use std::path::PathBuf;
use tokio::fs;
use tokio::io::AsyncWriteExt;

use crate::common::errors::{DomainError, Result};

#[derive(Clone)]
pub struct NextcloudChunkedUploadService {
    pub base_dir: PathBuf,
}

impl NextcloudChunkedUploadService {
    pub fn new(base_dir: PathBuf) -> Self {
        Self { base_dir }
    }

    pub fn new_stub() -> Self {
        Self {
            base_dir: PathBuf::from("./storage/.uploads/nextcloud"),
        }
    }

    /// Validate that a path component contains no traversal characters.
    fn validate_path_component(name: &str, label: &str) -> Result<()> {
        if name.is_empty()
            || name.contains('/')
            || name.contains('\\')
            || name.contains("..")
            || name == "."
        {
            return Err(DomainError::validation_error(format!(
                "ChunkedUpload: invalid {}: contains path traversal characters",
                label
            )));
        }
        Ok(())
    }

    /// Build a session directory path and verify it's inside base_dir.
    fn safe_session_dir(&self, user: &str, upload_id: &str) -> Result<PathBuf> {
        Self::validate_path_component(user, "username")?;
        Self::validate_path_component(upload_id, "upload_id")?;
        Ok(self.base_dir.join(user).join(upload_id))
    }

    /// Create a new upload session directory.
    pub async fn create_session(&self, user: &str, upload_id: &str) -> Result<()> {
        let session_dir = self.safe_session_dir(user, upload_id)?;
        fs::create_dir_all(&session_dir)
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
        Ok(())
    }

    /// Resolve and validate the filesystem path for a chunk file.
    ///
    /// Public so the interface layer can stream an HTTP body straight into
    /// the chunk file without copying through the service. The service
    /// retains responsibility for path-component validation; the caller
    /// owns the I/O (open, write, fsync, size enforcement, cleanup on
    /// failure). All three `validate_path_component` calls run before the
    /// path is constructed, so a returned `PathBuf` is always inside
    /// `base_dir/{user}/{upload_id}`.
    pub fn safe_chunk_path(
        &self,
        user: &str,
        upload_id: &str,
        chunk_name: &str,
    ) -> Result<PathBuf> {
        Self::validate_path_component(chunk_name, "chunk_name")?;
        Ok(self.safe_session_dir(user, upload_id)?.join(chunk_name))
    }

    /// Store a chunk in the session directory. Buffers `data` in memory —
    /// use [`safe_chunk_path`](Self::safe_chunk_path) + the
    /// `interfaces/upload_spool::stream_body_to_path` helper to stream the
    /// HTTP body directly to disk and avoid materialising the whole chunk
    /// in RAM.
    pub async fn store_chunk(
        &self,
        user: &str,
        upload_id: &str,
        chunk_name: &str,
        data: &[u8],
    ) -> Result<()> {
        let chunk_path = self.safe_chunk_path(user, upload_id, chunk_name)?;
        let mut file = fs::File::create(&chunk_path)
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
        file.write_all(data)
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
        Ok(())
    }

    /// Assemble all chunks in numeric order into a temp file, computing
    /// the BLAKE3 of the concatenated stream **during** the same read/
    /// write pass (hash-on-write).
    ///
    /// Returns `(temp_path, total_size, blake3_hex)`. The caller passes
    /// the hash to the upload service as `pre_computed_hash` so the
    /// downstream dedup layer never has to re-read the assembled file
    /// to compute it — saving one full file-sized read pass per upload.
    ///
    /// The read/hash/write loop runs inside `spawn_blocking` because
    /// BLAKE3 is CPU-bound and would otherwise starve the Tokio worker
    /// running other connections; synchronous I/O is used inside the
    /// blocking thread because the workload is sequential and the
    /// async reactor overhead would only slow it down. For files larger
    /// than ~10 MB BLAKE3's Rayon mode parallelises across cores —
    /// mirrors what `ChunkedUploadService::complete_upload_inner` does
    /// for the REST chunked path.
    pub async fn assemble(&self, user: &str, upload_id: &str) -> Result<(PathBuf, u64, String)> {
        let session_dir = self.safe_session_dir(user, upload_id)?;
        let mut entries: Vec<String> = Vec::new();

        let mut dir = fs::read_dir(&session_dir)
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;

        while let Some(entry) = dir
            .next_entry()
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?
        {
            let name = entry.file_name().to_string_lossy().to_string();
            if name == ".file" {
                continue; // Skip the assembly marker.
            }
            entries.push(name);
        }

        // Sort chunks numerically (Nextcloud sends them as "00001", "00002", ...).
        entries.sort();

        let temp_path = session_dir.join(".assembled");
        let chunk_paths: Vec<PathBuf> = entries.iter().map(|n| session_dir.join(n)).collect();
        let assembled_for_blocking = temp_path.clone();

