only if the command-line argument to do that was given
                            Some((MacroSource::Environment, _))
                                if self.args.environment_overrides =>
                            {
                                continue
                            }
                            _ if skip_if_defined => continue,
                            _ => {}
                        }

                        let value = match self.macros.remove(name) {
                            Some((_, mut old_value)) if append => {
                                // TODO eagerly expand if appending to eagerly-expanded macro
                                old_value.extend(TokenString::text(" "));
                                old_value.extend(value);
                                old_value
                            }
                            _ => value,
                        };
                        self.macros.insert(name.into(), (MacroSource::File, value));
                    }
                    LineType::Unknown => {
                        panic!(
                            "error: line {}: unknown line {:?}",
                            line_number, line_tokens
                        );
                    }
                }
            }
        }
        self
    }

    fn special_target_has_prereq(&self, target: &str, name: &str) -> bool {
        let targets = self.targets.borrow();
        match targets.get(target) {
            Some(target) => {
                let target = target.borrow();
                target.prerequisites.is_empty() || target.prerequisites.iter().any(|e| e == name)
            }
            None => false,
        }
    }

    pub fn get_target(&self, name: &str) -> Rc<RefCell<Target>> {
        // TODO implement .POSIX
        let follow_gnu = true;

        let vpath_options = match self.macros.get("VPATH") {
            Some((_, vpath)) if follow_gnu => {
                let vpath = self.expand_macros(vpath, None);
                env::split_paths(&vpath).collect()
            }
            _ => vec![],
        };

        let targets = self.targets.borrow();
        let mut new_target = None;
        let exists_but_infer_anyway = if follow_gnu {
            match targets.get(name) {
                Some(target) => {
                    let target = target.borrow();
                    target.commands.is_empty()
                }
                None => false,
            }
        } else {
            false
        };
        if !targets.contains_key(name) || exists_but_infer_anyway {
            // When no target rule is found to update a target, the inference rules shall
            // be checked. The suffix of the target to be built...
            let suffix = Path::new(name)
                .extension()
                .map_or_else(String::new, |ext| format!(".{}", ext.to_string_lossy()));
            // is compared to the list of suffixes specified by the .SUFFIXES special
            // targets. If the .s1 suffix is found in .SUFFIXES...
            if self.special_target_has_prereq(".SUFFIXES", &suffix) || suffix.is_empty() {
                // the inference rules shall be searched in the order defined...
                'rules: for rule in &self.inference_rules {
                    // for the first .s2.s1 rule...
                    if rule.product == suffix {
                        // whose prerequisite file ($*.s2) exists.
                        let prereq_path =
                            Path::new(name).with_extension(rule.prereq.trim_start_matches('.'));
                        let prereq_path_options = if prereq_path.is_absolute() {
                            vec![prereq_path]
                        } else {
                            let mut options = vec![prereq_path.clone()];
                            options
                                .extend(vpath_options.iter().map(|vpath| vpath.join(&prereq_path)));
                            options
                        };
                        for prereq in prereq_path_options {
                            if prereq.exists() {
                                new_target = Some(Target {
                                    name: name.into(),
                                    prerequisites: vec![prereq.to_string_lossy().into()],
                                    commands: rule.commands.clone(),
                                    already_updated: Cell::new(false),
                                });
                                break 'rules;
                            }
                        }
                    }
                }
            }
        }

        if !targets.contains_key(name) && new_target.is_none() {
            // well, inference didn't work. is there a default?
            if let Some(default) = targets.get(".DEFAULT") {
                let default = default.borrow();
                let commands = default.commands.clone();
                drop(default);
                new_target = Some(Target {
                    name: name.into(),
                    prerequisites: vec![],
                    commands,
                    already_updated: Cell::new(false),
                });
            } else {
                // if it already exists, it counts as up-to-date
                if Path::new(name).exists() {
                    new_target = Some(Target {
                        name: name.into(),
                        prerequisites: vec![],
                        commands: vec![],
                        already_updated: Cell::new(true),
                    });
                }
            }
        }

