rumdl_lib/rules/

md057_existing_relative_links.rs

//!
//! Rule MD057: Existing relative links
//!
//! See [docs/md057.md](../../docs/md057.md) for full documentation, configuration, and examples.

use crate::rule::{CrossFileScope, LintError, LintResult, LintWarning, Rule, RuleCategory, Severity};
use crate::utils::element_cache::ElementCache;
use crate::workspace_index::{FileIndex, extract_cross_file_links};
use regex::Regex;
use std::collections::HashMap;
use std::env;
use std::path::{Path, PathBuf};
use std::sync::LazyLock;
use std::sync::{Arc, Mutex};

mod md057_config;
use md057_config::MD057Config;

// Thread-safe cache for file existence checks to avoid redundant filesystem operations
static FILE_EXISTENCE_CACHE: LazyLock<Arc<Mutex<HashMap<PathBuf, bool>>>> =
    LazyLock::new(|| Arc::new(Mutex::new(HashMap::new())));

// Reset the file existence cache (typically between rule runs)
fn reset_file_existence_cache() {
    if let Ok(mut cache) = FILE_EXISTENCE_CACHE.lock() {
        cache.clear();
    }
}

// Check if a file exists with caching
fn file_exists_with_cache(path: &Path) -> bool {
    match FILE_EXISTENCE_CACHE.lock() {
        Ok(mut cache) => *cache.entry(path.to_path_buf()).or_insert_with(|| path.exists()),
        Err(_) => path.exists(), // Fallback to uncached check on mutex poison
    }
}

/// Check if a file exists, also trying markdown extensions for extensionless links.
/// This supports wiki-style links like `[Link](page)` that resolve to `page.md`.
fn file_exists_or_markdown_extension(path: &Path) -> bool {
    // First, check exact path
    if file_exists_with_cache(path) {
        return true;
    }

    // If the path has no extension, try adding markdown extensions
    if path.extension().is_none() {
        for ext in MARKDOWN_EXTENSIONS {
            // MARKDOWN_EXTENSIONS includes the dot, e.g., ".md"
            let path_with_ext = path.with_extension(&ext[1..]);
            if file_exists_with_cache(&path_with_ext) {
                return true;
            }
        }
    }

    false
}

// Regex to match the start of a link - simplified for performance
static LINK_START_REGEX: LazyLock<Regex> = LazyLock::new(|| Regex::new(r"!?\[[^\]]*\]").unwrap());

/// Regex to extract the URL from an angle-bracketed markdown link
/// Format: `](<URL>)` or `](<URL> "title")`
/// This handles URLs with parentheses like `](<path/(with)/parens.md>)`
static URL_EXTRACT_ANGLE_BRACKET_REGEX: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r#"\]\(\s*<([^>]+)>(#[^\)\s]*)?\s*(?:"[^"]*")?\s*\)"#).unwrap());

/// Regex to extract the URL from a normal markdown link (without angle brackets)
/// Format: `](URL)` or `](URL "title")`
static URL_EXTRACT_REGEX: LazyLock<Regex> =
    LazyLock::new(|| Regex::new("\\]\\(\\s*([^>\\)\\s#]+)(#[^)\\s]*)?\\s*(?:\"[^\"]*\")?\\s*\\)").unwrap());

/// Regex to detect URLs with explicit schemes (should not be checked as relative links)
/// Matches: scheme:// or scheme: (per RFC 3986)
/// This covers http, https, ftp, file, smb, mailto, tel, data, macappstores, etc.
static PROTOCOL_DOMAIN_REGEX: LazyLock<Regex> =
    LazyLock::new(|| Regex::new(r"^([a-zA-Z][a-zA-Z0-9+.-]*://|[a-zA-Z][a-zA-Z0-9+.-]*:|www\.)").unwrap());

// Current working directory
static CURRENT_DIR: LazyLock<PathBuf> = LazyLock::new(|| env::current_dir().unwrap_or_else(|_| PathBuf::from(".")));

/// Convert a hex digit (0-9, a-f, A-F) to its numeric value.
/// Returns None for non-hex characters.
#[inline]
fn hex_digit_to_value(byte: u8) -> Option<u8> {
    match byte {
        b'0'..=b'9' => Some(byte - b'0'),
        b'a'..=b'f' => Some(byte - b'a' + 10),
        b'A'..=b'F' => Some(byte - b'A' + 10),
        _ => None,
    }
}

/// Supported markdown file extensions
const MARKDOWN_EXTENSIONS: &[&str] = &[
    ".md",
    ".markdown",
    ".mdx",
    ".mkd",
    ".mkdn",
    ".mdown",
    ".mdwn",
    ".qmd",
    ".rmd",
];

/// Rule MD057: Existing relative links should point to valid files or directories.
#[derive(Debug, Clone, Default)]
pub struct MD057ExistingRelativeLinks {
    /// Base directory for resolving relative links
    base_path: Arc<Mutex<Option<PathBuf>>>,
}

impl MD057ExistingRelativeLinks {
    /// Create a new instance with default settings
    pub fn new() -> Self {
        Self::default()
    }

    /// Set the base path for resolving relative links
    pub fn with_path<P: AsRef<Path>>(self, path: P) -> Self {
        let path = path.as_ref();
        let dir_path = if path.is_file() {
            path.parent().map(|p| p.to_path_buf())
        } else {
            Some(path.to_path_buf())
        };

        if let Ok(mut guard) = self.base_path.lock() {
            *guard = dir_path;
        }
        self
    }

    #[allow(unused_variables)]
    pub fn from_config_struct(config: MD057Config) -> Self {
        Self::default()
    }

    /// Check if a URL is external or should be skipped for validation.
    ///
    /// Returns `true` (skip validation) for:
    /// - URLs with protocols: `https://`, `http://`, `ftp://`, `mailto:`, etc.
    /// - Bare domains: `www.example.com`, `example.com`
    /// - Email addresses: `user@example.com` (without `mailto:`)
    /// - Template variables: `{{URL}}`, `{{% include %}}`
    /// - Absolute web URL paths: `/api/docs`, `/blog/post.html`
    ///
    /// Returns `false` (validate) for:
    /// - Relative filesystem paths: `./file.md`, `../parent/file.md`, `file.md`
    #[inline]
    fn is_external_url(&self, url: &str) -> bool {
        if url.is_empty() {
            return false;
        }

        // Quick checks for common external URL patterns
        if PROTOCOL_DOMAIN_REGEX.is_match(url) || url.starts_with("www.") {
            return true;
        }

        // Skip template variables (Handlebars/Mustache/Jinja2 syntax)
        // Examples: {{URL}}, {{#URL}}, {{> partial}}, {{% include %}}, {{ variable }}
        if url.starts_with("{{") || url.starts_with("{%") {
            return true;
        }

        // Simple check: if URL contains @, it's almost certainly an email address
        // File paths with @ are extremely rare, so this is a safe heuristic
        if url.contains('@') {
            return true; // It's an email address, skip it
        }

