//! ModelCraft's files.
//!
//! A `.modelcraft` file ([`write`], [`read`]; docs/formats/modelcraft.md) is a ZIP package of four
//! parts, stored uncompressed so each can be read with any unzip tool:
//!
//! - `modelcraft.json`: the manifest. The format tag (`modelcraft/1`), the program that wrote
//!   it, the geometry the model is built on (the SolidCraft design and the imported 3MF meshes,
//!   each a path and the SHA-256 of its content, opened again when the model is), and the size
//!   and SHA-256 of every other part.
//! - `model.json`: the model definition (unit system, sets, materials, sections, reference
//!   points, couplings, boundary conditions, loads, steps) as pretty-printed JSON with a stable
//!   key order, so two versions of a model diff line by line.
//! - `mesh.bin`: nodes, elements and geometry tags in a compact little-endian binary form
//!   ([`mesh`]).
//! - `journal.json`: the commands that built the model, one per line: a script that replays.
//!
//! The same model always gives the same bytes. Reading treats the file as hostile: every size is
//! capped before anything is allocated, every part's checksum is verified, and the model is
//! rebuilt through the same checked methods commands use, so a file cannot hold what commands
//! would refuse. Reading and writing work on bytes (they build for the browser); only [`fs`],
//! [`recovery`] and [`roots`] touch the file system.
#![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
#![forbid(unsafe_code)]

pub mod fs;
pub mod mesh;
pub mod recovery;
pub mod roots;

use std::collections::BTreeMap;
use std::io::{Cursor, Read, Write};

use modelcraft_model::Model;
use serde::{Deserialize, Serialize};
use serde_json::Value;
use sha2::{Digest, Sha256};

/// The format tag of the files this version writes and reads.
pub const FORMAT: &str = "modelcraft/1";

/// The file name extension.
pub const EXTENSION: &str = "modelcraft";

/// Largest file read.
pub const MAX_FILE_BYTES: u64 = 8 << 30;

/// Largest manifest, model definition or journal part.
pub const MAX_TEXT_PART_BYTES: u64 = 256 << 20;

/// Most journal entries read.
pub const MAX_JOURNAL_ENTRIES: usize = 1_000_000;

/// Most imported meshes a model refers to.
pub const MAX_MESH_SOURCES: usize = 10_000;

/// Longest geometry path, command id.
pub const MAX_PATH_LEN: usize = 4096;
const MAX_COMMAND_LEN: usize = 256;

const MANIFEST: &str = "modelcraft.json";
const MODEL: &str = "model.json";
const MESH: &str = "mesh.bin";
const JOURNAL: &str = "journal.json";

#[derive(Debug, Clone, PartialEq, thiserror::Error)]
pub enum Error {
    /// Not a `.modelcraft` file, or a damaged or invalid one.
    #[error("{0}")]
    Invalid(String),
    /// A `.modelcraft` file of a format version this program does not read.
    #[error("{0}")]
    Version(String),
    #[error("limit reached: {0}")]
    Limit(String),
    /// The file system refused.
    #[error("{0}")]
    Io(String),
    /// The path lies outside the folders file access is confined to ([`roots::Roots`]).
    #[error("{0}")]
    Refused(String),
}

pub type Result<T> = std::result::Result<T, Error>;

fn invalid<T>(message: impl Into<String>) -> Result<T> {
    Err(Error::Invalid(message.into()))
}

/// A model error met while reading `part`.
pub(crate) fn model_error(part: &str, e: modelcraft_model::Error) -> Error {
    match e {
        modelcraft_model::Error::Limit(m) => Error::Limit(format!("{part}: {m}")),
        e => Error::Invalid(format!("{part}: {e}")),
    }
}

/// The lower-case hexadecimal SHA-256 of `bytes`.
pub fn sha256_hex(bytes: &[u8]) -> String {
    Sha256::digest(bytes).iter().map(|b| format!("{b:02x}")).collect()
}

