//! Patch manifest, integrity and rollback primitives.

use crate::PatchError;
use serde::{Deserialize, Serialize};
use std::fs;
use std::path::{Component, Path, PathBuf};

/// Current patch manifest schema version.
pub const PATCH_MANIFEST_VERSION: u32 = 1;

/// Persisted manifest for a generated patch set.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct PatchManifest {
    /// Manifest schema version.
    #[serde(default = "default_patch_manifest_version")]
    pub version: u32,
    /// Stable patch identifier.
    pub patch_id: String,
    /// Source resource version identifier.
    pub source_version: String,
    /// Target resource version identifier.
    pub target_version: String,
    /// Files covered by this patch set.
    pub files: Vec<PatchManifestFile>,
    /// Rollback metadata for the publication layer.
    pub rollback: PatchRollback,
}

impl PatchManifest {
    /// Builds a manifest-level integrity summary from recorded file metadata.
    pub fn integrity_summary(&self) -> PatchIntegrity {
        PatchIntegrity {
            file_count: self.files.len(),
            source_bytes: self.files.iter().map(|file| file.source_size).sum(),
            target_bytes: self.files.iter().map(|file| file.target_size).sum(),
        }
    }
}

/// One release-relative file entry in a patch manifest.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct PatchManifestFile {
    /// Release-relative path.
    pub path: PathBuf,
    /// Patch algorithm used to produce the target bytes.
    pub patch_kind: PatchKind,
    /// Expected BLAKE3 hash of the source bytes.
    pub source_blake3: String,
    /// Expected BLAKE3 hash of the target bytes.
    pub target_blake3: String,
    /// Expected source byte length.
    pub source_size: u64,
    /// Expected target byte length.
    pub target_size: u64,
}

/// Patch algorithm family used by one manifest file.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum PatchKind {
    /// Deterministic binary hunk patch.
    Binary,
    /// RFC 6902 JSON Patch.
    Json,
    /// UTF-8 text patch.
    Text,
    /// UnityFS TextAsset replacement patch.
    UnityFsTextAsset,
}

/// Rollback metadata owned by higher-level publication code.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct PatchRollback {
    /// Previous `current` pointer target before publication.
    pub previous_current_target: Option<PathBuf>,
    /// Published target path that can be removed on rollback.
    pub remove_target_path: Option<PathBuf>,
}

/// Manifest-level integrity summary.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct PatchIntegrity {
    /// Number of manifest files verified or summarized.
    pub file_count: usize,
    /// Total source bytes.
    pub source_bytes: u64,
    /// Total target bytes.
    pub target_bytes: u64,
}

/// Verifies all manifest files against source and target roots.
pub fn verify_patch_manifest_files(
    source_root: &Path,
    target_root: &Path,
    manifest: &PatchManifest,
) -> crate::Result<PatchIntegrity> {
    if manifest.version != PATCH_MANIFEST_VERSION {
        return Err(PatchError::ApplyFailed(format!(
            "unsupported patch manifest version {}",
            manifest.version
        )));
    }

    let mut integrity = PatchIntegrity {
        file_count: 0,
        source_bytes: 0,
        target_bytes: 0,
    };
    for file in &manifest.files {
        let source_path = resolve_manifest_path(source_root, &file.path)?;
        let target_path = resolve_manifest_path(target_root, &file.path)?;
        let source = read_manifest_file(&source_path, "source")?;
        let target = read_manifest_file(&target_path, "target")?;
        verify_patch_file_bytes(&source, &target, file)?;
        integrity.file_count += 1;
        integrity.source_bytes += source.len() as u64;
        integrity.target_bytes += target.len() as u64;
    }
    Ok(integrity)
}

