//! Minimalistic snapshot testing for Rust.
//!
//! # Introduction
//!
//! `expect_test` is a small addition over plain `assert_eq!` testing approach,
//! which allows to automatically update tests results.
//!
//! The core of the library is the `expect!` macro. It can be though of as a
//! super-charged string literal, which can update itself.
//!
//! Let's see an example:
//!
//! ```no_run
//! use expect_test::expect;
//!
//! let expected = expect![["5"]];
//! let actual = 2 + 2;
//! expected.assert_eq(&actual.to_string())
//! ```
//!
//! Running this code will produce a test failure, as `"5"` is indeed not equal
//! to `"4"`. Running the test with `UPDATE_EXPECT=1` env variable however would
//! "magically" update the code to:
//!
//! ```no_run
//! # use expect_test::expect;
//! let actual = 2 + 2;
//! let expected = expect![["4"]];
//! expected.assert_eq(&actual.to_string())
//! ```
//!
//! This becomes very useful when you have a lot of tests with verbose and
//! potentially changing expected output.
//!
//! Under the hood, `expect!` macro uses `file!` and `line!` to record source
//! position at compile time. At runtime, this position is used to patch the
//! file in-place, if `UPDATE_EXPECT` is set.
//!
//! # Guide
//!
//! `expect!` returns an instance of `Expect` struct, which holds position
//! information and a string literal. Use `Expect::assert_eq` for string
//! comparison. Use `Expect::assert_eq` for verbose debug comparison. Note that
//! leading indentation is automatically removed.
//!
//! ```
//! use expect_test::expect;
//!
//! #[derive(Debug)]
//! struct Foo {
//!     value: i32,
//! }
//!
//! let actual = Foo { value: 92 };
//! let expected = expect![["
//!     Foo {
//!         value: 92,
//!     }
//! "]];
//! expected.assert_debug_eq(&actual);
//! ```
//!
//! Be careful with `assert_debug_eq` -- in general, stability of the debug
//! representation is not guaranteed. However, even if it changes, you can
//! quickly update all the tests by running the test suite with `UPDATE_EXPECT`
//! environmental variable set.
//!
//! If the expected data is to verbose for inline test, you can store it in the
//! external file using `expect_file!` macro:
//!
//! ```no_run
//! use expect_test::expect_file;
//!
//! let actual = 42;
//! let expected = expect_file!["the-answer.txt"];
//! expected.assert_eq(&actual.to_string());
//! ```
//!
//! File path is relative to the root of the Cargo workspace.
//!
//! # Suggested Workflows
//!
//! I like to use data-driven test with `expect_test`. I usually define a single
//! driver function `check` and then call it from individual tests:
//!
//! ```
//! use expect_test::{expect, Expect};
//!
//! fn check(actual: i32, expect: Expect) {
//!     let actual = actual.to_string();
//!     expect.assert_eq(&actual);
//! }
//!
//! #[test]
//! fn test_addition() {
//!     check(90 + 2, expect![["92"]]);
//! }
//!
//! #[test]
//! fn test_multiplication() {
//!     check(46 * 2, expect![["92"]]);
//! }
//! ```
//!
//! Each test's body is a single call to `check`. All the variation in tests
//! comes from the input data.
//!
//! When writing new test, I usually copy-paste and old one, leave the `expect`
//! blank and use `UPDATE_EXPECT` to fill the value for me:
//!
//! ```
//! # use expect_test::{expect, Expect};
//! # fn check(_: i32, _: Expect) {}
//! #[test]
//! fn test_division() {
//!     check(92 / 2, expect![[]])
//! }
//! ```
//!
//! See
//! https://blog.janestreet.com/using-ascii-waveforms-to-test-hardware-designs/
//! for a cool example of snapshot testing in the wild!
use std::{
    collections::HashMap,
    env, fmt, fs, mem,
    ops::Range,
    panic,
    path::{Path, PathBuf},
    sync::Mutex,
};

use difference::Changeset;
use once_cell::sync::Lazy;

const HELP: &str = "
You can update all `expect![[]]` tests by running:

    env UPDATE_EXPECT=1 cargo test

To update a single test, place the cursor on `expect` token and use `run` feature of rust-analyzer.
";

fn update_expect() -> bool {
    env::var("UPDATE_EXPECT").is_ok()
}

/// Creates an instance of `Expect` from string literal:
///
/// ```
/// # use expect_test::expect;
/// expect![["
///     Foo { value: 92 }
/// "]];
/// ```
///
/// Leading indentation is stripped.
#[macro_export]
macro_rules! expect {
    [[$data:literal]] => {$crate::Expect {
        position: $crate::Position {
            file: file!(),
            line: line!(),
            column: column!(),
        },
        data: $data,
    }};
    [[]] => { $crate::expect![[""]] };
}

/// Creates an instance of `ExpectFile` from workspace-relative path:
///
/// ```
/// # use expect_test::expect_file;
/// expect_file!["/crates/foo/test_data/bar.html"];
/// ```
#[macro_export]
macro_rules! expect_file {
    [$path:expr] => {$crate::ExpectFile {
        path: std::path::PathBuf::from($path)
    }};
}

