/* Copyright (C) 2019  C. McEnroe <june@causal.agency>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <assert.h>
#include <err.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>
#include <wchar.h>

#include "term.h"

#define MIN(a, b) ((a) < (b) ? (a) : (b))
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define BOX(l, x, u) MIN(MAX((x), (l)), (u))

static void unhandled(const char *format, ...) {
	if (isatty(STDERR_FILENO)) return;
	va_list ap;
	va_start(ap, format);
	char buf[256];
	vsnprintf(buf, sizeof(buf), format, ap);
	warnx("unhandled %s", buf);
	va_end(ap);
}

static struct Cell *cell(struct Term *term, uint y, uint x) {
	assert(y < term->rows);
	assert(x < term->cols);
	return &term->cells[y * term->cols + x];
}

static void erase(struct Style style, struct Cell *a, struct Cell *b) {
	for (; a <= b; ++a) {
		a->style = style;
		a->ch = L' ';
	}
}

static void move(struct Cell *dst, struct Cell *src, uint len) {
	memmove(dst, src, sizeof(*dst) * len);
}

static void scrollUp(struct Term *term, uint top, uint n) {
	move(
		cell(term, top, 0),
		cell(term, top + n, 0),
		term->cols * (1 + term->scroll.bot - top - n)
	);
	erase(
		term->style,
		cell(term, 1 + term->scroll.bot - n, 0),
		cell(term, term->scroll.bot, term->cols - 1)
	);
}

static void scrollDown(struct Term *term, uint top, uint n) {
	move(
		cell(term, top + n, 0),
		cell(term, top, 0),
		term->cols * (1 + term->scroll.bot - top - n)
	);
	erase(
		term->style,
		cell(term, top, 0),
		cell(term, top + n - 1, term->cols - 1)
	);
}

typedef void Action(struct Term *, wchar_t);

#define ACTION(name) \
	static void name(struct Term *t, wchar_t _ch __attribute__((unused)))

enum {
	Def,
	Esc,
	G0,
	CSI,
	OSC,
	OSCEsc,
};

ACTION(nop)    { (void)t; }
ACTION(esc)    { t->state = Esc; }
ACTION(g0)     { t->state = G0; }
ACTION(osc)    { t->state = OSC; }
ACTION(oscEsc) { t->state = OSCEsc; }
ACTION(csi) {
	t->state = CSI;
	memset(&t->param, 0, sizeof(t->param));
}

static void csiParam(struct Term *t, wchar_t ch) {
	if (ch == L'?') {
		t->param.q = true;
	} else if (ch == L';') {
		t->param.n++;
		t->param.i++;
		t->param.i %= ParamCap;
	} else if (ch >= L'0' && ch <= L'9') {
		t->param.s[t->param.i] *= 10;
		t->param.s[t->param.i] += ch - L'0';
		if (!t->param.n) t->param.n++;
	} else {
		// FIXME: Allow other characters in CSI params.
		unhandled("CSI %lc", ch);
		return;
	}
	t->state = CSI;
}

static void escUnhandled(struct Term *t, wchar_t ch) {
	(void)t;
	unhandled("ESC %lc", ch);
}

#define Y t->y
#define X t->x
#define B (t->rows - 1)
#define R (t->cols - 1)
#define C(y, x) cell(t, y, x)
#define P(i, z) ((i) < t->param.n ? t->param.s[(i)] : (z))

ACTION(bs)  { if (X) X--; }
ACTION(ht)  { X = MIN(X - X % 8 + 8, R); }
ACTION(cr)  { X = 0; }
ACTION(cuu) { Y -= MIN(P(0, 1), Y); }
ACTION(cud) { Y  = MIN(Y + P(0, 1), B); }
ACTION(cuf) { X  = MIN(X + P(0, 1), R); }
ACTION(cub) { X -= MIN(P(0, 1), X); }
ACTION(cnl) { X = 0; cud(t, 0); }
ACTION(cpl) { X = 0; cuu(t, 0); }
ACTION(cha) { X = MIN(P(0, 1) - 1, R); }
ACTION(vpa) { Y = MIN(P(0, 1) - 1, B); }
ACTION(cup) {
	Y = MIN(P(0, 1) - 1, B);
	X = MIN(P(1, 1) - 1, R);
}
ACTION(decsc) {
	t->save.y = Y;
	t->save.x = X;
}
ACTION(decrc) {
	Y = t->save.y;
	X = t->save.x;
}