        // Bare domain check (e.g., "example.com")
        // Note: We intentionally DON'T skip all TLDs like .org, .net, etc.
        // Links like [text](nodejs.org/path) without a protocol are broken -
        // they'll be treated as relative paths by markdown renderers.
        // Flagging them helps users find missing protocols.
        // We only skip .com as a minimal safety net for the most common case.
        if url.ends_with(".com") {
            return true;
        }

        // Absolute URL paths (e.g., /api/docs, /blog/post.html) are treated as web paths
        // and skipped. These are typically routes for published documentation sites,
        // not filesystem paths that can be validated locally.
        if url.starts_with('/') {
            return true;
        }

        // Framework path aliases (resolved by build tools like Vite, webpack, etc.)
        // These are not filesystem paths but module/asset aliases
        // Examples: ~/assets/image.png, @images/photo.jpg, @/components/Button.vue
        if url.starts_with('~') || url.starts_with('@') {
            return true;
        }

        // All other cases (relative paths, etc.) are not external
        false
    }

    /// Check if the URL is a fragment-only link (internal document link)
    #[inline]
    fn is_fragment_only_link(&self, url: &str) -> bool {
        url.starts_with('#')
    }

    /// Decode URL percent-encoded sequences in a path.
    /// Converts `%20` to space, `%2F` to `/`, etc.
    /// Returns the original string if decoding fails or produces invalid UTF-8.
    fn url_decode(path: &str) -> String {
        // Quick check: if no percent sign, return as-is
        if !path.contains('%') {
            return path.to_string();
        }

        let bytes = path.as_bytes();
        let mut result = Vec::with_capacity(bytes.len());
        let mut i = 0;

        while i < bytes.len() {
            if bytes[i] == b'%' && i + 2 < bytes.len() {
                // Try to parse the two hex digits following %
                let hex1 = bytes[i + 1];
                let hex2 = bytes[i + 2];
                if let (Some(d1), Some(d2)) = (hex_digit_to_value(hex1), hex_digit_to_value(hex2)) {
                    result.push(d1 * 16 + d2);
                    i += 3;
                    continue;
                }
            }
            result.push(bytes[i]);
            i += 1;
        }

        // Convert to UTF-8, falling back to original if invalid
        String::from_utf8(result).unwrap_or_else(|_| path.to_string())
    }

    /// Strip query parameters and fragments from a URL for file existence checking.
    /// URLs like `path/to/image.png?raw=true` or `file.md#section` should check
    /// for `path/to/image.png` or `file.md` respectively.
    ///
    /// Note: In standard URLs, query parameters (`?`) come before fragments (`#`),
    /// so we check for `?` first. If a URL has both, only the query is stripped here
    /// (fragments are handled separately by the regex in `contribute_to_index`).
    fn strip_query_and_fragment(url: &str) -> &str {
        // Find the first occurrence of '?' or '#', whichever comes first
        // This handles both standard URLs (? before #) and edge cases (# before ?)
        let query_pos = url.find('?');
        let fragment_pos = url.find('#');

        match (query_pos, fragment_pos) {
            (Some(q), Some(f)) => {
                // Both exist - strip at whichever comes first
                &url[..q.min(f)]
            }
            (Some(q), None) => &url[..q],
            (None, Some(f)) => &url[..f],
            (None, None) => url,
        }
    }

    /// Resolve a relative link against a provided base path
    fn resolve_link_path_with_base(link: &str, base_path: &Path) -> PathBuf {
        base_path.join(link)
    }
}

impl Rule for MD057ExistingRelativeLinks {
    fn name(&self) -> &'static str {
        "MD057"
    }

    fn description(&self) -> &'static str {
        "Relative links should point to existing files"
    }

    fn category(&self) -> RuleCategory {
        RuleCategory::Link
    }

    fn should_skip(&self, ctx: &crate::lint_context::LintContext) -> bool {
        ctx.content.is_empty() || !ctx.likely_has_links_or_images()
    }

    fn check(&self, ctx: &crate::lint_context::LintContext) -> LintResult {
        let content = ctx.content;

        // Early returns for performance
        if content.is_empty() || !content.contains('[') {
            return Ok(Vec::new());
        }

        // Quick check for any potential links before expensive operations
        if !content.contains("](") {
            return Ok(Vec::new());
        }

        // Reset the file existence cache for a fresh run
        reset_file_existence_cache();

        let mut warnings = Vec::new();

        // Determine base path for resolving relative links
        // ALWAYS compute from ctx.source_file for each file - do not reuse cached base_path
        // This ensures each file resolves links relative to its own directory
        let base_path: Option<PathBuf> = {
            // First check if base_path was explicitly set via with_path() (for tests)
            let explicit_base = self.base_path.lock().ok().and_then(|g| g.clone());
            if explicit_base.is_some() {
                explicit_base
            } else if let Some(ref source_file) = ctx.source_file {
                // Resolve symlinks to get the actual file location
                // This ensures relative links are resolved from the target's directory,
                // not the symlink's directory
                let resolved_file = source_file.canonicalize().unwrap_or_else(|_| source_file.clone());
                resolved_file
                    .parent()
                    .map(|p| p.to_path_buf())
                    .or_else(|| Some(CURRENT_DIR.clone()))
            } else {
                // No source file available - cannot validate relative links
                None
            }
        };

        // If we still don't have a base path, we can't validate relative links
        let Some(base_path) = base_path else {
            return Ok(warnings);
        };

        // Use LintContext links instead of expensive regex parsing
        if !ctx.links.is_empty() {
            // Use LineIndex for correct position calculation across all line ending types
            let line_index = &ctx.line_index;

            // Create element cache once for all links
            let element_cache = ElementCache::new(content);

            // Pre-collect lines to avoid repeated line iteration
            let lines: Vec<&str> = content.lines().collect();

            for link in &ctx.links {
                let line_idx = link.line - 1;
                if line_idx >= lines.len() {
                    continue;
                }

                let line = lines[line_idx];

                // Quick check for link pattern in this line
                if !line.contains("](") {
                    continue;
                }

                // Find all links in this line using optimized regex
                for link_match in LINK_START_REGEX.find_iter(line) {
                    let start_pos = link_match.start();
                    let end_pos = link_match.end();

                    // Calculate absolute position using LineIndex
                    let line_start_byte = line_index.get_line_start_byte(line_idx + 1).unwrap_or(0);
                    let absolute_start_pos = line_start_byte + start_pos;

                    // Skip if this link is in a code span
                    if element_cache.is_in_code_span(absolute_start_pos) {
                        continue;
                    }

                    // Find the URL part after the link text
                    // Try angle-bracket regex first (handles URLs with parens like `<path/(with)/parens.md>`)
                    // Then fall back to normal URL regex
                    let caps_and_url = URL_EXTRACT_ANGLE_BRACKET_REGEX
                        .captures_at(line, end_pos - 1)
                        .and_then(|caps| caps.get(1).map(|g| (caps, g)))
                        .or_else(|| {
                            URL_EXTRACT_REGEX
                                .captures_at(line, end_pos - 1)
                                .and_then(|caps| caps.get(1).map(|g| (caps, g)))
                        });

                    if let Some((_caps, url_group)) = caps_and_url {
                        let url = url_group.as_str().trim();

