laddu-data 0.23.0

use std::{
    path::{Path, PathBuf},
    sync::{
        Arc,
        mpsc::{self, Receiver, Sender, SyncSender},
    },
    thread::{self, JoinHandle},
};

use laddu_physics::vectors::RealVec4;
use oxyroot::{Branch, ReaderTree, RootFile, WriterTree};

use crate::{
    LadduDataError, LadduDataResult, Name,
    data::{BatchAssembler, EventBatch},
    io::{
        DataFragment, EventSink, EventSource, FragmentedSource, OutputMode, OutputPath, ReadPlan,
        SinkState, SourceBuild, SourceBuildOptions, SourceCapabilities, WritePlan, build_source,
        fragmented_batches, sink_error, source_error,
    },
    schema::{
        ColumnInfo, ColumnType, PhysicalColumnRole, PhysicalSchemaPlan, Precision, Schema,
        SchemaColumnNames, SchemaInferenceOptions, SchemaWriteOptions, WriteWeightColumn,
    },
};

mod encode;

use encode::root_output_columns;

/// Event source backed by one or more ROOT TTrees.
#[derive(Clone, Debug)]
pub struct RootSource {
    files: Arc<[Arc<PathBuf>]>,
    tree_name: Name,
    schema: Arc<Schema>,
    options: RootReadOptions,
}

/// Schema, validation, glob, and tree-selection options for ROOT reads.
#[derive(Clone, Debug)]
pub struct RootReadOptions {
    /// Infer a logical schema when none is supplied.
    pub infer_schema: bool,
    /// Validate required columns in every matched file.
    pub validate_all_files: bool,
    /// Sort glob results for deterministic global row order.
    pub sort_glob: bool,
    /// TTree selection policy.
    pub tree: RootTreeSelection,
    /// Logical schema inference options.
    pub schema_inference: SchemaInferenceOptions,
}

impl Default for RootReadOptions {
    fn default() -> Self {
        Self {
            infer_schema: true,
            validate_all_files: true,
            sort_glob: true,
            tree: RootTreeSelection::First,
            schema_inference: SchemaInferenceOptions::default(),
        }
    }
}

/// Policy for selecting a TTree from each ROOT file.
#[derive(Clone, Debug, Default)]
pub enum RootTreeSelection {
    /// Select the first TTree.
    #[default]
    First,
    /// Select a TTree by name.
    Named(Name),
}

/// Key identifying one TTree within a ROOT file.
#[derive(Clone, Debug)]
pub struct RootFragmentKey {
    /// Input file path.
    pub file: Arc<PathBuf>,
    /// TTree name.
    pub tree_name: Name,
}

/// Introspection metadata for one ROOT branch.
#[derive(Clone, Debug)]
pub struct RootColumnInfo {
    /// Branch name.
    pub name: Name,
    /// Rust item type reported by the reader.
    pub item_type_name: String,
    /// ROOT interpretation string.
    pub interpretation: String,
    /// Number of branch entries.
    pub entries: i64,
}

impl RootSource {
    /// Opens files matching a glob with default options.
    ///
    /// # Errors
    ///
    /// Returns [`LadduDataError`] when the glob is invalid or empty, a ROOT
    /// file or tree cannot be read, or schemas are incompatible.
    pub fn open(pattern: impl AsRef<str>) -> LadduDataResult<Self> {
        Self::builder(pattern).build()
    }

    /// Creates a configurable source builder for a file glob.
    pub fn builder(pattern: impl AsRef<str>) -> RootSourceBuilder {
        RootSourceBuilder {
            pattern: pattern.as_ref().to_owned(),
            schema: None,
            options: RootReadOptions::default(),
        }
    }

    /// Returns matched files in global row order.
    pub fn files(&self) -> &[Arc<PathBuf>] {
        &self.files
    }

    /// Returns the selected TTree name.
    pub fn tree_name(&self) -> &str {
        self.tree_name.as_ref()
    }

    /// Lists TTrees in one ROOT file.
    ///
    /// # Errors
    ///
    /// Returns [`LadduDataError`] when the ROOT file cannot be opened or read.
    pub fn tree_names(path: impl AsRef<Path>) -> LadduDataResult<Vec<Name>> {
        let path = path.as_ref();
        let mut file = RootFile::open(path)
            .map_err(|error| source_error("open ROOT file", path.display(), error))?;
        let key_names: Vec<String> = file.keys_name().map(str::to_owned).collect();

        let mut out = Vec::new();

        for name in key_names {
            if file.get_tree(&name).is_ok() {
                out.push(Name::from(name));
            }
        }

        Ok(out)
    }

    /// Lists branch metadata for a selected or first TTree.
    ///
    /// # Errors
    ///
    /// Returns [`LadduDataError`] when the file or tree cannot be read, no tree
    /// exists, or branch metadata is invalid.
    pub fn columns(
        path: impl AsRef<Path>,
        tree: Option<&str>,
    ) -> LadduDataResult<Vec<RootColumnInfo>> {
        let path = path.as_ref();
        let mut file = RootFile::open(path)
            .map_err(|error| source_error("open ROOT file", path.display(), error))?;

        let tree_name = match tree {
            Some(name) => Name::from(name),
            None => first_tree_name(&mut file, path)?,
        };

        let tree = file.get_tree(tree_name.as_ref()).map_err(|error| {
            source_error(
                "read ROOT tree",
                format!("{}::{tree_name}", path.display()),
                error,
            )
        })?;

