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

    const NativePaths = @This();
    const NativeTargetInfo = std.zig.system.NativeTargetInfo;

    arena: Allocator,
    include_dirs: std.ArrayListUnmanaged([]const u8) = .{},
    lib_dirs: std.ArrayListUnmanaged([]const u8) = .{},
    framework_dirs: std.ArrayListUnmanaged([]const u8) = .{},
    rpaths: std.ArrayListUnmanaged([]const u8) = .{},
    warnings: std.ArrayListUnmanaged([]const u8) = .{},

    pub fn detect(arena: Allocator, native_info: NativeTargetInfo) !NativePaths {
        const native_target = native_info.target;
        var self: NativePaths = .{ .arena = arena };
        var is_nix = false;
        if (process.getEnvVarOwned(arena, "NIX_CFLAGS_COMPILE")) |nix_cflags_compile| {
            is_nix = true;
            var it = mem.tokenizeScalar(u8, nix_cflags_compile, ' ');
            while (true) {
                const word = it.next() orelse break;
                if (mem.eql(u8, word, "-isystem")) {
                    const include_path = it.next() orelse {
                        try self.addWarning("Expected argument after -isystem in NIX_CFLAGS_COMPILE");
                        break;
                    };
                    try self.addIncludeDir(include_path);
                } else if (mem.eql(u8, word, "-iframework")) {
                    const framework_path = it.next() orelse {
                        try self.addWarning("Expected argument after -iframework in NIX_CFLAGS_COMPILE");
                        break;
                    };
                    try self.addFrameworkDir(framework_path);
                } else {
                    if (mem.startsWith(u8, word, "-frandom-seed=")) {
                        continue;
                    }
                    try self.addWarningFmt("Unrecognized C flag from NIX_CFLAGS_COMPILE: {s}", .{word});
                }
            }
        } else |err| switch (err) {
            error.InvalidUtf8 => {},
            error.EnvironmentVariableNotFound => {},
            error.OutOfMemory => |e| return e,
        }
        if (process.getEnvVarOwned(arena, "NIX_LDFLAGS")) |nix_ldflags| {
            is_nix = true;
            var it = mem.tokenizeScalar(u8, nix_ldflags, ' ');
            while (true) {
                const word = it.next() orelse break;
                if (mem.eql(u8, word, "-rpath")) {
                    const rpath = it.next() orelse {
                        try self.addWarning("Expected argument after -rpath in NIX_LDFLAGS");
                        break;
                    };
                    try self.addRPath(rpath);
                } else if (word.len > 2 and word[0] == '-' and word[1] == 'L') {
                    const lib_path = word[2..];
                    try self.addLibDir(lib_path);
                    try self.addRPath(lib_path);
                } else {
                    try self.addWarningFmt("Unrecognized C flag from NIX_LDFLAGS: {s}", .{word});
                    break;
                }
            }
        } else |err| switch (err) {
            error.InvalidUtf8 => {},
            error.EnvironmentVariableNotFound => {},
            error.OutOfMemory => |e| return e,
        }
        if (is_nix) {
            return self;
        }

        // TODO: consider also adding homebrew paths

        // TODO: consider also adding macports paths

        if (comptime builtin.target.isDarwin()) {
            if (std.zig.system.darwin.isSdkInstalled(arena)) sdk: {
                const sdk = std.zig.system.darwin.getSdk(arena, native_target) orelse break :sdk;
                try self.addLibDir(try std.fs.path.join(arena, &.{ sdk.path, "usr/lib" }));
                try self.addFrameworkDir(try std.fs.path.join(arena, &.{ sdk.path, "System/Library/Frameworks" }));
                try self.addIncludeDir(try std.fs.path.join(arena, &.{ sdk.path, "usr/include" }));
                return self;
            }
            return self;
        }

        if (builtin.os.tag == .solaris) {
            try self.addLibDir("/usr/lib/64");
            try self.addLibDir("/usr/local/lib/64");
            try self.addLibDir("/lib/64");

            try self.addIncludeDir("/usr/include");
            try self.addIncludeDir("/usr/local/include");

            return self;
        }

        if (builtin.os.tag != .windows) {
            const triple = try native_target.linuxTriple(arena);

            const qual = native_target.ptrBitWidth();

            // TODO: $ ld --verbose | grep SEARCH_DIR

            // the output contains some paths that end with lib64, maybe include them too?

