//------------------------------------------------------------------------------
//  offscreen.zig
//
//  Render to an offscreen rendertarget texture, and use this texture
//  for rendering to the display.
//------------------------------------------------------------------------------
const std = @import("std");
const stbi = @import("stbi");
const sokol = @import("sokol");
const slog = sokol.log;
const sg = sokol.gfx;
const sapp = sokol.app;
const sglue = sokol.glue;
const simgui = sokol.imgui;
const sappimgui = sokol.appimgui;
const ig = @import("cimgui_docking");
const vec3 = @import("math.zig").Vec3;
const mat4 = @import("math.zig").Mat4;
const shd = @import("shaders/main.glsl.zig");

const state = struct {
    var alloc: std.mem.Allocator = undefined;
    var io: std.Io = undefined;
    const Width = 800;
    const Height = 800;
    const offscreen = struct {
        var pass: sg.Pass = .{};
        var pip: sg.Pipeline = .{};
        var bind: sg.Bindings = .{};
        var vs: shd.VsParams = .{
            .position = .{ 0, 0 },
        };
        var fs: shd.FsParams = .{
            .resolution = .{ Width, Height },
            .rayCount = 16,
            .maxSteps = 4,
            .size = 1.0,
        };

        var pixels: [state.Width * state.Height * 4]u8 = @splat(255);
        var pixels_updated: bool = true;
        var pixels_img: sg.Image = undefined;
    };
    const display = struct {
        var pass_action: sg.PassAction = .{};
        var pip: sg.Pipeline = .{};
        var bind: sg.Bindings = .{};
    };
};

export fn init() void {
    sg.setup(.{
        .environment = sglue.environment(),
        .logger = .{ .func = slog.func },
    });

    simgui.setup(.{
        .logger = .{ .func = slog.func },
    });
    sappimgui.setup();
    ig.igGetIO().*.ConfigFlags |= ig.ImGuiConfigFlags_DockingEnable;

    state.offscreen.pass.action.colors[0] = .{
        .load_action = .LOAD,
        .store_action = .STORE,
    };
    state.offscreen.pass.action.depth = .{
        .load_action = .LOAD,
        .store_action = .STORE,
    };

    state.display.pass_action.colors[0] = .{
        .load_action = .CLEAR,
    };

    const offscreen_width = state.Width;
    const offscreen_height = state.Height;
    const offscreen_sample_count = 1;
    const color_img = sg.makeImage(.{
        .usage = .{ .color_attachment = true },
        .width = offscreen_width,
        .height = offscreen_height,
        .sample_count = offscreen_sample_count,
        .pixel_format = .RGBA8,
    });
    state.offscreen.pixels_img = sg.makeImage(.{
        .usage = .{ .dynamic_update = true },
        .width = offscreen_width,
        .height = offscreen_height,
        .sample_count = offscreen_sample_count,
        .pixel_format = .RGBA8,
    });
    const depth_img = sg.makeImage(.{
        .usage = .{ .depth_stencil_attachment = true },
        .width = offscreen_width,
        .height = offscreen_height,
        .sample_count = offscreen_sample_count,
        .pixel_format = .DEPTH,
    });

    state.offscreen.pass.attachments.colors[0] = sg.makeView(.{
        .color_attachment = .{ .image = color_img },
    });
    state.offscreen.pass.attachments.depth_stencil = sg.makeView(.{
        .depth_stencil_attachment = .{ .image = depth_img },
    });

    state.offscreen.bind.views[shd.VIEW_off_tex] = sg.makeView(.{
        .texture = .{ .image = state.offscreen.pixels_img },
    });
    state.display.bind.views[shd.VIEW_scr_tex] = sg.makeView(.{
        .texture = .{ .image = color_img },
    });

    const vbuf = sg.makeBuffer(.{ .data = sg.asRange(&[6]f32{
        -1.0, -1.0,
        -1.0, 3.0,
        3.0,  -1.0,
    }) });
    state.offscreen.bind.vertex_buffers[0] = vbuf;
    state.display.bind.vertex_buffers[0] = vbuf;

    // shader and pipeline object for the default render pass
    state.offscreen.pip = sg.makePipeline(.{
        .shader = sg.makeShader(shd.offscreenShaderDesc(sg.queryBackend())),
        .layout = init: {
            var l = sg.VertexLayoutState{};
            l.attrs[shd.ATTR_offscreen_vpos] = .{ .format = .FLOAT2 };
            break :init l;
        },
        .cull_mode = .BACK,
        .sample_count = offscreen_sample_count,
        .depth = .{
            .pixel_format = .DEPTH,
            .compare = .LESS_EQUAL,
            .write_enabled = true,
        },
        .colors = init: {
            var c: [sg.max_color_attachments]sg.ColorTargetState = @splat(.{});
            c[0].pixel_format = .RGBA8;
            break :init c;
        },
    });

    state.display.pip = sg.makePipeline(.{
        .shader = sg.makeShader(shd.defaultShaderDesc(sg.queryBackend())),
        .layout = init: {
            var l = sg.VertexLayoutState{};
            l.attrs[shd.ATTR_default_vpos] = .{ .format = .FLOAT2 };
            break :init l;
        },
        .cull_mode = .BACK,
        .depth = .{
            .compare = .LESS_EQUAL,
            .write_enabled = true,
        },
    });

