const std = @import("std");
const builtin = @import("builtin");
const Allocator = std.mem.Allocator;

/// Append a value to an environment variable such as PATH.
/// The returned value is always allocated so it must be freed.
pub fn appendEnv(
    alloc: Allocator,
    current: []const u8,
    value: []const u8,
) ![]u8 {
    // If there is no prior value, we return it as-is
    if (current.len == 0) return try alloc.dupe(u8, value);

    // Otherwise we must prefix.
    const sep = switch (builtin.os.tag) {
        .windows => ";",
        else => ":",
    };

    return try std.fmt.allocPrint(alloc, "{s}{s}{s}", .{
        current,
        sep,
        value,
    });
}

test "appendEnv empty" {
    const testing = std.testing;
    const alloc = testing.allocator;

    const result = try appendEnv(alloc, "", "foo");
    defer alloc.free(result);
    try testing.expectEqualStrings(result, "foo");
}

test "appendEnv existing" {
    const testing = std.testing;
    const alloc = testing.allocator;

    const result = try appendEnv(alloc, "a:b", "foo");
    defer alloc.free(result);
    if (builtin.os.tag == .windows) {
        try testing.expectEqualStrings(result, "a:b;foo");
    } else {
        try testing.expectEqualStrings(result, "a:b:foo");
    }
}