use anyhow::Result;
use chrono::{DateTime, Utc};
use http_body_util::BodyExt;
use hyper::body::Incoming;
use md5::{Digest, Md5};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use tokio::fs;
use tokio::io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt, BufWriter};
use uuid::Uuid;

use crate::s3_error::S3Error;

// ============================
// Result types
// ============================

pub struct PutResult {
    pub size: u64,
    pub md5: String,
}

pub struct GetResult {
    pub key: String,
    pub size: u64,
    pub last_modified: DateTime<Utc>,
    pub md5: String,
    pub metadata: HashMap<String, String>,
    pub body: tokio::fs::File,
    pub content_length: u64,
}

pub struct HeadResult {
    pub key: String,
    pub size: u64,
    pub last_modified: DateTime<Utc>,
    pub md5: String,
    pub metadata: HashMap<String, String>,
}

pub struct CopyResult {
    pub size: u64,
    pub md5: String,
    pub last_modified: DateTime<Utc>,
}

pub struct ListObjectEntry {
    pub key: String,
    pub size: u64,
    pub last_modified: DateTime<Utc>,
    pub md5: String,
}

pub struct ListObjectsResult {
    pub contents: Vec<ListObjectEntry>,
    pub common_prefixes: Vec<String>,
    pub is_truncated: bool,
    pub next_continuation_token: Option<String>,
    pub prefix: String,
    pub delimiter: String,
    pub max_keys: usize,
}

pub struct BucketInfo {
    pub name: String,
    pub creation_date: DateTime<Utc>,
}

pub struct MultipartUploadInfo {
    pub upload_id: String,
    pub bucket: String,
    pub key: String,
    pub initiated: DateTime<Utc>,
}

pub struct CompleteMultipartResult {
    pub etag: String,
    pub size: u64,
}

// ============================
// Multipart metadata (disk format, compatible with TS)
// ============================

#[derive(Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct MultipartMetadata {
    upload_id: String,
    bucket: String,
    key: String,
    initiated: String,
    metadata: HashMap<String, String>,
    parts: Vec<PartMetadata>,
}

#[derive(Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct PartMetadata {
    part_number: u32,
    etag: String,
    size: u64,
    last_modified: String,
}

// ============================
// FileStore
// ============================

pub struct FileStore {
    root_dir: PathBuf,
}

impl FileStore {
    pub fn new(root_dir: PathBuf) -> Self {
        Self { root_dir }
    }

    pub async fn initialize(&self) -> Result<()> {
        fs::create_dir_all(&self.root_dir).await?;
        Ok(())
    }

    pub async fn reset(&self) -> Result<()> {
        if self.root_dir.exists() {
            fs::remove_dir_all(&self.root_dir).await?;
        }
        fs::create_dir_all(&self.root_dir).await?;
        Ok(())
    }

    // ============================
    // Bucket operations
    // ============================

    pub async fn list_buckets(&self) -> Result<Vec<BucketInfo>> {
        let mut buckets = Vec::new();
        let mut entries = fs::read_dir(&self.root_dir).await?;

        while let Some(entry) = entries.next_entry().await? {
            let meta = entry.metadata().await?;
            if meta.is_dir() {
                let name = entry.file_name().to_string_lossy().to_string();
                // Skip hidden dirs like .multipart
                if name.starts_with('.') {
                    continue;
                }
                let creation_date: DateTime<Utc> = meta
                    .created()
                    .unwrap_or(meta.modified().unwrap_or(std::time::SystemTime::UNIX_EPOCH))
                    .into();
                buckets.push(BucketInfo {
                    name,
                    creation_date,
                });
            }
        }

        buckets.sort_by(|a, b| a.name.cmp(&b.name));
        Ok(buckets)
    }

    pub async fn bucket_exists(&self, bucket: &str) -> bool {
        self.root_dir.join(bucket).is_dir()
    }

    pub async fn create_bucket(&self, bucket: &str) -> Result<()> {
        let bucket_path = self.root_dir.join(bucket);
        fs::create_dir_all(&bucket_path).await?;
        Ok(())
    }

    pub async fn delete_bucket(&self, bucket: &str) -> Result<()> {
        let bucket_path = self.root_dir.join(bucket);

        if !bucket_path.is_dir() {
            return Err(S3Error::no_such_bucket().into());
        }