        Ok(tree
            .branches_r()
            .into_iter()
            .map(|branch| RootColumnInfo {
                name: Name::from(branch.name()),
                item_type_name: branch.item_type_name(),
                interpretation: branch.interpretation(),
                entries: branch.entries(),
            })
            .collect())
    }
}

/// Builder for a [`RootSource`].
pub struct RootSourceBuilder {
    pattern: String,
    schema: Option<Arc<Schema>>,
    options: RootReadOptions,
}

impl RootSourceBuilder {
    /// Supplies an explicit logical schema and disables inference.
    pub fn schema(mut self, schema: Arc<Schema>) -> Self {
        self.schema = Some(schema);
        self.options.infer_schema = false;
        self
    }

    /// Enables or disables logical schema inference.
    pub fn infer_schema(mut self, value: bool) -> Self {
        self.options.infer_schema = value;
        self
    }

    /// Selects a TTree by name.
    pub fn tree(mut self, name: impl Into<Name>) -> Self {
        self.options.tree = RootTreeSelection::Named(name.into());
        self
    }

    /// Selects the first TTree.
    pub fn first_tree(mut self) -> Self {
        self.options.tree = RootTreeSelection::First;
        self
    }

    /// Requires a physical weight column during inference.
    pub fn require_weight(mut self, value: bool) -> Self {
        self.options.schema_inference.require_weight = value;
        self
    }

    /// Chooses whether every matched file is schema-validated eagerly.
    pub fn validate_all_files(mut self, value: bool) -> Self {
        self.options.validate_all_files = value;
        self
    }

    /// Chooses whether matched paths are sorted.
    pub fn sort_glob(mut self, value: bool) -> Self {
        self.options.sort_glob = value;
        self
    }

    /// Replaces logical schema inference options.
    pub fn schema_inference(mut self, options: SchemaInferenceOptions) -> Self {
        self.options.schema_inference = options;
        self
    }

    /// Resolves files and tree, validates schema, and builds the source.
    ///
    /// # Errors
    ///
    /// Returns [`LadduDataError`] when the glob is invalid or empty, files or
    /// trees cannot be read, schema inference fails, or files disagree.
    pub fn build(self) -> LadduDataResult<RootSource> {
        let RootSourceBuilder {
            pattern,
            schema: explicit_schema,
            options,
        } = self;
        let tree_selection = options.tree.clone();
        let infer_options = options.schema_inference.clone();
        let validate_options = options.schema_inference.clone();
        let SourceBuild {
            files,
            context: tree_name,
            schema,
        } = build_source(
            SourceBuildOptions {
                pattern: &pattern,
                sort: options.sort_glob,
                format: "ROOT",
                explicit_schema,
                infer_schema: options.infer_schema,
                validate_all_files: options.validate_all_files,
            },
            move |path| resolve_tree_name(path, &tree_selection),
            move |path, tree_name| {
                let columns = root_columns(path, tree_name.as_ref())?;
                Schema::infer_from_columns(
                    columns.iter().map(OwnedColumnInfo::as_column_info),
                    &infer_options,
                )
            },
            move |path, schema, tree_name| {
                validate_root_file(path, tree_name.as_ref(), schema, &validate_options)
            },
        )?;

        Ok(RootSource {
            files,
            tree_name,
            schema,
            options,
        })
    }
}

impl EventSource for RootSource {
    fn schema(&self) -> LadduDataResult<Arc<Schema>> {
        Ok(Arc::clone(&self.schema))
    }

    fn capabilities(&self) -> SourceCapabilities {
        SourceCapabilities {
            exact_len: true,
            exact_weighted_total: false,
            random_access: false,
            deterministic_partitioning: true,
            predicate_pushdown: false,
            projection_pushdown: true,
            streaming: true,
        }
    }

    fn num_events(&self) -> LadduDataResult<Option<u64>> {
        Ok(Some(self.fragments()?.iter().map(|f| f.rows).sum()))
    }

    fn batches(
        &self,
        plan: ReadPlan,
    ) -> LadduDataResult<Box<dyn Iterator<Item = LadduDataResult<EventBatch>> + Send>> {
        fragmented_batches(Arc::new(self.clone()), plan)
    }
}

impl FragmentedSource for RootSource {
    type Key = RootFragmentKey;

    fn fragments(&self) -> LadduDataResult<Vec<DataFragment<Self::Key>>> {
        let mut fragments = Vec::new();
        let mut global_start = 0_u64;

        for path in self.files.iter() {
            let resource = path.as_ref().display().to_string();
            let mut file = RootFile::open(path.as_ref())
                .map_err(|error| source_error("open ROOT file", &resource, error))?;
            let tree = file.get_tree(self.tree_name.as_ref()).map_err(|error| {
                source_error(
                    "read ROOT tree",
                    format!("{resource}::{}", self.tree_name),
                    error,
                )
            })?;

