use std::cell::RefCell;
use std::collections::HashMap;
use std::collections::HashSet;
use std::env;
use std::fmt;
use std::rc::Rc;

use eyre::{bail, Result, WrapErr};
use regex::Regex;

#[cfg(feature = "full")]
use super::functions;
use super::token::{Token, TokenString};
use super::ItemSource;

#[derive(Debug, Clone)]
pub struct Macro {
    pub source: ItemSource,
    pub text: TokenString,
    #[cfg(feature = "full")]
    pub eagerly_expanded: bool,
}

pub trait LookupInternal: for<'a> Fn(&'a str) -> Result<String> {}

impl<F: for<'a> Fn(&'a str) -> Result<String>> LookupInternal for F {}

#[cfg(feature = "full")]
#[derive(Clone, Debug)]
pub enum ExportConfig {
    Only(HashSet<String>),
    AllBut(HashSet<String>),
}

#[cfg(feature = "full")]
impl ExportConfig {
    pub fn all_but() -> Self {
        Self::AllBut(HashSet::new())
    }

    pub fn only() -> Self {
        Self::Only(HashSet::new())
    }

    pub fn add_all<'a, I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
        match self {
            Self::Only(exported) => {
                exported.extend(iter.into_iter().map(|x| x.to_owned()));
            }
            Self::AllBut(not_exported) => {
                for added in iter {
                    not_exported.remove(added);
                }
            }
        }
    }

    pub fn remove_all<'a, I: IntoIterator<Item = &'a str>>(&mut self, iter: I) {
        match self {
            Self::Only(exported) => {
                for removed in iter {
                    exported.remove(removed);
                }
            }
            Self::AllBut(not_exported) => {
                not_exported.extend(iter.into_iter().map(|x| x.into()));
            }
        }
    }

    fn same_type(&self) -> Self {
        match self {
            Self::Only(_) => Self::only(),
            Self::AllBut(_) => Self::all_but(),
        }
    }

    fn should_export(&self, x: &str) -> bool {
        match self {
            Self::Only(exported) => exported.contains(x),
            Self::AllBut(not_exported) => !not_exported.contains(x),
        }
    }
}

#[derive(Clone)]
pub struct Set<'parent, 'lookup> {
    parent: Option<&'parent Set<'parent, 'lookup>>,
    pub data: HashMap<String, Macro>,
    lookup_internal: Option<&'lookup dyn LookupInternal>,
    #[cfg(feature = "full")]
    pub to_eval: Rc<RefCell<Vec<String>>>,
    #[cfg(feature = "full")]
    pub exported: ExportConfig,
    warnings: Rc<RefCell<HashSet<String>>>,
}

impl<'parent, 'lookup> Set<'parent, 'lookup> {
    pub fn new() -> Self {
        Self {
            parent: None,
            data: HashMap::new(),
            lookup_internal: None,
            #[cfg(feature = "full")]
            to_eval: Rc::new(RefCell::new(Vec::new())),
            #[cfg(feature = "full")]
            exported: ExportConfig::only(),
            warnings: Default::default(),
        }
    }

    pub fn add_builtins(&mut self) {
        for (k, v) in builtins() {
            self.data.insert(
                k.into(),
                Macro {
                    source: ItemSource::Builtin,
                    text: v,
                    #[cfg(feature = "full")]
                    eagerly_expanded: false,
                },
            );
        }
    }

    pub fn add_env(&mut self) {
        for (k, v) in env::vars() {
            if k != "MAKEFLAGS" && k != "SHELL" {
                self.data.insert(
                    k,
                    Macro {
                        source: ItemSource::Environment,
                        text: TokenString::text(v),
                        #[cfg(feature = "full")]
                        eagerly_expanded: false,
                    },
                );
            }
        }
    }

    fn lookup_internal(&self, name: &str) -> Result<String> {
        if let Some(lookup) = self.lookup_internal {
            lookup(name)
        } else if let Some(parent) = self.parent {
            parent.lookup_internal(name)
        } else {
            bail!(
                "tried to lookup {:?} but no lookup function is available",
                name
            )
        }
    }

    pub fn get(&self, name: &str) -> Option<&Macro> {
        self.data
            .get(name)
            .or_else(|| self.parent.and_then(|parent| parent.get(name)))
    }

    pub fn set(&mut self, name: String, r#macro: Macro) {
        self.data.insert(name, r#macro);
    }

    #[cfg(feature = "full")]
    pub fn is_defined(&self, name: &str) -> bool {
        self.get(name).map_or(false, |x| !x.text.is_empty())
    }

    // `remove` is fine, but I think for "remove-and-return" `pop` is better
    pub fn pop(&mut self, name: &str) -> Option<Macro> {
        // TODO figure out a better way to handle inheritance
        self.data
            .remove(name)
            .or_else(|| self.parent.and_then(|p| p.get(name).cloned()))
    }

    pub fn extend(
        &mut self,
        other: HashMap<String, Macro>,
        #[cfg(feature = "full")] other_exports: ExportConfig,
    ) {
        #[cfg(feature = "full")]
        match (&mut self.exported, other_exports) {
            (ExportConfig::Only(se), ExportConfig::Only(oe)) => {
                se.extend(oe);
            }
            (ExportConfig::AllBut(sne), ExportConfig::AllBut(one)) => {
                sne.extend(one);
            }
            (ExportConfig::Only(se), ExportConfig::AllBut(one)) => {
                se.extend(other.keys().cloned().filter(|name| !one.contains(name)));
            }
            (ExportConfig::AllBut(sne), ExportConfig::Only(oe)) => {
                sne.extend(other.keys().cloned().filter(|name| !oe.contains(name)));
            }
        }
        self.data.extend(other);
    }