                        // Skip empty URLs
                        if url.is_empty() {
                            continue;
                        }

                        // Skip external URLs, absolute paths, and fragment-only links
                        if self.is_external_url(url) || self.is_fragment_only_link(url) {
                            continue;
                        }

                        // Strip query parameters and fragments before checking file existence
                        let file_path = Self::strip_query_and_fragment(url);

                        // URL-decode the path to handle percent-encoded characters
                        let decoded_path = Self::url_decode(file_path);

                        // Resolve the relative link against the base path
                        let resolved_path = Self::resolve_link_path_with_base(&decoded_path, &base_path);

                        // Check if the file exists, also trying markdown extensions for extensionless links
                        if file_exists_or_markdown_extension(&resolved_path) {
                            continue; // File exists, no warning needed
                        }

                        // For .html/.htm links, check if a corresponding markdown source exists
                        let has_md_source = if let Some(ext) = resolved_path.extension().and_then(|e| e.to_str())
                            && (ext.eq_ignore_ascii_case("html") || ext.eq_ignore_ascii_case("htm"))
                            && let (Some(stem), Some(parent)) = (
                                resolved_path.file_stem().and_then(|s| s.to_str()),
                                resolved_path.parent(),
                            ) {
                            MARKDOWN_EXTENSIONS.iter().any(|md_ext| {
                                let source_path = parent.join(format!("{stem}{md_ext}"));
                                file_exists_with_cache(&source_path)
                            })
                        } else {
                            false
                        };

                        if has_md_source {
                            continue; // Markdown source exists, link is valid
                        }

                        // File doesn't exist and no source file found
                        // Use actual URL position from regex capture group
                        // Note: capture group positions are absolute within the line string
                        let url_start = url_group.start();
                        let url_end = url_group.end();

                        warnings.push(LintWarning {
                            rule_name: Some(self.name().to_string()),
                            line: link.line,
                            column: url_start + 1, // 1-indexed
                            end_line: link.line,
                            end_column: url_end + 1, // 1-indexed
                            message: format!("Relative link '{url}' does not exist"),
                            severity: Severity::Error,
                            fix: None,
                        });
                    }
                }
            }
        }

        // Also process images - they have URLs already parsed
        for image in &ctx.images {
            let url = image.url.as_ref();

            // Skip empty URLs
            if url.is_empty() {
                continue;
            }

            // Skip external URLs, absolute paths, and fragment-only links
            if self.is_external_url(url) || self.is_fragment_only_link(url) {
                continue;
            }

            // Strip query parameters and fragments before checking file existence
            let file_path = Self::strip_query_and_fragment(url);

            // URL-decode the path to handle percent-encoded characters
            let decoded_path = Self::url_decode(file_path);

            // Resolve the relative link against the base path
            let resolved_path = Self::resolve_link_path_with_base(&decoded_path, &base_path);

            // Check if the file exists, also trying markdown extensions for extensionless links
            if file_exists_or_markdown_extension(&resolved_path) {
                continue; // File exists, no warning needed
            }

            // For .html/.htm links, check if a corresponding markdown source exists
            let has_md_source = if let Some(ext) = resolved_path.extension().and_then(|e| e.to_str())
                && (ext.eq_ignore_ascii_case("html") || ext.eq_ignore_ascii_case("htm"))
                && let (Some(stem), Some(parent)) = (
                    resolved_path.file_stem().and_then(|s| s.to_str()),
                    resolved_path.parent(),
                ) {
                MARKDOWN_EXTENSIONS.iter().any(|md_ext| {
                    let source_path = parent.join(format!("{stem}{md_ext}"));
                    file_exists_with_cache(&source_path)
                })
            } else {
                false
            };

            if has_md_source {
                continue; // Markdown source exists, link is valid
            }

            // File doesn't exist and no source file found
            // Images already have correct position from parser
            warnings.push(LintWarning {
                rule_name: Some(self.name().to_string()),
                line: image.line,
                column: image.start_col + 1,
                end_line: image.line,
                end_column: image.start_col + 1 + url.len(),
                message: format!("Relative link '{url}' does not exist"),
                severity: Severity::Error,
                fix: None,
            });
        }

        Ok(warnings)
    }

    fn fix(&self, ctx: &crate::lint_context::LintContext) -> Result<String, LintError> {
        Ok(ctx.content.to_string())
    }

    fn as_any(&self) -> &dyn std::any::Any {
        self
    }

    fn default_config_section(&self) -> Option<(String, toml::Value)> {
        // No configurable options for this rule
        None
    }

    fn from_config(config: &crate::config::Config) -> Box<dyn Rule>
    where
        Self: Sized,
    {
        let rule_config = crate::rule_config_serde::load_rule_config::<MD057Config>(config);
        Box::new(Self::from_config_struct(rule_config))
    }

    fn cross_file_scope(&self) -> CrossFileScope {
        CrossFileScope::Workspace
    }

    fn contribute_to_index(&self, ctx: &crate::lint_context::LintContext, index: &mut FileIndex) {
        // Use the shared utility for cross-file link extraction
        // This ensures consistent position tracking between CLI and LSP
        for link in extract_cross_file_links(ctx) {
            index.add_cross_file_link(link);
        }
    }

    fn cross_file_check(
        &self,
        file_path: &Path,
        file_index: &FileIndex,
        workspace_index: &crate::workspace_index::WorkspaceIndex,
    ) -> LintResult {
        let mut warnings = Vec::new();

        // Get the directory containing this file for resolving relative links
        let file_dir = file_path.parent();

        for cross_link in &file_index.cross_file_links {
            // URL-decode the path for filesystem operations
            // The stored path is URL-encoded (e.g., "%F0%9F%91%A4" for emoji 👤)
            let decoded_target = Self::url_decode(&cross_link.target_path);

            // Skip absolute/protocol-relative paths (web paths, not filesystem paths)
            if decoded_target.starts_with('/') {
                continue;
            }

            // Resolve relative path
            let target_path = if let Some(dir) = file_dir {
                dir.join(&decoded_target)
            } else {
                Path::new(&decoded_target).to_path_buf()
            };

            // Normalize the path (handle .., ., etc.)
            let target_path = normalize_path(&target_path);

            // Check if the target file exists
            let file_exists = workspace_index.contains_file(&target_path) || target_path.exists();

            if !file_exists {
                // For .html/.htm links, check if a corresponding markdown source exists
                // This handles doc sites (mdBook, etc.) where .md is compiled to .html
                let has_md_source = if let Some(ext) = target_path.extension().and_then(|e| e.to_str())
                    && (ext.eq_ignore_ascii_case("html") || ext.eq_ignore_ascii_case("htm"))
                    && let (Some(stem), Some(parent)) =
                        (target_path.file_stem().and_then(|s| s.to_str()), target_path.parent())
                {
                    MARKDOWN_EXTENSIONS.iter().any(|md_ext| {
                        let source_path = parent.join(format!("{stem}{md_ext}"));
                        workspace_index.contains_file(&source_path) || source_path.exists()
                    })
                } else {
                    false
                };

                if !has_md_source {
                    warnings.push(LintWarning {
                        rule_name: Some(self.name().to_string()),
                        line: cross_link.line,
                        column: cross_link.column,
                        end_line: cross_link.line,
                        end_column: cross_link.column + cross_link.target_path.len(),
                        message: format!("Relative link '{}' does not exist", cross_link.target_path),
                        severity: Severity::Error,
                        fix: None,
                    });
                }
            }
        }