            let tree_resource = format!("{resource}::{}", self.tree_name);
            let rows = usize_from_i64(tree.entries(), "negative TTree entry count", &tree_resource)?
                as u64;

            fragments.push(DataFragment {
                key: RootFragmentKey {
                    file: Arc::clone(path),
                    tree_name: self.tree_name.clone(),
                },
                global_start,
                rows,
            });

            global_start += rows;
        }

        Ok(fragments)
    }

    fn read_fragment_range(
        &self,
        key: &Self::Key,
        local_start: usize,
        local_len: usize,
        chunk_size: Option<usize>,
    ) -> LadduDataResult<Box<dyn Iterator<Item = LadduDataResult<EventBatch>> + Send>> {
        if matches!(chunk_size, Some(0)) {
            return Err(LadduDataError::InvalidArgument(
                "chunk_size must be nonzero",
            ));
        }

        Ok(Box::new(RootBatchIter::spawn(
            Arc::clone(&self.schema),
            self.options.clone(),
            key.clone(),
            local_start,
            local_len,
            chunk_size,
        )))
    }
}

struct RootBatchIter {
    rx: Receiver<LadduDataResult<EventBatch>>,
    state: RootBatchState,
}

enum RootBatchState {
    Receiving(JoinHandle<()>),
    Done,
}

impl RootBatchIter {
    fn spawn(
        schema: Arc<Schema>,
        options: RootReadOptions,
        key: RootFragmentKey,
        local_start: usize,
        local_len: usize,
        chunk_size: Option<usize>,
    ) -> Self {
        // Keep at most one decoded batch ahead of the consumer so ROOT I/O
        // cannot silently exceed the dataset's memory-derived chunk budget.
        let (tx, rx) = mpsc::sync_channel(1);

        let handle = thread::spawn(move || {
            if let Err(err) = read_root_range_and_send_batches(
                schema,
                options,
                key,
                local_start,
                local_len,
                chunk_size,
                tx.clone(),
            ) {
                let _ = tx.send(Err(err));
            }
        });

        Self {
            rx,
            state: RootBatchState::Receiving(handle),
        }
    }

    fn join_if_needed(&mut self) -> Option<LadduDataResult<EventBatch>> {
        let state = std::mem::replace(&mut self.state, RootBatchState::Done);
        match state {
            RootBatchState::Done => None,
            RootBatchState::Receiving(handle) => {
                if handle.join().is_err() {
                    Some(Err(LadduDataError::Source(
                        "ROOT reader thread panicked".into(),
                    )))
                } else {
                    None
                }
            }
        }
    }
}

impl Iterator for RootBatchIter {
    type Item = LadduDataResult<EventBatch>;

    fn next(&mut self) -> Option<Self::Item> {
        if matches!(self.state, RootBatchState::Done) {
            return None;
        }

        match self.rx.recv() {
            Ok(item) => Some(item),
            Err(_) => self.join_if_needed(),
        }
    }
}

fn read_root_range_and_send_batches(
    schema: Arc<Schema>,
    options: RootReadOptions,
    key: RootFragmentKey,
    local_start: usize,
    local_len: usize,
    chunk_size: Option<usize>,
    tx: SyncSender<LadduDataResult<EventBatch>>,
) -> LadduDataResult<()> {
    let resource = format!("{}::{}", key.file.as_ref().display(), key.tree_name);
    let mut file = RootFile::open(key.file.as_ref())
        .map_err(|error| source_error("open ROOT file", &resource, error))?;
    let tree = file
        .get_tree(key.tree_name.as_ref())
        .map_err(|error| source_error("read ROOT tree", &resource, error))?;

    let mut readers =
        RootColumnReaders::new(&tree, &schema, &options.schema_inference.column_names)?;

    for _ in 0..local_start {
        readers.skip_one()?;
    }

    let mut remaining = local_len;
    let batch_size = chunk_size.unwrap_or(local_len.max(1));

    while remaining > 0 {
        let take = remaining.min(batch_size);
        let batch = readers.read_batch(Arc::clone(&schema), take)?;

        tx.send(Ok(batch))
            .map_err(|error| source_error("send ROOT batch", &resource, error))?;

        remaining -= take;
    }

    Ok(())
}

struct RootColumnReaders<'a> {
    p4s: Vec<[RootFloatIter<'a>; 4]>,
    scalars: Vec<RootFloatIter<'a>>,
    weights: Option<RootFloatIter<'a>>,
}

impl<'a> RootColumnReaders<'a> {
    fn new(
        tree: &'a ReaderTree,
        schema: &Schema,
        column_names: &SchemaColumnNames,
    ) -> LadduDataResult<Self> {
        let plan = PhysicalSchemaPlan::for_read(schema, column_names);
        let mut p4s: Vec<[Option<RootFloatIter<'a>>; 4]> = (0..schema.n_p4s())
            .map(|_| std::array::from_fn(|_| None))
            .collect();
        let mut scalars: Vec<Option<RootFloatIter<'a>>> =
            (0..schema.n_scalars()).map(|_| None).collect();
        let mut weights = None;