        drop(targets);
        if let Some(new_target) = new_target {
            let mut targets = self.targets.borrow_mut();
            targets.insert(new_target.name.clone(), Rc::new(RefCell::new(new_target)));
        }

        let targets = self.targets.borrow();
        targets.get(name).expect("Target not found!").clone()
    }

    pub fn update_target(&self, name: &str) {
        let target = self.get_target(name);
        let target = target.borrow();
        target.update(self);
    }

    fn expand_macros(&self, text: &TokenString, target: Option<&Target>) -> String {
        let mut result = String::new();
        for token in text.tokens() {
            match token {
                Token::Text(t) => result.push_str(t),
                Token::MacroExpansion { name, replacement } => {
                    let internal_macro_names = &['@', '?', '<', '*'][..];
                    let internal_macro_suffices = &['D', 'F'][..];
                    let just_internal = name.len() == 1 && name.starts_with(internal_macro_names);
                    let suffixed_internal = name.len() == 2
                        && name.starts_with(internal_macro_names)
                        && name.ends_with(internal_macro_suffices);
                    let macro_value = if just_internal || suffixed_internal {
                        let target = target.expect("internal macro but no current target!");
                        let macro_pieces = if name.starts_with('@') {
                            // The $@ shall evaluate to the full target name of the
                            // current target.
                            vec![target.name.clone()]
                        } else if name.starts_with('?') {
                            // The $? macro shall evaluate to the list of prerequisites
                            // that are newer than the current target.
                            target
                                .prerequisites
                                .iter()
                                .filter(|prereq| {
                                    self.get_target(prereq)
                                        .borrow()
                                        .newer_than(target)
                                        .unwrap_or(false)
                                })
                                .cloned()
                                .collect()
                        } else if name.starts_with('<') {
                            // In an inference rule, the $< macro shall evaluate to the
                            // filename whose existence allowed the inference rule to be
                            // chosen for the target. In the .DEFAULT rule, the $< macro
                            // shall evaluate to the current target name.
                            target.prerequisites.clone()
                        } else if name.starts_with('*') {
                            // The $* macro shall evaluate to the current target name with
                            // its suffix deleted.
                            vec![Path::new(name).with_extension("").to_string_lossy().into()]
                        } else {
                            unreachable!()
                        };

                        let macro_pieces = if name.ends_with('D') {
                            macro_pieces
                                .into_iter()
                                .map(|x| {
                                    Path::new(&x)
                                        .parent()
                                        .expect("no parent")
                                        .to_string_lossy()
                                        .into()
                                })
                                .collect()
                        } else if name.ends_with('F') {
                            macro_pieces
                                .into_iter()
                                .map(|x| {
                                    Path::new(&x)
                                        .file_name()
                                        .expect("no filename")
                                        .to_string_lossy()
                                        .into()
                                })
                                .collect()
                        } else {
                            macro_pieces
                        };

                        macro_pieces.join(" ")
                    } else {
                        match self.macros.get(name) {
                            Some((_, macro_value)) => self.expand_macros(&macro_value, target),
                            None => String::new(),
                        }
                    };
                    let macro_value = match replacement {
                        Some((subst1, subst2)) => {
                            let subst1 = self.expand_macros(subst1, target);
                            let subst1_suffix = regex::escape(&subst1);
                            let subst1_suffix =
                                Regex::new(&format!(r"{}\b", subst1_suffix)).unwrap();
                            let subst2 = self.expand_macros(subst2, target);
                            subst1_suffix.replace_all(&macro_value, subst2).to_string()
                        }
                        None => macro_value,
                    };
                    result.push_str(&macro_value);
                }
            }
        }
        result
    }
}

impl fmt::Display for Makefile {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let header = |f: &mut fmt::Formatter, t: &str| {
            writeln!(f, "{}\n{:=^width$}", t, "", width = t.len())
        };
        header(f, "Inference Rules")?;
        for rule in &self.inference_rules {
            writeln!(f, "{}", rule)?;
        }
        writeln!(f)?;

        header(f, "Macros")?;
        for (k, (_, v)) in &self.macros {
            writeln!(f, "{}={}", k, v)?;
        }
        writeln!(f)?;

        header(f, "Targets")?;
        for target in self.targets.borrow().values() {
            writeln!(f, "{}", target.borrow())?;
        }