        Ok(warnings)
    }
}

/// Normalize a path by resolving . and .. components
fn normalize_path(path: &Path) -> PathBuf {
    let mut components = Vec::new();

    for component in path.components() {
        match component {
            std::path::Component::ParentDir => {
                // Go up one level if possible
                if !components.is_empty() {
                    components.pop();
                }
            }
            std::path::Component::CurDir => {
                // Skip current directory markers
            }
            _ => {
                components.push(component);
            }
        }
    }

    components.iter().collect()
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::workspace_index::CrossFileLinkIndex;
    use std::fs::File;
    use std::io::Write;
    use tempfile::tempdir;

    #[test]
    fn test_strip_query_and_fragment() {
        // Test query parameter stripping
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.png?raw=true"),
            "file.png"
        );
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.png?raw=true&version=1"),
            "file.png"
        );
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.png?"),
            "file.png"
        );

        // Test fragment stripping
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.md#section"),
            "file.md"
        );
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.md#"),
            "file.md"
        );

        // Test both query and fragment (query comes first, per RFC 3986)
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.md?raw=true#section"),
            "file.md"
        );

        // Test no query or fragment
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.png"),
            "file.png"
        );

        // Test with path
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("path/to/image.png?raw=true"),
            "path/to/image.png"
        );
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("path/to/image.png?raw=true#anchor"),
            "path/to/image.png"
        );

        // Edge case: fragment before query (non-standard but possible)
        assert_eq!(
            MD057ExistingRelativeLinks::strip_query_and_fragment("file.md#section?query"),
            "file.md"
        );
    }

    #[test]
    fn test_url_decode() {
        // Simple space encoding
        assert_eq!(
            MD057ExistingRelativeLinks::url_decode("penguin%20with%20space.jpg"),
            "penguin with space.jpg"
        );

        // Path with encoded spaces
        assert_eq!(
            MD057ExistingRelativeLinks::url_decode("assets/my%20file%20name.png"),
            "assets/my file name.png"
        );

        // Multiple encoded characters
        assert_eq!(
            MD057ExistingRelativeLinks::url_decode("hello%20world%21.md"),
            "hello world!.md"
        );

        // Lowercase hex
        assert_eq!(MD057ExistingRelativeLinks::url_decode("%2f%2e%2e"), "/..");

        // Uppercase hex
        assert_eq!(MD057ExistingRelativeLinks::url_decode("%2F%2E%2E"), "/..");

        // Mixed case hex
        assert_eq!(MD057ExistingRelativeLinks::url_decode("%2f%2E%2e"), "/..");

        // No encoding - return as-is
        assert_eq!(
            MD057ExistingRelativeLinks::url_decode("normal-file.md"),
            "normal-file.md"
        );

        // Incomplete percent encoding - leave as-is
        assert_eq!(MD057ExistingRelativeLinks::url_decode("file%2.txt"), "file%2.txt");

        // Percent at end - leave as-is
        assert_eq!(MD057ExistingRelativeLinks::url_decode("file%"), "file%");

        // Invalid hex digits - leave as-is
        assert_eq!(MD057ExistingRelativeLinks::url_decode("file%GG.txt"), "file%GG.txt");

        // Plus sign (should NOT be decoded - that's form encoding, not URL encoding)
        assert_eq!(MD057ExistingRelativeLinks::url_decode("file+name.txt"), "file+name.txt");

        // Empty string
        assert_eq!(MD057ExistingRelativeLinks::url_decode(""), "");

        // UTF-8 multi-byte characters (é = C3 A9 in UTF-8)
        assert_eq!(MD057ExistingRelativeLinks::url_decode("caf%C3%A9.md"), "café.md");

        // Multiple consecutive encoded characters
        assert_eq!(MD057ExistingRelativeLinks::url_decode("%20%20%20"), "   ");

        // Encoded path separators
        assert_eq!(
            MD057ExistingRelativeLinks::url_decode("path%2Fto%2Ffile.md"),
            "path/to/file.md"
        );

        // Mixed encoded and non-encoded
        assert_eq!(
            MD057ExistingRelativeLinks::url_decode("hello%20world/foo%20bar.md"),
            "hello world/foo bar.md"
        );

        // Special characters that are commonly encoded
        assert_eq!(MD057ExistingRelativeLinks::url_decode("file%5B1%5D.md"), "file[1].md");

        // Percent at position that looks like encoding but isn't valid
        assert_eq!(MD057ExistingRelativeLinks::url_decode("100%pure.md"), "100%pure.md");
    }

    #[test]
    fn test_url_encoded_filenames() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create a file with spaces in the name
        let file_with_spaces = base_path.join("penguin with space.jpg");
        File::create(&file_with_spaces)
            .unwrap()
            .write_all(b"image data")
            .unwrap();

        // Create a subdirectory with spaces
        let subdir = base_path.join("my images");
        std::fs::create_dir(&subdir).unwrap();
        let nested_file = subdir.join("photo 1.png");
        File::create(&nested_file).unwrap().write_all(b"photo data").unwrap();

        // Test content with URL-encoded links
        let content = r#"
# Test Document with URL-Encoded Links

![Penguin](penguin%20with%20space.jpg)
![Photo](my%20images/photo%201.png)
![Missing](missing%20file.jpg)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only have one warning for the missing file
        assert_eq!(
            result.len(),
            1,
            "Should only warn about missing%20file.jpg. Got: {result:?}"
        );
        assert!(
            result[0].message.contains("missing%20file.jpg"),
            "Warning should mention the URL-encoded filename"
        );
    }

    #[test]
    fn test_external_urls() {
        let rule = MD057ExistingRelativeLinks::new();

        // Common web protocols
        assert!(rule.is_external_url("https://example.com"));
        assert!(rule.is_external_url("http://example.com"));
        assert!(rule.is_external_url("ftp://example.com"));
        assert!(rule.is_external_url("www.example.com"));
        assert!(rule.is_external_url("example.com"));

        // Special URI schemes
        assert!(rule.is_external_url("file:///path/to/file"));
        assert!(rule.is_external_url("smb://server/share"));
        assert!(rule.is_external_url("macappstores://apps.apple.com/"));
        assert!(rule.is_external_url("mailto:user@example.com"));
        assert!(rule.is_external_url("tel:+1234567890"));
        assert!(rule.is_external_url("data:text/plain;base64,SGVsbG8="));
        assert!(rule.is_external_url("javascript:void(0)"));
        assert!(rule.is_external_url("ssh://git@github.com/repo"));
        assert!(rule.is_external_url("git://github.com/repo.git"));

