/**
 * @file vga.c
 * @brief Display driver supporting both VGA text mode and graphical framebuffer.
 *
 * Supports two modes depending on what GRUB provides:
 *   - EGA text mode: writes character+attribute pairs to the text buffer
 *   - Graphical (RGB) framebuffer: renders an embedded 8x16 bitmap font
 *     to the pixel framebuffer provided by GRUB
 *
 * The mode is detected at init time from the global fb_info structure,
 * which kernel_main populates from the multiboot2 framebuffer tag.
 *
 * This driver registers itself via the REGISTER_DRIVER macro and is
 * automatically discovered during boot.
 */

#include "vga.h"
#include "driver.h"
#include "port_io.h"
#include "pmm.h"
#include "framebuffer.h"
#include "font8x16.h"
#include <string.h>

/* Debug helpers defined in kernel.c */
extern void offset_print(const char *str);
extern void print_hex(uint32_t val);

/* ================================================================
 * Common state
 * ================================================================ */

/** Current text cursor position. */
static uint32_t cursor_row = 0;
static uint32_t cursor_col = 0;

/** Columns and rows of the text grid. */
static uint32_t text_cols = 80;
static uint32_t text_rows = 25;

/** Current color attribute (foreground | background << 4). */
static uint8_t text_attr = 0x07;

/** Display mode: 0 = text, 1 = pixel. */
static int display_mode = 0;

/* ================================================================
 * Text mode (EGA) internals
 * ================================================================ */

/** VGA text-mode framebuffer default base. */
#define VGA_TEXT_BUFFER 0xB8000
static uint16_t *text_buffer = (uint16_t *)VGA_TEXT_BUFFER;

static inline uint16_t vga_entry(char c, uint8_t attr) {
    return (uint16_t)c | ((uint16_t)attr << 8);
}

static void text_update_cursor(void) {
    uint16_t pos = (uint16_t)(cursor_row * text_cols + cursor_col);
    outb(0x3D4, 0x0F);
    outb(0x3D5, (uint8_t)(pos & 0xFF));
    outb(0x3D4, 0x0E);
    outb(0x3D5, (uint8_t)((pos >> 8) & 0xFF));
}

static void text_scroll(void) {
    for (uint32_t i = 0; i < (text_rows - 1) * text_cols; i++) {
        text_buffer[i] = text_buffer[i + text_cols];
    }
    uint16_t blank = vga_entry(' ', text_attr);
    for (uint32_t i = (text_rows - 1) * text_cols; i < text_rows * text_cols; i++) {
        text_buffer[i] = blank;
    }
    cursor_row = text_rows - 1;
}

static void text_clear(void) {
    uint16_t blank = vga_entry(' ', text_attr);
    for (uint32_t i = 0; i < text_cols * text_rows; i++) {
        text_buffer[i] = blank;
    }
    cursor_row = 0;
    cursor_col = 0;
    text_update_cursor();
}

static void text_putchar(char c) {
    if (c == '\n') {
        cursor_col = 0;
        cursor_row++;
    } else if (c == '\r') {
        cursor_col = 0;
    } else if (c == '\t') {
        cursor_col = (cursor_col + 8) & ~7u;
        if (cursor_col >= text_cols) {
            cursor_col = 0;
            cursor_row++;
        }
    } else if (c == '\b') {
        if (cursor_col > 0) {
            cursor_col--;
            text_buffer[cursor_row * text_cols + cursor_col] = vga_entry(' ', text_attr);
        }
    } else {
        text_buffer[cursor_row * text_cols + cursor_col] = vga_entry(c, text_attr);
        cursor_col++;
        if (cursor_col >= text_cols) {
            cursor_col = 0;
            cursor_row++;
        }
    }
    if (cursor_row >= text_rows) {
        text_scroll();
    }
    text_update_cursor();
}

/* ================================================================
 * Pixel mode (graphical framebuffer) internals
 * ================================================================ */

/** Pointer to the pixel framebuffer. */
static uint8_t *pixel_fb = (uint8_t *)0;

