//! Payments received against issued invoices.
//!
//! Money is integer paise throughout. Payment status is never stored: it is derived from the
//! payment rows, the invoice total and the due date, so deleting a payment reverts it for free.
//! The issued invoice row is not touched by any of this.

use crate::gst::rupees_to_paise;
use crate::models::PaymentSummary;
use crate::AppState;
use chrono::{FixedOffset, NaiveDate, Utc};
use rusqlite::{params, Connection, OptionalExtension};
use serde::{Deserialize, Serialize};
use tauri::State;

const MODES: &[&str] = &["bank_transfer", "upi", "cash", "cheque", "other"];
/// Upper bound on one payment (paise); keeps sums far from i64 overflow.
const MAX_PAISE: i64 = 100_000_000_000;

#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct Payment {
    pub id: i64,
    pub invoice_id: i64,
    pub paid_on: String,
    /// Cash received.
    pub amount_paise: i64,
    /// Tax deducted at source by the client; settles the invoice like cash does.
    pub tds_paise: i64,
    pub mode: String,
    pub reference: String,
    pub notes: String,
    pub created_at: String,
    /// Name of the Payment Entry on ERPNext once this payment was sent; `None` until then.
    #[serde(default)]
    pub erpnext_payment_entry: Option<String>,
}

#[derive(Debug, Clone, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct PaymentInput {
    pub invoice_id: i64,
    pub paid_on: String,
    pub amount_paise: i64,
    #[serde(default)]
    pub tds_paise: i64,
    pub mode: String,
    #[serde(default)]
    pub reference: String,
    #[serde(default)]
    pub notes: String,
}

/// Today's date in India (IST, UTC+05:30), as YYYY-MM-DD. Due dates are plain calendar dates.
pub fn today_ist() -> String {
    let ist = FixedOffset::east_opt(5 * 3600 + 1800).expect("valid offset");
    Utc::now()
        .with_timezone(&ist)
        .date_naive()
        .format("%Y-%m-%d")
        .to_string()
}

/// Derives the payment summary. Only an issued invoice takes payments; anything else is `none`
/// with a zero balance (a cancelled invoice is owed nothing). `settled` is cash plus TDS.
/// Overdue means a due date strictly before `today` while a balance remains; it wins over
/// `partially_paid`, and the paid amounts still show the partial payment.
pub fn derive_summary(
    status: &str,
    total_paise: i64,
    paid_paise: i64,
    tds_paise: i64,
    due_date: &str,
    today: &str,
) -> PaymentSummary {
    if status != "issued" {
        return PaymentSummary {
            paid_paise,
            tds_paise,
            balance_paise: 0,
            payment_status: "none".to_string(),
        };
    }
    let settled = paid_paise + tds_paise;
    let balance = (total_paise - settled).max(0);
    let overdue = balance > 0
        && NaiveDate::parse_from_str(due_date.trim(), "%Y-%m-%d").is_ok()
        && due_date.trim() < today;
    let payment_status = if balance == 0 && total_paise > 0 {
        "paid"
    } else if overdue {
        "overdue"
    } else if settled > 0 {
        "partially_paid"
    } else {
        "unpaid"
    };
    PaymentSummary {
        paid_paise,
        tds_paise,
        balance_paise: balance,
        payment_status: payment_status.to_string(),
    }
}

/// Summary for one invoice read from the payments table.
pub fn summary_for(
    conn: &Connection,
    invoice_id: i64,
    status: &str,
    total: f64,
    due_date: &str,
) -> rusqlite::Result<PaymentSummary> {
    let (paid, tds): (i64, i64) = conn.query_row(
        "SELECT COALESCE(SUM(amount_paise), 0), COALESCE(SUM(tds_paise), 0)
         FROM payments WHERE invoice_id = ?1",
        params![invoice_id],
        |r| Ok((r.get(0)?, r.get(1)?)),
    )?;
    Ok(derive_summary(
        status,
        rupees_to_paise(total),
        paid,
        tds,
        due_date,
        &today_ist(),
    ))
}

