//! Parser for query language using pest

use pest::Parser;
use pest_derive::Parser;

use super::parsed_query::*;

#[derive(Parser)]
#[grammar = "parser/query/grammar.pest"]
pub struct QueryParser;

/// Error type for query parsing
#[derive(Debug, Clone, PartialEq)]
pub enum QueryParseError {
    SyntaxError(String),
    InvalidNumber(String),
}

impl std::fmt::Display for QueryParseError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            QueryParseError::SyntaxError(msg) => write!(f, "Syntax error: {}", msg),
            QueryParseError::InvalidNumber(msg) => write!(f, "Invalid number: {}", msg),
        }
    }
}

impl std::error::Error for QueryParseError {}

/// Parse a query string into a ParsedQuery
pub fn parse_query(input: &str) -> Result<ParsedQuery, QueryParseError> {
    let pairs = QueryParser::parse(Rule::query, input)
        .map_err(|e| QueryParseError::SyntaxError(e.to_string()))?;

    let mut from_clause = None;
    let mut operations = Vec::new();
    let mut aggregation = None;

    for pair in pairs {
        if pair.as_rule() == Rule::query {
            for inner_pair in pair.into_inner() {
                match inner_pair.as_rule() {
                    Rule::from_clause => {
                        from_clause = Some(parse_from_clause(inner_pair)?);
                    }
                    Rule::operation => {
                        operations.push(parse_operation(inner_pair)?);
                    }
                    Rule::aggregation => {
                        aggregation = Some(parse_aggregation(inner_pair)?);
                    }
                    Rule::EOI => {}
                    _ => {}
                }
            }
        }
    }

    let from = from_clause.ok_or_else(|| {
        QueryParseError::SyntaxError("Query must start with 'from' clause".to_string())
    })?;

    Ok(ParsedQuery {
        from,
        operations,
        aggregation,
    })
}

fn parse_from_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedFromClause, QueryParseError> {
    for inner_pair in pair.into_inner() {
        if inner_pair.as_rule() == Rule::entity_selector {
            let selector = parse_entity_selector(inner_pair)?;
            return Ok(ParsedFromClause { selector });
        }
    }
    Err(QueryParseError::SyntaxError(
        "Invalid from clause".to_string(),
    ))
}

fn parse_entity_selector(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedEntitySelector, QueryParseError> {
    let text = pair.as_str();
    if text == "*" {
        Ok(ParsedEntitySelector::Wildcard)
    } else {
        Ok(ParsedEntitySelector::Type(text.to_string()))
    }
}

fn parse_operation(pair: pest::iterators::Pair<Rule>) -> Result<ParsedOperation, QueryParseError> {
    let inner_pair = pair
        .into_inner()
        .next()
        .ok_or_else(|| QueryParseError::SyntaxError("Empty operation".to_string()))?;

    match inner_pair.as_rule() {
        Rule::where_clause => parse_where_clause(inner_pair),
        Rule::related_clause => parse_related_clause(inner_pair),
        Rule::order_clause => parse_order_clause(inner_pair),
        Rule::limit_clause => parse_limit_clause(inner_pair),
        _ => Err(QueryParseError::SyntaxError(format!(
            "Unknown operation: {:?}",
            inner_pair.as_rule()
        ))),
    }
}

fn parse_where_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedOperation, QueryParseError> {
    for inner_pair in pair.into_inner() {
        if inner_pair.as_rule() == Rule::compound_condition {
            let compound = parse_compound_condition(inner_pair)?;
            return Ok(ParsedOperation::Where(compound));
        }
    }
    Err(QueryParseError::SyntaxError(
        "Invalid where clause".to_string(),
    ))
}

fn parse_compound_condition(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedCompoundCondition, QueryParseError> {
    let mut conditions = Vec::new();
    let mut combinators = Vec::new();

    for inner_pair in pair.into_inner() {
        match inner_pair.as_rule() {
            Rule::condition => {
                conditions.push(parse_condition(inner_pair)?);
            }
            Rule::combinator => {
                let combinator = match inner_pair.as_str().to_lowercase().as_str() {
                    "and" => ParsedCombinator::And,
                    "or" => ParsedCombinator::Or,
                    _ => {
                        return Err(QueryParseError::SyntaxError(format!(
                            "Unknown combinator: {}",
                            inner_pair.as_str()
                        )))
                    }
                };
                combinators.push(combinator);
            }
            _ => {}
        }
    }