        for column in plan.columns() {
            let reader = open_float_reader(tree, column.name().as_ref())?;
            match column.role() {
                PhysicalColumnRole::P4 { index, component } => {
                    p4s[index][component] = Some(reader);
                }
                PhysicalColumnRole::Scalar { index } => {
                    scalars[index] = Some(reader);
                }
                PhysicalColumnRole::Weight => {
                    weights = Some(reader);
                }
            }
        }

        let p4s = p4s
            .into_iter()
            .map(|parts| {
                let [e, px, py, pz] = parts;
                Ok([
                    e.ok_or_else(|| {
                        LadduDataError::Source(
                            "physical schema plan did not bind ROOT E branch".into(),
                        )
                    })?,
                    px.ok_or_else(|| {
                        LadduDataError::Source(
                            "physical schema plan did not bind ROOT px branch".into(),
                        )
                    })?,
                    py.ok_or_else(|| {
                        LadduDataError::Source(
                            "physical schema plan did not bind ROOT py branch".into(),
                        )
                    })?,
                    pz.ok_or_else(|| {
                        LadduDataError::Source(
                            "physical schema plan did not bind ROOT pz branch".into(),
                        )
                    })?,
                ])
            })
            .collect::<LadduDataResult<Vec<_>>>()?;
        let scalars = scalars
            .into_iter()
            .map(|reader| {
                reader.ok_or_else(|| {
                    LadduDataError::Source(
                        "physical schema plan did not bind ROOT scalar branch".into(),
                    )
                })
            })
            .collect::<LadduDataResult<Vec<_>>>()?;

        Ok(Self {
            p4s,
            scalars,
            weights,
        })
    }

    fn skip_one(&mut self) -> LadduDataResult<()> {
        for [e, px, py, pz] in self.p4s.iter_mut() {
            e.next_f64()?;
            px.next_f64()?;
            py.next_f64()?;
            pz.next_f64()?;
        }

        for scalar in self.scalars.iter_mut() {
            scalar.next_f64()?;
        }

        if let Some(weights) = self.weights.as_mut() {
            weights.next_f64()?;
        }

        Ok(())
    }

    fn read_batch(&mut self, schema: Arc<Schema>, len: usize) -> LadduDataResult<EventBatch> {
        let mut p4s = Vec::with_capacity(schema.n_p4s());
        let mut scalars = Vec::with_capacity(schema.n_scalars());

        for [e, px, py, pz] in self.p4s.iter_mut() {
            let mut col = Vec::with_capacity(len);
            for _ in 0..len {
                col.push(RealVec4 {
                    e: e.next_f64()?,
                    px: px.next_f64()?,
                    py: py.next_f64()?,
                    pz: pz.next_f64()?,
                });
            }
            p4s.push(col);
        }

        for reader in self.scalars.iter_mut() {
            let mut col = Vec::with_capacity(len);
            for _ in 0..len {
                col.push(reader.next_f64()?);
            }
            scalars.push(col);
        }

        let weights = if let Some(reader) = self.weights.as_mut() {
            let mut col = Vec::with_capacity(len);
            for _ in 0..len {
                col.push(reader.next_f64()?);
            }
            Some(col)
        } else {
            None
        };

        BatchAssembler::from_columns(
            schema,
            p4s.into_iter().map(Arc::from).collect(),
            scalars.into_iter().map(Arc::from).collect(),
            weights.map(Arc::from),
        )
    }
}

enum RootFloatIter<'a> {
    F64 {
        name: Name,
        iter: Box<dyn Iterator<Item = f64> + 'a>,
    },
    F32 {
        name: Name,
        iter: Box<dyn Iterator<Item = f32> + 'a>,
    },
}

impl<'a> RootFloatIter<'a> {
    fn next_f64(&mut self) -> LadduDataResult<f64> {
        match self {
            Self::F64 { name, iter } => iter
                .next()
                .ok_or_else(|| source_error("read ROOT branch", name, "ROOT branch ended early")),
            Self::F32 { name, iter } => iter
                .next()
                .map(f64::from)
                .ok_or_else(|| source_error("read ROOT branch", name, "ROOT branch ended early")),
        }
    }
}

fn open_float_reader<'a>(tree: &'a ReaderTree, name: &str) -> LadduDataResult<RootFloatIter<'a>> {
    let branch =
        find_branch(tree, name).ok_or_else(|| LadduDataError::MissingColumn(Name::from(name)))?;

    match root_column_type(branch) {
        ColumnType::F64 => Ok(RootFloatIter::F64 {
            name: Name::from(name),
            iter: Box::new(
                branch
                    .as_iter::<f64>()
                    .map_err(|error| source_error("open ROOT branch", name, error))?,
            ),
        }),
        ColumnType::F32 => Ok(RootFloatIter::F32 {
            name: Name::from(name),
            iter: Box::new(
                branch
                    .as_iter::<f32>()
                    .map_err(|error| source_error("open ROOT branch", name, error))?,
            ),
        }),
        ColumnType::Other => Err(source_error(
            "decode ROOT branch",
            name,
            format!(
                "column {name} has unsupported ROOT type {} interpreted as {}",
                branch.item_type_name(),
                branch.interpretation()
            ),
        )),
    }
}

fn find_branch<'a>(tree: &'a ReaderTree, name: &str) -> Option<&'a Branch> {
    tree.branch(name).or_else(|| {
        tree.branches_r()
            .into_iter()
            .find(|branch| branch.name() == name)
    })
}

