//! Input validation shared by the REST handlers, the sync push checks and the importer (SPEC §8.6, §9.6, §9.7).
//!
//! Strings are trimmed of leading and trailing whitespace and their length is counted in Unicode code points after
//! trimming; the trimmed value is what the server stores.

use chrono::{DateTime, Datelike, Utc};
use kvitt_domain::Period;

use crate::error::AppError;
use crate::time::STOCKHOLM;

/// Category icon tokens (SPEC §9.7, exhaustive; `key`, `shield` and `account_balance` added by D-054).
pub const ICONS: [&str; 33] = [
    "shopping_cart",
    "restaurant",
    "local_cafe",
    "home",
    "bolt",
    "water_drop",
    "wifi",
    "directions_car",
    "train",
    "local_gas_station",
    "flight",
    "hotel",
    "luggage",
    "movie",
    "music_note",
    "sports_esports",
    "fitness_center",
    "medical_services",
    "medication",
    "shopping_bag",
    "checkroom",
    "pets",
    "child_care",
    "school",
    "card_giftcard",
    "celebration",
    "build",
    "chair",
    "subscriptions",
    "category",
    "key",
    "shield",
    "account_balance",
];

/// Colour tokens (SPEC §9.7, exhaustive; `slate` and `amber` added by D-054).
pub const COLORS: [&str; 14] = [
    "green", "orange", "brown", "yellow", "blue", "teal", "purple", "red", "pink", "grey",
    "indigo", "lime", "slate", "amber",
];

/// Account name: 1 to 60 code points (SPEC §9.6).
pub const ACCOUNT_NAME_MAX: usize = 60;
/// Category name: 1 to 40 code points.
pub const CATEGORY_NAME_MAX: usize = 40;
/// User display name: 1 to 40 code points.
pub const DISPLAY_NAME_MAX: usize = 40;
/// Device name: 1 to 60 code points.
pub const DEVICE_NAME_MAX: usize = 60;
/// Expense and template description: 1 to 100 code points.
pub const DESCRIPTION_MAX: usize = 100;
/// Expense and template notes: 0 to 1000 code points.
pub const NOTES_MAX: usize = 1000;
/// How far back a template's `start_period` may lie, in months (SPEC §9.6, AC-9.8).
pub const START_PERIOD_BACKFILL_MONTHS: u32 = 12;

/// Trims `value` and checks its length in code points is within `min..=max`. Returns the trimmed value.
pub fn text(field: &str, value: &str, min: usize, max: usize) -> Result<String, AppError> {
    let trimmed = value.trim();
    let len = trimmed.chars().count();
    if len < min || len > max {
        return Err(AppError::validation(
            field,
            format!("{field} must be {min} to {max} characters after trimming"),
        ));
    }
    Ok(trimmed.to_owned())
}

/// Notes: trimmed, 0 to `NOTES_MAX` code points, no control characters other than newline (SPEC §8.6).
pub fn notes(field: &str, value: &str) -> Result<String, AppError> {
    let trimmed = text(field, value, 0, NOTES_MAX)?;
    if trimmed.chars().any(|c| c.is_control() && c != '\n') {
        return Err(AppError::validation(
            field,
            format!("{field} may not contain control characters other than newline"),
        ));
    }
    Ok(trimmed)
}

/// An icon token of SPEC §9.7.
pub fn icon(value: &str) -> Result<String, AppError> {
    if ICONS.contains(&value) {
        Ok(value.to_owned())
    } else {
        Err(AppError::validation(
            "icon",
            "icon is not a token of SPEC §9.7",
        ))
    }
}

/// A colour token of SPEC §9.7.
pub fn color(value: &str) -> Result<String, AppError> {
    if COLORS.contains(&value) {
        Ok(value.to_owned())
    } else {
        Err(AppError::validation(
            "color",
            "color is not a token of SPEC §9.7",
        ))
    }
}

