//! Low-level metadata (Postgres `group_files`) + blob bytes (filesystem) storage
//! for §11.6 group-shared FILES collections. A near-clone of [`crate::files_repo`]
//! keyed by the owning `group_id` instead of `app_id`.
//!
//! The security-sensitive disk mechanics — the atomic write+checksum protocol and
//! checksum-on-read — are **not** duplicated: they come from the owner-relative
//! free functions in [`crate::files_repo`] (`write_atomic_at` / `read_verify_at` /
//! `final_path_at`), called with this repo's owner sub-path. Group blobs shard at
//! `<root>/files/groups/<group_id>/<collection>/<id[0:2]>/<id>` — a `groups/` infix
//! disjoint from the per-app `files/<app_id>/...` subtree, so the orphan sweeper
//! ([crate::files_sweep]) covers both with one walk. Authorization, group
//! resolution, value validation, and content-type sanitization live one layer up
//! in `GroupFilesServiceImpl`.

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

use async_trait::async_trait;
use chrono::{DateTime, Utc};
use picloud_shared::{FileMeta, FileUpdate, FilesListPage, GroupId, NewFile};
use sqlx::PgPool;
use uuid::Uuid;

use crate::files_repo::{
    decode_cursor, encode_cursor, final_path_at, read_verify_at, write_atomic_at, FileUpdated,
    FilesRepoError,
};

const FILES_LIST_MAX_LIMIT: u32 = 1_000;
const FILES_LIST_DEFAULT_LIMIT: u32 = 100;

#[derive(Debug, thiserror::Error)]
pub enum GroupFilesRepoError {
    #[error("database error: {0}")]
    Db(#[from] sqlx::Error),

    #[error("filesystem error: {0}")]
    Io(String),

    #[error("invalid collection name: {0}")]
    InvalidCollection(String),

    /// Bytes on disk no longer match the stored checksum (or are missing).
    #[error("file content corrupted (checksum mismatch)")]
    Corrupted,

    #[error("invalid pagination cursor")]
    InvalidCursor,
}

impl From<FilesRepoError> for GroupFilesRepoError {
    fn from(e: FilesRepoError) -> Self {
        match e {
            FilesRepoError::Db(e) => Self::Db(e),
            FilesRepoError::Io(s) => Self::Io(s),
            FilesRepoError::InvalidCollection(c) => Self::InvalidCollection(c),
            FilesRepoError::Corrupted => Self::Corrupted,
            FilesRepoError::InvalidCursor => Self::InvalidCursor,
        }
    }
}

/// The owner-relative subdirectory of a **group**'s shared blobs under
/// `<root>/files/`: `groups/<group_id>`. A UUID app-dir can never equal the
/// literal `groups`, so app and group blob trees can't collide.
pub(crate) fn group_owner_dir(group_id: GroupId) -> PathBuf {
    Path::new("groups").join(group_id.into_inner().to_string())
}

#[async_trait]
pub trait GroupFilesRepo: Send + Sync {
    async fn create(
        &self,
        group_id: GroupId,
        collection: &str,
        new: NewFile,
    ) -> Result<FileMeta, GroupFilesRepoError>;

    async fn head(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
    ) -> Result<Option<FileMeta>, GroupFilesRepoError>;

    /// Reads + checksum-verifies the bytes. `Ok(None)` when no row exists;
    /// `Err(Corrupted)` when the row exists but the bytes are missing/mismatched.
    async fn get(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
    ) -> Result<Option<Vec<u8>>, GroupFilesRepoError>;

    /// `Ok(None)` when no row exists (the service maps that to `NotFound`).
    async fn update(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
        upd: FileUpdate,
    ) -> Result<Option<FileUpdated>, GroupFilesRepoError>;

    async fn delete(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
    ) -> Result<Option<FileMeta>, GroupFilesRepoError>;

    async fn list(
        &self,
        group_id: GroupId,
        collection: &str,
        cursor: Option<&str>,
        limit: u32,
    ) -> Result<FilesListPage, GroupFilesRepoError>;
}

/// Filesystem-bytes + Postgres-metadata repo for group-shared files.
pub struct FsGroupFilesRepo {
    pool: PgPool,
    root: PathBuf,
}

impl FsGroupFilesRepo {
    #[must_use]
    pub fn new(pool: PgPool, root: PathBuf) -> Self {
        Self { pool, root }
    }

