//! Simple section-based blob storage for values.
//!
//! This module provides a minimal blob storage optimized for storing values where
//! the size is tracked externally (in an index entry). Unlike the segmented variable
//! journal, this format does not include a size prefix since the caller already
//! knows the size.
//!
//! # Format
//!
//! Each entry is stored as:
//!
//! ```text
//! +---+---+---+---+---+---+---+---+---+---+---+---+
//! |     Compressed Data (variable)    |   CRC32   |
//! +---+---+---+---+---+---+---+---+---+---+---+---+
//! ```
//!
//! - **Compressed Data**: zstd compressed (if enabled) or raw codec output
//! - **CRC32**: 4-byte checksum of the compressed data
//!
//! # Read Flow
//!
//! 1. Get `(offset, size)` from index entry
//! 2. Read `size` bytes directly from blob at byte offset
//! 3. Last 4 bytes are CRC32, verify it
//! 4. Decompress remaining bytes if compression enabled
//! 5. Decode value

use super::manager::{Config as ManagerConfig, Manager, WriteFactory};
use crate::{Context, journal::Error};
use commonware_codec::{Codec, CodecShared, FixedSize};
use commonware_cryptography::{Crc32, crc32};
#[cfg(any(test, feature = "test-utils"))]
use commonware_runtime::{Blob as _, ReadOptions, Storage, WriteOptions};
use commonware_runtime::{BufMut, Error as RError, Handle};
use std::{io::Cursor, num::NonZeroUsize};
use zstd::{bulk::compress, decode_all};

/// Physical overhead appended to every frame: the CRC32 of the frame's data.
pub(crate) const CHECKSUM_SIZE: usize = crc32::Digest::SIZE;

/// Configuration for blob storage.
#[derive(Clone)]
pub struct Config<C> {
    /// The partition to use for storing blobs.
    pub partition: String,

    /// Optional compression level (using `zstd`) to apply to data before storing.
    pub compression: Option<u8>,

    /// The codec configuration to use for encoding and decoding items.
    pub codec_config: C,

    /// The size of the write buffer to use for each blob.
    pub write_buffer: NonZeroUsize,
}

/// The glob's state, boxed so the public [Glob] handle stays pointer-sized.
struct Inner<E: Context, V: Codec> {
    manager: Manager<E, WriteFactory>,

    /// Compression level (if enabled).
    compression: Option<u8>,

    /// Codec configuration.
    codec_config: V::Cfg,
}

impl<E: Context, V: CodecShared> Inner<E, V> {
    /// See [Glob::init].
    async fn init(context: E, cfg: Config<V::Cfg>) -> Result<Self, Error> {
        let manager_cfg = ManagerConfig {
            partition: cfg.partition,
            factory: WriteFactory {
                capacity: cfg.write_buffer,
                pool: context.storage_buffer_pool().clone(),
            },
        };
        let manager = Manager::init(context, manager_cfg).await?;

        Ok(Self {
            manager,
            compression: cfg.compression,
            codec_config: cfg.codec_config,
        })
    }

    /// See [Glob::append].
    async fn append(&mut self, section: u64, value: &V) -> Result<(u64, u32), Error> {
        // Encode and optionally compress, then append checksum
        let buf = if let Some(level) = self.compression {
            // Compressed: encode first, then compress, then append checksum
            let encoded = value.encode();
            let mut compressed =
                compress(&encoded, level as i32).map_err(|_| Error::CompressionFailed)?;
            let checksum = Crc32::checksum(&compressed);
            compressed.put_u32(checksum);
            compressed
        } else {
            // Uncompressed: pre-allocate exact size to avoid copying
            let entry_size = value.encode_size() + CHECKSUM_SIZE;
            let mut buf = Vec::with_capacity(entry_size);
            value.write(&mut buf);
            let checksum = Crc32::checksum(&buf);
            buf.put_u32(checksum);
            buf
        };

        // Write to blob
        let entry_size = u32::try_from(buf.len()).map_err(|_| Error::ValueTooLarge)?;
        let writer = self.manager.get_or_create(section).await?;
        let offset = writer.size();
        writer.write_at(offset, buf).await.map_err(Error::Runtime)?;

        Ok((offset, entry_size))
    }

    /// See [Glob::get].
    async fn get(&self, section: u64, offset: u64, size: u32) -> Result<V, Error> {
        let writer = self
            .manager
            .get(section)?
            .ok_or(Error::SectionOutOfRange(section))?;

