const std = @import("std");
const Build = std.Build;
const OptimizeMode = std.builtin.OptimizeMode;
const ResolvedTarget = Build.ResolvedTarget;
const Dependency = Build.Dependency;
const sokol = @import("sokol");
const cimgui = @import("cimgui");

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

    const opt_docking = b.option(bool, "docking", "Build with docking support") orelse false;

    // Get the matching Zig module name, C header search path and C library for
    // vanilla imgui vs the imgui docking branch.
    const cimgui_conf = cimgui.getConfig(opt_docking);

    // note that the sokol dependency is built with `.with_sokol_imgui = true`
    const dep_sokol = b.dependency("sokol", .{
        .target = target,
        .optimize = optimize,
        .with_sokol_imgui = true,
    });
    const dep_cimgui = b.dependency("cimgui", .{
        .target = target,
        .optimize = optimize,
    });

    // inject the cimgui header search path into the sokol C library compile step
    dep_sokol.artifact("sokol_clib").addIncludePath(dep_cimgui.path(cimgui_conf.include_dir));

    // shaders
    dep_sokol.artifact("sokol_clib").addIncludePath(b.path("ext/cimgui"));
    const dep_shdc = dep_sokol.builder.dependency("shdc", .{});
    const shdc_step = try sokol.shdc.createSourceFile(b, .{
        .shdc_dep = dep_shdc,
        .input = "src/shader/quad.glsl",
        .output = "src/shader/quad.glsl.zig",
        .slang = .{ .glsl430 = true },
    });

    // main module with sokol and cimgui imports
    const mod_main = b.createModule(.{
        .root_source_file = b.path("src/main.zig"),
        .target = target,
        .optimize = optimize,
        .imports = &.{
            .{ .name = "sokol", .module = dep_sokol.module("sokol") },
            .{ .name = cimgui_conf.module_name, .module = dep_cimgui.module(cimgui_conf.module_name) },
        },
    });
    const mod_options = b.addOptions();
    mod_options.addOption(bool, "docking", opt_docking);
    mod_main.addOptions("build_options", mod_options);

    // from here on different handling for native vs wasm builds
    if (target.result.cpu.arch.isWasm()) {
        try buildWasm(b, .{
            .mod_main = mod_main,
            .dep_sokol = dep_sokol,
            .dep_cimgui = dep_cimgui,
            .cimgui_clib_name = cimgui_conf.clib_name,
        });
    } else {
        const exe = try buildNative(b, mod_main);
        exe.step.dependOn(shdc_step);
    }
}

fn buildNative(b: *Build, mod: *Build.Module) !*Build.Step.Compile {
    const exe = b.addExecutable(.{
        .name = "demo",
        .root_module = mod,
    });
    b.installArtifact(exe);
    b.step("run", "Run demo").dependOn(&b.addRunArtifact(exe).step);
    return exe;
}

const BuildWasmOptions = struct {
    mod_main: *Build.Module,
    dep_sokol: *Dependency,
    dep_cimgui: *Dependency,
    cimgui_clib_name: []const u8,
};

fn buildWasm(b: *Build, opts: BuildWasmOptions) !void {
    // build the main file into a library, this is because the WASM 'exe'
    // needs to be linked in a separate build step with the Emscripten linker
    const demo = b.addLibrary(.{
        .name = "demo",
        .root_module = opts.mod_main,
    });

    // get the Emscripten SDK dependency from the sokol dependency
    const dep_emsdk = opts.dep_sokol.builder.dependency("emsdk", .{});

    // need to inject the Emscripten system header include path into
    // the cimgui C library otherwise the C/C++ code won't find
    // C stdlib headers
    const emsdk_incl_path = dep_emsdk.path("upstream/emscripten/cache/sysroot/include");
    opts.dep_cimgui.artifact(opts.cimgui_clib_name).addSystemIncludePath(emsdk_incl_path);

    // all C libraries need to depend on the sokol library, when building for
    // WASM this makes sure that the Emscripten SDK has been setup before
    // C compilation is attempted (since the sokol C library depends on the
    // Emscripten SDK setup step)
    opts.dep_cimgui.artifact(opts.cimgui_clib_name).step.dependOn(&opts.dep_sokol.artifact("sokol_clib").step);

    // create a build step which invokes the Emscripten linker
    const link_step = try sokol.emLinkStep(b, .{
        .lib_main = demo,
        .target = opts.mod_main.resolved_target.?,
        .optimize = opts.mod_main.optimize.?,
        .emsdk = dep_emsdk,
        .use_webgl2 = true,
        .use_emmalloc = true,
        .use_filesystem = false,
        .shell_file_path = opts.dep_sokol.path("src/sokol/web/shell.html"),
    });
    // attach to default target
    b.getInstallStep().dependOn(&link_step.step);
    // ...and a special run step to start the web build output via 'emrun'
    const run = sokol.emRunStep(b, .{ .name = "demo", .emsdk = dep_emsdk });
    run.step.dependOn(&link_step.step);
    b.step("run", "Run demo").dependOn(&run.step);
}