#include <string.h>
#include <stdio.h>

#include "terminal.h"

//#define BUF_COLUMNS (100)
//#define BUF_LINES   (75)

#define BUF_COLUMNS (80)
#define BUF_LINES   (24)

typedef unsigned char flag;

struct modes {
  flag keyboard_action : 1;  // KAM     - Keyboard Action Mode
  flag insert_replace : 1;   // IRM     - Insertion-Replacement Mode
  flag linefeed_newline : 1; // LNM     - Linefeed/Newline Mode
  flag local_echo : 1;       // SRM     - Send/Receive Mode
  flag cursor_key : 1;       // DECCKM  - Cursor Key Mode
  flag column : 1;           // DECCOLM - Column Mode (80/132)
  flag scroll : 1;           // DECSCLM - Smooth Scroll Mode
  flag screen : 1;           // DECSCNM - Screen Mode (normal/reverse)
  flag origin : 1;           // DECOM   - Origin Mode
  flag auto_wrap : 1;        // DECAWM  - Auto Wrap Mode
  flag auto_repeat : 1;      // DECARM  - Auto Repeat Mode
  flag cursor_enable : 1;    // DECTCEM - Text Cursor Enable Mode
};

struct char_attribs {        // SGR
  flag underline : 1;
  flag reverse : 1;
  flag blink : 1;
  flag bold : 1;
};

struct line_attribs {        // DECSWL when neither is set
  flag double_width : 1;     // DECDWL - Can be set without DHL
  flag double_height_t : 1;  // DECDHL Top Half - DHL is always also DWL
  flag double_height_b : 1;  // DECDHL Bottom Half
};

struct position {
  int col;
  int line;
};

struct bounds {
  int min;
  int max;
};

struct cell {
  struct char_attribs att;
  unsigned char glyph;
};

struct line {
  struct line_attribs att;
  struct cell cells[BUF_COLUMNS];
};

struct page {
  int col_count;
  int line_count;
  struct bounds scroll;
  struct line lines[BUF_LINES];
};

struct terminal {
  struct page pagebuf;
  struct modes modes;
  unsigned char tabstops[BUF_COLUMNS];
  struct position cursor;
};

static const struct char_attribs blank_char_att = {
  .underline = 0,
  .reverse = 0,
  .blink = 0,
  .bold = 0
};

static const struct line_attribs blank_line_att = {
  .double_width = 0,
  .double_height_t = 0,
  .double_height_b = 0
};

static Terminal singleton_terminal = {
  .pagebuf = { BUF_COLUMNS, BUF_LINES, {0, BUF_LINES-1}, { {}, {} } },
  .modes = {},
  .tabstops = {},
  {0, 0}
};

int bounded_move(int *pos, int amt, struct bounds b)
{
  int orig_pos = *pos;
  int actual_move = amt;

  *pos += amt;
  if (amt < 0) {
    if (*pos < b.min) *pos = b.min;
  } else {
    if (*pos > b.max) *pos = b.max;
  }
  actual_move = *pos - orig_pos;

  return actual_move;
}

void bounded_set(int *pos, int new_pos, struct bounds b)
{
  if (new_pos < b.min)
    *pos = b.min;
  else if (new_pos > b.max)
    *pos = b.max;
  else
    *pos = new_pos;
}

struct bounds Terminal_cursorHBounds(Terminal *term)
{
  struct bounds b = { 0, 0 };

  b.min = 0;
  b.max = term->pagebuf.col_count - 1;

  return b;
}

struct bounds Terminal_cursorVBounds(Terminal *term, int scroll_region)
{
  struct bounds b = { 0, 0 };

  if (scroll_region) {
    b.min = term->pagebuf.scroll.min;
    b.max = term->pagebuf.scroll.max;
  } else {
    b.min = 0;
    b.max = term->pagebuf.line_count - 1;
  }

  return b;
}

Terminal *Terminal_new(void)
{
  Terminal_init(&singleton_terminal);
  return &singleton_terminal;
}

