// User application entry points for edit.

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>
#include <string.h>
#include <ntlite/syscall.h>

#define GLYPH_W 8
#define GLYPH_H 16

#define MAX_LINES 512
#define MAX_LINE  256
#define PATH_MAX2 260
#define MSG_MAX   160
#define MAX_SCREEN_COLS 256
#define MAX_SCREEN_ROWS 128

#define COL_BG      0x000000u
#define COL_FG      0xC8C8C8u
#define COL_DIM     0x808080u
#define COL_STATUS  0x303030u
#define COL_STATUSF 0xFFFFFFu
#define COL_CURSOR  0xE0E0E0u
#define COL_CURSORF 0x000000u

#define EDIT_KEY_ESC       INPUT_KEY_ESCAPE
#define EDIT_KEY_BACKSPACE INPUT_KEY_BACKSPACE
#define EDIT_KEY_TAB       INPUT_KEY_TAB
#define EDIT_KEY_Q         INPUT_KEY_Q
#define EDIT_KEY_S         INPUT_KEY_S
#define EDIT_KEY_ENTER     INPUT_KEY_ENTER
#define EDIT_KEY_HOME      INPUT_KEY_HOME
#define EDIT_KEY_UP        INPUT_KEY_UP
#define EDIT_KEY_PGUP      INPUT_KEY_PAGE_UP
#define EDIT_KEY_LEFT      INPUT_KEY_LEFT
#define EDIT_KEY_RIGHT     INPUT_KEY_RIGHT
#define EDIT_KEY_END       INPUT_KEY_END
#define EDIT_KEY_DOWN      INPUT_KEY_DOWN
#define EDIT_KEY_PGDN      INPUT_KEY_PAGE_DOWN
#define EDIT_KEY_DEL       INPUT_KEY_DELETE

typedef struct LINE {
    int  len;
    char text[MAX_LINE];
} LINE;

static LINE gLines[MAX_LINES];
static int  gLineCount = 1;
static int  gCx = 0;
static int  gCy = 0;
static int  gTop = 0;
static int  gLeft = 0;
static int  gCols = 80;
static int  gRows = 25;
static bool gDirty = false;
static bool gQuitArmed = false;
static char gFilename[PATH_MAX2] = "untitled.txt";
static char gMessage[MSG_MAX] = "ready";

typedef struct SCREEN_CELL {
    char c;
    uint32_t fg;
    uint32_t bg;
} SCREEN_CELL;

static SCREEN_CELL gScreenCache[MAX_SCREEN_COLS * MAX_SCREEN_ROWS];
static bool gScreenCacheValid = false;

// Implements the invalidate screen cache operation.
static void invalidate_screen_cache(void) {
    gScreenCacheValid = false;
}

// Updates screen size.
static void update_screen_size(void) {
    int pxW = 0, pxH = 0;
    int oldCols = gCols;
    int oldRows = gRows;

    if (SysGetScreenSize(&pxW, &pxH) == 0 && pxW > 0 && pxH > 0) {
        gCols = pxW / GLYPH_W;
        gRows = pxH / GLYPH_H;

        if (gCols < 20) gCols = 20;
        if (gRows < 5)  gRows = 5;
        if (gCols > MAX_SCREEN_COLS) gCols = MAX_SCREEN_COLS;
        if (gRows > MAX_SCREEN_ROWS) gRows = MAX_SCREEN_ROWS;
    }

    if (gCols != oldCols || gRows != oldRows)
        invalidate_screen_cache();
}

// Updates cell.
static void put_cell(int col, int row, char c, uint32_t fg, uint32_t bg) {
    if (col < 0 || row < 0 || col >= gCols || row >= gRows)
        return;

    if (!c) c = ' ';

    if (col < MAX_SCREEN_COLS && row < MAX_SCREEN_ROWS) {
        SCREEN_CELL* cell = &gScreenCache[row * MAX_SCREEN_COLS + col];
        if (gScreenCacheValid && cell->c == c && cell->fg == fg && cell->bg == bg)
            return;

        cell->c = c;
        cell->fg = fg;
        cell->bg = bg;
    }

    SysPutScreenChar(c, col * GLYPH_W, row * GLYPH_H, fg, bg);
}

// Clears row.
static void clear_row(int row, uint32_t bg) {
    for (int x = 0; x < gCols; x++) put_cell(x, row, ' ', COL_FG, bg);
}