ACTION(ed) {
	erase(
		t->style,
		(P(0, 0) == 0 ? C(Y, X) : C(0, 0)),
		(P(0, 0) == 1 ? C(Y, X) : C(B, R))
	);
}
ACTION(el) {
	erase(
		t->style,
		(P(0, 0) == 0 ? C(Y, X) : C(Y, 0)),
		(P(0, 0) == 1 ? C(Y, X) : C(Y, R))
	);
}
ACTION(ech) {
	erase(t->style, C(Y, X), C(Y, MIN(X + P(0, 1) - 1, R)));
}

ACTION(dch) {
	uint n = BOX(1, P(0, 1), t->cols - X);
	move(C(Y, X), C(Y, X + n), t->cols - X - n);
	erase(t->style, C(Y, t->cols - n), C(Y, R));
}
ACTION(ich) {
	uint n = BOX(1, P(0, 1), t->cols - X);
	move(C(Y, X + n), C(Y, X), t->cols - X - n);
	erase(t->style, C(Y, X), C(Y, X + n - 1));
}

ACTION(dl) { scrollUp(t, Y, BOX(1, P(0, 1), t->scroll.bot - Y)); }
ACTION(il) { scrollDown(t, Y, BOX(1, P(0, 1), t->scroll.bot - Y)); }

ACTION(nl) {
	if (Y == t->scroll.bot) {
		scrollUp(t, t->scroll.top, 1);
	} else {
		Y = MIN(Y + 1, B);
	}
}
ACTION(ri) {
	if (Y == t->scroll.top) {
		scrollDown(t, t->scroll.top, 1);
	} else {
		if (Y) Y--;
	}
}
ACTION(su) {
	scrollUp(t, t->scroll.top, BOX(1, P(0, 1), t->scroll.bot - t->scroll.top));
}
ACTION(sd) {
	scrollDown(t, t->scroll.top, BOX(1, P(0, 1), t->scroll.bot - t->scroll.top));
}
ACTION(decstbm) {
	t->scroll.bot = MIN(P(1, t->rows) - 1, B);
	t->scroll.top = MIN(P(0, 1) - 1, t->scroll.bot);
}

enum {
	IRM = 4,
	DECAWM = 7,
	DECTCEM = 25,
};

static void mode(struct Term *t, wchar_t ch) {
	enum Mode mode = 0;
	for (uint i = 0; i < t->param.n; ++i) {
		if (t->param.q) {
			switch (t->param.s[i]) {
				break; case 1: // DECCKM
				break; case DECAWM: mode |= Wrap;
				break; case 12: // "Start Blinking Cursor"
				break; case DECTCEM: mode |= Cursor;
				break; default: {
					if (t->param.s[i] < 1000) {
						unhandled("DECSET/DECRST %u", t->param.s[i]);
					}
				}
			}
		} else {
			switch (t->param.s[i]) {
				break; case IRM: mode |= Insert;
				break; default: unhandled("SM/RM %u", t->param.s[i]);
			}
		}
	}
	t->mode = (ch == L'h' ? t->mode | mode : t->mode & ~mode);
}

enum {
	Reset,
	SetBold,
	SetDim,
	SetItalic,
	SetUnderline,
	SetBlink,
	SetReverse = 7,

	UnsetBoldDim = 22,
	UnsetItalic,
	UnsetUnderline,
	UnsetBlink,
	UnsetReverse = 27,

	SetFg0 = 30,
	SetFg7 = 37,
	SetFg,
	ResetFg,
	SetBg0 = 40,
	SetBg7 = 47,
	SetBg,
	ResetBg,

	SetFg8 = 90,
	SetFgF = 97,
	SetBg8 = 100,
	SetBgF = 107,

	Color256 = 5,
};

static const struct Style Default = { .bg = -1, .fg = -1 };

