talon-core 0.4.2

//! Link graph types and resolution logic.
//!
//! Implements wikilink resolution against the indexed note set, producing
//! directed edges for the link graph with backlink computation.

use crate::numeric::count_u32;
use crate::text::frontmatter::{WikiLink, normalize_keyword, normalize_vault_path};
use serde::{Deserialize, Serialize};
use std::collections::HashSet;
use std::hash::BuildHasher;

mod resolver;
pub use resolver::LinkResolver;

// ── Link graph types ────────────────────────────────────────────────────────

/// A resolved link between two notes in the vault.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct ResolvedLink {
    /// Source note path (where the link appears).
    pub from_path: String,
    /// Target note path (where the link resolves to).
    pub to_path: String,
    /// Display alias (if `[[target|alias]]`).
    pub alias: Option<String>,
    /// Section heading anchor (if `[[target#heading]]`).
    pub heading: Option<String>,
    /// Raw target text (before resolution).
    pub raw_target: String,
}

/// A note reference used for wikilink resolution.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct NoteReference {
    /// Vault-relative path.
    pub vault_path: String,
    /// Note title (from frontmatter or filename).
    pub title: Option<String>,
    /// Normalized aliases from frontmatter.
    pub aliases: Vec<String>,
}

/// Link graph edge for database storage.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct LinkEdge {
    /// Source note path.
    pub from_path: String,
    /// Target note path.
    pub to_path: String,
    /// Whether the target was resolved.
    pub resolved: bool,
    /// Raw target text.
    pub raw_target: String,
    /// Display alias.
    pub alias: Option<String>,
    /// Section heading anchor.
    pub heading: Option<String>,
}

/// Link graph statistics.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct LinkGraphStats {
    /// Total number of links (edges).
    pub total_links: u32,
    /// Number of resolved links.
    pub resolved_links: u32,
    /// Number of unresolved links.
    pub unresolved_links: u32,
    /// Number of unique target paths.
    pub unique_targets: u32,
    /// Number of nodes with no outgoing links.
    pub isolated_nodes: u32,
}

/// Resolves a single wikilink target against the note reference set.
///
/// Returns the resolved vault path, or `None` if the target doesn't match any note.
///
/// # Algorithm
/// 1. Normalize the target (NFD, lowercase, remove `.md` suffix).
/// 2. For each note, check:
///    - Path match (exact, with/without `.md`)
///    - Unique path suffix or basename match (Obsidian-style shortest path)
///    - Title match
///    - Alias match
/// 3. Return first match.
#[must_use]
pub fn resolve_wiki_link_target(target: &str, notes: &[NoteReference]) -> Option<String> {
    let normalized_target = normalize_keyword(&normalize_vault_path(target));
    let normalized_stem = normalized_target
        .strip_suffix(".md")
        .unwrap_or(&normalized_target)
        .to_string();
    let normalized_with_ext = if has_markdown_extension(&normalized_target) {
        normalized_target.clone()
    } else {
        format!("{normalized_target}.md")
    };
    let target_contains_path = normalized_stem.contains('/');
    let mut suffix_matches = Vec::new();

    for note in notes {
        let normalized_path = normalize_keyword(&normalize_vault_path(&note.vault_path));
        let normalized_path_stem = normalized_path
            .strip_suffix(".md")
            .unwrap_or(&normalized_path)
            .to_string();

        if normalized_path == normalized_target
            || normalized_path == normalized_with_ext
            || normalized_path_stem == normalized_stem
        {
            return Some(note.vault_path.clone());
        }

        let suffix_matches_note = if target_contains_path {
            path_has_component_suffix(&normalized_path_stem, &normalized_stem)
        } else {
            basename(&normalized_path_stem) == normalized_stem
        };
        if suffix_matches_note {
            suffix_matches.push(note.vault_path.clone());
        }
    }

    if suffix_matches.len() == 1 {
        return suffix_matches.into_iter().next();
    }

    for note in notes {
        let normalized_title = note
            .title
            .as_ref()
            .map(|t| normalize_keyword(t))
            .unwrap_or_default();
        let normalized_aliases: HashSet<String> = note
            .aliases
            .iter()
            .map(|alias| normalize_keyword(alias))
            .collect();

        // Title match
        let matches_title =
            normalized_title == normalized_target || normalized_title == normalized_stem;

        // Alias match
        let matches_alias = normalized_aliases.contains(&normalized_target)
            || normalized_aliases.contains(&normalized_stem);

        if matches_title || matches_alias {
            return Some(note.vault_path.clone());
        }
    }