        // Read via buffered writer (handles read-through for buffered data)
        let buf = writer.read_at(offset, size as usize).await?.coalesce();

        // Entry format: [compressed_data] [crc32 (4 bytes)]
        if buf.len() < CHECKSUM_SIZE {
            return Err(Error::Runtime(RError::BlobInsufficientLength));
        }

        let data_len = buf.len() - CHECKSUM_SIZE;
        let compressed_data = &buf.as_ref()[..data_len];
        let stored_checksum = u32::from_be_bytes(
            buf.as_ref()[data_len..]
                .try_into()
                .expect("checksum is 4 bytes"),
        );

        // Verify checksum
        let checksum = Crc32::checksum(compressed_data);
        if checksum != stored_checksum {
            return Err(Error::ChecksumMismatch(stored_checksum, checksum));
        }

        // Decompress if needed and decode
        let value = if self.compression.is_some() {
            let decompressed =
                decode_all(Cursor::new(compressed_data)).map_err(|_| Error::DecompressionFailed)?;
            V::decode_cfg(decompressed.as_ref(), &self.codec_config).map_err(Error::Codec)?
        } else {
            V::decode_cfg(compressed_data, &self.codec_config).map_err(Error::Codec)?
        };

        Ok(value)
    }

    /// See [Glob::verify].
    async fn verify(&self, section: u64, offset: u64, size: u32) -> Result<bool, Error> {
        // A frame is at least its checksum trailer.
        if (size as usize) < CHECKSUM_SIZE {
            return Ok(false);
        }
        let Some(writer) = self.manager.get(section)? else {
            return Ok(false);
        };

        let buf = match writer.read_at(offset, size as usize).await {
            Ok(buf) => buf.coalesce(),
            Err(RError::BlobInsufficientLength | RError::OffsetOverflow) => return Ok(false),
            Err(err) => return Err(Error::Runtime(err)),
        };
        let data_len = buf.len() - CHECKSUM_SIZE;
        let stored_checksum = u32::from_be_bytes(
            buf.as_ref()[data_len..]
                .try_into()
                .expect("checksum is 4 bytes"),
        );
        Ok(Crc32::checksum(&buf.as_ref()[..data_len]) == stored_checksum)
    }

    /// See [Glob::inject].
    #[cfg(test)]
    async fn inject(&mut self, section: u64, offset: u64, buf: Vec<u8>) -> Result<(), Error> {
        let writer = self.manager.get_or_create(section).await?;
        writer.write_at(offset, buf).await.map_err(Error::Runtime)
    }

    /// See [Glob::sync].
    async fn sync(&mut self, sections: impl crate::Sections) -> Result<(), Error> {
        self.manager.sync(sections).await
    }

    /// See [Glob::start_sync].
    async fn start_sync(&mut self, sections: impl crate::Sections) -> Result<Handle<()>, Error> {
        self.manager.start_sync(sections).await
    }

    /// See [Glob::sync_all].
    async fn sync_all(&mut self) -> Result<(), Error> {
        self.manager.sync_all().await
    }

    /// See [Glob::size].
    fn size(&self, section: u64) -> Result<u64, Error> {
        self.manager.size(section)
    }

    /// See [Glob::rewind].
    async fn rewind(&mut self, section: u64, size: u64) -> Result<(), Error> {
        self.manager.rewind(section, size).await
    }

    /// See [Glob::rewind_section].
    async fn rewind_section(&mut self, section: u64, size: u64) -> Result<(), Error> {
        self.manager.rewind_section(section, size).await
    }

    /// See [Glob::prune].
    async fn prune(&mut self, min: u64) -> Result<bool, Error> {
        self.manager.prune(min).await
    }

    /// See [Glob::pruned].
    const fn pruned(&self, section: u64) -> bool {
        self.manager.pruned(section)
    }

    /// See [Glob::oldest_section].
    fn oldest_section(&self) -> Option<u64> {
        self.manager.oldest_section()
    }

    /// See [Glob::newest_section].
    fn newest_section(&self) -> Option<u64> {
        self.manager.newest_section()
    }

    /// See [Glob::sections].
    fn sections(&self) -> impl Iterator<Item = u64> + '_ {
        self.manager.sections()
    }

    /// See [Glob::remove_section].
    async fn remove_section(&mut self, section: u64) -> Result<bool, Error> {
        self.manager.remove_section(section).await
    }

    /// See [Glob::destroy].
    async fn destroy(self) -> Result<(), Error> {
        self.manager.destroy().await
    }
}

