//! WASM skill runner — executes WASM modules in a wasmtime sandbox.
//!
//! **Status**: Active module — fully implemented with real wasmtime integration.
//! Unlike Director/A2A (feature-gated off), this module is compiled by default
//! but only invoked when a `.wasm` skill is loaded. No feature gate needed.
//!
//! Guest modules target `wasm32-wasi` and communicate via stdin/stdout JSON.
//! Host provides optional functions: `zclaw_log`, `zclaw_http_fetch`, `zclaw_file_read`.

use async_trait::async_trait;
use serde_json::Value;
use std::io::Read as IoRead;
use std::path::PathBuf;
use tracing::{debug, warn};
use wasmtime::*;
use wasmtime_wasi::p1::{self, WasiP1Ctx};
use wasmtime_wasi::DirPerms;
use wasmtime_wasi::FilePerms;
use wasmtime_wasi::WasiCtxBuilder;
use zclaw_types::Result;

use crate::{Skill, SkillContext, SkillManifest, SkillResult};

/// Maximum WASM binary size (10 MB).
const MAX_WASM_SIZE: usize = 10 * 1024 * 1024;

/// Maximum HTTP response body size for host function (1 MB).
const MAX_HTTP_RESPONSE_SIZE: usize = 1024 * 1024;

/// Fuel per second of CPU time (heuristic: ~10M instructions/sec).
const FUEL_PER_SEC: u64 = 10_000_000;

/// WASM skill that runs in a wasmtime sandbox.
#[derive(Debug)]
pub struct WasmSkill {
    manifest: SkillManifest,
    wasm_bytes: Vec<u8>,
}

impl WasmSkill {
    /// Load and validate a WASM skill from the given `.wasm` file.
    pub fn new(manifest: SkillManifest, wasm_path: PathBuf) -> Result<Self> {
        let metadata = std::fs::metadata(&wasm_path).map_err(|e| {
            zclaw_types::ZclawError::ToolError(format!(
                "Cannot read WASM file {}: {}",
                wasm_path.display(),
                e
            ))
        })?;

        let file_size = metadata.len() as usize;
        if file_size > MAX_WASM_SIZE {
            return Err(zclaw_types::ZclawError::InvalidInput(format!(
                "WASM file too large: {} bytes (max {} bytes)",
                file_size, MAX_WASM_SIZE
            )));
        }

        let wasm_bytes = std::fs::read(&wasm_path).map_err(|e| {
            zclaw_types::ZclawError::ToolError(format!(
                "Failed to read WASM file {}: {}",
                wasm_path.display(),
                e
            ))
        })?;

        // Validate the module before accepting it.
        let engine = Engine::new(&create_engine_config())
            .map_err(|e| zclaw_types::ZclawError::ToolError(format!("Engine init failed: {}", e)))?;
        Module::validate(&engine, &wasm_bytes).map_err(|e| {
            zclaw_types::ZclawError::InvalidInput(format!("Invalid WASM module: {}", e))
        })?;

        Ok(Self {
            manifest,
            wasm_bytes,
        })
    }
}

#[async_trait]
impl Skill for WasmSkill {
    fn manifest(&self) -> &SkillManifest {
        &self.manifest
    }

    async fn execute(&self, context: &SkillContext, input: Value) -> Result<SkillResult> {
        let start = std::time::Instant::now();

        let wasm_bytes = self.wasm_bytes.clone();
        let timeout_secs = context.timeout_secs;
        let network_allowed = context.network_allowed;
        let file_access_allowed = context.file_access_allowed;
        let working_dir = context.working_dir.clone();
        let env_vars = context.env.clone();

        let input_json = serde_json::to_string(&input).unwrap_or_default();

        // Run synchronous wasmtime calls on a blocking thread.
        let result = tokio::task::spawn_blocking(move || -> Result<SkillResult> {
            run_wasm(
                &wasm_bytes,
                &input_json,
                timeout_secs,
                network_allowed,
                file_access_allowed,
                working_dir.as_deref(),
                &env_vars,
            )
        })
        .await
        .map_err(|e| zclaw_types::ZclawError::ToolError(format!("WASM task panicked: {}", e)))?;

        let duration_ms = start.elapsed().as_millis() as u64;
        match result {
            Ok(mut sr) => {
                sr.duration_ms = Some(duration_ms);
                Ok(sr)
            }
            Err(e) => Ok(SkillResult {
                success: false,
                output: Value::Null,
                error: Some(e.to_string()),
                duration_ms: Some(duration_ms),
                tokens_used: None,
            }),
        }
    }
}

