package transfers

import (
	"testing"

	"git.petrovv.com/nikola/money/internal/config"
	"git.petrovv.com/nikola/money/internal/model"
)

// txn builds a transaction the way the index hands them out.
func txn(id int64, account, date, desc string, amount int64) model.Transaction {
	return model.Transaction{
		ID:          id,
		AccountSlug: account,
		Currency:    "EUR",
		MinorDigits: 2,
		Date:        date,
		Description: desc,
		AmountMinor: amount,
	}
}

func engine(defs ...config.Transfer) *Engine {
	return New(&config.Rules{Transfer: defs})
}

var topUp = config.Transfer{
	FromAccount: "nlb", FromDesc: "*TO REVOLUT*",
	ToAccount: "revolut", ToDesc: "*FROM NLB*",
}

// The two legs of one movement, dated a weekend apart, are one transfer.
func TestPairsTheTwoLegs(t *testing.T) {
	res := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-09", "Top-up from NLB", 50000),
		txn(3, "nlb", "2026-03-07", "LIDL SOFIA", -2000),
	})

	if len(res.Pairs) != 1 {
		t.Fatalf("pairs = %+v, want exactly one", res.Pairs)
	}
	if res.Pairs[0].Out.ID != 1 || res.Pairs[0].In.ID != 2 {
		t.Errorf("paired %d→%d, want 1→2", res.Pairs[0].Out.ID, res.Pairs[0].In.ID)
	}
	if len(res.Unmatched) != 0 {
		t.Errorf("unmatched = %+v, want none; the shopping matches no side", res.Unmatched)
	}
	if res.Paired[0] != 1 || res.Orphaned[0] != 0 {
		t.Errorf("counts = %d paired, %d orphaned; want 1 and 0", res.Paired[0], res.Orphaned[0])
	}
}

// Money that left and never arrived is the case the whole feature exists to
// surface: it is not a transfer, it is one leg on its own.
func TestLegWithoutACounterpartIsUnmatched(t *testing.T) {
	res := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
	})

	if len(res.Pairs) != 0 {
		t.Fatalf("pairs = %+v, want none", res.Pairs)
	}
	if len(res.Unmatched) != 1 || res.Unmatched[0].Txn.ID != 1 || !res.Unmatched[0].Out {
		t.Fatalf("unmatched = %+v, want the leaving leg", res.Unmatched)
	}
	if res.Paired[0] != 0 || res.Orphaned[0] != 1 {
		t.Errorf("counts = %d paired, %d orphaned; want 0 and 1", res.Paired[0], res.Orphaned[0])
	}
}

// A definition that catches nothing at all is dead, and reports as such
// separately from one that catches legs it cannot pair.
func TestDefinitionMatchingNothing(t *testing.T) {
	res := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "LIDL SOFIA", -2000),
	})
	if res.Paired[0] != 0 || res.Orphaned[0] != 0 {
		t.Errorf("counts = %d paired, %d orphaned; want both zero", res.Paired[0], res.Orphaned[0])
	}
}

// Within one currency the amount is the evidence, so by default it must agree
// exactly: a movement that arrives short a fee is not the same movement
// leaving, unless the definition says the route charges one.
func TestAmountMustAgreeWithinACurrency(t *testing.T) {
	res := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 49500),
	})
	if len(res.Pairs) != 0 {
		t.Errorf("pairs = %+v, want none: the amounts differ", res.Pairs)
	}
	if len(res.Unmatched) != 2 {
		t.Errorf("unmatched = %+v, want both legs reported", res.Unmatched)
	}
}

// Across currencies the amounts are unrelated -- there are no exchange rates
// here -- so the dates carry the pairing on their own.
func TestCrossCurrencyPairsOnDateAlone(t *testing.T) {
	arrived := txn(2, "revolut", "2026-03-07", "Top-up from NLB", 97790)
	arrived.Currency = "BGN"

	res := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		arrived,
	})
	if len(res.Pairs) != 1 {
		t.Fatalf("pairs = %+v, want the exchange paired", res.Pairs)
	}
	if res.Pairs[0].In.Currency == res.Pairs[0].Out.Currency {
		t.Error("expected the pair to span two currencies")
	}

	// The window still bounds it.
	late := arrived
	late.Date = "2026-03-20"
	res = engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		late,
	})
	if len(res.Pairs) != 0 {
		t.Errorf("pairs = %+v, want none beyond the window", res.Pairs)
	}
}

// With no amount to go on, the nearest date decides, so two exchanges in flight
// at once pair in order rather than crossing over.
func TestCrossCurrencyPicksTheNearestDate(t *testing.T) {
	arriving := func(id int64, date string, amount int64) model.Transaction {
		in := txn(id, "revolut", date, "Top-up from NLB", amount)
		in.Currency = "BGN"
		return in
	}
	res := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-02", "TRANSFER TO REVOLUT LTD", -50000),
		txn(3, "nlb", "2026-03-10", "TRANSFER TO REVOLUT LTD", -20000),
		arriving(2, "2026-03-03", 97790),
		arriving(4, "2026-03-11", 39116),
	})
	if len(res.Pairs) != 2 {
		t.Fatalf("pairs = %+v, want both exchanges paired", res.Pairs)
	}
	for _, p := range res.Pairs {
		if p.In.ID != p.Out.ID+1 {
			t.Errorf("paired %d->%d, want each exchange with its own counterpart",
				p.Out.ID, p.In.ID)
		}
	}
}

