#include "compat.h"
#include "screen.h"
#include "unicode/grapheme.h"
#include <stdlib.h>
#include <string.h>

/*
 * A snapshot keeps one converted copy of each viewport row. An update
 * copies a row again only when the terminal reports a new key for it.
 * Cluster cells refer to an arena of [length, code points...] records that
 * the snapshot owns, so a renderer never reads the terminal's cluster table.
 */
struct term_snapshot {
    struct term_view view;
    uint32_t palette[TERM_PALETTE_SIZE];
    uint64_t source;                /* serial of the terminal it copied */

    struct term_cell *cells;        /* rows * cols */
    uint64_t *keys;                 /* per row */
    uint32_t *row_clusters;         /* arena records each row holds */
    struct term_span *selection;    /* per row */
    size_t cell_cap;
    int row_cap;

    uint32_t *arena;
    uint32_t arena_len, arena_cap, arena_dead;
};

struct term_snapshot *term_snapshot_new(void)
{
    struct term_snapshot *s = calloc(1, sizeof(*s));
    if (s)
        s->view.palette = s->palette;
    return s;
}

void term_snapshot_free(struct term_snapshot *s)
{
    if (!s)
        return;
    free(s->cells);
    free(s->keys);
    free(s->row_clusters);
    free(s->selection);
    free(s->arena);
    free(s);
}

static bool reserve(struct term_snapshot *s, int cols, int rows)
{
    size_t cells = (size_t)cols * (size_t)rows;
    if (cells > s->cell_cap) {
        struct term_cell *c = realloc(s->cells, cells * sizeof(*c));
        if (!c)
            return false;
        s->cells = c;
        s->cell_cap = cells;
    }
    if (rows > s->row_cap) {
        uint64_t *k = realloc(s->keys, (size_t)rows * sizeof(*k));
        if (k)
            s->keys = k;
        uint32_t *rc = realloc(s->row_clusters, (size_t)rows * sizeof(*rc));
        if (rc)
            s->row_clusters = rc;
        struct term_span *sel = realloc(s->selection, (size_t)rows * sizeof(*sel));
        if (sel)
            s->selection = sel;
        if (!k || !rc || !sel)
            return false;
        s->row_cap = rows;
    }
    return true;
}

/* Attribute contributions of the low and high byte of cell flags. */
static uint16_t lo_attrs[256], hi_attrs[256];
static uint8_t hi_underline[256];
void term_snapshot_tables_init(void)
{
    for (int b = 0; b < 256; b++) {
        uint16_t lo = 0, hi = 0;
        if (b & CELL_BOLD) lo |= TERM_ATTR_BOLD;
        if (b & CELL_ITALIC) lo |= TERM_ATTR_ITALIC;
        if (b & CELL_STRIKE) lo |= TERM_ATTR_STRIKE;
        if (b & CELL_OVERLINE) lo |= TERM_ATTR_OVERLINE;
        if (b & CELL_EMOJI) lo |= TERM_ATTR_EMOJI;
        if (b & CELL_TEXT) lo |= TERM_ATTR_TEXT;
        uint16_t f = (uint16_t)(b << 8);
        if (f & CELL_FAINT) hi |= TERM_ATTR_FAINT;
        if (f & CELL_LINK) hi |= TERM_ATTR_LINK;
        uint8_t ul = 0;
        if (f & CELL_DOUBLE_UNDERLINE) ul = TERM_UNDERLINE_DOUBLE;
        else if (f & CELL_CURLY_UNDERLINE) ul = TERM_UNDERLINE_CURLY;
        else if (f & CELL_DOTTED_UNDERLINE) ul = TERM_UNDERLINE_DOTTED;
        else if (f & CELL_DASHED_UNDERLINE) ul = TERM_UNDERLINE_DASHED;
        lo_attrs[b] = lo;
        hi_attrs[b] = hi;
        hi_underline[b] = ul;
    }
}

