//! High-level paste operations.
//!
//! Each function combines local storage and DHT interaction
//! into a single call: put, get, delete, pin/unpin.

use std::time::Duration;

use tesseras_dht::Node;

use crate::base58;
use crate::crypto;
use crate::paste::{CHUNK_SIZE, FORMAT_VERSION_CHUNKED, MAX_PASTE_SIZE, Paste};
use crate::store::PasteStore;

/// Timeout for blocking DHT lookups.
const OP_TIMEOUT: Duration = Duration::from_secs(30);

/// Errors from paste operations.
#[derive(Debug)]
pub enum PasteError {
    InvalidKey,
    NotFound,
    Expired,
    DecryptionFailed,
    TooLarge,
    Internal(String),
}

impl std::fmt::Display for PasteError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::InvalidKey => write!(f, "invalid key"),
            Self::NotFound => write!(f, "not found"),
            Self::Expired => write!(f, "expired"),
            Self::DecryptionFailed => write!(f, "decryption failed"),
            Self::TooLarge => write!(f, "paste too large"),
            Self::Internal(msg) => write!(f, "internal: {msg}"),
        }
    }
}

/// Parse a manifest content into a list of chunk hashes.
fn parse_manifest(content: &[u8]) -> Option<Vec<[u8; 32]>> {
    if content.len() < 2 {
        return None;
    }
    let count = u16::from_be_bytes([content[0], content[1]]) as usize;
    if content.len() != 2 + count * 32 {
        return None;
    }
    let mut hashes = Vec::with_capacity(count);
    for i in 0..count {
        let start = 2 + i * 32;
        let mut hash = [0u8; 32];
        hash.copy_from_slice(&content[start..start + 32]);
        hashes.push(hash);
    }
    Some(hashes)
}

/// Fetch paste data from local store (pastes + chunks),
/// falling back to a DHT lookup.
fn fetch_paste_data(
    node: &mut Node,
    store: &PasteStore,
    hash: &[u8],
) -> Result<Vec<u8>, PasteError> {
    if let Some(local) = store.get_paste(hash) {
        return Ok(local);
    }
    if let Some(local) = store.get_chunk(hash) {
        return Ok(local);
    }
    let vals = node.get_blocking(hash, OP_TIMEOUT);
    if vals.is_empty() {
        return Err(PasteError::NotFound);
    }
    match vals.iter().find(|v| {
        Paste::from_bytes(v)
            .map(|p| Paste::content_key(&p.content) == *hash)
            .unwrap_or(false)
    }) {
        Some(v) => Ok(v.clone()),
        None => Err(PasteError::NotFound),
    }
}

/// Decode the hash portion of a key string ("hash#enckey" or "hash").
/// Returns the 32-byte hash.
fn parse_hash(key_str: &str) -> Result<Vec<u8>, PasteError> {
    let hash_b58 = key_str.split_once('#').map(|(h, _)| h).unwrap_or(key_str);
    let hash = base58::decode(hash_b58).ok_or(PasteError::InvalidKey)?;
    if hash.len() != 32 {
        return Err(PasteError::InvalidKey);
    }
    Ok(hash)
}

/// Store a single paste. If `encrypt` is true, encrypts the content
/// and returns "hash#enckey" in base58. Otherwise returns just the hash.
///
/// For content larger than [`CHUNK_SIZE`], use the chunked protocol
/// (PUTC + PUTM) from the client instead.
pub fn put_paste(
    node: &mut Node,
    store: &PasteStore,
    content: &[u8],
    ttl_secs: u64,
    encrypt: bool,
) -> Result<String, PasteError> {
    if content.len() > MAX_PASTE_SIZE {
        return Err(PasteError::TooLarge);
    }

    let (paste_content, enc_key) = if encrypt {
        let key = crypto::generate_key();
        (crypto::encrypt(&key, content), Some(key))
    } else {
        (content.to_vec(), None)
    };

    let paste = Paste::new(paste_content, ttl_secs);
    let serialized = paste.to_bytes();
    let hash = Paste::content_key(&paste.content);

    store
        .put_paste(&hash, &serialized)
        .map_err(|e| PasteError::Internal(e.to_string()))?;

    let dht_ttl = std::cmp::min(ttl_secs, u16::MAX as u64) as u16;
    node.put(&hash, &serialized, dht_ttl, false);

    let hash_b58 = base58::encode(&hash);
    let label = if encrypt { "encrypted" } else { "public" };
    log::info!(
        "put: stored {label} paste {hash_b58} ({} bytes)",
        content.len()
    );

    match enc_key {
        Some(key) => Ok(format!("{hash_b58}#{}", base58::encode(&key))),
        None => Ok(hash_b58),
    }
}

