use std::{
    cell::{Cell, RefCell},
    sync::Arc,
};

use rand::Rng as _;
use rand_chacha::ChaCha8Rng;
use tracing::{instrument, Level};
use turso_core::{CompletionType, File, Result};

use crate::model::FAULT_ERROR_MSG;
pub(crate) struct SimulatorFile {
    pub(crate) inner: Arc<dyn File>,
    pub(crate) fault: Cell<bool>,

    /// Number of `pread` function calls (both success and failures).
    pub(crate) nr_pread_calls: Cell<usize>,

    /// Number of `pread` function calls with injected fault.
    pub(crate) nr_pread_faults: Cell<usize>,

    /// Number of `pwrite` function calls (both success and failures).
    pub(crate) nr_pwrite_calls: Cell<usize>,

    /// Number of `pwrite` function calls with injected fault.
    pub(crate) nr_pwrite_faults: Cell<usize>,

    /// Number of `sync` function calls (both success and failures).
    pub(crate) nr_sync_calls: Cell<usize>,

    /// Number of `sync` function calls with injected fault.
    pub(crate) nr_sync_faults: Cell<usize>,

    pub(crate) page_size: usize,

    pub(crate) rng: RefCell<ChaCha8Rng>,

    pub latency_probability: usize,

    pub sync_completion: RefCell<Option<Arc<turso_core::Completion>>>,
}

unsafe impl Send for SimulatorFile {}
unsafe impl Sync for SimulatorFile {}

impl SimulatorFile {
    pub(crate) fn inject_fault(&self, fault: bool) {
        self.fault.replace(fault);
    }

    pub(crate) fn stats_table(&self) -> String {
        let sum_calls =
            self.nr_pread_calls.get() + self.nr_pwrite_calls.get() + self.nr_sync_calls.get();
        let sum_faults = self.nr_pread_faults.get() + self.nr_pwrite_faults.get();
        let stats_table = [
            "op           calls   faults".to_string(),
            "--------- -------- --------".to_string(),
            format!(
                "pread     {:8} {:8}",
                self.nr_pread_calls.get(),
                self.nr_pread_faults.get()
            ),
            format!(
                "pwrite    {:8} {:8}",
                self.nr_pwrite_calls.get(),
                self.nr_pwrite_faults.get()
            ),
            format!(
                "sync      {:8} {:8}",
                self.nr_sync_calls.get(),
                0 // No fault counter for sync
            ),
            "--------- -------- --------".to_string(),
            format!("total     {sum_calls:8} {sum_faults:8}"),
        ];

        stats_table.join("\n")
    }

    #[instrument(skip_all, level = Level::TRACE)]
    fn generate_latency_duration(&self) -> Option<std::time::Duration> {
        let mut rng = self.rng.borrow_mut();
        // Chance to introduce some latency
        rng.gen_bool(self.latency_probability as f64 / 100.0)
            .then(|| std::time::Duration::from_millis(rng.gen_range(20..50)))
    }
}

impl File for SimulatorFile {
    fn lock_file(&self, exclusive: bool) -> Result<()> {
        if self.fault.get() {
            return Err(turso_core::LimboError::InternalError(
                FAULT_ERROR_MSG.into(),
            ));
        }
        self.inner.lock_file(exclusive)
    }

    fn unlock_file(&self) -> Result<()> {
        if self.fault.get() {
            return Err(turso_core::LimboError::InternalError(
                FAULT_ERROR_MSG.into(),
            ));
        }
        self.inner.unlock_file()
    }

    fn pread(
        &self,
        pos: usize,
        mut c: turso_core::Completion,
    ) -> Result<Arc<turso_core::Completion>> {
        self.nr_pread_calls.set(self.nr_pread_calls.get() + 1);
        if self.fault.get() {
            tracing::debug!("pread fault");
            self.nr_pread_faults.set(self.nr_pread_faults.get() + 1);
            return Err(turso_core::LimboError::InternalError(
                FAULT_ERROR_MSG.into(),
            ));
        }
        if let Some(latency) = self.generate_latency_duration() {
            let CompletionType::Read(read_completion) = &mut c.completion_type else {
                unreachable!();
            };
            let before = self.rng.borrow_mut().gen_bool(0.5);
            let dummy_complete = Box::new(|_, _| {});
            let prev_complete = std::mem::replace(&mut read_completion.complete, dummy_complete);
            let new_complete = move |res, bytes_read| {
                if before {
                    std::thread::sleep(latency);
                }
                (prev_complete)(res, bytes_read);
                if !before {
                    std::thread::sleep(latency);
                }
            };
            read_completion.complete = Box::new(new_complete);
        };
        self.inner.pread(pos, c)
    }

    fn pwrite(
        &self,
        pos: usize,
        buffer: Arc<RefCell<turso_core::Buffer>>,
        mut c: turso_core::Completion,
    ) -> Result<Arc<turso_core::Completion>> {
        self.nr_pwrite_calls.set(self.nr_pwrite_calls.get() + 1);
        if self.fault.get() {
            tracing::debug!("pwrite fault");
            self.nr_pwrite_faults.set(self.nr_pwrite_faults.get() + 1);
            return Err(turso_core::LimboError::InternalError(
                FAULT_ERROR_MSG.into(),
            ));
        }
        if let Some(latency) = self.generate_latency_duration() {
            let CompletionType::Write(write_completion) = &mut c.completion_type else {
                unreachable!();
            };
            let before = self.rng.borrow_mut().gen_bool(0.5);
            let dummy_complete = Box::new(|_| {});
            let prev_complete = std::mem::replace(&mut write_completion.complete, dummy_complete);
            let new_complete = move |res| {
                if before {
                    std::thread::sleep(latency);
                }
                (prev_complete)(res);
                if !before {
                    std::thread::sleep(latency);
                }
            };
            write_completion.complete = Box::new(new_complete);
        };
        self.inner.pwrite(pos, buffer, c)
    }

    fn sync(&self, mut c: turso_core::Completion) -> Result<Arc<turso_core::Completion>> {
        self.nr_sync_calls.set(self.nr_sync_calls.get() + 1);
        if self.fault.get() {
            // TODO: Enable this when https://github.com/tursodatabase/turso/issues/2091 is fixed.
            tracing::debug!("ignoring sync fault because it causes false positives with current simulator design");
            self.fault.set(false);
        }
        if let Some(latency) = self.generate_latency_duration() {
            let CompletionType::Sync(sync_completion) = &mut c.completion_type else {
                unreachable!();
            };
            let before = self.rng.borrow_mut().gen_bool(0.5);
            let dummy_complete = Box::new(|_| {});
            let prev_complete = std::mem::replace(&mut sync_completion.complete, dummy_complete);
            let new_complete = move |res| {
                if before {
                    std::thread::sleep(latency);
                }
                (prev_complete)(res);
                if !before {
                    std::thread::sleep(latency);
                }
            };
            sync_completion.complete = Box::new(new_complete);
        };
        let c = self.inner.sync(c)?;
        *self.sync_completion.borrow_mut() = Some(c.clone());
        Ok(c)
    }

    fn size(&self) -> Result<u64> {
        self.inner.size()
    }
}

impl Drop for SimulatorFile {
    fn drop(&mut self) {
        self.inner.unlock_file().expect("Failed to unlock file");
    }
}

struct Latency {}