use serde_json::{json, Value};
use std::collections::HashSet;

fn positive_units(amount: &str, decimals: u8) -> Result<u64, String> {
    let (whole, fraction) = amount.split_once('.').unwrap_or((amount, ""));
    if whole.is_empty() || amount.ends_with('.') ||
        !whole.bytes().chain(fraction.bytes()).all(|b| b.is_ascii_digit()) {
        return Err("Use a positive decimal amount, such as 12.5.".into());
    }
    let width = usize::from(decimals);
    if fraction.len() > width {
        return Err(format!("This mint allows {decimals} decimal places."));
    }
    let units = format!("{whole}{fraction}{}", "0".repeat(width - fraction.len()));
    let parsed = units.trim_start_matches('0').parse::<u64>()
        .map_err(|_| "Amount is zero or exceeds the SPL token limit.".to_string())?;
    Ok(parsed)
}

pub fn plan(input: &Value) -> Result<Value, String> {
    let decimals = input["decimals"].as_u64().and_then(|v| u8::try_from(v).ok())
        .ok_or("Invalid mint decimals.")?;
    let lines = input["list"].as_str().ok_or("Paste a recipient list.")?;
    if lines.len() > 20000 { return Err("The list is too large. Use up to 100 wallets.".into()); }
    let mut seen = HashSet::new();
    let mut rows = Vec::new();
    let mut total = 0u64;
    for (index, line) in lines.lines().enumerate() {
        let line = line.trim();
        if line.is_empty() { continue; }
        let number = index + 1;
        let (wallet, amount) = line.split_once(',').ok_or_else(|| format!("Row {number} needs wallet,amount."))?;
        let wallet = crate::validate_address(wallet).map_err(|_| format!("Row {number} has an invalid wallet address."))?;
        if !seen.insert(wallet.clone()) {
            return Err(format!("Row {number} repeats a wallet. Combine its amounts into one row."));
        }
        let units = positive_units(amount.trim(), decimals).map_err(|e| format!("Row {number}: {e}"))?;
        total = total.checked_add(units).ok_or("Total exceeds the SPL token limit.")?;
        rows.push(json!({"wallet":wallet,"units":units.to_string(),"amount":crate::format_amount(&units.to_string(),decimals)?}));
        if rows.len() > 100 { return Err("Use up to 100 wallets per plan.".into()); }
    }
    if rows.is_empty() { return Err("Add at least one wallet and amount.".into()); }
    let batches: Vec<_> = rows.chunks(3).map(|batch| batch.to_vec()).collect();
    Ok(json!({"rows":rows,"batches":batches,"total":crate::format_amount(&total.to_string(),decimals)?,"totalUnits":total.to_string()}))
}