#[derive(Clone, Debug)]
struct OwnedColumnInfo {
    name: Name,
    dtype: ColumnType,
}

impl OwnedColumnInfo {
    fn as_column_info(&self) -> ColumnInfo<'_> {
        ColumnInfo {
            name: self.name.as_ref(),
            dtype: self.dtype,
        }
    }
}

fn root_columns(path: &Path, tree_name: &str) -> LadduDataResult<Vec<OwnedColumnInfo>> {
    let resource = format!("{}::{tree_name}", path.display());
    let mut file = RootFile::open(path)
        .map_err(|error| source_error("open ROOT file", path.display(), error))?;
    let tree = file
        .get_tree(tree_name)
        .map_err(|error| source_error("read ROOT tree", &resource, error))?;

    Ok(tree
        .branches_r()
        .into_iter()
        .map(|branch| OwnedColumnInfo {
            name: Name::from(branch.name()),
            dtype: root_column_type(branch),
        })
        .collect())
}

fn validate_root_file(
    path: &Path,
    tree_name: &str,
    schema: &Schema,
    options: &SchemaInferenceOptions,
) -> LadduDataResult<()> {
    let columns = root_columns(path, tree_name)?;

    schema.validate_required_columns(columns.iter().map(OwnedColumnInfo::as_column_info), options)
}

fn root_column_type(branch: &Branch) -> ColumnType {
    match branch.interpretation().as_str() {
        "f64" => ColumnType::F64,
        "f32" => ColumnType::F32,
        _ => match branch.item_type_name().as_str() {
            "double" | "Double_t" | "ROOT::Double_t" => ColumnType::F64,
            "float" | "Float_t" | "ROOT::Float_t" => ColumnType::F32,
            _ => ColumnType::Other,
        },
    }
}

fn resolve_tree_name(path: &Path, selection: &RootTreeSelection) -> LadduDataResult<Name> {
    let mut file = RootFile::open(path)
        .map_err(|error| source_error("open ROOT file", path.display(), error))?;

    match selection {
        RootTreeSelection::Named(name) => {
            file.get_tree(name.as_ref()).map_err(|error| {
                source_error(
                    "read ROOT tree",
                    format!("{}::{name}", path.display()),
                    error,
                )
            })?;
            Ok(name.clone())
        }
        RootTreeSelection::First => first_tree_name(&mut file, path),
    }
}

fn first_tree_name(file: &mut RootFile, path: &Path) -> LadduDataResult<Name> {
    let key_names: Vec<String> = file.keys_name().map(str::to_owned).collect();

    for name in key_names {
        if file.get_tree(&name).is_ok() {
            return Ok(Name::from(name));
        }
    }

    Err(source_error(
        "resolve first ROOT tree",
        path.display(),
        "no TTree found in ROOT file",
    ))
}

fn usize_from_i64(value: i64, message: &'static str, resource: &str) -> LadduDataResult<usize> {
    if value < 0 {
        return Err(source_error("read ROOT entry count", resource, message));
    }

    usize::try_from(value).map_err(|_| {
        source_error(
            "read ROOT entry count",
            resource,
            "entry count overflows usize",
        )
    })
}

/// Event sink that writes a ROOT TTree on a background thread.
pub struct RootSink {
    output: OutputPath,
    options: RootWriteOptions,
    resolved_path: Option<PathBuf>,
    event_schema: Option<Arc<Schema>>,
    senders: Option<RootColumnSenders>,
    writer_thread: Option<JoinHandle<LadduDataResult<()>>>,
    state: SinkState,
}

/// ROOT tree and physical schema write options.
#[derive(Clone, Debug)]
pub struct RootWriteOptions {
    /// Output TTree name.
    pub tree_name: Name,
    /// Physical schema write options.
    pub schema_write: SchemaWriteOptions,
}

impl Default for RootWriteOptions {
    fn default() -> Self {
        Self {
            tree_name: Name::from("tree"),
            schema_write: SchemaWriteOptions::default(),
        }
    }
}

impl RootSink {
    /// Creates a sink with default options.
    pub fn create(path: impl Into<PathBuf>) -> Self {
        Self::builder(path).build()
    }

    /// Creates a configurable sink builder.
    pub fn builder(path: impl Into<PathBuf>) -> RootSinkBuilder {
        RootSinkBuilder {
            output: OutputPath::new(path),
            options: RootWriteOptions::default(),
        }
    }

    /// Returns the concrete path after writing has begun.
    pub fn resolved_path(&self) -> Option<&Path> {
        self.resolved_path.as_deref()
    }
}

/// Builder for a [`RootSink`].
pub struct RootSinkBuilder {
    output: OutputPath,
    options: RootWriteOptions,
}

impl RootSinkBuilder {
    /// Sets the output path mode.
    pub fn output_mode(mut self, mode: OutputMode) -> Self {
        self.output = self.output.with_mode(mode);
        self
    }

    /// Selects single-file output.
    pub fn single_file(self) -> Self {
        self.output_mode(OutputMode::SingleFile)
    }

    /// Selects one output file per rank.
    pub fn per_rank_files(self) -> Self {
        self.output_mode(OutputMode::PerRankFiles)
    }

