use serde::Deserialize;
use serde_json::json;
use std::collections::HashMap;
use std::fs;
use std::path::{Path, PathBuf};
use std::sync::RwLock;

use crate::config::SkillsConfig;

#[derive(Debug, Clone)]
pub struct Skill {
    pub name: String,
    pub description: String,
    pub body: String,
    pub source: SkillSource,
    pub path: PathBuf,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SkillSource {
    User,
    UserAgent,
    Project,
    ProjectAgent,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SkillScope {
    User,
    Project,
}

impl SkillScope {
    pub fn parse(value: &str) -> Option<Self> {
        match value {
            "user" => Some(Self::User),
            "project" => Some(Self::Project),
            _ => None,
        }
    }

    pub fn as_str(&self) -> &'static str {
        match self {
            Self::User => "user",
            Self::Project => "project",
        }
    }
}

impl From<SkillScope> for SkillSource {
    fn from(value: SkillScope) -> Self {
        match value {
            SkillScope::User => SkillSource::User,
            SkillScope::Project => SkillSource::Project,
        }
    }
}

#[derive(Debug)]
pub struct SkillRuntime {
    config: SkillsConfig,
    catalog: RwLock<SkillCatalog>,
}

impl Default for SkillRuntime {
    fn default() -> Self {
        Self {
            config: SkillsConfig::default(),
            catalog: RwLock::new(SkillCatalog::default()),
        }
    }
}

impl SkillRuntime {
    pub fn from_config(config: SkillsConfig) -> Self {
        let catalog = SkillCatalog::discover(&config);
        Self {
            config,
            catalog: RwLock::new(catalog),
        }
    }

    pub fn reload(&self) -> Result<SkillCatalog, String> {
        let catalog = SkillCatalog::discover(&self.config);
        let mut guard = self.catalog.write().expect("skills rwlock poisoned");
        *guard = catalog.clone();
        Ok(catalog)
    }

    pub fn is_empty(&self) -> bool {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .is_empty()
    }

    pub fn len(&self) -> usize {
        self.catalog.read().expect("skills rwlock poisoned").len()
    }

    pub fn system_index_prompt(&self) -> Option<String> {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .system_index_prompt()
    }

    pub fn discovery_event_payload(&self) -> serde_json::Value {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .discovery_event_payload()
    }

    pub fn offered_event_payload(&self) -> serde_json::Value {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .offered_event_payload()
    }

    pub fn activation_payload(&self, name: &str) -> Result<String, String> {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .activation_payload(name)
    }

    pub fn activation_event_payload(&self, name: &str) -> Result<serde_json::Value, String> {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .activation_event_payload(name)
    }

    pub fn list_skills(&self) -> Vec<Skill> {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .skills
            .clone()
    }

    pub fn get_skill(&self, name: &str) -> Option<Skill> {
        self.catalog
            .read()
            .expect("skills rwlock poisoned")
            .find_skill(name)
            .cloned()
    }

    pub fn create_skill(
        &self,
        scope: SkillScope,
        name: &str,
        description: &str,
        body: &str,
        reload: bool,
    ) -> Result<Skill, String> {
        validate_skill_name(name)?;
        let path = skill_file_path(scope, name)?;
        if path.exists() {
            return Err(format!(
                "skill '{}' already exists at {}",
                name,
                path.display()
            ));
        }

        write_skill_file(&path, name, description, body)?;
        let skill = parse_skill_file(&path, scope.into())?;
        if reload {
            let _ = self.reload()?;
        }
        Ok(skill)
    }

    pub fn update_skill(
        &self,
        scope: SkillScope,
        name: &str,
        description: Option<&str>,
        body: Option<&str>,
        reload: bool,
    ) -> Result<Skill, String> {
        validate_skill_name(name)?;
        let path = skill_file_path(scope, name)?;
        if !path.exists() {
            return Err(format!("skill '{}' not found at {}", name, path.display()));
        }

        let existing = parse_skill_file(&path, scope.into())?;
        let next_description = description.unwrap_or(&existing.description);
        let next_body = body.unwrap_or(&existing.body);

        write_skill_file(&path, name, next_description, next_body)?;
        let skill = parse_skill_file(&path, scope.into())?;
        if reload {
            let _ = self.reload()?;
        }
        Ok(skill)
    }

    pub fn delete_skill(
        &self,
        scope: SkillScope,
        name: &str,
        reload: bool,
    ) -> Result<PathBuf, String> {
        validate_skill_name(name)?;
        let dir = skill_dir_path(scope, name)?;
        if !dir.exists() {
            return Err(format!("skill '{}' not found at {}", name, dir.display()));
        }