/// Verifies one manifest file entry against source and target bytes.
pub fn verify_patch_file_bytes(
    source: &[u8],
    target: &[u8],
    file: &PatchManifestFile,
) -> crate::Result<()> {
    let source_hash = blake3_hex(source);
    let target_hash = blake3_hex(target);
    if source_hash != file.source_blake3 || source.len() as u64 != file.source_size {
        return Err(PatchError::ApplyFailed(format!(
            "patch source integrity mismatch {}: expected hash={} bytes={}, actual hash={} bytes={}",
            file.path.display(),
            file.source_blake3,
            file.source_size,
            source_hash,
            source.len()
        )));
    }
    if target_hash != file.target_blake3 || target.len() as u64 != file.target_size {
        return Err(PatchError::ApplyFailed(format!(
            "patch target integrity mismatch {}: expected hash={} bytes={}, actual hash={} bytes={}",
            file.path.display(),
            file.target_blake3,
            file.target_size,
            target_hash,
            target.len()
        )));
    }
    Ok(())
}

fn resolve_manifest_path(root: &Path, relative: &Path) -> crate::Result<PathBuf> {
    if relative.is_absolute() {
        return Err(PatchError::ApplyFailed(format!(
            "patch manifest path must be relative: {}",
            relative.display()
        )));
    }
    for component in relative.components() {
        match component {
            Component::Normal(_) | Component::CurDir => {}
            _ => {
                return Err(PatchError::ApplyFailed(format!(
                    "patch manifest path escapes release root: {}",
                    relative.display()
                )))
            }
        }
    }
    Ok(root.join(relative))
}

fn read_manifest_file(path: &Path, label: &str) -> crate::Result<Vec<u8>> {
    fs::read(path).map_err(|error| {
        PatchError::ApplyFailed(format!(
            "failed to read patch {label} file {}: {error}",
            path.display()
        ))
    })
}

fn blake3_hex(bytes: &[u8]) -> String {
    blake3::hash(bytes).to_hex().to_string()
}

fn default_patch_manifest_version() -> u32 {
    PATCH_MANIFEST_VERSION
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn verify_patch_manifest_files_accepts_matching_roots() {
        let temp = tempfile::tempdir().unwrap();
        let source_root = temp.path().join("source");
        let target_root = temp.path().join("target");
        fs::create_dir_all(source_root.join("TableBundles")).unwrap();
        fs::create_dir_all(target_root.join("TableBundles")).unwrap();
        let source = b"before";
        let target = b"after";
        fs::write(source_root.join("TableBundles/file.bytes"), source).unwrap();
        fs::write(target_root.join("TableBundles/file.bytes"), target).unwrap();

        let manifest = manifest_for("TableBundles/file.bytes", source, target);
        let integrity = verify_patch_manifest_files(&source_root, &target_root, &manifest).unwrap();

        assert_eq!(
            integrity,
            PatchIntegrity {
                file_count: 1,
                source_bytes: source.len() as u64,
                target_bytes: target.len() as u64,
            }
        );
        assert_eq!(manifest.integrity_summary(), integrity);
    }

    #[test]
    fn verify_patch_manifest_files_rejects_path_escape() {
        let temp = tempfile::tempdir().unwrap();
        let manifest = manifest_for("../escape", b"source", b"target");

        let error = verify_patch_manifest_files(temp.path(), temp.path(), &manifest).unwrap_err();

        assert!(matches!(error, PatchError::ApplyFailed(_)));
    }

    #[test]
    fn verify_patch_file_bytes_rejects_hash_mismatch() {
        let mut manifest = manifest_for("file.bin", b"source", b"target");
        manifest.files[0].target_blake3 = blake3_hex(b"other");

        let error = verify_patch_file_bytes(b"source", b"target", &manifest.files[0]).unwrap_err();

        assert!(matches!(error, PatchError::ApplyFailed(_)));
    }

    fn manifest_for(path: &str, source: &[u8], target: &[u8]) -> PatchManifest {
        PatchManifest {
            version: PATCH_MANIFEST_VERSION,
            patch_id: "patch-id".to_string(),
            source_version: "source-version".to_string(),
            target_version: "target-version".to_string(),
            files: vec![PatchManifestFile {
                path: PathBuf::from(path),
                patch_kind: PatchKind::Binary,
                source_blake3: blake3_hex(source),
                target_blake3: blake3_hex(target),
                source_size: source.len() as u64,
                target_size: target.len() as u64,
            }],
            rollback: PatchRollback {
                previous_current_target: None,
                remove_target_path: None,
            },
        }
    }
}