// Draws text.
static void draw_text(int col, int row, const char* s, uint32_t fg, uint32_t bg) {
    while (*s && col < gCols) put_cell(col++, row, *s++, fg, bg);
}

// Implements the msg set operation.
static void msg_set(const char* s) {
    size_t n = strlen(s);
    if (n >= sizeof(gMessage)) n = sizeof(gMessage) - 1;
    memcpy(gMessage, s, n);
    gMessage[n] = 0;
}

// Appends char.
static void append_char(char* b, size_t cap, size_t* p, char c) {
    if (*p + 1 < cap) b[(*p)++] = c;
    b[*p < cap ? *p : cap - 1] = 0;
}

// Appends str.
static void append_str(char* b, size_t cap, size_t* p, const char* s) {
    while (*s) append_char(b, cap, p, *s++);
}

// Appends u32.
static void append_u32(char* b, size_t cap, size_t* p, uint32_t v) {
    char tmp[12];
    int n = 0;
    if (v == 0) { append_char(b, cap, p, '0'); return; }
    while (v && n < (int)sizeof(tmp)) {
        tmp[n++] = (char)('0' + (v % 10u));
        v /= 10u;
    }
    while (n > 0) append_char(b, cap, p, tmp[--n]);
}

// Implements the key to char operation.
static char key_to_char(INPUT_KEY key, uint32_t mods) {
    if (key >= INPUT_KEY_A && key <= INPUT_KEY_Z) {
        bool shifted = (mods & INPUT_MOD_SHIFT) != 0;
        bool caps = (mods & INPUT_MOD_CAPS_LOCK) != 0;
        char c = (char)('a' + (key - INPUT_KEY_A));
        return (shifted ^ caps) ? (char)(c - 'a' + 'A') : c;
    }

    typedef struct { INPUT_KEY key; char normal; char shifted; } PAIR;
    static const PAIR map[] = {
        { INPUT_KEY_1, '1', '!' }, { INPUT_KEY_2, '2', '@' },
        { INPUT_KEY_3, '3', '#' }, { INPUT_KEY_4, '4', '$' },
        { INPUT_KEY_5, '5', '%' }, { INPUT_KEY_6, '6', '^' },
        { INPUT_KEY_7, '7', '&' }, { INPUT_KEY_8, '8', '*' },
        { INPUT_KEY_9, '9', '(' }, { INPUT_KEY_0, '0', ')' },
        { INPUT_KEY_MINUS, '-', '_' }, { INPUT_KEY_EQUAL, '=', '+' },
        { INPUT_KEY_LEFT_BRACKET, '[', '{' }, { INPUT_KEY_RIGHT_BRACKET, ']', '}' },
        { INPUT_KEY_BACKSLASH, '\\', '|' }, { INPUT_KEY_SEMICOLON, ';', ':' },
        { INPUT_KEY_APOSTROPHE, '\'', '"' }, { INPUT_KEY_GRAVE, '`', '~' },
        { INPUT_KEY_COMMA, ',', '<' }, { INPUT_KEY_PERIOD, '.', '>' },
        { INPUT_KEY_SLASH, '/', '?' }, { INPUT_KEY_SPACE, ' ', ' ' },
    };
    bool shifted = (mods & INPUT_MOD_SHIFT) != 0;
    for (size_t i = 0; i < sizeof(map) / sizeof(map[0]); i++) {
        if (map[i].key == key) return shifted ? map[i].shifted : map[i].normal;
    }
    return 0;
}

// Implements the clamp cursor operation.
static void clamp_cursor(void) {
    if (gLineCount < 1) gLineCount = 1;
    if (gCy < 0) gCy = 0;
    if (gCy >= gLineCount) gCy = gLineCount - 1;
    if (gCx < 0) gCx = 0;
    if (gCx > gLines[gCy].len) gCx = gLines[gCy].len;
}

// Implements the ensure visible operation.
static void ensure_visible(void) {
    int textRows = gRows - 2;
    if (textRows < 1) textRows = 1;

    if (gCy < gTop) gTop = gCy;
    if (gCy >= gTop + textRows) gTop = gCy - textRows + 1;
    if (gTop < 0) gTop = 0;

    if (gCx < gLeft) gLeft = gCx;
    if (gCx >= gLeft + gCols) gLeft = gCx - gCols + 1;
    if (gLeft < 0) gLeft = 0;
}