/// Core WASM execution logic (blocking).
fn run_wasm(
    wasm_bytes: &[u8],
    input_json: &str,
    timeout_secs: u64,
    network_allowed: bool,
    file_access_allowed: bool,
    working_dir: Option<&std::path::Path>,
    env_vars: &std::collections::HashMap<String, String>,
) -> Result<SkillResult> {
    let config = create_engine_config();
    let engine = Engine::new(&config)
        .map_err(|e| zclaw_types::ZclawError::ToolError(format!("Engine creation failed: {}", e)))?;

    let module = Module::from_binary(&engine, wasm_bytes)
        .map_err(|e| zclaw_types::ZclawError::ToolError(format!("Module compilation failed: {}", e)))?;

    // Set up WASI context with piped stdin/stdout.
    let stdout_pipe = wasmtime_wasi::p2::pipe::MemoryOutputPipe::new(1024 * 1024); // 1 MB capacity

    let mut wasi_builder = WasiCtxBuilder::new();
    wasi_builder
        .stdin(Box::new(wasmtime_wasi::p2::pipe::MemoryInputPipe::new(
            input_json.as_bytes().to_vec(),
        )))
        .stdout(Box::new(stdout_pipe.clone()))
        .stderr(Box::new(wasmtime_wasi::p2::pipe::SinkOutputStream));

    // Pass skill context as environment variables.
    let env_pairs: Vec<(String, String)> = env_vars
        .iter()
        .map(|(k, v)| (k.clone(), v.clone()))
        .collect();
    if !env_pairs.is_empty() {
        wasi_builder.envs(&env_pairs);
    }

    // Optionally preopen working directory (read-only).
    if file_access_allowed {
        if let Some(dir) = working_dir {
            wasi_builder
                .preopened_dir(dir, "/workspace", DirPerms::READ, FilePerms::READ)
                .map_err(|e| {
                    zclaw_types::ZclawError::ToolError(format!("Failed to preopen dir: {}", e))
                })?;
        }
    }

    let wasi_ctx: WasiP1Ctx = wasi_builder.build_p1();

    let mut linker: Linker<WasiP1Ctx> = Linker::new(&engine);
    p1::add_to_linker_sync(&mut linker, |t| t)
        .map_err(|e| zclaw_types::ZclawError::ToolError(format!("WASI linker setup failed: {}", e)))?;

    // Add host functions.
    add_host_functions(&mut linker, network_allowed)?;

    let fuel = timeout_secs * FUEL_PER_SEC;
    let mut store = Store::new(&engine, wasi_ctx);
    store.set_fuel(fuel).map_err(|e| {
        zclaw_types::ZclawError::ToolError(format!("Failed to set fuel: {}", e))
    })?;

    let instance = linker
        .instantiate(&mut store, &module)
        .map_err(|e| zclaw_types::ZclawError::ToolError(format!("WASM instantiation failed: {}", e)))?;

    // Run the `_start` function.
    let start_fn = instance
        .get_typed_func::<(), ()>(&mut store, "_start")
        .map_err(|e| {
            zclaw_types::ZclawError::ToolError(format!("WASM module has no _start: {}", e))
        })?;

    start_fn
        .call(&mut store, ())
        .map_err(|e| zclaw_types::ZclawError::ToolError(format!("WASM execution failed: {}", e)))?;

    // Read captured stdout.
    let stdout_data = stdout_pipe.contents();
    let stdout_str = String::from_utf8_lossy(&stdout_data);

    debug!("[WasmSkill] stdout length: {} bytes", stdout_str.len());

    // Try to parse as JSON.
    let output = if stdout_str.trim().is_empty() {
        Value::Null
    } else {
        serde_json::from_str::<Value>(stdout_str.trim())
            .unwrap_or_else(|_| Value::String(stdout_str.trim().to_string()))
    };

    Ok(SkillResult::success(output))
}

/// Configure wasmtime engine with sandbox settings.
fn create_engine_config() -> Config {
    let mut config = Config::new();
    config
        .consume_fuel(true)
        .max_wasm_stack(2 << 20) // 2 MB stack
        .wasm_memory64(false);
    config
}

/// Add ZCLAW host functions to the wasmtime linker.
fn add_host_functions(linker: &mut Linker<WasiP1Ctx>, network_allowed: bool) -> Result<()> {
    linker
        .func_wrap(
            "env",
            "zclaw_log",
            |mut caller: Caller<'_, WasiP1Ctx>, ptr: u32, len: u32| {
                let msg = read_guest_string(&mut caller, ptr, len);
                debug!("[WasmSkill] guest log: {}", msg);
            },
        )
        .map_err(|e| {
            zclaw_types::ZclawError::ToolError(format!("Failed to add zclaw_log: {}", e))
        })?;

