use std::collections::HashMap;
use std::fs::File;

use serde::{Deserialize, Serialize, Serializer};
use serde::ser::SerializeSeq;
use version_check::Version;

use rustc_feature::{ACCEPTED_FEATURES, ACTIVE_FEATURES, Feature, Features, REMOVED_FEATURES, STABLE_REMOVED_FEATURES, State};

use crate::formatter::MyFormatter;

#[derive(Serialize, Deserialize)]
struct FeatureInfo {
    name: String,
    state: String,
    since: String
}

impl FeatureInfo {
    fn from(f: &Feature) -> Self {
        FeatureInfo {
            name: f.name.as_str().to_string(),
            state: state_str(f),
            since: f.since.to_string()
        }
    }
}

pub(crate) fn update_compiler_features_json(compiler_features_json_path: &str) {
    let current_features: Vec<FeatureInfo> = serde_json::from_reader(File::open(compiler_features_json_path).unwrap()).unwrap();
    let feature_map: HashMap<_, _> = current_features
        .iter()
        .map(|f| -> ((&str, &str), &str) { ((&f.name, &f.state), &f.since) })
        .collect();

    let f = File::create(compiler_features_json_path).unwrap();
    let mut serializer = serde_json::Serializer::with_formatter(f, MyFormatter::new());

    let compiler_version = Version::read().unwrap().to_string();

    let mut seq = serializer.serialize_seq(None).unwrap();
    [ACCEPTED_FEATURES, ACTIVE_FEATURES, REMOVED_FEATURES, STABLE_REMOVED_FEATURES]
        .iter()
        .flat_map(|features| features.iter().map(FeatureInfo::from))
        .for_each(|f| seq.serialize_element(&replace_version_placeholder(&feature_map, &compiler_version, f)).unwrap());
    seq.end().unwrap();
}

fn replace_version_placeholder(
    feature_map: &HashMap<(&str, &str), &str>,
    compiler_version: &str,
    f: FeatureInfo
) -> FeatureInfo {
    // After https://github.com/rust-lang/rust/pull/100591, compiler uses `CURRENT_RUSTC_VERSION` placeholder
    // as value of `since` field which means that feature is available in the current compiler.
    // It's ok for the compiler, but the plugin should work with different compiler versions,
    // so it needs some concrete version when the feature became available to annotate code properly.
    //
    // The main idea to solve this problem is to use already saved values:
    // - if feature has placeholder and we didn't meet it before,
    //   the current compiler version will be used to replace the placeholder.
    //   Here we assume that this code is launched with the same (or almost the same) rustc version
    //   as in rustc master
    // - otherwise, just use version saved previously
    if f.since == "CURRENT_RUSTC_VERSION" {
        let old_feature = feature_map.get(&(&f.name, &f.state));
        let since = if let Some(v) = old_feature { v } else { compiler_version };
        FeatureInfo {
            since: since.to_string(),
            ..f
        }
    } else { f }
}

fn state_str(feature: &Feature) -> String {
    match feature.state {
        State::Accepted => "accepted",
        State::Active { .. } => {
            if Features::default().incomplete(feature.name) {
                "incomplete"
            } else {
                "active"
            }
        },
        State::Removed { .. } => "removed",
        State::Stabilized { .. } => "stabilized"
    }.to_string()
}