// Implements the render operation.
static void render(void) {
    update_screen_size();

    clamp_cursor();
    ensure_visible();

    char status[256];
    size_t p = 0;
    append_str(status, sizeof(status), &p, " edit ");
    append_str(status, sizeof(status), &p, gFilename);
    append_str(status, sizeof(status), &p, gDirty ? " *  " : "    ");
    append_str(status, sizeof(status), &p, "Ctrl+S save  Ctrl+Q quit  Ln ");
    append_u32(status, sizeof(status), &p, (uint32_t)(gCy + 1));
    append_str(status, sizeof(status), &p, ", Col ");
    append_u32(status, sizeof(status), &p, (uint32_t)(gCx + 1));

    size_t statusLen = p;
    for (int sx = 0; sx < gCols; sx++) {
        char c = ((size_t)sx < statusLen) ? status[sx] : ' ';
        put_cell(sx, 0, c, COL_STATUSF, COL_STATUS);
    }

    int textRows = gRows - 2;
    for (int sy = 0; sy < textRows; sy++) {
        int row = sy + 1;
        int li = gTop + sy;

        for (int sx = 0; sx < gCols; sx++) {
            int ci = gLeft + sx;
            char c = ' ';
            bool atCursor = false;

            if (li < gLineCount) {
                LINE* ln = &gLines[li];
                c = (ci < ln->len) ? ln->text[ci] : ' ';
                atCursor = (li == gCy && ci == gCx);
            }

            put_cell(sx, row, c, atCursor ? COL_CURSORF : COL_FG,
                              atCursor ? COL_CURSOR  : COL_BG);
        }
    }

    size_t messageLen = strlen(gMessage);
    for (int sx = 0; sx < gCols; sx++) {
        char c = ((size_t)sx < messageLen) ? gMessage[sx] : ' ';
        put_cell(sx, gRows - 1, c, COL_STATUSF, COL_STATUS);
    }

    gScreenCacheValid = true;
}

// Inserts char at cursor.
static void insert_char_at_cursor(char c) {
    LINE* ln = &gLines[gCy];
    if (ln->len >= MAX_LINE - 1) { msg_set("line too long"); return; }
    memmove(&ln->text[gCx + 1], &ln->text[gCx], (size_t)(ln->len - gCx + 1));
    ln->text[gCx] = c;
    ln->len++;
    gCx++;
    gDirty = true;
}

// Implements the newline at cursor operation.
static void newline_at_cursor(void) {
    if (gLineCount >= MAX_LINES) { msg_set("too many lines"); return; }

    for (int i = gLineCount; i > gCy + 1; i--) gLines[i] = gLines[i - 1];

    LINE* cur = &gLines[gCy];
    LINE* next = &gLines[gCy + 1];
    int tail = cur->len - gCx;
    if (tail > 0) memcpy(next->text, &cur->text[gCx], (size_t)tail);
    next->len = tail;
    next->text[next->len] = 0;

    cur->len = gCx;
    cur->text[cur->len] = 0;

    gLineCount++;
    gCy++;
    gCx = 0;
    gDirty = true;
}

// Implements the backspace at cursor operation.
static void backspace_at_cursor(void) {
    if (gCx > 0) {
        LINE* ln = &gLines[gCy];
        memmove(&ln->text[gCx - 1], &ln->text[gCx], (size_t)(ln->len - gCx + 1));
        ln->len--;
        gCx--;
        gDirty = true;
        return;
    }

    if (gCy <= 0) return;

    LINE* prev = &gLines[gCy - 1];
    LINE* cur  = &gLines[gCy];
    if (prev->len + cur->len >= MAX_LINE) { msg_set("join would make line too long"); return; }

    int oldLen = prev->len;
    memcpy(&prev->text[prev->len], cur->text, (size_t)cur->len + 1);
    prev->len += cur->len;

    for (int i = gCy; i < gLineCount - 1; i++) gLines[i] = gLines[i + 1];
    gLineCount--;
    gCy--;
    gCx = oldLen;
    gDirty = true;
}

