/*
 * ansi - show ANSI art in a modern terminal, or turn it into plain text.
 *
 * An .ans file is CP437 text with ANSI escape codes, usually laid out for an
 * 80-column terminal that wraps it. ansi draws it into a grid the way a BBS
 * terminal would (cursor moves, wrapping, iCE colours, the SAUCE record), then
 * writes the grid out as UTF-8: in colour, as plain characters, or in
 * monochrome with coloured areas redrawn as shading.
 */
#define _POSIX_C_SOURCE 200809L

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

#define VERSION "1.0.0"
#define MAX_WIDTH 1000
#define MAX_CELLS (1u << 24)   /* about 80 MB of grid; art past it is dropped */

/* CP437 as UTF-8. 0x01-0x1F are the glyphs art uses them for, not controls. */
static const char *const cp437[256] = {
    " ", "☺", "☻", "♥", "♦", "♣", "♠", "•",
    "◘", "○", "◙", "♂", "♀", "♪", "♫", "☼",
    "►", "◄", "↕", "‼", "¶", "§", "▬", "↨",
    "↑", "↓", "→", "←", "∟", "↔", "▲", "▼",
    " ", "!", "\"", "#", "$", "%", "&", "'",
    "(", ")", "*", "+", ",", "-", ".", "/",
    "0", "1", "2", "3", "4", "5", "6", "7",
    "8", "9", ":", ";", "<", "=", ">", "\?",
    "@", "A", "B", "C", "D", "E", "F", "G",
    "H", "I", "J", "K", "L", "M", "N", "O",
    "P", "Q", "R", "S", "T", "U", "V", "W",
    "X", "Y", "Z", "[", "\\", "]", "^", "_",
    "`", "a", "b", "c", "d", "e", "f", "g",
    "h", "i", "j", "k", "l", "m", "n", "o",
    "p", "q", "r", "s", "t", "u", "v", "w",
    "x", "y", "z", "{", "|", "}", "~", "⌂",
    "Ç", "ü", "é", "â", "ä", "à", "å", "ç",
    "ê", "ë", "è", "ï", "î", "ì", "Ä", "Å",
    "É", "æ", "Æ", "ô", "ö", "ò", "û", "ù",
    "ÿ", "Ö", "Ü", "¢", "£", "¥", "₧", "ƒ",
    "á", "í", "ó", "ú", "ñ", "Ñ", "ª", "º",
    "¿", "⌐", "¬", "½", "¼", "¡", "«", "»",
    "░", "▒", "▓", "│", "┤", "╡", "╢", "╖",
    "╕", "╣", "║", "╗", "╝", "╜", "╛", "┐",
    "└", "┴", "┬", "├", "─", "┼", "╞", "╟",
    "╚", "╔", "╩", "╦", "╠", "═", "╬", "╧",
    "╨", "╤", "╥", "╙", "╘", "╒", "╓", "╫",
    "╪", "┘", "┌", "█", "▄", "▌", "▐", "▀",
    "α", "ß", "Γ", "π", "Σ", "σ", "µ", "τ",
    "Φ", "Θ", "Ω", "δ", "∞", "φ", "ε", "∩",
    "≡", "±", "≥", "≤", "⌠", "⌡", "÷", "≈",
    "°", "∙", "·", "√", "ⁿ", "²", "■", " ",
};

/* How bright each of the 16 CGA colours looks (CIE L*, 0-100). */
static const double lightness[16] = {
    0.0000, 35.0952, 60.5599, 45.6931, 19.6482, 40.3255, 63.0540, 69.6102,
    36.1459, 60.2599, 88.9731, 97.4042, 46.5096, 65.7308, 91.9852, 100.0000
};

enum mode { COLOUR, PLAIN, MONO };

typedef struct {
    unsigned char ch;           /* CP437 byte; 0 is stored as a space */
    unsigned char fg, bg;       /* 0-7 */
    unsigned char bold, blink;  /* blink is iCE: the bright background */
} cell;

typedef struct {
    char title[36], author[21], group[21], date[9];
    unsigned width, height, comments, flags;
    unsigned char datatype, filetype;
    int present;
} sauce;

typedef struct {
    cell *cells;
    size_t rows, cap;
    unsigned width;
} grid;

static const char *progname = "ansi";

static void *xrealloc(void *p, size_t n)
{
    p = realloc(p, n);
    if (!p) {
        fprintf(stderr, "%s: out of memory\n", progname);
        exit(2);
    }
    return p;
}