/// Simple section-based blob storage for values.
///
/// Uses [`buffer::Write`](commonware_runtime::buffer::Write) for batching writes.
/// Reads go directly to blobs without any caching (ideal for large values that
/// shouldn't pollute a page cache).
///
/// Mutating functions consume the glob and return it only on success: an error (or a dropped
/// future) destroys the handle. Mutations on pruned sections fail with
/// [Error::AlreadyPrunedToSection] without mutating. Check [Glob::pruned] first to keep the
/// handle.
pub struct Glob<E: Context, V: Codec>(Box<Inner<E, V>>);

impl<E: Context, V: CodecShared> std::fmt::Debug for Glob<E, V> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Glob")
            .field("oldest_section", &self.oldest_section())
            .field("newest_section", &self.newest_section())
            .finish_non_exhaustive()
    }
}

impl<E: Context, V: CodecShared> Glob<E, V> {
    /// Initialize blob storage, opening existing section blobs.
    pub async fn init(context: E, cfg: Config<V::Cfg>) -> Result<Self, Error> {
        Ok(Self(Box::new(Inner::init(context, cfg).await?)))
    }

    /// Append value to section.
    ///
    /// The returned offset is the byte offset where the entry was written.
    /// The returned size is the total bytes written (compressed_data + crc32).
    /// Both should be stored in the index entry for later retrieval.
    pub async fn append(mut self, section: u64, value: &V) -> Result<(Self, u64, u32), Error> {
        let (offset, size) = self.0.append(section, value).await?;
        Ok((self, offset, size))
    }

    /// Read value at offset with known size (from index entry).
    ///
    /// The offset should be the byte offset returned by `append()`.
    /// Reads directly from blob without any caching.
    pub async fn get(&self, section: u64, offset: u64, size: u32) -> Result<V, Error> {
        self.0.get(section, offset, size).await
    }

    /// Check whether the entry at `(offset, size)` in `section` has a valid trailing checksum.
    ///
    /// Returns `Ok(false)` if the frame is smaller than its checksum trailer, the section
    /// does not exist, the range is not fully covered by the section, or the checksum does
    /// not match. Other read failures are propagated.
    pub(super) async fn verify(&self, section: u64, offset: u64, size: u32) -> Result<bool, Error> {
        self.0.verify(section, offset, size).await
    }

    /// Inject arbitrary bytes at `offset` in `section`, bypassing entry framing.
    #[cfg(test)]
    pub(super) async fn inject(
        &mut self,
        section: u64,
        offset: u64,
        buf: Vec<u8>,
    ) -> Result<(), Error> {
        self.0.inject(section, offset, buf).await
    }

    /// Sync the given `sections` to disk (flushes write buffers).
    pub async fn sync(mut self, sections: impl crate::Sections) -> Result<Self, Error> {
        self.0.sync(sections).await?;
        Ok(self)
    }

    /// Start syncing the given `sections` to disk.
    ///
    /// An error reported by the returned [Handle] is fatal to the glob: the caller
    /// must stop using the returned glob.
    pub async fn start_sync(
        mut self,
        sections: impl crate::Sections,
    ) -> Result<(Self, Handle<()>), Error> {
        let handle = self.0.start_sync(sections).await?;
        Ok((self, handle))
    }

    /// Sync all sections to disk.
    pub async fn sync_all(mut self) -> Result<Self, Error> {
        self.0.sync_all().await?;
        Ok(self)
    }

    /// Get the current size of a section (including buffered data).
    pub fn size(&self, section: u64) -> Result<u64, Error> {
        self.0.size(section)
    }

    /// Rewind to a specific section and size.
    ///
    /// Truncates the section to the given size and removes all sections after it.
    pub async fn rewind(mut self, section: u64, size: u64) -> Result<Self, Error> {
        self.0.rewind(section, size).await?;
        Ok(self)
    }

    /// Rewind only the given section to a specific size.
    ///
    /// Unlike `rewind`, this does not affect other sections.
    pub async fn rewind_section(mut self, section: u64, size: u64) -> Result<Self, Error> {
        self.0.rewind_section(section, size).await?;
        Ok(self)
    }

    /// Prune sections before min.
    pub async fn prune(mut self, min: u64) -> Result<(Self, bool), Error> {
        let pruned = self.0.prune(min).await?;
        Ok((self, pruned))
    }

    /// Returns true when `section` is below the prune floor.
    ///
    /// The floor only tracks prunes from the current execution and resets at init, so a
    /// section pruned in a previous execution reports false.
    pub fn pruned(&self, section: u64) -> bool {
        self.0.pruned(section)
    }