// Releases at cursor.
static void delete_at_cursor(void) {
    LINE* ln = &gLines[gCy];
    if (gCx < ln->len) {
        memmove(&ln->text[gCx], &ln->text[gCx + 1], (size_t)(ln->len - gCx));
        ln->len--;
        gDirty = true;
        return;
    }

    if (gCy + 1 >= gLineCount) return;

    LINE* next = &gLines[gCy + 1];
    if (ln->len + next->len >= MAX_LINE) { msg_set("join would make line too long"); return; }

    memcpy(&ln->text[ln->len], next->text, (size_t)next->len + 1);
    ln->len += next->len;
    for (int i = gCy + 1; i < gLineCount - 1; i++) gLines[i] = gLines[i + 1];
    gLineCount--;
    gDirty = true;
}

// Moves left.
static void move_left(void) {
    if (gCx > 0) gCx--;
    else if (gCy > 0) { gCy--; gCx = gLines[gCy].len; }
}

// Moves right.
static void move_right(void) {
    if (gCx < gLines[gCy].len) gCx++;
    else if (gCy + 1 < gLineCount) { gCy++; gCx = 0; }
}

// Moves up.
static void move_up(void) {
    if (gCy > 0) gCy--;
    if (gCx > gLines[gCy].len) gCx = gLines[gCy].len;
}

// Moves down.
static void move_down(void) {
    if (gCy + 1 < gLineCount) gCy++;
    if (gCx > gLines[gCy].len) gCx = gLines[gCy].len;
}

// Updates file.
static void save_file(void) {
    uint32_t h = 0;
    SYS_PATH_HANDLE_REQUEST pathReq = { SysSvFromCstr(gFilename), &h };
    uint32_t st = SysCreateFile(&pathReq);
    if (st != 0) st = SysOpenFile(&pathReq);
    if (st != 0) { msg_set("save failed: cannot open file"); return; }

    SysTruncateFile(h, 0);
    SysSeekFile(h, 0);

    for (int i = 0; i < gLineCount; i++) {
        size_t written = 0;
        if (gLines[i].len) {
            SYS_FILE_IO_REQUEST writeReq = SysMakeFileIoRequest(h, gLines[i].text, (size_t)gLines[i].len, &written);
            st = SysWriteFile(&writeReq);
            if (st != 0) { SysCloseHandle(h); msg_set("save failed: write error"); return; }
        }
        if (i + 1 < gLineCount) {
            const char nl = '\n';
            SYS_FILE_IO_REQUEST newlineReq = SysMakeFileIoRequest(h, &nl, 1, &written);
            st = SysWriteFile(&newlineReq);
            if (st != 0) { SysCloseHandle(h); msg_set("save failed: write error"); return; }
        }
    }

    SysCloseHandle(h);
    gDirty = false;
    msg_set("saved");
}

// Implements the reset buffer operation.
static void reset_buffer(void) {
    gLineCount = 1;
    gLines[0].len = 0;
    gLines[0].text[0] = 0;
    gCx = gCy = gTop = gLeft = 0;
    gDirty = false;
}

// Loads file.
static void load_file(void) {
    reset_buffer();

    uint32_t h = 0;
    SYS_PATH_HANDLE_REQUEST pathReq = { SysSvFromCstr(gFilename), &h };
    if (SysOpenFile(&pathReq) != 0) {
        msg_set("new file");
        return;
    }

    char buf[512];
    size_t got = 0;
    bool truncated = false;
    for (;;) {
        SYS_FILE_IO_REQUEST readReq = SysMakeFileIoRequest(h, buf, sizeof(buf), &got);
        if (SysReadFile(&readReq) != 0 || got == 0) break;
        for (size_t i = 0; i < got; i++) {
            char c = buf[i];
            if (c == '\r') continue;
            if (c == '\n') {
                if (gLineCount < MAX_LINES) {
                    gLineCount++;
                    gLines[gLineCount - 1].len = 0;
                    gLines[gLineCount - 1].text[0] = 0;
                } else truncated = true;
                continue;
            }
            if (c < 0x20 && c != '\t') continue;
            LINE* ln = &gLines[gLineCount - 1];
            if (ln->len + 1 < MAX_LINE) {
                ln->text[ln->len++] = (c == '\t') ? ' ' : c;
                ln->text[ln->len] = 0;
            } else truncated = true;
        }
    }
    SysCloseHandle(h);
    msg_set(truncated ? "loaded, truncated long file" : "loaded");
}

