use ruff_formatter::FormatOptions;
use ruff_python_formatter::{format_module, PyFormatOptions};
use similar::TextDiff;
use std::fmt::{Formatter, Write};
use std::io::BufReader;
use std::path::Path;
use std::{fmt, fs};

#[test]
fn black_compatibility() {
    let test_file = |input_path: &Path| {
        let content = fs::read_to_string(input_path).unwrap();

        let options_path = input_path.with_extension("options.json");

        let options: PyFormatOptions = if let Ok(options_file) = fs::File::open(options_path) {
            let reader = BufReader::new(options_file);
            serde_json::from_reader(reader).expect("Options to be a valid Json file")
        } else {
            PyFormatOptions::default()
        };

        let printed = format_module(&content, options.clone()).unwrap_or_else(|err| {
            panic!(
                "Formatting of {} to succeed but encountered error {err}",
                input_path.display()
            )
        });

        let expected_path = input_path.with_extension("py.expect");
        let expected_output = fs::read_to_string(&expected_path)
            .unwrap_or_else(|_| panic!("Expected Black output file '{expected_path:?}' to exist"));

        let formatted_code = printed.as_code();

        ensure_stability_when_formatting_twice(formatted_code, options, input_path);

        if formatted_code == expected_output {
            // Black and Ruff formatting matches. Delete any existing snapshot files because the Black output
            // already perfectly captures the expected output.
            // The following code mimics insta's logic generating the snapshot name for a test.
            let workspace_path = std::env::var("CARGO_MANIFEST_DIR").unwrap();

            let mut components = input_path.components().rev();
            let file_name = components.next().unwrap();
            let test_suite = components.next().unwrap();

            let snapshot_name = format!(
                "black_compatibility@{}__{}.snap",
                test_suite.as_os_str().to_string_lossy(),
                file_name.as_os_str().to_string_lossy()
            );

            let snapshot_path = Path::new(&workspace_path)
                .join("tests/snapshots")
                .join(snapshot_name);
            if snapshot_path.exists() && snapshot_path.is_file() {
                // SAFETY: This is a convenience feature. That's why we don't want to abort
                // when deleting a no longer needed snapshot fails.
                fs::remove_file(&snapshot_path).ok();
            }

            let new_snapshot_path = snapshot_path.with_extension("snap.new");
            if new_snapshot_path.exists() && new_snapshot_path.is_file() {
                // SAFETY: This is a convenience feature. That's why we don't want to abort
                // when deleting a no longer needed snapshot fails.
                fs::remove_file(&new_snapshot_path).ok();
            }
        } else {
            // Black and Ruff have different formatting. Write out a snapshot that covers the differences
            // today.
            let mut snapshot = String::new();
            write!(snapshot, "{}", Header::new("Input")).unwrap();
            write!(snapshot, "{}", CodeFrame::new("py", &content)).unwrap();

            write!(snapshot, "{}", Header::new("Black Differences")).unwrap();

            let diff = TextDiff::from_lines(expected_output.as_str(), formatted_code)
                .unified_diff()
                .header("Black", "Ruff")
                .to_string();

            write!(snapshot, "{}", CodeFrame::new("diff", &diff)).unwrap();

            write!(snapshot, "{}", Header::new("Ruff Output")).unwrap();
            write!(snapshot, "{}", CodeFrame::new("py", &formatted_code)).unwrap();

            write!(snapshot, "{}", Header::new("Black Output")).unwrap();
            write!(snapshot, "{}", CodeFrame::new("py", &expected_output)).unwrap();

            insta::with_settings!({
                omit_expression => true,
                input_file => input_path,
                prepend_module_to_snapshot => false,
            }, {
                insta::assert_snapshot!(snapshot);
            });
        }
    };

    insta::glob!("../resources", "test/fixtures/black/**/*.py", test_file);
}

#[test]
fn format() {
    let test_file = |input_path: &Path| {
        let content = fs::read_to_string(input_path).unwrap();

        let options = PyFormatOptions::default();
        let printed = format_module(&content, options.clone()).expect("Formatting to succeed");
        let formatted_code = printed.as_code();

