use std::collections::{HashMap, HashSet};

use serde::{Deserialize, Serialize};

use crate::{
	context::*,
	paths, resolve, runner,
	task::*,
	types::*,
	util::{cjson, error::*, fs},
};

// TODO: Generate dynamically from paths module
const TASK_ENV: &[(&str, &str)] = &[
	("PATH", "/usr/sbin:/usr/bin:/sbin:/bin"),
	("HOME", "/build"),
	("DESTDIR", "/build/dest"),
	("DLDIR", "/build/downloads"),
	("SYSROOT", "/build/sysroot"),
	("WORKDIR", "/build/work"),
	("BUILD_PREFIX", "/opt/toolchain"),
	("PREFIX", "/usr"),
];

#[derive(Clone, Debug, Serialize)]
struct TaskInput<'ctx> {
	pub id: &'ctx TaskRef<'ctx>,
	pub inherit: Option<&'ctx InputHash>,
	pub depends: &'ctx HashMap<DependencyHash, Dependency>,
	pub output: &'ctx HashMap<String, String>,
	pub run: &'ctx str,
	pub env: &'ctx HashMap<String, String>,
}

impl<'ctx> TaskInput<'ctx> {
	fn input_hash(&self) -> InputHash {
		InputHash(StringHash(
			cjson::digest::<InputHasher, _>(self).unwrap().into(),
		))
	}
}

#[derive(Clone, Debug, Deserialize, Serialize)]
struct TaskMeta {
	pub id: TaskID,
	pub inherit: Vec<InputHash>,
	pub depends: HashMap<DependencyHash, Dependency>,
	pub input_hash: InputHash,
	pub output: HashMap<String, ArchiveHash>,
}

impl TaskMeta {
	fn load(input_hash: &InputHash) -> Result<TaskMeta> {
		let filename = paths::task_meta_filename(input_hash);
		let file = fs::open(&filename)?;

		serde_json::from_reader(file)
			.with_context(|| format!("Failed to read task metadata from {}", filename))
	}

	fn save(&self) -> Result<()> {
		let tmp_filename = paths::task_meta_tmp_filename(&self.input_hash);
		let filename = paths::task_meta_filename(&self.input_hash);

		cjson::to_file(&tmp_filename, self)
			.with_context(|| format!("Failed to write task metadata to {}", tmp_filename))?;

		fs::rename(tmp_filename, filename)?;

		Ok(())
	}
}

#[derive(Debug)]
pub struct Executor<'ctx> {
	ctx: &'ctx Context,
	tasks_blocked: HashSet<TaskRef<'ctx>>,
	tasks_runnable: Vec<TaskRef<'ctx>>,
	tasks_done: HashMap<TaskRef<'ctx>, TaskMeta>,
	rdeps: HashMap<TaskRef<'ctx>, Vec<TaskRef<'ctx>>>,
	env: HashMap<String, String>,
}

impl<'ctx> Executor<'ctx> {
	pub fn new(ctx: &'ctx Context, taskset: HashSet<TaskRef<'ctx>>) -> Result<Self> {
		let env: HashMap<String, String> = TASK_ENV
			.iter()
			.map(|(k, v)| (k.to_string(), v.to_string()))
			.collect();

		let mut exc = Executor {
			ctx,
			tasks_blocked: HashSet::new(),
			tasks_runnable: Vec::new(),
			tasks_done: HashMap::new(),
			rdeps: HashMap::new(),
			env,
		};

		for task in taskset {
			let mut has_depends = false;
			for dep in ctx.get_dependent_tasks(&task) {
				let rdep = exc.rdeps.entry(dep.clone()).or_default();
				rdep.push(task.clone());
				has_depends = true;
			}

			if has_depends {
				exc.tasks_blocked.insert(task);
			} else {
				exc.tasks_runnable.push(task);
			}
		}

		fs::mkdir(paths::TASK_STATE_DIR)?;