    // Validate that all combinators are the same type
    let combinator = if combinators.is_empty() {
        ParsedCombinator::default()
    } else {
        let first = &combinators[0];
        for c in &combinators[1..] {
            if c != first {
                return Err(QueryParseError::SyntaxError(
                    "Cannot mix AND and OR in the same WHERE clause. Use separate WHERE clauses instead.".to_string(),
                ));
            }
        }
        first.clone()
    };

    Ok(ParsedCompoundCondition {
        conditions,
        combinator,
    })
}

fn parse_condition(pair: pest::iterators::Pair<Rule>) -> Result<ParsedCondition, QueryParseError> {
    let mut inner = pair.into_inner();

    let field_pair = inner
        .next()
        .ok_or_else(|| QueryParseError::SyntaxError("Missing field in condition".to_string()))?;

    let field = match field_pair.as_rule() {
        Rule::metadata_field => {
            let metadata_name = field_pair
                .into_inner()
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Invalid metadata field".to_string()))?
                .as_str()
                .to_string();
            ParsedField::Metadata(metadata_name)
        }
        Rule::field_name => ParsedField::Regular(field_pair.as_str().to_string()),
        _ => {
            return Err(QueryParseError::SyntaxError(
                "Invalid field in condition".to_string(),
            ));
        }
    };

    let operator_pair = inner
        .next()
        .ok_or_else(|| QueryParseError::SyntaxError("Missing operator in condition".to_string()))?;
    let operator = parse_operator(operator_pair)?;

    let value_pair = inner
        .next()
        .ok_or_else(|| QueryParseError::SyntaxError("Missing value in condition".to_string()))?;
    let value = parse_value(value_pair)?;

    Ok(ParsedCondition {
        field,
        operator,
        value,
    })
}

fn parse_operator(pair: pest::iterators::Pair<Rule>) -> Result<ParsedOperator, QueryParseError> {
    match pair.as_str() {
        "==" => Ok(ParsedOperator::Equal),
        "!=" => Ok(ParsedOperator::NotEqual),
        ">" => Ok(ParsedOperator::GreaterThan),
        "<" => Ok(ParsedOperator::LessThan),
        ">=" => Ok(ParsedOperator::GreaterOrEqual),
        "<=" => Ok(ParsedOperator::LessOrEqual),
        "contains" => Ok(ParsedOperator::Contains),
        "startswith" => Ok(ParsedOperator::StartsWith),
        "endswith" => Ok(ParsedOperator::EndsWith),
        "in" => Ok(ParsedOperator::In),
        _ => Err(QueryParseError::SyntaxError(format!(
            "Unknown operator: {}",
            pair.as_str()
        ))),
    }
}

fn parse_value(pair: pest::iterators::Pair<Rule>) -> Result<ParsedQueryValue, QueryParseError> {
    let inner = pair
        .into_inner()
        .next()
        .ok_or_else(|| QueryParseError::SyntaxError("Empty value".to_string()))?;

