//! This build script ensures that clippy is not compiled with an
//! incompatible version of rust. It will panic with a descriptive
//! error message instead.
//!
//! We specifially want to ensure that clippy is only built with a
//! rustc version that is newer or equal to the one specified in the
//! `min_version.txt` file.
//!
//! `min_version.txt` is in the repo but also in the `.gitignore` to
//! make sure that it is not updated manually by accident. Only CI
//! should update that file.
//!
//! This build script was originally taken from the Rocket web framework:
//! https://github.com/SergioBenitez/Rocket

extern crate rustc_version;
extern crate ansi_term;

use std::env;
use rustc_version::{version_meta, version_meta_for, Channel, Version, VersionMeta};
use ansi_term::Colour::Red;

fn main() {
    check_rustc_version();

    // Forward the profile to the main compilation
    println!("cargo:rustc-env=PROFILE={}", env::var("PROFILE").unwrap());
    // Don't rebuild even if nothing changed
    println!("cargo:rerun-if-changed=build.rs");
}

fn check_rustc_version() {
    let string = include_str!("min_version.txt");
    let min_version_meta = version_meta_for(string)
        .expect("Could not parse version string in min_version.txt");
    let current_version_meta = version_meta()
        .expect("Could not retrieve current rustc version information from ENV");

    let min_version = min_version_meta.clone().semver;
    let min_date_str = min_version_meta.clone().commit_date
        .expect("min_version.txt does not contain a rustc commit date");

    // Dev channel (rustc built from git) does not have any date or commit information in rustc -vV
    // `current_version_meta.commit_date` would crash, so we return early here.
    if current_version_meta.channel == Channel::Dev {
        return
    }

    let current_version = current_version_meta.clone().semver;
    let current_date_str = current_version_meta.clone().commit_date
        .expect("current rustc version information does not contain a rustc commit date");

    let print_version_err = |version: &Version, date: &str| {
        eprintln!("> {} {}. {} {}.\n",
                  "Installed rustc version is:",
                  format!("{} ({})", version, date),
                  "Minimum required rustc version:",
                  format!("{} ({})", min_version, min_date_str));
    };

    if !correct_channel(&current_version_meta) {
        eprintln!("\n{} {}",
                  Red.bold().paint("error:"),
                  "clippy requires a nightly version of Rust.");
        print_version_err(&current_version, &*current_date_str);
        eprintln!("{}{}{}",
                  "See the README (",
                  "https://github.com/rust-lang-nursery/rust-clippy#usage",
                  ") for more information.");
        panic!("Aborting compilation due to incompatible compiler.")
    }

    let current_date = str_to_ymd(&current_date_str).unwrap();
    let min_date = str_to_ymd(&min_date_str).unwrap();

    if current_date < min_date {
        eprintln!("\n{} {}",
                  Red.bold().paint("error:"),
                  "clippy does not support this version of rustc nightly.");
        eprintln!("> {}{}{}",
                  "Use `",
                  "rustup update",
                  "` or your preferred method to update Rust.");
        print_version_err(&current_version, &*current_date_str);
        panic!("Aborting compilation due to incompatible compiler.")
    }
}

fn correct_channel(version_meta: &VersionMeta) -> bool {
    match version_meta.channel {
        Channel::Stable | Channel::Beta => {
            false
        },
        Channel::Nightly | Channel::Dev => {
            true
        }
    }
}

/// Convert a string of %Y-%m-%d to a single u32 maintaining ordering.
fn str_to_ymd(ymd: &str) -> Option<u32> {
    let ymd: Vec<u32> = ymd.split("-").filter_map(|s| s.parse::<u32>().ok()).collect();
    if ymd.len() != 3 {
        return None
    }

    let (y, m, d) = (ymd[0], ymd[1], ymd[2]);
    Some((y << 9) | (m << 5) | d)
}