		Ok(exc)
	}

	// Treats both "depends" and "inherit" as dependencies
	fn deps_satisfied(&self, task_ref: &TaskRef) -> bool {
		self.ctx
			.get_dependent_tasks(task_ref)
			.into_iter()
			.all(|dep| self.tasks_done.contains_key(&dep))
	}

	fn task_deps(&self, task: &TaskRef) -> HashMap<DependencyHash, Dependency> {
		let task_def = &self.ctx[task.id];
		task_def
			.fetch
			.iter()
			.map(|Fetch { name, sha256 }| Dependency::Fetch {
				name: name.clone(),
				sha256: *sha256,
			})
			.chain(
				resolve::runtime_depends(self.ctx, self.ctx.get_build_depends(task))
					.expect("invalid runtime depends of build_depends")
					.iter()
					.filter_map(|dep| self.tasks_done[&dep.task].output.get(dep.output))
					.map(|&output| Dependency::BuildTask { output }),
			)
			.chain(
				resolve::runtime_depends(self.ctx, self.ctx.get_target_depends(task))
					.expect("invalid runtime depends of target_depends")
					.iter()
					.filter_map(|dep| self.tasks_done[&dep.task].output.get(dep.output))
					.map(|&output| Dependency::TargetTask { output }),
			)
			.map(|dep| (dep.dependency_hash(), dep))
			.collect()
	}

	fn run_one(&self, task_ref: &TaskRef, runner: &impl runner::Runner) -> Result<TaskMeta> {
		let task_def = &self.ctx[&task_ref.id];
		let task_deps = self.task_deps(&task_ref);
		let task_output = task_def
			.output
			.iter()
			.map(|(name, Output { path, .. })| {
				(
					name.clone(),
					path.as_ref().map(String::as_str).unwrap_or(".").to_string(),
				)
			})
			.collect();
		let env = self.env.clone();

		let (inherit_chain, inherit_hash) = if let Some(inherit_dep) = &task_def.inherit {
			let inherit_meta = &self.tasks_done[&self.ctx.inherit_ref(inherit_dep)];
			let mut inherit_chain = inherit_meta.inherit.clone();
			inherit_chain.push(inherit_meta.input_hash);
			(inherit_chain, Some(&inherit_meta.input_hash))
		} else {
			(Vec::new(), None)
		};

		let input_hash = TaskInput {
			id: &task_ref,
			inherit: inherit_hash,
			depends: &task_deps,
			output: &task_output,
			run: &task_def.action.run,
			env: &env,
		}
		.input_hash();

		// Use cached result
		if let Ok(meta) = TaskMeta::load(&input_hash) {
			return Ok(meta);
		}

		// Remove metadata first to ensure task invalidation
		fs::ensure_removed(&paths::task_meta_filename(&input_hash))?;

		let state_dir = paths::task_state_dir(&input_hash);
		fs::ensure_removed(&state_dir)?;
		fs::mkdir(&state_dir)?;

		let task = runner::Task {
			id: task_ref.id.clone(),
			run: task_def.action.run.clone(),
			input_hash,
			inherit: inherit_chain.clone(),
			depends: task_deps.clone(),
			output: task_output,
			env,
		};

		let output = runner.run(&task)?;

		let meta = TaskMeta {
			id: task_ref.id.clone(),
			inherit: inherit_chain,
			depends: task_deps,
			input_hash,
			output,
		};
		meta.save()?;

		Ok(meta)
	}

	fn update_runnable(&mut self, task_ref: &TaskRef) {
		let rdeps = self.rdeps.get(task_ref);

		for rdep in rdeps.unwrap_or(&Vec::new()) {
			if !self.tasks_blocked.contains(rdep) {
				continue;
			}
			if self.deps_satisfied(rdep) {
				self.tasks_blocked.remove(rdep);
				self.tasks_runnable.push(rdep.clone());
			}
		}
	}

	pub fn run(&mut self, runner: &impl runner::Runner) -> Result<()> {
		while let Some(task_ref) = self.tasks_runnable.pop() {
			let meta = self.run_one(&task_ref, runner)?;
			self.tasks_done.insert(task_ref.clone(), meta);

			self.update_runnable(&task_ref);
		}

		assert!(self.tasks_blocked.is_empty(), "No runnable tasks left");

		println!("Summary");
		for task in self.tasks_done.values() {
			println!("");
			println!("{} ( {} )", task.id, task.input_hash);
			for (output, hash) in &task.output {
				println!("-> {} ( {} )", output, hash);
			}
		}
		Ok(())
	}
}