// Legs further apart than the window are not the same movement.
func TestWindowBoundsThePairing(t *testing.T) {
	inside := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-01", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-06", "Top-up from NLB", 50000),
	})
	if len(inside.Pairs) != 1 {
		t.Errorf("pairs = %+v, want one at exactly the window", inside.Pairs)
	}

	outside := engine(topUp).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-01", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 50000),
	})
	if len(outside.Pairs) != 0 {
		t.Errorf("pairs = %+v, want none beyond the window", outside.Pairs)
	}
}

// Two identical monthly transfers must pair in order rather than crossing over,
// or the dates in the report would be wrong even though the totals were right.
func TestIdenticalTransfersPairInOrder(t *testing.T) {
	res := engine(topUp).Analyze([]model.Transaction{
		txn(4, "revolut", "2026-04-02", "Top-up from NLB", 50000),
		txn(1, "nlb", "2026-03-01", "TRANSFER TO REVOLUT LTD", -50000),
		txn(3, "nlb", "2026-04-01", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-02", "Top-up from NLB", 50000),
	})
	if len(res.Pairs) != 2 {
		t.Fatalf("pairs = %+v, want two", res.Pairs)
	}
	for _, p := range res.Pairs {
		if p.In.ID != p.Out.ID+1 {
			t.Errorf("paired %d→%d, want each transfer with its own month", p.Out.ID, p.In.ID)
		}
	}
}

// A transaction belongs to one transfer. The first definition to claim a leg
// keeps it, exactly as the first matching rule keeps a tag.
func TestFirstDefinitionClaimsTheLeg(t *testing.T) {
	broad := config.Transfer{
		FromAccount: "nlb", FromDesc: "*TRANSFER*",
		ToAccount: "revolut", ToDesc: "*NLB*",
	}
	res := engine(topUp, broad).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 50000),
	})
	if len(res.Pairs) != 1 || res.Pairs[0].Def != 0 {
		t.Fatalf("pairs = %+v, want one claimed by the first definition", res.Pairs)
	}
	if res.Paired[1] != 0 || res.Orphaned[1] != 0 {
		t.Errorf("the shadowed definition reports %d paired, %d orphaned; want zero",
			res.Paired[1], res.Orphaned[1])
	}
}

// Direction is part of the definition: the arriving leg is an inflow and the
// leaving leg an outflow, so a definition written backwards pairs nothing.
func TestDirectionMatters(t *testing.T) {
	backwards := config.Transfer{
		FromAccount: "revolut", FromDesc: "*FROM NLB*",
		ToAccount: "nlb", ToDesc: "*TO REVOLUT*",
	}
	res := engine(backwards).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 50000),
	})
	if len(res.Pairs) != 0 {
		t.Errorf("pairs = %+v, want none: neither leg is on the side it was named for", res.Pairs)
	}
	if len(res.Unmatched) != 0 {
		t.Errorf("unmatched = %+v, want none either", res.Unmatched)
	}
}

// Money moved inside one account (a savings pocket, say) is still a pair.
func TestSameAccountBothSides(t *testing.T) {
	pocket := config.Transfer{
		FromAccount: "revolut", FromDesc: "*TO VAULT*",
		ToAccount: "revolut", ToDesc: "*FROM VAULT*",
	}
	res := engine(pocket).Analyze([]model.Transaction{
		txn(1, "revolut", "2026-03-06", "Move to Vault", -10000),
		txn(2, "revolut", "2026-03-06", "Move from Vault", 10000),
	})
	if len(res.Pairs) != 1 {
		t.Errorf("pairs = %+v, want one within the account", res.Pairs)
	}
}

// tolerant is the same route on a bank that takes a fee on the way: 1% of the
// leaving leg, so a 500.00 transfer may arrive as little as 495.00.
var tolerant = config.Transfer{
	FromAccount: "nlb", FromDesc: "*TO REVOLUT*",
	ToAccount: "revolut", ToDesc: "*FROM NLB*",
	TolerancePct: 1,
}

// A route that charges pairs anyway, and says what it cost.
func TestToleranceAdmitsAFee(t *testing.T) {
	res := engine(tolerant).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 49500),
	})
	if len(res.Pairs) != 1 {
		t.Fatalf("pairs = %+v, want the fee tolerated", res.Pairs)
	}
	if fee := res.Pairs[0].Fee(); fee != 500 {
		t.Errorf("fee = %d, want 500: the pair leaves the report, so the fee has to be reported", fee)
	}
}

// The tolerance is a bound, not an invitation: past it the legs are still two
// separate things.
func TestToleranceStopsAtItsBound(t *testing.T) {
	res := engine(tolerant).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 49499),
	})
	if len(res.Pairs) != 0 {
		t.Errorf("pairs = %+v, want none: 5.01 is more than 1%% of 500.00", res.Pairs)
	}
}

