use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::fs::File;
use std::io::{BufWriter, Write};

use crate::connection::AppState;
use crate::models::connection::DatabaseType;
use crate::query::{execute_sql_statement_with_options, QueryExecutionOptions};
use crate::sql_dialect::{build_table_data_select_sql, TableDataSelectSqlOptions};

const TABLE_DATA_EXPORT_PAGE_SIZE: usize = 10_000;

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct TableCsvExportOptions {
    pub file_path: String,
    pub connection_id: String,
    pub database: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub schema: Option<String>,
    pub table_name: String,
    #[serde(default)]
    pub columns: Vec<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub page_size: Option<usize>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub timeout_secs: Option<u64>,
}

pub(crate) fn escape_csv(value: &str) -> String {
    format!("\"{}\"", value.replace('"', "\"\""))
}

pub(crate) fn value_to_csv_text(value: &Value) -> String {
    match value {
        Value::Null => String::new(),
        Value::Bool(v) => v.to_string(),
        Value::Number(v) => v.to_string(),
        Value::String(v) => v.clone(),
        other => other.to_string(),
    }
}

pub(crate) fn value_to_query_result_csv_text(value: &Value) -> String {
    match value {
        Value::Null => "NULL".to_string(),
        other => value_to_csv_text(other),
    }
}

/// Format query-result rows as CSV text without a header row, using the
/// query-result NULL semantics (NULL → "NULL"). Used by the streaming
/// query-result export for batches after the first.
pub fn format_query_result_csv_rows(rows: &[Vec<Value>]) -> String {
    rows.iter()
        .map(|row| {
            row.iter().map(|cell| escape_csv(&value_to_query_result_csv_text(cell))).collect::<Vec<_>>().join(",")
        })
        .collect::<Vec<_>>()
        .join("\n")
}

fn format_csv_with_value_formatter(
    columns: &[String],
    rows: &[Vec<Value>],
    value_formatter: fn(&Value) -> String,
) -> String {
    let header = columns.iter().map(|col| escape_csv(col)).collect::<Vec<_>>().join(",");
    let body = rows
        .iter()
        .map(|row| row.iter().map(|cell| escape_csv(&value_formatter(cell))).collect::<Vec<_>>().join(","))
        .collect::<Vec<_>>()
        .join("\n");
    format!("{header}\n{body}")
}

pub fn format_csv(columns: &[String], rows: &[Vec<Value>]) -> String {
    format_csv_with_value_formatter(columns, rows, value_to_csv_text)
}

pub fn format_query_result_csv(columns: &[String], rows: &[Vec<Value>]) -> String {
    format_csv_with_value_formatter(columns, rows, value_to_query_result_csv_text)
}

fn write_csv_row(writer: &mut impl Write, values: impl IntoIterator<Item = String>) -> Result<(), String> {
    let mut first = true;
    for value in values {
        if !first {
            writer.write_all(b",").map_err(|err| err.to_string())?;
        }
        first = false;
        writer.write_all(escape_csv(&value).as_bytes()).map_err(|err| err.to_string())?;
    }
    Ok(())
}

async fn connection_database_type(state: &AppState, connection_id: &str) -> Result<DatabaseType, String> {
    state
        .configs
        .read()
        .await
        .get(connection_id)
        .map(|config| config.db_type)
        .ok_or_else(|| format!("Connection config not found: {connection_id}"))
}

pub async fn export_table_data_csv_core(state: &AppState, options: TableCsvExportOptions) -> Result<u64, String> {
    let database_type = connection_database_type(state, &options.connection_id).await?;
    let page_size = options.page_size.unwrap_or(TABLE_DATA_EXPORT_PAGE_SIZE).max(1);
    let mut writer =
        BufWriter::new(File::create(&options.file_path).map_err(|err| format!("Failed to write CSV file: {err}"))?);
    writer.write_all("\u{FEFF}".as_bytes()).map_err(|err| err.to_string())?;

    let mut offset = 0usize;
    let mut rows_exported = 0u64;
    let mut wrote_header = false;

    loop {
        let sql = build_table_data_select_sql(TableDataSelectSqlOptions {
            database_type: Some(database_type),
            schema: options.schema.clone(),
            table_name: options.table_name.clone(),
            table_type: None,
            primary_keys: Vec::new(),
            columns: options.columns.clone(),
            fallback_order_columns: Vec::new(),
            order_by: None,
            limit: Some(page_size),
            offset: Some(offset),
            where_input: None,
            include_row_id: false,
        });
        let result = execute_sql_statement_with_options(
            state,
            &options.connection_id,
            &options.database,
            &sql,
            options.schema.as_deref(),
            None,
            QueryExecutionOptions {
                max_rows: Some(page_size),
                timeout_secs: options.timeout_secs,
                ..Default::default()
            },
        )
        .await?;

        if !wrote_header {
            write_csv_row(&mut writer, result.columns)?;
            wrote_header = true;
        }

        let fetched = result.rows.len();
        if fetched == 0 {
            break;
        }
        for row in result.rows {
            writer.write_all(b"\n").map_err(|err| err.to_string())?;
            write_csv_row(&mut writer, row.iter().map(value_to_csv_text))?;
        }

        rows_exported += fetched as u64;
        if fetched < page_size {
            break;
        }
        offset += fetched;
    }

    if rows_exported == 0 {
        writer.write_all(b"\n").map_err(|err| err.to_string())?;
    }
    writer.flush().map_err(|err| err.to_string())?;
    Ok(rows_exported)
}

#[cfg(test)]
mod tests {
    use super::{format_csv, format_query_result_csv};
    use serde_json::json;

    #[test]
    fn formats_csv_with_header_and_escaped_values() {
        let out = format_csv(&["id".to_string(), "name".to_string()], &[vec![json!(1), json!("Ada \"Lovelace\"")]]);
        assert_eq!(out, "\"id\",\"name\"\n\"1\",\"Ada \"\"Lovelace\"\"\"");
    }

    #[test]
    fn formats_null_as_empty_cell() {
        let out = format_csv(&["id".to_string(), "note".to_string()], &[vec![json!(1), Value::Null]]);
        assert_eq!(out, "\"id\",\"note\"\n\"1\",\"\"");
    }

    #[test]
    fn formats_query_result_null_as_null_text() {
        let out = format_query_result_csv(&["id".to_string(), "note".to_string()], &[vec![json!(1), Value::Null]]);
        assert_eq!(out, "\"id\",\"note\"\n\"1\",\"NULL\"");
    }

    use serde_json::Value;
}