#[cfg(feature = "csv")]
use arrow::buffer::Buffer;
use polars_core::prelude::*;
use polars_io::cloud::CloudOptions;
use polars_io::csv::read::{
    CommentPrefix, CsvEncoding, CsvParseOptions, CsvReadOptions, NullValues,
    read_until_start_and_infer_schema,
};
use polars_io::path_utils::expand_paths;
use polars_io::utils::compression::CompressedReader;
use polars_io::{HiveOptions, RowIndex};
use polars_utils::mmap::MemSlice;
use polars_utils::pl_path::PlRefPath;
use polars_utils::slice_enum::Slice;

use crate::prelude::*;

#[derive(Clone)]
#[cfg(feature = "csv")]
pub struct LazyCsvReader {
    sources: ScanSources,
    glob: bool,
    cache: bool,
    read_options: CsvReadOptions,
    cloud_options: Option<CloudOptions>,
    include_file_paths: Option<PlSmallStr>,
}

#[cfg(feature = "csv")]
impl LazyCsvReader {
    /// Re-export to shorten code.
    pub fn map_parse_options<F: Fn(CsvParseOptions) -> CsvParseOptions>(
        mut self,
        map_func: F,
    ) -> Self {
        self.read_options = self.read_options.map_parse_options(map_func);
        self
    }

    pub fn new_paths(paths: Buffer<PlRefPath>) -> Self {
        Self::new_with_sources(ScanSources::Paths(paths))
    }

    pub fn new_with_sources(sources: ScanSources) -> Self {
        LazyCsvReader {
            sources,
            glob: true,
            cache: true,
            read_options: Default::default(),
            cloud_options: Default::default(),
            include_file_paths: None,
        }
    }

    pub fn new(path: PlRefPath) -> Self {
        Self::new_with_sources(ScanSources::Paths(Buffer::from_iter([path])))
    }

    /// Skip this number of rows after the header location.
    #[must_use]
    pub fn with_skip_rows_after_header(mut self, offset: usize) -> Self {
        self.read_options.skip_rows_after_header = offset;
        self
    }

    /// Add a row index column.
    #[must_use]
    pub fn with_row_index(mut self, row_index: Option<RowIndex>) -> Self {
        self.read_options.row_index = row_index;
        self
    }

    /// Try to stop parsing when `n` rows are parsed. During multithreaded parsing the upper bound `n` cannot
    /// be guaranteed.
    #[must_use]
    pub fn with_n_rows(mut self, num_rows: Option<usize>) -> Self {
        self.read_options.n_rows = num_rows;
        self
    }

    /// Sets the number of threads used for CSV parsing.
    #[must_use]
    pub fn with_n_threads(mut self, n_threads: Option<usize>) -> Self {
        self.read_options.n_threads = n_threads;
        self
    }

    /// Set the number of rows to use when inferring the csv schema.
    /// The default is 100 rows.
    /// Setting to [None] will do a full table scan, which is very slow.
    #[must_use]
    pub fn with_infer_schema_length(mut self, num_rows: Option<usize>) -> Self {
        self.read_options.infer_schema_length = num_rows;
        self
    }

    /// Continue with next batch when a ParserError is encountered.
    #[must_use]
    pub fn with_ignore_errors(mut self, ignore: bool) -> Self {
        self.read_options.ignore_errors = ignore;
        self
    }

    /// Set the CSV file's schema
    #[must_use]
    pub fn with_schema(mut self, schema: Option<SchemaRef>) -> Self {
        self.read_options.schema = schema;
        self
    }

    /// Skip the first `n` rows during parsing. The header will be parsed at row `n`.
    /// Note that by row we mean valid CSV, encoding and comments are respected.
    #[must_use]
    pub fn with_skip_rows(mut self, skip_rows: usize) -> Self {
        self.read_options.skip_rows = skip_rows;
        self
    }

    /// Skip the first `n` lines during parsing. The header will be parsed at line `n`.
    /// We don't respect CSV escaping when skipping lines.
    #[must_use]
    pub fn with_skip_lines(mut self, skip_lines: usize) -> Self {
        self.read_options.skip_lines = skip_lines;
        self
    }

    /// Overwrite the schema with the dtypes in this given Schema. The given schema may be a subset
    /// of the total schema.
    #[must_use]
    pub fn with_dtype_overwrite(mut self, schema: Option<SchemaRef>) -> Self {
        self.read_options.schema_overwrite = schema;
        self
    }

    /// Set whether the CSV file has headers
    #[must_use]
    pub fn with_has_header(mut self, has_header: bool) -> Self {
        self.read_options.has_header = has_header;
        self
    }

