//! Repository skill scanner.
//!
//! Scans repositories for SKILL.md files and upserts skill records.

use crate::error::AppError;
use chrono::Utc;
use git2::Repository;
use models::ActiveModelTrait;
use models::projects::project_skill::ActiveModel as SkillActiveModel;
use models::projects::project_skill::Column as C;
use models::projects::project_skill::Entity as SkillEntity;
use models::repos::repo::Model as RepoModel;
use sea_orm::{ColumnTrait, EntityTrait, QueryFilter, Set};
use sha1::Digest;
use std::path::Path;
use uuid::Uuid;

const SKILL_ROOTS: &[(&str, &str)] = &[(".claude/skills", "claude"), (".codex/skills", "codex")];
const ROOT_SKILL_SYSTEM: &str = "root";

fn should_descend_dir(name: &str) -> bool {
    name != ".git"
}

/// Skill discovery result from a single repository.
#[derive(Debug)]
pub struct DiscoveredSkill {
    /// URL-safe slug derived from the directory name.
    pub slug: String,
    /// Human-readable name (from frontmatter or slug).
    pub name: String,
    /// Short description (from frontmatter).
    pub description: Option<String>,
    /// Raw markdown body after the frontmatter.
    pub content: String,
    /// Parsed frontmatter as JSON.
    pub metadata: serde_json::Value,
    /// Relative path of the SKILL.md file in the repository.
    pub relative_path: Option<String>,
    /// Skill system/source directory, e.g. "claude" or "codex".
    pub system: Option<String>,
    /// Git commit SHA where this skill was found (git hook path only).
    pub commit_sha: Option<String>,
    /// Git blob SHA-1 of the SKILL.md file.
    pub blob_hash: Option<String>,
}

/// Compute the git blob SHA-1 hash of `content`.
/// Format: "blob {len}\0{data}"
fn git_blob_hash(content: &[u8]) -> String {
    let size = content.len();
    let header = format!("blob {}\0", size);
    let mut hasher = sha1::Sha1::new();
    hasher.update(header.as_bytes());
    hasher.update(content);
    hex::encode(hasher.finalize())
}

fn parse_frontmatter(frontmatter: Option<&str>) -> serde_json::Value {
    frontmatter
        .and_then(|fm| serde_json::from_str(fm).ok())
        .or_else(|| frontmatter.and_then(|fm| serde_yaml::from_str(fm).ok()))
        .unwrap_or_default()
}

/// Parse a SKILL.md file and extract metadata + content.
fn parse_skill_file(slug: &str, raw: &str) -> DiscoveredSkill {
    let (frontmatter, content) = extract_frontmatter(raw);
    let metadata = parse_frontmatter(frontmatter);

    let name = metadata
        .get("name")
        .and_then(|v| v.as_str())
        .map(String::from)
        .unwrap_or_else(|| slug.replace('-', " ").replace('_', " "));

    let description = metadata
        .get("description")
        .and_then(|v| v.as_str())
        .map(String::from);

    DiscoveredSkill {
        slug: slug.to_string(),
        name,
        description,
        content: content.trim().to_string(),
        metadata,
        relative_path: None,
        system: None,
        commit_sha: None,
        blob_hash: None,
    }
}

/// Split frontmatter (--- ... ---) from markdown content.
fn extract_frontmatter(raw: &str) -> (Option<&str>, &str) {
    let trimmed = raw.trim_start();
    if !trimmed.starts_with("---") {
        return (None, trimmed);
    }
    if let Some(end) = trimmed[3..].find("---") {
        let fm = &trimmed[3..end + 3];
        let rest = trimmed[3 + end + 3..].trim_start();
        (Some(fm), rest)
    } else {
        (None, trimmed)
    }
}

/// Recursively scan supported skill roots for `SKILL.md` files (filesystem walk, non-bare repos).
/// The skill slug is `{short_repo_id}/{system}/{relative_skill_dir}`.
pub fn scan_repo_for_skills(
    repo_path: &Path,
    repo_id: Uuid,
) -> Result<Vec<DiscoveredSkill>, AppError> {
    let repo_id_prefix = &repo_id.to_string()[..8];
    let mut discovered = Vec::new();

    for (root, system) in SKILL_ROOTS {
        let root_path = repo_path.join(root);
        if root_path.exists() {
            scan_skill_root_fs(&root_path, repo_id_prefix, system, root, &mut discovered);
        }
    }
    scan_root_skill_pack_fs(repo_path, repo_id_prefix, &mut discovered);