/** Framebuffer parameters. */
static uint32_t fb_pitch  = 0;
static uint32_t fb_width  = 0;
static uint32_t fb_height = 0;
static uint32_t fb_bpp    = 0;

/** RGB field info. */
static uint8_t fb_red_pos   = 16, fb_red_size   = 8;
static uint8_t fb_green_pos =  8, fb_green_size = 8;
static uint8_t fb_blue_pos  =  0, fb_blue_size  = 8;

/**
 * Pack an RGB color into the framebuffer's native pixel format.
 */
static inline uint32_t pack_color(uint8_t r, uint8_t g, uint8_t b) {
    (void)fb_red_size; (void)fb_green_size; (void)fb_blue_size;
    return ((uint32_t)r << fb_red_pos) |
           ((uint32_t)g << fb_green_pos) |
           ((uint32_t)b << fb_blue_pos);
}

/**
 * Set a single pixel in the framebuffer.
 */
static inline void pixel_set(uint32_t x, uint32_t y, uint32_t color) {
    if (x >= fb_width || y >= fb_height) return;
    uint32_t offset = y * fb_pitch + x * (fb_bpp / 8);
    uint32_t bytes = fb_bpp / 8;

    if (bytes == 4) {
        *(volatile uint32_t *)(pixel_fb + offset) = color;
    } else if (bytes == 3) {
        pixel_fb[offset]     = (uint8_t)(color & 0xFF);
        pixel_fb[offset + 1] = (uint8_t)((color >> 8) & 0xFF);
        pixel_fb[offset + 2] = (uint8_t)((color >> 16) & 0xFF);
    } else if (bytes == 2) {
        *(volatile uint16_t *)(pixel_fb + offset) = (uint16_t)color;
    }
}

/**
 * VGA color index to 24-bit RGB mapping.
 */
static const uint32_t vga_palette[16] = {
    0x000000, /* 0  black */
    0x0000AA, /* 1  blue */
    0x00AA00, /* 2  green */
    0x00AAAA, /* 3  cyan */
    0xAA0000, /* 4  red */
    0xAA00AA, /* 5  magenta */
    0xAA5500, /* 6  brown */
    0xAAAAAA, /* 7  light grey */
    0x555555, /* 8  dark grey */
    0x5555FF, /* 9  light blue */
    0x55FF55, /* 10 light green */
    0x55FFFF, /* 11 light cyan */
    0xFF5555, /* 12 light red */
    0xFF55FF, /* 13 light magenta */
    0xFFFF55, /* 14 yellow */
    0xFFFFFF, /* 15 white */
};

/**
 * Get packed foreground/background colors from text_attr.
 */
static void attr_to_colors(uint32_t *fg_out, uint32_t *bg_out) {
    uint8_t fg_idx = text_attr & 0x0F;
    uint8_t bg_idx = (text_attr >> 4) & 0x0F;
    uint32_t fg_rgb = vga_palette[fg_idx];
    uint32_t bg_rgb = vga_palette[bg_idx];
    *fg_out = pack_color((fg_rgb >> 16) & 0xFF, (fg_rgb >> 8) & 0xFF, fg_rgb & 0xFF);
    *bg_out = pack_color((bg_rgb >> 16) & 0xFF, (bg_rgb >> 8) & 0xFF, bg_rgb & 0xFF);
}

/**
 * Render a single glyph at character grid position (col, row).
 */
static void pixel_render_char(uint32_t col, uint32_t row, char c) {
    uint32_t fg, bg;
    attr_to_colors(&fg, &bg);

    const uint8_t *glyph;
    if (c >= FONT_FIRST && c <= FONT_LAST) {
        glyph = font8x16_data[c - FONT_FIRST];
    } else {
        glyph = 0; /* NULL = solid block for unknown chars */
    }

    uint32_t px = col * FONT_WIDTH;
    uint32_t py = row * FONT_HEIGHT;

    for (uint32_t y = 0; y < FONT_HEIGHT; y++) {
        uint8_t bits = glyph ? glyph[y] : 0xFF;
        for (uint32_t x = 0; x < FONT_WIDTH; x++) {
            uint32_t color = (bits & (0x80 >> x)) ? fg : bg;
            pixel_set(px + x, py + y, color);
        }
    }
}