    /// Sets the chunk size used by the parser. This influences performance.
    /// This can be used as a way to reduce memory usage during the parsing at the cost of performance.
    pub fn with_chunk_size(mut self, chunk_size: usize) -> Self {
        self.read_options.chunk_size = chunk_size;
        self
    }

    /// Set the CSV file's column separator as a byte character
    #[must_use]
    pub fn with_separator(self, separator: u8) -> Self {
        self.map_parse_options(|opts| opts.with_separator(separator))
    }

    /// Set the comment prefix for this instance. Lines starting with this prefix will be ignored.
    #[must_use]
    pub fn with_comment_prefix(self, comment_prefix: Option<PlSmallStr>) -> Self {
        self.map_parse_options(|opts| {
            opts.with_comment_prefix(comment_prefix.clone().map(|s| {
                if s.len() == 1 && s.chars().next().unwrap().is_ascii() {
                    CommentPrefix::Single(s.as_bytes()[0])
                } else {
                    CommentPrefix::Multi(s)
                }
            }))
        })
    }

    /// Set the `char` used as quote char. The default is `b'"'`. If set to [`None`] quoting is disabled.
    #[must_use]
    pub fn with_quote_char(self, quote_char: Option<u8>) -> Self {
        self.map_parse_options(|opts| opts.with_quote_char(quote_char))
    }

    /// Set the `char` used as end of line. The default is `b'\n'`.
    #[must_use]
    pub fn with_eol_char(self, eol_char: u8) -> Self {
        self.map_parse_options(|opts| opts.with_eol_char(eol_char))
    }

    /// Set values that will be interpreted as missing/ null.
    #[must_use]
    pub fn with_null_values(self, null_values: Option<NullValues>) -> Self {
        self.map_parse_options(|opts| opts.with_null_values(null_values.clone()))
    }

    /// Treat missing fields as null.
    pub fn with_missing_is_null(self, missing_is_null: bool) -> Self {
        self.map_parse_options(|opts| opts.with_missing_is_null(missing_is_null))
    }

    /// Cache the DataFrame after reading.
    #[must_use]
    pub fn with_cache(mut self, cache: bool) -> Self {
        self.cache = cache;
        self
    }

    /// Reduce memory usage at the expense of performance
    #[must_use]
    pub fn with_low_memory(mut self, low_memory: bool) -> Self {
        self.read_options.low_memory = low_memory;
        self
    }

    /// Set  [`CsvEncoding`]
    #[must_use]
    pub fn with_encoding(self, encoding: CsvEncoding) -> Self {
        self.map_parse_options(|opts| opts.with_encoding(encoding))
    }

    /// Automatically try to parse dates/datetimes and time.
    /// If parsing fails, columns remain of dtype [`DataType::String`].
    #[cfg(feature = "temporal")]
    pub fn with_try_parse_dates(self, try_parse_dates: bool) -> Self {
        self.map_parse_options(|opts| opts.with_try_parse_dates(try_parse_dates))
    }

    /// Raise an error if CSV is empty (otherwise return an empty frame)
    #[must_use]
    pub fn with_raise_if_empty(mut self, raise_if_empty: bool) -> Self {
        self.read_options.raise_if_empty = raise_if_empty;
        self
    }

    /// Truncate lines that are longer than the schema.
    #[must_use]
    pub fn with_truncate_ragged_lines(self, truncate_ragged_lines: bool) -> Self {
        self.map_parse_options(|opts| opts.with_truncate_ragged_lines(truncate_ragged_lines))
    }

    #[must_use]
    pub fn with_decimal_comma(self, decimal_comma: bool) -> Self {
        self.map_parse_options(|opts| opts.with_decimal_comma(decimal_comma))
    }

    #[must_use]
    /// Expand path given via globbing rules.
    pub fn with_glob(mut self, toggle: bool) -> Self {
        self.glob = toggle;
        self
    }

    pub fn with_cloud_options(mut self, cloud_options: Option<CloudOptions>) -> Self {
        self.cloud_options = cloud_options;
        self
    }

    /// Modify a schema before we run the lazy scanning.
    ///
    /// Important! Run this function latest in the builder!
    pub fn with_schema_modify<F>(mut self, f: F) -> PolarsResult<Self>
    where
        F: Fn(Schema) -> PolarsResult<Schema>,
    {
        let n_threads = self.read_options.n_threads;

        let infer_schema = |bytes: MemSlice| {
            let mut reader = CompressedReader::try_new(bytes)?;

            let (inferred_schema, _) =
                read_until_start_and_infer_schema(&self.read_options, None, None, &mut reader)?;

