//! Queue Index - High-performance priority queue with mmap persistence
//! 
//! This crate provides a Rust implementation of the queue index with FFI exports
//! for integration with Go. It uses memory-mapped files for persistence and
//! std::sync::Mutex for thread-safe operations.

use std::ffi::{CStr, CString};
use std::os::raw::{c_char, c_int};
use std::path::PathBuf;
use std::ptr;
use std::sync::{Arc, Mutex};

mod index;
mod storage;
mod task;

pub use index::QueueIndexImpl as QueueIndex;
pub use storage::IndexStorage;
pub use task::Task;

use index::QueueIndexImpl;

/// Opaque handle for queue index
pub struct QiIndex {
    inner: Arc<Mutex<QueueIndexImpl>>,
    last_error: Mutex<Option<String>>,
}

/// Task structure - matches C FFI layout
#[repr(C)]
pub struct QiTask {
    pub id: [c_char; 64],
    pub job_name: [c_char; 128],
    pub priority: i64,
    pub created_at: i64,
    pub next_retry: i64,
    pub status: [c_char; 16],
    pub retries: u32,
}

impl QiTask {
    fn from_task(task: &Task) -> Self {
        let mut qi_task = QiTask {
            id: [0; 64],
            job_name: [0; 128],
            priority: task.priority,
            created_at: task.created_at,
            next_retry: task.next_retry,
            status: [0; 16],
            retries: task.retries,
        };
        
        // Copy strings with null termination
        Self::copy_str(&mut qi_task.id, &task.id, 64);
        Self::copy_str(&mut qi_task.job_name, &task.job_name, 128);
        Self::copy_str(&mut qi_task.status, &task.status, 16);
        
        qi_task
    }
    
    fn copy_str(dest: &mut [c_char], src: &str, max_len: usize) {
        let bytes = src.as_bytes();
        let len = bytes.len().min(max_len - 1);
        for i in 0..len {
            dest[i] = bytes[i] as c_char;
        }
        dest[len] = 0;
    }
    
    fn to_task(&self) -> Task {
        Task {
            id: Self::cstr_to_string(&self.id),
            job_name: Self::cstr_to_string(&self.job_name),
            priority: self.priority,
            created_at: self.created_at,
            next_retry: self.next_retry,
            status: Self::cstr_to_string(&self.status),
            retries: self.retries,
        }
    }
    
    fn cstr_to_string(arr: &[c_char]) -> String {
        let bytes: Vec<u8> = arr.iter()
            .take_while(|&&c| c != 0)
            .map(|&c| c as u8)
            .collect();
        String::from_utf8_lossy(&bytes).to_string()
    }
}

/// Open or create a queue index at the given directory
/// 
/// # Safety
/// path must be a valid null-terminated UTF-8 string
#[no_mangle]
pub unsafe extern "C" fn qi_open(path: *const c_char) -> *mut QiIndex {
    if path.is_null() {
        return ptr::null_mut();
    }
    
    let path_str = match CStr::from_ptr(path).to_str() {
        Ok(s) => s,
        Err(_) => return ptr::null_mut(),
    };
    
    let path_buf = PathBuf::from(path_str);
    
    let result = std::panic::catch_unwind(|| {
        match QueueIndexImpl::open(path_buf) {
            Ok(inner) => {
                let index = QiIndex {
                    inner: Arc::new(Mutex::new(inner)),
                    last_error: Mutex::new(None),
                };
                Box::into_raw(Box::new(index))
            }
            Err(e) => {
                eprintln!("Failed to open queue index: {}", e);
                ptr::null_mut()
            }
        }
    });
    
    match result {
        Ok(ptr) => ptr,
        Err(_) => {
            eprintln!("Panic in qi_open");
            ptr::null_mut()
        }
    }
}

/// Close and free a queue index
/// 
/// # Safety
/// idx must be a valid pointer returned by qi_open, or null
#[no_mangle]
pub unsafe extern "C" fn qi_close(idx: *mut QiIndex) {
    if !idx.is_null() {
        let _ = std::panic::catch_unwind(|| {
            drop(Box::from_raw(idx));
        });
    }
}