    // zclaw_http_fetch(url_ptr, url_len, out_ptr, out_cap) -> bytes_written (-1 = error)
    // Performs a synchronous GET request. Result is written to guest memory as JSON string.
    let net = network_allowed;
    linker
        .func_wrap(
            "env",
            "zclaw_http_fetch",
            move |mut caller: Caller<'_, WasiP1Ctx>,
                  url_ptr: u32,
                  url_len: u32,
                  out_ptr: u32,
                  out_cap: u32|
                  -> i32 {
                if !net {
                    warn!("[WasmSkill] guest called zclaw_http_fetch — denied (network not allowed)");
                    return -1;
                }

                let url = read_guest_string(&mut caller, url_ptr, url_len);
                if url.is_empty() {
                    return -1;
                }

                // Security: validate URL scheme to prevent SSRF.
                // Only http:// and https:// are allowed.
                let parsed = match url::Url::parse(&url) {
                    Ok(u) => u,
                    Err(_) => {
                        warn!("[WasmSkill] http_fetch denied — invalid URL: {}", url);
                        return -1;
                    }
                };
                let scheme = parsed.scheme();
                if scheme != "http" && scheme != "https" {
                    warn!("[WasmSkill] http_fetch denied — unsupported scheme: {}", scheme);
                    return -1;
                }
                // Block private/loopback hosts to prevent SSRF
                if let Some(host) = parsed.host_str() {
                    let lower = host.to_lowercase();
                    if lower == "localhost"
                        || lower.starts_with("127.")
                        || lower.starts_with("10.")
                        || lower.starts_with("192.168.")
                        || lower.starts_with("169.254.")
                        || lower.starts_with("0.")
                        || lower.ends_with(".internal")
                        || lower.ends_with(".local")
                    {
                        warn!("[WasmSkill] http_fetch denied — private/loopback host: {}", host);
                        return -1;
                    }
                    // Also block 172.16.0.0/12 range
                    if lower.starts_with("172.") {
                        if let Ok(second) = lower.split('.').nth(1).unwrap_or("0").parse::<u8>() {
                            if (16..=31).contains(&second) {
                                warn!("[WasmSkill] http_fetch denied — private host (172.16-31.x.x): {}", host);
                                return -1;
                            }
                        }
                    }
                }

                debug!("[WasmSkill] guest http_fetch: {}", url);

                // Synchronous HTTP GET (we're already on a blocking thread)
                let agent = ureq::Agent::config_builder()
                    .timeout_global(Some(std::time::Duration::from_secs(10)))
                    .build()
                    .new_agent();
                let response = agent.get(&url).call();

                match response {
                    Ok(mut resp) => {
                        // Enforce response size limit before reading body
                        let content_length = resp.header("content-length")
                            .and_then(|v| v.to_str().ok())
                            .and_then(|v| v.parse::<usize>().ok());
                        if let Some(len) = content_length {
                            if len > MAX_HTTP_RESPONSE_SIZE {
                                warn!("[WasmSkill] http_fetch denied — response too large: {} bytes (max {})", len, MAX_HTTP_RESPONSE_SIZE);
                                return -1;
                            }
                        }
                        let mut body = String::new();
                        match resp.body_mut().read_to_string(&mut body) {
                            Ok(_) => {
                                if body.len() > MAX_HTTP_RESPONSE_SIZE {
                                    warn!("[WasmSkill] http_fetch — response exceeded limit after read, truncating");
                                    body.truncate(MAX_HTTP_RESPONSE_SIZE);
                                }
                                write_guest_bytes(&mut caller, out_ptr, out_cap, body.as_bytes())
                            }
                            Err(e) => {
                                warn!("[WasmSkill] http_fetch body read error: {}", e);
                                -1
                            }
                        }
                    }
                    }
                    Err(e) => {
                        warn!("[WasmSkill] http_fetch error for {}: {}", url, e);
                        -1
                    }
                }
            },
        )
        .map_err(|e| {
            zclaw_types::ZclawError::ToolError(format!("Failed to add zclaw_http_fetch: {}", e))
        })?;

    // zclaw_file_read(path_ptr, path_len, out_ptr, out_cap) -> bytes_written (-1 = error)
    // Reads a file from the preopened /workspace directory. Paths must be relative.
    linker
        .func_wrap(
            "env",
            "zclaw_file_read",
            |mut caller: Caller<'_, WasiP1Ctx>,
             path_ptr: u32,
             path_len: u32,
             out_ptr: u32,
             out_cap: u32|
             -> i32 {
                let path = read_guest_string(&mut caller, path_ptr, path_len);
                if path.is_empty() {
                    return -1;
                }