        fs::remove_dir_all(&dir)
            .map_err(|err| format!("failed to delete skill directory: {}", err))?;
        if reload {
            let _ = self.reload()?;
        }
        Ok(dir)
    }
}

impl crate::agent::SkillProvider for SkillRuntime {
    fn system_index_prompt(&self) -> Option<String> {
        SkillRuntime::system_index_prompt(self)
    }
}

impl SkillSource {
    fn as_str(&self) -> &'static str {
        match self {
            SkillSource::User => "user",
            SkillSource::UserAgent => "user_agent",
            SkillSource::Project => "project",
            SkillSource::ProjectAgent => "project_agent",
        }
    }
}

#[derive(Debug, Clone)]
pub struct SkillCatalog {
    skills: Vec<Skill>,
    max_index_chars: usize,
    max_listed_skills: usize,
}

impl Default for SkillCatalog {
    fn default() -> Self {
        Self {
            skills: Vec::new(),
            max_index_chars: 4_000,
            max_listed_skills: 32,
        }
    }
}

impl SkillCatalog {
    pub fn discover(config: &SkillsConfig) -> Self {
        if !config.enabled {
            return Self {
                max_index_chars: config.max_index_chars,
                max_listed_skills: config.max_listed_skills,
                ..Self::default()
            };
        }

        let cwd = std::env::current_dir().unwrap_or_else(|_| PathBuf::from("."));
        let mut merged: HashMap<String, Skill> = HashMap::new();
        let mut sources_seen = 0usize;

        // Load from least specific to most specific so later sources win on conflicts.
        for source in source_order(&config.sources) {
            sources_seen += 1;
            let root = source_root(source, &cwd);

            let Some(root) = root else { continue };
            for skill in load_skills_from_root(&root, source) {
                if let Some(existing) = merged.get(&skill.name) {
                    tracing::warn!(
                        skill = %skill.name,
                        old_source = %existing.source.as_str(),
                        new_source = %skill.source.as_str(),
                        "Duplicate skill name found; overriding with later source"
                    );
                }
                merged.insert(skill.name.clone(), skill);
            }
        }

        let mut skills: Vec<Skill> = merged.into_values().collect();
        skills.sort_by(|a, b| a.name.cmp(&b.name));

        tracing::info!(
            sources_seen,
            discovered = skills.len(),
            "Skills discovery completed"
        );

        Self {
            skills,
            max_index_chars: config.max_index_chars,
            max_listed_skills: config.max_listed_skills,
        }
    }

    pub fn is_empty(&self) -> bool {
        self.skills.is_empty()
    }

    pub fn len(&self) -> usize {
        self.skills.len()
    }

    pub fn system_index_prompt(&self) -> Option<String> {
        if self.skills.is_empty() {
            return None;
        }

        let mut prompt = String::from(
            "You have access to skills discovered from local skill directories. Use a skill only when the user's request clearly matches the skill description.\nIf a skill is needed, call tool skill_activate with {\"name\": \"<skill-name>\"}.\nAvailable skills:\n",
        );

        for skill in self.skills.iter().take(self.max_listed_skills) {
            let line = format!("- {}: {}\n", skill.name, skill.description);
            if prompt.len() + line.len() > self.max_index_chars {
                prompt.push_str("- ... (truncated)\n");
                break;
            }
            prompt.push_str(&line);
        }

        Some(prompt)
    }

    pub fn discovery_event_payload(&self) -> serde_json::Value {
        self.catalog_event_payload()
    }

    pub fn offered_event_payload(&self) -> serde_json::Value {
        self.catalog_event_payload()
    }

    pub fn activation_payload(&self, name: &str) -> Result<String, String> {
        let skill = self
            .find_skill(name)
            .ok_or_else(|| format!("skill '{}' not found", name))?;

        if skill.body.is_empty() {
            return Ok(format!(
                "SKILL LOADED: {}\nDescription: {}\nNo additional body instructions found.",
                skill.name, skill.description
            ));
        }

        Ok(format!(
            "SKILL LOADED: {}\nDescription: {}\nSource: {}\nPath: {}\n\n{}",
            skill.name,
            skill.description,
            skill.source.as_str(),
            skill.path.display(),
            skill.body
        ))
    }

    pub fn activation_event_payload(&self, name: &str) -> Result<serde_json::Value, String> {
        let skill = self
            .find_skill(name)
            .ok_or_else(|| format!("skill '{}' not found", name))?;