    /// Selects output mode from the write plan.
    pub fn auto_output(self) -> Self {
        self.output_mode(OutputMode::Auto)
    }

    /// Sets the output TTree name.
    pub fn tree(mut self, name: impl Into<Name>) -> Self {
        self.options.tree_name = name.into();
        self
    }

    /// Replaces physical schema write options.
    pub fn schema_write(mut self, options: SchemaWriteOptions) -> Self {
        self.options.schema_write = options;
        self
    }

    /// Sets physical column naming conventions.
    pub fn column_names(mut self, column_names: SchemaColumnNames) -> Self {
        self.options.schema_write.column_names = column_names;
        self
    }

    /// Sets floating-point output precision.
    pub fn precision(mut self, precision: Precision) -> Self {
        self.options.schema_write.precision = precision;
        self
    }

    /// Sets the weight-column emission policy.
    pub fn write_weight_column(mut self, value: WriteWeightColumn) -> Self {
        self.options.schema_write.write_weight_column = value;
        self
    }

    /// Builds the sink.
    pub fn build(self) -> RootSink {
        RootSink {
            output: self.output,
            options: self.options,
            resolved_path: None,
            event_schema: None,
            senders: None,
            writer_thread: None,
            state: SinkState::Idle,
        }
    }
}

impl EventSink for RootSink {
    fn begin(&mut self, schema: Arc<Schema>, plan: WritePlan) -> LadduDataResult<()> {
        match self.state {
            SinkState::Idle => {}
            SinkState::Writing => {
                return Err(LadduDataError::Sink("ROOT sink already initialized".into()));
            }
            SinkState::Failed => {
                return Err(LadduDataError::Sink(
                    "ROOT sink requires abort after failure".into(),
                ));
            }
        }

        let path = self.output.resolve(plan, "root")?;
        OutputPath::create_parent_dirs(&path)?;

        let columns = root_output_columns(
            &schema,
            self.options.schema_write.write_weight_column,
            &self.options.schema_write,
        );

        let (senders, receivers) = root_channels(&columns, self.options.schema_write.precision);

        let writer_path = path.clone();
        let tree_name = self.options.tree_name.clone();

        let handle = thread::spawn(move || write_root_tree(writer_path, tree_name, receivers));

        self.resolved_path = Some(path);
        self.event_schema = Some(schema);
        self.senders = Some(senders);
        self.writer_thread = Some(handle);
        self.state = SinkState::Writing;

        Ok(())
    }

    fn write_batch(&mut self, batch: &EventBatch) -> LadduDataResult<()> {
        if !matches!(self.state, SinkState::Writing) {
            return Err(LadduDataError::Sink(
                match self.state {
                    SinkState::Idle => "ROOT sink not initialized",
                    SinkState::Failed => "ROOT sink requires abort after failure",
                    SinkState::Writing => unreachable!(),
                }
                .into(),
            ));
        }

        let event_schema = self
            .event_schema
            .as_ref()
            .ok_or_else(|| LadduDataError::Sink("ROOT sink not initialized".into()))?;

        if event_schema.as_ref() != batch.schema().as_ref() {
            return Err(LadduDataError::Sink(
                "batch schema does not match ROOT sink schema".into(),
            ));
        }

        let senders = self
            .senders
            .as_ref()
            .ok_or_else(|| LadduDataError::Sink("ROOT sink not initialized".into()))?;

        let plan = PhysicalSchemaPlan::for_write(
            batch.schema(),
            &self.options.schema_write,
            self.options.schema_write.write_weight_column,
        );

        for row in 0..batch.len() {
            for (index, column) in plan.columns().iter().enumerate() {
                let value = match column.role() {
                    PhysicalColumnRole::P4 { index, component } => {
                        batch.p4_at(index, row).components()[component]
                    }
                    PhysicalColumnRole::Scalar { index } => batch.scalar_at(index, row),
                    PhysicalColumnRole::Weight => batch.weights_at(row),
                };
                if let Err(error) = senders.send(index, value) {
                    self.state = SinkState::Failed;
                    return Err(sink_error("send ROOT column", column.name(), error));
                }
            }
        }

        Ok(())
    }

    fn finish(&mut self) -> LadduDataResult<()> {
        if matches!(self.state, SinkState::Idle) {
            return Ok(());
        }
        if matches!(self.state, SinkState::Failed) {
            return Err(LadduDataError::Sink(
                "ROOT sink requires abort after failure".into(),
            ));
        }

        self.senders.take();

        if let Some(handle) = self.writer_thread.take() {
            match handle.join() {
                Ok(Ok(())) => {}
                Ok(Err(error)) => {
                    self.state = SinkState::Failed;
                    return Err(error);
                }
                Err(_) => {
                    self.state = SinkState::Failed;
                    return Err(LadduDataError::Sink("ROOT writer thread panicked".into()));
                }
            }
        }

        self.event_schema = None;
        self.state = SinkState::Idle;
        Ok(())
    }

