/* 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 <err.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>
#include <wchar.h>

#include "stream.h"

#define MIN(a, b) ((a) < (b) ? (a) : (b))

enum {
	NUL, SOH, STX, ETX, EOT, ENQ, ACK, BEL,
	BS, HT, NL, VT, NP, CR, SO, SI,
	DLE, DC1, DC2, DC3, DC4, NAK, SYN, ETB,
	CAN, EM, SUB, ESC, FS, GS, RS, US,
	DEL = 0x7F,
};

struct Style {
	bool bold, italic, underline, reverse;
	int bg, fg;
};
static const struct Style Default = { .bg = -1, .fg = -1 };

struct Cell {
	struct Style style;
	wchar_t ch;
};

static uint rows, cols;
static uint y, x;

static bool insert;
static struct {
	uint top, bot;
} scroll;

static struct Style style;
static struct Cell *cells;

static struct Cell *cell(uint y, uint x) {
	return &cells[y * cols + x];
}

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

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

static char updateNUL(wchar_t ch) {
	switch (ch) {
		break; case ESC: return ESC;

		break; case BS: if (x) x--;
		break; case CR: x = 0;

		break; case NL: {
			if (y == scroll.bot) {
				move(
					cell(scroll.top, 0), cell(scroll.top + 1, 0),
					cols * (scroll.bot - scroll.top)
				);
				clear(cell(scroll.bot, 0), cell(scroll.bot, cols - 1));
			} else {
				y = MIN(y + 1, rows - 1);
			}
		}

		break; default: {
			// FIXME: Nowhere for these warnings to go.
			if (ch < ' ') {
				warnx("unhandled \\x%02X", ch);
				return NUL;
			}

			int width = wcwidth(ch);
			if (width < 0) {
				warnx("unhandled \\u%X", ch);
				return NUL;
			}
			if (x + width > cols) {
				warnx("cannot fit '%lc'", ch);
				return NUL;
			}

			if (insert) {
				move(cell(y, x + width), cell(y, x), cols - x - width);
			}
			cell(y, x)->style = style;
			cell(y, x)->ch = ch;

			for (int i = 1; i < width; ++i) {
				cell(y, x + i)->style = style;
				cell(y, x + i)->ch = '\0';
			}
			x = MIN(x + width, cols - 1);
		}
	}
	return NUL;
}

enum {
	CSI = '[',
	OSC = ']',
	ST  = '\\',
};

static char updateESC(wchar_t ch) {
	static bool discard;
	if (discard) {
		discard = false;
		return NUL;
	}
	switch (ch) {
		case '(': discard = true; return ESC;
		case '=': return NUL;
		case '>': return NUL;
		case CSI: return CSI;
		case OSC: return OSC;
		// FIXME: Nowhere for this warning to go.
		default: warnx("unhandled ESC %lc", ch); return NUL;
	}
}

enum {
	Reset,
	Bold,
	Italic = 3,
	Underline,
	Reverse = 7,
	NotBold = 22,
	NotItalic,
	NotUnderline,
	NotReverse,
	Fg0 = 30,
	Fg7 = 37,
	Fg,
	FgDefault,
	Bg0,
	Bg7 = 47,
	Bg,
	BgDefault,
	Fg8 = 90,
	Fg15 = 97,
	Bg8 = 100,
	Bg15 = 107,
	Color256 = 5,
};

static void updateSGR(uint ps[], uint n) {
	for (uint i = 0; i < n; ++i) {
		switch (ps[i]) {
			break; case Reset: style = Default;

			break; case Bold:      style.bold = true;
			break; case Italic:    style.italic = true;
			break; case Underline: style.underline = true;
			break; case Reverse:   style.reverse = true;

			break; case NotBold:      style.bold = false;
			break; case NotItalic:    style.italic = false;
			break; case NotUnderline: style.underline = false;
			break; case NotReverse:   style.reverse = false;

