delta-arrow-reader 0.1.3

use std::collections::BTreeMap;

use crate::{DeltaReaderError, error::InvalidConfigurationSnafu};

const DEFAULT_MAX_CONCURRENT_FILE_READS_PER_PARTITION: usize = 3;
const DEFAULT_OUTPUT_BUFFER_CAPACITY_PER_PARTITION: usize = 1;
const DEFAULT_NATIVE_ASYNC_PREFETCH_FILE_COUNT_PER_PARTITION: usize = 2;
const DEFAULT_PARQUET_METADATA_SIZE_HINT: usize = 64 * 1024;

/// Storage options forwarded to Delta object-store construction.
pub type DeltaStorageOptions = BTreeMap<String, String>;

/// Delta snapshot selected for a table load.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum DeltaSnapshotSelection {
    /// Load the latest available snapshot.
    #[default]
    Latest,
    /// Load one exact Delta log version.
    Version(u64),
}

/// Backend used to read Delta data files.
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq)]
pub enum DeltaReaderBackend {
    /// Use the official Delta Kernel data-file reader.
    OfficialKernel,
    /// Use the native asynchronous Parquet reader.
    #[default]
    NativeAsync,
}

/// Bounded execution settings for one Delta scan.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct DeltaReaderExecutionOptions {
    reader_backend: DeltaReaderBackend,
    max_concurrent_file_reads_per_scan: Option<usize>,
    max_concurrent_file_reads_per_partition: usize,
    output_buffer_capacity_per_partition: usize,
    native_async_prefetch_file_count_per_partition: usize,
    parquet_metadata_size_hint: Option<usize>,
    parquet_full_file_read_threshold: Option<usize>,
}

impl DeltaReaderExecutionOptions {
    /// Returns the baseline execution settings.
    pub const fn new() -> Self {
        Self {
            reader_backend: DeltaReaderBackend::NativeAsync,
            max_concurrent_file_reads_per_scan: None,
            max_concurrent_file_reads_per_partition:
                DEFAULT_MAX_CONCURRENT_FILE_READS_PER_PARTITION,
            output_buffer_capacity_per_partition: DEFAULT_OUTPUT_BUFFER_CAPACITY_PER_PARTITION,
            native_async_prefetch_file_count_per_partition:
                DEFAULT_NATIVE_ASYNC_PREFETCH_FILE_COUNT_PER_PARTITION,
            parquet_metadata_size_hint: Some(DEFAULT_PARQUET_METADATA_SIZE_HINT),
            parquet_full_file_read_threshold: None,
        }
    }

    /// Returns the selected data-file reader backend.
    pub const fn reader_backend(&self) -> DeltaReaderBackend {
        self.reader_backend
    }

    /// Returns the optional scan-wide file-read limit.
    pub const fn max_concurrent_file_reads_per_scan(&self) -> Option<usize> {
        self.max_concurrent_file_reads_per_scan
    }

    /// Returns the per-partition file-read limit.
    pub const fn max_concurrent_file_reads_per_partition(&self) -> usize {
        self.max_concurrent_file_reads_per_partition
    }

    /// Returns the per-partition output buffer capacity.
    pub const fn output_buffer_capacity_per_partition(&self) -> usize {
        self.output_buffer_capacity_per_partition
    }

    /// Returns the NativeAsync per-partition file prefetch depth.
    pub const fn native_async_prefetch_file_count_per_partition(&self) -> usize {
        self.native_async_prefetch_file_count_per_partition
    }

    /// Returns the NativeAsync Parquet metadata size hint.
    pub const fn parquet_metadata_size_hint(&self) -> Option<usize> {
        self.parquet_metadata_size_hint
    }

    /// Returns the NativeAsync full-file read threshold.
    pub const fn parquet_full_file_read_threshold(&self) -> Option<usize> {
        self.parquet_full_file_read_threshold
    }

    /// Selects a data-file reader backend.
    pub fn with_reader_backend(
        mut self,
        value: DeltaReaderBackend,
    ) -> Result<Self, DeltaReaderError> {
        self.reader_backend = value;
        self.validate()?;
        Ok(self)
    }