        // Email addresses without mailto: protocol
        // These are clearly not file links and should be skipped
        assert!(rule.is_external_url("user@example.com"));
        assert!(rule.is_external_url("steering@kubernetes.io"));
        assert!(rule.is_external_url("john.doe+filter@company.co.uk"));
        assert!(rule.is_external_url("user_name@sub.domain.com"));
        assert!(rule.is_external_url("firstname.lastname+tag@really.long.domain.example.org"));

        // Template variables should be skipped (not checked as relative links)
        assert!(rule.is_external_url("{{URL}}")); // Handlebars/Mustache
        assert!(rule.is_external_url("{{#URL}}")); // Handlebars block helper
        assert!(rule.is_external_url("{{> partial}}")); // Handlebars partial
        assert!(rule.is_external_url("{{ variable }}")); // Mustache with spaces
        assert!(rule.is_external_url("{{% include %}}")); // Jinja2/Hugo shortcode
        assert!(rule.is_external_url("{{")); // Even partial matches (regex edge case)

        // Absolute web URL paths should be skipped (not validated)
        // These are typically routes for published documentation sites
        assert!(rule.is_external_url("/api/v1/users"));
        assert!(rule.is_external_url("/blog/2024/release.html"));
        assert!(rule.is_external_url("/react/hooks/use-state.html"));
        assert!(rule.is_external_url("/pkg/runtime"));
        assert!(rule.is_external_url("/doc/go1compat"));
        assert!(rule.is_external_url("/index.html"));
        assert!(rule.is_external_url("/assets/logo.png"));

        // Framework path aliases should be skipped (resolved by build tools)
        // Tilde prefix (common in Vite, Nuxt, Astro for project root)
        assert!(rule.is_external_url("~/assets/image.png"));
        assert!(rule.is_external_url("~/components/Button.vue"));
        assert!(rule.is_external_url("~assets/logo.svg")); // Nuxt style without /

        // @ prefix (common in Vue, webpack, Vite aliases)
        assert!(rule.is_external_url("@/components/Header.vue"));
        assert!(rule.is_external_url("@images/photo.jpg"));
        assert!(rule.is_external_url("@assets/styles.css"));

        // Relative paths should NOT be external (should be validated)
        assert!(!rule.is_external_url("./relative/path.md"));
        assert!(!rule.is_external_url("relative/path.md"));
        assert!(!rule.is_external_url("../parent/path.md"));
    }

    #[test]
    fn test_framework_path_aliases() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Test content with framework path aliases (should all be skipped)
        let content = r#"
# Framework Path Aliases

![Image 1](~/assets/penguin.jpg)
![Image 2](~assets/logo.svg)
![Image 3](@images/photo.jpg)
![Image 4](@/components/icon.svg)
[Link](@/pages/about.md)

This is a [real missing link](missing.md) that should be flagged.
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only have one warning for the real missing link
        assert_eq!(
            result.len(),
            1,
            "Should only warn about missing.md, not framework aliases. Got: {result:?}"
        );
        assert!(
            result[0].message.contains("missing.md"),
            "Warning should be for missing.md"
        );
    }

    #[test]
    fn test_url_decode_security_path_traversal() {
        // Ensure URL decoding doesn't enable path traversal attacks
        // The decoded path is still validated against the base path
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create a file in the temp directory
        let file_in_base = base_path.join("safe.md");
        File::create(&file_in_base).unwrap().write_all(b"# Safe").unwrap();

        // Test with encoded path traversal attempt
        // Use a path that definitely won't exist on any platform (not /etc/passwd which exists on Linux)
        // %2F = /, so ..%2F..%2Fnonexistent%2Ffile = ../../nonexistent/file
        // %252F = %2F (double encoded), so ..%252F..%252F = ..%2F..%2F (literal, won't decode to ..)
        let content = r#"
[Traversal attempt](..%2F..%2Fnonexistent_dir_12345%2Fmissing.md)
[Double encoded](..%252F..%252Fnonexistent%252Ffile.md)
[Safe link](safe.md)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // The traversal attempts should still be flagged as missing
        // (they don't exist relative to base_path after decoding)
        assert_eq!(
            result.len(),
            2,
            "Should have warnings for traversal attempts. Got: {result:?}"
        );
    }

    #[test]
    fn test_url_encoded_utf8_filenames() {
        // Test with actual UTF-8 encoded filenames
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create files with unicode names
        let cafe_file = base_path.join("café.md");
        File::create(&cafe_file).unwrap().write_all(b"# Cafe").unwrap();

        let content = r#"
[Café link](caf%C3%A9.md)
[Missing unicode](r%C3%A9sum%C3%A9.md)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only warn about the missing file
        assert_eq!(
            result.len(),
            1,
            "Should only warn about missing résumé.md. Got: {result:?}"
        );
        assert!(
            result[0].message.contains("r%C3%A9sum%C3%A9.md"),
            "Warning should mention the URL-encoded filename"
        );
    }

    #[test]
    fn test_url_encoded_emoji_filenames() {
        // URL-encoded emoji paths should be correctly resolved
        // 👤 = U+1F464 = F0 9F 91 A4 in UTF-8
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create directory with emoji in name: 👤 Personal
        let emoji_dir = base_path.join("👤 Personal");
        std::fs::create_dir(&emoji_dir).unwrap();

        // Create file in that directory: TV Shows.md
        let file_path = emoji_dir.join("TV Shows.md");
        File::create(&file_path)
            .unwrap()
            .write_all(b"# TV Shows\n\nContent here.")
            .unwrap();

        // Test content with URL-encoded emoji link
        // %F0%9F%91%A4 = 👤, %20 = space
        let content = r#"
# Test Document

[TV Shows](./%F0%9F%91%A4%20Personal/TV%20Shows.md)
[Missing](./%F0%9F%91%A4%20Personal/Missing.md)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only warn about the missing file, not the valid emoji path
        assert_eq!(result.len(), 1, "Should only warn about missing file. Got: {result:?}");
        assert!(
            result[0].message.contains("Missing.md"),
            "Warning should be for Missing.md, got: {}",
            result[0].message
        );
    }

    #[test]
    fn test_no_warnings_without_base_path() {
        let rule = MD057ExistingRelativeLinks::new();
        let content = "[Link](missing.md)";

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();
        assert!(result.is_empty(), "Should have no warnings without base path");
    }

    #[test]
    fn test_existing_and_missing_links() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create an existing file
        let exists_path = base_path.join("exists.md");
        File::create(&exists_path).unwrap().write_all(b"# Test File").unwrap();

        // Verify the file exists
        assert!(exists_path.exists(), "exists.md should exist for this test");

        // Create test content with both existing and missing links
        let content = r#"
# Test Document

[Valid Link](exists.md)
[Invalid Link](missing.md)
[External Link](https://example.com)
[Media Link](image.jpg)
        "#;

