//! The value sources of a jitexpr expression on a segment.

use columnar::{
    Cardinality, Column, ColumnType, DynamicColumn, DynamicColumnHandle,
    MonotonicallyMappableToU64, RowId, StrColumn,
};
use jitexpr::compile::CompiledFnCtx;
use jitexpr::types::{VarType, VariableValue};

use super::dynamic_term_dictionary::DynamicTermDictionary;
use crate::aggregation::value_source::{ValueSource, ValueSourceDictionary};
use crate::query::doc_predicate_query::var_type_for_column_type;
use crate::{DocId, TantivyError, COLLECT_BLOCK_BUFFER_LEN};

/// The value source of a jitexpr expression on a segment.
///
/// Each input takes the first value of the doc. A doc without a value for an input gets null for
/// that input. The expression is evaluated once per doc, and a null result means that the doc has
/// no value. A doc therefore has at most one value.
///
/// Why the first value only: using all of the values of multivalued inputs would require
/// evaluating the cartesian product of the values of the inputs, which explodes with several
/// multivalued inputs.
///
/// Values use the monotonic `u64` mapping of fast fields. `Str` results are interned in a
/// [`DynamicTermDictionary`] owned by the source: their values are term ords in first-seen order.
pub(super) struct JitExprValueSource {
    compiled_fn: CompiledFnCtx,
    column_type: ColumnType,
    /// Invariant: `inputs[i]` is bound to `compiled_fn.inputs()[i]`, and has the same type.
    inputs: Vec<InputColumn>,
    /// Interns the `Str` results.
    term_dictionary: DynamicTermDictionary,
}

impl JitExprValueSource {
    /// Precondition: `column_type` is the column type of the result type of `compiled_fn`.
    ///
    /// Panics if `inputs` do not match the inputs of `compiled_fn`.
    pub(super) fn new(
        compiled_fn: CompiledFnCtx,
        column_type: ColumnType,
        inputs: Vec<InputColumn>,
    ) -> JitExprValueSource {
        // Evaluating the function with inputs of the wrong type is undefined behavior.
        assert_eq!(compiled_fn.inputs().len(), inputs.len());
        for (compiled_input, input) in compiled_fn.inputs().iter().zip(&inputs) {
            assert_eq!(compiled_input.r#type, input.var_type);
        }
        JitExprValueSource {
            compiled_fn,
            column_type,
            inputs,
            term_dictionary: DynamicTermDictionary::default(),
        }
    }
}

impl std::fmt::Debug for JitExprValueSource {
    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        formatter
            .debug_struct("JitExprValueSource")
            .field("column_type", &self.column_type)
            .field("num_inputs", &self.inputs.len())
            .finish()
    }
}

impl ValueSource for JitExprValueSource {
    fn column_type(&self) -> ColumnType {
        self.column_type
    }

    fn load_block(
        &mut self,
        docs: &[DocId],
        values: &mut Vec<u64>,
        docids: &mut Vec<DocId>,
        _row_ids: &mut Vec<RowId>,
    ) -> Cardinality {
        values.clear();
        docids.clear();
        for input in &mut self.inputs {
            input.load_block(docs);
        }
        let JitExprValueSource {
            compiled_fn,
            inputs,
            term_dictionary,
            ..
        } = self;
        let result_type: VarType = compiled_fn.result_type();
        let mut args: Vec<VariableValue> = Vec::with_capacity(inputs.len());
        for (doc_pos, &doc) in docs.iter().enumerate() {
            args.clear();
            for input in inputs.iter() {
                args.push(input.value(doc_pos));
            }
            // SAFETY: `args` follow the compiled inputs, with their types (see `new`). The strings
            // are borrowed from `inputs`, which are not modified during the call.
            let result: VariableValue = unsafe { compiled_fn.call(&args) };
            // SAFETY: `result` has the result type of the compiled function.
            let Some(value) = (unsafe { encode_result(result, result_type, term_dictionary) })
            else {
                continue;
            };
            values.push(value);
            docids.push(doc);
        }
        if values.len() == docs.len() {
            // Each doc has exactly one value, in the order of `docs`.
            return Cardinality::Full;
        }
        Cardinality::Optional
    }

    fn term_dictionary(&self) -> Option<&dyn ValueSourceDictionary> {
        if self.column_type != ColumnType::Str {
            return None;
        }
        Some(&self.term_dictionary)
    }
}

