const std = @import("std");

/// Returns the sum of a slice of i32 values.
pub fn sum(values: []const i32) i64 {
    var total: i64 = 0;
    for (values) |v| total += v;
    return total;
}

/// Returns the product of a slice of i32 values.
/// Returns 1 for an empty slice (identity element).
pub fn product(values: []const i32) i64 {
    var result: i64 = 1;
    for (values) |v| result *= v;
    return result;
}

/// Returns the minimum value, or null for an empty slice.
pub fn min(values: []const i32) ?i32 {
    if (values.len == 0) return null;
    var m = values[0];
    for (values[1..]) |v| {
        if (v < m) m = v;
    }
    return m;
}

/// Returns the maximum value, or null for an empty slice.
pub fn max(values: []const i32) ?i32 {
    if (values.len == 0) return null;
    var m = values[0];
    for (values[1..]) |v| {
        if (v > m) m = v;
    }
    return m;
}

test "sum empty" {
    try std.testing.expectEqual(@as(i64, 0), sum(&.{}));
}

test "sum positive values" {
    try std.testing.expectEqual(@as(i64, 15), sum(&.{ 1, 2, 3, 4, 5 }));
}

test "sum with negatives" {
    try std.testing.expectEqual(@as(i64, 0), sum(&.{ -3, -2, -1, 0, 1, 2, 3 }));
}

test "product empty" {
    try std.testing.expectEqual(@as(i64, 1), product(&.{}));
}

test "product small" {
    try std.testing.expectEqual(@as(i64, 120), product(&.{ 1, 2, 3, 4, 5 }));
}

test "min and max" {
    const data = [_]i32{ 3, 1, 4, 1, 5, 9, 2, 6 };
    try std.testing.expectEqual(@as(?i32, 1), min(&data));
    try std.testing.expectEqual(@as(?i32, 9), max(&data));
}

test "min max empty" {
    try std.testing.expectEqual(@as(?i32, null), min(&.{}));
    try std.testing.expectEqual(@as(?i32, null), max(&.{}));
}