                // Security: validate path stays within /workspace sandbox.
                // Reject absolute paths, and filter any path component that
                // is ".." (e.g. "foo/../../etc/passwd").
                let joined = std::path::Path::new("/workspace").join(&path);
                let mut safe = true;
                for comp in joined.components() {
                    match comp {
                        std::path::Component::ParentDir => {
                            safe = false;
                            break;
                        }
                        std::path::Component::RootDir | std::path::Component::Prefix(_) => {
                            safe = false;
                            break;
                        }
                        _ => {} // Normal, CurDir — ok
                    }
                }
                if !safe {
                    warn!("[WasmSkill] guest file_read denied — path escapes sandbox: {}", path);
                    return -1;
                }

                match std::fs::read(&joined) {
                    Ok(data) => write_guest_bytes(&mut caller, out_ptr, out_cap, &data),
                    Err(e) => {
                        debug!("[WasmSkill] file_read error for {}: {}", path, e);
                        -1
                    }
                }
            },
        )
        .map_err(|e| {
            zclaw_types::ZclawError::ToolError(format!("Failed to add zclaw_file_read: {}", e))
        })?;

    Ok(())
}

/// Read a string from WASM guest memory.
fn read_guest_string(caller: &mut Caller<'_, WasiP1Ctx>, ptr: u32, len: u32) -> String {
    let mem = match caller.get_export("memory") {
        Some(Extern::Memory(m)) => m,
        _ => return String::new(),
    };
    let offset = ptr as usize;
    let length = len as usize;
    let data = mem.data(&caller);
    if offset + length > data.len() {
        return String::new();
    }
    String::from_utf8_lossy(&data[offset..offset + length]).into_owned()
}

/// Write bytes to WASM guest memory. Returns the number of bytes written, or -1 on overflow.
fn write_guest_bytes(caller: &mut Caller<'_, WasiP1Ctx>, ptr: u32, cap: u32, data: &[u8]) -> i32 {
    let mem = match caller.get_export("memory") {
        Some(Extern::Memory(m)) => m,
        _ => return -1,
    };
    let offset = ptr as usize;
    let capacity = cap as usize;
    let write_len = data.len().min(capacity);
    if offset + write_len > mem.data_size(&caller) {
        return -1;
    }
    // Safety: we've bounds-checked the write region.
    mem.data_mut(&mut *caller)[offset..offset + write_len].copy_from_slice(&data[..write_len]);
    write_len as i32
}


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

    fn test_manifest(id: &str) -> SkillManifest {
        SkillManifest {
            id: zclaw_types::SkillId::new(id),
            name: "Test".into(),
            description: "Test skill".into(),
            version: "1.0".into(),
            author: None,
            mode: crate::SkillMode::Wasm,
            capabilities: vec![],
            input_schema: None,
            output_schema: None,
            tags: vec![],
            category: None,
            triggers: vec![],
            tools: vec![],
            enabled: true,
        }
    }

    #[test]
    fn test_oversized_rejection() {
        let dir = std::env::temp_dir().join("zclaw_test_oversized");
        let _ = std::fs::create_dir(&dir);
        let wasm_path = dir.join("big.wasm");
        let big_data = vec![0u8; MAX_WASM_SIZE + 1];
        std::fs::write(&wasm_path, &big_data).unwrap();

        let result = WasmSkill::new(test_manifest("test-oversized"), wasm_path.clone());
        let _ = std::fs::remove_file(&wasm_path);
        assert!(result.is_err());
        let err_msg = result.unwrap_err().to_string();
        assert!(
            err_msg.contains("too large"),
            "Expected 'too large', got: {}",
            err_msg
        );
    }

    #[test]
    fn test_invalid_binary_rejection() {
        let dir = std::env::temp_dir().join("zclaw_test_invalid");
        let _ = std::fs::create_dir(&dir);
        let wasm_path = dir.join("bad.wasm");
        std::fs::write(&wasm_path, b"not a real wasm module").unwrap();

        let result = WasmSkill::new(test_manifest("test-invalid"), wasm_path.clone());
        let _ = std::fs::remove_file(&wasm_path);
        assert!(result.is_err());
        let err_msg = result.unwrap_err().to_string();
        assert!(
            err_msg.contains("Invalid WASM module"),
            "Expected 'Invalid WASM module', got: {}",
            err_msg
        );
    }
}