fn rupees(paise: i64) -> String {
    format!("₹{}.{:02}", paise / 100, paise % 100)
}

fn map_payment(r: &rusqlite::Row) -> rusqlite::Result<Payment> {
    Ok(Payment {
        id: r.get(0)?,
        invoice_id: r.get(1)?,
        paid_on: r.get(2)?,
        amount_paise: r.get(3)?,
        tds_paise: r.get(4)?,
        mode: r.get(5)?,
        reference: r.get(6)?,
        notes: r.get(7)?,
        created_at: r.get(8)?,
        erpnext_payment_entry: r
            .get::<_, Option<String>>(9)?
            .filter(|e| !e.trim().is_empty()),
    })
}

const COLS: &str = "id, invoice_id, paid_on, amount_paise, tds_paise, mode, reference, notes, created_at, erpnext_payment_entry";

pub fn record_payment_impl(conn: &mut Connection, input: PaymentInput) -> Result<Payment, String> {
    let db = |e: rusqlite::Error| e.to_string();

    NaiveDate::parse_from_str(input.paid_on.trim(), "%Y-%m-%d")
        .map_err(|_| "Payment date must be a date like 2026-04-01".to_string())?;
    if !MODES.contains(&input.mode.as_str()) {
        return Err(format!("Unknown payment mode \"{}\"", input.mode));
    }
    if input.amount_paise < 0 || input.tds_paise < 0 {
        return Err("Amounts cannot be negative".into());
    }
    if input.amount_paise > MAX_PAISE || input.tds_paise > MAX_PAISE {
        return Err("That amount is too large".into());
    }
    if input.amount_paise + input.tds_paise == 0 {
        return Err("Enter an amount received or TDS deducted".into());
    }

    let tx = conn.transaction().map_err(db)?;
    let (status, total): (String, f64) = tx
        .query_row(
            "SELECT status, total FROM invoices WHERE id = ?1",
            params![input.invoice_id],
            |r| Ok((r.get(0)?, r.get(1)?)),
        )
        .optional()
        .map_err(db)?
        .ok_or_else(|| "Invoice not found".to_string())?;
    if status != "issued" {
        return Err(format!(
            "Payments can only be recorded on an issued invoice (this one is {status})"
        ));
    }
    let total_paise = rupees_to_paise(total);
    let settled: i64 = tx
        .query_row(
            "SELECT COALESCE(SUM(amount_paise + tds_paise), 0) FROM payments WHERE invoice_id = ?1",
            params![input.invoice_id],
            |r| r.get(0),
        )
        .map_err(db)?;
    let balance = total_paise - settled;
    let incoming = input.amount_paise + input.tds_paise;
    if incoming > balance {
        return Err(format!(
            "This payment of {} (cash plus TDS) is more than the outstanding balance of {}",
            rupees(incoming),
            rupees(balance.max(0))
        ));
    }

    let now = chrono::Utc::now().to_rfc3339();
    tx.execute(
        "INSERT INTO payments (invoice_id, paid_on, amount_paise, tds_paise, mode, reference, notes, created_at)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8)",
        params![
            input.invoice_id,
            input.paid_on.trim(),
            input.amount_paise,
            input.tds_paise,
            input.mode,
            input.reference.trim(),
            input.notes.trim(),
            now
        ],
    )
    .map_err(db)?;
    let id = tx.last_insert_rowid();
    let payment = tx
        .query_row(
            &format!("SELECT {COLS} FROM payments WHERE id = ?1"),
            params![id],
            map_payment,
        )
        .map_err(db)?;
    tx.commit().map_err(db)?;
    Ok(payment)
}

