#include <stdlib.h>
#include <gba_console.h>
#include <gba_video.h>
#include <gba_interrupt.h>
#include <gba_systemcalls.h>
#include <gba_input.h>
#include <gba_base.h>
#include <gba_dma.h>
#include <maxmod.h>
#include <mm_types.h>

#include "together_8_img_bin.h"
#include "together_8_pal_bin.h"

// Define any soundbank includes here
#include "soundbank.h"
#include "soundbank_bin.h"

// Global mixing buffer for maxmod
u8 mixing_buffer[MM_MIXLEN_16KHZ] __attribute__((aligned(4)));

// Set the two variables below to start the palette fade

// The number of steps to fade the palette to black
const u8 palette_fade_steps = 12;
// The current step of the palette fade, set this to above to start the fade, the fade will decrement this value until it reaches 0
u8 palette_fade_step = 0;

const u8 fade_pause_frames = 120;
u8 fade_pause_frame_count = 0;

// Function Prototypes
void initializeSystem(void);
void loadIntroScreen(void);
void fadePaletteStep(void);

int main(void) {
    // Initialize GBA system and maxmod
    initializeSystem();
    
    // Load intro screen
    loadIntroScreen();

    // Wait for VBlank before starting music
    VBlankIntrWait();
    mmStart(MOD_MOZARTSONATA, MM_PLAY_LOOP);
    
    // Main game loop
    while(1) {
        VBlankIntrWait();
        
        // Update sound system
        mmFrame();
        
        // Game logic goes here
        scanKeys();
        u16 keys = keysDown();
        
        // Check for key presses
        if (keys & KEY_A) {
            mmEffect(SFX_WEAPON);
        }
        
        if ((keys & KEY_START) && palette_fade_step == 0) {
            // Start the palette fade
            palette_fade_step = palette_fade_steps;
        }
        else if (keys & KEY_SELECT) {
            // Reset the palette to the original
            DMA3COPY(together_8_pal_bin, BG_PALETTE, together_8_pal_bin_size >> 1);
        }
        
        fadePaletteStep();
    }
    
    return 0;
}

void initializeSystem(void) {
    // Initialize GBA display and interrupt system
    irqInit();
    irqSet(IRQ_VBLANK, mmVBlank);
    irqEnable(IRQ_VBLANK);
    
    // Initialize display registers for Mode 4 (8-bit paletted bitmap)
    SetMode(MODE_4 | BG2_ON);  // Mode 4 + Enable BG2
    
    mmInitDefault((mm_addr)soundbank_bin, 8);
}

void loadIntroScreen(void) {    
    // Wait for VBlank before copying
    VBlankIntrWait();

    // Load the palette
    // Palette size needs to be in 16-bit units (divide by 2)
    DMA3COPY(together_8_pal_bin, BG_PALETTE, together_8_pal_bin_size >> 1);
    
    // Copy image data to first frame buffer
    // Image size needs to be in 16-bit units (divide by 2)
    DMA3COPY(together_8_img_bin, (void*)VRAM, together_8_img_bin_size >> 1);
}

// increment the palette fade step by 1
void fadePaletteStep(void) {
    if (fade_pause_frame_count > fade_pause_frames) {
        ++fade_pause_frame_count;
        return;
    }
    fade_pause_frame_count = 0;

    if (palette_fade_steps && palette_fade_step) {
        // Calculate how much to keep of each color component in this step
        // As palette_fade_step goes from palette_fade_steps down to 1, 
        // this ratio goes from 1.0 down to nearly 0.0
        // -1 is so the last step is fully black.
        u16 keep_ratio = (((u16)palette_fade_step - 1) << 7) / (u16)palette_fade_steps;
        
        // fade the palette to black, by iterating over the palette memory one position at a time
        for (u16 i = 0; i < 256; ++i) {
            u16 color = ((u16*)together_8_pal_bin)[i];
            
            // Extract RGB components (GBA uses 5 bits per component)
            u16 r = (color & 0x1F);
            u16 g = (color >> 5) & 0x1F;
            u16 b = (color >> 10) & 0x1F;
            
            // Reduce each component based on current step
            r = (r * keep_ratio) >> 7;
            g = (g * keep_ratio) >> 7;
            b = (b * keep_ratio) >> 7;
            
            // Recombine the components
            u16 new_color = (b << 10) | (g << 5) | r;
            
            BG_PALETTE[i] = new_color;
        }
        
        --palette_fade_step;
    }
}