        // Initialize rule with the base path (default: check all files including media)
        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        // Test the rule
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should have two warnings: missing.md and image.jpg (both don't exist)
        assert_eq!(result.len(), 2);
        let messages: Vec<_> = result.iter().map(|w| w.message.as_str()).collect();
        assert!(messages.iter().any(|m| m.contains("missing.md")));
        assert!(messages.iter().any(|m| m.contains("image.jpg")));
    }

    #[test]
    fn test_angle_bracket_links() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create an existing file
        let exists_path = base_path.join("exists.md");
        File::create(&exists_path).unwrap().write_all(b"# Test File").unwrap();

        // Create test content with angle bracket links
        let content = r#"
# Test Document

[Valid Link](<exists.md>)
[Invalid Link](<missing.md>)
[External Link](<https://example.com>)
    "#;

        // Test with default settings
        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should have one warning for missing.md
        assert_eq!(result.len(), 1, "Should have exactly one warning");
        assert!(
            result[0].message.contains("missing.md"),
            "Warning should mention missing.md"
        );
    }

    #[test]
    fn test_angle_bracket_links_with_parens() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create directory structure with parentheses in path
        let app_dir = base_path.join("app");
        std::fs::create_dir(&app_dir).unwrap();
        let upload_dir = app_dir.join("(upload)");
        std::fs::create_dir(&upload_dir).unwrap();
        let page_file = upload_dir.join("page.tsx");
        File::create(&page_file)
            .unwrap()
            .write_all(b"export default function Page() {}")
            .unwrap();

        // Create test content with angle bracket links containing parentheses
        let content = r#"
# Test Document with Paths Containing Parens

[Upload Page](<app/(upload)/page.tsx>)
[Unix pipe](<https://en.wikipedia.org/wiki/Pipeline_(Unix)>)
[Missing](<app/(missing)/file.md>)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only have one warning for the missing file
        assert_eq!(
            result.len(),
            1,
            "Should have exactly one warning for missing file. Got: {result:?}"
        );
        assert!(
            result[0].message.contains("app/(missing)/file.md"),
            "Warning should mention app/(missing)/file.md"
        );
    }

    #[test]
    fn test_all_file_types_checked() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create a test with various file types - all should be checked
        let content = r#"
[Image Link](image.jpg)
[Video Link](video.mp4)
[Markdown Link](document.md)
[PDF Link](file.pdf)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should warn about all missing files regardless of extension
        assert_eq!(result.len(), 4, "Should have warnings for all missing files");
    }

    #[test]
    fn test_code_span_detection() {
        let rule = MD057ExistingRelativeLinks::new();

        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let rule = rule.with_path(base_path);

        // Test with document structure
        let content = "This is a [link](nonexistent.md) and `[not a link](not-checked.md)` in code.";

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only find the real link, not the one in code
        assert_eq!(result.len(), 1, "Should only flag the real link");
        assert!(result[0].message.contains("nonexistent.md"));
    }

    #[test]
    fn test_inline_code_spans() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create test content with links in inline code spans
        let content = r#"
# Test Document

This is a normal link: [Link](missing.md)

This is a code span with a link: `[Link](another-missing.md)`

Some more text with `inline code [Link](yet-another-missing.md) embedded`.

    "#;

        // Initialize rule with the base path
        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        // Test the rule
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only have warning for the normal link, not for links in code spans
        assert_eq!(result.len(), 1, "Should have exactly one warning");
        assert!(
            result[0].message.contains("missing.md"),
            "Warning should be for missing.md"
        );
        assert!(
            !result.iter().any(|w| w.message.contains("another-missing.md")),
            "Should not warn about link in code span"
        );
        assert!(
            !result.iter().any(|w| w.message.contains("yet-another-missing.md")),
            "Should not warn about link in inline code"
        );
    }

    #[test]
    fn test_extensionless_link_resolution() {
        // Create a temporary directory for test files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create a markdown file WITHOUT specifying .md extension in the link
        let page_path = base_path.join("page.md");
        File::create(&page_path).unwrap().write_all(b"# Page").unwrap();

        // Test content with extensionless link that should resolve to page.md
        let content = r#"
# Test Document

[Link without extension](page)
[Link with extension](page.md)
[Missing link](nonexistent)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only have warning for nonexistent link
        // Both "page" and "page.md" should resolve to the same file
        assert_eq!(result.len(), 1, "Should only warn about nonexistent link");
        assert!(
            result[0].message.contains("nonexistent"),
            "Warning should be for 'nonexistent' not 'page'"
        );
    }

    // Cross-file validation tests
    #[test]
    fn test_cross_file_scope() {
        let rule = MD057ExistingRelativeLinks::new();
        assert_eq!(rule.cross_file_scope(), CrossFileScope::Workspace);
    }

    #[test]
    fn test_contribute_to_index_extracts_markdown_links() {
        let rule = MD057ExistingRelativeLinks::new();
        let content = r#"
# Document

[Link to docs](./docs/guide.md)
[Link with fragment](./other.md#section)
[External link](https://example.com)
[Image link](image.png)
[Media file](video.mp4)
"#;

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let mut index = FileIndex::new();
        rule.contribute_to_index(&ctx, &mut index);

        // Should only index markdown file links
        assert_eq!(index.cross_file_links.len(), 2);

        // Check first link
        assert_eq!(index.cross_file_links[0].target_path, "./docs/guide.md");
        assert_eq!(index.cross_file_links[0].fragment, "");

        // Check second link (with fragment)
        assert_eq!(index.cross_file_links[1].target_path, "./other.md");
        assert_eq!(index.cross_file_links[1].fragment, "section");
    }

    #[test]
    fn test_contribute_to_index_skips_external_and_anchors() {
        let rule = MD057ExistingRelativeLinks::new();
        let content = r#"
# Document

[External](https://example.com)
[Another external](http://example.org)
[Fragment only](#section)
[FTP link](ftp://files.example.com)
[Mail link](mailto:test@example.com)
[WWW link](www.example.com)
"#;

        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let mut index = FileIndex::new();
        rule.contribute_to_index(&ctx, &mut index);

        // Should not index any of these
        assert_eq!(index.cross_file_links.len(), 0);
    }

    #[test]
    fn test_cross_file_check_valid_link() {
        use crate::workspace_index::WorkspaceIndex;

        let rule = MD057ExistingRelativeLinks::new();

        // Create a workspace index with the target file
        let mut workspace_index = WorkspaceIndex::new();
        workspace_index.insert_file(PathBuf::from("docs/guide.md"), FileIndex::new());

        // Create file index with a link to an existing file
        let mut file_index = FileIndex::new();
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "guide.md".to_string(),
            fragment: "".to_string(),
            line: 5,
            column: 1,
        });

        // Run cross-file check from docs/index.md
        let warnings = rule
            .cross_file_check(Path::new("docs/index.md"), &file_index, &workspace_index)
            .unwrap();

        // Should have no warnings - file exists
        assert!(warnings.is_empty());
    }