    /// Sets or clears the scan-wide file-read limit.
    pub fn with_max_concurrent_file_reads_per_scan(
        mut self,
        value: Option<usize>,
    ) -> Result<Self, DeltaReaderError> {
        self.max_concurrent_file_reads_per_scan = value;
        self.validate()?;
        Ok(self)
    }

    /// Sets the per-partition file-read limit.
    pub fn with_max_concurrent_file_reads_per_partition(
        mut self,
        value: usize,
    ) -> Result<Self, DeltaReaderError> {
        self.max_concurrent_file_reads_per_partition = value;
        self.validate()?;
        Ok(self)
    }

    /// Sets the per-partition output buffer capacity.
    pub fn with_output_buffer_capacity_per_partition(
        mut self,
        value: usize,
    ) -> Result<Self, DeltaReaderError> {
        self.output_buffer_capacity_per_partition = value;
        self.validate()?;
        Ok(self)
    }

    /// Sets the NativeAsync per-partition file prefetch depth.
    pub fn with_native_async_prefetch_file_count_per_partition(
        mut self,
        value: usize,
    ) -> Result<Self, DeltaReaderError> {
        self.native_async_prefetch_file_count_per_partition = value;
        self.validate()?;
        Ok(self)
    }

    /// Sets or clears the NativeAsync Parquet metadata size hint.
    pub fn with_parquet_metadata_size_hint(
        mut self,
        value: Option<usize>,
    ) -> Result<Self, DeltaReaderError> {
        self.parquet_metadata_size_hint = value;
        self.validate()?;
        Ok(self)
    }

    /// Sets or clears the NativeAsync full-file read threshold.
    pub fn with_parquet_full_file_read_threshold(
        mut self,
        value: Option<usize>,
    ) -> Result<Self, DeltaReaderError> {
        self.parquet_full_file_read_threshold = value;
        self.validate()?;
        Ok(self)
    }

    /// Validates all execution bounds.
    pub fn validate(&self) -> Result<(), DeltaReaderError> {
        validate_optional_positive(
            self.max_concurrent_file_reads_per_scan,
            "max_concurrent_file_reads_per_scan_must_be_positive",
        )?;
        validate_positive(
            self.max_concurrent_file_reads_per_partition,
            "max_concurrent_file_reads_per_partition_must_be_positive",
        )?;
        validate_positive(
            self.output_buffer_capacity_per_partition,
            "output_buffer_capacity_per_partition_must_be_positive",
        )?;
        validate_optional_positive(
            self.parquet_metadata_size_hint,
            "parquet_metadata_size_hint_must_be_positive",
        )?;
        validate_optional_positive(
            self.parquet_full_file_read_threshold,
            "parquet_full_file_read_threshold_must_be_positive",
        )?;

        Ok(())
    }

    pub(crate) fn resolved_max_concurrent_file_reads_per_scan(
        &self,
        target_partitions: usize,
    ) -> usize {
        self.max_concurrent_file_reads_per_scan.unwrap_or_else(|| {
            target_partitions
                .saturating_mul(self.max_concurrent_file_reads_per_partition)
                .max(1)
        })
    }
}

impl Default for DeltaReaderExecutionOptions {
    fn default() -> Self {
        Self::new()
    }
}

fn validate_positive(value: usize, reason: &'static str) -> Result<(), DeltaReaderError> {
    if value == 0 {
        return InvalidConfigurationSnafu { reason }.fail();
    }
    Ok(())
}

fn validate_optional_positive(
    value: Option<usize>,
    reason: &'static str,
) -> Result<(), DeltaReaderError> {
    if value == Some(0) {
        return InvalidConfigurationSnafu { reason }.fail();
    }
    Ok(())
}

#[cfg(test)]
mod tests {
    use crate::DeltaReaderPhase;

    use super::{
        DeltaReaderBackend, DeltaReaderExecutionOptions, DeltaSnapshotSelection,
        DeltaStorageOptions,
    };

