/// Secrets layer for bucket credentials.
///
/// Credentials never appear in `lakehouse.toml`. Each bucket entry has an
/// opaque `secret_ref` handle, resolved at startup by a `SecretsProvider`.
///
/// MVP ships `FileSecretsProvider` — reads a TOML file at a path given by
/// `LAKEHOUSE_SECRETS` env var, defaulting to `/etc/lakehouse/secrets.toml`.
/// The file should be root-owned, mode 0600, never in git.
///
/// Future providers (Vault, SOPS, OS keyring) implement the same trait.

use async_trait::async_trait;
use serde::Deserialize;
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::Arc;

#[derive(Debug, Clone)]
pub struct BucketCredentials {
    pub access_key: String,
    pub secret_key: String,
}

// Redact credentials when debug-printing — NEVER let these end up in logs.
impl BucketCredentials {
    pub fn redacted(&self) -> String {
        let prefix: String = self.access_key.chars().take(4).collect();
        format!("access_key={}... (redacted)", prefix)
    }
}

#[async_trait]
pub trait SecretsProvider: Send + Sync {
    /// Resolve a handle to credentials. Returns Err if the handle is unknown.
    async fn resolve(&self, handle: &str) -> Result<BucketCredentials, String>;

    /// List known handles (for diagnostics only, never values).
    async fn list_handles(&self) -> Vec<String>;
}

#[derive(Debug, Deserialize)]
struct RawSecretEntry {
    access_key: String,
    secret_key: String,
}

/// File-backed secrets provider.
pub struct FileSecretsProvider {
    path: PathBuf,
    cache: tokio::sync::RwLock<HashMap<String, BucketCredentials>>,
}

impl FileSecretsProvider {
    pub fn new(path: impl Into<PathBuf>) -> Self {
        Self {
            path: path.into(),
            cache: tokio::sync::RwLock::new(HashMap::new()),
        }
    }

    /// Default path: env var `LAKEHOUSE_SECRETS` or `/etc/lakehouse/secrets.toml`.
    pub fn from_env() -> Self {
        let path = std::env::var("LAKEHOUSE_SECRETS")
            .unwrap_or_else(|_| "/etc/lakehouse/secrets.toml".to_string());
        Self::new(path)
    }

    /// Arc wrapper for convenient injection.
    pub fn shared(path: impl Into<PathBuf>) -> Arc<dyn SecretsProvider> {
        Arc::new(Self::new(path))
    }

    /// Load and populate the cache. Call once at startup.
    pub async fn load(&self) -> Result<usize, String> {
        if !self.path.exists() {
            tracing::info!(
                "secrets file {} not present — running with zero credentials configured",
                self.path.display()
            );
            return Ok(0);
        }
        check_permissions(&self.path)?;
        let content = std::fs::read_to_string(&self.path)
            .map_err(|e| format!("read secrets file: {e}"))?;
        let raw: HashMap<String, RawSecretEntry> = toml::from_str(&content)
            .map_err(|e| format!("parse secrets file: {e}"))?;

        let mut cache = self.cache.write().await;
        for (handle, entry) in raw {
            cache.insert(handle.clone(), BucketCredentials {
                access_key: entry.access_key,
                secret_key: entry.secret_key,
            });
        }
        let count = cache.len();
        tracing::info!("secrets: loaded {count} handles from {}", self.path.display());
        Ok(count)
    }
}

#[async_trait]
impl SecretsProvider for FileSecretsProvider {
    async fn resolve(&self, handle: &str) -> Result<BucketCredentials, String> {
        let cache = self.cache.read().await;
        cache
            .get(handle)
            .cloned()
            .ok_or_else(|| format!("secret handle not found: {handle}"))
    }

    async fn list_handles(&self) -> Vec<String> {
        self.cache.read().await.keys().cloned().collect()
    }
}

/// Reject world-readable secrets files. Fail closed.
fn check_permissions(path: &Path) -> Result<(), String> {
    #[cfg(unix)]
    {
        use std::os::unix::fs::PermissionsExt;
        let meta = std::fs::metadata(path)
            .map_err(|e| format!("stat secrets file: {e}"))?;
        let mode = meta.permissions().mode() & 0o777;
        if mode & 0o044 != 0 {
            return Err(format!(
                "secrets file {} is group/world-readable (mode {:o}); chmod 600 to proceed",
                path.display(), mode
            ));
        }
    }
    let _ = path;
    Ok(())
}

/// A zero-handles provider for tests / purely-local setups.
pub struct EmptySecretsProvider;

#[async_trait]
impl SecretsProvider for EmptySecretsProvider {
    async fn resolve(&self, handle: &str) -> Result<BucketCredentials, String> {
        Err(format!("no secrets provider configured (wanted handle '{handle}')"))
    }
    async fn list_handles(&self) -> Vec<String> { Vec::new() }
}