//! Content-Addressable Store (CAS)
//!
//! Lagrer binærfiler identifisert av SHA-256 hash.
//! Katalogstruktur: `{root}/{hash[0..2]}/{hash[2..4]}/{hash}`
//! Deduplisering er innebygd — identisk innhold gir identisk hash.

use sha2::{Digest, Sha256};
use std::path::{Path, PathBuf};
use tokio::io::AsyncWriteExt;

/// CAS-lagring med filsystem-backend.
#[derive(Clone)]
pub struct CasStore {
    root: PathBuf,
}

/// Resultat fra en CAS-skriveoperasjon.
pub struct StoreResult {
    /// SHA-256 hex-digest (64 tegn).
    pub hash: String,
    /// Antall bytes lagret.
    pub size: u64,
    /// `true` hvis filen allerede fantes (deduplisert).
    pub already_existed: bool,
}

impl CasStore {
    /// Opprett en ny CAS-store med gitt rot-katalog.
    /// Oppretter rot-katalogen hvis den ikke finnes.
    pub async fn new(root: impl Into<PathBuf>) -> std::io::Result<Self> {
        let root = root.into();
        tokio::fs::create_dir_all(&root).await?;
        Ok(Self { root })
    }

    /// Lagre bytes i CAS. Returnerer hash og metadata.
    /// Hvis filen allerede finnes (identisk hash), skrives ingenting — deduplisering.
    pub async fn store(&self, data: &[u8]) -> std::io::Result<StoreResult> {
        let hash = Self::sha256(data);
        let size = data.len() as u64;
        let path = self.path_for(&hash);

        if path.exists() {
            return Ok(StoreResult {
                hash,
                size,
                already_existed: true,
            });
        }

        // Opprett prefix-kataloger
        if let Some(parent) = path.parent() {
            tokio::fs::create_dir_all(parent).await?;
        }

        // Skriv til temp-fil, deretter atomisk rename.
        // Dette hindrer at en halvskrevet fil blir lest av andre prosesser.
        let tmp_path = self.tmp_path(&hash);
        if let Some(parent) = tmp_path.parent() {
            tokio::fs::create_dir_all(parent).await?;
        }

        let mut file = tokio::fs::File::create(&tmp_path).await?;
        file.write_all(data).await?;
        file.flush().await?;
        // Synkroniser til disk for dataintegritet
        file.sync_all().await?;
        drop(file);

        // Atomisk rename — trygt selv ved strømbrudd
        tokio::fs::rename(&tmp_path, &path).await?;

        tracing::info!(hash = %hash, size = size, "Lagret ny fil i CAS");

        Ok(StoreResult {
            hash,
            size,
            already_existed: false,
        })
    }

    /// Sjekk om en hash finnes i CAS.
    pub fn exists(&self, hash: &str) -> bool {
        self.path_for(hash).exists()
    }

    /// Full filbane for en gitt hash.
    /// Struktur: `{root}/{hash[0..2]}/{hash[2..4]}/{hash}`
    pub fn path_for(&self, hash: &str) -> PathBuf {
        let (prefix1, rest) = hash.split_at(2.min(hash.len()));
        let (prefix2, _) = rest.split_at(2.min(rest.len()));
        self.root.join(prefix1).join(prefix2).join(hash)
    }

    /// Beregn SHA-256 hex-digest for gitte bytes.
    pub fn sha256(data: &[u8]) -> String {
        let mut hasher = Sha256::new();
        hasher.update(data);
        hex::encode(hasher.finalize())
    }

    /// Slett en fil fra CAS. Returnerer antall bytes frigitt, eller 0 hvis filen ikke fantes.
    pub async fn delete(&self, hash: &str) -> std::io::Result<u64> {
        let path = self.path_for(hash);
        match tokio::fs::metadata(&path).await {
            Ok(meta) => {
                let size = meta.len();
                tokio::fs::remove_file(&path).await?;
                tracing::info!(hash = %hash, size = size, "Slettet fil fra CAS");
                Ok(size)
            }
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(0),
            Err(e) => Err(e),
        }
    }

    /// Beregn total diskbruk for CAS-katalogen (bytes).
    /// Bruker `du -sb` for ytelse — traverserer filsystemet direkte.
    pub async fn disk_usage_bytes(&self) -> std::io::Result<u64> {
        let output = tokio::process::Command::new("du")
            .args(["-sb", self.root.to_str().unwrap_or(".")])
            .output()
            .await?;
        if !output.status.success() {
            return Err(std::io::Error::new(
                std::io::ErrorKind::Other,
                "du-kommando feilet",
            ));
        }
        let stdout = String::from_utf8_lossy(&output.stdout);
        let bytes: u64 = stdout
            .split_whitespace()
            .next()
            .and_then(|s| s.parse().ok())
            .unwrap_or(0);
        Ok(bytes)
    }

    /// Sjekk diskbruk-prosent for partisjonen CAS ligger på.
    pub async fn disk_usage_percent(&self) -> std::io::Result<f64> {
        let output = tokio::process::Command::new("df")
            .args(["--output=pcent", self.root.to_str().unwrap_or("/")])
            .output()
            .await?;
        if !output.status.success() {
            return Err(std::io::Error::new(
                std::io::ErrorKind::Other,
                "df-kommando feilet",
            ));
        }
        let stdout = String::from_utf8_lossy(&output.stdout);
        // Output: "Use%\n 42%\n"
        let pct: f64 = stdout
            .lines()
            .nth(1)
            .and_then(|line| line.trim().trim_end_matches('%').parse().ok())
            .unwrap_or(0.0);
        Ok(pct)
    }