    fn abort(&mut self) -> LadduDataResult<()> {
        // Disconnect all channels before joining so the ROOT writer can finish
        // its iterator and close the file. The file is deliberately retained
        // and may contain an incomplete tree.
        self.senders.take();
        let result = if let Some(handle) = self.writer_thread.take() {
            match handle.join() {
                Ok(result) => result,
                Err(_) => Err(LadduDataError::Sink("ROOT writer thread panicked".into())),
            }
        } else {
            Ok(())
        };

        self.event_schema = None;
        self.state = SinkState::Idle;
        result
    }
}

impl Drop for RootSink {
    fn drop(&mut self) {
        let _ = self.abort();
    }
}

enum RootColumnSenders {
    F64(Vec<Sender<f64>>),
    F32(Vec<Sender<f32>>),
}

impl RootColumnSenders {
    fn send(&self, index: usize, value: f64) -> LadduDataResult<()> {
        match self {
            Self::F64(senders) => senders[index]
                .send(value)
                .map_err(|e| LadduDataError::Sink(e.to_string())),
            Self::F32(senders) => senders[index]
                .send(value as f32)
                .map_err(|e| LadduDataError::Sink(e.to_string())),
        }
    }
}

enum RootColumnReceivers {
    F64(Vec<(Name, Receiver<f64>)>),
    F32(Vec<(Name, Receiver<f32>)>),
}

fn root_channels(
    columns: &[Name],
    precision: Precision,
) -> (RootColumnSenders, RootColumnReceivers) {
    match precision {
        Precision::F64 => {
            let mut senders = Vec::with_capacity(columns.len());
            let mut receivers = Vec::with_capacity(columns.len());

            for name in columns {
                let (tx, rx) = mpsc::channel();
                senders.push(tx);
                receivers.push((name.clone(), rx));
            }

            (
                RootColumnSenders::F64(senders),
                RootColumnReceivers::F64(receivers),
            )
        }
        Precision::F32 => {
            let mut senders = Vec::with_capacity(columns.len());
            let mut receivers = Vec::with_capacity(columns.len());

            for name in columns {
                let (tx, rx) = mpsc::channel();
                senders.push(tx);
                receivers.push((name.clone(), rx));
            }

            (
                RootColumnSenders::F32(senders),
                RootColumnReceivers::F32(receivers),
            )
        }
    }
}

fn write_root_tree(
    path: PathBuf,
    tree_name: Name,
    receivers: RootColumnReceivers,
) -> LadduDataResult<()> {
    let resource = format!("{}::{tree_name}", path.display());
    let mut file = RootFile::create(&path)
        .map_err(|error| sink_error("create ROOT file", path.display(), error))?;
    let mut tree = WriterTree::new(tree_name.as_ref());

    match receivers {
        RootColumnReceivers::F64(receivers) => {
            for (name, rx) in receivers {
                tree.new_branch(name.as_ref(), rx.into_iter());
            }
        }
        RootColumnReceivers::F32(receivers) => {
            for (name, rx) in receivers {
                tree.new_branch(name.as_ref(), rx.into_iter());
            }
        }
    }

    tree.write(&mut file)
        .map_err(|error| sink_error("write ROOT tree", &resource, error))?;
    file.close()
        .map_err(|error| sink_error("close ROOT file", &resource, error))?;

    Ok(())
}

#[cfg(test)]
mod tests {
    use std::sync::atomic::{AtomicU64, Ordering};

    use super::*;
    use crate::data::{Dataset, EventBatchBuilder};

    fn temp_path(ext: &str) -> PathBuf {
        static NEXT_TEMP_FILE_ID: AtomicU64 = AtomicU64::new(0);

        let nanos = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_nanos();
        let id = NEXT_TEMP_FILE_ID.fetch_add(1, Ordering::Relaxed);

        std::env::temp_dir().join(format!(
            "laddu-root-test-{}-{nanos}-{id}.{ext}",
            std::process::id()
        ))
    }

    fn v(x: f64) -> RealVec4 {
        RealVec4 {
            e: x + 0.3,
            px: x,
            py: x + 0.1,
            pz: x + 0.2,
        }
    }

    fn schema() -> Arc<Schema> {
        Arc::new(Schema::new(["p"], ["mass"], true).unwrap())
    }

    fn batch() -> EventBatch {
        let schema = schema();
        let mut builder = EventBatchBuilder::new(schema);

        for i in 0..4 {
            builder
                .push_weighted([v(i as f64)], [100.0 + i as f64], 10.0 + i as f64)
                .unwrap();
        }

        builder.finish().unwrap()
    }

    #[test]
    fn root_sink_and_source_roundtrip_named_tree_with_f32_precision() {
        let path = temp_path("root");
        let batch = batch();

        let mut sink = RootSink::builder(path.clone())
            .tree("events")
            .precision(Precision::F32)
            .build();

        sink.begin(Arc::clone(batch.schema()), WritePlan::default())
            .unwrap();
        sink.write_batch(&batch).unwrap();
        sink.finish().unwrap();

        let tree_names = RootSource::tree_names(&path).unwrap();
        assert!(tree_names.iter().any(|name| name.as_ref() == "events"));

        let columns = RootSource::columns(&path, Some("events")).unwrap();
        let names = columns
            .iter()
            .map(|col| col.name.to_string())
            .collect::<Vec<_>>();