    match inner.as_rule() {
        Rule::string => {
            let string_content = inner
                .into_inner()
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Empty string".to_string()))?
                .as_str()
                .to_string();
            Ok(ParsedQueryValue::String(string_content))
        }
        Rule::number => {
            let num_str = inner.as_str();
            let num = num_str.parse::<f64>().map_err(|_| {
                QueryParseError::InvalidNumber(format!("Cannot parse number: {}", num_str))
            })?;
            Ok(ParsedQueryValue::Number(num))
        }
        Rule::boolean => {
            let bool_val = inner.as_str() == "true";
            Ok(ParsedQueryValue::Boolean(bool_val))
        }
        Rule::currency => {
            let mut inner_pairs = inner.into_inner();
            let num_str = inner_pairs
                .next()
                .ok_or_else(|| {
                    QueryParseError::SyntaxError("Missing amount in currency".to_string())
                })?
                .as_str();
            let amount = num_str.parse::<f64>().map_err(|_| {
                QueryParseError::InvalidNumber(format!("Cannot parse currency amount: {}", num_str))
            })?;
            let code = inner_pairs
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Missing currency code".to_string()))?
                .as_str()
                .to_string();
            Ok(ParsedQueryValue::Currency { amount, code })
        }
        Rule::datetime => Ok(ParsedQueryValue::DateTime(inner.as_str().to_string())),
        Rule::reference => Ok(ParsedQueryValue::Reference(inner.as_str().to_string())),
        Rule::path => {
            let string_pair = inner
                .into_inner()
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Missing path string".to_string()))?;
            let path_content = string_pair
                .into_inner()
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Empty path".to_string()))?
                .as_str()
                .to_string();
            Ok(ParsedQueryValue::Path(path_content))
        }
        Rule::enum_value => {
            let string_pair = inner
                .into_inner()
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Missing enum string".to_string()))?;
            let enum_content = string_pair
                .into_inner()
                .next()
                .ok_or_else(|| QueryParseError::SyntaxError("Empty enum".to_string()))?
                .as_str()
                .to_string();
            Ok(ParsedQueryValue::Enum(enum_content))
        }
        Rule::list => {
            let mut values = Vec::new();
            for list_item in inner.into_inner() {
                if list_item.as_rule() == Rule::value {
                    values.push(parse_value(list_item)?);
                }
            }
            Ok(ParsedQueryValue::List(values))
        }
        _ => Err(QueryParseError::SyntaxError(format!(
            "Unknown value type: {:?}",
            inner.as_rule()
        ))),
    }
}

fn parse_related_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedOperation, QueryParseError> {
    let mut degree = None;
    let mut selector = None;

    for inner_pair in pair.into_inner() {
        match inner_pair.as_rule() {
            Rule::degree => {
                let degree_pair = inner_pair
                    .into_inner()
                    .next()
                    .ok_or_else(|| QueryParseError::SyntaxError("Invalid degree".to_string()))?;
                let degree_num = degree_pair.as_str().parse::<usize>().map_err(|_| {
                    QueryParseError::InvalidNumber(format!(
                        "Invalid degree number: {}",
                        degree_pair.as_str()
                    ))
                })?;
                degree = Some(degree_num);
            }
            Rule::entity_selector => {
                selector = Some(parse_entity_selector(inner_pair)?);
            }
            _ => {}
        }
    }

    Ok(ParsedOperation::Related { degree, selector })
}

fn parse_order_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedOperation, QueryParseError> {
    let mut field = None;
    let mut direction = ParsedDirection::default();

    for inner_pair in pair.into_inner() {
        match inner_pair.as_rule() {
            Rule::order_field => {
                // order_field can be either metadata_field or field_name
                let field_pair = inner_pair.into_inner().next().ok_or_else(|| {
                    QueryParseError::SyntaxError("Invalid order field".to_string())
                })?;

                match field_pair.as_rule() {
                    Rule::metadata_field => {
                        let metadata_name = field_pair
                            .into_inner()
                            .next()
                            .ok_or_else(|| {
                                QueryParseError::SyntaxError("Invalid metadata field".to_string())
                            })?
                            .as_str()
                            .to_string();
                        field = Some(ParsedField::Metadata(metadata_name));
                    }
                    Rule::field_name => {
                        field = Some(ParsedField::Regular(field_pair.as_str().to_string()));
                    }
                    _ => {
                        return Err(QueryParseError::SyntaxError(
                            "Invalid field in order clause".to_string(),
                        ));
                    }
                }
            }
            Rule::direction => {
                direction = match inner_pair.as_str() {
                    "asc" => ParsedDirection::Ascending,
                    "desc" => ParsedDirection::Descending,
                    _ => ParsedDirection::default(),
                };
            }
            _ => {}
        }
    }

    let field = field
        .ok_or_else(|| QueryParseError::SyntaxError("Missing field in order clause".to_string()))?;