static unsigned char *slurp(const char *path, size_t *len)
{
    FILE *f = strcmp(path, "-") ? fopen(path, "rb") : stdin;
    if (!f) {
        fprintf(stderr, "%s: %s: %s\n", progname, path, strerror(errno));
        return NULL;
    }
    size_t cap = 65536, n = 0;
    unsigned char *buf = xrealloc(NULL, cap);
    for (;;) {
        size_t got = fread(buf + n, 1, cap - n, f);
        n += got;
        if (n < cap)
            break;
        buf = xrealloc(buf, cap *= 2);
    }
    if (ferror(f)) {
        fprintf(stderr, "%s: %s: read error\n", progname, path);
        free(buf);
        buf = NULL;
    }
    if (f != stdin)
        fclose(f);
    *len = n;
    return buf;
}

static void field(char *dst, const unsigned char *src, size_t n)
{
    memcpy(dst, src, n);
    dst[n] = '\0';
    for (size_t i = n; i > 0 && (dst[i - 1] == ' ' || dst[i - 1] == '\0'); i--)
        dst[i - 1] = '\0';
}

static unsigned u16(const unsigned char *p) { return p[0] | p[1] << 8; }

/* Read the SAUCE record and shorten len to the art itself. */
static void read_sauce(const unsigned char *data, size_t *len, sauce *s)
{
    memset(s, 0, sizeof *s);
    s->width = 80;
    if (*len >= 128 && !memcmp(data + *len - 128, "SAUCE00", 7)) {
        const unsigned char *r = data + *len - 128;
        s->present = 1;
        field(s->title, r + 7, 35);
        field(s->author, r + 42, 20);
        field(s->group, r + 62, 20);
        field(s->date, r + 82, 8);
        s->datatype = r[94];
        s->filetype = r[95];
        s->comments = r[104];
        s->flags = r[105];
        s->height = u16(r + 98);
        if (s->datatype == 1 && s->filetype <= 1 && u16(r + 96) && u16(r + 96) <= MAX_WIDTH)
            s->width = u16(r + 96);
        size_t trailer = 128 + (s->comments ? 5 + 64 * s->comments : 0);
        *len = *len > trailer ? *len - trailer : 0;
    }
    const unsigned char *eof = memchr(data, 0x1A, *len);
    if (eof)
        *len = eof - data;
}

/* The cell at x, y, growing the grid to reach it; NULL past MAX_CELLS. */
static cell *at(grid *g, unsigned x, size_t y)
{
    if (y >= MAX_CELLS / g->width)
        return NULL;
    if (y >= g->rows) {
        size_t want = y + 1;
        if (want > g->cap) {
            g->cap = want * 2;
            g->cells = xrealloc(g->cells, g->cap * g->width * sizeof(cell));
        }
        for (size_t r = g->rows; r < want; r++)
            for (unsigned c = 0; c < g->width; c++)
                g->cells[r * g->width + c] = (cell){' ', 7, 0, 0, 0};
        g->rows = want;
    }
    return &g->cells[y * g->width + x];
}

/* Lay the art out in a grid, the way an ANSI-BBS terminal of the given width would. */
static void render(grid *g, const unsigned char *d, size_t n)
{
    unsigned x = 0, sx = 0, w = g->width;
    size_t y = 0, sy = 0;
    unsigned char fg = 7, bg = 0, bold = 0, blink = 0;