    /// Returns the number of the oldest section.
    pub fn oldest_section(&self) -> Option<u64> {
        self.0.oldest_section()
    }

    /// Returns the number of the newest section.
    pub fn newest_section(&self) -> Option<u64> {
        self.0.newest_section()
    }

    /// Returns an iterator over all section numbers.
    pub fn sections(&self) -> impl Iterator<Item = u64> + '_ {
        self.0.sections()
    }

    /// Remove a specific section. Returns true if the section existed and was removed.
    pub async fn remove_section(mut self, section: u64) -> Result<(Self, bool), Error> {
        let removed = self.0.remove_section(section).await?;
        Ok((self, removed))
    }

    /// Destroy all blobs.
    pub async fn destroy(self) -> Result<(), Error> {
        self.0.destroy().await
    }
}

/// Flip one byte inside value frame `frame` of the blob at `name`, breaking that frame's CRC
/// while leaving every other frame valid. Models a value torn by a crash after its index entry
/// became durable. Addresses uncompressed fixed-size frames: `frame_size` is the encoded value
/// size plus its CRC32.
#[cfg(any(test, feature = "test-utils"))]
pub async fn corrupt_frame(
    storage: &impl Storage,
    partition: &str,
    name: &[u8],
    frame: u64,
    frame_size: u64,
) {
    let offset = frame * frame_size;
    let (blob, size) = storage.open(partition, name).await.unwrap();
    assert!(offset < size, "corruption target must be inside the blob");
    let byte = blob
        .read_at(offset, 1, ReadOptions::default())
        .await
        .unwrap()
        .coalesce();
    blob.write_at(offset, vec![byte.as_ref()[0] ^ 0xFF], WriteOptions::SYNC)
        .await
        .unwrap();
}

#[cfg(test)]
mod tests {
    use super::*;
    use commonware_macros::test_traced;
    use commonware_runtime::{Runner, Supervisor as _, deterministic};
    use commonware_utils::NZUsize;

    fn test_cfg() -> Config<()> {
        Config {
            partition: "test-partition".into(),
            compression: None,
            codec_config: (),
            write_buffer: NZUsize!(1024),
        }
    }

    #[test_traced]
    fn test_glob_append_and_get() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            // Append a value
            let value: i32 = 42;
            let (glob, offset, size) = glob.append(1, &value).await.expect("Failed to append");
            assert_eq!(offset, 0);

            // Get the value back
            let retrieved = glob.get(1, offset, size).await.expect("Failed to get");
            assert_eq!(retrieved, value);

            // Sync and verify
            let glob = glob.sync(1).await.expect("Failed to sync");
            let retrieved = glob.get(1, offset, size).await.expect("Failed to get");
            assert_eq!(retrieved, value);

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_multiple_values() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let mut glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            // Append multiple values
            let values: Vec<i32> = vec![1, 2, 3, 4, 5];
            let mut locations = Vec::new();

            for value in &values {
                let offset;
                let size;
                (glob, offset, size) = glob.append(1, value).await.expect("Failed to append");
                locations.push((offset, size));
            }

            // Get all values back
            for (i, (offset, size)) in locations.iter().enumerate() {
                let retrieved = glob.get(1, *offset, *size).await.expect("Failed to get");
                assert_eq!(retrieved, values[i]);
            }

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_with_compression() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let cfg = Config {
                partition: "test-partition".into(),
                compression: Some(3), // zstd level 3
                codec_config: (),
                write_buffer: NZUsize!(1024),
            };
            let glob: Glob<_, [u8; 100]> = Glob::init(context.child("storage"), cfg)
                .await
                .expect("Failed to init glob");

            // Append a value
            let value: [u8; 100] = [0u8; 100]; // Compressible data
            let (glob, offset, size) = glob.append(1, &value).await.expect("Failed to append");

            // Size should be smaller due to compression
            assert!(size < 100 + 4);

            // Get the value back
            let retrieved = glob.get(1, offset, size).await.expect("Failed to get");
            assert_eq!(retrieved, value);

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_prune() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let mut glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            // Append to multiple sections
            for section in 1..=5 {
                (glob, _, _) = glob
                    .append(section, &(section as i32))
                    .await
                    .expect("Failed to append");
                glob = glob.sync(section).await.expect("Failed to sync");
            }

            // Prune sections < 3
            let (glob, _) = glob.prune(3).await.expect("Failed to prune");