/// `amount_ore` within 1 to 1 000 000 000 (SPEC §9.6).
pub fn amount(field: &str, amount_ore: i64) -> Result<i64, AppError> {
    if kvitt_domain::amount_in_range(amount_ore) {
        Ok(amount_ore)
    } else {
        Err(AppError::validation(field, "amount_out_of_range"))
    }
}

/// A period `YYYY-MM`.
pub fn period(field: &str, value: &str) -> Result<Period, AppError> {
    value
        .parse::<Period>()
        .map_err(|_| AppError::validation(field, format!("{field} must be YYYY-MM")))
}

/// The current month in Europe/Stockholm.
pub fn current_period(now: DateTime<Utc>) -> Result<Period, AppError> {
    let local = now.with_timezone(&STOCKHOLM);
    let year = u16::try_from(local.year()).map_err(AppError::internal)?;
    let month = u8::try_from(local.month()).map_err(AppError::internal)?;
    Period::new(year, month).ok_or_else(|| AppError::internal("current month out of range"))
}

/// `period` minus `months` months, or `None` before year 1.
pub fn months_before(period: Period, months: u32) -> Option<Period> {
    let index = i64::from(period.year()) * 12 + i64::from(period.month()) - 1 - i64::from(months);
    let year = u16::try_from(index.div_euclid(12)).ok()?;
    let month = u8::try_from(index.rem_euclid(12) + 1).ok()?;
    Period::new(year, month)
}

/// A template `start_period`: `YYYY-MM`, not earlier than 12 months before the current month (SPEC §9.6).
pub fn start_period(value: &str, now: DateTime<Utc>) -> Result<Period, AppError> {
    let p = period("start_period", value)?;
    let earliest = months_before(current_period(now)?, START_PERIOD_BACKFILL_MONTHS);
    if earliest.is_some_and(|earliest| p < earliest) {
        return Err(AppError::validation(
            "start_period",
            "start_period may be at most 12 months before the current month",
        ));
    }
    Ok(p)
}

/// `day_of_month` within 1 to 31.
pub fn day_of_month(value: i64) -> Result<u8, AppError> {
    u8::try_from(value)
        .ok()
        .filter(|d| (1..=31).contains(d))
        .ok_or_else(|| AppError::validation("day_of_month", "day_of_month must be 1 to 31"))
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn text_counts_code_points_after_trimming() {
        assert_eq!(text("name", "  Åsa  ", 1, 3).unwrap(), "Åsa");
        assert!(text("name", "   ", 1, 3).is_err());
        assert!(text("name", "Åsaa", 1, 3).is_err());
    }

    #[test]
    fn notes_allow_newline_only() {
        assert_eq!(notes("notes", "a\nb").unwrap(), "a\nb");
        assert!(notes("notes", "a\tb").is_err());
        assert!(notes("notes", "a\u{7}b").is_err());
    }

    #[test]
    fn months_before_crosses_years() {
        let p: Period = "2026-10".parse().unwrap();
        assert_eq!(months_before(p, 12).unwrap().to_string(), "2025-10");
        assert_eq!(months_before(p, 10).unwrap().to_string(), "2025-12");
        assert_eq!(months_before(p, 9).unwrap().to_string(), "2026-01");
    }

    #[test]
    fn tokens() {
        assert!(icon("pets").is_ok());
        assert!(icon("dog").is_err());
        assert!(color("lime").is_ok());
        assert!(color("black").is_err());
    }

    #[test]
    fn tokens_added_by_schema_2() {
        for token in ["key", "shield", "account_balance"] {
            assert!(icon(token).is_ok(), "{token}");
        }
        for token in ["slate", "amber"] {
            assert!(color(token).is_ok(), "{token}");
        }
        assert_eq!(ICONS.len(), 33);
        assert_eq!(COLORS.len(), 14);
        let mut icons = ICONS.to_vec();
        icons.sort_unstable();
        icons.dedup();
        assert_eq!(icons.len(), ICONS.len(), "icon tokens are distinct");
        let mut colors = COLORS.to_vec();
        colors.sort_unstable();
        colors.dedup();
        assert_eq!(colors.len(), COLORS.len(), "colour tokens are distinct");
    }
}