//! Content Resolver - Fetches content from storage network
//!
//! Resolves CIDs by contacting storage nodes, fetching chunks,
//! and reassembling content.

use crate::cid::ContentId;
use crate::error::{Error, Result};
use std::collections::HashMap;
use std::sync::Arc;
use tokio::sync::RwLock;

/// Content resolver configuration
#[derive(Debug, Clone)]
pub struct ResolverConfig {
    /// Storage node endpoints
    pub nodes: Vec<String>,
    /// Request timeout in seconds
    pub timeout_secs: u64,
    /// Maximum concurrent requests
    pub max_concurrent: usize,
    /// Retry count for failed requests
    pub retries: u32,
}

impl Default for ResolverConfig {
    fn default() -> Self {
        Self {
            nodes: vec![],
            timeout_secs: 30,
            max_concurrent: 10,
            retries: 3,
        }
    }
}

/// Resolves content from the storage network
pub struct ContentResolver {
    /// Resolver configuration
    config: ResolverConfig,
    /// Storage node endpoints
    nodes: Vec<String>,
    /// Node health status
    node_health: Arc<RwLock<HashMap<String, NodeHealth>>>,
}

/// Node health tracking
#[derive(Debug, Clone)]
#[derive(Default)]
struct NodeHealth {
    /// Successful requests
    successes: u64,
    /// Failed requests
    failures: u64,
    /// Last response time (ms)
    latency_ms: u32,
    /// Last check timestamp
    last_check: u64,
}


impl ContentResolver {
    /// Create a new resolver with node list
    pub fn new(nodes: Vec<String>) -> Self {
        let config = ResolverConfig {
            nodes: nodes.clone(),
            ..Default::default()
        };
        Self {
            config,
            nodes,
            node_health: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Create a new resolver with configuration
    pub fn with_config(config: ResolverConfig) -> Self {
        let nodes = config.nodes.clone();
        Self {
            config,
            nodes,
            node_health: Arc::new(RwLock::new(HashMap::new())),
        }
    }

    /// Get the resolver configuration
    pub fn config(&self) -> &ResolverConfig {
        &self.config
    }

    /// Resolve content by CID
    pub async fn resolve(&self, cid: &ContentId) -> Result<Vec<u8>> {
        if self.nodes.is_empty() {
            return Err(Error::Network("No storage nodes configured".to_string()));
        }

        // Find providers for this CID
        let providers = self.find_providers(cid).await?;
        if providers.is_empty() {
            return Err(Error::NotFound(format!(
                "No providers found for CID {}",
                cid.to_string_repr()
            )));
        }

        // For small content, try direct fetch
        if cid.size <= 1024 * 1024 {
            return self.fetch_direct(cid, &providers).await;
        }

        // Fetch metadata to determine chunk count
        let metadata = self.fetch_metadata(cid, &providers).await?;

        // Validate metadata matches CID
        if metadata.size != cid.size {
            return Err(Error::ReassemblyFailed(format!(
                "Metadata size {} doesn't match CID size {}",
                metadata.size, cid.size
            )));
        }

        // Fetch all chunks and reassemble
        let mut all_data = Vec::with_capacity(metadata.size as usize);
        for chunk_index in 0..metadata.chunk_count {
            let chunk_data = self.fetch_chunk(cid, chunk_index, &providers).await?;

            // Validate chunk size (except possibly the last chunk)
            if chunk_index < metadata.chunk_count - 1 && chunk_data.len() != metadata.chunk_size {
                return Err(Error::ReassemblyFailed(format!(
                    "Chunk {} size {} doesn't match expected {}",
                    chunk_index, chunk_data.len(), metadata.chunk_size
                )));
            }

            all_data.extend_from_slice(&chunk_data);
        }

        // Trim to exact size (last chunk might have padding)
        all_data.truncate(metadata.size as usize);

        // Verify CID matches
        if !cid.verify(&all_data) {
            return Err(Error::ReassemblyFailed(
                "Content hash does not match CID".to_string(),
            ));
        }

        Ok(all_data)
    }

    /// Fetch small content directly
    async fn fetch_direct(&self, cid: &ContentId, providers: &[String]) -> Result<Vec<u8>> {
        for provider in providers {
            match self.fetch_content_from_provider(provider, cid).await {
                Ok(data) => {
                    // Verify before returning
                    if cid.verify(&data) {
                        return Ok(data);
                    }
                }
                Err(_) => continue,
            }
        }

        Err(Error::NotFound(format!(
            "Could not fetch content for CID {}",
            cid.to_string_repr()
        )))
    }

    /// Fetch content from a single provider
    async fn fetch_content_from_provider(
        &self,
        provider: &str,
        _cid: &ContentId,
    ) -> Result<Vec<u8>> {
        let start = std::time::Instant::now();