/// Store a single chunk in the chunks directory.
/// Returns the chunk hash in base58.
pub fn put_chunk(
    store: &PasteStore,
    content: &[u8],
    ttl_secs: u64,
) -> Result<String, PasteError> {
    if content.len() > CHUNK_SIZE {
        return Err(PasteError::TooLarge);
    }
    let paste = Paste::new(content.to_vec(), ttl_secs);
    let serialized = paste.to_bytes();
    let hash = Paste::content_key(&paste.content);
    store
        .put_chunk(&hash, &serialized)
        .map_err(|e| PasteError::Internal(e.to_string()))?;
    Ok(base58::encode(&hash))
}

/// Store a chunked-paste manifest (version 2).
/// The manifest is announced to the DHT immediately;
/// chunks are replicated via the periodic republish cycle.
pub fn put_manifest(
    node: &mut Node,
    store: &PasteStore,
    content: &[u8],
    ttl_secs: u64,
) -> Result<String, PasteError> {
    if parse_manifest(content).is_none() {
        return Err(PasteError::Internal("invalid manifest".into()));
    }
    let manifest = Paste {
        version: FORMAT_VERSION_CHUNKED,
        content: content.to_vec(),
        created_at: std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs(),
        ttl_secs,
    };
    let serialized = manifest.to_bytes();
    let hash = Paste::content_key(&manifest.content);
    store
        .put_paste(&hash, &serialized)
        .map_err(|e| PasteError::Internal(e.to_string()))?;
    let dht_ttl = std::cmp::min(ttl_secs, u16::MAX as u64) as u16;
    node.put(&hash, &serialized, dht_ttl, false);
    let hash_b58 = base58::encode(&hash);
    log::info!("put: stored manifest {hash_b58}");
    Ok(hash_b58)
}

/// Retrieve a paste by key ("hash#enckey" or bare "hash").
/// Tries local store first, then falls back to a blocking DHT lookup.
/// Transparently reassembles chunked (version-2) pastes.
pub fn get_paste(
    node: &mut Node,
    store: &PasteStore,
    key_str: &str,
) -> Result<Vec<u8>, PasteError> {
    let (hash_b58, enc_key_b58) = match key_str.split_once('#') {
        Some((h, k)) => (h, Some(k)),
        None => (key_str, None),
    };

    let hash = base58::decode(hash_b58).ok_or(PasteError::InvalidKey)?;
    if hash.len() != 32 {
        return Err(PasteError::InvalidKey);
    }

    let data = fetch_paste_data(node, store, &hash)?;
    let paste = Paste::from_bytes(&data).ok_or(PasteError::InvalidKey)?;

    if paste.is_expired() && !store.is_pinned(&hash) {
        return Err(PasteError::Expired);
    }

    // Reassemble chunked paste (version 2 = manifest).
    let content = if paste.version == FORMAT_VERSION_CHUNKED {
        let chunk_hashes = parse_manifest(&paste.content)
            .ok_or(PasteError::Internal("corrupt manifest".into()))?;
        let mut assembled = Vec::new();
        for chunk_hash in &chunk_hashes {
            let chunk_data = fetch_paste_data(node, store, chunk_hash)?;
            let chunk_paste = Paste::from_bytes(&chunk_data)
                .ok_or(PasteError::Internal("corrupt chunk".into()))?;
            assembled.extend_from_slice(&chunk_paste.content);
        }
        assembled
    } else {
        paste.content
    };

    if let Some(kb58) = enc_key_b58 {
        let key_bytes = base58::decode(kb58).ok_or(PasteError::InvalidKey)?;
        if key_bytes.len() != crypto::KEY_SIZE {
            return Err(PasteError::InvalidKey);
        }
        let mut key = [0u8; crypto::KEY_SIZE];
        key.copy_from_slice(&key_bytes);
        crypto::decrypt(&key, &content)
            .ok_or(PasteError::DecryptionFailed)
    } else {
        Ok(content)
    }
}

/// Delete a paste from local store and the DHT.
/// Creates a block marker so the paste is not
/// re-imported from the DHT by sync.
/// For chunked pastes, also deletes all chunks.
pub fn delete_paste(
    node: &mut Node,
    store: &PasteStore,
    key_str: &str,
) -> Result<(), PasteError> {
    let hash = parse_hash(key_str)?;

    // If this is a chunked manifest, delete its chunks too.
    if let Some(data) = store.get_paste(&hash) {
        if let Some(paste) = Paste::from_bytes(&data) {
            if paste.version == FORMAT_VERSION_CHUNKED {
                if let Some(chunk_hashes) = parse_manifest(&paste.content) {
                    for chunk_hash in &chunk_hashes {
                        store.block(chunk_hash);
                        store.remove_chunk(chunk_hash);
                        node.delete(chunk_hash);
                    }
                }
            }
        }
    }

    store.block(&hash);
    store.remove_paste(&hash);
    store.unpin(&hash).ok();
    node.delete(&hash);
    let hash_b58 = key_str.split_once('#').map(|(h, _)| h).unwrap_or(key_str);
    log::info!("del: removed paste {hash_b58}");
    Ok(())
}

/// Parse a key and resolve the 32-byte hash (stripping any #enckey).
pub fn resolve_hash(key: &str) -> Result<Vec<u8>, PasteError> {
    parse_hash(key)
}