    Ok(discovered)
}

fn scan_skill_root_fs(
    root_path: &Path,
    repo_id_prefix: &str,
    system: &str,
    root: &str,
    discovered: &mut Vec<DiscoveredSkill>,
) {
    let mut stack = vec![root_path.to_path_buf()];
    while let Some(dir) = stack.pop() {
        let entries = match std::fs::read_dir(&dir) {
            Ok(e) => e,
            Err(_) => continue,
        };
        for entry in entries.flatten() {
            let path = entry.path();
            if path.is_dir() {
                stack.push(path);
                continue;
            }
            if !is_skill_file_name(&path) {
                continue;
            }

            let Some(parent) = path.parent() else {
                continue;
            };
            let relative_skill_dir = parent
                .strip_prefix(root_path)
                .ok()
                .and_then(path_to_slug)
                .filter(|s| !s.is_empty());
            let Some(relative_skill_dir) = relative_skill_dir else {
                continue;
            };
            let slug = format!("{}/{}/{}", repo_id_prefix, system, relative_skill_dir);
            if let Ok(raw) = std::fs::read(&path) {
                let blob_hash = git_blob_hash(&raw);
                let mut skill = parse_skill_file(&slug, &String::from_utf8_lossy(&raw));
                skill.blob_hash = Some(blob_hash);
                skill.system = Some(system.to_string());
                skill.relative_path = Some(format!("{}/{}/SKILL.md", root, relative_skill_dir));
                skill.metadata =
                    enrich_metadata(skill.metadata, system, skill.relative_path.as_deref());
                discovered.push(skill);
            }
        }
    }
}

fn scan_root_skill_pack_fs(
    repo_path: &Path,
    repo_id_prefix: &str,
    discovered: &mut Vec<DiscoveredSkill>,
) {
    let entries = match std::fs::read_dir(repo_path) {
        Ok(entries) => entries,
        Err(_) => return,
    };

    for entry in entries.flatten() {
        let path = entry.path();
        if !path.is_dir() {
            continue;
        }
        let Some(dir_name) = path.file_name().and_then(|n| n.to_str()) else {
            continue;
        };
        if dir_name == ".git" || dir_name == ".claude" || dir_name == ".codex" {
            continue;
        }

        let skill_file = path.join("SKILL.md");
        if !skill_file.exists() {
            continue;
        }
        let relative_skill_dir = slugify_segment(dir_name);
        if relative_skill_dir.is_empty() {
            continue;
        }
        let slug = format!("{}/{}", repo_id_prefix, relative_skill_dir);
        if let Ok(raw) = std::fs::read(&skill_file) {
            let blob_hash = git_blob_hash(&raw);
            let mut skill = parse_skill_file(&slug, &String::from_utf8_lossy(&raw));
            skill.blob_hash = Some(blob_hash);
            skill.system = Some(ROOT_SKILL_SYSTEM.to_string());
            skill.relative_path = Some(format!("{}/SKILL.md", relative_skill_dir));
            skill.metadata = enrich_metadata(
                skill.metadata,
                ROOT_SKILL_SYSTEM,
                skill.relative_path.as_deref(),
            );
            discovered.push(skill);
        }
    }
}

/// Scan git tree objects for `SKILL.md` files (works for bare repos).
/// Traverses the HEAD commit tree using libgit2, reading blob content from objects.
pub fn scan_repo_tree_for_skills(
    git_repo: &Repository,
    repo_id: Uuid,
) -> Result<Vec<DiscoveredSkill>, AppError> {
    let repo_id_prefix = &repo_id.to_string()[..8];
    let head = git_repo
        .head()
        .map_err(|e| AppError::InternalServerError(format!("no HEAD: {e}")))?;
    let tree = head
        .peel_to_tree()
        .map_err(|e| AppError::InternalServerError(format!("no tree: {e}")))?;

    let mut discovered = Vec::new();
    let mut stack: Vec<(git2::Tree<'_>, String)> = vec![(tree, String::new())];

    while let Some((current_tree, prefix)) = stack.pop() {
        for entry in current_tree.iter() {
            let name = match entry.name() {
                Some(n) => n,
                None => continue,
            };
            let entry_path = if prefix.is_empty() {
                name.to_string()
            } else {
                format!("{}/{}", prefix, name)
            };

            match entry.kind() {
                Some(git2::ObjectType::Tree) => {
                    if should_descend_dir(name) {
                        if let Ok(subtree) =
                            entry.to_object(git_repo).and_then(|o| o.peel_to_tree())
                        {
                            stack.push((subtree, entry_path));
                        }
                    }
                }
                Some(git2::ObjectType::Blob) if name.eq_ignore_ascii_case("SKILL.md") => {
                    let Some((system, relative_skill_dir, legacy_slug)) =
                        skill_location_from_path(&entry_path)
                    else {
                        continue;
                    };