    for (size_t i = 0; i < n;) {
        unsigned char b = d[i];
        if (b == 0x1B && i + 1 < n && d[i + 1] == '[') {
            size_t j = i + 2, ps = j;
            while (j < n && d[j] >= 0x30 && d[j] <= 0x3F)
                j++;
            size_t pe = j;
            while (j < n && d[j] >= 0x20 && d[j] <= 0x2F)
                j++;
            if (j >= n || d[j] < 0x40 || d[j] > 0x7E)
                break;                  /* a broken sequence ends the art */
            unsigned char cmd = d[j];
            i = j + 1;
            if (pe > ps && d[ps] == '?')
                continue;               /* private modes, such as line wrap */
            unsigned p[16], np = 0;
            if (pe > ps) {
                p[0] = 0;
                np = 1;
                for (size_t k = ps; k < pe; k++) {
                    if (d[k] == ';') {
                        if (np < 16)
                            p[np++] = 0;
                    } else if (d[k] >= '0' && d[k] <= '9' && np <= 16) {
                        p[np - 1] = p[np - 1] * 10 + (d[k] - '0');
                    }
                }
            }
            unsigned arg = np && p[0] ? p[0] : 1;
            switch (cmd) {
            case 'm':
                if (!np)
                    p[np++] = 0;
                for (unsigned k = 0; k < np; k++) {
                    unsigned v = p[k];
                    if (v == 0)
                        fg = 7, bg = 0, bold = 0, blink = 0;
                    else if (v == 1)
                        bold = 1;
                    else if (v == 5)
                        blink = 1;
                    else if (v == 22)
                        bold = 0;
                    else if (v == 25)
                        blink = 0;
                    else if (v >= 30 && v <= 37)
                        fg = v - 30;
                    else if (v == 39)
                        fg = 7;
                    else if (v >= 40 && v <= 47)
                        bg = v - 40;
                    else if (v == 49)
                        bg = 0;
                }
                break;
            case 'C': x = x + arg < w ? x + arg : w; break;
            case 'D': x = x > arg ? x - arg : 0; break;
            case 'A': y = y > arg ? y - arg : 0; break;
            case 'B': y += arg; break;
            case 'H':
            case 'f':
                y = (np && p[0] ? p[0] : 1) - 1;
                x = (np > 1 && p[1] ? p[1] : 1) - 1;
                if (x > w - 1)
                    x = w - 1;
                break;
            case 's': sx = x, sy = y; break;
            case 'u': x = sx, y = sy; break;
            case 'J':
                if (arg == 2)
                    g->rows = 0, x = 0, y = 0;
                break;
            }
            continue;
        }
        i++;
        if (b == '\r') {
            x = 0;
        } else if (b == '\n') {
            x = 0, y++;
        } else if (b == 0x1B) {
            /* a lone escape */
        } else {
            unsigned count = b == '\t' ? 8 - x % 8 : 1;
            unsigned char ch = b == '\t' || b == 0 ? ' ' : b;
            while (count--) {
                if (x >= w)
                    x = 0, y++;     /* wrap only when the next character arrives */
                cell *c = at(g, x, y);
                if (c)
                    *c = (cell){ch, fg, bg, bold, blink};
                x++;
            }
        }
    }
}

static int same(const cell *a, const cell *b)
{
    return a->fg == b->fg && a->bg == b->bg && a->bold == b->bold && a->blink == b->blink;
}

static int level(double l)
{
    return l < 15 ? 0 : l < 40 ? 1 : l < 60 ? 2 : l < 85 ? 3 : 4;
}

/* How much of a cell the foreground covers, top half and bottom half; -1 if not a block. */
static double cover(unsigned char ch, int half)
{
    switch (ch) {
    case ' ':  return 0;
    case 0xDB: return 1;                    /* full block */
    case 0xDF: return half ? 0 : 1;         /* upper half */
    case 0xDC: return half ? 1 : 0;         /* lower half */
    case 0xDD: case 0xDE: return .5;        /* left and right halves */
    case 0xB0: return .25;
    case 0xB1: return .5;
    case 0xB2: return .75;
    default:   return -1;
    }
}

/* One character standing in for a coloured cell: shading by brightness, half blocks for halves. */
static const char *mono(const cell *c)
{
    static const char *const shade[5] = {" ", "░", "▒", "▓", "█"};
    if (cover(c->ch, 0) < 0)
        return cp437[c->ch];
    double f = lightness[c->fg + 8 * c->bold], b = lightness[c->bg + 8 * c->blink];
    int top = level(cover(c->ch, 0) * f + (1 - cover(c->ch, 0)) * b);
    int bot = level(cover(c->ch, 1) * f + (1 - cover(c->ch, 1)) * b);
    if (top - bot >= 2)
        return "▀";
    if (bot - top >= 2)
        return "▄";
    return shade[top > bot ? top : bot];
}

static void emit(const grid *g, enum mode m, FILE *out)
{
    /* Lines are built first so that trailing blank ones can be dropped. */
    char **lines = xrealloc(NULL, (g->rows + 1) * sizeof *lines);
    size_t nlines = 0;
    for (size_t y = 0; y < g->rows; y++) {
        const cell *row = &g->cells[y * g->width];
        unsigned len = g->width;
        while (len && row[len - 1].ch == ' ' && !row[len - 1].bg && !row[len - 1].blink)
            len--;
        size_t cap = 64 + len * 24, n = 0;
        char *s = xrealloc(NULL, cap);
        const cell *last = NULL;
        for (unsigned x = 0; x < len; x++) {
            const cell *c = &row[x];
            const char *glyph = m == MONO ? mono(c) : cp437[c->ch];
            if (m == COLOUR) {
                int keep = last && (same(c, last) ||
                                    (c->ch == ' ' && c->bg == last->bg && c->blink == last->blink));
                if (!keep) {
                    n += sprintf(s + n, "\033[0;%s%d;%dm", c->bold ? "1;" : "",
                                 30 + c->fg, (c->blink ? 100 : 40) + c->bg);
                    last = c;
                }
            }
            size_t gl = strlen(glyph);
            memcpy(s + n, glyph, gl);
            n += gl;
        }
        if (m == COLOUR && len)
            n += sprintf(s + n, "\033[0m");
        else
            while (n && s[n - 1] == ' ')
                n--;
        s[n] = '\0';
        lines[nlines++] = s;
    }
    while (nlines && !*lines[nlines - 1])
        free(lines[--nlines]);
    for (size_t i = 0; i < nlines; i++) {
        fputs(lines[i], out);
        fputc('\n', out);
        free(lines[i]);
    }
    free(lines);
}