/// A file the model is built on: its path and the SHA-256 of the content that was opened.
///
/// A relative path is relative to the folder of the `.modelcraft` file that refers to it.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(try_from = "SourceFileRepr", into = "SourceFileRepr")]
pub struct SourceFile {
    path: String,
    sha256: String,
}

#[derive(Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
struct SourceFileRepr {
    path: String,
    sha256: String,
}

impl TryFrom<SourceFileRepr> for SourceFile {
    type Error = Error;
    fn try_from(r: SourceFileRepr) -> Result<SourceFile> {
        SourceFile::new(r.path, r.sha256)
    }
}

impl From<SourceFile> for SourceFileRepr {
    fn from(s: SourceFile) -> Self {
        SourceFileRepr { path: s.path, sha256: s.sha256 }
    }
}

impl SourceFile {
    /// A path (1 to [`MAX_PATH_LEN`] bytes, no control characters) and a lower-case hexadecimal
    /// SHA-256.
    pub fn new(path: impl Into<String>, sha256: impl Into<String>) -> Result<SourceFile> {
        let (path, sha256) = (path.into(), sha256.into());
        if path.is_empty() || path.len() > MAX_PATH_LEN || path.chars().any(char::is_control) {
            return invalid(format!("a geometry path must be 1 to {MAX_PATH_LEN} bytes with no control characters"));
        }
        if sha256.len() != 64 || !sha256.bytes().all(|b| b.is_ascii_digit() || (b'a'..=b'f').contains(&b)) {
            return invalid(format!("`{}` is not a SHA-256 (64 lower-case hexadecimal digits)", sha256.chars().take(80).collect::<String>()));
        }
        Ok(SourceFile { path, sha256 })
    }

    /// The file `path`, with the hash of `bytes` (what was read from it).
    pub fn of(path: impl Into<String>, bytes: &[u8]) -> Result<SourceFile> {
        SourceFile::new(path, sha256_hex(bytes))
    }

    pub fn path(&self) -> &str {
        &self.path
    }

    pub fn sha256(&self) -> &str {
        &self.sha256
    }

    /// The same content at another path.
    pub fn with_path(&self, path: impl Into<String>) -> Result<SourceFile> {
        SourceFile::new(path, self.sha256.clone())
    }
}

/// The geometry a model is built on.
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Geometry {
    /// The SolidCraft design.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub design: Option<SourceFile>,
    /// Face-tagged 3MF meshes, in the order they were imported (their surfaces follow each other
    /// in that order).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub meshes: Vec<SourceFile>,
}

/// One journal entry: a command id and its parameters.
pub type JournalEntry = (String, Value);

/// What a `.modelcraft` file holds.
#[derive(Debug, Clone, Default, PartialEq)]
pub struct ModelFile {
    pub model: Model,
    pub geometry: Geometry,
    pub journal: Vec<JournalEntry>,
}

#[derive(Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
struct Manifest {
    format: String,
    generator: String,
    #[serde(default)]
    geometry: Geometry,
    parts: BTreeMap<String, Part>,
}

#[derive(Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
struct Part {
    bytes: u64,
    sha256: String,
}

#[derive(Deserialize)]
#[serde(deny_unknown_fields)]
struct JournalLine {
    command: String,
    #[serde(default)]
    params: Value,
}

/// A journal entry as written (borrowed, so saving copies no parameters).
#[derive(Serialize)]
struct JournalLineRef<'a> {
    command: &'a str,
    params: &'a Value,
}

fn json_error(part: &str, e: serde_json::Error) -> Error {
    Error::Invalid(format!("{part}: {e}"))
}

/// The journal as text: one entry per line, so a diff shows the commands added.
fn journal_text(journal: &[JournalEntry]) -> Result<Vec<u8>> {
    let mut out = b"[".to_vec();
    for (i, (command, params)) in journal.iter().enumerate() {
        out.extend_from_slice(if i == 0 { b"\n  " } else { b",\n  " });
        serde_json::to_writer(&mut out, &JournalLineRef { command, params }).map_err(|e| json_error(JOURNAL, e))?;
    }
    out.extend_from_slice(if journal.is_empty() { b"]\n" } else { b"\n]\n" });
    Ok(out)
}