/**
 * Scroll the pixel framebuffer up by one text row (FONT_HEIGHT pixels).
 */
static void pixel_scroll(void) {
    uint32_t row_bytes = FONT_HEIGHT * fb_pitch;
    uint32_t total_text_bytes = text_rows * row_bytes;

    /* Move all rows up by one */
    memcpy(pixel_fb, pixel_fb + row_bytes, total_text_bytes - row_bytes);

    /* Clear the last text row */
    uint32_t dummy, bg;
    attr_to_colors(&dummy, &bg);
    uint32_t last_row_y = (text_rows - 1) * FONT_HEIGHT;
    for (uint32_t y = last_row_y; y < last_row_y + FONT_HEIGHT; y++) {
        for (uint32_t x = 0; x < text_cols * FONT_WIDTH; x++) {
            pixel_set(x, y, bg);
        }
    }
    cursor_row = text_rows - 1;
}

static void pixel_clear(void) {
    uint32_t dummy, bg;
    attr_to_colors(&dummy, &bg);
    for (uint32_t y = 0; y < fb_height; y++) {
        for (uint32_t x = 0; x < fb_width; x++) {
            pixel_set(x, y, bg);
        }
    }
    cursor_row = 0;
    cursor_col = 0;
}

static void pixel_putchar(char c) {
    if (c == '\n') {
        cursor_col = 0;
        cursor_row++;
    } else if (c == '\r') {
        cursor_col = 0;
    } else if (c == '\t') {
        cursor_col = (cursor_col + 8) & ~7u;
        if (cursor_col >= text_cols) {
            cursor_col = 0;
            cursor_row++;
        }
    } else if (c == '\b') {
        if (cursor_col > 0) {
            cursor_col--;
            pixel_render_char(cursor_col, cursor_row, ' ');
        }
    } else {
        pixel_render_char(cursor_col, cursor_row, c);
        cursor_col++;
        if (cursor_col >= text_cols) {
            cursor_col = 0;
            cursor_row++;
        }
    }
    if (cursor_row >= text_rows) {
        pixel_scroll();
    }
}

/* ================================================================
 * Public interface
 * ================================================================ */

void vga_clear(void) {
    if (display_mode == 0)
        text_clear();
    else
        pixel_clear();
}

void vga_set_color(vga_color_t fg, vga_color_t bg) {
    text_attr = (uint8_t)fg | ((uint8_t)bg << 4);
}

void vga_putchar(char c) {
    if (display_mode == 0)
        text_putchar(c);
    else
        pixel_putchar(c);
}

void vga_puts(const char *str) {
    while (*str) {
        vga_putchar(*str);
        str++;
    }
}

void vga_put_hex(uint32_t val) {
    const char *hex = "0123456789ABCDEF";
    vga_putchar('0');
    vga_putchar('x');
    for (int i = 28; i >= 0; i -= 4) {
        vga_putchar(hex[(val >> i) & 0xF]);
    }
}

void vga_put_dec(uint32_t val) {
    if (val == 0) {
        vga_putchar('0');
        return;
    }
    char buf[12];
    int pos = 0;
    while (val > 0) {
        buf[pos++] = '0' + (val % 10);
        val /= 10;
    }
    while (pos > 0) {
        vga_putchar(buf[--pos]);
    }
}

void vga_show_mem_stats(void) {
    uint32_t mem_kb = pmm_get_memory_size() + 1024;

    vga_set_color(VGA_LIGHT_CYAN, VGA_BLACK);
    vga_puts("=== ClaudeOS Memory Statistics ===\n");