/// A source with the same value for all of the docs.
#[derive(Debug)]
pub(super) struct ConstantValueSource {
    column_type: ColumnType,
    /// In the monotonic `u64` mapping. For `Str`, the term ord of the only term of
    /// `term_dictionary`.
    value: u64,
    term_dictionary: DynamicTermDictionary,
}

impl ConstantValueSource {
    /// Evaluates a compiled function without any input. Returns `None` if the result is null.
    ///
    /// Precondition: `column_type` is the column type of the result type of `compiled_fn`.
    pub(super) fn evaluate(
        mut compiled_fn: CompiledFnCtx,
        column_type: ColumnType,
    ) -> Option<ConstantValueSource> {
        assert!(compiled_fn.inputs().is_empty());
        let result_type: VarType = compiled_fn.result_type();
        let mut term_dictionary = DynamicTermDictionary::default();
        // SAFETY: the function has no input.
        let result: VariableValue = unsafe { compiled_fn.call(&[]) };
        // SAFETY: `result` has the result type of the compiled function.
        let value = unsafe { encode_result(result, result_type, &mut term_dictionary) }?;
        Some(ConstantValueSource {
            column_type,
            value,
            term_dictionary,
        })
    }
}

impl ValueSource for ConstantValueSource {
    fn column_type(&self) -> ColumnType {
        self.column_type
    }

    fn load_block(
        &mut self,
        docs: &[DocId],
        values: &mut Vec<u64>,
        _docids: &mut Vec<DocId>,
        _row_ids: &mut Vec<RowId>,
    ) -> Cardinality {
        values.clear();
        values.resize(docs.len(), self.value);
        Cardinality::Full
    }

    fn term_dictionary(&self) -> Option<&dyn ValueSourceDictionary> {
        if self.column_type != ColumnType::Str {
            return None;
        }
        Some(&self.term_dictionary)
    }
}

/// Encodes a result in the monotonic `u64` mapping. Returns `None` for a null result.
///
/// `Str` results are interned in `term_dictionary`, and encoded as their term ord.
///
/// # Safety
///
/// `result` must have the type `result_type`.
unsafe fn encode_result(
    result: VariableValue,
    result_type: VarType,
    term_dictionary: &mut DynamicTermDictionary,
) -> Option<u64> {
    // SAFETY: guaranteed by the caller.
    unsafe {
        match result_type {
            VarType::Bool => result.as_bool().map(bool::to_u64),
            VarType::I64 => result.as_i64().map(i64::to_u64),
            VarType::U64 => result.as_u64(),
            VarType::F64 => result.as_f64().map(f64::to_u64),
            VarType::Str => result
                .as_str()
                .map(|term: &str| term_dictionary.intern(term.as_bytes())),
            VarType::None => None,
        }
    }
}

/// A fast-field column bound to an input of the compiled expression.
pub(super) struct InputColumn {
    var_type: VarType,
    /// Values in their monotonic `u64` mapping. Term ords for a `Str` input.
    column: Column<u64>,
    /// The dictionary of the term ords. `Some` if and only if `var_type` is `Str`.
    str_column: Option<StrColumn>,
    /// `first_values[i]` is the first value of `docs[i]`, for the docs of the last block.
    first_values: Vec<Option<u64>>,
    /// The terms of `first_values`, for a `Str` input.
    block_terms: BlockTerms,
}

impl InputColumn {
    /// Opens the column of `handle`, for an input of type `var_type`.
    pub(super) fn open(
        handle: &DynamicColumnHandle,
        var_type: VarType,
    ) -> crate::Result<InputColumn> {
        let column_type = handle.column_type();
        if var_type_for_column_type(column_type) != Some(var_type) {
            return Err(TantivyError::InternalError(format!(
                "an input of type {var_type:?} cannot be bound to a column of type {column_type}"
            )));
        }
        let (column, str_column) = if var_type == VarType::Str {
            let DynamicColumn::Str(str_column) = handle.open()? else {
                return Err(TantivyError::InternalError(
                    "a text column could not be opened as a text column".to_string(),
                ));
            };
            (str_column.ords().clone(), Some(str_column))
        } else {
            let Some(column) = handle.open_u64_lenient()? else {
                return Err(TantivyError::InternalError(format!(
                    "a column of type {column_type} could not be opened as u64"
                )));
            };
            (column, None)
        };
        Ok(InputColumn {
            var_type,
            column,
            str_column,
            first_values: Vec::with_capacity(COLLECT_BLOCK_BUFFER_LEN),
            block_terms: BlockTerms::default(),
        })
    }