        // Check if bucket is empty (ignore hidden files)
        let mut entries = fs::read_dir(&bucket_path).await?;
        while let Some(_entry) = entries.next_entry().await? {
            return Err(S3Error::bucket_not_empty().into());
        }

        fs::remove_dir_all(&bucket_path).await?;
        Ok(())
    }

    // ============================
    // Object operations
    // ============================

    pub async fn put_object(
        &self,
        bucket: &str,
        key: &str,
        body: Incoming,
        metadata: HashMap<String, String>,
    ) -> Result<PutResult> {
        if !self.bucket_exists(bucket).await {
            return Err(S3Error::no_such_bucket().into());
        }

        let object_path = self.object_path(bucket, key);
        if let Some(parent) = object_path.parent() {
            fs::create_dir_all(parent).await?;
        }

        let file = fs::File::create(&object_path).await?;
        let mut writer = BufWriter::new(file);
        let mut hasher = Md5::new();
        let mut total_size: u64 = 0;

        // Stream body frames directly to file
        let mut body = body;
        loop {
            match body.frame().await {
                Some(Ok(frame)) => {
                    if let Ok(data) = frame.into_data() {
                        hasher.update(&data);
                        total_size += data.len() as u64;
                        writer.write_all(&data).await?;
                    }
                }
                Some(Err(e)) => {
                    return Err(anyhow::anyhow!("Body read error: {}", e));
                }
                None => break,
            }
        }

        writer.flush().await?;
        drop(writer);

        let md5_hex = format!("{:x}", hasher.finalize());

        // Write MD5 sidecar
        let md5_path = format!("{}.md5", object_path.display());
        fs::write(&md5_path, &md5_hex).await?;

        // Write metadata sidecar
        let metadata_path = format!("{}.metadata.json", object_path.display());
        let metadata_json = serde_json::to_string_pretty(&metadata)?;
        fs::write(&metadata_path, metadata_json).await?;

        Ok(PutResult {
            size: total_size,
            md5: md5_hex,
        })
    }

    pub async fn put_object_bytes(
        &self,
        bucket: &str,
        key: &str,
        data: &[u8],
        metadata: HashMap<String, String>,
    ) -> Result<PutResult> {
        if !self.bucket_exists(bucket).await {
            return Err(S3Error::no_such_bucket().into());
        }

        let object_path = self.object_path(bucket, key);
        if let Some(parent) = object_path.parent() {
            fs::create_dir_all(parent).await?;
        }

        let mut hasher = Md5::new();
        hasher.update(data);
        let md5_hex = format!("{:x}", hasher.finalize());

        fs::write(&object_path, data).await?;

        // Write MD5 sidecar
        let md5_path = format!("{}.md5", object_path.display());
        fs::write(&md5_path, &md5_hex).await?;

        // Write metadata sidecar
        let metadata_path = format!("{}.metadata.json", object_path.display());
        let metadata_json = serde_json::to_string_pretty(&metadata)?;
        fs::write(&metadata_path, metadata_json).await?;

        Ok(PutResult {
            size: data.len() as u64,
            md5: md5_hex,
        })
    }

    pub async fn get_object(
        &self,
        bucket: &str,
        key: &str,
        range: Option<(u64, u64)>,
    ) -> Result<GetResult> {
        let object_path = self.object_path(bucket, key);

        if !object_path.exists() {
            return Err(S3Error::no_such_key().into());
        }

        let file_meta = fs::metadata(&object_path).await?;
        let size = file_meta.len();
        let last_modified: DateTime<Utc> = file_meta.modified()?.into();

        let md5 = self.read_md5(&object_path).await;
        let metadata = self.read_metadata(&object_path).await;

        let mut file = fs::File::open(&object_path).await?;

        let content_length = if let Some((start, end)) = range {
            file.seek(std::io::SeekFrom::Start(start)).await?;
            end - start + 1
        } else {
            size
        };