    /// Belt-and-suspenders path guard (the service validates at the SDK
    /// boundary). Mirrors `FsFilesRepo::guard_collection`.
    fn guard_collection(collection: &str) -> Result<(), GroupFilesRepoError> {
        if collection.is_empty()
            || collection.contains('/')
            || collection.contains('\\')
            || collection.contains("..")
            || collection.contains('\0')
        {
            return Err(GroupFilesRepoError::InvalidCollection(
                collection.to_string(),
            ));
        }
        Ok(())
    }

    fn write_atomic(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
        bytes: &[u8],
    ) -> Result<String, GroupFilesRepoError> {
        Ok(write_atomic_at(
            &self.root,
            &group_owner_dir(group_id),
            collection,
            id,
            bytes,
        )?)
    }
}

#[async_trait]
impl GroupFilesRepo for FsGroupFilesRepo {
    async fn create(
        &self,
        group_id: GroupId,
        collection: &str,
        new: NewFile,
    ) -> Result<FileMeta, GroupFilesRepoError> {
        Self::guard_collection(collection)?;
        let id = Uuid::new_v4();
        let size = i64::try_from(new.data.len()).unwrap_or(i64::MAX);
        let checksum = self.write_atomic(group_id, collection, id, &new.data)?;

        let row: GroupFileRow = sqlx::query_as(
            "INSERT INTO group_files \
                (group_id, collection, id, name, content_type, size_bytes, checksum_sha256) \
             VALUES ($1, $2, $3, $4, $5, $6, $7) \
             RETURNING id, collection, name, content_type, size_bytes, \
                       checksum_sha256, created_at, updated_at",
        )
        .bind(group_id.into_inner())
        .bind(collection)
        .bind(id)
        .bind(&new.name)
        .bind(&new.content_type)
        .bind(size)
        .bind(&checksum)
        .fetch_one(&self.pool)
        .await?;
        Ok(row.into_meta())
    }

    async fn head(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
    ) -> Result<Option<FileMeta>, GroupFilesRepoError> {
        Self::guard_collection(collection)?;
        let row: Option<GroupFileRow> = sqlx::query_as(
            "SELECT id, collection, name, content_type, size_bytes, \
                    checksum_sha256, created_at, updated_at \
             FROM group_files WHERE group_id = $1 AND collection = $2 AND id = $3",
        )
        .bind(group_id.into_inner())
        .bind(collection)
        .bind(id)
        .fetch_optional(&self.pool)
        .await?;
        Ok(row.map(GroupFileRow::into_meta))
    }

    async fn get(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
    ) -> Result<Option<Vec<u8>>, GroupFilesRepoError> {
        Self::guard_collection(collection)?;
        let row: Option<(String,)> = sqlx::query_as(
            "SELECT checksum_sha256 FROM group_files \
             WHERE group_id = $1 AND collection = $2 AND id = $3",
        )
        .bind(group_id.into_inner())
        .bind(collection)
        .bind(id)
        .fetch_optional(&self.pool)
        .await?;
        let Some((stored_checksum,)) = row else {
            return Ok(None);
        };
        let bytes = read_verify_at(
            &self.root,
            &group_owner_dir(group_id),
            collection,
            id,
            &stored_checksum,
        )?;
        Ok(Some(bytes))
    }

    async fn update(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
        upd: FileUpdate,
    ) -> Result<Option<FileUpdated>, GroupFilesRepoError> {
        Self::guard_collection(collection)?;
        let Some(prev) = self.head(group_id, collection, id).await? else {
            return Ok(None);
        };
        let size = i64::try_from(upd.data.len()).unwrap_or(i64::MAX);
        let checksum = self.write_atomic(group_id, collection, id, &upd.data)?;