    fn warn(&self, text: String) {
        if !self.warnings.borrow().contains(&text) {
            log::warn!("{}", &text);
            self.warnings.borrow_mut().insert(text);
        }
    }

    pub fn expand(&self, text: &TokenString) -> Result<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 name = self
                        .expand(name)
                        .wrap_err_with(|| format!("while expanding \"{}\"", name))?;
                    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 {
                        self.lookup_internal(&name)
                            .wrap_err_with(|| format!("while expanding $\"{}\"", name))?
                    } else {
                        self.get(&name).map_or_else(
                            || {
                                self.warn(format!("undefined macro {}", name));
                                Ok(String::new())
                            },
                            |x| {
                                self.expand(&x.text)
                                    .wrap_err_with(|| format!("while expanding \"{}\"", &x.text))
                            },
                        )?
                    };
                    let macro_value = match replacement {
                        Some((subst1, subst2)) => {
                            let subst1 = self.expand(subst1)?;
                            let subst1_suffix = regex::escape(&subst1);
                            let subst1_suffix = Regex::new(&format!(r"{}(\s|$)", subst1_suffix))
                                .context("formed invalid regex somehow")?;
                            let subst2 = self.expand(subst2)?;
                            subst1_suffix
                                .replace_all(&macro_value, |c: &regex::Captures| {
                                    format!("{}{}", subst2, c.get(1).unwrap().as_str())
                                })
                                .to_string()
                        }
                        None => macro_value,
                    };
                    result.push_str(&macro_value);
                }
                #[cfg(feature = "full")]
                Token::FunctionCall { name, args } => {
                    let name = self.expand(name)?;
                    let fn_result =
                        functions::expand_call(&name, args, self, Some(Rc::clone(&self.to_eval)))?;
                    log::trace!("expanded {} into \"{}\"", token, &fn_result);
                    result.push_str(&fn_result);
                }
            }
        }
        Ok(result)
    }

    #[cfg(feature = "full")]
    pub fn origin(&self, name: &str) -> &'static str {
        match self.data.get(name) {
            None => self.parent.map_or("undefined", |p| p.origin(name)),
            Some(Macro {
                source: ItemSource::Builtin,
                ..
            }) => "default",
            Some(Macro {
                source: ItemSource::Environment,
                ..
            }) => "environment",
            // TODO figure out when to return "environment override"
            Some(Macro {
                source: ItemSource::File { .. },
                ..
            }) => "file",
            Some(Macro {
                source: ItemSource::CommandLineOrMakeflags,
                ..
            }) => "command line",
            // TODO handle override
            Some(Macro {
                source: ItemSource::FunctionCall,
                ..
            }) => "automatic",
        }
    }

    pub fn with_lookup<'l, 's: 'l>(&'s self, lookup: &'l dyn LookupInternal) -> Set<'s, 'l> {
        Set {
            parent: Some(self),
            data: HashMap::new(),
            lookup_internal: Some(lookup),
            #[cfg(feature = "full")]
            to_eval: Rc::clone(&self.to_eval),
            #[cfg(feature = "full")]
            exported: self.exported.same_type(),
            warnings: Rc::clone(&self.warnings),
        }
    }

    pub fn with_overlay<'s>(&'s self) -> Set<'s, 'lookup> {
        Set {
            parent: Some(self),
            data: HashMap::new(),
            lookup_internal: None,
            #[cfg(feature = "full")]
            to_eval: Rc::clone(&self.to_eval),
            #[cfg(feature = "full")]
            exported: self.exported.same_type(),
            warnings: Rc::clone(&self.warnings),
        }
    }

    #[cfg(feature = "full")]
    pub fn resolve_exports(&self) -> Result<Vec<(&str, String)>> {
        let own_exports = self
            .data
            .iter()
            .filter(|(name, _)| self.exported.should_export(name))
            .map(|(name, value)| self.expand(&value.text).map(|text| (name.as_ref(), text)))
            .collect::<Result<Vec<_>>>()?;
        Ok(if let Some(parent) = self.parent {
            let mut parent_exports = parent.resolve_exports()?;
            parent_exports.extend(own_exports);
            parent_exports
        } else {
            own_exports
        })
    }
}

impl fmt::Display for Set<'_, '_> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let pieces = self
            .data
            .iter()
            .map(|(k, x)| format!("{}={}", k, &x.text))
            .collect::<Vec<_>>();
        write!(f, "{}", pieces.join("\n"))
    }
}

fn builtins() -> Vec<(&'static str, TokenString)> {
    // Fuck it, might as well.
    macro_rules! handle {
        ($value:ident) => {
            stringify!($value).parse().unwrap()
        };
        ($value:literal) => {
            $value.parse().unwrap()
        };
        ($value:expr) => {
            $value
        };
    }
    macro_rules! make {
        ($($name:ident=$value:tt)+) => {vec![$(
            (stringify!($name), handle!($value))
        ),+]};
    }

    make![
        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=""
    ]
}

#[cfg(test)]
mod test {
    use super::*;

    type R = Result<()>;

    #[test]
    fn subst() -> R {
        let mut macros = Set::new();
        macros.set(
            "oof".to_owned(),
            Macro {
                source: ItemSource::Builtin,
                text: TokenString::text("bruh; swag; yeet;"),
                #[cfg(feature = "full")]
                eagerly_expanded: false,
            },
        );
        assert_eq!(macros.expand(&"$(oof:;=?)".parse()?)?, "bruh? swag? yeet?");
        Ok(())
    }
}