ACTION(sgr) {
	uint n = t->param.i + 1;
	for (uint i = 0; i < n; ++i) {
		switch (t->param.s[i]) {
			break; case Reset: t->style = Default;
			
			break; case SetBold: t->style.attr &= ~Dim; t->style.attr |= Bold;
			break; case SetDim:  t->style.attr &= ~Bold; t->style.attr |= Dim;
			break; case SetItalic:    t->style.attr |= Italic;
			break; case SetUnderline: t->style.attr |= Underline;
			break; case SetBlink:     t->style.attr |= Blink;
			break; case SetReverse:   t->style.attr |= Reverse;

			break; case UnsetBoldDim:   t->style.attr &= ~(Bold | Dim);
			break; case UnsetItalic:    t->style.attr &= ~Italic;
			break; case UnsetUnderline: t->style.attr &= ~Underline;
			break; case UnsetBlink:     t->style.attr &= ~Blink;
			break; case UnsetReverse:   t->style.attr &= ~Reverse;

			break; case SetFg: {
				if (++i < n && t->param.s[i] == Color256) {
					if (++i < n) t->style.fg = t->param.s[i];
				}
			}
			break; case SetBg: {
				if (++i < n && t->param.s[i] == Color256) {
					if (++i < n) t->style.bg = t->param.s[i];
				}
			}

			break; case ResetFg: t->style.fg = Default.fg;
			break; case ResetBg: t->style.bg = Default.bg;

			break; default: {
				if (t->param.s[i] >= SetFg0 && t->param.s[i] <= SetFg7) {
					t->style.fg = t->param.s[i] - SetFg0;
				} else if (t->param.s[i] >= SetBg0 && t->param.s[i] <= SetBg7) {
					t->style.bg = t->param.s[i] - SetBg0;
				} else if (t->param.s[i] >= SetFg8 && t->param.s[i] <= SetFgF) {
					t->style.fg = 8 + t->param.s[i] - SetFg8;
				} else if (t->param.s[i] >= SetBg8 && t->param.s[i] <= SetBgF) {
					t->style.bg = 8 + t->param.s[i] - SetBg8;
				}
			}
		}
	}
}

static void add(struct Term *t, wchar_t ch) {
	int width = wcwidth(ch);
	if (width < 0) {
		unhandled("\\u%02X", ch);
		return;
	}
	if (X + width > t->cols) {
		unhandled("'%lc' too wide", ch);
		return;
	}

	if (t->mode & Insert) {
		move(C(Y, X + width), C(Y, X), t->cols - X - width);
	}

	C(Y, X)->style = t->style;
	C(Y, X)->ch = ch;
	for (int i = 1; i < width; ++i) {
		C(Y, X + i)->style = t->style;
		C(Y, X + i)->ch = L'\0';
	}

	if (t->mode & Wrap && X + width >= t->cols) {
		cr(t, 0);
		nl(t, 0);
	} else {
		X = MIN(X + width, R);
	}
}

#define S(s) break; case (s): switch (ch)
#define A(c, a) break; case (c): (a)(term, ch)
#define D(a) break; default: (a)(term, ch)
void termUpdate(struct Term *term, wchar_t ch) {
	uint state = term->state;
	term->state = Def;
	switch (state) {
		default: abort();

		S(Def) {
			A(BEL, nop);
			A(BS,  bs);
			A(HT,  ht);
			A(NL,  nl);
			A(CR,  cr);
			A(ESC, esc);
			D(add);
		}

		S(Esc) {
			A('(', g0);
			A('7', decsc);
			A('8', decrc);
			A('=', nop);
			A('>', nop);
			A('M', ri);
			A('[', csi);
			A(']', osc);
			D(escUnhandled);
		}
		S(G0) {
			D(nop);
		}

		S(CSI) {
			A('@', ich);
			A('A', cuu);
			A('B', cud);
			A('C', cuf);
			A('D', cub);
			A('E', cnl);
			A('F', cpl);
			A('G', cha);
			A('H', cup);
			A('J', ed);
			A('K', el);
			A('L', il);
			A('M', dl);
			A('P', dch);
			A('S', su);
			A('T', sd);
			A('X', ech);
			A('d', vpa);
			A('h', mode);
			A('l', mode);
			A('m', sgr);
			A('r', decstbm);
			A('t', nop);
			D(csiParam);
		}