void Terminal_defaultModes(Terminal *t)
{
  t->modes.auto_wrap = 0;
  t->modes.insert_replace = 0;
  t->modes.cursor_enable = 1;
}

void Terminal_clearScreen(Terminal *t)
{
  int i, j;
  struct cell *c;
  struct line *l;

  for (i = 0; i < t->pagebuf.line_count; i++) {
    l = &t->pagebuf.lines[i];
    l->att = blank_line_att;
    for (j = 0; j < t->pagebuf.col_count; j++) {
      c = &l->cells[j];

      c->att = blank_char_att;
      c->glyph = 0;
    }
  }
}

void Terminal_clearTabs(Terminal *t)
{
  int i;
  for (i = 0; i < t->pagebuf.col_count; i++) {
    t->tabstops[i] = 0;
  }
}

void Terminal_defaultTabs(Terminal *t)
{
  int i;
  for (i = 8; i < t->pagebuf.col_count; i += 8) {
    t->tabstops[i] = 1;
  }
}

void Terminal_setTab(Terminal *t)
{
  t->tabstops[t->cursor.col] = 1;
}

void Terminal_clearTab(Terminal *t)
{
  t->tabstops[t->cursor.col] = 0;
}

void Terminal_defaultScrollRegion(Terminal *t)
{
  t->pagebuf.scroll.min = 0;
  t->pagebuf.scroll.max = t->pagebuf.line_count - 1;
}

void Terminal_init(Terminal *t)
{
  t->pagebuf.col_count = BUF_COLUMNS;
  t->pagebuf.line_count = BUF_LINES;
  Terminal_defaultModes(t);
  Terminal_clearScreen(t);
  Terminal_clearTabs(t);
  Terminal_defaultTabs(t);
  Terminal_defaultScrollRegion(t);
  t->cursor.col = 0;
  t->cursor.line = 0;
}

void Terminal_bufferDump(Terminal *t)
{
  int i, j;
  struct cell *c;
  for (i = 0; i < t->pagebuf.line_count; i++) {
    for (j = 0; j < t->pagebuf.col_count; j++) {
      c = &t->pagebuf.lines[i].cells[j];
      if (c->glyph) {
        putchar(c->glyph);
      } else {
        putchar(' ');
      }
    }
    putchar('\n');
  }
}

void Terminal_setAutoWrap(Terminal *t, int mode)
{
  t->modes.auto_wrap = mode;
}

void Terminal_scroll(Terminal *t, int lines)
{
  struct line *scroll_top;
  struct line *scroll_keep;
  struct line *scroll_clear;
  int direction, total_lines, keep_lines, clear_lines;
  struct bounds b;
  size_t scroll_size, clear_size;

  if (lines < 0) {
    lines = -lines;
    direction = -1;
  } else {
    direction = 1;
  }

  b = Terminal_cursorVBounds(t, 1);
  total_lines = b.max + 1 - b.min;
  keep_lines = total_lines - lines;
  if (keep_lines < 0) {
    keep_lines = 0;
  }
  clear_lines = total_lines - keep_lines;
  scroll_size = keep_lines * (sizeof (struct line));
  clear_size = clear_lines * (sizeof (struct line));

  if (direction > 0) {
    scroll_top = &t->pagebuf.lines[b.min];
    scroll_clear = &t->pagebuf.lines[b.min + keep_lines];

    if (keep_lines) {
      scroll_keep = &t->pagebuf.lines[b.min + lines];
      memmove(scroll_top, scroll_keep, scroll_size);
    }
  } else {
    scroll_top = &t->pagebuf.lines[b.min + clear_lines];
    scroll_clear = &t->pagebuf.lines[b.min];

    if (keep_lines) {
      scroll_keep = &t->pagebuf.lines[b.min];
      memmove(scroll_top, scroll_keep, scroll_size);
    }
  }
  memset(scroll_clear, 0, clear_size);
}