        let row: GroupFileRow = sqlx::query_as(
            "UPDATE group_files SET \
                name = COALESCE($4, name), \
                content_type = COALESCE($5, content_type), \
                size_bytes = $6, \
                checksum_sha256 = $7, \
                updated_at = NOW() \
             WHERE group_id = $1 AND collection = $2 AND id = $3 \
             RETURNING id, collection, name, content_type, size_bytes, \
                       checksum_sha256, created_at, updated_at",
        )
        .bind(group_id.into_inner())
        .bind(collection)
        .bind(id)
        .bind(upd.name.as_deref())
        .bind(upd.content_type.as_deref())
        .bind(size)
        .bind(&checksum)
        .fetch_one(&self.pool)
        .await?;
        Ok(Some(FileUpdated {
            new: row.into_meta(),
            prev,
        }))
    }

    async fn delete(
        &self,
        group_id: GroupId,
        collection: &str,
        id: Uuid,
    ) -> Result<Option<FileMeta>, GroupFilesRepoError> {
        Self::guard_collection(collection)?;
        let mut tx = self.pool.begin().await?;
        let row: Option<GroupFileRow> = sqlx::query_as(
            "SELECT id, collection, name, content_type, size_bytes, \
                    checksum_sha256, created_at, updated_at \
             FROM group_files WHERE group_id = $1 AND collection = $2 AND id = $3 \
             FOR UPDATE",
        )
        .bind(group_id.into_inner())
        .bind(collection)
        .bind(id)
        .fetch_optional(&mut *tx)
        .await?;

        let Some(row) = row else {
            tx.rollback().await?;
            return Ok(None);
        };

        sqlx::query("DELETE FROM group_files WHERE group_id = $1 AND collection = $2 AND id = $3")
            .bind(group_id.into_inner())
            .bind(collection)
            .bind(id)
            .execute(&mut *tx)
            .await?;
        tx.commit().await?;

        // Row gone; unlink the bytes. A failure here leaves an orphan file
        // (reclaimed by the sweep) — not fatal.
        let path = final_path_at(&self.root, &group_owner_dir(group_id), collection, id);
        if let Err(e) = std::fs::remove_file(&path) {
            if e.kind() != std::io::ErrorKind::NotFound {
                tracing::warn!(path = %path.display(), error = %e, "group files: unlink after delete failed (orphan)");
            }
        }
        Ok(Some(row.into_meta()))
    }

    async fn list(
        &self,
        group_id: GroupId,
        collection: &str,
        cursor: Option<&str>,
        limit: u32,
    ) -> Result<FilesListPage, GroupFilesRepoError> {
        Self::guard_collection(collection)?;
        let limit = if limit == 0 {
            FILES_LIST_DEFAULT_LIMIT
        } else {
            limit.min(FILES_LIST_MAX_LIMIT)
        };
        let last_id = match cursor {
            Some(c) => Some(decode_cursor(c)?),
            None => None,
        };
        let take = i64::from(limit) + 1;
        let rows: Vec<GroupFileRow> = sqlx::query_as(
            "SELECT id, collection, name, content_type, size_bytes, \
                    checksum_sha256, created_at, updated_at \
             FROM group_files \
             WHERE group_id = $1 AND collection = $2 \
               AND ($3::uuid IS NULL OR id > $3) \
             ORDER BY id ASC \
             LIMIT $4",
        )
        .bind(group_id.into_inner())
        .bind(collection)
        .bind(last_id)
        .bind(take)
        .fetch_all(&self.pool)
        .await?;

        let mut files: Vec<FileMeta> = rows.into_iter().map(GroupFileRow::into_meta).collect();
        let next_cursor = if files.len() > limit as usize {
            files.truncate(limit as usize);
            files.last().map(|m| encode_cursor(m.id))
        } else {
            None
        };
        Ok(FilesListPage { files, next_cursor })
    }
}

#[derive(sqlx::FromRow)]
struct GroupFileRow {
    id: Uuid,
    collection: String,
    name: String,
    content_type: String,
    size_bytes: i64,
    checksum_sha256: String,
    created_at: DateTime<Utc>,
    updated_at: DateTime<Utc>,
}

impl GroupFileRow {
    fn into_meta(self) -> FileMeta {
        FileMeta {
            id: self.id,
            collection: self.collection,
            name: self.name,
            content_type: self.content_type,
            size: u64::try_from(self.size_bytes).unwrap_or(0),
            checksum: self.checksum_sha256,
            created_at: self.created_at,
            updated_at: self.updated_at,
        }
    }
}