			break; case Fg: {
				if (++i < n && ps[i] == Color256) {
					if (++i < n) style.fg = ps[i];
				}
			}
			break; case Bg: {
				if (++i < n && ps[i] == Color256) {
					if (++i < n) style.bg = ps[i];
				}
			}

			break; case FgDefault: style.fg = -1;
			break; case BgDefault: style.bg = -1;

			break; default: {
				if (ps[i] >= Fg0 && ps[i] <= Fg7) {
					style.fg = ps[i] - Fg0;
				} else if (ps[i] >= Bg0 && ps[i] <= Bg7) {
					style.bg = ps[i] - Bg0;
				} else if (ps[i] >= Fg8 && ps[i] <= Fg15) {
					style.fg = 8 + ps[i] - Fg8;
				} else if (ps[i] >= Bg8 && ps[i] <= Bg15) {
					style.bg = 8 + ps[i] - Bg8;
				}
			}
		}
	}
}

// SGR toggling all attributes and setting both colors in 256 palette.
enum { PSCap = 4 + 2 * 3 };

enum {
	DEC = '?',
	CUU = 'A',
	CUD,
	CUF,
	CUB,
	CNL,
	CPL,
	CHA,
	CUP,
	ED  = 'J',
	EL,
	DL  = 'M',
	DCH = 'P',
	VPA = 'd',
	SM  = 'h',
	RM  = 'l',
	SGR,
	DECSTBM = 'r',
};

enum {
	Insert = 4,
};

static char updateCSI(wchar_t ch) {
	static bool dec;
	if (ch == DEC) {
		dec = true;
		return CSI;
	}

	static uint n, p, ps[PSCap];
	if (ch == ';') {
		n++;
		p++;
		ps[p %= PSCap] = 0;
		return CSI;
	}
	if (ch >= '0' && ch <= '9') {
		ps[p] *= 10;
		ps[p] += ch - '0';
		if (!n) n++;
		return CSI;
	}

	switch (ch) {
		break; case CUU: y -= MIN((n ? ps[0] : 1), y);
		break; case CUD: y  = MIN(y + (n ? ps[0] : 1), rows - 1);
		break; case CUF: x  = MIN(x + (n ? ps[0] : 1), cols - 1);
		break; case CUB: x -= MIN((n ? ps[0] : 1), x);
		break; case CNL: y  = MIN(y + (n ? ps[0] : 1), rows - 1); x = 0;
		break; case CPL: y -= MIN((n ? ps[0] : 1), y); x = 0;
		break; case CHA: x  = MIN((n ? ps[0] - 1 : 0), cols - 1);
		break; case VPA: y  = MIN((n ? ps[0] - 1 : 0), rows - 1);
		break; case CUP: {
			y = MIN((n > 0 ? ps[0] - 1 : 0), rows - 1);
			x = MIN((n > 1 ? ps[1] - 1 : 0), cols - 1);
		}

		break; case ED: {
			struct Cell *a = cell(0, 0);
			struct Cell *b = cell(rows - 1, cols - 1);
			if (ps[0] == 0) a = cell(y, x);
			if (ps[0] == 1) b = cell(y, x);
			clear(a, b);
		}
		break; case EL: {
			struct Cell *a = cell(y, 0);
			struct Cell *b = cell(y, cols - 1);
			if (ps[0] == 0) a = cell(y, x);
			if (ps[0] == 1) b = cell(y, x);
			clear(a, b);
		}

		break; case DL: {
			uint i = MIN((n ? ps[0] : 1), rows - y);
			move(cell(y, 0), cell(y + i, 0), cols * (rows - y - i));
			clear(cell(rows - i, 0), cell(rows - 1, cols - 1));
		}
		break; case DCH: {
			uint i = MIN((n ? ps[0] : 1), cols - x);
			move(cell(y, x), cell(y, x + i), cols - x - i);
			clear(cell(y, cols - i), cell(y, cols - 1));
		}