        Ok(json!({
            "name": skill.name,
            "description": skill.description,
            "source": skill.source.as_str(),
            "path": skill.path.display().to_string(),
            "body_chars": skill.body.len(),
        }))
    }

    fn find_skill(&self, name: &str) -> Option<&Skill> {
        self.skills.iter().find(|s| s.name == name)
    }

    fn catalog_event_payload(&self) -> serde_json::Value {
        json!({
            "count": self.skills.len(),
            "skills": self.skills.iter().map(|skill| json!({
                "name": skill.name,
                "description": skill.description,
                "source": skill.source.as_str(),
                "path": skill.path.display().to_string(),
            })).collect::<Vec<_>>()
        })
    }
}

fn source_order(sources: &[String]) -> Vec<SkillSource> {
    let mut result = Vec::new();
    for source in sources {
        match source.as_str() {
            "user" => {
                if !result.contains(&SkillSource::User) {
                    result.push(SkillSource::User);
                }
            }
            "user_agent" => {
                if !result.contains(&SkillSource::UserAgent) {
                    result.push(SkillSource::UserAgent);
                }
            }
            "project" => {
                if !result.contains(&SkillSource::Project) {
                    result.push(SkillSource::Project);
                }
            }
            "project_agent" => {
                if !result.contains(&SkillSource::ProjectAgent) {
                    result.push(SkillSource::ProjectAgent);
                }
            }
            unknown => {
                tracing::warn!(source = %unknown, "Unknown skills source ignored");
            }
        }
    }

    if result.is_empty() {
        vec![
            SkillSource::User,
            SkillSource::UserAgent,
            SkillSource::Project,
            SkillSource::ProjectAgent,
        ]
    } else {
        result
    }
}

fn validate_skill_name(name: &str) -> Result<(), String> {
    if name.trim().is_empty() {
        return Err("skill name cannot be empty".to_string());
    }
    if name.contains('/') || name.contains('\\') || name.contains("..") {
        return Err("skill name must not contain path separators or '..'".to_string());
    }
    Ok(())
}

pub fn project_skills_root() -> Result<PathBuf, String> {
    let cwd =
        std::env::current_dir().map_err(|err| format!("failed to get current dir: {}", err))?;
    Ok(cwd.join(".picobot").join("skills"))
}

fn project_agent_skills_root(cwd: &Path) -> PathBuf {
    cwd.join(".agents").join("skills")
}

fn user_skills_root() -> Option<PathBuf> {
    dirs::home_dir().map(|p| p.join(".picobot").join("skills"))
}

fn user_agent_skills_root() -> Option<PathBuf> {
    dirs::home_dir().map(|p| p.join(".agents").join("skills"))
}

fn source_root(source: SkillSource, cwd: &Path) -> Option<PathBuf> {
    match source {
        SkillSource::User => user_skills_root(),
        SkillSource::UserAgent => user_agent_skills_root(),
        SkillSource::Project => Some(cwd.join(".picobot").join("skills")),
        SkillSource::ProjectAgent => Some(project_agent_skills_root(cwd)),
    }
}

fn root_for_scope(scope: SkillScope) -> Result<PathBuf, String> {
    match scope {
        SkillScope::User => {
            user_skills_root().ok_or_else(|| "failed to resolve home directory".to_string())
        }
        SkillScope::Project => project_skills_root(),
    }
}

fn skill_dir_path(scope: SkillScope, name: &str) -> Result<PathBuf, String> {
    Ok(root_for_scope(scope)?.join(name))
}

fn skill_file_path(scope: SkillScope, name: &str) -> Result<PathBuf, String> {
    Ok(skill_dir_path(scope, name)?.join("SKILL.md"))
}

fn render_skill_file(name: &str, description: &str, body: &str) -> Result<String, String> {
    if description.trim().is_empty() {
        return Err("description is required and cannot be empty".to_string());
    }

