//! Pure RFC 4180 CSV parsing and comparison. Preview never changes state.
use crate::{
    domain::{Holiday, valid_country},
    error::{Result, ensure},
};
use chrono::{Datelike, NaiveDate};
use serde::Serialize;
use std::collections::BTreeMap;

#[derive(Debug, Serialize)]
pub struct ImportPreview {
    pub additions: Vec<Holiday>,
    pub existing: usize,
    pub duplicates: usize,
    pub conflicts: Vec<String>,
    pub errors: Vec<String>,
}

pub fn compare(input: &str, saved: &[Holiday]) -> Result<ImportPreview> {
    ensure(
        input.len() <= 262_144,
        crate::i18n::text("err_csv_is_limited_to_256_kib_e30936"),
    )?;
    let mut preview = ImportPreview {
        additions: vec![],
        existing: 0,
        duplicates: 0,
        conflicts: vec![],
        errors: vec![],
    };
    let mut reader = csv::ReaderBuilder::new()
        .trim(csv::Trim::All)
        .from_reader(input.trim_start_matches('\u{feff}').as_bytes());
    let headers = match reader.headers() {
        Ok(h) => h.iter().map(str::to_ascii_lowercase).collect::<Vec<_>>(),
        Err(_) => {
            preview
                .errors
                .push(crate::i18n::text("err_could_not_read_csv_headers_2bbd8d").into());
            return Ok(preview);
        }
    };
    let positions = ["country", "date", "name"].map(|key| headers.iter().position(|h| h == key));
    let [Some(country), Some(date), Some(name)] = positions else {
        preview
            .errors
            .push(crate::i18n::text("err_use_the_csv_headers_country_date_name_7d9639").into());
        return Ok(preview);
    };
    if headers.len() != 3 {
        preview.errors.push(
            crate::i18n::text("err_csv_must_have_exactly_three_columns_country_date_723e07").into(),
        );
        return Ok(preview);
    }
    let existing: BTreeMap<_, _> = saved
        .iter()
        .map(|h| ((h.country.clone(), h.date), h.name.clone()))
        .collect();
    let mut seen = BTreeMap::new();
    for (index, row) in reader.records().enumerate() {
        if index >= 2000 {
            preview
                .errors
                .push(crate::i18n::text("err_import_is_limited_to_2_000_rows_6e1c86").into());
            break;
        }
        let line = index + 2;
        let row = match row {
            Ok(row) => row,
            Err(_) => {
                preview.errors.push(crate::i18n::message(
                    "err_row_line_invalid_csv_or_column_count_be7745",
                    &[("line", (line).to_string())],
                ));
                continue;
            }
        };
        let country = row[country].to_ascii_uppercase();
        let parsed = ["%Y-%m-%d", "%d-%m-%Y"].into_iter().find_map(|format| {
            NaiveDate::parse_from_str(&row[date], format)
                .ok()
                .filter(|d| {
                    (2000..=2100).contains(&d.year()) && d.format(format).to_string() == row[date]
                })
        });
        if !valid_country(&country)
            || parsed.is_none()
            || row[name].is_empty()
            || row[name].len() > 120
        {
            preview.errors.push(crate::i18n::message(
                "err_row_line_use_an_iso_country_code_dd_mm_yyyy_or_y_bf011e",
                &[("line", (line).to_string())],
            ));
            continue;
        }
        let holiday = Holiday {
            country,
            date: parsed.unwrap(),
            name: row[name].into(),
        };
        let key = (holiday.country.clone(), holiday.date);
        if let Some(previous) = seen.insert(key.clone(), holiday.name.clone()) {
            if previous == holiday.name {
                preview.duplicates += 1;
            } else {
                preview.errors.push(crate::i18n::message(
                    "err_row_line_two_different_names_for_p0_on_p1_4c127b",
                    &[
                        ("line", (line).to_string()),
                        ("p0", (holiday.country).to_string()),
                        ("p1", (holiday.date.format("%d-%m-%Y")).to_string()),
                    ],
                ));
            }
            continue;
        }
        if let Some(name) = existing.get(&key) {
            if name == &holiday.name {
                preview.existing += 1;
            } else {
                preview.conflicts.push(crate::i18n::message(
                    "err__p0_p1_existing_p2_is_kept_p3_will_not_replace_i_053cc0",
                    &[
                        ("p0", (holiday.country).to_string()),
                        ("p1", (holiday.date.format("%d-%m-%Y")).to_string()),
                        ("p2", (name).to_string()),
                        ("p3", (holiday.name).to_string()),
                    ],
                ));
            }
        } else {
            preview.additions.push(holiday);
        }
    }
    if saved.len() + preview.additions.len() > 2000 {
        preview
            .errors
            .push(crate::i18n::text("err_the_team_would_exceed_2_000_holidays_496996").into());
    }
    preview
        .additions
        .sort_by(|a, b| (&a.country, a.date).cmp(&(&b.country, b.date)));
    Ok(preview)
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn csv_handles_bom_quotes_countries_duplicates_and_preserves_existing_names() {
        let saved = vec![Holiday {
            country: "CY".into(),
            date: "2026-01-01".parse().unwrap(),
            name: "New Year".into(),
        }];
        let p=compare("\u{feff}date,name,country\r\n2026-01-01,New Year,CY\r\n2026-01-01,\"New Year, holiday\",am\r\n2026-01-01,\"New Year, holiday\",AM\r\n2026-12-25,Christmas,CY",&saved).unwrap();
        assert!(p.errors.is_empty());
        assert_eq!(p.existing, 1);
        assert_eq!(p.duplicates, 1);
        assert_eq!(p.additions.len(), 2);
        let p = compare("country,date,name\nCY,2026-01-01,Changed", &saved).unwrap();
        assert!(p.additions.is_empty());
        assert_eq!(p.conflicts.len(), 1);
        assert_eq!(saved[0].name, "New Year");
    }
    #[test]
    fn invalid_rows_and_conflicting_input_duplicates_block_import() {
        let p=compare("country,date,name\nXX,2026-01-01,Invalid country\nCY,2026-02-30,Invalid date\nAM,2026-01-01,One\nAM,2026-01-01,Two\nCY,2026-01-01",&[]).unwrap();
        assert_eq!(p.errors.len(), 4);
        assert!(
            !compare("date,label\n2026-01-01,Holiday", &[])
                .unwrap()
                .errors
                .is_empty()
        );
    }
}