    #[test]
    fn test_cross_file_check_missing_link() {
        use crate::workspace_index::WorkspaceIndex;

        let rule = MD057ExistingRelativeLinks::new();

        // Create an empty workspace index
        let workspace_index = WorkspaceIndex::new();

        // Create file index with a link to a missing file
        let mut file_index = FileIndex::new();
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "missing.md".to_string(),
            fragment: "".to_string(),
            line: 5,
            column: 1,
        });

        // Run cross-file check
        let warnings = rule
            .cross_file_check(Path::new("docs/index.md"), &file_index, &workspace_index)
            .unwrap();

        // Should have one warning for the missing file
        assert_eq!(warnings.len(), 1);
        assert!(warnings[0].message.contains("missing.md"));
        assert!(warnings[0].message.contains("does not exist"));
    }

    #[test]
    fn test_cross_file_check_parent_path() {
        use crate::workspace_index::WorkspaceIndex;

        let rule = MD057ExistingRelativeLinks::new();

        // Create a workspace index with the target file at the root
        let mut workspace_index = WorkspaceIndex::new();
        workspace_index.insert_file(PathBuf::from("readme.md"), FileIndex::new());

        // Create file index with a parent path link
        let mut file_index = FileIndex::new();
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "../readme.md".to_string(),
            fragment: "".to_string(),
            line: 5,
            column: 1,
        });

        // Run cross-file check from docs/guide.md
        let warnings = rule
            .cross_file_check(Path::new("docs/guide.md"), &file_index, &workspace_index)
            .unwrap();

        // Should have no warnings - file exists at normalized path
        assert!(warnings.is_empty());
    }

    #[test]
    fn test_cross_file_check_html_link_with_md_source() {
        // Test that .html links are accepted when corresponding .md source exists
        // This supports mdBook and similar doc generators that compile .md to .html
        use crate::workspace_index::WorkspaceIndex;

        let rule = MD057ExistingRelativeLinks::new();

        // Create a workspace index with the .md source file
        let mut workspace_index = WorkspaceIndex::new();
        workspace_index.insert_file(PathBuf::from("docs/guide.md"), FileIndex::new());

        // Create file index with an .html link (from another rule like MD051)
        let mut file_index = FileIndex::new();
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "guide.html".to_string(),
            fragment: "section".to_string(),
            line: 10,
            column: 5,
        });

        // Run cross-file check from docs/index.md
        let warnings = rule
            .cross_file_check(Path::new("docs/index.md"), &file_index, &workspace_index)
            .unwrap();

        // Should have no warnings - .md source exists for the .html link
        assert!(
            warnings.is_empty(),
            "Expected no warnings for .html link with .md source, got: {warnings:?}"
        );
    }

    #[test]
    fn test_cross_file_check_html_link_without_source() {
        // Test that .html links without corresponding .md source ARE flagged
        use crate::workspace_index::WorkspaceIndex;

        let rule = MD057ExistingRelativeLinks::new();

        // Create an empty workspace index
        let workspace_index = WorkspaceIndex::new();

        // Create file index with an .html link to a non-existent file
        let mut file_index = FileIndex::new();
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "missing.html".to_string(),
            fragment: "".to_string(),
            line: 10,
            column: 5,
        });

        // Run cross-file check from docs/index.md
        let warnings = rule
            .cross_file_check(Path::new("docs/index.md"), &file_index, &workspace_index)
            .unwrap();

        // Should have one warning - no .md source exists
        assert_eq!(warnings.len(), 1, "Expected 1 warning for .html link without source");
        assert!(warnings[0].message.contains("missing.html"));
    }

    #[test]
    fn test_normalize_path_function() {
        // Test simple cases
        assert_eq!(
            normalize_path(Path::new("docs/guide.md")),
            PathBuf::from("docs/guide.md")
        );

        // Test current directory removal
        assert_eq!(
            normalize_path(Path::new("./docs/guide.md")),
            PathBuf::from("docs/guide.md")
        );

        // Test parent directory resolution
        assert_eq!(
            normalize_path(Path::new("docs/sub/../guide.md")),
            PathBuf::from("docs/guide.md")
        );

        // Test multiple parent directories
        assert_eq!(normalize_path(Path::new("a/b/c/../../d.md")), PathBuf::from("a/d.md"));
    }

    #[test]
    fn test_html_link_with_md_source() {
        // Links to .html files should pass if corresponding .md source exists
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Create guide.md (source file)
        let md_file = base_path.join("guide.md");
        File::create(&md_file).unwrap().write_all(b"# Guide").unwrap();

        let content = r#"
[Read the guide](guide.html)
[Also here](getting-started.html)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // guide.html passes (guide.md exists), getting-started.html fails
        assert_eq!(
            result.len(),
            1,
            "Should only warn about missing source. Got: {result:?}"
        );
        assert!(result[0].message.contains("getting-started.html"));
    }

    #[test]
    fn test_htm_link_with_md_source() {
        // .htm extension should also check for markdown source
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let md_file = base_path.join("page.md");
        File::create(&md_file).unwrap().write_all(b"# Page").unwrap();

        let content = "[Page](page.htm)";

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert!(
            result.is_empty(),
            "Should not warn when .md source exists for .htm link"
        );
    }

    #[test]
    fn test_html_link_finds_various_markdown_extensions() {
        // Should find .mdx, .markdown, etc. as source files
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        File::create(base_path.join("doc.md")).unwrap();
        File::create(base_path.join("tutorial.mdx")).unwrap();
        File::create(base_path.join("guide.markdown")).unwrap();

        let content = r#"
[Doc](doc.html)
[Tutorial](tutorial.html)
[Guide](guide.html)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert!(
            result.is_empty(),
            "Should find all markdown variants as source files. Got: {result:?}"
        );
    }

    #[test]
    fn test_html_link_in_subdirectory() {
        // Should find markdown source in subdirectories
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let docs_dir = base_path.join("docs");
        std::fs::create_dir(&docs_dir).unwrap();
        File::create(docs_dir.join("guide.md"))
            .unwrap()
            .write_all(b"# Guide")
            .unwrap();

        let content = "[Guide](docs/guide.html)";

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert!(result.is_empty(), "Should find markdown source in subdirectory");
    }

    #[test]
    fn test_absolute_path_skipped_in_check() {
        // Test that absolute paths are skipped during link validation
        // This fixes the bug where /pkg/runtime was being flagged
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"
# Test Document

[Go Runtime](/pkg/runtime)
[Go Runtime with Fragment](/pkg/runtime#section)
[API Docs](/api/v1/users)
[Blog Post](/blog/2024/release.html)
[React Hook](/react/hooks/use-state.html)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should have NO warnings - all absolute paths should be skipped
        assert!(
            result.is_empty(),
            "Absolute paths should be skipped. Got warnings: {result:?}"
        );
    }

    #[test]
    fn test_absolute_path_skipped_in_cross_file_check() {
        // Test that absolute paths are skipped in cross_file_check()
        use crate::workspace_index::WorkspaceIndex;

        let rule = MD057ExistingRelativeLinks::new();