    #[derive(serde::Serialize)]
    struct SkillFrontmatterOwned {
        name: String,
        description: String,
    }

    let yaml = serde_yaml::to_string(&SkillFrontmatterOwned {
        name: name.to_string(),
        description: description.to_string(),
    })
    .map_err(|err| format!("failed to render skill frontmatter: {}", err))?;

    let yaml = yaml.trim_start_matches("---\n");
    let body = body.trim();
    if body.is_empty() {
        Ok(format!("---\n{}---\n", yaml))
    } else {
        Ok(format!("---\n{}---\n{}\n", yaml, body))
    }
}

fn write_skill_file(path: &Path, name: &str, description: &str, body: &str) -> Result<(), String> {
    let content = render_skill_file(name, description, body)?;
    if let Some(parent) = path.parent() {
        fs::create_dir_all(parent)
            .map_err(|err| format!("failed to create skill directory: {}", err))?;
    }
    fs::write(path, content).map_err(|err| format!("failed to write skill file: {}", err))
}

fn load_skills_from_root(root: &Path, source: SkillSource) -> Vec<Skill> {
    let mut out = Vec::new();
    if !root.exists() {
        return out;
    }

    let entries = match fs::read_dir(root) {
        Ok(entries) => entries,
        Err(err) => {
            tracing::warn!(path = %root.display(), error = %err, "Failed to read skills directory");
            return out;
        }
    };

    for entry in entries.flatten() {
        let path = entry.path();
        if !path.is_dir() {
            continue;
        }
        let skill_md = path.join("SKILL.md");
        if !skill_md.exists() {
            continue;
        }

        match parse_skill_file(&skill_md, source) {
            Ok(skill) => out.push(skill),
            Err(err) => {
                tracing::warn!(path = %skill_md.display(), error = %err, "Skipping invalid skill file");
            }
        }
    }

    out
}

#[derive(Debug, Deserialize)]
struct SkillFrontmatter {
    description: String,
    #[serde(default)]
    name: Option<String>,
}

fn parse_skill_file(path: &Path, source: SkillSource) -> Result<Skill, String> {
    let content = fs::read_to_string(path).map_err(|e| format!("failed to read file: {}", e))?;

    let (frontmatter_raw, body) =
        split_frontmatter(&content).ok_or_else(|| "missing YAML frontmatter block".to_string())?;

    let frontmatter: SkillFrontmatter = serde_yaml::from_str(frontmatter_raw)
        .map_err(|e| format!("invalid YAML frontmatter: {}", e))?;

    let description = frontmatter.description.trim();
    if description.is_empty() {
        return Err("description is required and cannot be empty".to_string());
    }

    let dir_name = path
        .parent()
        .and_then(|p| p.file_name())
        .map(|s| s.to_string_lossy().to_string())
        .unwrap_or_else(|| "unknown-skill".to_string());

    let name = frontmatter.name.unwrap_or(dir_name).trim().to_string();

    Ok(Skill {
        name,
        description: description.to_string(),
        body: body.trim().to_string(),
        source,
        path: path.to_path_buf(),
    })
}

fn split_frontmatter(content: &str) -> Option<(&str, &str)> {
    let rest = content.strip_prefix("---\n")?;
    let marker = "\n---\n";
    let idx = rest.find(marker)?;
    let frontmatter = &rest[..idx];
    let body = &rest[idx + marker.len()..];
    Some((frontmatter, body))
}

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

    static CWD_TEST_LOCK: Mutex<()> = Mutex::new(());

    struct CurrentDirGuard {
        previous: PathBuf,
    }

    impl CurrentDirGuard {
        fn enter(path: &Path) -> Self {
            let previous = std::env::current_dir().unwrap();
            std::env::set_current_dir(path).unwrap();
            Self { previous }
        }
    }

    impl Drop for CurrentDirGuard {
        fn drop(&mut self) {
            let _ = std::env::set_current_dir(&self.previous);
        }
    }

    #[test]
    fn test_split_frontmatter() {
        let input = "---\ndescription: demo\n---\nhello";
        let (fm, body) = split_frontmatter(input).unwrap();
        assert!(fm.contains("description"));
        assert_eq!(body, "hello");
    }

    #[test]
    fn test_parse_skill_file_requires_description() {
        let dir = tempfile::tempdir().unwrap();
        let skill_dir = dir.path().join("demo");
        fs::create_dir_all(&skill_dir).unwrap();
        let skill_md = skill_dir.join("SKILL.md");
        fs::write(&skill_md, "---\nname: demo\n---\ncontent").unwrap();

        let err = parse_skill_file(&skill_md, SkillSource::Project).unwrap_err();
        assert!(err.contains("description"));
    }

    #[test]
    fn test_activation_payload_contains_body() {
        let dir = tempfile::tempdir().unwrap();
        let skill_dir = dir.path().join("demo");
        fs::create_dir_all(&skill_dir).unwrap();
        let skill_md = skill_dir.join("SKILL.md");
        fs::write(
            &skill_md,
            "---\nname: demo\ndescription: demo skill\n---\nStep A\nStep B",
        )
        .unwrap();

        let skill = parse_skill_file(&skill_md, SkillSource::Project).unwrap();
        let catalog = SkillCatalog {
            skills: vec![skill],
            max_index_chars: 1000,
            max_listed_skills: 10,
        };

        let payload = catalog.activation_payload("demo").unwrap();
        assert!(payload.contains("SKILL LOADED: demo"));
        assert!(payload.contains("Step A"));
    }