        Ok(GetResult {
            key: key.to_string(),
            size,
            last_modified,
            md5,
            metadata,
            body: file,
            content_length,
        })
    }

    pub async fn head_object(&self, bucket: &str, key: &str) -> Result<HeadResult> {
        let object_path = self.object_path(bucket, key);

        if !object_path.exists() {
            return Err(S3Error::no_such_key().into());
        }

        // Only stat the file, don't open it
        let file_meta = fs::metadata(&object_path).await?;
        let size = file_meta.len();
        let last_modified: DateTime<Utc> = file_meta.modified()?.into();

        let md5 = self.read_md5(&object_path).await;
        let metadata = self.read_metadata(&object_path).await;

        Ok(HeadResult {
            key: key.to_string(),
            size,
            last_modified,
            md5,
            metadata,
        })
    }

    pub async fn delete_object(&self, bucket: &str, key: &str) -> Result<()> {
        let object_path = self.object_path(bucket, key);
        let md5_path = format!("{}.md5", object_path.display());
        let metadata_path = format!("{}.metadata.json", object_path.display());

        // S3 doesn't error if object doesn't exist
        let _ = fs::remove_file(&object_path).await;
        let _ = fs::remove_file(&md5_path).await;
        let _ = fs::remove_file(&metadata_path).await;

        // Clean up empty parent directories up to bucket level
        let bucket_path = self.root_dir.join(bucket);
        let mut current = object_path.parent().map(|p| p.to_path_buf());
        while let Some(dir) = current {
            if dir == bucket_path {
                break;
            }
            if fs::read_dir(&dir).await.is_ok() {
                let mut entries = fs::read_dir(&dir).await?;
                if entries.next_entry().await?.is_none() {
                    let _ = fs::remove_dir(&dir).await;
                } else {
                    break;
                }
            }
            current = dir.parent().map(|p| p.to_path_buf());
        }

        Ok(())
    }

    pub async fn copy_object(
        &self,
        src_bucket: &str,
        src_key: &str,
        dest_bucket: &str,
        dest_key: &str,
        metadata_directive: &str,
        new_metadata: Option<HashMap<String, String>>,
    ) -> Result<CopyResult> {
        let src_path = self.object_path(src_bucket, src_key);
        let dest_path = self.object_path(dest_bucket, dest_key);

        if !src_path.exists() {
            return Err(S3Error::no_such_key().into());
        }

        if !self.bucket_exists(dest_bucket).await {
            return Err(S3Error::no_such_bucket().into());
        }

        if let Some(parent) = dest_path.parent() {
            fs::create_dir_all(parent).await?;
        }

        // Copy object file
        fs::copy(&src_path, &dest_path).await?;

        // Handle metadata
        if metadata_directive == "COPY" {
            let src_meta_path = format!("{}.metadata.json", src_path.display());
            let dest_meta_path = format!("{}.metadata.json", dest_path.display());
            let _ = fs::copy(&src_meta_path, &dest_meta_path).await;
        } else if let Some(meta) = new_metadata {
            let dest_meta_path = format!("{}.metadata.json", dest_path.display());
            let json = serde_json::to_string_pretty(&meta)?;
            fs::write(&dest_meta_path, json).await?;
        }

        // Copy MD5
        let src_md5_path = format!("{}.md5", src_path.display());
        let dest_md5_path = format!("{}.md5", dest_path.display());
        let _ = fs::copy(&src_md5_path, &dest_md5_path).await;

        let file_meta = fs::metadata(&dest_path).await?;
        let md5 = self.read_md5(&dest_path).await;
        let last_modified: DateTime<Utc> = file_meta.modified()?.into();

        Ok(CopyResult {
            size: file_meta.len(),
            md5,
            last_modified,
        })
    }

    pub async fn list_objects(
        &self,
        bucket: &str,
        prefix: &str,
        delimiter: &str,
        max_keys: usize,
        continuation_token: Option<&str>,
    ) -> Result<ListObjectsResult> {
        let bucket_path = self.root_dir.join(bucket);

        if !bucket_path.is_dir() {
            return Err(S3Error::no_such_bucket().into());
        }

        // Collect all object keys recursively
        let mut keys = Vec::new();
        self.collect_keys(&bucket_path, &bucket_path, &mut keys)
            .await?;

