#include "render.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <termios.h>
#include <fcntl.h>
#include <signal.h>

#define UPPER "\xe2\x96\x80"   // ▀ U+2580

static struct termios orig_termios;
static bool raw_active = false;

static void on_winch(int s);

void term_restore(void) {
    if (raw_active) {
        tcsetattr(STDIN_FILENO, TCSAFLUSH, &orig_termios);
        raw_active = false;
    }
    // show cursor, leave alt screen, reset colors
    printf("\x1b[0m\x1b[?25h\x1b[?1049l");
    fflush(stdout);
}

void term_init(void) {
    tcgetattr(STDIN_FILENO, &orig_termios);
    struct termios raw = orig_termios;
    raw.c_lflag &= ~(ECHO | ICANON | ISIG);
    raw.c_iflag &= ~(IXON | ICRNL);
    raw.c_cc[VMIN] = 0;
    raw.c_cc[VTIME] = 0;
    tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw);
    raw_active = true;
    // enter alt screen, hide cursor, clear
    printf("\x1b[?1049h\x1b[?25l\x1b[2J\x1b[H");
    fflush(stdout);
    signal(SIGWINCH, on_winch);
    render_force_full();
    atexit(term_restore);
}

// large reusable output buffer
static char outbuf[SCREEN_W * (SCREEN_H/2) * 40 + 4096];

// previous frame's pixels, for inter-frame diffing
static u8 prev_fb[SCREEN_H][SCREEN_W][3];
static bool need_full = true;              // force a complete repaint
static volatile sig_atomic_t resized = 0;  // set by SIGWINCH

void render_force_full(void) { need_full = true; }
static void on_winch(int s) { (void)s; resized = 1; }

void render_frame(GB *gb) {
    PPU *p = &gb->ppu;
    char *o = outbuf;

    if (resized) { resized = 0; need_full = true; o += sprintf(o, "\x1b[2J"); }

    // Terminal SGR (color) state persists across cursor moves, so we can keep
    // one fg/bg tracker for the whole frame even when we jump over unchanged
    // cells. Reset each frame since we emit a final \x1b[0m.
    int pr = -1, pg = -1, pb = -1;   // last-emitted fg
    int PR = -1, PG = -1, PB = -1;   // last-emitted bg
    int cur_row = -2, cur_col = -2;  // terminal cell just written (0-indexed)

    for (int y = 0; y < SCREEN_H; y += 2) {
        int row = y / 2;
        for (int x = 0; x < SCREEN_W; x++) {
            u8 *top = p->fb[y][x];
            u8 *bot = p->fb[y+1][x];
            if (!need_full) {
                u8 *pt = prev_fb[y][x], *pb2 = prev_fb[y+1][x];
                if (top[0]==pt[0] && top[1]==pt[1] && top[2]==pt[2] &&
                    bot[0]==pb2[0] && bot[1]==pb2[1] && bot[2]==pb2[2])
                    continue;   // cell unchanged -> skip
            }
            // reposition cursor only when we're not already right after the
            // previously written cell
            if (row != cur_row || x != cur_col + 1)
                o += sprintf(o, "\x1b[%d;%dH", row + 1, x + 1);
            if (top[0] != pr || top[1] != pg || top[2] != pb) {
                o += sprintf(o, "\x1b[38;2;%d;%d;%dm", top[0], top[1], top[2]);
                pr = top[0]; pg = top[1]; pb = top[2];
            }
            if (bot[0] != PR || bot[1] != PG || bot[2] != PB) {
                o += sprintf(o, "\x1b[48;2;%d;%d;%dm", bot[0], bot[1], bot[2]);
                PR = bot[0]; PG = bot[1]; PB = bot[2];
            }
            memcpy(o, UPPER, 3); o += 3;
            cur_row = row; cur_col = x;
        }
    }

    // status line: static text, only (re)draw on a full repaint
    if (need_full) {
        o += sprintf(o, "\x1b[0m\x1b[%d;1H\x1b[38;2;150;150;150m %.*s  "
                        "[wasd/arrows] z:A x:B space:sel enter:start q:quit",
                        SCREEN_H/2 + 1, 15, gb->cart.title);
    }

    memcpy(prev_fb, p->fb, sizeof(prev_fb));
    need_full = false;

    if (o != outbuf) {                 // nothing changed -> write nothing
        o += sprintf(o, "\x1b[0m");
        fwrite(outbuf, 1, o - outbuf, stdout);
        fflush(stdout);
    }
}

// ---- input with decay-based "hold" emulation ----
static int hold[8];   // frames remaining for each BTN bit position
#define HOLD_FRAMES 4

static void press(int bit) {
    for (int i = 0; i < 8; i++) if ((1 << i) == bit) hold[i] = HOLD_FRAMES;
}

bool input_poll(GB *gb) {
    unsigned char buf[64];
    int n = read(STDIN_FILENO, buf, sizeof(buf));
    bool quit = false;
    for (int i = 0; i < n; i++) {
        unsigned char ch = buf[i];
        if (ch == 0x1b && i + 2 < n && buf[i+1] == '[') {
            switch (buf[i+2]) {
                case 'A': press(BTN_UP); break;
                case 'B': press(BTN_DOWN); break;
                case 'C': press(BTN_RIGHT); break;
                case 'D': press(BTN_LEFT); break;
            }
            i += 2;
            continue;
        }
        switch (ch) {
            case 'w': press(BTN_UP); break;
            case 's': press(BTN_DOWN); break;
            case 'a': press(BTN_LEFT); break;
            case 'd': press(BTN_RIGHT); break;
            case 'z': case 'j': press(BTN_A); break;
            case 'x': case 'k': press(BTN_B); break;
            case '\r': case '\n': press(BTN_START); break;
            case ' ': press(BTN_SELECT); break;
            case 'q': case 3: quit = true; break;
        }
    }
    // build button state from decay counters
    u8 b = 0;
    for (int i = 0; i < 8; i++) {
        if (hold[i] > 0) { hold[i]--; b |= (1 << i); }
    }
    gb->buttons = b;
    if (b) gb_request_interrupt(gb, INT_JOYPAD);
    return !quit;
}