    /// Loads the first value of each doc of `docs`.
    ///
    /// Panics if the dictionary of a text column is corrupted.
    fn load_block(&mut self, docs: &[DocId]) {
        // `first_vals` does not write the entries of the docs without a value: we reset them.
        self.first_values.clear();
        self.first_values.resize(docs.len(), None);
        self.column.first_vals(docs, &mut self.first_values);
        if let Some(str_column) = &self.str_column {
            self.block_terms.load(str_column, &self.first_values);
        }
    }

    /// Returns the value of `docs[doc_pos]`, for the `docs` of the last `load_block` call.
    #[inline]
    fn value(&self, doc_pos: usize) -> VariableValue<'_> {
        let Some(value) = self.first_values[doc_pos] else {
            return VariableValue::none();
        };
        match self.var_type {
            VarType::Bool => VariableValue::from(bool::from_u64(value)),
            VarType::I64 => VariableValue::from(i64::from_u64(value)),
            VarType::U64 => VariableValue::from(value),
            VarType::F64 => VariableValue::from(f64::from_u64(value)),
            VarType::Str => VariableValue::from(self.block_terms.term(value)),
            VarType::None => VariableValue::none(),
        }
    }
}

/// The terms of the term ords of a block, fetched with a single dictionary lookup.
#[derive(Default)]
struct BlockTerms {
    /// The distinct term ords of the block, sorted.
    sorted_ords: Vec<u64>,
    /// The concatenated terms, in the order of `sorted_ords`.
    buffer: String,
    /// `buffer[offsets[i]..offsets[i + 1]]` is the term of `sorted_ords[i]`.
    offsets: Vec<usize>,
}

impl BlockTerms {
    /// Panics if the dictionary is corrupted: `load_block` cannot return an error.
    fn load(&mut self, str_column: &StrColumn, term_ords: &[Option<u64>]) {
        let BlockTerms {
            sorted_ords,
            buffer,
            offsets,
        } = self;
        sorted_ords.clear();
        sorted_ords.extend(term_ords.iter().flatten());
        sorted_ords.sort_unstable();
        sorted_ords.dedup();
        buffer.clear();
        offsets.clear();
        offsets.push(0);
        let all_found = str_column
            .dictionary()
            .sorted_ords_to_term_cb(sorted_ords, |term| {
                let term_str =
                    std::str::from_utf8(term).expect("fast-field string dictionary is corrupted");
                buffer.push_str(term_str);
                offsets.push(buffer.len());
            })
            .expect("fast-field string dictionary is corrupted");
        assert!(all_found, "fast-field string dictionary is corrupted");
    }

    /// Precondition: `term_ord` is one of the term ords of the last `load` call.
    #[inline]
    fn term(&self, term_ord: u64) -> &str {
        let idx = self
            .sorted_ords
            .binary_search(&term_ord)
            .expect("the term ord belongs to the block");
        &self.buffer[self.offsets[idx]..self.offsets[idx + 1]]
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::aggregation::{JitExprValueSourceProvider, ValueSourceProvider};
    use crate::schema::{Schema, FAST, STRING};
    use crate::Index;

    /// One segment: doc `i` has `number = i` and `label = labels[i]`, except for the docs of
    /// `null_docs`, which have neither.
    fn create_index(labels: &[&str], null_docs: &[usize]) -> Index {
        let mut schema_builder = Schema::builder();
        let number = schema_builder.add_u64_field("number", FAST);
        let label = schema_builder.add_text_field("label", STRING | FAST);
        let index = Index::create_in_ram(schema_builder.build());
        let mut writer = index.writer_for_tests().unwrap();
        for (doc_pos, label_value) in labels.iter().enumerate() {
            if null_docs.contains(&doc_pos) {
                writer.add_document(doc!()).unwrap();
            } else {
                writer
                    .add_document(doc!(number => doc_pos as u64, label => *label_value))
                    .unwrap();
            }
        }
        writer.commit().unwrap();
        index
    }

    fn open_source(index: &Index, expression: &str) -> Box<dyn ValueSource> {
        let expression = jitexpr::ast::deserialize(expression).unwrap();
        let provider = JitExprValueSourceProvider::new(expression).unwrap();
        let searcher = index.reader().unwrap().searcher();
        provider
            .for_segment(searcher.segment_reader(0), None)
            .unwrap()
    }