// Implements the skip spaces operation.
static const char* skip_spaces(const char* s) {
    while (s && (*s == ' ' || *s == '\t')) s++;
    return s;
}

// Implements the skip token operation.
static const char* skip_token(const char* s) {
    s = skip_spaces(s);
    if (!s || !*s) return s;
    if (*s == '"') {
        s++;
        while (*s && *s != '"') s++;
        if (*s == '"') s++;
        return s;
    }
    while (*s && *s != ' ' && *s != '\t') s++;
    return s;
}

// Returns token.
static bool read_token(const char* s, char* out, size_t cap) {
    s = skip_spaces(s);
    if (!s || !*s || cap == 0) return false;
    size_t n = 0;
    if (*s == '"') {
        s++;
        while (*s && *s != '"') {
            if (n + 1 < cap) out[n++] = *s;
            s++;
        }
    } else {
        while (*s && *s != ' ' && *s != '\t') {
            if (n + 1 < cap) out[n++] = *s;
            s++;
        }
    }
    out[n] = 0;
    return n != 0;
}

// Parses filename from cmdline.
static void parse_filename_from_cmdline(void) {
    SYS_PEB* peb = SysGetPeb();
    const char* cmd = (peb && peb->CommandLine.Data) ? peb->CommandLine.Data : NULL;
    const char* arg = skip_token(cmd);
    if (read_token(arg, gFilename, sizeof(gFilename))) return;
    strcpy(gFilename, "untitled.txt");
}

// Implements the editor loop operation.
static void editor_loop(void) {
    while (true) {
        render();

        INPUT_KEY key = SysReadKey();
        uint32_t mods = SysGetKeyModifiers();
        bool ctrl = (mods & INPUT_MOD_CTRL) != 0;

        if (ctrl && key == EDIT_KEY_Q) {
            if (gDirty && !gQuitArmed) {
                gQuitArmed = true;
                msg_set("unsaved changes: press Ctrl+Q again to quit");
                continue;
            }
            break;
        }

        gQuitArmed = false;

        if (ctrl && key == EDIT_KEY_S) { save_file(); continue; }
        if (key == EDIT_KEY_ESC) { msg_set("Ctrl+Q quits, Ctrl+S saves"); continue; }

        switch (key) {
            case EDIT_KEY_LEFT:      move_left(); break;
            case EDIT_KEY_RIGHT:     move_right(); break;
            case EDIT_KEY_UP:        move_up(); break;
            case EDIT_KEY_DOWN:      move_down(); break;
            case EDIT_KEY_HOME:      gCx = 0; break;
            case EDIT_KEY_END:       gCx = gLines[gCy].len; break;
            case EDIT_KEY_PGUP: {
                int n = gRows - 2;
                if (n < 1) n = 1;
                gCy -= n;
                clamp_cursor();
                break;
            }
            case EDIT_KEY_PGDN: {
                int n = gRows - 2;
                if (n < 1) n = 1;
                gCy += n;
                clamp_cursor();
                break;
            }
            case EDIT_KEY_BACKSPACE: backspace_at_cursor(); break;
            case EDIT_KEY_DEL:       delete_at_cursor(); break;
            case EDIT_KEY_ENTER:     newline_at_cursor(); break;
            case EDIT_KEY_TAB:
                for (int i = 0; i < 4; i++) insert_char_at_cursor(' ');
                break;
            default: {
                char c = key_to_char(key, mods);
                if (!ctrl && c >= 0x20 && c <= 0x7E) insert_char_at_cursor(c);
                break;
            }
        }
    }
}

// Prints the requested operation.
static void print(const char* s) {
    SYS_WRITE_CONSOLE_REQUEST req = { SysSvFromCstr(s) };
    SysWriteConsole(&req);
}

// Runs the requested operation.
int main(void) {
    parse_filename_from_cmdline();
    load_file();
    SysClearScreen(COL_BG);
    invalidate_screen_cache();
    editor_loop();
    SysClearScreen(0x012456);
    invalidate_screen_cache();
    print("edit: goodbye\n");
    SysExitProcess(0);
    return 0;
}