const std = @import("std");
const builtin = @import("builtin");

pub fn build(b: *std.Build) !void {
    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});
    _ = target;
    _ = optimize;
}

/// Setup the step to point to the proper Apple SDK for libc and
/// frameworks. When running on a Darwin host, this uses the native
/// SDK installed on the system via `xcrun`. When cross-compiling from
/// a non-Darwin host, it falls back to Zig's bundled Darwin headers.
pub fn addPaths(
    b: *std.Build,
    step: *std.Build.Step.Compile,
) !void {
    // The cache. This always uses b.allocator and never frees memory
    // (which is idiomatic for a Zig build exe). We cache the libc txt
    // file we create because it is expensive to generate (subprocesses).
    const Cache = struct {
        const Key = struct {
            arch: std.Target.Cpu.Arch,
            os: std.Target.Os.Tag,
            abi: std.Target.Abi,
        };

        const Value = union(enum) {
            native: struct {
                libc: std.Build.LazyPath,
                framework: []const u8,
                system_include: []const u8,
                library: []const u8,
            },
            cross: struct {
                libc: std.Build.LazyPath,
            },
        };

        var map: std.AutoHashMapUnmanaged(Key, ?Value) = .{};
    };

    const target = step.rootModuleTarget();
    const gop = try Cache.map.getOrPut(b.allocator, .{
        .arch = target.cpu.arch,
        .os = target.os.tag,
        .abi = target.abi,
    });

    if (!gop.found_existing) init: {
        if (comptime builtin.os.tag.isDarwin()) darwin: {
            // Detect our SDK using the "findNative" Zig stdlib function.
            // This is really important because it forces using `xcrun` to
            // find the SDK path.
            const libc = std.zig.LibCInstallation.findNative(.{
                .allocator = b.allocator,
                .target = &step.rootModuleTarget(),
                .verbose = false,
            }) catch break :darwin;

            // Render the file compatible with the `--libc` Zig flag.
            var stream: std.io.Writer.Allocating = .init(b.allocator);
            defer stream.deinit();
            try libc.render(&stream.writer);

            // Create a temporary file to store the libc path because
            // `--libc` expects a file path.
            const wf = b.addWriteFiles();
            const path = wf.add("libc.txt", stream.written());

            // Determine our framework path. Zig has a bug where it doesn't
            // parse this from the libc txt file for `-framework` flags:
            // https://github.com/ziglang/zig/issues/24024
            const framework_path = framework: {
                const down1 = std.fs.path.dirname(libc.sys_include_dir.?).?;
                const down2 = std.fs.path.dirname(down1).?;
                break :framework try std.fs.path.join(b.allocator, &.{
                    down2,
                    "System",
                    "Library",
                    "Frameworks",
                });
            };

            const library_path = library: {
                const down1 = std.fs.path.dirname(libc.sys_include_dir.?).?;
                break :library try std.fs.path.join(b.allocator, &.{
                    down1,
                    "lib",
                });
            };

            gop.value_ptr.* = .{ .native = .{
                .libc = path,
                .framework = framework_path,
                .system_include = libc.sys_include_dir.?,
                .library = library_path,
            } };

            break :init;
        }

        // Cross-compiling to Darwin from a non-Darwin host.
        // Zig only bundles macOS headers, so for other Apple platforms
        // we leave the value as null to produce a descriptive error.
        if (target.os.tag != .macos) {
            gop.value_ptr.* = null;
            break :init;
        }

        // Fall back to Zig's bundled Darwin headers for libc resolution.
        const zig_lib_path = b.graph.zig_lib_directory.path.?;
        const include_dir = b.pathJoin(&.{
            zig_lib_path, "libc", "include", "any-macos-any",
        });

        const wf = b.addWriteFiles();
        const path = wf.add("libc.txt", b.fmt(
            \\include_dir={s}
            \\sys_include_dir={s}
            \\crt_dir=
            \\msvc_lib_dir=
            \\kernel32_lib_dir=
            \\gcc_dir=
            \\
        , .{ include_dir, include_dir }));

        gop.value_ptr.* = .{ .cross = .{ .libc = path } };
    }

    const value = gop.value_ptr.* orelse return switch (target.os.tag) {
        // Return a more descriptive error. Before we just returned the
        // generic error but this was confusing a lot of community members.
        // It costs us nothing in the build script to return something better.
        .macos => error.XcodeMacOSSDKNotFound,
        .ios => error.XcodeiOSSDKNotFound,
        .tvos => error.XcodeTVOSSDKNotFound,
        .watchos => error.XcodeWatchOSSDKNotFound,
        else => error.XcodeAppleSDKNotFound,
    };

    switch (value) {
        .native => |native| {
            step.setLibCFile(native.libc);

            // This is only necessary until this bug is fixed:
            // https://github.com/ziglang/zig/issues/24024
            step.root_module.addSystemFrameworkPath(.{ .cwd_relative = native.framework });
            step.root_module.addSystemIncludePath(.{ .cwd_relative = native.system_include });
            step.root_module.addLibraryPath(.{ .cwd_relative = native.library });
        },
        .cross => |cross| {
            step.setLibCFile(cross.libc);
        },
    }
}