        // TODO: HTTP request to provider
        // GET {provider}/content/{cid}
        let result: Result<Vec<u8>> = Err(Error::Network("Not implemented".to_string()));

        // Update health stats
        let latency_ms = start.elapsed().as_millis() as u32;
        self.update_health(provider, result.is_ok(), latency_ms).await;

        result
    }

    /// Find providers for a CID
    async fn find_providers(&self, _cid: &ContentId) -> Result<Vec<String>> {
        // TODO: Query DHT for providers
        // For now, return all configured nodes
        Ok(self.nodes.clone())
    }

    /// Fetch content metadata
    async fn fetch_metadata(&self, cid: &ContentId, providers: &[String]) -> Result<ContentMetadata> {
        for provider in providers {
            match self.query_metadata(provider, cid).await {
                Ok(metadata) => return Ok(metadata),
                Err(_) => continue, // Try next provider
            }
        }

        Err(Error::NotFound("Could not fetch metadata".to_string()))
    }

    /// Query metadata from a single provider
    async fn query_metadata(&self, _provider: &str, cid: &ContentId) -> Result<ContentMetadata> {
        // TODO: HTTP request to provider
        // For now, calculate from size
        let chunk_size = 1024 * 1024; // 1 MB
        let chunk_count = (cid.size as usize).div_ceil(chunk_size);

        Ok(ContentMetadata {
            size: cid.size,
            chunk_count,
            chunk_size,
        })
    }

    /// Fetch a single chunk
    async fn fetch_chunk(
        &self,
        cid: &ContentId,
        chunk_index: usize,
        providers: &[String],
    ) -> Result<Vec<u8>> {
        // Try to fetch from multiple providers
        for provider in providers {
            match self.fetch_chunk_from_provider(provider, cid, chunk_index).await {
                Ok(data) => return Ok(data),
                Err(_) => continue,
            }
        }

        Err(Error::NotFound(format!(
            "Could not fetch chunk {} for CID {}",
            chunk_index,
            cid.to_string_repr()
        )))
    }

    /// Fetch chunk from a single provider
    async fn fetch_chunk_from_provider(
        &self,
        provider: &str,
        _cid: &ContentId,
        _chunk_index: usize,
    ) -> Result<Vec<u8>> {
        let start = std::time::Instant::now();

        // TODO: HTTP request to provider
        // GET {provider}/chunks/{cid}/{chunk_index}
        let result: Result<Vec<u8>> = Err(Error::Network("Not implemented".to_string()));

        // Update health stats
        let latency_ms = start.elapsed().as_millis() as u32;
        self.update_health(provider, result.is_ok(), latency_ms).await;

        result
    }

    /// Update node health stats
    async fn update_health(&self, node: &str, success: bool, latency_ms: u32) {
        let mut health = self.node_health.write().await;
        let entry = health.entry(node.to_string()).or_default();

        if success {
            entry.successes += 1;
        } else {
            entry.failures += 1;
        }
        entry.latency_ms = latency_ms;
        entry.last_check = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_secs();
    }

    /// Cleanup stale health entries
    pub async fn cleanup(&self, max_age_secs: u64) {
        let now = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_secs();

        let mut health = self.node_health.write().await;
        health.retain(|_, h| now - h.last_check < max_age_secs);
    }

    /// Get nodes sorted by health
    pub async fn sorted_nodes(&self) -> Vec<String> {
        let health = self.node_health.read().await;

        let mut nodes: Vec<_> = self.nodes.to_vec();

        nodes.sort_by(|a, b| {
            let health_a = health.get(a);
            let health_b = health.get(b);

            match (health_a, health_b) {
                (Some(ha), Some(hb)) => {
                    // Sort by success rate, then latency
                    let rate_a = if ha.successes + ha.failures > 0 {
                        ha.successes as f64 / (ha.successes + ha.failures) as f64
                    } else {
                        0.5
                    };
                    let rate_b = if hb.successes + hb.failures > 0 {
                        hb.successes as f64 / (hb.successes + hb.failures) as f64
                    } else {
                        0.5
                    };

                    rate_b
                        .partial_cmp(&rate_a)
                        .unwrap_or(std::cmp::Ordering::Equal)
                        .then_with(|| ha.latency_ms.cmp(&hb.latency_ms))
                }
                (Some(_), None) => std::cmp::Ordering::Less,
                (None, Some(_)) => std::cmp::Ordering::Greater,
                (None, None) => std::cmp::Ordering::Equal,
            }
        });

        nodes
    }
}

/// Content metadata from storage network
#[derive(Debug, Clone)]
struct ContentMetadata {
    /// Total size in bytes
    size: u64,
    /// Number of chunks
    chunk_count: usize,
    /// Size of each chunk
    chunk_size: usize,
}