    /// Returns the values and docids of a block. `docids` is only filled for a non-full block.
    fn load_block(
        source: &mut dyn ValueSource,
        docs: &[DocId],
    ) -> (Cardinality, Vec<u64>, Vec<DocId>) {
        let mut values = Vec::new();
        let mut docids = Vec::new();
        let mut row_ids = Vec::new();
        let cardinality = source.load_block(docs, &mut values, &mut docids, &mut row_ids);
        if cardinality.is_full() {
            docids.clear();
        }
        (cardinality, values, docids)
    }

    fn terms(source: &dyn ValueSource, term_ords: &[u64]) -> Vec<String> {
        let mut terms = Vec::new();
        let all_found = source
            .term_dictionary()
            .unwrap()
            .sorted_ords_to_term_cb(term_ords, &mut |term| {
                terms.push(String::from_utf8(term.to_vec()).unwrap())
            })
            .unwrap();
        assert!(all_found);
        terms
    }

    #[test]
    fn test_block_cardinality() {
        let index = create_index(&["a", "b", "c", "d"], &[2]);
        let mut source = open_source(&index, "(ADD number 10u64)");
        assert_eq!(source.column_type(), ColumnType::U64);
        assert!(source.term_dictionary().is_none());

        // All of the docs have a value.
        let (cardinality, values, _) = load_block(&mut *source, &[0, 1, 3]);
        assert_eq!(cardinality, Cardinality::Full);
        assert_eq!(values, vec![10, 11, 13]);

        // Doc 2 has no value. The buffers of the previous block are cleared.
        let (cardinality, values, docids) = load_block(&mut *source, &[1, 2, 3]);
        assert_eq!(cardinality, Cardinality::Optional);
        assert_eq!(values, vec![11, 13]);
        assert_eq!(docids, vec![1, 3]);

        let (cardinality, values, docids) = load_block(&mut *source, &[2]);
        assert_eq!(cardinality, Cardinality::Optional);
        assert!(values.is_empty());
        assert!(docids.is_empty());
    }

    #[test]
    fn test_text_term_ords_are_stable_across_blocks() {
        let index = create_index(&["b", "a", "b", "c", "a"], &[]);
        let mut source = open_source(&index, "(UPPER label)");
        assert_eq!(source.column_type(), ColumnType::Str);
        assert!(!source.term_dictionary().unwrap().ords_sorted_with_terms());

        let (cardinality, first_block_ords, _) = load_block(&mut *source, &[0, 1, 2]);
        assert_eq!(cardinality, Cardinality::Full);
        // Ords are assigned in first-seen order.
        assert_eq!(first_block_ords, vec![0, 1, 0]);

        let (_, second_block_ords, _) = load_block(&mut *source, &[3, 4]);
        assert_eq!(second_block_ords, vec![2, 1]);
        assert_eq!(source.term_dictionary().unwrap().num_terms(), 3);
        assert_eq!(terms(&*source, &[0, 1, 2]), vec!["B", "A", "C"]);
    }

    #[test]
    fn test_constant_source() {
        let index = create_index(&["a", "b"], &[]);
        let mut source = open_source(&index, r#"(UPPER "x")"#);
        assert_eq!(source.column_type(), ColumnType::Str);
        let (cardinality, values, _) = load_block(&mut *source, &[0, 1]);
        assert_eq!(cardinality, Cardinality::Full);
        assert_eq!(values, vec![0, 0]);
        assert_eq!(terms(&*source, &[0]), vec!["X"]);

        // A null constant is a source without any value.
        let mut source = open_source(&index, "(ADD absent 1u64)");
        let (cardinality, values, docids) = load_block(&mut *source, &[0, 1]);
        assert!(!cardinality.is_full());
        assert!(values.is_empty());
        assert!(docids.is_empty());
    }
}