            // The public accessor mirrors the guard
            assert!(glob.pruned(1));
            assert!(glob.pruned(2));
            assert!(!glob.pruned(3));

            // Sections 1 and 2 should be gone
            assert!(glob.get(1, 0, 8).await.is_err());
            assert!(glob.get(2, 0, 8).await.is_err());

            // Sections 3-5 should still exist
            assert!(glob.0.manager.blobs.contains_key(&3));
            assert!(glob.0.manager.blobs.contains_key(&4));
            assert!(glob.0.manager.blobs.contains_key(&5));

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_checksum_mismatch() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            // Append a value
            let value: i32 = 42;
            let (glob, offset, size) = glob.append(1, &value).await.expect("Failed to append");
            let mut glob = glob.sync(1).await.expect("Failed to sync");

            // Corrupt the data by writing directly to the underlying blob
            let writer = glob.0.manager.blobs.get_mut(&1).unwrap();
            writer
                .write_at(offset, vec![0xFF, 0xFF, 0xFF, 0xFF])
                .await
                .expect("Failed to corrupt");
            writer.sync().await.expect("Failed to sync");

            // Get should fail with checksum mismatch
            let result = glob.get(1, offset, size).await;
            assert!(matches!(result, Err(Error::ChecksumMismatch(_, _))));

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_rewind() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let mut glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            // Append multiple values and track sizes
            let values: Vec<i32> = vec![1, 2, 3, 4, 5];
            let mut locations = Vec::new();

            for value in &values {
                let offset;
                let size;
                (glob, offset, size) = glob.append(1, value).await.expect("Failed to append");
                locations.push((offset, size));
            }
            glob = glob.sync(1).await.expect("Failed to sync");

            // Rewind to after the third value
            let (third_offset, third_size) = locations[2];
            let rewind_size = third_offset + u64::from(third_size);
            let glob = glob
                .rewind_section(1, rewind_size)
                .await
                .expect("Failed to rewind");

            // First three values should still be readable
            for (i, (offset, size)) in locations.iter().take(3).enumerate() {
                let retrieved = glob.get(1, *offset, *size).await.expect("Failed to get");
                assert_eq!(retrieved, values[i]);
            }

            // Fourth and fifth values should fail (reading past end of blob)
            let (fourth_offset, fourth_size) = locations[3];
            let result = glob.get(1, fourth_offset, fourth_size).await;
            assert!(result.is_err());

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_persistence() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let cfg = test_cfg();

            // Create and populate glob
            let glob: Glob<_, i32> = Glob::init(context.child("first"), cfg.clone())
                .await
                .expect("Failed to init glob");

            let value: i32 = 42;
            let (glob, offset, size) = glob.append(1, &value).await.expect("Failed to append");
            let glob = glob.sync(1).await.expect("Failed to sync");
            drop(glob);

            // Reopen and verify
            let glob: Glob<_, i32> = Glob::init(context.child("second"), cfg)
                .await
                .expect("Failed to reinit glob");

            let retrieved = glob.get(1, offset, size).await.expect("Failed to get");
            assert_eq!(retrieved, value);

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_get_invalid_size() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            let (glob, offset, _size) = glob.append(1, &42).await.expect("Failed to append");
            let glob = glob.sync(1).await.expect("Failed to sync");

            // Size 0 - should fail
            assert!(glob.get(1, offset, 0).await.is_err());

            // Size < CRC_SIZE (1, 2, 3 bytes) - should fail with BlobInsufficientLength
            for size in 1..4u32 {
                let result = glob.get(1, offset, size).await;
                assert!(matches!(
                    result,
                    Err(Error::Runtime(RError::BlobInsufficientLength))
                ));
            }

            glob.destroy().await.expect("Failed to destroy");
        });
    }

    #[test_traced]
    fn test_glob_get_wrong_size() {
        let executor = deterministic::Runner::default();
        executor.start(|context| async move {
            let glob: Glob<_, i32> = Glob::init(context.child("storage"), test_cfg())
                .await
                .expect("Failed to init glob");

            let (glob, offset, correct_size) = glob.append(1, &42).await.expect("Failed to append");
            let glob = glob.sync(1).await.expect("Failed to sync");

            // Size too small (but >= CRC_SIZE) - checksum mismatch
            let result = glob.get(1, offset, correct_size - 1).await;
            assert!(matches!(result, Err(Error::ChecksumMismatch(_, _))));

            glob.destroy().await.expect("Failed to destroy");
        });
    }
}