/// The bytes of a `.modelcraft` file holding `model`, built on `geometry` by the commands in
/// `journal`. The same arguments always give the same bytes.
pub fn write(model: &Model, geometry: &Geometry, journal: &[JournalEntry]) -> Result<Vec<u8>> {
    if geometry.meshes.len() > MAX_MESH_SOURCES {
        return Err(Error::Limit(format!("a model refers to at most {MAX_MESH_SOURCES} imported meshes")));
    }
    let mut model_json = serde_json::to_vec_pretty(&model.without_mesh()).map_err(|e| json_error(MODEL, e))?;
    model_json.push(b'\n');
    let mesh = mesh::encode(model)?;
    let journal = journal_text(journal)?;
    let parts = [(MODEL, model_json), (MESH, mesh), (JOURNAL, journal)];
    let manifest = Manifest {
        format: FORMAT.into(),
        generator: format!("ModelCraft {}", env!("CARGO_PKG_VERSION")),
        geometry: geometry.clone(),
        parts: parts.iter().map(|(name, bytes)| (name.to_string(), Part { bytes: bytes.len() as u64, sha256: sha256_hex(bytes) })).collect(),
    };
    let mut manifest_json = serde_json::to_vec_pretty(&manifest).map_err(|e| json_error(MANIFEST, e))?;
    manifest_json.push(b'\n');

    let total: usize = parts.iter().map(|(_, b)| b.len()).sum::<usize>() + manifest_json.len();
    let mut zip = zip::ZipWriter::new(Cursor::new(Vec::with_capacity(total.saturating_add(1024))));
    let zip_error = |e: zip::result::ZipError| Error::Io(format!("cannot build the package: {e}"));
    for (name, bytes) in std::iter::once((MANIFEST, &manifest_json)).chain(parts.iter().map(|(n, b)| (*n, b))) {
        // Fixed time and permissions: the bytes depend on the model only.
        let options = zip::write::SimpleFileOptions::default()
            .compression_method(zip::CompressionMethod::Stored)
            .last_modified_time(zip::DateTime::default())
            .unix_permissions(0o644)
            .large_file(bytes.len() as u64 >= u64::from(u32::MAX));
        zip.start_file(name, options).map_err(zip_error)?;
        zip.write_all(bytes).map_err(|e| Error::Io(format!("cannot build the package: {e}")))?;
    }
    Ok(zip.finish().map_err(zip_error)?.into_inner())
}

/// Read a part of at most `cap` bytes, checking its size and ZIP checksum.
fn read_part(zip: &mut zip::ZipArchive<Cursor<&[u8]>>, name: &str, cap: u64, file_len: usize) -> Result<Vec<u8>> {
    let mut f = zip.by_name(name).map_err(|e| Error::Invalid(format!("no `{name}` part: {e}")))?;
    let size = f.size();
    if size > cap {
        return Err(Error::Limit(format!("part `{name}` is {size} bytes (at most {cap})")));
    }
    // Declared sizes are not trusted for allocation beyond the input itself.
    let mut buf = Vec::with_capacity(usize::try_from(size).unwrap_or(usize::MAX).min(file_len));
    (&mut f).take(cap.saturating_add(1)).read_to_end(&mut buf).map_err(|e| Error::Invalid(format!("part `{name}` is damaged: {e}")))?;
    if buf.len() as u64 != size {
        return invalid(format!("part `{name}` is damaged: {} bytes where {size} were declared", buf.len()));
    }
    Ok(buf)
}