        ensure_stability_when_formatting_twice(formatted_code, options, input_path);

        let mut snapshot = format!("## Input\n{}", CodeFrame::new("py", &content));

        let options_path = input_path.with_extension("options.json");
        if let Ok(options_file) = fs::File::open(options_path) {
            let reader = BufReader::new(options_file);
            let options: Vec<PyFormatOptions> =
                serde_json::from_reader(reader).expect("Options to be a valid Json file");

            writeln!(snapshot, "## Outputs").unwrap();

            for (i, options) in options.into_iter().enumerate() {
                let printed =
                    format_module(&content, options.clone()).expect("Formatting to succeed");
                let formatted_code = printed.as_code();

                ensure_stability_when_formatting_twice(formatted_code, options.clone(), input_path);

                writeln!(
                    snapshot,
                    "### Output {}\n{}{}",
                    i + 1,
                    CodeFrame::new("", &DisplayPyOptions(&options)),
                    CodeFrame::new("py", &formatted_code)
                )
                .unwrap();
            }
        } else {
            let options = PyFormatOptions::default();
            let printed = format_module(&content, options.clone()).expect("Formatting to succeed");
            let formatted_code = printed.as_code();

            ensure_stability_when_formatting_twice(formatted_code, options, input_path);

            writeln!(
                snapshot,
                "## Output\n{}",
                CodeFrame::new("py", &formatted_code)
            )
            .unwrap();
        }

        insta::with_settings!({
            omit_expression => true,
            input_file => input_path,
            prepend_module_to_snapshot => false,
        }, {
            insta::assert_snapshot!(snapshot);
        });
    };

    insta::glob!("../resources", "test/fixtures/ruff/**/*.py", test_file);
}

/// Format another time and make sure that there are no changes anymore
fn ensure_stability_when_formatting_twice(
    formatted_code: &str,
    options: PyFormatOptions,
    input_path: &Path,
) {
    let reformatted = match format_module(formatted_code, options) {
        Ok(reformatted) => reformatted,
        Err(err) => {
            panic!(
                "Expected formatted code of {} to be valid syntax: {err}:\
                    \n---\n{formatted_code}---\n",
                input_path.display()
            );
        }
    };

    if reformatted.as_code() != formatted_code {
        let diff = TextDiff::from_lines(formatted_code, reformatted.as_code())
            .unified_diff()
            .header("Formatted once", "Formatted twice")
            .to_string();
        panic!(
            r#"Reformatting the formatted code of {} a second time resulted in formatting changes.
---
{diff}---

Formatted once:
---
{formatted_code}---

Formatted twice:
---
{}---"#,
            input_path.display(),
            reformatted.as_code(),
        );
    }
}

struct Header<'a> {
    title: &'a str,
}

impl<'a> Header<'a> {
    fn new(title: &'a str) -> Self {
        Self { title }
    }
}

impl std::fmt::Display for Header<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        writeln!(f, "## {}", self.title)?;
        writeln!(f)
    }
}

struct CodeFrame<'a> {
    language: &'a str,
    code: &'a dyn std::fmt::Display,
}

impl<'a> CodeFrame<'a> {
    fn new(language: &'a str, code: &'a dyn std::fmt::Display) -> Self {
        Self { language, code }
    }
}

impl std::fmt::Display for CodeFrame<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        writeln!(f, "```{}", self.language)?;
        write!(f, "{}", self.code)?;
        writeln!(f, "```")?;
        writeln!(f)
    }
}

struct DisplayPyOptions<'a>(&'a PyFormatOptions);

impl fmt::Display for DisplayPyOptions<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        writeln!(
            f,
            r#"indent-style            = {indent_style}
line-width              = {line_width}
quote-style             = {quote_style:?}
magic-trailing-comma    = {magic_trailing_comma:?}"#,
            indent_style = self.0.indent_style(),
            line_width = self.0.line_width().value(),
            quote_style = self.0.quote_style(),
            magic_trailing_comma = self.0.magic_trailing_comma()
        )
    }
}