            // TODO: what is the best possible order of things?

            // TODO: some of these are suspect and should only be added on some systems. audit needed.

            try self.addIncludeDir("/usr/local/include");
            try self.addLibDirFmt("/usr/local/lib{d}", .{qual});
            try self.addLibDir("/usr/local/lib");

            try self.addIncludeDirFmt("/usr/include/{s}", .{triple});
            try self.addLibDirFmt("/usr/lib/{s}", .{triple});

            try self.addIncludeDir("/usr/include");
            try self.addLibDirFmt("/lib{d}", .{qual});
            try self.addLibDir("/lib");
            try self.addLibDirFmt("/usr/lib{d}", .{qual});
            try self.addLibDir("/usr/lib");

            // example: on a 64-bit debian-based linux distro, with zlib installed from apt:

            // zlib.h is in /usr/include (added above)

            // libz.so.1 is in /lib/x86_64-linux-gnu (added here)

            try self.addLibDirFmt("/lib/{s}", .{triple});

            // Distros like guix don't use FHS, so they rely on environment

            // variables to search for headers and libraries.

            // We use os.getenv here since this part won't be executed on

            // windows, to get rid of unnecessary error handling.

            if (std.os.getenv("C_INCLUDE_PATH")) |c_include_path| {
                var it = mem.tokenizeScalar(u8, c_include_path, ':');
                while (it.next()) |dir| {
                    try self.addIncludeDir(dir);
                }
            }

            if (std.os.getenv("CPLUS_INCLUDE_PATH")) |cplus_include_path| {
                var it = mem.tokenizeScalar(u8, cplus_include_path, ':');
                while (it.next()) |dir| {
                    try self.addIncludeDir(dir);
                }
            }

            if (std.os.getenv("LIBRARY_PATH")) |library_path| {
                var it = mem.tokenizeScalar(u8, library_path, ':');
                while (it.next()) |dir| {
                    try self.addLibDir(dir);
                }
            }
        }

        return self;
    }

    pub fn addIncludeDir(self: *NativePaths, s: []const u8) !void {
        return self.include_dirs.append(self.arena, s);
    }

    pub fn addIncludeDirFmt(self: *NativePaths, comptime fmt: []const u8, args: anytype) !void {
        const item = try std.fmt.allocPrint(self.arena, fmt, args);
        try self.include_dirs.append(self.arena, item);
    }

    pub fn addLibDir(self: *NativePaths, s: []const u8) !void {
        try self.lib_dirs.append(self.arena, s);
    }

    pub fn addLibDirFmt(self: *NativePaths, comptime fmt: []const u8, args: anytype) !void {
        const item = try std.fmt.allocPrint(self.arena, fmt, args);
        try self.lib_dirs.append(self.arena, item);
    }

    pub fn addWarning(self: *NativePaths, s: []const u8) !void {
        return self.warnings.append(self.arena, s);
    }

    pub fn addFrameworkDir(self: *NativePaths, s: []const u8) !void {
        return self.framework_dirs.append(self.arena, s);
    }

    pub fn addFrameworkDirFmt(self: *NativePaths, comptime fmt: []const u8, args: anytype) !void {
        const item = try std.fmt.allocPrint(self.arena, fmt, args);
        try self.framework_dirs.append(self.arena, item);
    }

    pub fn addWarningFmt(self: *NativePaths, comptime fmt: []const u8, args: anytype) !void {
        const item = try std.fmt.allocPrint(self.arena, fmt, args);
        try self.warnings.append(self.arena, item);
    }

    pub fn addRPath(self: *NativePaths, s: []const u8) !void {
        try self.rpaths.append(self.arena, s);
    }