//! Window Function SQL generation.

use crate::ast::*;
use crate::transpiler::conditions::ConditionToSql;
use crate::transpiler::dialect::Dialect;

/// Generate Window Function SQL (Pillar 8).
pub fn build_window(cmd: &Qail, dialect: Dialect) -> String {
    let generator = dialect.generator();
    let mut sql = String::from("SELECT ");

    let cols: Vec<String> = cmd
        .columns
        .iter()
        .map(|c| match c {
            Expr::Window {
                name,
                func,
                params,
                partition,
                order,
                frame,
            } => {
                let params_str = if params.is_empty() {
                    String::new()
                } else {
                    params
                        .iter()
                        .map(|v| v.to_string())
                        .collect::<Vec<_>>()
                        .join(", ")
                };

                let mut over_clause = String::from("OVER (");
                if !partition.is_empty() {
                    over_clause.push_str("PARTITION BY ");
                    let quoted_partition: Vec<String> = partition
                        .iter()
                        .map(|p| generator.quote_identifier(p))
                        .collect();
                    over_clause.push_str(&quoted_partition.join(", "));
                    if !order.is_empty() {
                        over_clause.push(' ');
                    }
                }
                if !order.is_empty() {
                    over_clause.push_str("ORDER BY ");
                    let order_parts: Vec<String> = order
                        .iter()
                        .map(|cage| {
                            let col_str = if let Some(cond) = cage.conditions.first() {
                                match &cond.left {
                                    Expr::Named(name) => generator.quote_identifier(name),
                                    expr => expr.to_string(),
                                }
                            } else {
                                return String::new();
                            };

                            match &cage.kind {
                                CageKind::Sort(SortOrder::Asc) => format!("{} ASC", col_str),
                                CageKind::Sort(SortOrder::Desc) => format!("{} DESC", col_str),
                                CageKind::Sort(SortOrder::AscNullsFirst) => {
                                    format!("{} ASC NULLS FIRST", col_str)
                                }
                                CageKind::Sort(SortOrder::AscNullsLast) => {
                                    format!("{} ASC NULLS LAST", col_str)
                                }
                                CageKind::Sort(SortOrder::DescNullsFirst) => {
                                    format!("{} DESC NULLS FIRST", col_str)
                                }
                                CageKind::Sort(SortOrder::DescNullsLast) => {
                                    format!("{} DESC NULLS LAST", col_str)
                                }
                                _ => String::new(),
                            }
                        })
                        .filter(|s| !s.is_empty())
                        .collect();
                    over_clause.push_str(&order_parts.join(", "));
                }

                if let Some(fr) = frame {
                    over_clause.push(' ');
                    match fr {
                        WindowFrame::Rows { start, end } => {
                            over_clause.push_str(&format!(
                                "ROWS BETWEEN {} AND {}",
                                bound_to_sql(start),
                                bound_to_sql(end)
                            ));
                        }
                        WindowFrame::Range { start, end } => {
                            over_clause.push_str(&format!(
                                "RANGE BETWEEN {} AND {}",
                                bound_to_sql(start),
                                bound_to_sql(end)
                            ));
                        }
                    }
                }

                over_clause.push(')');

                format!(
                    "{}({}) {} AS {}",
                    func,
                    params_str,
                    over_clause,
                    generator.quote_identifier(name)
                )
            }
            _ => c.to_string(),
        })
        .collect();

    sql.push_str(&cols.join(", "));
    sql.push_str(" FROM ");
    sql.push_str(&generator.quote_identifier(&cmd.table));

    let mut where_groups: Vec<String> = Vec::new();
    for cage in &cmd.cages {
        if let CageKind::Filter = cage.kind
            && !cage.conditions.is_empty()
        {
            let joiner = match cage.logical_op {
                LogicalOp::And => " AND ",
                LogicalOp::Or => " OR ",
            };
            let conditions: Vec<String> = cage
                .conditions
                .iter()
                .map(|c| c.to_sql(&generator, Some(cmd)))
                .collect();
            let group = conditions.join(joiner);
            if cage.logical_op == LogicalOp::Or && cage.conditions.len() > 1 {
                where_groups.push(format!("({})", group));
            } else {
                where_groups.push(group);
            }
        }
    }

    if !where_groups.is_empty() {
        sql.push_str(" WHERE ");
        sql.push_str(&where_groups.join(" AND "));
    }

    sql
}

fn bound_to_sql(bound: &FrameBound) -> String {
    match bound {
        FrameBound::UnboundedPreceding => "UNBOUNDED PRECEDING".to_string(),
        FrameBound::UnboundedFollowing => "UNBOUNDED FOLLOWING".to_string(),
        FrameBound::CurrentRow => "CURRENT ROW".to_string(),
        FrameBound::Preceding(n) => format!("{} PRECEDING", n),
        FrameBound::Following(n) => format!("{} FOLLOWING", n),
    }
}
