//! Toolchain lint source.

use core::str::{FromStr as _, Utf8Error};
use std::io;
use std::process::{Command, ExitStatus};

use anyhow::Context as _;
use itertools::Itertools as _;
use lint_policy::cargo::{LintSetting, LintTable, Lints};
use lint_policy::{Level, Linter};
use strum::{IntoEnumIterator as _, ParseError};

use crate::group::GroupTable;
use crate::source::LintGroups;

/// Query the toolchain version for the list of supported lints, panicking on any error.
///
/// # Panics
/// If an error occurs while running the toolchain or parsing the output.
pub(crate) fn read_lints(toolchain: &str) -> Lints {
	#[expect(
		clippy::expect_used,
		reason = "errors here are not deisgned to be recoverable"
	)]
	private_read_lints(toolchain)
		.with_context(|| format!("gathering lints from {toolchain:?}"))
		.expect("toolchain source error")
}

/// Query the toolchain version for the list of supported lints, panicking on any error.
///
/// # Panics
/// If an error occurs while running the toolchain or parsing the output.
pub(crate) fn read_groups(toolchain: &str) -> LintGroups {
	#[expect(
		clippy::expect_used,
		reason = "errors here are not deisgned to be recoverable"
	)]
	private_read_groups(toolchain)
		.with_context(|| format!("gathering lint groups from {toolchain:?}"))
		.expect("toolchain source error")
}

/// Possible errors that can occur while querying a toolchain version.
#[derive(Debug, thiserror::Error)]
pub(crate) enum ToolchainError {
	/// Executing a [Command] failed.
	#[error("failed to execute command: {0}")]
	Command(#[from] io::Error),
	/// The toolchain did not exit successfully.
	#[error("command exited with code {0}")]
	Status(ExitStatus),
	/// The output from the toolchain was not UTF-8.
	#[error("output is not utf8: {0}")]
	NotUtf8(#[from] Utf8Error),
}

/// Possible errors that can occur while parsing lines of the toolchain output.
#[derive(Debug, thiserror::Error)]
pub(crate) enum LineError {
	/// The output does not match the expected format.
	#[error("output is malformed: {0}")]
	Malformed(String),
	/// The lint level is not recognized.
	#[error("invalid level: {0}")]
	InvalidLevel(String),
}

/// Query the toolchain version for the list of supported lints.
///
/// # Errors
/// Either running the [Command] or parsing the output could fail.
fn private_read_lints(toolchain: &str) -> anyhow::Result<Lints> {
	let mut lints = Lints::default();
	let mut errors = Vec::new();

	for linter in Linter::iter() {
		let (l, e) = read_linter_lints(linter, toolchain)?;
		lints.set_lints_for(linter, l);
		errors.push(e);
	}

	if errors.iter().any(|e| !e.is_empty()) {
		for errors in &errors {
			#[expect(clippy::print_stderr, reason = "printing out actual error")]
			for error in errors {
				eprintln!("{error}");
			}
		}
		anyhow::bail!("encountered errors for toolchain");
	}

	Ok(lints)
}

/// Run the linter and parse its output.
///
/// # Errors
/// Either running the [Command] or parsing the output could fail.
fn read_linter_lints(
	linter: Linter,
	toolchain: &str,
) -> Result<(LintTable, Vec<LineError>), ToolchainError> {
	let mut command = match linter {
		Linter::Clippy => Command::new("clippy-driver"),
		Linter::Rust => Command::new("rustc"),
		Linter::Rustdoc => Command::new("rustdoc"),
	};
	let output = command.arg(toolchain).args(["-W", "help"]).output()?;

	if !output.status.success() {
		return Err(ToolchainError::Status(output.status));
	}

	let stdout = core::str::from_utf8(&output.stdout)?;

	let lint_begin_line = match linter {
		Linter::Rust => "Lint checks provided by rustc:",
		Linter::Clippy | Linter::Rustdoc => "Lint checks loaded by this crate:",
	};

	let lint_lines = stdout
		.lines()
		.skip_while(|&line| line != lint_begin_line)
		.skip(4)
		.take_while(|line| !line.is_empty());

	let lints = lint_lines.map(|line| {
		let (name, level) = line
			.trim()
			.split_once(' ')
			.ok_or_else(|| LineError::Malformed(line.to_owned()))
			.and_then(|(name, rest)| {
				rest.trim()
					.split_once(' ')
					.map(|(level, _)| (name, level))
					.ok_or_else(|| LineError::Malformed(line.to_owned()))
			})?;
		Level::from_str(level)
			.map(|level| (strip_lint_name(linter, name), LintSetting::level(level)))
			.map_err(|ParseError::VariantNotFound| LineError::InvalidLevel(level.to_owned()))
	});

	Ok(lints.partition_result())
}

/// Query the toolchain version for the list of supported lints, panicking on any error.
///
/// # Errors
/// Either running the [Command] or parsing the output could fail.
fn private_read_groups(toolchain: &str) -> anyhow::Result<LintGroups> {
	let mut groups = LintGroups::default();
	let mut errors = Vec::new();

	for linter in Linter::iter() {
		let (g, e) = read_linter_groups(linter, toolchain)?;
		groups.set_groups_for(linter, g);
		errors.push(e);
	}

	if errors.iter().any(|e| !e.is_empty()) {
		for errors in &errors {
			#[expect(clippy::print_stderr, reason = "printing out actual error")]
			for error in errors {
				eprintln!("{error}");
			}
		}
		anyhow::bail!("encountered errors for toolchain");
	}

	Ok(groups)
}

/// Run the linter and parse its output.
///
/// # Errors
/// Either running the [Command] or parsing the output could fail.
fn read_linter_groups(
	linter: Linter,
	toolchain: &str,
) -> Result<(GroupTable, Vec<LineError>), ToolchainError> {
	let mut command = match linter {
		Linter::Clippy => Command::new("clippy-driver"),
		Linter::Rust => Command::new("rustc"),
		Linter::Rustdoc => Command::new("rustdoc"),
	};
	let output = command.arg(toolchain).args(["-W", "help"]).output()?;

	if !output.status.success() {
		return Err(ToolchainError::Status(output.status));
	}

	let stdout = core::str::from_utf8(&output.stdout)?;

	let lint_begin_line = match linter {
		Linter::Rust => "Lint groups provided by rustc:",
		Linter::Clippy | Linter::Rustdoc => "Lint groups loaded by this crate:",
	};

	let lint_lines = stdout
		.lines()
		.skip_while(|&line| line != lint_begin_line)
		.skip(4)
		.take_while(|line| !line.is_empty());

	let lints = lint_lines.map(|line| {
		line.trim()
			.split_once(' ')
			.ok_or_else(|| LineError::Malformed(line.to_owned()))
			.map(|(name, rest)| {
				(
					strip_lint_name(linter, name),
					rest.split(',')
						.map(|s| strip_lint_name(linter, s))
						.collect::<Vec<_>>(),
				)
			})
	});

	Ok(lints.partition_result())
}

/// Strip the linter's name from the front of the lint name.
fn strip_lint_name(linter: Linter, name: &str) -> String {
	let name = name.trim();
	name.strip_prefix(linter.as_ref())
		.and_then(|name| name.strip_prefix("::"))
		.unwrap_or(name)
		.replace('-', "_")
}