//! 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;

/// 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,
    /// 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())
}

/// 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: serde_json::Value = frontmatter
        .map(|fm| serde_json::from_str(fm).unwrap_or_default())
        .unwrap_or_default();

    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,
        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 `repo_path` for `SKILL.md` files (filesystem walk, non-bare repos).
/// The skill slug is `{short_repo_id}/{parent_dir_name}` to ensure uniqueness across repos.
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();
    let mut stack = vec![repo_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);
            } else if path
                .file_name()
                .and_then(|n| n.to_str())
                .map(|s| s.to_lowercase())
                == Some("skill.md".to_string())
            {
                if let Some(dir_name) = path.parent()
                    .and_then(|p| p.file_name())
                    .and_then(|n| n.to_str())
                    .filter(|s| !s.starts_with('.'))
                {
                    let slug = format!("{}/{}", repo_id_prefix, dir_name);
                    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);
                        discovered.push(skill);
                    }
                }
            }
        }
    }

    Ok(discovered)
}

/// 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();
    // Stack: (tree, path_prefix relative to root)
    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 !name.starts_with('.') {
                        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.to_lowercase() == "skill.md" => {
                    // Derive skill name from parent directory
                    let dir_name = std::path::Path::new(&entry_path)
                        .parent()
                        .and_then(|p| p.file_name())
                        .and_then(|n| n.to_str())
                        .filter(|s| !s.starts_with('.'));
                    let Some(dir_name) = dir_name else { continue };

                    let slug = format!("{}/{}", repo_id_prefix, dir_name);
                    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);
                        discovered.push(skill);
                    }
                }
                _ => {}
            }
        }
    }

    Ok(discovered)
}

/// 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 with deduplication by {repo_id}+{blob_hash}.
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 {repo_id}+{blob_hash}, keep latest by commit_sha
    let mut deduped: std::collections::HashMap<String, DiscoveredSkill> = std::collections::HashMap::new();
    for skill in discovered {
        let key = format!("{}:{}", repo_id, skill.blob_hash.as_ref().unwrap_or(&skill.slug));
        match deduped.get(&key) {
            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(key, skill);
                }
            }
            None => {
                deduped.insert(key, 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_hash: std::collections::HashMap<_, _> = existing
        .into_iter()
        .map(|s| {
            let key = format!("{}:{}", s.repo_id.unwrap_or_default(), s.blob_hash.clone().unwrap_or_default());
            (key, 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_hash.get(&key) {
            if existing_skill.content != skill.content
                || existing_skill.metadata != json_meta
                || existing_skill.commit_sha != skill.commit_sha
            {
                let mut active: SkillActiveModel = existing_skill.clone().into();
                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_hash {
        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,
}