pub fn list_payments_impl(conn: &Connection, invoice_id: i64) -> Result<Vec<Payment>, String> {
    let mut stmt = conn
        .prepare(&format!(
            "SELECT {COLS} FROM payments WHERE invoice_id = ?1 ORDER BY paid_on ASC, id ASC"
        ))
        .map_err(|e| e.to_string())?;
    let rows = stmt
        .query_map(params![invoice_id], map_payment)
        .map_err(|e| e.to_string())?
        .collect::<rusqlite::Result<Vec<_>>>()
        .map_err(|e| e.to_string())?;
    Ok(rows)
}

pub fn delete_payment_impl(conn: &Connection, id: i64) -> Result<(), String> {
    let changed = conn
        .execute("DELETE FROM payments WHERE id = ?1", params![id])
        .map_err(|e| e.to_string())?;
    if changed == 0 {
        return Err("Payment not found".into());
    }
    Ok(())
}

#[tauri::command]
pub fn record_payment(state: State<AppState>, input: PaymentInput) -> Result<Payment, String> {
    let mut conn = state.db.lock().map_err(|e| e.to_string())?;
    record_payment_impl(&mut conn, input)
}

#[tauri::command]
pub fn list_payments(state: State<AppState>, invoice_id: i64) -> Result<Vec<Payment>, String> {
    let conn = state.db.lock().map_err(|e| e.to_string())?;
    list_payments_impl(&conn, invoice_id)
}

#[tauri::command]
pub fn delete_payment(state: State<AppState>, id: i64) -> Result<(), String> {
    let conn = state.db.lock().map_err(|e| e.to_string())?;
    delete_payment_impl(&conn, id)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::commands::invoice::{cancel_invoice_impl, issue_invoice_impl};
    use crate::models::InvoiceInput;
    use serde_json::json;
    use std::path::Path;

    /// An unregistered vendor issues without tax, so the invoice total is exactly the line amount.
    fn issued(conn: &mut Connection, amount: f64, due: &str) -> i64 {
        let input: InvoiceInput = serde_json::from_value(json!({
            "invoiceDate": "2026-04-01",
            "dueDate": due,
            "clientName": "Client Ltd",
            "taxType": "none",
            "taxRate": 0.0,
            "items": [{"description": "Design", "mode": "fixed", "amount": amount}],
        }))
        .unwrap();
        issue_invoice_impl(conn, Path::new("/nonexistent"), input, &json!({}))
            .unwrap()
            .id
    }

    fn pay(invoice_id: i64, amount: i64, tds: i64) -> PaymentInput {
        PaymentInput {
            invoice_id,
            paid_on: "2026-04-10".into(),
            amount_paise: amount,
            tds_paise: tds,
            mode: "bank_transfer".into(),
            reference: "UTR1".into(),
            notes: String::new(),
        }
    }

    fn summary(conn: &Connection, id: i64) -> PaymentSummary {
        let (status, total, due): (String, f64, String) = conn
            .query_row(
                "SELECT status, total, due_date FROM invoices WHERE id = ?1",
                params![id],
                |r| Ok((r.get(0)?, r.get(1)?, r.get(2)?)),
            )
            .unwrap();
        summary_for(conn, id, &status, total, &due).unwrap()
    }

    #[test]
    fn partial_then_full_payment_settles() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        assert_eq!(summary(&conn, id).payment_status, "unpaid");
        assert_eq!(summary(&conn, id).balance_paise, 100_000);

        record_payment_impl(&mut conn, pay(id, 40_000, 0)).unwrap();
        let s = summary(&conn, id);
        assert_eq!(
            (s.payment_status.as_str(), s.paid_paise, s.balance_paise),
            ("partially_paid", 40_000, 60_000)
        );

        record_payment_impl(&mut conn, pay(id, 60_000, 0)).unwrap();
        let s = summary(&conn, id);
        assert_eq!((s.payment_status.as_str(), s.balance_paise), ("paid", 0));
    }