                    let slug = if legacy_slug {
                        format!("{}/{}", repo_id_prefix, relative_skill_dir)
                    } else {
                        format!("{}/{}/{}", repo_id_prefix, system, relative_skill_dir)
                    };
                    if let Ok(blob) = entry.to_object(git_repo).and_then(|o| o.peel_to_blob()) {
                        let raw = blob.content();
                        let blob_hash = git_blob_hash(raw);
                        let mut skill = parse_skill_file(&slug, &String::from_utf8_lossy(raw));
                        skill.blob_hash = Some(blob_hash);
                        skill.system = Some(system.to_string());
                        skill.relative_path = Some(entry_path.clone());
                        skill.metadata =
                            enrich_metadata(skill.metadata, system, skill.relative_path.as_deref());
                        discovered.push(skill);
                    }
                }
                _ => {}
            }
        }
    }

    Ok(discovered)
}

fn is_skill_file_name(path: &Path) -> bool {
    path.file_name()
        .and_then(|n| n.to_str())
        .is_some_and(|name| name.eq_ignore_ascii_case("SKILL.md"))
}

fn path_to_slug(path: &Path) -> Option<String> {
    let parts: Vec<String> = path
        .components()
        .filter_map(|c| c.as_os_str().to_str())
        .map(slugify_segment)
        .filter(|s| !s.is_empty())
        .collect();
    (!parts.is_empty()).then(|| parts.join("/"))
}

fn slugify_segment(input: &str) -> String {
    let mut out = String::with_capacity(input.len());
    let mut last_dash = false;
    for ch in input.chars() {
        let ch = ch.to_ascii_lowercase();
        if ch.is_ascii_alphanumeric() || ch == '_' || ch == '-' {
            out.push(ch);
            last_dash = false;
        } else if !last_dash {
            out.push('-');
            last_dash = true;
        }
    }
    out.trim_matches('-').to_string()
}

fn skill_location_from_path(path: &str) -> Option<(&'static str, String, bool)> {
    let normalized = path.replace('\\', "/");
    for (root, system) in SKILL_ROOTS {
        let prefix = format!("{}/", root);
        let suffix = "/SKILL.md";
        if normalized.starts_with(&prefix) && normalized.ends_with(suffix) {
            let relative = &normalized[prefix.len()..normalized.len() - suffix.len()];
            let slug = relative
                .split('/')
                .map(slugify_segment)
                .filter(|s| !s.is_empty())
                .collect::<Vec<_>>()
                .join("/");
            if !slug.is_empty() {
                return Some((*system, slug, false));
            }
        }
    }

    let suffix = "/SKILL.md";
    if normalized.ends_with(suffix) && !normalized.starts_with('.') {
        let relative = &normalized[..normalized.len() - suffix.len()];
        if !relative.contains('/') {
            let slug = slugify_segment(relative);
            if !slug.is_empty() {
                return Some((ROOT_SKILL_SYSTEM, slug, true));
            }
        }
    }

    None
}

fn enrich_metadata(
    mut metadata: serde_json::Value,
    system: &str,
    relative_path: Option<&str>,
) -> serde_json::Value {
    if !metadata.is_object() {
        metadata = serde_json::json!({});
    }
    if let Some(obj) = metadata.as_object_mut() {
        obj.entry("system")
            .or_insert_with(|| serde_json::Value::String(system.to_string()));
        if let Some(relative_path) = relative_path {
            obj.entry("path")
                .or_insert_with(|| serde_json::Value::String(relative_path.to_string()));
        }
    }
    metadata
}

#[cfg(test)]
mod tests {
    use super::{scan_repo_for_skills, scan_repo_tree_for_skills};
    use git2::{Repository, Signature};
    use std::fs;
    use tempfile::tempdir;
    use uuid::Uuid;

    #[test]
    fn tree_scan_discovers_skills_under_hidden_dirs() {
        let temp = tempdir().expect("tempdir");
        let repo = Repository::init(temp.path()).expect("init repo");

        let skill_dir = temp
            .path()
            .join(".claude")
            .join("skills")
            .join("demo-skill");
        fs::create_dir_all(&skill_dir).expect("create skill dir");
        fs::write(
            skill_dir.join("SKILL.md"),
            "---\nname: Demo Skill\ndescription: test\n---\ncontent",
        )
        .expect("write skill");