        // Read/hash/write loop runs synchronously on the blocking pool.
        // BLAKE3 is computed in the same pass that copies bytes from chunk
        // files into the assembled file — no second read after the fact.
        let (total_size, hash) =
            tokio::task::spawn_blocking(move || -> std::io::Result<(u64, String)> {
                use std::io::{BufWriter as StdBufWriter, Read, Write};

                let raw_output = std::fs::OpenOptions::new()
                    .create(true)
                    .write(true)
                    .truncate(true)
                    .open(&assembled_for_blocking)?;

                // 512 KB write buffer — 8× fewer syscalls than 64 KB.
                let mut output = StdBufWriter::with_capacity(524_288, raw_output);
                let mut hasher = blake3::Hasher::new();
                let mut buf = vec![0u8; 524_288];
                let mut total: u64 = 0;

                // Files >10 MB benefit from BLAKE3's multi-threaded mode.
                // The threshold matches the REST chunked path's heuristic.
                const RAYON_THRESHOLD_PER_FRAME: usize = 128 * 1024;

                for chunk_path in &chunk_paths {
                    let mut chunk_file = std::fs::File::open(chunk_path)?;
                    loop {
                        let n = chunk_file.read(&mut buf)?;
                        if n == 0 {
                            break;
                        }
                        if n >= RAYON_THRESHOLD_PER_FRAME {
                            hasher.update_rayon(&buf[..n]);
                        } else {
                            hasher.update(&buf[..n]);
                        }
                        output.write_all(&buf[..n])?;
                        total += n as u64;
                    }
                }

                output.flush()?;
                // ── Durability boundary ─────────────────────────────────
                // sync_all is the actual fsync; without it, a power loss
                // before the kernel writeback timer (~5 s) loses
                // acknowledged data. Pull the inner File out of the
                // BufWriter so we can sync the underlying handle —
                // dropping the BufWriter wouldn't trigger fsync. macOS
                // caveat: fsync there flushes to the disk controller
                // only; true durability needs F_FULLFSYNC, not exposed
                // by std.
                let raw_output = output
                    .into_inner()
                    .map_err(|e| std::io::Error::other(format!("into_inner: {e}")))?;
                raw_output.sync_all()?;

                Ok((total, hasher.finalize().to_hex().to_string()))
            })
            .await
            .map_err(|e| {
                DomainError::internal_error("ChunkedUpload", format!("assemble task: {e}"))
            })?
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;

        Ok((temp_path, total_size, hash))
    }

    /// Delete the upload session directory.
    pub async fn cleanup(&self, user: &str, upload_id: &str) -> Result<()> {
        let session_dir = self.safe_session_dir(user, upload_id)?;
        if session_dir.exists() {
            fs::remove_dir_all(&session_dir)
                .await
                .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
        }
        Ok(())
    }

    /// Check if a session directory exists.
    pub async fn session_exists(&self, user: &str, upload_id: &str) -> bool {
        self.safe_session_dir(user, upload_id)
            .map(|p| p.exists())
            .unwrap_or(false)
    }

    /// Enumerate the chunks already stored in a session, plus the
    /// session directory's own mtime. Used by the PROPFIND handler
    /// to drive NextCloud's resume-upload flow — the Android client
    /// (and several mobile clients) issue PROPFIND on the session
    /// URL to discover which chunks are already uploaded, then only
    /// PUT the missing ones.
    ///
    /// Returns `None` when the session directory doesn't exist
    /// (handler maps to 404). The `.file` and `.assembled` markers
    /// are filtered out — they're internal bookkeeping, not real
    /// chunks the client uploaded.
    pub async fn list_chunks(&self, user: &str, upload_id: &str) -> Result<Option<SessionListing>> {
        let session_dir = self.safe_session_dir(user, upload_id)?;
        if !session_dir.exists() {
            return Ok(None);
        }

        let session_meta = fs::metadata(&session_dir)
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
        let session_mtime = session_meta
            .modified()
            .ok()
            .and_then(|t| t.duration_since(std::time::UNIX_EPOCH).ok())
            .map(|d| d.as_secs())
            .unwrap_or(0);