/// Add tasks to the index in a batch
/// 
/// # Safety
/// idx must be valid, tasks must point to count valid QiTask structs
#[no_mangle]
pub unsafe extern "C" fn qi_add_tasks(
    idx: *mut QiIndex,
    tasks: *const QiTask,
    count: u32,
) -> c_int {
    if idx.is_null() || tasks.is_null() || count == 0 {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        let task_slice = std::slice::from_raw_parts(tasks, count as usize);
        let rust_tasks: Vec<Task> = task_slice.iter().map(|t| t.to_task()).collect();
        
        match inner.add_tasks(&rust_tasks) {
            Ok(added) => added as c_int,
            Err(e) => {
                let mut error_guard = index.last_error.lock().unwrap();
                *error_guard = Some(e.to_string());
                -1
            }
        }
    });
    
    match result {
        Ok(n) => n,
        Err(_) => {
            eprintln!("Panic in qi_add_tasks");
            -1
        }
    }
}

/// Get the next batch of tasks from the priority queue
/// 
/// # Safety
/// idx must be valid, out_tasks must have space for max_count tasks, out_count must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_get_next_batch(
    idx: *mut QiIndex,
    out_tasks: *mut QiTask,
    max_count: u32,
    out_count: *mut u32,
) -> c_int {
    if idx.is_null() || out_tasks.is_null() || out_count.is_null() || max_count == 0 {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.get_next_batch(max_count as usize) {
            Ok(tasks) => {
                let count = tasks.len().min(max_count as usize);
                let out_slice = std::slice::from_raw_parts_mut(out_tasks, count);
                
                for (i, task) in tasks.iter().take(count).enumerate() {
                    out_slice[i] = QiTask::from_task(&task);
                }
                
                *out_count = count as u32;
                0
            }
            Err(e) => {
                let mut error_guard = index.last_error.lock().unwrap();
                *error_guard = Some(e.to_string());
                -1
            }
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => {
            eprintln!("Panic in qi_get_next_batch");
            -1
        }
    }
}

/// Peek at the next task without removing it
/// 
/// # Safety
/// idx must be valid, out_task must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_peek_next(
    idx: *mut QiIndex,
    out_task: *mut QiTask,
) -> c_int {
    if idx.is_null() || out_task.is_null() {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let inner = index.inner.lock().unwrap();
        
        match inner.peek_next() {
            Some(task) => {
                *out_task = QiTask::from_task(&task);
                0
            }
            None => -1 // No ready tasks
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => {
            eprintln!("Panic in qi_peek_next");
            -1
        }
    }
}

/// Get a task by ID
/// 
/// # Safety
/// idx must be valid, task_id must be a valid null-terminated string, out_task must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_get_task_by_id(
    idx: *mut QiIndex,
    task_id: *const c_char,
    out_task: *mut QiTask,
) -> c_int {
    if idx.is_null() || task_id.is_null() || out_task.is_null() {
        return -1;
    }
    
    let id_str = match CStr::from_ptr(task_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let inner = index.inner.lock().unwrap();
        
        match inner.get_task_by_id(id_str) {
            Some(task) => {
                *out_task = QiTask::from_task(&task);
                0
            }
            None => -1 // Task not found
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => {
            eprintln!("Panic in qi_get_task_by_id");
            -1
        }
    }
}

/// Get the last error message for an index
/// 
/// # Safety
/// idx must be valid. Returns a static string that must not be freed.
#[no_mangle]
pub unsafe extern "C" fn qi_last_error(idx: *mut QiIndex) -> *const c_char {
    if idx.is_null() {
        return ptr::null();
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let error_guard = index.last_error.lock().unwrap();
        
        match error_guard.as_ref() {
            Some(err) => {
                // Leak the CString to return a stable pointer
                // Caller must not free this
                CString::new(err.clone()).unwrap().into_raw()
            }
            None => ptr::null(),
        }
    });
    
    match result {
        Ok(ptr) => ptr,
        Err(_) => ptr::null(),
    }
}

/// Clear the last error
/// 
/// # Safety
/// idx must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_clear_error(idx: *mut QiIndex) {
    if idx.is_null() {
        return;
    }
    
    let _ = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut error_guard = index.last_error.lock().unwrap();
        *error_guard = None;
    });
}

/// Get the count of tasks with a given status
/// 
/// # Safety
/// idx must be valid, status must be a null-terminated string
#[no_mangle]
pub unsafe extern "C" fn qi_get_task_count(
    idx: *mut QiIndex,
    status: *const c_char,
) -> usize {
    if idx.is_null() || status.is_null() {
        return 0;
    }
    
    let status_str = match CStr::from_ptr(status).to_str() {
        Ok(s) => s,
        Err(_) => return 0,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let inner = index.inner.lock().unwrap();
        inner.get_task_count(status_str)
    });
    
    match result {
        Ok(count) => count,
        Err(_) => 0,
    }
}

/// Get all tasks ( allocates array - caller must call qi_free_task_array)
/// 
/// # Safety
/// idx must be valid, out_tasks and count must be valid pointers
#[no_mangle]
pub unsafe extern "C" fn qi_get_all_tasks(
    idx: *mut QiIndex,
    out_tasks: *mut *mut QiTask,
    count: *mut usize,
) -> c_int {
    if idx.is_null() || out_tasks.is_null() || count.is_null() {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let inner = index.inner.lock().unwrap();
        
        let tasks = inner.get_all_tasks();
        let len = tasks.len();
        
        if len == 0 {
            *out_tasks = ptr::null_mut();
            *count = 0;
            return 0;
        }
        