static uint32_t arena_add(struct term_snapshot *s, const struct gstore *g, uint32_t handle)
{
    uint32_t cps[GRAPHEME_MAX_LEN];
    int n = term_gstore_expand(g, handle, cps, GRAPHEME_MAX_LEN);
    if (n <= 0)
        return ' ';
    if (s->arena_len + (uint32_t)n + 1 > s->arena_cap) {
        uint32_t cap = s->arena_cap ? s->arena_cap * 2 : 256;
        while (cap < s->arena_len + (uint32_t)n + 1)
            cap *= 2;
        uint32_t *a = realloc(s->arena, cap * sizeof(*a));
        if (!a)
            return cps[0];
        s->arena = a;
        s->arena_cap = cap;
    }
    uint32_t off = s->arena_len;
    s->arena[off] = (uint32_t)n;
    memcpy(&s->arena[off + 1], cps, (size_t)n * sizeof(*cps));
    s->arena_len += (uint32_t)n + 1;
    return TERM_TEXT_CLUSTER | off;
}

/* Convert one stored row; returns the number of arena words it added. */
static uint32_t convert_row(struct term_snapshot *s, const struct gstore *g,
                            struct term_cell *dst,
                            const struct cell *src, int cols)
{
    uint32_t before = s->arena_len;
    for (int x = 0; x < cols; x++) {
        const struct cell *c = &src[x];
        uint16_t f = c->flags;
        uint8_t lo = (uint8_t)f, hi = (uint8_t)(f >> 8);
        uint16_t ul = hi_underline[hi];
        if (!ul && (f & CELL_UNDERLINE))
            ul = TERM_UNDERLINE_SINGLE;
        uint32_t text = c->c;
        if (TERM_EXPECT(text < 0x20, 0))
            text = text ? ' ' : 0;
        else if (TERM_EXPECT(grapheme_is_handle(text), 0))
            text = arena_add(s, g, text);
        dst[x] = (struct term_cell){
            .text = text,
            .fg = c->fg,
            .bg = c->bg,
            .attrs = (uint16_t)(lo_attrs[lo] | hi_attrs[hi] |
                                ul << TERM_ATTR_UNDERLINE_SHIFT),
            .width = (f & CELL_TRAIL) ? 0 : (f & CELL_WIDE) ? 2 : 1,
        };
    }
    return s->arena_len - before;
}

static bool term_snapshot_update_inner(struct term_snapshot *s, struct term *t)
{
    if (!s || !t)
        return false;
    int cols = t->cols, rows = t->rows;
    if (!reserve(s, cols, rows)) {
        s->view.size = (struct term_vector2i){ 0 };
        s->source = 0;
        return false;
    }

    bool resized = s->view.size.x != cols || s->view.size.y != rows;
    bool all = resized || s->source != t->serial;
    /* Reclaim cluster records once most of the arena is garbage. */
    if (s->arena_dead > 4096 && s->arena_dead * 2 > s->arena_len)
        all = true;
    if (all) {
        s->arena_len = 0;
        s->arena_dead = 0;
    }

    bool changed = all;
    term_hist_prepare_rows(&t->hist, cols);
    if (!term_hist_view_sync(&t->view, &t->hist, cols))
        return false;
    term_hist_view_refine(&t->view, &t->hist, cols, rows);
    uint64_t stack_keys[256];
    uint64_t *new_keys = rows <= 256 ? stack_keys : malloc((size_t)rows * sizeof(uint64_t));
    if (!new_keys)
        return false;
    for (int y = 0; y < rows; y++)
        new_keys[y] = term_screen_view_row_key(t, y);

    int scrolled = 0;
    if (!all && rows > 1) {
        int cand_k = 0;
        /* Find candidate scroll offset k by checking where top rows moved. */
        for (int p = 0; p < 2 && p < rows - 1 && !cand_k; p++) {
            uint64_t key = new_keys[p];
            if (!key)
                continue;
            for (int k = 1; p + k < rows; k++) {
                if (s->keys[p + k] == key) {
                    cand_k = k;
                    break;
                }
            }
        }

        if (cand_k > 0) {
            int total = rows - cand_k;
            int threshold = total / 2;
            int matches = 0, mismatches = 0;
            for (int y = 0; y < total; y++) {
                if (new_keys[y] == s->keys[y + cand_k]) {
                    if (++matches > threshold) {
                        scrolled = cand_k;
                        break;
                    }
                } else {
                    if (++mismatches > threshold)
                        break;
                }
            }
        }
    }

