//! FIXME: write short doc here

use std::{
    env,
    path::{Path, PathBuf},
    process::Command,
};

use ra_arena::{impl_arena_id, Arena, RawId};

use crate::Result;

#[derive(Default, Debug, Clone)]
pub struct Sysroot {
    crates: Arena<SysrootCrate, SysrootCrateData>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct SysrootCrate(RawId);
impl_arena_id!(SysrootCrate);

#[derive(Debug, Clone)]
struct SysrootCrateData {
    name: String,
    root: PathBuf,
    deps: Vec<SysrootCrate>,
}

impl Sysroot {
    pub fn core(&self) -> Option<SysrootCrate> {
        self.by_name("core")
    }

    pub fn alloc(&self) -> Option<SysrootCrate> {
        self.by_name("alloc")
    }

    pub fn std(&self) -> Option<SysrootCrate> {
        self.by_name("std")
    }

    pub fn crates<'a>(&'a self) -> impl Iterator<Item = SysrootCrate> + ExactSizeIterator + 'a {
        self.crates.iter().map(|(id, _data)| id)
    }

    pub fn discover(cargo_toml: &Path) -> Result<Sysroot> {
        let src = try_find_src_path(cargo_toml)?;

        if !src.exists() {
            Err(format!(
                "can't load standard library from sysroot\n\
                 {:?}\n\
                 try running `rustup component add rust-src` or set `RUST_SRC_PATH`",
                src,
            ))?;
        }

        let mut sysroot = Sysroot { crates: Arena::default() };
        for name in SYSROOT_CRATES.trim().lines() {
            let root = src.join(format!("lib{}", name)).join("lib.rs");
            if root.exists() {
                sysroot.crates.alloc(SysrootCrateData {
                    name: name.into(),
                    root,
                    deps: Vec::new(),
                });
            }
        }
        if let Some(std) = sysroot.std() {
            for dep in STD_DEPS.trim().lines() {
                if let Some(dep) = sysroot.by_name(dep) {
                    sysroot.crates[std].deps.push(dep)
                }
            }
        }
        if let Some(alloc) = sysroot.by_name("alloc") {
            if let Some(core) = sysroot.by_name("core") {
                sysroot.crates[alloc].deps.push(core);
            }
        }
        Ok(sysroot)
    }

    fn by_name(&self, name: &str) -> Option<SysrootCrate> {
        self.crates.iter().find(|(_id, data)| data.name == name).map(|(id, _data)| id)
    }
}

fn try_find_src_path(cargo_toml: &Path) -> Result<PathBuf> {
    if let Ok(path) = env::var("RUST_SRC_PATH") {
        return Ok(path.into());
    }

    let rustc_output = Command::new("rustc")
        .current_dir(cargo_toml.parent().unwrap())
        .args(&["--print", "sysroot"])
        .output()?;
    if !rustc_output.status.success() {
        Err("failed to locate sysroot")?;
    }
    let stdout = String::from_utf8(rustc_output.stdout)?;
    let sysroot_path = Path::new(stdout.trim());
    Ok(sysroot_path.join("lib/rustlib/src/rust/src"))
}

impl SysrootCrate {
    pub fn name(self, sysroot: &Sysroot) -> &str {
        &sysroot.crates[self].name
    }
    pub fn root(self, sysroot: &Sysroot) -> &Path {
        sysroot.crates[self].root.as_path()
    }
    pub fn root_dir(self, sysroot: &Sysroot) -> &Path {
        self.root(sysroot).parent().unwrap()
    }
    pub fn deps<'a>(self, sysroot: &'a Sysroot) -> impl Iterator<Item = SysrootCrate> + 'a {
        sysroot.crates[self].deps.iter().copied()
    }
}

const SYSROOT_CRATES: &str = "
std
core
alloc
collections
libc
panic_unwind
proc_macro
rustc_unicode
std_unicode
test
alloc_jemalloc
alloc_system
compiler_builtins
getopts
panic_unwind
panic_abort
rand
term
unwind
build_helper
rustc_asan
rustc_lsan
rustc_msan
rustc_tsan
syntax";

const STD_DEPS: &str = "
alloc
alloc_jemalloc
alloc_system
core
panic_abort
rand
compiler_builtins
unwind
rustc_asan
rustc_lsan
rustc_msan
rustc_tsan
build_helper";