/// Self-updating string literal.
#[derive(Debug)]
pub struct Expect {
    #[doc(hidden)]
    pub position: Position,
    #[doc(hidden)]
    pub data: &'static str,
}

/// Self-updating file.
#[derive(Debug)]
pub struct ExpectFile {
    #[doc(hidden)]
    pub path: PathBuf,
}

/// Position of original `expect!` in the source file.
#[derive(Debug)]
pub struct Position {
    #[doc(hidden)]
    pub file: &'static str,
    #[doc(hidden)]
    pub line: u32,
    #[doc(hidden)]
    pub column: u32,
}

impl fmt::Display for Position {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}:{}:{}", self.file, self.line, self.column)
    }
}

impl Expect {
    /// Checks if this expect is equal to `actual`.
    pub fn assert_eq(&self, actual: &str) {
        let trimmed = self.trimmed();
        if trimmed == actual {
            return;
        }
        Runtime::fail_expect(self, &trimmed, actual);
    }
    /// Checks if this expect is equal to `format!("{:#?}", actual)`.
    pub fn assert_debug_eq(&self, actual: &impl fmt::Debug) {
        let actual = format!("{:#?}\n", actual);
        self.assert_eq(&actual)
    }

    fn trimmed(&self) -> String {
        if !self.data.contains('\n') {
            return self.data.to_string();
        }
        trim_indent(self.data)
    }

    fn locate(&self, file: &str) -> Location {
        let mut target_line = None;
        let mut line_start = 0;
        for (i, line) in lines_with_ends(file).enumerate() {
            if i == self.position.line as usize - 1 {
                let pat = "expect![[";
                let offset = line.find(pat).unwrap();
                let literal_start = line_start + offset + pat.len();
                let indent = line.chars().take_while(|&it| it == ' ').count();
                target_line = Some((literal_start, indent));
                break;
            }
            line_start += line.len();
        }
        let (literal_start, line_indent) = target_line.unwrap();
        let literal_length =
            file[literal_start..].find("]]").expect("Couldn't find matching `]]` for `expect![[`.");
        let literal_range = literal_start..literal_start + literal_length;
        Location { line_indent, literal_range }
    }
}

impl ExpectFile {
    /// Checks if file contents is equal to `actual`.
    pub fn assert_eq(&self, actual: &str) {
        let expected = self.read();
        if actual == expected {
            return;
        }
        Runtime::fail_file(self, &expected, actual);
    }
    /// Checks if file contents is equal to `format!("{:#?}", actual)`.
    pub fn assert_debug_eq(&self, actual: &impl fmt::Debug) {
        let actual = format!("{:#?}\n", actual);
        self.assert_eq(&actual)
    }
    fn read(&self) -> String {
        fs::read_to_string(self.abs_path()).unwrap_or_default().replace("\r\n", "\n")
    }
    fn write(&self, contents: &str) {
        fs::write(self.abs_path(), contents).unwrap()
    }
    fn abs_path(&self) -> PathBuf {
        WORKSPACE_ROOT.join(&self.path)
    }
}

#[derive(Default)]
struct Runtime {
    help_printed: bool,
    per_file: HashMap<&'static str, FileRuntime>,
}
static RT: Lazy<Mutex<Runtime>> = Lazy::new(Default::default);

impl Runtime {
    fn fail_expect(expect: &Expect, expected: &str, actual: &str) {
        let mut rt = RT.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
        if update_expect() {
            println!("\x1b[1m\x1b[92mupdating\x1b[0m: {}", expect.position);
            rt.per_file
                .entry(expect.position.file)
                .or_insert_with(|| FileRuntime::new(expect))
                .update(expect, actual);
            return;
        }
        rt.panic(expect.position.to_string(), expected, actual);
    }

    fn fail_file(expect: &ExpectFile, expected: &str, actual: &str) {
        let mut rt = RT.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
        if update_expect() {
            println!("\x1b[1m\x1b[92mupdating\x1b[0m: {}", expect.path.display());
            expect.write(actual);
            return;
        }
        rt.panic(expect.path.display().to_string(), expected, actual);
    }

    fn panic(&mut self, position: String, expected: &str, actual: &str) {
        let print_help = !mem::replace(&mut self.help_printed, true);
        let help = if print_help { HELP } else { "" };

        let diff = Changeset::new(actual, expected, "\n");

        println!(
            "\n
\x1b[1m\x1b[91merror\x1b[97m: expect test failed\x1b[0m
   \x1b[1m\x1b[34m-->\x1b[0m {}
{}
\x1b[1mExpect\x1b[0m:
----
{}
----