        // Allocate array
        let layout = std::alloc::Layout::array::<QiTask>(len).unwrap();
        let ptr = std::alloc::alloc(layout) as *mut QiTask;
        
        if ptr.is_null() {
            return -1;
        }
        
        // Copy tasks
        for (i, task) in tasks.iter().enumerate() {
            std::ptr::write(ptr.add(i), QiTask::from_task(&task));
        }
        
        *out_tasks = ptr;
        *count = len;
        0
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Get tasks by status
/// 
/// # Safety
/// idx must be valid, status must be a valid null-terminated string
/// out_tasks and count must be valid pointers
#[no_mangle]
pub unsafe extern "C" fn qi_get_tasks_by_status(
    idx: *mut QiIndex,
    status: *const c_char,
    out_tasks: *mut *mut QiTask,
    count: *mut usize,
) -> c_int {
    if idx.is_null() || status.is_null() || out_tasks.is_null() || count.is_null() {
        return -1;
    }
    
    let status_str = match CStr::from_ptr(status).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let inner = index.inner.lock().unwrap();
        
        let all_tasks = inner.get_all_tasks();
        let filtered: Vec<Task> = all_tasks
            .into_iter()
            .filter(|t| t.status == status_str)
            .collect();
        
        let len = filtered.len();
        if len == 0 {
            *out_tasks = ptr::null_mut();
            *count = 0;
            return 0;
        }
        
        // Allocate array
        let layout = std::alloc::Layout::array::<QiTask>(len).unwrap();
        let ptr = std::alloc::alloc(layout) as *mut QiTask;
        
        if ptr.is_null() {
            return -1;
        }
        
        // Copy tasks
        for (i, task) in filtered.iter().enumerate() {
            std::ptr::write(ptr.add(i), QiTask::from_task(task));
        }
        
        *out_tasks = ptr;
        *count = len;
        0
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Update tasks by ID
/// 
/// # Safety
/// idx must be valid, tasks must point to count valid QiTask structs
#[no_mangle]
pub unsafe extern "C" fn qi_update_tasks(
    idx: *mut QiIndex,
    tasks: *const QiTask,
    count: u32,
) -> c_int {
    if idx.is_null() || tasks.is_null() || count == 0 {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        let task_slice = std::slice::from_raw_parts(tasks, count as usize);
        let rust_tasks: Vec<Task> = task_slice.iter().map(|t| t.to_task()).collect();
        
        inner.update_tasks(&rust_tasks) as c_int
    });
    
    match result {
        Ok(n) => n,
        Err(_) => -1,
    }
}

/// Remove tasks by ID
/// 
/// # Safety
/// idx must be valid, task_ids must point to count valid null-terminated strings
#[no_mangle]
pub unsafe extern "C" fn qi_remove_tasks(
    idx: *mut QiIndex,
    task_ids: *const *const c_char,
    count: u32,
) -> c_int {
    if idx.is_null() || task_ids.is_null() || count == 0 {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        let ids_slice = std::slice::from_raw_parts(task_ids, count as usize);
        let ids: Vec<String> = ids_slice
            .iter()
            .filter_map(|&p| if p.is_null() { None } else { CStr::from_ptr(p).to_str().ok().map(|s| s.to_string()) })
            .collect();
        
        inner.remove_tasks(&ids) as c_int
    });
    
    match result {
        Ok(n) => n,
        Err(_) => -1,
    }
}

/// Retry a task
/// 
/// # Safety
/// idx must be valid, task_id must be a valid null-terminated string
#[no_mangle]
pub unsafe extern "C" fn qi_retry_task(
    idx: *mut QiIndex,
    task_id: *const c_char,
    next_retry_at: i64,
    max_retries: u32,
) -> c_int {
    if idx.is_null() || task_id.is_null() {
        return -1;
    }
    