		// FIXME: Nowhere for these warnings to go.
		break; case SM: {
			if (dec) break;
			switch (ps[0]) {
				break; case Insert: insert = true;
				break; default: warnx("unhandled SM %u", ps[0]);
			}
		}
		break; case RM: {
			if (dec) break;
			switch (ps[0]) {
				break; case Insert: insert = false;
				break; default: warnx("unhandled RM %u", ps[0]);
			}
		}

		break; case SGR: updateSGR(ps, p + 1);

		break; case DECSTBM: {
			scroll.top = (n > 0 ? ps[0] - 1 : 0);
			scroll.bot = (n > 1 ? ps[1] - 1 : rows - 1);
		}

		break; case 't': // ignore
		// FIXME: Nowhere for this warning to go.
		break; default: warnx("unhandled CSI %lc", ch);
	}

	dec = false;
	ps[n = p = 0] = 0;
	return NUL;
}

static char updateOSC(wchar_t ch) {
	static bool esc;
	switch (ch) {
		break; case BEL: return NUL;
		break; case ESC: esc = true;
		break; case ST: {
			if (!esc) break;
			esc = false;
			return NUL;
		}
	}
	return OSC;
}

void termUpdate(wchar_t ch) {
	static char seq;
	switch (seq) {
		break; case NUL: seq = updateNUL(ch);
		break; case ESC: seq = updateESC(ch);
		break; case CSI: seq = updateCSI(ch);
		break; case OSC: seq = updateOSC(ch);
	}
}

void termInit(uint _rows, uint _cols) {
	rows = _rows;
	cols = _cols;
	cells = calloc(rows * cols, sizeof(*cells));
	if (!cells) err(EX_OSERR, "calloc");

	style = Default;
	clear(cell(0, 0), cell(rows - 1, cols - 1));
	scroll.bot = rows - 1;
}

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, "%c%c%c", ESC, CSI, SGR);
	}

	uint ps[PSCap];
	uint n = 0;
	if (next->bold != prev->bold) {
		ps[n++] = (next->bold ? Bold : NotBold);
	}
	if (next->italic != prev->italic) {
		ps[n++] = (next->italic ? Italic : NotItalic);
	}
	if (next->underline != prev->underline) {
		ps[n++] = (next->underline ? Underline : NotUnderline);
	}
	if (next->reverse != prev->reverse) {
		ps[n++] = (next->reverse ? Reverse : NotReverse);
	}
	if (next->bg != prev->bg) {
		if (next->bg == -1) {
			ps[n++] = BgDefault;
		} else if (next->bg < 8) {
			ps[n++] = Bg0 + next->bg;
		} else if (next->bg < 16) {
			ps[n++] = Bg8 + next->bg - 8;
		} else {
			ps[n++] = Bg;
			ps[n++] = Color256;
			ps[n++] = next->bg;
		}
	}
	if (next->fg != prev->fg) {
		if (next->fg == -1) {
			ps[n++] = FgDefault;
		} else if (next->fg < 8) {
			ps[n++] = Fg0 + next->fg;
		} else if (next->fg < 16) {
			ps[n++] = Fg8 + next->fg - 8;
		} else {
			ps[n++] = Fg;
			ps[n++] = Color256;
			ps[n++] = next->fg;
		}
	}

	if (0 > fprintf(file, "%c%c%u", ESC, CSI, ps[0])) return -1;
	for (uint i = 1; i < n; ++i) {
		if (0 > fprintf(file, ";%u", ps[i])) return -1;
	}
	return fprintf(file, "%c", SGR);
}

int termSnapshot(int _fd) {
	int fd = dup(_fd);
	if (fd < 0) return -1;

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

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

	int n = fprintf(
		file,
		"%c%c%d%c"
		"%c%c%u;%u%c"
		"%c%c%u;%u%c",
		ESC, CSI, Insert, (insert ? SM : RM),
		ESC, CSI, scroll.top, scroll.bot, DECSTBM,
		ESC, CSI, y, x, CUP
	);
	if (n < 0) goto fail;

	return fclose(file);

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