    #[test]
    fn tds_counts_towards_settling() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        // 10% TDS: the client pays 900.00 in cash and deducts 100.00.
        record_payment_impl(&mut conn, pay(id, 90_000, 10_000)).unwrap();
        let s = summary(&conn, id);
        assert_eq!(
            (
                s.payment_status.as_str(),
                s.paid_paise,
                s.tds_paise,
                s.balance_paise
            ),
            ("paid", 90_000, 10_000, 0)
        );
        // TDS alone is a valid payment too.
        let id2 = issued(&mut conn, 500.0, "2999-01-01");
        record_payment_impl(&mut conn, pay(id2, 0, 5_000)).unwrap();
        assert_eq!(summary(&conn, id2).payment_status, "partially_paid");
    }

    #[test]
    fn overpayment_is_rejected_including_tds() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        let err = record_payment_impl(&mut conn, pay(id, 100_001, 0)).unwrap_err();
        assert!(
            err.contains("more than the outstanding balance of ₹1000.00"),
            "{err}"
        );
        // Cash plus TDS is what counts.
        assert!(record_payment_impl(&mut conn, pay(id, 95_000, 6_000)).is_err());
        record_payment_impl(&mut conn, pay(id, 50_000, 0)).unwrap();
        let err = record_payment_impl(&mut conn, pay(id, 50_001, 0)).unwrap_err();
        assert!(err.contains("₹500.00"), "{err}");
        let n: i64 = conn
            .query_row("SELECT COUNT(*) FROM payments", [], |r| r.get(0))
            .unwrap();
        assert_eq!(n, 1);
    }

    #[test]
    fn invalid_input_is_rejected() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        assert!(record_payment_impl(&mut conn, pay(id, 0, 0)).is_err());
        assert!(record_payment_impl(&mut conn, pay(id, -1, 0)).is_err());
        assert!(record_payment_impl(&mut conn, pay(id, 100, -5)).is_err());
        let mut bad = pay(id, 100, 0);
        bad.mode = "barter".into();
        assert!(record_payment_impl(&mut conn, bad).is_err());
        let mut bad = pay(id, 100, 0);
        bad.paid_on = "10/04/2026".into();
        assert!(record_payment_impl(&mut conn, bad).is_err());
        assert!(record_payment_impl(&mut conn, pay(9999, 100, 0)).is_err());
        // The table CHECKs hold even if a caller bypasses the command validation.
        assert!(conn
            .execute(
                "INSERT INTO payments (invoice_id, paid_on, amount_paise, tds_paise, mode, created_at)
                 VALUES (?1, '2026-04-10', 0, 0, 'cash', 'now')",
                params![id]
            )
            .is_err());
    }

    #[test]
    fn draft_and_cancelled_invoices_take_no_payments() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        cancel_invoice_impl(&mut conn, id, "mistake").unwrap();
        let err = record_payment_impl(&mut conn, pay(id, 100, 0)).unwrap_err();
        assert!(err.contains("issued invoice"), "{err}");
        let s = summary(&conn, id);
        assert_eq!((s.payment_status.as_str(), s.balance_paise), ("none", 0));

        let id2 = issued(&mut conn, 1000.0, "2999-01-01");
        conn.execute(
            "UPDATE invoices SET status = 'draft' WHERE id = ?1",
            params![id2],
        )
        .unwrap();
        assert!(record_payment_impl(&mut conn, pay(id2, 100, 0)).is_err());
    }

    #[test]
    fn an_invoice_with_payments_cannot_be_cancelled() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        let p = record_payment_impl(&mut conn, pay(id, 100, 0)).unwrap();
        let err = cancel_invoice_impl(&mut conn, id, "").unwrap_err();
        assert!(err.contains("payments"), "{err}");
        delete_payment_impl(&conn, p.id).unwrap();
        cancel_invoice_impl(&mut conn, id, "").unwrap();
    }