    None
}

fn basename(path_stem: &str) -> &str {
    path_stem.rsplit('/').next().unwrap_or(path_stem)
}

fn path_has_component_suffix(path_stem: &str, target_stem: &str) -> bool {
    path_stem
        .strip_suffix(target_stem)
        .is_some_and(|prefix| prefix.is_empty() || prefix.ends_with('/'))
}

fn has_markdown_extension(path: &str) -> bool {
    std::path::Path::new(path)
        .extension()
        .is_some_and(|extension| extension.eq_ignore_ascii_case("md"))
}

/// Resolves all wikilinks from a source note against the note reference set.
///
/// Returns resolved links (those that match an indexed note).
#[must_use]
pub fn resolve_wiki_links(
    from_path: &str,
    links: &[WikiLink],
    notes: &[NoteReference],
) -> Vec<ResolvedLink> {
    let mut resolved = Vec::new();

    for link in links {
        let to_path = resolve_wiki_link_target(&link.target, notes);
        if let Some(to_path) = to_path {
            resolved.push(ResolvedLink {
                from_path: from_path.to_string(),
                to_path,
                alias: link.alias.clone(),
                heading: link.heading.clone(),
                raw_target: link.raw_target.clone(),
            });
        }
    }

    resolved
}

/// Builds a link graph edge list from resolved links.
#[must_use]
pub fn build_link_edges(from_path: &str, resolved: &[ResolvedLink]) -> Vec<LinkEdge> {
    resolved
        .iter()
        .map(|r| LinkEdge {
            from_path: from_path.to_string(),
            to_path: r.to_path.clone(),
            resolved: true,
            raw_target: r.raw_target.clone(),
            alias: r.alias.clone(),
            heading: r.heading.clone(),
        })
        .collect()
}

/// Computes backlinks: for each target, find all sources that link to it.
#[must_use]
pub fn compute_backlinks(edges: &[LinkEdge]) -> std::collections::BTreeMap<String, Vec<String>> {
    let mut backlinks: std::collections::BTreeMap<String, std::collections::BTreeSet<String>> =
        std::collections::BTreeMap::new();

    for edge in edges {
        if edge.resolved {
            backlinks
                .entry(edge.to_path.clone())
                .or_default()
                .insert(edge.from_path.clone());
        }
    }

    backlinks
        .into_iter()
        .map(|(k, v)| (k, v.into_iter().collect()))
        .collect()
}

/// Finds unresolved links (links whose targets don't resolve to any indexed note).
#[must_use]
pub fn find_unresolved_links<S: BuildHasher>(
    from_path: &str,
    links: &[WikiLink],
    notes: &[NoteReference],
    ignored_link_targets: &HashSet<String, S>,
) -> Vec<ResolvedLink> {
    let mut unresolved = Vec::new();

    for link in links {
        if resolve_wiki_link_target(&link.target, notes).is_none()
            && !is_ignored_link_target(&link.target, ignored_link_targets)
        {
            unresolved.push(ResolvedLink {
                from_path: from_path.to_string(),
                to_path: String::new(),
                alias: link.alias.clone(),
                heading: link.heading.clone(),
                raw_target: link.raw_target.clone(),
            });
        }
    }

    unresolved
}

fn is_ignored_link_target<S: BuildHasher>(
    target: &str,
    ignored_link_targets: &HashSet<String, S>,
) -> bool {
    let normalized_target = normalize_keyword(&normalize_vault_path(target));
    if ignored_link_targets.contains(&normalized_target) {
        return true;
    }

    normalized_target
        .rsplit('/')
        .next()
        .is_some_and(|name| ignored_link_targets.contains(name))
}

/// Computes link graph statistics.
#[must_use]
pub fn compute_link_stats(edges: &[LinkEdge], note_paths: &[String]) -> LinkGraphStats {
    let total_links = count_u32(edges.len());
    let resolved_links = count_u32(edges.iter().filter(|e| e.resolved).count());
    let unresolved_links = count_u32(edges.iter().filter(|e| !e.resolved).count());

    let unique_targets: std::collections::BTreeSet<String> = edges
        .iter()
        .filter(|e| e.resolved)
        .map(|e| e.to_path.clone())
        .collect();

    let sources_with_outgoing: std::collections::BTreeSet<String> =
        edges.iter().map(|e| e.from_path.clone()).collect();
    let isolated_nodes = note_paths
        .iter()
        .filter(|p| !sources_with_outgoing.contains(p.as_str()))
        .count();

    LinkGraphStats {
        total_links,
        resolved_links,
        unresolved_links,
        unique_targets: count_u32(unique_targets.len()),
        isolated_nodes: count_u32(isolated_nodes),
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used)]
mod tests;