//! Filesystem-backed managed temporary store.
//!
//! Allocations live under `<app_data_dir>/managed-tmp/<opaque-handle>/`.

use std::path::{Path, PathBuf};

use async_trait::async_trait;
use serde::{Deserialize, Serialize};

use domain::ports::{LocalPath, ManagedTempStore};
use domain::{
    ManagedTempAllocation, ManagedTempError, ManagedTempGcReport, ManagedTempHandle,
    ManagedTempKind, ManagedTempLease, ManagedTempState, ProjectId,
};

const MANAGED_TMP_DIR: &str = "managed-tmp";
const METADATA_FILE: &str = "metadata.json";
const DATA_NAME: &str = "data";

/// Filesystem implementation for global IdeA-managed temporary allocations.
#[derive(Debug, Clone)]
pub struct FsManagedTempStore {
    root: PathBuf,
}

impl FsManagedTempStore {
    /// Builds the store under `<app_data_dir>/managed-tmp`.
    #[must_use]
    pub fn new(app_data_dir: impl Into<PathBuf>) -> Self {
        Self {
            root: app_data_dir.into().join(MANAGED_TMP_DIR),
        }
    }

    /// Returns the global managed temp root.
    #[must_use]
    pub fn root(&self) -> &Path {
        &self.root
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
struct StoredLease {
    handle: ManagedTempHandle,
    kind: ManagedTempKind,
    owner_project_id: Option<ProjectId>,
    purpose: String,
    state: ManagedTempState,
    created_at_ms: u64,
    last_access_at_ms: u64,
    expires_at_ms: Option<u64>,
    released_at_ms: Option<u64>,
}

impl StoredLease {
    fn from_allocation(allocation: ManagedTempAllocation) -> Self {
        Self {
            handle: allocation.handle,
            kind: allocation.kind,
            owner_project_id: allocation.owner_project_id,
            purpose: allocation.purpose,
            state: ManagedTempState::Active,
            created_at_ms: allocation.created_at_ms,
            last_access_at_ms: allocation.created_at_ms,
            expires_at_ms: allocation.expires_at_ms,
            released_at_ms: None,
        }
    }

    fn is_expired(&self, now_ms: u64) -> bool {
        self.expires_at_ms.is_some_and(|expires| expires <= now_ms)
    }

    fn to_lease(&self, path: PathBuf) -> ManagedTempLease {
        ManagedTempLease {
            handle: self.handle.clone(),
            kind: self.kind,
            owner_project_id: self.owner_project_id,
            purpose: self.purpose.clone(),
            path: LocalPath::new(path.to_string_lossy().into_owned()),
            state: self.state,
            created_at_ms: self.created_at_ms,
            last_access_at_ms: self.last_access_at_ms,
            expires_at_ms: self.expires_at_ms,
            released_at_ms: self.released_at_ms,
        }
    }
}

fn io_error(err: std::io::Error) -> ManagedTempError {
    ManagedTempError::Store(err.to_string())
}

fn serde_error(err: serde_json::Error) -> ManagedTempError {
    ManagedTempError::Store(err.to_string())
}

fn allocation_dir(root: &Path, handle: &ManagedTempHandle) -> PathBuf {
    root.join(handle.as_str())
}

fn metadata_path(root: &Path, handle: &ManagedTempHandle) -> PathBuf {
    allocation_dir(root, handle).join(METADATA_FILE)
}

fn data_path(root: &Path, handle: &ManagedTempHandle) -> PathBuf {
    allocation_dir(root, handle).join(DATA_NAME)
}

fn ensure_under_root(root: &Path, candidate: &Path) -> Result<(), ManagedTempError> {
    if candidate.starts_with(root) {
        Ok(())
    } else {
        Err(ManagedTempError::Invalid(
            "managed temp path escaped root".to_owned(),
        ))
    }
}

async fn read_stored(
    root: &Path,
    handle: &ManagedTempHandle,
) -> Result<StoredLease, ManagedTempError> {
    let path = metadata_path(root, handle);
    let bytes = tokio::fs::read(&path).await.map_err(|err| {
        if err.kind() == std::io::ErrorKind::NotFound {
            ManagedTempError::NotFound
        } else {
            io_error(err)
        }
    })?;
    let stored: StoredLease = serde_json::from_slice(&bytes).map_err(serde_error)?;
    if stored.handle != *handle {
        return Err(ManagedTempError::Invalid(
            "managed temp metadata handle mismatch".to_owned(),
        ));
    }
    Ok(stored)
}

async fn write_stored(root: &Path, stored: &StoredLease) -> Result<(), ManagedTempError> {
    let path = metadata_path(root, &stored.handle);
    let bytes = serde_json::to_vec_pretty(stored).map_err(serde_error)?;
    tokio::fs::write(path, bytes).await.map_err(io_error)
}