    let id_str = match CStr::from_ptr(task_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.retry_task(id_str, next_retry_at, max_retries) {
            Ok(true) => 0,
            Ok(false) => -1,
            Err(_) => -1,
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Move a task to DLQ
/// 
/// # Safety
/// idx must be valid, task_id and reason must be valid null-terminated strings
#[no_mangle]
pub unsafe extern "C" fn qi_move_to_dlq(
    idx: *mut QiIndex,
    task_id: *const c_char,
    reason: *const c_char,
) -> c_int {
    if idx.is_null() || task_id.is_null() || reason.is_null() {
        return -1;
    }
    
    let id_str = match CStr::from_ptr(task_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let reason_str = match CStr::from_ptr(reason).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.move_to_dlq(id_str, reason_str) {
            Ok(true) => 0,
            Ok(false) => -1,
            Err(_) => -1,
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Renew lease for a task
/// 
/// # Safety
/// idx must be valid, all string args must be valid null-terminated strings
#[no_mangle]
pub unsafe extern "C" fn qi_renew_lease(
    idx: *mut QiIndex,
    task_id: *const c_char,
    worker_id: *const c_char,
    lease_expiry: i64,
) -> c_int {
    if idx.is_null() || task_id.is_null() || worker_id.is_null() {
        return -1;
    }
    
    let id_str = match CStr::from_ptr(task_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let worker_str = match CStr::from_ptr(worker_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.renew_lease(id_str, worker_str, lease_expiry) {
            Ok(true) => 0,
            Ok(false) => -1,
            Err(_) => -1,
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Release lease for a task
/// 
/// # Safety
/// idx must be valid, task_id and worker_id must be valid null-terminated strings
#[no_mangle]
pub unsafe extern "C" fn qi_release_lease(
    idx: *mut QiIndex,
    task_id: *const c_char,
    worker_id: *const c_char,
) -> c_int {
    if idx.is_null() || task_id.is_null() || worker_id.is_null() {
        return -1;
    }
    
    let id_str = match CStr::from_ptr(task_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let worker_str = match CStr::from_ptr(worker_id).to_str() {
        Ok(s) => s,
        Err(_) => return -1,
    };
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.release_lease(id_str, worker_str) {
            Ok(true) => 0,
            Ok(false) => -1,
            Err(_) => -1,
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Rebuild the index from storage
/// 
/// # Safety
/// idx must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_rebuild_index(idx: *mut QiIndex) -> c_int {
    if idx.is_null() {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.rebuild_index() {
            Ok(_) => 0,
            Err(_) => -1,
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Compact the index storage
/// 
/// # Safety
/// idx must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_compact_index(idx: *mut QiIndex) -> c_int {
    if idx.is_null() {
        return -1;
    }
    
    let result = std::panic::catch_unwind(|| {
        let index = &*idx;
        let mut inner = index.inner.lock().unwrap();
        
        match inner.compact_index() {
            Ok(_) => 0,
            Err(_) => -1,
        }
    });
    
    match result {
        Ok(rc) => rc,
        Err(_) => -1,
    }
}

/// Free a task array allocated by qi_get_all_tasks
/// 
/// # Safety
/// tasks must be a valid pointer returned by qi_get_all_tasks, or null
#[no_mangle]
pub unsafe extern "C" fn qi_free_task_array(tasks: *mut QiTask, count: usize) {
    if !tasks.is_null() && count > 0 {
        let layout = std::alloc::Layout::array::<QiTask>(count).unwrap();
        std::alloc::dealloc(tasks as *mut u8, layout);
    }
}

/// Free a string array
/// 
/// # Safety
/// strings must be a valid pointer, or null
#[no_mangle]
pub unsafe extern "C" fn qi_free_string_array(strings: *mut *mut c_char, count: usize) {
    if !strings.is_null() && count > 0 {
        let slice = std::slice::from_raw_parts(strings, count);
        for &s in slice {
            if !s.is_null() {
                let _ = CString::from_raw(s);
            }
        }
        let layout = std::alloc::Layout::array::<*mut c_char>(count).unwrap();
        std::alloc::dealloc(strings as *mut u8, layout);
    }
}

/// Get index version
/// 
/// # Safety
/// idx must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_get_index_version(idx: *mut QiIndex) -> u64 {
    if idx.is_null() {
        return 0;
    }
    1 // Version 1 for now
}

/// Get index modification time
/// 
/// # Safety
/// idx must be valid
#[no_mangle]
pub unsafe extern "C" fn qi_get_index_mtime(idx: *mut QiIndex) -> i64 {
    if idx.is_null() {
        return 0;
    }
    // Return current time as placeholder
    chrono::Utc::now().timestamp()
}