    /// Rot-katalogen for CAS.
    pub fn root(&self) -> &Path {
        &self.root
    }

    /// Temp-filbane brukt under skriving (unngår korrupte reads).
    fn tmp_path(&self, hash: &str) -> PathBuf {
        self.root.join("tmp").join(format!("{hash}.tmp"))
    }

    /// Slett temp-filer eldre enn `max_age` fra CAS tmp-katalogen.
    /// Returnerer (antall slettet, bytes frigitt).
    pub async fn cleanup_tmp(&self, max_age: std::time::Duration) -> std::io::Result<(usize, u64)> {
        let tmp_dir = self.root.join("tmp");
        if !tmp_dir.exists() {
            return Ok((0, 0));
        }

        let mut deleted = 0usize;
        let mut freed = 0u64;
        let now = std::time::SystemTime::now();

        let mut entries = tokio::fs::read_dir(&tmp_dir).await?;
        while let Some(entry) = entries.next_entry().await? {
            let meta = match entry.metadata().await {
                Ok(m) => m,
                Err(_) => continue,
            };
            if !meta.is_file() {
                continue;
            }
            let modified = match meta.modified() {
                Ok(t) => t,
                Err(_) => continue,
            };
            let age = now.duration_since(modified).unwrap_or_default();
            if age > max_age {
                let size = meta.len();
                if let Ok(()) = tokio::fs::remove_file(entry.path()).await {
                    deleted += 1;
                    freed += size;
                    tracing::debug!(
                        file = %entry.file_name().to_string_lossy(),
                        age_secs = age.as_secs(),
                        size,
                        "Slettet gammel temp-fil"
                    );
                }
            }
        }

        Ok((deleted, freed))
    }
}

/// Start periodisk opprydding av CAS tmp-filer.
/// Kjører hver time, sletter filer eldre enn 1 time.
pub fn start_tmp_cleanup_loop(cas: CasStore) {
    tokio::spawn(async move {
        // Vent 45 sekunder etter oppstart
        tokio::time::sleep(std::time::Duration::from_secs(45)).await;
        tracing::info!("CAS tmp-opprydding startet (intervall: 1t, TTL: 1t)");

        let max_age = std::time::Duration::from_secs(3600); // 1 time
        let interval = std::time::Duration::from_secs(3600); // 1 time

        loop {
            match cas.cleanup_tmp(max_age).await {
                Ok((deleted, freed)) => {
                    if deleted > 0 {
                        tracing::info!(
                            deleted,
                            freed_kb = freed / 1024,
                            "CAS tmp-opprydding: {} filer slettet, {} KB frigitt",
                            deleted,
                            freed / 1024,
                        );
                    }
                }
                Err(e) => {
                    tracing::warn!(error = %e, "CAS tmp-opprydding feilet");
                }
            }
            tokio::time::sleep(interval).await;
        }
    });
}

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

    fn test_root() -> PathBuf {
        PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("target").join("test-cas")
    }

    #[tokio::test]
    async fn store_and_retrieve() {
        let root = test_root().join("store_and_retrieve");
        let _ = tokio::fs::remove_dir_all(&root).await;

        let cas = CasStore::new(&root).await.unwrap();
        let data = b"hello world";
        let result = cas.store(data).await.unwrap();

        // SHA-256 av "hello world"
        assert_eq!(
            result.hash,
            "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9"
        );
        assert_eq!(result.size, 11);
        assert!(!result.already_existed);

        // Filen skal finnes på riktig path
        let path = cas.path_for(&result.hash);
        assert!(path.exists());
        let content = tokio::fs::read(&path).await.unwrap();
        assert_eq!(content, data);

        // Katalogstruktur: b9/4d/{full hash}
        assert!(path.to_string_lossy().contains("/b9/4d/"));

        // Cleanup
        let _ = tokio::fs::remove_dir_all(&root).await;
    }

    #[tokio::test]
    async fn deduplication() {
        let root = test_root().join("deduplication");
        let _ = tokio::fs::remove_dir_all(&root).await;

        let cas = CasStore::new(&root).await.unwrap();
        let data = b"duplicate content";

        let first = cas.store(data).await.unwrap();
        assert!(!first.already_existed);

        let second = cas.store(data).await.unwrap();
        assert!(second.already_existed);
        assert_eq!(first.hash, second.hash);

        let _ = tokio::fs::remove_dir_all(&root).await;
    }

    #[tokio::test]
    async fn exists_check() {
        let root = test_root().join("exists_check");
        let _ = tokio::fs::remove_dir_all(&root).await;

        let cas = CasStore::new(&root).await.unwrap();

        assert!(!cas.exists("nonexistent_hash"));

        let result = cas.store(b"test").await.unwrap();
        assert!(cas.exists(&result.hash));

        let _ = tokio::fs::remove_dir_all(&root).await;
    }

    #[tokio::test]
    async fn different_content_different_hash() {
        let root = test_root().join("different_content");
        let _ = tokio::fs::remove_dir_all(&root).await;

        let cas = CasStore::new(&root).await.unwrap();

        let a = cas.store(b"content A").await.unwrap();
        let b = cas.store(b"content B").await.unwrap();

        assert_ne!(a.hash, b.hash);
        assert!(cas.exists(&a.hash));
        assert!(cas.exists(&b.hash));

        let _ = tokio::fs::remove_dir_all(&root).await;
    }

    #[test]
    fn path_structure() {
        let cas = CasStore {
            root: PathBuf::from("/srv/synops/media/cas"),
        };
        let hash = "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9";
        let path = cas.path_for(hash);
        assert_eq!(
            path,
            PathBuf::from("/srv/synops/media/cas/b9/4d/b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9")
        );
    }
}