use super::funejson::Value;
use super::units_convert::convert_units;

fn is_decimal(text: &str) -> bool {
    let mut parts = text.splitn(2, '.');
    let whole = parts.next().unwrap_or("");
    let ok_whole = !whole.is_empty() && whole.bytes().all(|b| b.is_ascii_digit());
    match parts.next() {
        None => ok_whole,
        Some(f) => ok_whole && !f.is_empty() && f.bytes().all(|b| b.is_ascii_digit()),
    }
}

fn metric(unit: &str) -> Option<(&'static str, &'static str)> {
    match unit {
        "mg" | "g" | "kg" => Some(("g", "kg")),
        "mL" | "L" => Some(("mL", "L")),
        _ => None,
    }
}

/// Digits and 10^scale of decimal text. The inputs are bounded (15 digits in,
/// 12 decimal places out of units.convert), so this always fits in i128.
fn parse_decimal(text: &str) -> (i128, i128) {
    let (whole, fraction) = text.split_once('.').unwrap_or((text, ""));
    let digits: i128 = format!("{}{}", whole, fraction).parse().expect("decimal digits");
    (digits, 10i128.pow(fraction.len() as u32))
}

fn half_up(numerator: i128, denominator: i128) -> i128 {
    (numerator * 2 + denominator) / (denominator * 2)
}

fn format_scaled(value: i128, decimals: u32) -> String {
    let unit = 10i128.pow(decimals);
    let whole = (value / unit).to_string();
    if decimals == 0 {
        return whole;
    }
    let fraction = format!("{:0width$}", value % unit, width = decimals as usize);
    let fraction = fraction.trim_end_matches('0');
    if fraction.is_empty() {
        whole
    } else {
        format!("{}.{}", whole, fraction)
    }
}

fn check_portions(name: &str, value: i64) {
    if !(1..=10000).contains(&value) {
        panic!("{} must be a whole number from 1 to 10000, received {}", name, value);
    }
}

/// Scale a recipe from one number of portions to another.
///
/// The scaling is exact (decimal text times a fraction), and each quantity is
/// rounded once, to the precision a kitchen weighs to: whole grams or
/// millilitres from 10 up, one decimal place from 1 to 10, two below 1.
/// Metric amounts move between g and kg, mL and L, at 1000. Counted items
/// (each) round up, since half an egg short is short. Any other unit keeps its
/// name and is rounded to two decimal places.
///
/// # Panics
/// Panics on portions outside 1 to 10000, a malformed quantity or an empty unit.
pub fn scale_recipe(ingredients: &[RecipeQuantity], from_portions: i64, to_portions: i64) -> Vec<RecipeQuantity> {
    check_portions("fromPortions", from_portions);
    check_portions("toPortions", to_portions);
    let to = to_portions as i128;
    let from = from_portions as i128;
    ingredients
        .iter()
        .map(|ingredient| {
            let name = ingredient.name.clone();
            let quantity = ingredient.quantity.as_str();
            let unit = ingredient.unit.as_str();
            if !is_decimal(quantity) {
                panic!(
                    "quantity must be a non-negative decimal like \"12.5\", received \"{}\" for \"{}\"",
                    quantity, name
                );
            }
            let (whole, fraction) = quantity.split_once('.').unwrap_or((quantity, ""));
            let trimmed_fraction = fraction.trim_end_matches('0');
            let significant = format!("{}{}", whole, trimmed_fraction);
            if significant.trim_start_matches('0').len() > 15 || trimmed_fraction.len() > 15 {
                panic!(
                    "quantity \"{}\" for \"{}\" has too many digits: at most 15 significant digits and 15 decimal places",
                    quantity, name
                );
            }
            if unit.is_empty() {
                panic!("unit must not be empty for \"{}\"", name);
            }

            if let Some((small, large)) = metric(unit) {
                let (n, scale) = parse_decimal(&convert_units(quantity, unit, small, 12));
                let num = n * to;
                let den = scale * from;
                let decimals: u32 = if num < den {
                    2
                } else if num < den * 10 {
                    1
                } else {
                    0
                };
                let rounded = half_up(num * 10i128.pow(decimals), den);
                if decimals == 0 && rounded >= 1000 {
                    return RecipeQuantity {
                        name,
                        quantity: convert_units(&rounded.to_string(), small, large, 3),
                        unit: large.to_string(),
                    };
                }
                return RecipeQuantity { name, quantity: format_scaled(rounded, decimals), unit: small.to_string() };
            }
            // Trailing zeros dropped, so "1.000000000000000000000" stays small.
            let normal = if trimmed_fraction.is_empty() {
                whole.to_string()
            } else {
                format!("{}.{}", whole, trimmed_fraction)
            };
            let (n, scale) = parse_decimal(&normal);
            let num = n * to;
            let den = scale * from;
            if unit == "each" {
                return RecipeQuantity { name, quantity: ((num + den - 1) / den).to_string(), unit: unit.to_string() };
            }
            RecipeQuantity { name, quantity: format_scaled(half_up(num * 100, den), 2), unit: unit.to_string() }
        })
        .collect()
}

pub fn recipe_quantity_from_value(v: &Value) -> RecipeQuantity {
    RecipeQuantity {
        name: v.get("name").as_str().to_string(),
        quantity: v.get("quantity").as_str().to_string(),
        unit: v.get("unit").as_str().to_string(),
    }
}

pub fn recipe_quantity_to_value(q: &RecipeQuantity) -> Value {
    Value::obj(vec![
        ("name", Value::str(&q.name)),
        ("quantity", Value::str(&q.quantity)),
        ("unit", Value::str(&q.unit)),
    ])
}

pub fn fune_vector(args: &[Value]) -> Value {
    let ingredients: Vec<RecipeQuantity> = args[0].as_arr().iter().map(recipe_quantity_from_value).collect();
    Value::Arr(
        scale_recipe(&ingredients, args[1].as_i64(), args[2].as_i64())
            .iter()
            .map(recipe_quantity_to_value)
            .collect(),
    )
}