        let mut index = repo.index().expect("index");
        index
            .add_path(std::path::Path::new(".claude/skills/demo-skill/SKILL.md"))
            .expect("add skill");
        index.write().expect("write index");
        let tree_id = index.write_tree().expect("write tree");
        let tree = repo.find_tree(tree_id).expect("find tree");
        let sig = Signature::now("tester", "tester@example.com").expect("signature");
        repo.commit(Some("HEAD"), &sig, &sig, "add skill", &tree, &[])
            .expect("commit");

        let discovered = scan_repo_tree_for_skills(&repo, Uuid::nil()).expect("scan tree");

        assert_eq!(discovered.len(), 1);
        assert_eq!(discovered[0].name, "Demo Skill");
        assert_eq!(discovered[0].slug, "00000000/claude/demo-skill");
        assert_eq!(
            discovered[0].metadata["system"],
            serde_json::Value::String("claude".into())
        );
    }

    #[test]
    fn tree_scan_keeps_claude_and_codex_skills_separate() {
        let temp = tempdir().expect("tempdir");
        let repo = Repository::init(temp.path()).expect("init repo");

        for root in [".claude", ".codex"] {
            let skill_dir = temp.path().join(root).join("skills").join("review");
            fs::create_dir_all(&skill_dir).expect("create skill dir");
            fs::write(
                skill_dir.join("SKILL.md"),
                format!("---\nname: {} Review\n---\ncontent", root),
            )
            .expect("write skill");
        }

        let mut index = repo.index().expect("index");
        index
            .add_path(std::path::Path::new(".claude/skills/review/SKILL.md"))
            .expect("add claude skill");
        index
            .add_path(std::path::Path::new(".codex/skills/review/SKILL.md"))
            .expect("add codex skill");
        index.write().expect("write index");
        let tree_id = index.write_tree().expect("write tree");
        let tree = repo.find_tree(tree_id).expect("find tree");
        let sig = Signature::now("tester", "tester@example.com").expect("signature");
        repo.commit(Some("HEAD"), &sig, &sig, "add skills", &tree, &[])
            .expect("commit");

        let mut slugs = scan_repo_tree_for_skills(&repo, Uuid::nil())
            .expect("scan tree")
            .into_iter()
            .map(|s| s.slug)
            .collect::<Vec<_>>();
        slugs.sort();

        assert_eq!(
            slugs,
            vec!["00000000/claude/review", "00000000/codex/review"]
        );
    }

    #[test]
    fn scans_root_level_skill_pack_layout() {
        let temp = tempdir().expect("tempdir");
        let repo = Repository::init(temp.path()).expect("init repo");

        let skill_dir = temp.path().join("code-review");
        fs::create_dir_all(&skill_dir).expect("create skill dir");
        fs::write(skill_dir.join("SKILL.md"), "# Code Review\n\ncontent").expect("write skill");

        let mut index = repo.index().expect("index");
        index
            .add_path(std::path::Path::new("code-review/SKILL.md"))
            .expect("add skill");
        index.write().expect("write index");
        let tree_id = index.write_tree().expect("write tree");
        let tree = repo.find_tree(tree_id).expect("find tree");
        let sig = Signature::now("tester", "tester@example.com").expect("signature");
        repo.commit(Some("HEAD"), &sig, &sig, "add skill", &tree, &[])
            .expect("commit");

        let fs_discovered = scan_repo_for_skills(temp.path(), Uuid::nil()).expect("scan fs");
        let tree_discovered = scan_repo_tree_for_skills(&repo, Uuid::nil()).expect("scan tree");

        assert_eq!(fs_discovered.len(), 1);
        assert_eq!(tree_discovered.len(), 1);
        assert_eq!(fs_discovered[0].slug, "00000000/code-review");
        assert_eq!(tree_discovered[0].slug, "00000000/code-review");
        assert_eq!(
            tree_discovered[0].metadata["system"],
            serde_json::Value::String("root".into())
        );
    }
}

/// Scan a git2::Repository for skills and upsert them into the database.
/// Uses filesystem walk for normal repos, git tree traversal for bare repos.
pub async fn scan_and_sync_skills(
    db: &db::database::AppDatabase,
    project_uuid: Uuid,
    repo: &RepoModel,
) -> Result<ScanSyncResult, AppError> {
    // Open with git2 to get the actual workdir
    let git_repo = match Repository::open(&repo.storage_path) {
        Ok(r) => r,
        Err(e) => {
            tracing::warn!("failed to open git repo {}: {:?}", repo.storage_path, e);
            return Ok(ScanSyncResult {
                discovered: 0,
                created: 0,
                updated: 0,
                removed: 0,
            });
        }
    };

    let commit_sha = git_repo
        .head()
        .ok()
        .and_then(|h| h.target())
        .map(|oid| oid.to_string());

