//go:build unit

package payment

import (
	"math"
	"testing"
)

func TestYuanToFen(t *testing.T) {
	tests := []struct {
		name    string
		input   string
		want    int64
		wantErr bool
	}{
		// Normal values
		{name: "one yuan", input: "1.00", want: 100},
		{name: "ten yuan fifty fen", input: "10.50", want: 1050},
		{name: "one fen", input: "0.01", want: 1},
		{name: "large amount", input: "99999.99", want: 9999999},

		// Edge: zero
		{name: "zero no decimal", input: "0", want: 0},
		{name: "zero with decimal", input: "0.00", want: 0},

		// IEEE 754 precision edge case: 1.15 * 100 = 114.99999... in float64
		{name: "ieee754 precision 1.15", input: "1.15", want: 115},

		// More precision edge cases
		{name: "ieee754 precision 0.1", input: "0.1", want: 10},
		{name: "ieee754 precision 0.2", input: "0.2", want: 20},
		{name: "ieee754 precision 33.33", input: "33.33", want: 3333},

		// Large value
		{name: "hundred thousand", input: "100000.00", want: 10000000},

		// Integer without decimal
		{name: "integer 5", input: "5", want: 500},
		{name: "integer 100", input: "100", want: 10000},

		// Single decimal place
		{name: "single decimal 1.5", input: "1.5", want: 150},

		// Negative values
		{name: "negative one yuan", input: "-1.00", want: -100},
		{name: "negative with fen", input: "-10.50", want: -1050},

		// Invalid inputs
		{name: "empty string", input: "", wantErr: true},
		{name: "alphabetic", input: "abc", wantErr: true},
		{name: "double dot", input: "1.2.3", wantErr: true},
		{name: "spaces", input: "  ", wantErr: true},
		{name: "special chars", input: "$10.00", wantErr: true},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got, err := YuanToFen(tt.input)
			if tt.wantErr {
				if err == nil {
					t.Errorf("YuanToFen(%q) expected error, got %d", tt.input, got)
				}
				return
			}
			if err != nil {
				t.Fatalf("YuanToFen(%q) unexpected error: %v", tt.input, err)
			}
			if got != tt.want {
				t.Errorf("YuanToFen(%q) = %d, want %d", tt.input, got, tt.want)
			}
		})
	}
}

func TestFenToYuan(t *testing.T) {
	tests := []struct {
		name string
		fen  int64
		want float64
	}{
		{name: "one yuan", fen: 100, want: 1.0},
		{name: "ten yuan fifty fen", fen: 1050, want: 10.5},
		{name: "one fen", fen: 1, want: 0.01},
		{name: "zero", fen: 0, want: 0.0},
		{name: "large amount", fen: 9999999, want: 99999.99},
		{name: "negative", fen: -100, want: -1.0},
		{name: "negative with fen", fen: -1050, want: -10.5},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got := FenToYuan(tt.fen)
			if math.Abs(got-tt.want) > 1e-9 {
				t.Errorf("FenToYuan(%d) = %f, want %f", tt.fen, got, tt.want)
			}
		})
	}
}

func TestYuanToFenRoundTrip(t *testing.T) {
	// Verify that converting yuan->fen->yuan preserves the value.
	cases := []struct {
		yuan string
		fen  int64
	}{
		{"0.01", 1},
		{"1.00", 100},
		{"10.50", 1050},
		{"99999.99", 9999999},
	}

	for _, tc := range cases {
		fen, err := YuanToFen(tc.yuan)
		if err != nil {
			t.Fatalf("YuanToFen(%q) unexpected error: %v", tc.yuan, err)
		}
		if fen != tc.fen {
			t.Errorf("YuanToFen(%q) = %d, want %d", tc.yuan, fen, tc.fen)
		}
		yuan := FenToYuan(fen)
		// Parse expected yuan back for comparison
		expectedYuan := FenToYuan(tc.fen)
		if math.Abs(yuan-expectedYuan) > 1e-9 {
			t.Errorf("round-trip: FenToYuan(%d) = %f, want %f", fen, yuan, expectedYuan)
		}
	}
}