#[async_trait]
impl ManagedTempStore for FsManagedTempStore {
    async fn allocate(
        &self,
        allocation: ManagedTempAllocation,
    ) -> Result<ManagedTempLease, ManagedTempError> {
        let handle = allocation.handle.clone();
        let dir = allocation_dir(&self.root, &handle);
        let data = data_path(&self.root, &handle);
        ensure_under_root(&self.root, &dir)?;
        ensure_under_root(&self.root, &data)?;
        tokio::fs::create_dir_all(&self.root)
            .await
            .map_err(io_error)?;
        tokio::fs::create_dir(&dir).await.map_err(io_error)?;
        match allocation.kind {
            ManagedTempKind::Directory => tokio::fs::create_dir(&data).await.map_err(io_error)?,
            ManagedTempKind::File => {
                tokio::fs::OpenOptions::new()
                    .write(true)
                    .create_new(true)
                    .open(&data)
                    .await
                    .map_err(io_error)?;
            }
        }
        let stored = StoredLease::from_allocation(allocation);
        write_stored(&self.root, &stored).await?;
        Ok(stored.to_lease(data))
    }

    async fn resolve(
        &self,
        handle: &ManagedTempHandle,
        now_ms: u64,
    ) -> Result<ManagedTempLease, ManagedTempError> {
        let mut stored = read_stored(&self.root, handle).await?;
        if stored.state != ManagedTempState::Active || stored.is_expired(now_ms) {
            return Err(ManagedTempError::NotFound);
        }
        let data = data_path(&self.root, handle);
        ensure_under_root(&self.root, &data)?;
        if tokio::fs::metadata(&data).await.is_err() {
            return Err(ManagedTempError::NotFound);
        }
        stored.last_access_at_ms = now_ms;
        write_stored(&self.root, &stored).await?;
        Ok(stored.to_lease(data))
    }

    async fn release(
        &self,
        handle: &ManagedTempHandle,
        now_ms: u64,
    ) -> Result<ManagedTempLease, ManagedTempError> {
        let mut stored = read_stored(&self.root, handle).await?;
        stored.state = ManagedTempState::Released;
        stored.released_at_ms = Some(now_ms);
        stored.last_access_at_ms = now_ms;
        write_stored(&self.root, &stored).await?;
        Ok(stored.to_lease(data_path(&self.root, handle)))
    }

    async fn gc(&self, now_ms: u64) -> Result<ManagedTempGcReport, ManagedTempError> {
        let mut deleted = 0usize;
        let mut entries = match tokio::fs::read_dir(&self.root).await {
            Ok(entries) => entries,
            Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                return Ok(ManagedTempGcReport { deleted: 0 })
            }
            Err(err) => return Err(io_error(err)),
        };
        while let Some(entry) = entries.next_entry().await.map_err(io_error)? {
            let file_type = entry.file_type().await.map_err(io_error)?;
            if !file_type.is_dir() {
                continue;
            }
            let raw_handle = entry.file_name().to_string_lossy().into_owned();
            let Ok(handle) = ManagedTempHandle::new(raw_handle) else {
                continue;
            };
            let Ok(stored) = read_stored(&self.root, &handle).await else {
                continue;
            };
            if stored.state == ManagedTempState::Released || stored.is_expired(now_ms) {
                tokio::fs::remove_dir_all(entry.path())
                    .await
                    .map_err(io_error)?;
                deleted += 1;
            }
        }
        Ok(ManagedTempGcReport { deleted })
    }

    async fn purge_all(&self) -> Result<ManagedTempGcReport, ManagedTempError> {
        let mut deleted = 0usize;
        let mut entries = match tokio::fs::read_dir(&self.root).await {
            Ok(entries) => entries,
            Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                return Ok(ManagedTempGcReport { deleted: 0 });
            }
            Err(err) => return Err(io_error(err)),
        };
        while let Some(entry) = entries.next_entry().await.map_err(io_error)? {
            let path = entry.path();
            let removed = match entry.file_type().await {
                Ok(file_type) if file_type.is_dir() => tokio::fs::remove_dir_all(&path).await,
                Ok(_) => tokio::fs::remove_file(&path).await,
                Err(err) => Err(err),
            };
            if removed.is_ok() {
                deleted += 1;
            }
        }
        Ok(ManagedTempGcReport { deleted })
    }
}