    Ok(ParsedOperation::Order { field, direction })
}

fn parse_limit_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedOperation, QueryParseError> {
    for inner_pair in pair.into_inner() {
        if inner_pair.as_rule() == Rule::number {
            let limit = inner_pair.as_str().parse::<usize>().map_err(|_| {
                QueryParseError::InvalidNumber(format!(
                    "Invalid limit number: {}",
                    inner_pair.as_str()
                ))
            })?;
            return Ok(ParsedOperation::Limit(limit));
        }
    }
    Err(QueryParseError::SyntaxError(
        "Invalid limit clause".to_string(),
    ))
}

// --- Aggregation parsing ---

fn parse_aggregation(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedAggregation, QueryParseError> {
    let inner_pair = pair
        .into_inner()
        .next()
        .ok_or_else(|| QueryParseError::SyntaxError("Empty aggregation".to_string()))?;

    match inner_pair.as_rule() {
        Rule::select_clause => parse_select_clause(inner_pair),
        Rule::count_clause => parse_count_clause(inner_pair),
        Rule::sum_clause => parse_sum_clause(inner_pair),
        Rule::average_clause => parse_average_clause(inner_pair),
        Rule::median_clause => parse_median_clause(inner_pair),
        _ => Err(QueryParseError::SyntaxError(format!(
            "Unknown aggregation: {:?}",
            inner_pair.as_rule()
        ))),
    }
}

fn parse_select_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedAggregation, QueryParseError> {
    let mut fields = Vec::new();
    for inner_pair in pair.into_inner() {
        if inner_pair.as_rule() == Rule::select_field {
            fields.push(parse_field_ref(inner_pair)?);
        }
    }
    if fields.is_empty() {
        return Err(QueryParseError::SyntaxError(
            "Select requires at least one field".to_string(),
        ));
    }
    Ok(ParsedAggregation::Select(fields))
}

fn parse_count_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedAggregation, QueryParseError> {
    let field = pair
        .into_inner()
        .next()
        .map(|p| parse_field_from_rule(p))
        .transpose()?;
    Ok(ParsedAggregation::Count(field))
}

fn parse_sum_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedAggregation, QueryParseError> {
    let field = parse_aggregation_field(pair)?;
    Ok(ParsedAggregation::Sum(field))
}

fn parse_average_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedAggregation, QueryParseError> {
    let field = parse_aggregation_field(pair)?;
    Ok(ParsedAggregation::Average(field))
}

fn parse_median_clause(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedAggregation, QueryParseError> {
    let field = parse_aggregation_field(pair)?;
    Ok(ParsedAggregation::Median(field))
}

fn parse_aggregation_field(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedField, QueryParseError> {
    let field_pair = pair
        .into_inner()
        .find(|p| p.as_rule() == Rule::aggregation_field)
        .ok_or_else(|| {
            QueryParseError::SyntaxError("Missing field in aggregation".to_string())
        })?;

    let inner = field_pair.into_inner().next().ok_or_else(|| {
        QueryParseError::SyntaxError("Invalid aggregation field".to_string())
    })?;

    parse_field_from_rule(inner)
}

/// Parse a field reference from a select_field or aggregation_field wrapper rule.
fn parse_field_ref(pair: pest::iterators::Pair<Rule>) -> Result<ParsedField, QueryParseError> {
    let inner = pair.into_inner().next().ok_or_else(|| {
        QueryParseError::SyntaxError("Invalid field reference".to_string())
    })?;
    parse_field_from_rule(inner)
}

/// Parse a metadata_field or field_name rule into a ParsedField.
fn parse_field_from_rule(
    pair: pest::iterators::Pair<Rule>,
) -> Result<ParsedField, QueryParseError> {
    match pair.as_rule() {
        Rule::metadata_field => {
            let name = pair
                .into_inner()
                .next()
                .ok_or_else(|| {
                    QueryParseError::SyntaxError("Invalid metadata field".to_string())
                })?
                .as_str()
                .to_string();
            Ok(ParsedField::Metadata(name))
        }
        Rule::field_name => Ok(ParsedField::Regular(pair.as_str().to_string())),
        _ => Err(QueryParseError::SyntaxError(format!(
            "Expected field, got {:?}",
            pair.as_rule()
        ))),
    }
}