        for expected in ["p_e", "p_px", "p_py", "p_pz", "mass", "weight"] {
            assert!(
                names.iter().any(|name| name == expected),
                "missing {expected}"
            );
        }

        let source = RootSource::builder(path.to_str().unwrap())
            .tree("events")
            .build()
            .unwrap();

        assert_eq!(source.tree_name(), "events");
        assert_eq!(source.num_events().unwrap(), Some(4));

        let read_batches: Vec<EventBatch> = source
            .batches(ReadPlan {
                chunk_size: Some(2),
                #[cfg(feature = "mpi")]
                distribution: Default::default(),
            })
            .unwrap()
            .map(Result::unwrap)
            .collect();

        assert_eq!(
            read_batches.iter().map(EventBatch::len).collect::<Vec<_>>(),
            vec![2, 2]
        );

        let read = EventBatch::concat(&read_batches).unwrap();

        assert_eq!(read.scalar_column(0), &[100.0, 101.0, 102.0, 103.0]);
        assert_eq!(read.weights_column().unwrap(), &[10.0, 11.0, 12.0, 13.0]);
        assert!((read.p4_at(0, 2).e - 2.3).abs() < 1.0e-6);

        let _ = std::fs::remove_file(path);
    }

    #[test]
    fn root_source_infers_first_tree_when_no_tree_is_named() {
        let path = temp_path("root");
        let batch = batch();

        let mut sink = RootSink::builder(path.clone()).tree("first_tree").build();

        sink.begin(Arc::clone(batch.schema()), WritePlan::default())
            .unwrap();
        sink.write_batch(&batch).unwrap();
        sink.finish().unwrap();

        let source = RootSource::builder(path.to_str().unwrap())
            .first_tree()
            .build()
            .unwrap();

        assert_eq!(source.tree_name(), "first_tree");

        let read = EventBatch::concat(
            &source
                .batches(ReadPlan::default())
                .unwrap()
                .map(Result::unwrap)
                .collect::<Vec<_>>(),
        )
        .unwrap();

        assert_eq!(read.scalar_column(0), &[100.0, 101.0, 102.0, 103.0]);

        let _ = std::fs::remove_file(path);
    }

    #[test]
    fn negative_root_entry_count_error_includes_operation_and_resource() {
        let error =
            usize_from_i64(-1, "negative TTree entry count", "events.root::events").unwrap_err();
        let message = error.to_string();
        assert!(message.contains("read ROOT entry count `events.root::events`"));
        assert!(message.contains("negative TTree entry count"));
    }

    #[test]
    fn root_source_named_missing_tree_fails() {
        let path = temp_path("root");
        let batch = batch();

        let mut sink = RootSink::builder(path.clone()).tree("events").build();

        sink.begin(Arc::clone(batch.schema()), WritePlan::default())
            .unwrap();
        sink.write_batch(&batch).unwrap();
        sink.finish().unwrap();

        let err = RootSource::builder(path.to_str().unwrap())
            .tree("missing")
            .build()
            .unwrap_err();

        assert!(matches!(err, LadduDataError::Source(_)));

        let _ = std::fs::remove_file(path);
    }

    #[test]
    fn root_sink_rejects_batches_with_different_schema() {
        let path = temp_path("root");
        let batch = batch();

        let mut sink = RootSink::builder(path.clone()).tree("events").build();

        sink.begin(Arc::clone(batch.schema()), WritePlan::default())
            .unwrap();

        let other_schema = Arc::new(Schema::new(["q"], ["mass"], true).unwrap());
        let mut builder = EventBatchBuilder::new(other_schema);
        builder.push_weighted([v(1.0)], [1.0], 1.0).unwrap();
        let other = builder.finish().unwrap();

        let err = sink.write_batch(&other).unwrap_err();
        assert!(matches!(err, LadduDataError::Sink(msg) if msg.contains("schema")));

        sink.finish().unwrap();
        let _ = std::fs::remove_file(path);
    }

    #[test]
    fn dataset_write_to_root_applies_dataset_transformations_before_writing() {
        let path = temp_path("root");

        let dataset = Dataset::from_batch(batch()).filter(|ev| ev.scalar(0) >= 102.0);

        let mut sink = RootSink::builder(path.clone()).tree("events").build();

        dataset.write_to(&mut sink).unwrap();

        let source = RootSource::builder(path.to_str().unwrap())
            .tree("events")
            .build()
            .unwrap();

        let read = EventBatch::concat(
            &source
                .batches(ReadPlan::default())
                .unwrap()
                .map(Result::unwrap)
                .collect::<Vec<_>>(),
        )
        .unwrap();

        assert_eq!(read.scalar_column(0), &[102.0, 103.0]);
        assert_eq!(read.weights_column().unwrap(), &[12.0, 13.0]);

        let _ = std::fs::remove_file(path);
    }

    #[test]
    fn root_batch_iter_disconnect_is_terminal_after_joining_reader() {
        let (tx, rx) = mpsc::sync_channel(1);
        drop(tx);
        let handle = thread::spawn(|| {});
        let mut iter = RootBatchIter {
            rx,
            state: RootBatchState::Receiving(handle),
        };

        assert!(iter.next().is_none());
        assert!(iter.next().is_none());
    }
}