\x1b[1mActual\x1b[0m:
----
{}
----

\x1b[1mDiff\x1b[0m:
----
{}
----
",
            position, help, expected, actual, diff
        );
        // Use resume_unwind instead of panic!() to prevent a backtrace, which is unnecessary noise.
        panic::resume_unwind(Box::new(()));
    }
}

struct FileRuntime {
    path: PathBuf,
    original_text: String,
    patchwork: Patchwork,
}

impl FileRuntime {
    fn new(expect: &Expect) -> FileRuntime {
        let path = WORKSPACE_ROOT.join(expect.position.file);
        let original_text = fs::read_to_string(&path).unwrap();
        let patchwork = Patchwork::new(original_text.clone());
        FileRuntime { path, original_text, patchwork }
    }
    fn update(&mut self, expect: &Expect, actual: &str) {
        let loc = expect.locate(&self.original_text);
        let patch = format_patch(loc.line_indent.clone(), actual);
        self.patchwork.patch(loc.literal_range, &patch);
        fs::write(&self.path, &self.patchwork.text).unwrap()
    }
}

#[derive(Debug)]
struct Location {
    line_indent: usize,
    literal_range: Range<usize>,
}

#[derive(Debug)]
struct Patchwork {
    text: String,
    indels: Vec<(Range<usize>, usize)>,
}

impl Patchwork {
    fn new(text: String) -> Patchwork {
        Patchwork { text, indels: Vec::new() }
    }
    fn patch(&mut self, mut range: Range<usize>, patch: &str) {
        self.indels.push((range.clone(), patch.len()));
        self.indels.sort_by_key(|(delete, _insert)| delete.start);

        let (delete, insert) = self
            .indels
            .iter()
            .take_while(|(delete, _)| delete.start < range.start)
            .map(|(delete, insert)| (delete.end - delete.start, insert))
            .fold((0usize, 0usize), |(x1, y1), (x2, y2)| (x1 + x2, y1 + y2));

        for pos in &mut [&mut range.start, &mut range.end] {
            **pos -= delete;
            **pos += insert;
        }

        self.text.replace_range(range, &patch);
    }
}

fn format_patch(line_indent: usize, patch: &str) -> String {
    let mut max_hashes = 0;
    let mut cur_hashes = 0;
    for byte in patch.bytes() {
        if byte != b'#' {
            cur_hashes = 0;
            continue;
        }
        cur_hashes += 1;
        max_hashes = max_hashes.max(cur_hashes);
    }
    let hashes = &"#".repeat(max_hashes + 1);
    let indent = &" ".repeat(line_indent);
    let is_multiline = patch.contains('\n');

    let mut buf = String::new();
    buf.push('r');
    buf.push_str(hashes);
    buf.push('"');
    if is_multiline {
        buf.push('\n');
    }
    let mut final_newline = false;
    for line in lines_with_ends(patch) {
        if is_multiline && !line.trim().is_empty() {
            buf.push_str(indent);
            buf.push_str("    ");
        }
        buf.push_str(line);
        final_newline = line.ends_with('\n');
    }
    if final_newline {
        buf.push_str(indent);
    }
    buf.push('"');
    buf.push_str(hashes);
    buf
}

static WORKSPACE_ROOT: Lazy<PathBuf> = Lazy::new(|| {
    let my_manifest = env::var("CARGO_MANIFEST_DIR").unwrap();
    // Heuristic, see https://github.com/rust-lang/cargo/issues/3946
    Path::new(&my_manifest)
        .ancestors()
        .filter(|it| it.join("Cargo.toml").exists())
        .last()
        .unwrap()
        .to_path_buf()
});

fn trim_indent(mut text: &str) -> String {
    if text.starts_with('\n') {
        text = &text[1..];
    }
    let indent = text
        .lines()
        .filter(|it| !it.trim().is_empty())
        .map(|it| it.len() - it.trim_start().len())
        .min()
        .unwrap_or(0);

    lines_with_ends(text)
        .map(
            |line| {
                if line.len() <= indent {
                    line.trim_start_matches(' ')
                } else {
                    &line[indent..]
                }
            },
        )
        .collect()
}

fn lines_with_ends(text: &str) -> LinesWithEnds {
    LinesWithEnds { text }
}

struct LinesWithEnds<'a> {
    text: &'a str,
}

impl<'a> Iterator for LinesWithEnds<'a> {
    type Item = &'a str;
    fn next(&mut self) -> Option<&'a str> {
        if self.text.is_empty() {
            return None;
        }
        let idx = self.text.find('\n').map_or(self.text.len(), |it| it + 1);
        let (res, next) = self.text.split_at(idx);
        self.text = next;
        Some(res)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_format_patch() {
        let patch = format_patch(0, "hello\nworld\n");
        expect![[r##"
            r#"
                hello
                world
            "#"##]]
        .assert_eq(&patch);

        let patch = format_patch(4, "single line");
        expect![[r##"r#"single line"#"##]].assert_eq(&patch);
    }

    #[test]
    fn test_patchwork() {
        let mut patchwork = Patchwork::new("one two three".to_string());
        patchwork.patch(4..7, "zwei");
        patchwork.patch(0..3, "один");
        patchwork.patch(8..13, "3");
        expect![[r#"
            Patchwork {
                text: "один zwei 3",
                indels: [
                    (
                        0..3,
                        8,
                    ),
                    (
                        4..7,
                        4,
                    ),
                    (
                        8..13,
                        1,
                    ),
                ],
            }
        "#]]
        .assert_debug_eq(&patchwork);
    }
}