    #[test]
    fn public_defaults_match_the_frozen_baseline() {
        let options = DeltaReaderExecutionOptions::new();

        assert_eq!(
            DeltaSnapshotSelection::default(),
            DeltaSnapshotSelection::Latest
        );
        assert_eq!(
            DeltaReaderBackend::default(),
            DeltaReaderBackend::NativeAsync
        );
        assert_eq!(DeltaReaderExecutionOptions::default(), options);
        assert_eq!(options.reader_backend(), DeltaReaderBackend::NativeAsync);
        assert_eq!(options.max_concurrent_file_reads_per_scan(), None);
        assert_eq!(options.max_concurrent_file_reads_per_partition(), 3);
        assert_eq!(options.output_buffer_capacity_per_partition(), 1);
        assert_eq!(options.native_async_prefetch_file_count_per_partition(), 2);
        assert_eq!(options.parquet_metadata_size_hint(), Some(65_536));
        assert_eq!(options.parquet_full_file_read_threshold(), None);
        assert_eq!(DeltaStorageOptions::default(), DeltaStorageOptions::new());
        assert_eq!(
            DeltaSnapshotSelection::Version(7),
            DeltaSnapshotSelection::Version(7)
        );
    }

    #[test]
    fn builders_set_every_public_option() -> Result<(), Box<dyn std::error::Error>> {
        let options = DeltaReaderExecutionOptions::new()
            .with_reader_backend(DeltaReaderBackend::OfficialKernel)?
            .with_max_concurrent_file_reads_per_scan(Some(8))?
            .with_max_concurrent_file_reads_per_partition(4)?
            .with_output_buffer_capacity_per_partition(2)?
            .with_native_async_prefetch_file_count_per_partition(0)?
            .with_parquet_metadata_size_hint(None)?
            .with_parquet_full_file_read_threshold(Some(1024))?;

        assert_eq!(options.reader_backend(), DeltaReaderBackend::OfficialKernel);
        assert_eq!(options.max_concurrent_file_reads_per_scan(), Some(8));
        assert_eq!(options.max_concurrent_file_reads_per_partition(), 4);
        assert_eq!(options.output_buffer_capacity_per_partition(), 2);
        assert_eq!(options.native_async_prefetch_file_count_per_partition(), 0);
        assert_eq!(options.parquet_metadata_size_hint(), None);
        assert_eq!(options.parquet_full_file_read_threshold(), Some(1024));
        Ok(())
    }

    #[test]
    fn invalid_bounds_return_redacted_configuration_errors() {
        let invalid = [
            DeltaReaderExecutionOptions::new().with_max_concurrent_file_reads_per_scan(Some(0)),
            DeltaReaderExecutionOptions::new().with_max_concurrent_file_reads_per_partition(0),
            DeltaReaderExecutionOptions::new().with_output_buffer_capacity_per_partition(0),
            DeltaReaderExecutionOptions::new().with_parquet_metadata_size_hint(Some(0)),
            DeltaReaderExecutionOptions::new().with_parquet_full_file_read_threshold(Some(0)),
        ];

        for result in invalid {
            let error = result.expect_err("invalid execution options must fail");
            assert_eq!(error.phase(), DeltaReaderPhase::Configuration);
            assert_eq!(error.as_str(), "invalid_configuration");
        }
    }

    #[test]
    fn independent_bounds_preserve_the_frozen_reader_behavior()
    -> Result<(), Box<dyn std::error::Error>> {
        let options = DeltaReaderExecutionOptions::new()
            .with_max_concurrent_file_reads_per_scan(Some(2))?
            .with_native_async_prefetch_file_count_per_partition(4)?;

        assert_eq!(options.max_concurrent_file_reads_per_scan(), Some(2));
        assert_eq!(options.max_concurrent_file_reads_per_partition(), 3);
        assert_eq!(options.native_async_prefetch_file_count_per_partition(), 4);
        Ok(())
    }

    #[test]
    fn scan_capacity_resolves_once_from_the_fixed_partition_target()
    -> Result<(), Box<dyn std::error::Error>> {
        let defaults = DeltaReaderExecutionOptions::new();
        assert_eq!(defaults.resolved_max_concurrent_file_reads_per_scan(4), 12);
        assert_eq!(
            defaults.resolved_max_concurrent_file_reads_per_scan(usize::MAX),
            usize::MAX
        );

        let explicit = defaults.with_max_concurrent_file_reads_per_scan(Some(7))?;
        assert_eq!(explicit.resolved_max_concurrent_file_reads_per_scan(4), 7);
        Ok(())
    }
}