        // Apply prefix filter
        if !prefix.is_empty() {
            keys.retain(|k| k.starts_with(prefix));
        }

        keys.sort();

        // Handle continuation token
        if let Some(token) = continuation_token {
            if let Some(pos) = keys.iter().position(|k| k.as_str() > token) {
                keys = keys[pos..].to_vec();
            } else {
                keys.clear();
            }
        }

        // Handle delimiter and pagination
        let mut common_prefixes: Vec<String> = Vec::new();
        let mut common_prefix_set = std::collections::HashSet::new();
        let mut contents: Vec<ListObjectEntry> = Vec::new();
        let mut is_truncated = false;

        for key in &keys {
            if !delimiter.is_empty() {
                let remaining = &key[prefix.len()..];
                if let Some(delim_idx) = remaining.find(delimiter) {
                    let cp = format!(
                        "{}{}",
                        prefix,
                        &remaining[..delim_idx + delimiter.len()]
                    );
                    if common_prefix_set.insert(cp.clone()) {
                        common_prefixes.push(cp);
                    }
                    continue;
                }
            }

            if contents.len() >= max_keys {
                is_truncated = true;
                break;
            }

            let object_path = self.object_path(bucket, key);
            if let Ok(meta) = fs::metadata(&object_path).await {
                let md5 = self.read_md5(&object_path).await;
                let last_modified: DateTime<Utc> = meta.modified().unwrap_or(std::time::SystemTime::UNIX_EPOCH).into();
                contents.push(ListObjectEntry {
                    key: key.clone(),
                    size: meta.len(),
                    last_modified,
                    md5,
                });
            }
        }

        let next_continuation_token = if is_truncated {
            contents.last().map(|e| e.key.clone())
        } else {
            None
        };

        common_prefixes.sort();

        Ok(ListObjectsResult {
            contents,
            common_prefixes,
            is_truncated,
            next_continuation_token,
            prefix: prefix.to_string(),
            delimiter: delimiter.to_string(),
            max_keys,
        })
    }

    // ============================
    // Multipart operations
    // ============================

    fn multipart_dir(&self) -> PathBuf {
        self.root_dir.join(".multipart")
    }

    pub async fn initiate_multipart(
        &self,
        bucket: &str,
        key: &str,
        metadata: HashMap<String, String>,
    ) -> Result<String> {
        let upload_id = Uuid::new_v4().to_string().replace('-', "");
        let upload_dir = self.multipart_dir().join(&upload_id);
        fs::create_dir_all(&upload_dir).await?;

        let meta = MultipartMetadata {
            upload_id: upload_id.clone(),
            bucket: bucket.to_string(),
            key: key.to_string(),
            initiated: Utc::now().to_rfc3339(),
            metadata,
            parts: Vec::new(),
        };

        let meta_path = upload_dir.join("metadata.json");
        let json = serde_json::to_string_pretty(&meta)?;
        fs::write(&meta_path, json).await?;

        Ok(upload_id)
    }

    pub async fn upload_part(
        &self,
        upload_id: &str,
        part_number: u32,
        body: Incoming,
    ) -> Result<(String, u64)> {
        let upload_dir = self.multipart_dir().join(upload_id);
        if !upload_dir.is_dir() {
            return Err(S3Error::no_such_upload().into());
        }

        let part_path = upload_dir.join(format!("part-{}", part_number));
        let file = fs::File::create(&part_path).await?;
        let mut writer = BufWriter::new(file);
        let mut hasher = Md5::new();
        let mut size: u64 = 0;

        let mut body = body;
        loop {
            match body.frame().await {
                Some(Ok(frame)) => {
                    if let Ok(data) = frame.into_data() {
                        hasher.update(&data);
                        size += data.len() as u64;
                        writer.write_all(&data).await?;
                    }
                }
                Some(Err(e)) => {
                    return Err(anyhow::anyhow!("Body read error: {}", e));
                }
                None => break,
            }
        }

        writer.flush().await?;
        drop(writer);

        let etag = format!("{:x}", hasher.finalize());

        // Update metadata
        self.update_multipart_metadata(upload_id, part_number, &etag, size)
            .await?;

