const std = @import("std");
const builtin = @import("builtin");
const assert = std.debug.assert;
const objc = @import("objc");

const log = std.log.scoped(.os);

/// Ensure that the locale is set.
pub fn ensureLocale() void {
    assert(builtin.link_libc);

    // Get our LANG env var. We use this many times but we also need
    // the original value later.
    const lang = std.os.getenv("LANG") orelse "";

    // On macOS, pre-populate the LANG env var with system preferences.
    // When launching the .app, LANG is not set so we must query it from the
    // OS. When launching from the CLI, LANG is usually set by the parent
    // process.
    if (comptime builtin.target.isDarwin()) {
        // Set the lang if it is not set or if its empty.
        if (lang.len == 0) {
            setLangFromCocoa();
        }
    }

    // Set the locale to whatever is set in env vars.
    if (setlocale(LC_ALL, "")) |v| {
        log.info("setlocale from env result={s}", .{v});
        return;
    }

    // setlocale failed. This is probably because the LANG env var is
    // invalid. Try to set it without the LANG var set to use the system
    // default.
    if (std.os.getenv("LANG")) |old_lang| {
        if (old_lang.len > 0) {
            // We don't need to do both of these things but we do them
            // both to be sure that lang is either empty or unset completely.
            _ = setenv("LANG", "", 1);
            _ = unsetenv("LANG");

            if (setlocale(LC_ALL, "")) |v| {
                log.info("setlocale after unset lang result={s}", .{v});
                return;
            }
        }
    }

    // Failure again... fallback to en_US.UTF-8
    log.warn("setlocale failed with LANG and system default. Falling back to en_US.UTF-8", .{});
    if (setlocale(LC_ALL, "en_US.UTF-8")) |v| {
        log.info("setlocale default result={s}", .{v});
        return;
    } else log.err("setlocale failed even with the fallback, uncertain results", .{});
}

/// This sets the LANG environment variable based on the macOS system
/// preferences selected locale settings.
fn setLangFromCocoa() void {
    const pool = objc.AutoreleasePool.init();
    defer pool.deinit();

    // The classes we're going to need.
    const NSLocale = objc.Class.getClass("NSLocale") orelse {
        log.err("NSLocale class not found. Locale may be incorrect.", .{});
        return;
    };

    // Get our current locale and extract the language code ("en") and
    // country code ("US")
    const locale = NSLocale.msgSend(objc.Object, objc.sel("currentLocale"), .{});
    const lang = locale.getProperty(objc.Object, "languageCode");
    const country = locale.getProperty(objc.Object, "countryCode");

    // Get our UTF8 string values
    const c_lang = lang.getProperty([*:0]const u8, "UTF8String");
    const c_country = country.getProperty([*:0]const u8, "UTF8String");

    // Convert them to Zig slices
    const z_lang = std.mem.sliceTo(c_lang, 0);
    const z_country = std.mem.sliceTo(c_country, 0);

    // Format them into a buffer
    var buf: [128]u8 = undefined;
    const env_value = std.fmt.bufPrintZ(&buf, "{s}_{s}.UTF-8", .{ z_lang, z_country }) catch |err| {
        log.err("error setting locale from system. err={}", .{err});
        return;
    };
    log.info("detected system locale={s}", .{env_value});

    // Set it onto our environment
    if (setenv("LANG", env_value.ptr, 1) < 0) {
        log.err("error setting locale env var", .{});
        return;
    }
}

const LC_ALL: c_int = 6; // from locale.h
const LC_ALL_MASK: c_int = 0x7fffffff; // from locale.h
const locale_t = ?*anyopaque;
extern "c" fn setenv(name: ?[*]const u8, value: ?[*]const u8, overwrite: c_int) c_int;
extern "c" fn unsetenv(name: ?[*]const u8) c_int;
extern "c" fn setlocale(category: c_int, locale: ?[*]const u8) ?[*:0]u8;
extern "c" fn newlocale(category: c_int, locale: ?[*]const u8, base: locale_t) locale_t;
extern "c" fn freelocale(v: locale_t) void;