void Terminal_cursorRel(Terminal *t, int direction, int count, int scroll)
{
  int *axis;
  struct bounds b;
  int move, result;
  int obey_margins = 1;

  switch (direction) {
  case DIR_UP:
    axis = &t->cursor.line;
    move = -count;
    b = Terminal_cursorVBounds(t, obey_margins);
    break;
  case DIR_DOWN:
    axis = &t->cursor.line;
    move = count;
    b = Terminal_cursorVBounds(t, obey_margins);
    break;
  case DIR_FORWARD:
    axis = &t->cursor.col;
    move = count;
    b = Terminal_cursorHBounds(t);
    break;
  case DIR_BACK:
    axis = &t->cursor.col;
    move = -count;
    b = Terminal_cursorHBounds(t);
    break;
  default:
    return;
  }

  result = bounded_move(axis, move, b);

  if (result != move && scroll) {
    if (direction == DIR_UP || direction == DIR_DOWN) {
      Terminal_scroll(t, move - result);
    }
  }
}

void Terminal_cursorAbsH(Terminal *t, int column)
{
  bounded_set(&t->cursor.col, column, Terminal_cursorHBounds(t));
}

void Terminal_cursorAbsV(Terminal *t, int line)
{
  int obey_margins = 0;
  bounded_set(&t->cursor.line, line, Terminal_cursorVBounds(t, obey_margins));
}

void Terminal_cursorAbs(Terminal *t, int column, int line)
{
  Terminal_cursorAbsH(t, column);
  Terminal_cursorAbsV(t, line);
}

void Terminal_carriageReturn(Terminal *t)
{
  Terminal_cursorAbsH(t, 0);
}

void Terminal_lineFeed(Terminal *t)
{
  Terminal_cursorRel(t, DIR_DOWN, 1, 1);
}

void Terminal_newLine(Terminal *t)
{
  Terminal_carriageReturn(t);
  Terminal_lineFeed(t);
}

void Terminal_backspace(Terminal *t)
{
  Terminal_cursorRel(t, DIR_BACK, 1, 0);
}

void Terminal_horizontalTab(Terminal *t, int count)
{
  int i, target_col;
  struct bounds b = Terminal_cursorHBounds(t);

  target_col = -1;
  for (i = t->cursor.col+1; i < b.max; i++) {
    if (t->tabstops[i] == 1) {
      if (count == 1) {
        target_col = i;
        break;
      } else {
        count--;
      }
    }
  }

  if (target_col == -1) {
    t->cursor.col = b.max + 1;
  } else {
    Terminal_cursorAbsH(t, target_col);
  }
}

void Terminal_backTab(Terminal *t, int count)
{
  int i;
  for (i = t->cursor.col-1; i >= 0; i--) {
    if (t->tabstops[i] == 1) {
      if (count == 1) {
        t->cursor.col = i;
        return;
      } else {
        count--;
      }
    }
  }
  t->cursor.col = 0;
}


void Terminal_insertGraphic(Terminal *t, unsigned char code, int count)
{
  struct line *l;
  int line, remain, from, to;

  from = t->cursor.col;
  line = t->pagebuf.col_count - from;
  if (count > line) count = line;
  remain = line - count;

  if (remain) {
    to = from + count;
    l = &t->pagebuf.lines[t->cursor.line];
    memmove(&l->cells[to], &l->cells[from], sizeof (struct cell) * remain);
  }

  while (count--) {
    l->cells[from].att = blank_char_att;
    l->cells[from++].glyph = code;
  }
}

void Terminal_putGraphic(Terminal *t, unsigned char code)
{
  int *col = &t->cursor.col;
  int *line = &t->cursor.line;

  /* Cursor pointing just past the end of line means we either need to wrap
     or move back to the last position of the line */

  if (*col == t->pagebuf.col_count) {
    if (t->modes.auto_wrap == 1) {
      Terminal_newLine(t);
    } else {
      *col -= 1;
    }
  }

  t->pagebuf.lines[*line].cells[*col].glyph = code;
  *col += 1;
}