        // Create an empty workspace index (no files exist)
        let workspace_index = WorkspaceIndex::new();

        // Create file index with absolute path links (should be skipped)
        let mut file_index = FileIndex::new();
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "/pkg/runtime.md".to_string(),
            fragment: "".to_string(),
            line: 5,
            column: 1,
        });
        file_index.add_cross_file_link(CrossFileLinkIndex {
            target_path: "/api/v1/users.md".to_string(),
            fragment: "section".to_string(),
            line: 10,
            column: 1,
        });

        // Run cross-file check
        let warnings = rule
            .cross_file_check(Path::new("docs/index.md"), &file_index, &workspace_index)
            .unwrap();

        // Should have NO warnings - absolute paths should be skipped
        assert!(
            warnings.is_empty(),
            "Absolute paths should be skipped in cross_file_check. Got warnings: {warnings:?}"
        );
    }

    #[test]
    fn test_protocol_relative_url_not_skipped() {
        // Test that protocol-relative URLs (//example.com) are NOT skipped as absolute paths
        // They should still be caught by is_external_url() though
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"
# Test Document

[External](//example.com/page)
[Another](//cdn.example.com/asset.js)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should have NO warnings - protocol-relative URLs are external and should be skipped
        assert!(
            result.is_empty(),
            "Protocol-relative URLs should be skipped. Got warnings: {result:?}"
        );
    }

    #[test]
    fn test_email_addresses_skipped() {
        // Test that email addresses without mailto: are skipped
        // These are clearly not file links (the @ symbol is definitive)
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"
# Test Document

[Contact](user@example.com)
[Steering](steering@kubernetes.io)
[Support](john.doe+filter@company.co.uk)
[User](user_name@sub.domain.com)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should have NO warnings - email addresses are clearly not file links and should be skipped
        assert!(
            result.is_empty(),
            "Email addresses should be skipped. Got warnings: {result:?}"
        );
    }

    #[test]
    fn test_email_addresses_vs_file_paths() {
        // Test that email addresses (anything with @) are skipped
        // Note: File paths with @ are extremely rare, so we treat anything with @ as an email
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"
# Test Document

[Email](user@example.com)  <!-- Should be skipped (email) -->
[Email2](steering@kubernetes.io)  <!-- Should be skipped (email) -->
[Email3](user@file.md)  <!-- Should be skipped (has @, treated as email) -->
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // All should be skipped - anything with @ is treated as an email
        assert!(
            result.is_empty(),
            "All email addresses should be skipped. Got: {result:?}"
        );
    }

    #[test]
    fn test_diagnostic_position_accuracy() {
        // Test that diagnostics point to the URL, not the link text
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Position markers:     0         1         2         3
        //                       0123456789012345678901234567890123456789
        let content = "prefix [text](missing.md) suffix";
        //             The URL "missing.md" starts at 0-indexed position 14
        //             which is 1-indexed column 15, and ends at 0-indexed 24 (1-indexed column 25)

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 1, "Should have exactly one warning");
        assert_eq!(result[0].line, 1, "Should be on line 1");
        assert_eq!(result[0].column, 15, "Should point to start of URL 'missing.md'");
        assert_eq!(result[0].end_column, 25, "Should point past end of URL 'missing.md'");
    }

    #[test]
    fn test_diagnostic_position_angle_brackets() {
        // Test position accuracy with angle bracket links
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        // Position markers:     0         1         2
        //                       012345678901234567890
        let content = "[link](<missing.md>)";
        //             The URL "missing.md" starts at 0-indexed position 8 (1-indexed column 9)

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 1, "Should have exactly one warning");
        assert_eq!(result[0].line, 1, "Should be on line 1");
        assert_eq!(result[0].column, 9, "Should point to start of URL in angle brackets");
    }

    #[test]
    fn test_diagnostic_position_multiline() {
        // Test that line numbers are correct for links on different lines
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"# Title
Some text on line 2
[link on line 3](missing1.md)
More text
[link on line 5](missing2.md)"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 2, "Should have two warnings");

        // First warning should be on line 3
        assert_eq!(result[0].line, 3, "First warning should be on line 3");
        assert!(result[0].message.contains("missing1.md"));

        // Second warning should be on line 5
        assert_eq!(result[1].line, 5, "Second warning should be on line 5");
        assert!(result[1].message.contains("missing2.md"));
    }

    #[test]
    fn test_diagnostic_position_with_spaces() {
        // Test position with URLs that have spaces in parentheses
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = "[link]( missing.md )";
        //             0123456789012345678901
        //             0-indexed position 8 is 'm' in 'missing.md' (after space and paren)
        //             which is 1-indexed column 9

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 1, "Should have exactly one warning");
        // The regex captures the URL without leading/trailing spaces
        assert_eq!(result[0].column, 9, "Should point to URL after stripping spaces");
    }

    #[test]
    fn test_diagnostic_position_image() {
        // Test that image diagnostics also have correct positions
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = "![alt text](missing.jpg)";

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        assert_eq!(result.len(), 1, "Should have exactly one warning for image");
        assert_eq!(result[0].line, 1);
        // Images use start_col from the parser, which should point to the URL
        assert!(result[0].column > 0, "Should have valid column position");
        assert!(result[0].message.contains("missing.jpg"));
    }

    #[test]
    fn test_wikilinks_skipped() {
        // Wikilinks should not trigger MD057 warnings
        // They use a different linking system (e.g., Obsidian, wiki software)
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"# Test Document

[[Microsoft#Windows OS]]
[[SomePage]]
[[Page With Spaces]]
[[path/to/page#section]]
[[page|Display Text]]

This is a [real missing link](missing.md) that should be flagged.
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);
        let result = rule.check(&ctx).unwrap();

        // Should only warn about the regular markdown link, not wikilinks
        assert_eq!(
            result.len(),
            1,
            "Should only warn about missing.md, not wikilinks. Got: {result:?}"
        );
        assert!(
            result[0].message.contains("missing.md"),
            "Warning should be for missing.md, not wikilinks"
        );
    }

    #[test]
    fn test_wikilinks_not_added_to_index() {
        // Wikilinks should not be added to the cross-file link index
        let temp_dir = tempdir().unwrap();
        let base_path = temp_dir.path();

        let content = r#"# Test Document

[[Microsoft#Windows OS]]
[[SomePage#section]]
[Regular Link](other.md)
"#;

        let rule = MD057ExistingRelativeLinks::new().with_path(base_path);
        let ctx = crate::lint_context::LintContext::new(content, crate::config::MarkdownFlavor::Standard, None);

        let mut file_index = FileIndex::new();
        rule.contribute_to_index(&ctx, &mut file_index);

        // Should only have the regular markdown link (if it's a markdown file)
        // Wikilinks should not be added
        let cross_file_links = &file_index.cross_file_links;
        assert_eq!(
            cross_file_links.len(),
            1,
            "Only regular markdown links should be indexed, not wikilinks. Got: {cross_file_links:?}"
        );
        assert_eq!(file_index.cross_file_links[0].target_path, "other.md");
    }
}