        Ok((etag, size))
    }

    async fn update_multipart_metadata(
        &self,
        upload_id: &str,
        part_number: u32,
        etag: &str,
        size: u64,
    ) -> Result<()> {
        let meta_path = self.multipart_dir().join(upload_id).join("metadata.json");
        let content = fs::read_to_string(&meta_path).await?;
        let mut meta: MultipartMetadata = serde_json::from_str(&content)?;

        // Remove existing part with same number
        meta.parts.retain(|p| p.part_number != part_number);

        meta.parts.push(PartMetadata {
            part_number,
            etag: etag.to_string(),
            size,
            last_modified: Utc::now().to_rfc3339(),
        });

        meta.parts.sort_by_key(|p| p.part_number);

        let json = serde_json::to_string_pretty(&meta)?;
        fs::write(&meta_path, json).await?;

        Ok(())
    }

    pub async fn complete_multipart(
        &self,
        upload_id: &str,
        parts: &[(u32, String)],
    ) -> Result<CompleteMultipartResult> {
        let upload_dir = self.multipart_dir().join(upload_id);
        if !upload_dir.is_dir() {
            return Err(S3Error::no_such_upload().into());
        }

        // Read metadata to get bucket/key
        let meta_path = upload_dir.join("metadata.json");
        let content = fs::read_to_string(&meta_path).await?;
        let meta: MultipartMetadata = serde_json::from_str(&content)?;

        let object_path = self.object_path(&meta.bucket, &meta.key);
        if let Some(parent) = object_path.parent() {
            fs::create_dir_all(parent).await?;
        }

        // Concatenate parts into final object, stream each part
        let dest_file = fs::File::create(&object_path).await?;
        let mut writer = BufWriter::new(dest_file);
        let mut hasher = Md5::new();
        let mut total_size: u64 = 0;

        for (part_number, _etag) in parts {
            let part_path = upload_dir.join(format!("part-{}", part_number));
            if !part_path.exists() {
                return Err(anyhow::anyhow!("Part {} not found", part_number));
            }

            let mut part_file = fs::File::open(&part_path).await?;
            let mut buf = vec![0u8; 64 * 1024]; // 64KB buffer
            loop {
                let n = part_file.read(&mut buf).await?;
                if n == 0 {
                    break;
                }
                hasher.update(&buf[..n]);
                writer.write_all(&buf[..n]).await?;
                total_size += n as u64;
            }
        }

        writer.flush().await?;
        drop(writer);

        let etag = format!("{:x}", hasher.finalize());

        // Write MD5 sidecar
        let md5_path = format!("{}.md5", object_path.display());
        fs::write(&md5_path, &etag).await?;

        // Write metadata sidecar
        let metadata_path = format!("{}.metadata.json", object_path.display());
        let metadata_json = serde_json::to_string_pretty(&meta.metadata)?;
        fs::write(&metadata_path, metadata_json).await?;

        // Clean up multipart directory
        let _ = fs::remove_dir_all(&upload_dir).await;

        Ok(CompleteMultipartResult {
            etag,
            size: total_size,
        })
    }

    pub async fn abort_multipart(&self, upload_id: &str) -> Result<()> {
        let upload_dir = self.multipart_dir().join(upload_id);
        if !upload_dir.is_dir() {
            return Err(S3Error::no_such_upload().into());
        }
        fs::remove_dir_all(&upload_dir).await?;
        Ok(())
    }

    pub async fn list_multipart_uploads(
        &self,
        bucket: &str,
    ) -> Result<Vec<MultipartUploadInfo>> {
        let multipart_dir = self.multipart_dir();
        if !multipart_dir.is_dir() {
            return Ok(Vec::new());
        }

        let mut uploads = Vec::new();
        let mut entries = fs::read_dir(&multipart_dir).await?;

        while let Some(entry) = entries.next_entry().await? {
            if !entry.metadata().await?.is_dir() {
                continue;
            }

            let meta_path = entry.path().join("metadata.json");
            if let Ok(content) = fs::read_to_string(&meta_path).await {
                if let Ok(meta) = serde_json::from_str::<MultipartMetadata>(&content) {
                    if meta.bucket == bucket {
                        let initiated = DateTime::parse_from_rfc3339(&meta.initiated)
                            .map(|dt| dt.with_timezone(&Utc))
                            .unwrap_or_else(|_| Utc::now());