static void info(const char *path, const sauce *s, const grid *g, FILE *out)
{
    static const char *const types[] = {"ASCII", "ANSi", "ANSiMation"};
    fprintf(out, "%s\n", path);
    if (!s->present) {
        fprintf(out, "  no SAUCE record; laid out at %u columns, %zu row%s\n", g->width, g->rows,
                g->rows == 1 ? "" : "s");
        return;
    }
    if (*s->title)  fprintf(out, "  title    %s\n", s->title);
    if (*s->author) fprintf(out, "  author   %s\n", s->author);
    if (*s->group)  fprintf(out, "  group    %s\n", s->group);
    if (strlen(s->date) == 8)
        fprintf(out, "  date     %.4s-%.2s-%.2s\n", s->date, s->date + 4, s->date + 6);
    fprintf(out, "  size     %ux%u", s->width, s->height ? s->height : (unsigned)g->rows);
    if (s->datatype == 1 && s->filetype <= 2)
        fprintf(out, ", %s", types[s->filetype]);
    if (s->flags & 1)
        fprintf(out, ", iCE colours");
    fputc('\n', out);
}

static void usage(FILE *out)
{
    fprintf(out,
        "usage: %s [-p | -m] [-w WIDTH] [FILE...]\n"
        "       %s info FILE...\n"
        "\n"
        "Show ANSI art (CP437 with ANSI colour codes, as .ans files are) in a UTF-8\n"
        "terminal, laid out the way a BBS terminal would draw it. With no FILE, or\n"
        "when FILE is -, it reads standard input.\n"
        "\n"
        "  -p, --plain     the characters only, no colour\n"
        "  -m, --mono      no colour, with coloured areas redrawn as shading by\n"
        "                  brightness (for newsgroups and mail that show no colour)\n"
        "  -w, --width N   lay the art out N columns wide (default: SAUCE, else 80)\n"
        "  info            print each file's SAUCE record: title, artist, size\n"
        "  -h, --help      show this help\n"
        "  -V, --version   show the version\n"
        "\n"
        "Examples:\n"
        "  %s piece.ans | less -R\n"
        "  %s --mono piece.ans > piece.txt\n",
        progname, progname, progname, progname);
}

int main(int argc, char **argv)
{
    enum mode m = COLOUR;
    unsigned width = 0;
    int show_info = 0, status = 0, files = 0;

    for (int i = 1; i < argc; i++) {
        const char *a = argv[i];
        if (!strcmp(a, "-h") || !strcmp(a, "--help") || !strcmp(a, "help")) {
            usage(stdout);
            return 0;
        } else if (!strcmp(a, "-V") || !strcmp(a, "--version")) {
            printf("%s %s\n", progname, VERSION);
            return 0;
        } else if (!strcmp(a, "-p") || !strcmp(a, "--plain")) {
            m = PLAIN;
        } else if (!strcmp(a, "-m") || !strcmp(a, "--mono")) {
            m = MONO;
        } else if (!strcmp(a, "-w") || !strcmp(a, "--width")) {
            if (++i >= argc || (width = (unsigned)strtoul(argv[i], NULL, 10)) < 1 || width > 1000) {
                fprintf(stderr, "%s: --width needs a number from 1 to 1000\n", progname);
                return 1;
            }
        } else if (!strcmp(a, "info") && files == 0 && !show_info) {
            show_info = 1;
        } else if (a[0] == '-' && a[1]) {
            fprintf(stderr, "%s: unknown option %s\n", progname, a);
            usage(stderr);
            return 1;
        } else {
            argv[++files] = argv[i];    /* keep the file names at the front */
        }
    }
    if (!files)
        argv[++files] = "-";

    for (int f = 1; f <= files; f++) {
        size_t len;
        unsigned char *data = slurp(argv[f], &len);
        if (!data) {
            status = 2;
            continue;
        }
        sauce s;
        read_sauce(data, &len, &s);
        grid g = {NULL, 0, 0, width ? width : s.width};
        render(&g, data, len);
        if (show_info)
            info(argv[f], &s, &g, stdout);
        else
            emit(&g, m, stdout);
        free(g.cells);
        free(data);
    }
    return status;
}