// The allowance is a share of the amount that left, so the same percentage
// means the same thing on a small transfer as on a large one -- and it is
// rounded, or 1% of 10.00 would admit 0.09 and miss the 0.10 fee it was
// chosen for.
func TestToleranceScalesWithTheAmount(t *testing.T) {
	res := engine(tolerant).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -1000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 990),
	})
	if len(res.Pairs) != 1 || res.Pairs[0].Fee() != 10 {
		t.Fatalf("pairs = %+v, want a 0.10 fee on 10.00 tolerated", res.Pairs)
	}

	res = engine(tolerant).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -1000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 950),
	})
	if len(res.Pairs) != 0 {
		t.Errorf("pairs = %+v, want none: 0.50 is 5%% of 10.00", res.Pairs)
	}
}

// A tolerance belongs to the definition that declares it and to no other, so
// one tolerant route cannot loosen a strict one written beside it.
func TestToleranceIsPerDefinition(t *testing.T) {
	strict := config.Transfer{
		FromAccount: "nlb", FromDesc: "*TO SAVINGS*",
		ToAccount: "savings", ToDesc: "*FROM NLB*",
	}
	res := engine(tolerant, strict).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-07", "Top-up from NLB", 49500),
		txn(3, "nlb", "2026-03-06", "TRANSFER TO SAVINGS", -50000),
		txn(4, "savings", "2026-03-07", "FROM NLB", 49500),
	})
	if len(res.Pairs) != 1 || res.Pairs[0].Def != 0 {
		t.Fatalf("pairs = %+v, want only the tolerant definition to pair", res.Pairs)
	}
	if len(res.Unmatched) != 2 {
		t.Errorf("unmatched = %+v, want both legs of the strict route reported", res.Unmatched)
	}
}

// Across currencies the amounts are in different units, so a fee cannot be
// computed from them -- subtracting one from the other would be a number
// meaning nothing.
func TestNoFeeAcrossCurrencies(t *testing.T) {
	arrived := txn(2, "revolut", "2026-03-07", "Top-up from NLB", 97790)
	arrived.Currency = "BGN"

	res := engine(tolerant).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		arrived,
	})
	if len(res.Pairs) != 1 {
		t.Fatalf("pairs = %+v, want the exchange paired", res.Pairs)
	}
	if fee := res.Pairs[0].Fee(); fee != 0 {
		t.Errorf("fee = %d, want 0 across currencies", fee)
	}
}

// With slack in the amount two candidates can sit the same number of days
// away, and then the nearer amount is the better evidence.
func TestEqualGapPrefersTheNearerAmount(t *testing.T) {
	res := engine(tolerant).Analyze([]model.Transaction{
		txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT LTD", -50000),
		txn(2, "revolut", "2026-03-05", "Top-up from NLB", 49600),
		txn(3, "revolut", "2026-03-07", "Top-up from NLB", 50000),
	})
	if len(res.Pairs) != 1 {
		t.Fatalf("pairs = %+v, want one", res.Pairs)
	}
	if res.Pairs[0].In.ID != 3 {
		t.Errorf("paired with %d, want 3: same gap, exact amount", res.Pairs[0].In.ID)
	}
}

// Want describes the missing side in the terms the pairing judges it by: the
// other definition half, the window, and the amount — exact by default,
// widened only by the definition's own tolerance, unchecked across currencies.
func TestWantDescribesTheMissingSide(t *testing.T) {
	eur := func(string) string { return "EUR" }

	out := Leg{Def: 0, Out: true, Txn: txn(1, "nlb", "2026-03-06", "TRANSFER TO REVOLUT", -50000)}
	got := engine(topUp).Want(out, eur)
	want := Wanted{Account: "revolut", Desc: "*FROM NLB*", From: "2026-03-01", To: "2026-03-11", Amount: 50000}
	if got != want {
		t.Errorf("arriving side = %+v, want %+v", got, want)
	}

	in := Leg{Def: 0, Txn: txn(2, "revolut", "2026-03-09", "Top-up from NLB", 50000)}
	got = engine(topUp).Want(in, eur)
	want = Wanted{Account: "nlb", Desc: "*TO REVOLUT*", From: "2026-03-04", To: "2026-03-14", Amount: -50000}
	if got != want {
		t.Errorf("leaving side = %+v, want %+v", got, want)
	}

	fee := topUp
	fee.TolerancePct = 1.5
	if got := engine(fee).Want(out, eur); got.TolerancePct != 1.5 || got.AnyAmount {
		t.Errorf("tolerant = %+v, want the definition's 1.5%%", got)
	}

	usd := func(slug string) string {
		if slug == "revolut" {
			return "USD"
		}
		return "EUR"
	}
	if got := engine(fee).Want(out, usd); !got.AnyAmount || got.TolerancePct != 0 {
		t.Errorf("cross-currency = %+v, want any amount and no tolerance", got)
	}
}