        Ok(())
    }
}

fn builtin_inference_rules() -> Vec<InferenceRule> {
    // This is a terrible idea.
    macro_rules! prepend_dot {
        ($x:tt) => {
            concat!(".", stringify!($x))
        };
        () => {
            ""
        };
    }

    macro_rules! make {
        {$(.$first:tt$(.$second:tt)?:
            $($cmd:literal)+)+} => {
            vec![$(
                InferenceRule {
                    product: prepend_dot!($($second)?).into(),
                    prereq: concat!(".", stringify!($first)).into(),
                    commands: vec![$(CommandLine::from($cmd.parse().unwrap())),+],
                }
            ),+]
        };
    }

    make! {
        .c:
            "$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<"
        .f:
            "$(FC) $(FFLAGS) $(LDFLAGS) -o $@ $<"
        .sh:
            "cp $< $@"
            "chmod a+x $@"

        .c.o:
            "$(CC) $(CFLAGS) -c $<"
        .f.o:
            "$(FC) $(FFLAGS) -c $<"
        .y.o:
            "$(YACC) $(YFLAGS) $<"
            "$(CC) $(CFLAGS) -c y.tab.c"
            "rm -f y.tab.c"
            "mv y.tab.o $@"
        .l.o:
            "$(LEX) $(LFLAGS) $<"
            "$(CC) $(CFLAGS) -c lex.yy.c"
            "rm -f lex.yy.c"
            "mv lex.yy.o $@"
        .y.c:
            "$(YACC) $(YFLAGS) $<"
            "mv y.tab.c $@"
        .l.c:
            "$(LEX) $(LFLAGS) $<"
            "mv lex.yy.c $@"
        .c.a:
            "$(CC) -c $(CFLAGS) $<"
            "$(AR) $(ARFLAGS) $@ $*.o"
            "rm -f $*.o"
        .f.a:
            "$(FC) -c $(FFLAGS) $<"
            "$(AR) $(ARFLAGS) $@ $*.o"
            "rm -f $*.o"
    }
}
fn builtin_macros() -> Vec<(&'static str, TokenString)> {
    // Fuck it, might as well.
    macro_rules! handle {
        ($value:ident) => {
            stringify!($value)
        };
        ($value:literal) => {
            $value
        };
    }
    macro_rules! make {
        ($($name:ident=$value:tt)+) => {vec![$(
            (stringify!($name), handle!($value).parse().unwrap())
        ),+]};
    }

    make![
        MAKE=makers
        AR=ar
        YACC=yacc
        YFLAGS=""
        LEX=lex
        LFLAGS=""
        LDFLAGS=""

        AS=as
        CC=cc
        CXX="g++"
        CPP="$(CC) -E"
        FC=f77
        PC=pc
        CO=co
        GET=get
        LINT=lint
        MAKEINFO=makeinfo
        TEX=tex
        TEXI2DVI=texi2dvi
        WEAVE=weave
        CWEAVE=cweave
        TANGLE=tangle
        CTANGLE=ctangle
        RM="rm -f"

        ARFLAGS="rv"
        CFLAGS=""
        FFLAGS=""
    ]
}
fn builtin_targets() -> Vec<Target> {
    // even i'm not going to do that just for this
    vec![Target {
        name: ".SUFFIXES".into(),
        prerequisites: vec![".o", ".c", ".y", ".l", ".a", ".sh", ".f"]
            .into_iter()
            .map(String::from)
            .collect(),
        commands: vec![],
        already_updated: Cell::new(false),
    }]
}