		S(OSC) {
			A(BEL, nop);
			A(ESC, oscEsc);
			D(osc);
		}
		S(OSCEsc) {
			A('\\', nop);
			D(osc);
		}
	}
}

struct Term *termAlloc(uint rows, uint cols) {
	size_t size = sizeof(struct Term) + sizeof(struct Cell) * rows * cols;
	struct Term *term = malloc(size);
	if (!term) err(EX_OSERR, "malloc");

	memset(term, 0, sizeof(*term));
	term->rows = rows;
	term->cols = cols;
	term->mode = Wrap | Cursor;
	term->scroll.bot = rows - 1;
	term->style = Default;
	erase(Default, cell(term, 0, 0), cell(term, rows - 1, cols - 1));

	return term;
}

static int
styleDiff(FILE *file, const struct Style *prev, const struct Style *next) {
	if (!memcmp(prev, next, sizeof(*prev))) return 0;
	if (!memcmp(next, &Default, sizeof(*next))) return fprintf(file, "\33[m");

	uint p[ParamCap];
	uint n = 0;

	enum Attr diff = prev->attr ^ next->attr;
	if (diff & (Bold | Dim)) {
		p[n++] = (
			next->attr & Bold ? SetBold
			: next->attr & Dim ? SetDim
			: UnsetBoldDim
		);
	}
	if (diff & Italic) {
		p[n++] = (next->attr & Italic ? SetItalic : UnsetItalic);
	}
	if (diff & Underline) {
		p[n++] = (next->attr & Underline ? SetUnderline : UnsetUnderline);
	}
	if (diff & Blink) {
		p[n++] = (next->attr & Blink ? SetBlink : UnsetBlink);
	}
	if (diff & Reverse) {
		p[n++] = (next->attr & Reverse ? SetReverse : UnsetReverse);
	}

	if (next->bg != prev->bg) {
		if (next->bg == -1) {
			p[n++] = ResetBg;
		} else if (next->bg < 8) {
			p[n++] = SetBg0 + next->bg;
		} else if (next->bg < 16) {
			p[n++] = SetBg8 + next->bg - 8;
		} else {
			p[n++] = SetBg;
			p[n++] = Color256;
			p[n++] = next->bg;
		}
	}
	if (next->fg != prev->fg) {
		if (next->fg == -1) {
			p[n++] = ResetFg;
		} else if (next->fg < 8) {
			p[n++] = SetFg0 + next->fg;
		} else if (next->fg < 16) {
			p[n++] = SetFg8 + next->fg - 8;
		} else {
			p[n++] = SetFg;
			p[n++] = Color256;
			p[n++] = next->fg;
		}
	}

	if (0 > fprintf(file, "\33[%u", p[0])) return -1;
	for (uint i = 1; i < n; ++i) {
		if (0 > fprintf(file, ";%u", p[i])) return -1;
	}
	return fprintf(file, "m");
}

int termSnapshot(struct Term *term, int _fd) {
	int fd = dup(_fd);
	if (fd < 0) return -1;

	FILE *file = fdopen(fd, "w");
	if (!file) return -1;

	int n = fprintf(file, "\33[%dl\33[?%dl\33[r\33[H\33[m", IRM, DECAWM);
	if (n < 0) goto fail;

	struct Style prev = Default;
	for (uint y = 0; y < term->rows; ++y) {
		if (y && 0 > fprintf(file, "\r\n")) goto fail;
		for (uint x = 0; x < term->cols; ++x) {
			struct Cell *c = cell(term, y, x);
			if (!c->ch) continue;
			if (0 > styleDiff(file, &prev, &c->style)) goto fail;
			if (0 > fprintf(file, "%lc", c->ch)) goto fail;
			prev = c->style;
		}
	}
	if (0 > styleDiff(file, &prev, &term->style)) goto fail;

	n = fprintf(
		file,
		"\33[%d%c"
		"\33[?%d%c"
		"\33[?%d%c"
		"\33[%u;%ur"
		"\33[%u;%uH",
		IRM, (term->mode & Insert ? 'h' : 'l'),
		DECAWM, (term->mode & Wrap ? 'h' : 'l'),
		DECTCEM, (term->mode & Cursor ? 'h' : 'l'),
		1 + term->scroll.top, 1 + term->scroll.bot,
		1 + term->y, 1 + term->x
	);
	if (n < 0) goto fail;

	return fclose(file);

fail:
	fclose(file);
	return -1;
}

#ifdef TERM_MAIN
#include <locale.h>

int main(void) {
	setlocale(LC_CTYPE, "");
	struct Term *term = termAlloc(24, 80);
	wint_t ch;
	while (WEOF != (ch = getwchar())) {
		termUpdate(term, ch);
	}
}

#endif