ejectest 0.3.0

mod scan_state;

use scan_state::{BraceAction, ScanState};

use crate::EjectError;

/// Byte range of the `#[cfg(test)] mod tests { ... }` block in source text.
#[derive(Debug)]
pub(crate) struct TestModuleRegion {
    /// Byte offset where `#[cfg(test)]` starts.
    pub(crate) outer_start: usize,
    /// Byte offset just past the closing `}` (and optional trailing newline).
    pub(crate) outer_end: usize,
    /// Byte offset of the first byte after the opening `{`.
    pub(crate) inner_start: usize,
    /// Byte offset of the closing `}`.
    pub(crate) inner_end: usize,
    /// Byte offset just past `#[cfg(test)]`, where extra outer attributes begin.
    pub(crate) attrs_start: usize,
    /// Byte offset where the `mod` keyword starts (end of extra outer attributes).
    pub(crate) attrs_end: usize,
}

/// Locate the `#[cfg(test)] mod tests { ... }` block in source text.
///
/// Skips matches that appear inside comments or string literals.
///
/// # Errors
///
/// Returns [`EjectError::NoTestModule`] if no inline test module is found.
/// Returns [`EjectError::AlreadyExternal`] if the test module uses a path attribute.
/// Returns [`EjectError::RegionNotFound`] if boundaries cannot be determined.
pub(crate) fn find_test_module_region(source: &str) -> Result<TestModuleRegion, EjectError> {
    let cfg_test = "#[cfg(test)]";
    let code_positions = find_cfg_test_in_code(source, cfg_test);

    log::debug!(
        "found {} #[cfg(test)] candidate(s) in code",
        code_positions.len()
    );
    for cfg_pos in code_positions {
        let after_cfg = cfg_pos + cfg_test.len();
        let rest = source.get(after_cfg..).ok_or(EjectError::RegionNotFound)?;

        if let Some(mod_offset) = find_mod_tests_after_attrs(rest) {
            let mod_pos = after_cfg + mod_offset;
            let after_kw = mod_pos + "mod tests".len();
            let after_mod = source.get(after_kw..).ok_or(EjectError::RegionNotFound)?;
            let trimmed = after_mod.trim_start();

            if trimmed.starts_with('{') {
                let ws_len = after_mod.len() - trimmed.len();
                let open_brace = after_kw + ws_len;
                let close_brace = find_matching_close_brace(source, open_brace)?;

                let mut outer_end = close_brace + 1;
                if source.get(outer_end..outer_end + 1) == Some("\n") {
                    outer_end += 1;
                }

                return Ok(TestModuleRegion {
                    outer_start: cfg_pos,
                    outer_end,
                    inner_start: open_brace + 1,
                    inner_end: close_brace,
                    attrs_start: after_cfg,
                    attrs_end: mod_pos,
                });
            } else if trimmed.starts_with(';') {
                return Err(EjectError::AlreadyExternal);
            }
        }
    }

    Err(EjectError::NoTestModule)
}

/// Find all byte offsets of `needle` that appear in actual code (not in
/// comments or string literals).
fn find_cfg_test_in_code(source: &str, needle: &str) -> Vec<usize> {
    let mut results = Vec::new();
    let mut state = ScanState::Normal;
    let bytes = source.as_bytes();

    for (idx, ch) in source.char_indices() {
        let is_normal = matches!(state, ScanState::Normal);

        if is_normal && starts_with_at(bytes, needle.as_bytes(), idx) {
            results.push(idx);
        }

        let action = state.advance(ch);
        state = action.next;
    }

    results
}

/// Check if `haystack` starting at `offset` begins with `needle`.
fn starts_with_at(haystack: &[u8], needle: &[u8], offset: usize) -> bool {
    let Some(slice) = haystack.get(offset..offset + needle.len()) else {
        return false;
    };
    slice == needle
}

/// After `#[cfg(test)]`, skip whitespace and extra attributes, then check for `mod tests`.
/// Returns the byte offset (relative to input) of `mod tests` if found.
fn find_mod_tests_after_attrs(source: &str) -> Option<usize> {
    let mut pos: usize = 0;

    loop {
        let rest = source.get(pos..)?;
        let trimmed = rest.trim_start();
        let ws_skipped = rest.len() - trimmed.len();
        pos += ws_skipped;

        if trimmed.starts_with("mod tests") {
            let after = trimmed.get("mod tests".len()..)?;
            let next_ch = after.chars().next();
            match next_ch {
                Some('{' | ';' | ' ' | '\t' | '\n' | '\r') | None => return Some(pos),
                _ => return None,
            }
        } else if trimmed.starts_with("#[") {
            let attr_body = trimmed.get(2..)?;
            let close = find_attr_close(attr_body)?;
            pos += 2 + close + 1;
        } else {
            return None;
        }
    }
}