    vga_set_color(VGA_WHITE, VGA_BLACK);
    vga_puts("  Total RAM:    ");
    vga_put_dec(mem_kb);
    vga_puts(" KiB (");
    vga_put_dec(mem_kb / 1024);
    vga_puts(" MiB)\n");

    vga_puts("  Kernel start: ");
    extern uint32_t _kernel_start;
    vga_put_hex((uint32_t)&_kernel_start);
    vga_puts("\n");

    vga_puts("  Kernel end:   ");
    extern uint32_t _kernel_end;
    vga_put_hex((uint32_t)&_kernel_end);
    vga_puts("\n");

    uint32_t kernel_size = (uint32_t)&_kernel_end - (uint32_t)&_kernel_start;
    vga_puts("  Kernel size:  ");
    vga_put_dec(kernel_size / 1024);
    vga_puts(" KiB\n");

    vga_set_color(VGA_LIGHT_CYAN, VGA_BLACK);
    vga_puts("==================================\n");
    vga_set_color(VGA_LIGHT_GREY, VGA_BLACK);
}

/* ================================================================
 * Driver registration
 * ================================================================ */

static driver_probe_result_t vga_probe(void) {
    return DRIVER_PROBE_OK;
}

int vga_init(void) {
    text_attr = (uint8_t)VGA_LIGHT_GREY | ((uint8_t)VGA_BLACK << 4);

    if (fb_info.type == FB_TYPE_EGA_TEXT || fb_info.addr == 0) {
        /* Text mode (or no framebuffer tag — assume legacy text mode) */
        display_mode = 0;
        text_cols = 80;
        text_rows = 25;

        if (fb_info.addr != 0) {
            text_buffer = (uint16_t *)(uint32_t)fb_info.addr;
            text_cols = fb_info.width;
            text_rows = fb_info.height;
        }

        offset_print("  VGA: text mode ");
        print_hex(text_cols);
        offset_print("  VGA: x ");
        print_hex(text_rows);
    } else if (fb_info.type == FB_TYPE_RGB) {
        /* Graphical framebuffer — render with bitmap font */
        display_mode = 1;
        pixel_fb   = (uint8_t *)(uint32_t)fb_info.addr;
        fb_pitch   = fb_info.pitch;
        fb_width   = fb_info.width;
        fb_height  = fb_info.height;
        fb_bpp     = fb_info.bpp;

        fb_red_pos     = fb_info.red_pos;
        fb_red_size    = fb_info.red_size;
        fb_green_pos   = fb_info.green_pos;
        fb_green_size  = fb_info.green_size;
        fb_blue_pos    = fb_info.blue_pos;
        fb_blue_size   = fb_info.blue_size;

        /* Calculate text grid from pixel dimensions */
        text_cols = fb_width / FONT_WIDTH;
        text_rows = fb_height / FONT_HEIGHT;
        if (text_cols == 0) text_cols = 1;
        if (text_rows == 0) text_rows = 1;

        offset_print("  VGA: pixel mode ");
        print_hex(fb_width);
        offset_print("  VGA: x ");
        print_hex(fb_height);
        offset_print("  VGA: bpp=");
        print_hex(fb_bpp);
        offset_print("  VGA: text grid ");
        print_hex(text_cols);
        offset_print("  VGA: x ");
        print_hex(text_rows);
        offset_print("  VGA: addr=");
        print_hex((uint32_t)pixel_fb);
    } else {
        /* Indexed or unknown — fall back to text mode */
        display_mode = 0;
        text_cols = 80;
        text_rows = 25;
        offset_print("  VGA: unknown fb type, assuming text mode\n");
    }

    vga_clear();

    vga_set_color(VGA_LIGHT_GREEN, VGA_BLACK);
    vga_puts("ClaudeOS v0.1 booting...\n\n");
    vga_set_color(VGA_LIGHT_GREY, VGA_BLACK);

    return 0;
}

/** VGA driver descriptor. */
static const driver_t vga_driver = {
    .name  = "vga",
    .probe = vga_probe,
    .init  = vga_init,
};

REGISTER_DRIVER(vga_driver);