    #[test]
    fn deleting_a_payment_reverts_the_status() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let id = issued(&mut conn, 1000.0, "2999-01-01");
        let full = record_payment_impl(&mut conn, pay(id, 100_000, 0)).unwrap();
        assert_eq!(summary(&conn, id).payment_status, "paid");
        delete_payment_impl(&conn, full.id).unwrap();
        let s = summary(&conn, id);
        assert_eq!(
            (s.payment_status.as_str(), s.balance_paise),
            ("unpaid", 100_000)
        );
        assert!(list_payments_impl(&conn, id).unwrap().is_empty());
        assert!(delete_payment_impl(&conn, full.id).is_err());
    }

    #[test]
    fn overdue_is_derived_from_due_date_and_balance() {
        let d = |due: &str, paid: i64, tds: i64| {
            derive_summary("issued", 100_000, paid, tds, due, "2026-05-10")
        };
        // Due today is not overdue yet; the day after is.
        assert_eq!(d("2026-05-10", 0, 0).payment_status, "unpaid");
        assert_eq!(d("2026-05-09", 0, 0).payment_status, "overdue");
        // Overdue wins over partially paid; the paid amount is still reported.
        let s = d("2026-05-09", 10_000, 0);
        assert_eq!(
            (s.payment_status.as_str(), s.paid_paise),
            ("overdue", 10_000)
        );
        // A settled invoice is never overdue.
        assert_eq!(d("2026-05-09", 90_000, 10_000).payment_status, "paid");
        // No usable due date means never overdue.
        assert_eq!(d("", 0, 0).payment_status, "unpaid");
        assert_eq!(d("not a date", 0, 0).payment_status, "unpaid");
        // Cancelled invoices are not owed.
        assert_eq!(
            derive_summary("cancelled", 100_000, 0, 0, "2020-01-01", "2026-05-10").balance_paise,
            0
        );
    }

    #[test]
    fn totals_are_integer_paise_without_float_drift() {
        let mut conn = crate::db::open_in_memory().unwrap();
        // 0.1 + 0.2 style amounts: 3 x 33.33 = 99.99.
        let id = issued(&mut conn, 99.99, "2999-01-01");
        record_payment_impl(&mut conn, pay(id, 3333, 0)).unwrap();
        record_payment_impl(&mut conn, pay(id, 3333, 0)).unwrap();
        record_payment_impl(&mut conn, pay(id, 3333, 0)).unwrap();
        let s = summary(&conn, id);
        assert_eq!(
            (s.paid_paise, s.balance_paise, s.payment_status.as_str()),
            (9999, 0, "paid")
        );
        let inv = super::super::invoice::get_invoice_impl(&conn, id).unwrap();
        assert_eq!(inv.total_paise, 9999);
    }

    #[test]
    fn list_invoices_joins_the_payment_sums() {
        let mut conn = crate::db::open_in_memory().unwrap();
        let a = issued(&mut conn, 1000.0, "2020-01-01");
        let b = issued(&mut conn, 200.0, "2999-01-01");
        record_payment_impl(&mut conn, pay(a, 30_000, 5_000)).unwrap();
        record_payment_impl(&mut conn, pay(a, 10_000, 0)).unwrap();
        record_payment_impl(&mut conn, pay(b, 20_000, 0)).unwrap();
        let rows = super::super::invoice::list_invoices_impl(&conn).unwrap();
        let get = |id: i64| rows.iter().find(|r| r.id == id).unwrap();
        let ra = get(a);
        assert_eq!(
            (
                ra.payment.paid_paise,
                ra.payment.tds_paise,
                ra.payment.balance_paise
            ),
            (40_000, 5_000, 55_000)
        );
        assert_eq!(ra.payment.payment_status, "overdue");
        assert_eq!(ra.total_paise, 100_000);
        assert_eq!(get(b).payment.payment_status, "paid");
        // The JSON keeps the existing fields and adds the flattened summary.
        let json = serde_json::to_value(ra).unwrap();
        assert_eq!(json["balancePaise"], 55_000);
        assert_eq!(json["paymentStatus"], "overdue");
        assert_eq!(json["total"], 1000.0);
    }
}