    // For bare repos (no workdir), scan git tree objects directly
    let mut discovered = if git_repo.is_bare() || git_repo.workdir().is_none() {
        match scan_repo_tree_for_skills(&git_repo, repo.id) {
            Ok(skills) => skills,
            Err(e) => {
                tracing::warn!("tree scan failed for repo {}: {:?}", repo.storage_path, e);
                vec![]
            }
        }
    } else {
        let workdir = git_repo.workdir().unwrap();
        scan_repo_for_skills(workdir, repo.id)?
    };

    // Fill in commit_sha for discovered skills
    for skill in &mut discovered {
        skill.commit_sha = commit_sha.clone();
    }

    sync_discovered_skills(db, project_uuid, repo.id, discovered).await
}

/// Sync discovered skills by stable slug.
async fn sync_discovered_skills(
    db: &db::database::AppDatabase,
    project_uuid: Uuid,
    repo_id: Uuid,
    discovered: Vec<DiscoveredSkill>,
) -> Result<ScanSyncResult, AppError> {
    if discovered.is_empty() {
        return Ok(ScanSyncResult {
            discovered: 0,
            created: 0,
            updated: 0,
            removed: 0,
        });
    }

    let now = Utc::now();
    let mut created = 0i64;
    let mut updated = 0i64;

    // Deduplicate by slug. The slug includes repo prefix + skill system + relative skill path.
    let mut deduped: std::collections::HashMap<String, DiscoveredSkill> =
        std::collections::HashMap::new();
    for skill in discovered {
        match deduped.get(&skill.slug) {
            Some(existing) => {
                // Keep the one with the later commit_sha
                if skill.commit_sha.as_ref().unwrap_or(&String::new())
                    > existing.commit_sha.as_ref().unwrap_or(&String::new())
                {
                    deduped.insert(skill.slug.clone(), skill);
                }
            }
            None => {
                deduped.insert(skill.slug.clone(), skill);
            }
        }
    }

    // Query existing skills for this repo
    let existing: Vec<_> = SkillEntity::find()
        .filter(C::ProjectUuid.eq(project_uuid))
        .filter(C::Source.eq("repo"))
        .filter(C::RepoId.eq(repo_id))
        .all(db)
        .await?;

    let existing_by_slug: std::collections::HashMap<_, _> =
        existing.into_iter().map(|s| (s.slug.clone(), s)).collect();

    let mut seen_keys = std::collections::HashSet::new();

    let discovered_count = deduped.len() as i64;
    for (key, skill) in deduped {
        seen_keys.insert(key.clone());
        let json_meta = serde_json::to_value(&skill.metadata).unwrap_or_default();

        if let Some(existing_skill) = existing_by_slug.get(&key) {
            if existing_skill.content != skill.content
                || existing_skill.metadata != json_meta
                || existing_skill.commit_sha != skill.commit_sha
                || existing_skill.blob_hash != skill.blob_hash
                || existing_skill.name != skill.name
                || existing_skill.description != skill.description
            {
                let mut active: SkillActiveModel = existing_skill.clone().into();
                active.name = Set(skill.name);
                active.description = Set(skill.description);
                active.content = Set(skill.content);
                active.metadata = Set(json_meta);
                active.commit_sha = Set(skill.commit_sha);
                active.blob_hash = Set(skill.blob_hash);
                active.updated_at = Set(now);
                active.update(db).await?;
                updated += 1;
            }
        } else {
            let active = SkillActiveModel {
                id: Set(0),
                project_uuid: Set(project_uuid),
                slug: Set(skill.slug),
                name: Set(skill.name),
                description: Set(skill.description),
                source: Set("repo".to_string()),
                repo_id: Set(Some(repo_id)),
                commit_sha: Set(skill.commit_sha),
                blob_hash: Set(skill.blob_hash),
                content: Set(skill.content),
                metadata: Set(json_meta),
                enabled: Set(true),
                created_by: Set(None),
                created_at: Set(now),
                updated_at: Set(now),
            };
            active.insert(db).await?;
            created += 1;
        }
    }

    // Remove skills that no longer exist in the repo
    let mut removed = 0i64;
    for (key, old_skill) in existing_by_slug {
        if !seen_keys.contains(&key) {
            SkillEntity::delete_by_id(old_skill.id).exec(db).await?;
            removed += 1;
        }
    }

    Ok(ScanSyncResult {
        discovered: discovered_count,
        created,
        updated,
        removed,
    })
}

/// Result of a scan + sync operation.
#[derive(Debug)]
pub struct ScanSyncResult {
    pub discovered: i64,
    pub created: i64,
    pub updated: i64,
    pub removed: i64,
}