/// Find the closing `]` of an attribute body, respecting string literals.
///
/// `source` starts just after the `[` in `#[...]`. Returns the byte offset
/// of the matching `]`.
pub(crate) fn find_attr_close(source: &str) -> Option<usize> {
    let mut in_string = false;
    let mut escaped = false;

    for (idx, ch) in source.char_indices() {
        if escaped {
            escaped = false;
            continue;
        }
        if in_string {
            match ch {
                '\\' => escaped = true,
                '"' => in_string = false,
                _ => {}
            }
        } else {
            match ch {
                '"' => in_string = true,
                ']' => return Some(idx),
                _ => {}
            }
        }
    }
    None
}

/// Find the byte offset of the `}` that matches the `{` at `open_pos`.
fn find_matching_close_brace(source: &str, open_pos: usize) -> Result<usize, EjectError> {
    let rest = source
        .get(open_pos + 1..)
        .ok_or(EjectError::RegionNotFound)?;
    let base = open_pos + 1;

    let mut depth: u32 = 1;
    let mut state = ScanState::Normal;

    for (offset, ch) in rest.char_indices() {
        let action = state.advance(ch);
        state = action.next;
        match action.brace {
            BraceAction::Open => depth += 1,
            BraceAction::Close => {
                depth -= 1;
                if depth == 0 {
                    return Ok(base + offset);
                }
            }
            BraceAction::None => {}
        }
    }

    Err(EjectError::RegionNotFound)
}

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

    #[test]
    fn basic_region() {
        let src = "fn main() {}\n\n#[cfg(test)]\nmod tests {\n    use super::*;\n}\n";
        let rg = find_test_module_region(src).expect("should find region");
        let outer = src.get(rg.outer_start..rg.outer_end).expect("valid range");
        assert!(outer.starts_with("#[cfg(test)]"));
        assert!(outer.contains("mod tests"));
    }

    #[test]
    fn already_external() {
        let src = "#[cfg(test)]\n#[path = \"t.rs\"]\nmod tests;\n";
        let err = find_test_module_region(src).expect_err("should fail");
        assert!(matches!(err, EjectError::AlreadyExternal));
    }

    #[test]
    fn no_test_module() {
        let src = "fn main() {}\n";
        let err = find_test_module_region(src).expect_err("should fail");
        assert!(matches!(err, EjectError::NoTestModule));
    }

    #[test]
    fn braces_in_string() {
        let src = concat!(
            "#[cfg(test)]\nmod tests {\n",
            "    fn t() { let ss = \"}\"; }\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should handle string braces");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("let ss"));
    }

    #[test]
    fn braces_in_comments() {
        let src = concat!(
            "#[cfg(test)]\nmod tests {\n",
            "    // }\n",
            "    /* } */\n",
            "    fn t() {}\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should handle comment braces");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("fn t()"));
    }

    #[test]
    fn same_line_cfg() {
        let src = "fn main() {}\n#[cfg(test)] mod tests {\n    fn t() {}\n}\n";
        let rg = find_test_module_region(src).expect("should find same-line cfg");
        assert!(
            src.get(rg.outer_start..rg.outer_end)
                .expect("valid")
                .starts_with("#[cfg(test)]")
        );
    }

    #[test]
    fn cfg_test_in_doc_comment_skipped() {
        let src = concat!(
            "/// No inline `#[cfg(test)] mod tests` here.\n",
            "pub fn foo() {}\n",
            "\n",
            "#[cfg(test)]\n",
            "mod tests {\n",
            "    fn real_test() {}\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should skip doc comment");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("real_test"));
    }

    #[test]
    fn char_literal_with_quote() {
        let src = concat!(
            "fn foo() { let _c = '\"'; }\n",
            "\n",
            "#[cfg(test)]\n",
            "mod tests {\n",
            "    fn real_test() {}\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should handle char literal with quote");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("real_test"));
    }

    #[test]
    fn cfg_test_in_string_literal_skipped() {
        let src = concat!(
            "fn foo() { let _s = \"#[cfg(test)] mod tests { }\"; }\n",
            "\n",
            "#[cfg(test)]\n",
            "mod tests {\n",
            "    fn real_test() {}\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should skip string literal");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("real_test"));
    }

    #[test]
    fn braces_in_raw_string() {
        let src = concat!(
            "#[cfg(test)]\nmod tests {\n",
            "    fn t() { let ss = r#\"}\"#; }\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should handle raw string braces");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("let ss"));
    }

    #[test]
    fn nested_block_comment_braces() {
        let src = concat!(
            "#[cfg(test)]\nmod tests {\n",
            "    /* /* } */ } */\n",
            "    fn t() {}\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should handle nested block comment");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("fn t()"));
    }

    #[test]
    fn attr_with_bracket_in_string() {
        let src = concat!(
            "#[cfg(test)]\n",
            "#[doc = \"contains ] bracket\"]\n",
            "mod tests {\n",
            "    fn t() {}\n",
            "}\n"
        );
        let rg = find_test_module_region(src).expect("should handle ] in attr string");
        let inner = src.get(rg.inner_start..rg.inner_end).expect("valid range");
        assert!(inner.contains("fn t()"));
    }
}