/// Read a `.modelcraft` file.
pub fn read(bytes: &[u8]) -> Result<ModelFile> {
    if bytes.len() as u64 > MAX_FILE_BYTES {
        return Err(Error::Limit(format!("the file is {} MB (at most {} MB)", bytes.len() >> 20, MAX_FILE_BYTES >> 20)));
    }
    if !bytes.starts_with(b"PK\x03\x04") {
        return invalid("not a ModelCraft file (not a ZIP package)");
    }
    let mut zip = zip::ZipArchive::new(Cursor::new(bytes)).map_err(|e| Error::Invalid(format!("not a ModelCraft file: {e}")))?;
    let names = [MANIFEST, MODEL, MESH, JOURNAL];
    let mut seen = Vec::with_capacity(zip.len());
    for name in zip.file_names() {
        if !names.contains(&name) {
            return invalid(format!("unexpected part `{}`", name.chars().take(80).collect::<String>()));
        }
        if seen.contains(&name) {
            return invalid(format!("part `{name}` appears twice"));
        }
        seen.push(name);
    }

    let manifest_bytes = read_part(&mut zip, MANIFEST, MAX_TEXT_PART_BYTES, bytes.len())?;
    let manifest: Value = serde_json::from_slice(&manifest_bytes).map_err(|e| json_error(MANIFEST, e))?;
    match manifest.get("format").and_then(Value::as_str) {
        Some(FORMAT) => {}
        Some(f) if f.starts_with("modelcraft/") => {
            return Err(Error::Version(format!(
                "the file is format `{}`; this version of ModelCraft reads `{FORMAT}`",
                f.chars().take(40).collect::<String>()
            )));
        }
        _ => return invalid(format!("not a ModelCraft file: `{MANIFEST}` has no `{FORMAT}` format tag")),
    }
    let manifest: Manifest = serde_json::from_value(manifest).map_err(|e| json_error(MANIFEST, e))?;
    if manifest.geometry.meshes.len() > MAX_MESH_SOURCES {
        return Err(Error::Limit(format!("a model refers to at most {MAX_MESH_SOURCES} imported meshes")));
    }
    if manifest.parts.len() != 3 {
        return invalid(format!("`{MANIFEST}` must list exactly the parts {MODEL}, {MESH} and {JOURNAL}"));
    }

    let mut part = |name: &str, cap: u64| -> Result<Vec<u8>> {
        let listed = manifest.parts.get(name).ok_or_else(|| Error::Invalid(format!("`{MANIFEST}` does not list `{name}`")))?;
        let data = read_part(&mut zip, name, cap, bytes.len())?;
        if data.len() as u64 != listed.bytes || sha256_hex(&data) != listed.sha256 {
            return invalid(format!("part `{name}` is damaged: its size or SHA-256 differs from the manifest"));
        }
        Ok(data)
    };
    let model_json = part(MODEL, MAX_TEXT_PART_BYTES)?;
    let mesh_bin = part(MESH, mesh::MAX_BYTES)?;
    let journal_json = part(JOURNAL, MAX_TEXT_PART_BYTES)?;

    let mut model: Model = serde_json::from_slice(&model_json).map_err(|e| json_error(MODEL, e))?;
    if !model.nodes().is_empty() || !model.elements().is_empty() || !model.classification().entities().is_empty() {
        return invalid(format!("`{MODEL}` holds mesh data; the mesh belongs in `{MESH}`"));
    }
    drop(model_json);
    mesh::decode_into(&mut model, &mesh_bin)?;
    drop(mesh_bin);
    let journal = read_journal(&journal_json)?;
    Ok(ModelFile { model, geometry: manifest.geometry, journal })
}

fn read_journal(bytes: &[u8]) -> Result<Vec<JournalEntry>> {
    let lines: Vec<JournalLine> = serde_json::from_slice(bytes).map_err(|e| json_error(JOURNAL, e))?;
    if lines.len() > MAX_JOURNAL_ENTRIES {
        return Err(Error::Limit(format!("a journal holds at most {MAX_JOURNAL_ENTRIES} commands")));
    }
    lines
        .into_iter()
        .enumerate()
        .map(|(i, line)| {
            if line.command.is_empty() || line.command.len() > MAX_COMMAND_LEN || line.command.chars().any(char::is_control) {
                return invalid(format!("{JOURNAL}: entry {}: not a command id", i + 1));
            }
            Ok((line.command, line.params))
        })
        .collect()
}