        let mut chunks: Vec<ChunkInfo> = Vec::new();
        let mut dir = fs::read_dir(&session_dir)
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
        while let Some(entry) = dir
            .next_entry()
            .await
            .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?
        {
            let name = entry.file_name().to_string_lossy().to_string();
            // Filter internal markers — `.file` is the NC-protocol
            // assembly trigger target (it never reaches the disk
            // because MOVE redirects it), `.assembled` is our own
            // staging file from `assemble()`. Surfacing either to
            // the client would confuse its chunk-count check.
            if name == ".file" || name == ".assembled" {
                continue;
            }
            let meta = entry
                .metadata()
                .await
                .map_err(|e| DomainError::internal_error("ChunkedUpload", e.to_string()))?;
            let size = meta.len();
            let mtime = meta
                .modified()
                .ok()
                .and_then(|t| t.duration_since(std::time::UNIX_EPOCH).ok())
                .map(|d| d.as_secs())
                .unwrap_or(0);
            chunks.push(ChunkInfo { name, size, mtime });
        }
        // Sort by chunk name so PROPFIND output is deterministic
        // (clients don't strictly require this, but reproducible
        // listings make debugging from logs much easier).
        chunks.sort_by(|a, b| a.name.cmp(&b.name));

        Ok(Some(SessionListing {
            session_mtime,
            chunks,
        }))
    }
}

/// One chunk file inside an upload session.
#[derive(Debug, Clone)]
pub struct ChunkInfo {
    pub name: String,
    pub size: u64,
    pub mtime: u64,
}

/// What `list_chunks` returns: the session's own mtime (for the
/// collection's `<d:getlastmodified>`) plus the list of stored
/// chunks.
#[derive(Debug, Clone)]
pub struct SessionListing {
    pub session_mtime: u64,
    pub chunks: Vec<ChunkInfo>,
}

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

    fn test_service() -> (NextcloudChunkedUploadService, tempfile::TempDir) {
        let dir = tempfile::tempdir().expect("create temp dir");
        let svc = NextcloudChunkedUploadService::new(dir.path().to_path_buf());
        (svc, dir)
    }

    #[tokio::test]
    async fn test_create_session() {
        let (svc, _dir) = test_service();
        svc.create_session("alice", "upload-001").await.unwrap();
        assert!(svc.session_exists("alice", "upload-001").await);
    }

    #[tokio::test]
    async fn test_session_not_exists_before_create() {
        let (svc, _dir) = test_service();
        assert!(!svc.session_exists("alice", "upload-999").await);
    }

    #[tokio::test]
    async fn test_store_and_assemble_chunks() {
        let (svc, _dir) = test_service();
        svc.create_session("alice", "upload-002").await.unwrap();

        svc.store_chunk("alice", "upload-002", "00001", b"Hello, ")
            .await
            .unwrap();
        svc.store_chunk("alice", "upload-002", "00002", b"World!")
            .await
            .unwrap();

        let (temp_path, size, hash) = svc.assemble("alice", "upload-002").await.unwrap();
        let assembled = fs::read(&temp_path).await.unwrap();
        assert_eq!(assembled, b"Hello, World!");
        assert_eq!(size, 13);
        // BLAKE3("Hello, World!") — proves hash-on-write happens during
        // the assemble pass, not via a re-read.
        assert_eq!(
            hash,
            "288a86a79f20a3d6dccdca7713beaed178798296bdfa7913fa2a62d9727bf8f8"
        );
    }

    #[tokio::test]
    async fn test_assemble_chunks_in_sorted_order() {
        let (svc, _dir) = test_service();
        svc.create_session("alice", "upload-003").await.unwrap();

        // Store out of order.
        svc.store_chunk("alice", "upload-003", "00003", b"C")
            .await
            .unwrap();
        svc.store_chunk("alice", "upload-003", "00001", b"A")
            .await
            .unwrap();
        svc.store_chunk("alice", "upload-003", "00002", b"B")
            .await
            .unwrap();

        let (temp_path, size, hash) = svc.assemble("alice", "upload-003").await.unwrap();
        let assembled = fs::read(&temp_path).await.unwrap();
        assert_eq!(assembled, b"ABC");
        assert_eq!(size, 3);
        // BLAKE3("ABC") — confirms sort happened (chunks were stored in
        // order 3,1,2 but the hash matches "ABC", not "CAB" or "BAC").
        assert_eq!(
            hash,
            "d1717274597cf0289694f75d96d444b992a096f1afd8e7bbfa6ebb1d360fedfc"
        );
    }

    #[tokio::test]
    async fn test_cleanup_removes_session() {
        let (svc, _dir) = test_service();
        svc.create_session("alice", "upload-004").await.unwrap();
        assert!(svc.session_exists("alice", "upload-004").await);

        svc.cleanup("alice", "upload-004").await.unwrap();
        assert!(!svc.session_exists("alice", "upload-004").await);
    }

    #[tokio::test]
    async fn test_cleanup_nonexistent_session_is_ok() {
        let (svc, _dir) = test_service();
        // Should not error.
        svc.cleanup("alice", "nonexistent").await.unwrap();
    }
}