            PolarsResult::Ok(inferred_schema)
        };

        let schema = match self.sources.clone() {
            ScanSources::Paths(paths) => {
                // TODO: Path expansion should happen when converting to the IR
                // https://github.com/pola-rs/polars/issues/17634
                let paths = expand_paths(
                    &paths[..],
                    self.glob(),
                    &[], // hidden_file_prefix
                    &mut self.cloud_options,
                )?;

                let Some(path) = paths.first() else {
                    polars_bail!(ComputeError: "no paths specified for this reader");
                };

                infer_schema(MemSlice::from_file(&polars_utils::open_file(
                    path.as_std_path(),
                )?)?)?
            },
            ScanSources::Files(files) => {
                let Some(file) = files.first() else {
                    polars_bail!(ComputeError: "no buffers specified for this reader");
                };

                infer_schema(MemSlice::from_file(file)?)?
            },
            ScanSources::Buffers(buffers) => {
                let Some(buffer) = buffers.first() else {
                    polars_bail!(ComputeError: "no buffers specified for this reader");
                };

                infer_schema(buffer.clone())?
            },
        };

        self.read_options.n_threads = n_threads;
        let mut schema = f(schema)?;

        // the dtypes set may be for the new names, so update again
        if let Some(overwrite_schema) = &self.read_options.schema_overwrite {
            for (name, dtype) in overwrite_schema.iter() {
                schema.with_column(name.clone(), dtype.clone());
            }
        }

        Ok(self.with_schema(Some(Arc::new(schema))))
    }

    pub fn with_include_file_paths(mut self, include_file_paths: Option<PlSmallStr>) -> Self {
        self.include_file_paths = include_file_paths;
        self
    }
}

impl LazyFileListReader for LazyCsvReader {
    /// Get the final [LazyFrame].
    fn finish(self) -> PolarsResult<LazyFrame> {
        let rechunk = self.rechunk();
        let row_index = self.row_index().cloned();
        let pre_slice = self.n_rows().map(|len| Slice::Positive { offset: 0, len });

        let lf: LazyFrame = DslBuilder::scan_csv(
            self.sources,
            self.read_options,
            UnifiedScanArgs {
                schema: None,
                cloud_options: self.cloud_options,
                hive_options: HiveOptions::new_disabled(),
                rechunk,
                cache: self.cache,
                glob: self.glob,
                hidden_file_prefix: None,
                projection: None,
                column_mapping: None,
                default_values: None,
                row_index,
                pre_slice,
                cast_columns_policy: CastColumnsPolicy::ERROR_ON_MISMATCH,
                missing_columns_policy: MissingColumnsPolicy::Raise,
                extra_columns_policy: ExtraColumnsPolicy::Raise,
                include_file_paths: self.include_file_paths,
                deletion_files: None,
                table_statistics: None,
                row_count: None,
            },
        )?
        .build()
        .into();
        Ok(lf)
    }

    fn finish_no_glob(self) -> PolarsResult<LazyFrame> {
        unreachable!();
    }

    fn glob(&self) -> bool {
        self.glob
    }

    fn sources(&self) -> &ScanSources {
        &self.sources
    }

    fn with_sources(mut self, sources: ScanSources) -> Self {
        self.sources = sources;
        self
    }

    fn with_n_rows(mut self, n_rows: impl Into<Option<usize>>) -> Self {
        self.read_options.n_rows = n_rows.into();
        self
    }

    fn with_row_index(mut self, row_index: impl Into<Option<RowIndex>>) -> Self {
        self.read_options.row_index = row_index.into();
        self
    }

    fn rechunk(&self) -> bool {
        self.read_options.rechunk
    }

    /// Rechunk the memory to contiguous chunks when parsing is done.
    fn with_rechunk(mut self, rechunk: bool) -> Self {
        self.read_options.rechunk = rechunk;
        self
    }

    /// Try to stop parsing when `n` rows are parsed. During multithreaded parsing the upper bound `n` cannot
    /// be guaranteed.
    fn n_rows(&self) -> Option<usize> {
        self.read_options.n_rows
    }

    /// Return the row index settings.
    fn row_index(&self) -> Option<&RowIndex> {
        self.read_options.row_index.as_ref()
    }

    fn concat_impl(&self, lfs: Vec<LazyFrame>) -> PolarsResult<LazyFrame> {
        // set to false, as the csv parser has full thread utilization
        let args = UnionArgs {
            rechunk: self.rechunk(),
            parallel: false,
            to_supertypes: false,
            from_partitioned_ds: true,
            ..Default::default()
        };
        concat_impl(&lfs, args)
    }

    /// [CloudOptions] used to list files.
    fn cloud_options(&self) -> Option<&CloudOptions> {
        self.cloud_options.as_ref()
    }
}