    if (scrolled > 0) {
        int k = scrolled;
        memmove(s->cells, s->cells + (size_t)k * cols,
                (size_t)(rows - k) * cols * sizeof(struct term_cell));
        memmove(s->row_clusters, s->row_clusters + k,
                (size_t)(rows - k) * sizeof(uint32_t));
        memmove(s->keys, s->keys + k,
                (size_t)(rows - k) * sizeof(uint64_t));
        for (int y = rows - k; y < rows; y++) {
            s->keys[y] = 0;
            s->row_clusters[y] = 0;
        }
    }

    for (int y = 0; y < rows; y++) {
        uint64_t key = new_keys[y];
        if (!all && s->keys[y] == key)
            continue;
        if (!all)
            s->arena_dead += s->row_clusters[y];
        const struct cell *src = term_screen_view_row(t, y);
        s->row_clusters[y] = convert_row(s, t->gstore, s->cells + (size_t)y * cols, src, cols);
        s->keys[y] = key;
        changed = true;
    }
    if (new_keys != stack_keys)
        free(new_keys);

    int stack[2][256];
    int *c0 = rows <= 256 ? stack[0] : malloc((size_t)rows * 2 * sizeof(int));
    if (!c0)
        return false;
    int *c1 = rows <= 256 ? stack[1] : c0 + rows;
    term_selection_view_spans(t, c0, c1);
    for (int y = 0; y < rows; y++) {
        struct term_span span = c1[y] >= c0[y] ? (struct term_span){ c0[y], c1[y] + 1 }
                                               : (struct term_span){ 0 };
        if (all || span.begin != s->selection[y].begin || span.end != s->selection[y].end)
            changed = true;
        s->selection[y] = span;
    }
    if (c0 != stack[0])
        free(c0);

    struct term_cursor cursor = term_cursor(t);
    int view_offset = term_view_offset(t);
    cursor.pos.y += view_offset;
    if (cursor.pos.y >= rows)
        cursor.visible = false;
    const struct term_cursor *old = &s->view.cursor;
    if (cursor.pos.x != old->pos.x || cursor.pos.y != old->pos.y ||
        cursor.style != old->style || cursor.visible != old->visible ||
        cursor.blink != old->blink ||
        s->view.scroll_offset != view_offset ||
        s->view.reverse_video != t->reverse_video)
        changed = true;
    if (all || s->view.palette_version != t->palette.version) {
        memcpy(s->palette, t->palette.colors, sizeof(s->palette));
        s->view.palette_version = t->palette.version;
        changed = true;
    }

    s->source = t->serial;
    s->view.size = (struct term_vector2i){ .x = cols, .y = rows };
    s->view.cursor = cursor;
    s->view.scroll_offset = view_offset;
    s->view.scrolled = scrolled;
    s->view.reverse_video = t->reverse_video;
    if (changed || scrolled)
        s->view.version++;
    return true;
}

bool term_snapshot_update(struct term_snapshot *s, struct term *t)
{
    if (!s || !t)
        return false;
    term_write_begin(t);
    bool ok = term_snapshot_update_inner(s, t);
    term_write_end(t);
    return ok;
}

const struct term_view *term_snapshot_view(const struct term_snapshot *s)
{
    return &s->view;
}

const struct term_cell *term_snapshot_row(const struct term_snapshot *s, int y)
{
    if (y < 0 || y >= s->view.size.y)
        return NULL;
    return s->cells + (size_t)y * s->view.size.x;
}

uint64_t term_snapshot_row_key(const struct term_snapshot *s, int y)
{
    if (y < 0 || y >= s->view.size.y)
        return 0;
    return s->keys[y];
}

struct term_span term_snapshot_row_selection(const struct term_snapshot *s, int y)
{
    if (y < 0 || y >= s->view.size.y)
        return (struct term_span){ 0 };
    return s->selection[y];
}

int term_snapshot_cluster(const struct term_snapshot *s, uint32_t text, uint32_t *cps, int cap)
{
    if (!(text & TERM_TEXT_CLUSTER)) {
        if (cap > 0)
            cps[0] = text;
        return 1;
    }
    uint32_t off = text & ~TERM_TEXT_CLUSTER;
    if (off >= s->arena_len)
        return 0;
    int n = (int)s->arena[off];
    for (int i = 0; i < n && i < cap; i++)
        cps[i] = s->arena[off + 1 + i];
    return n;
}