    #[test]
    fn test_runtime_create_update_delete_reload() {
        let _lock = CWD_TEST_LOCK.lock().unwrap();
        let temp_dir = tempfile::tempdir().unwrap();
        let _guard = CurrentDirGuard::enter(temp_dir.path());

        let runtime = SkillRuntime::from_config(SkillsConfig {
            enabled: true,
            sources: vec!["project".to_string()],
            max_index_chars: 4000,
            max_listed_skills: 32,
        });

        assert_eq!(runtime.len(), 0);

        let created = runtime
            .create_skill(
                SkillScope::Project,
                "demo-skill",
                "demo desc",
                "line 1",
                true,
            )
            .unwrap();
        assert_eq!(created.name, "demo-skill");
        assert_eq!(runtime.len(), 1);

        let updated = runtime
            .update_skill(
                SkillScope::Project,
                "demo-skill",
                Some("updated desc"),
                Some("line 2"),
                true,
            )
            .unwrap();
        assert_eq!(updated.description, "updated desc");
        assert!(
            runtime
                .activation_payload("demo-skill")
                .unwrap()
                .contains("line 2")
        );

        let deleted_path = runtime
            .delete_skill(SkillScope::Project, "demo-skill", true)
            .unwrap();
        assert!(!deleted_path.exists());
        assert_eq!(runtime.len(), 0);
    }

    #[test]
    fn test_source_order_supports_agent_sources() {
        let ordered = source_order(&[
            "user".to_string(),
            "user_agent".to_string(),
            "project".to_string(),
            "project_agent".to_string(),
            "project".to_string(),
            "unknown".to_string(),
        ]);

        assert_eq!(
            ordered,
            vec![
                SkillSource::User,
                SkillSource::UserAgent,
                SkillSource::Project,
                SkillSource::ProjectAgent,
            ]
        );
    }

    #[test]
    fn test_discover_loads_project_agent_skills() {
        let _lock = CWD_TEST_LOCK.lock().unwrap();
        let temp_dir = tempfile::tempdir().unwrap();
        let _guard = CurrentDirGuard::enter(temp_dir.path());

        let agent_skill_dir = temp_dir
            .path()
            .join(".agents")
            .join("skills")
            .join("demo-agent");
        fs::create_dir_all(&agent_skill_dir).unwrap();
        fs::write(
            agent_skill_dir.join("SKILL.md"),
            "---\ndescription: agent skill\n---\nUse agent",
        )
        .unwrap();

        let catalog = SkillCatalog::discover(&SkillsConfig {
            enabled: true,
            sources: vec!["project_agent".to_string()],
            max_index_chars: 4000,
            max_listed_skills: 32,
        });

        assert_eq!(catalog.len(), 1);
        let payload = catalog.activation_event_payload("demo-agent").unwrap();
        assert_eq!(payload["source"], "project_agent");
    }

    #[test]
    fn test_discover_prefers_project_agent_on_conflict() {
        let _lock = CWD_TEST_LOCK.lock().unwrap();
        let temp_dir = tempfile::tempdir().unwrap();
        let _guard = CurrentDirGuard::enter(temp_dir.path());

        let project_skill_dir = temp_dir.path().join(".picobot").join("skills").join("demo");
        fs::create_dir_all(&project_skill_dir).unwrap();
        fs::write(
            project_skill_dir.join("SKILL.md"),
            "---\ndescription: project version\n---\nProject body",
        )
        .unwrap();

        let agent_skill_dir = temp_dir.path().join(".agents").join("skills").join("demo");
        fs::create_dir_all(&agent_skill_dir).unwrap();
        fs::write(
            agent_skill_dir.join("SKILL.md"),
            "---\ndescription: agent version\n---\nAgent body",
        )
        .unwrap();

        let catalog = SkillCatalog::discover(&SkillsConfig {
            enabled: true,
            sources: vec!["project".to_string(), "project_agent".to_string()],
            max_index_chars: 4000,
            max_listed_skills: 32,
        });

        let payload = catalog.activation_payload("demo").unwrap();
        assert!(payload.contains("Source: project_agent"));
        assert!(payload.contains("Agent body"));
    }
}