    // a sampler object for sampling the render target texture
    state.offscreen.bind.samplers[shd.SMP_off_smp] = sg.makeSampler(.{
        .min_filter = .LINEAR,
        .mag_filter = .LINEAR,
        .wrap_u = .REPEAT,
        .wrap_v = .REPEAT,
    });
    state.display.bind.samplers[shd.SMP_scr_smp] = sg.makeSampler(.{
        .min_filter = .LINEAR,
        .mag_filter = .LINEAR,
        .wrap_u = .REPEAT,
        .wrap_v = .REPEAT,
    });
}

export fn event(ev: [*c]const sapp.Event) void {
    sappimgui.trackEvent(ev.*);
    _ = simgui.handleEvent(ev.*);

    switch (ev.*.type) {
        .KEY_DOWN => {
            if (ev.*.key_code == .ESCAPE) {
                sapp.requestQuit();
            }
        },
        else => {},
    }
}

// fn load_bmp(path: []const u8, buffer: []u8) !void {
//     var file = try std.Io.Dir.cwd().openFile(state.io, path, .{});
//     var read_buffer: [1024]u8 = undefined;
//     var reader = file.reader(state.io, &read_buffer).interface;
//     var bfType = try reader.takeInt(u16, .little);
//     var bfSize = try reader.takeInt(u32, .little);
//     var bfReserved = try reader.takeInt(u32, .little);
//     var bfOffBits = try reader.takeInt(u32, .little);
//     var biSize = try reader.takeInt(u32, .little);
//     var biWidth = try reader.takeInt(u32, .little);
//     var biHeight = try reader.takeInt(u32, .little);
//     var biPlanes = try reader.takeInt(u16, .little);
//     var biBitCount = try reader.takeInt(u16, .little);
//     var biCompression = try reader.takeInt(u32, .little);
//     var biSizeImage = try reader.takeInt(u32, .little);
//     var biXPelsPerMeter = try reader.takeInt(u32, .little);
//     var biYPelsPerMeter = try reader.takeInt(u32, .little);
//     var biClrUsed = try reader.takeInt(u32, .little);
//     var biClrImportant = try reader.takeInt(u32, .little);
//
//     if (buffer.len < biWidth * biHeight * biBitCount / 8) {
//         return error.BufferTooSmall;
//     }
//
//
// }

export fn frame() void {
    // call simgui.newFrame() before any ImGui calls
    sappimgui.trackFrame();
    simgui.newFrame(.{
        .width = sapp.width(),
        .height = sapp.height(),
        .delta_time = sapp.frameDuration(),
        .dpi_scale = sapp.dpiScale(),
    });

    // const dt: f32 = @floatCast(sapp.frameDuration() * 60);
    // const aspect = sapp.widthf() / sapp.heightf();
    state.offscreen.fs.resolution[0] = sapp.widthf();
    state.offscreen.fs.resolution[1] = sapp.heightf();

    if (ig.igBegin("abc", null, 0)) {
        // vs
        _ = ig.igDragFloat2("position", &state.offscreen.vs.position);

        // fs
        _ = ig.igInputInt("rayCount", &state.offscreen.fs.rayCount);
        _ = ig.igInputInt("maxSteps", &state.offscreen.fs.maxSteps);
        _ = ig.igDragFloatEx("size", &state.offscreen.fs.size, 0.1, 0, 100, "%f", 0);

        if (ig.igButton("load png")) {
            var x: c_int = 0;
            var y: c_int = 0;
            var n: c_int = 0;
            const img = stbi.stbi_load("test.png", &x, &y, &n, 0);
            @memcpy(&state.offscreen.pixels, img);
            stbi.stbi_image_free(img);
            state.offscreen.pixels_updated = true;
        }
    }
    ig.igEnd();

    if (state.offscreen.pixels_updated) {
        state.offscreen.pixels_updated = false;
        var imageData: sg.ImageData = .{};
        imageData.mip_levels[0] = sg.asRange(&state.offscreen.pixels);
        sg.updateImage(state.offscreen.pixels_img, imageData);
    }

    sg.beginPass(state.offscreen.pass);
    sg.applyPipeline(state.offscreen.pip);
    sg.applyBindings(state.offscreen.bind);
    sg.applyUniforms(shd.UB_vs_params, sg.asRange(&state.offscreen.vs));
    sg.applyUniforms(shd.UB_fs_params, sg.asRange(&state.offscreen.fs));
    sg.draw(0, 3, 1);
    sg.endPass();

    sg.beginPass(.{ .action = state.display.pass_action, .swapchain = sglue.swapchain() });
    sg.applyPipeline(state.display.pip);
    sg.applyBindings(state.display.bind);
    sg.draw(0, 3, 1);
    simgui.render();
    sg.endPass();

    sg.commit();
}

export fn cleanup() void {
    sappimgui.shutdown();
    simgui.shutdown();
    sg.shutdown();
}

pub fn main(_init: std.process.Init) void {
    state.alloc = _init.arena.allocator();
    state.io = _init.io;

    sapp.run(.{
        .init_cb = init,
        .frame_cb = frame,
        .event_cb = event,
        .cleanup_cb = cleanup,
        .sample_count = 4,
        .width = state.Width,
        .height = state.Height,
        .icon = .{ .sokol_default = true },
        .window_title = "offscreen.zig",
        .logger = .{ .func = slog.func },
    });
}