                        uploads.push(MultipartUploadInfo {
                            upload_id: meta.upload_id,
                            bucket: meta.bucket,
                            key: meta.key,
                            initiated,
                        });
                    }
                }
            }
        }

        Ok(uploads)
    }

    // ============================
    // Helpers
    // ============================

    fn object_path(&self, bucket: &str, key: &str) -> PathBuf {
        let encoded = encode_key(key);
        self.root_dir
            .join(bucket)
            .join(format!("{}._S3_object", encoded))
    }

    async fn read_md5(&self, object_path: &Path) -> String {
        let md5_path = format!("{}.md5", object_path.display());
        match fs::read_to_string(&md5_path).await {
            Ok(s) => s.trim().to_string(),
            Err(_) => {
                // Calculate MD5 if sidecar missing
                match self.calculate_md5(object_path).await {
                    Ok(hash) => {
                        let _ = fs::write(&md5_path, &hash).await;
                        hash
                    }
                    Err(_) => String::new(),
                }
            }
        }
    }

    async fn calculate_md5(&self, path: &Path) -> Result<String> {
        let mut file = fs::File::open(path).await?;
        let mut hasher = Md5::new();
        let mut buf = vec![0u8; 64 * 1024];
        loop {
            let n = file.read(&mut buf).await?;
            if n == 0 {
                break;
            }
            hasher.update(&buf[..n]);
        }
        Ok(format!("{:x}", hasher.finalize()))
    }

    async fn read_metadata(&self, object_path: &Path) -> HashMap<String, String> {
        let meta_path = format!("{}.metadata.json", object_path.display());
        match fs::read_to_string(&meta_path).await {
            Ok(s) => serde_json::from_str(&s).unwrap_or_default(),
            Err(_) => HashMap::new(),
        }
    }

    fn collect_keys<'a>(
        &'a self,
        bucket_path: &'a Path,
        dir: &'a Path,
        keys: &'a mut Vec<String>,
    ) -> std::pin::Pin<Box<dyn std::future::Future<Output = Result<()>> + Send + 'a>> {
        Box::pin(async move {
            let mut entries = match fs::read_dir(dir).await {
                Ok(e) => e,
                Err(_) => return Ok(()),
            };

            while let Some(entry) = entries.next_entry().await? {
                let meta = entry.metadata().await?;
                let name = entry.file_name().to_string_lossy().to_string();

                if meta.is_dir() {
                    self.collect_keys(bucket_path, &entry.path(), keys).await?;
                } else if name.ends_with("._S3_object")
                    && !name.ends_with(".metadata.json")
                    && !name.ends_with(".md5")
                {
                    let relative = entry
                        .path()
                        .strip_prefix(bucket_path)
                        .unwrap_or(Path::new(""))
                        .to_string_lossy()
                        .to_string();
                    let key = decode_key(relative.trim_end_matches("._S3_object"));
                    keys.push(key);
                }
            }

            Ok(())
        })
    }
}

// ============================
// Key encoding (identity on Linux)
// ============================

fn encode_key(key: &str) -> String {
    if cfg!(windows) {
        key.chars()
            .map(|c| match c {
                '<' | '>' | ':' | '"' | '\\' | '|' | '?' | '*' => {
                    format!("&{:02x}", c as u32)
                }
                _ => c.to_string(),
            })
            .collect()
    } else {
        key.to_string()
    }
}

fn decode_key(encoded: &str) -> String {
    if cfg!(windows) {
        let mut result = String::new();
        let mut chars = encoded.chars();
        while let Some(c) = chars.next() {
            if c == '&' {
                let hex: String = chars.by_ref().take(2).collect();
                if let Ok(byte) = u8::from_str_radix(&hex, 16) {
                    result.push(byte as char);
                } else {
                    result.push('&');
                    result.push_str(&hex);
                }
            } else {
                result.push(c);
            }
        }
        result
    } else {
        encoded.to_string()
    }
}