#include "module-list.h"
#include "module-text.h"
#include <math.h>
#include <stdlib.h>
#include <string.h>

struct PureList {
    unsigned fields;
    uint8_t text_fields[16];
    PureCell **items;
    size_t count, capacity;
    PureDraft *draft;     /* the stored copy, or NULL */
    size_t header;        /* draft bytes before the first item */
    uint64_t id, version; /* which list, and a number every change moves on */
    uint64_t shares;      /* copies made so far: an item made before the last one is shared */
    PureRetired *retired; /* where shared items go when the list lets them go */
    unsigned refs;        /* a shared copy's references */
    bool copy;            /* a shared copy: it owns its item array, not its items */
};

typedef enum { INSERTED, REMOVED, CHANGED, REPLACED } Change;
typedef struct {
    Change change;
    PureList *list;
    size_t at;
    unsigned field;
    PureCell *item; /* REMOVED: the removed item; REPLACED: the shared item a copy replaced */
    PureCell old;   /* CHANGED: the replaced cell */
} Entry;
typedef struct { PureCell *item; uint16_t text; uint8_t fields; } Retired;

static uint64_t lists_made;

/* An item's cells follow the list's share count when the item was made. One
 * made before the last share may be read by a shared copy, so it never
 * changes again (a change copies it) and is retired instead of freed. */
static PureCell *new_item(const PureList *list) {
    uint64_t *made = calloc(1, sizeof(*made) + (list->fields ? list->fields : 1) * sizeof(PureCell));
    if (!made) return NULL;
    *made = list->shares;
    return (PureCell *)(made + 1);
}

static bool shared(const PureList *list, const PureCell *item) { return ((const uint64_t *)item)[-1] < list->shares; }

static void free_cells(PureCell *item, unsigned fields, unsigned text) {
    for (unsigned f = 0; f < fields; ++f)
        if (text >> f & 1) free(item[f].text);
    free((uint64_t *)item - 1);
}

static unsigned text_mask(const PureList *list) {
    unsigned text = 0;
    for (unsigned f = 0; f < list->fields; ++f) text |= (unsigned)(list->text_fields[f] != 0) << f;
    return text;
}

static void free_item(const PureList *list, PureCell *item) {
    if (item) free_cells(item, list->fields, text_mask(list));
}

/* The list no longer has item: free it, or retire it while a copy may read it. */
static void let_go(PureList *list, PureCell *item) {
    if (!shared(list, item)) { free_item(list, item); return; }
    PureRetired *retired = list->retired;
    if (retired->count == retired->capacity) {
        size_t capacity = retired->capacity ? 2 * retired->capacity : 16;
        Retired *grown = realloc(retired->entries, capacity * sizeof(*grown));
        if (!grown) return; /* kept for good rather than freed while read */
        retired->entries = grown;
        retired->capacity = capacity;
    }
    ((Retired *)retired->entries)[retired->count++] = (Retired){item, (uint16_t)text_mask(list), (uint8_t)list->fields};
}

void pure_retired_free(PureRetired *retired) {
    Retired *entries = retired->entries;
    for (size_t i = 0; i < retired->count; ++i) free_cells(entries[i].item, entries[i].fields, entries[i].text);
    free(entries);
    *retired = (PureRetired){0};
}

PureList *pure_list_new(unsigned fields, const uint8_t *text_fields) {
    if (fields > 16) return NULL;
    PureList *list = calloc(1, sizeof(*list));
    if (!list) return NULL;
    list->fields = fields;
    memcpy(list->text_fields, text_fields, fields);
    list->id = __atomic_add_fetch(&lists_made, 1, __ATOMIC_RELAXED);
    return list;
}

void pure_list_free(PureList *list) {
    if (!list) return;
    if (list->copy) {
        if (__atomic_sub_fetch(&list->refs, 1, __ATOMIC_ACQ_REL)) return;
    } else
        for (size_t i = 0; i < list->count; ++i) let_go(list, list->items[i]);
    free(list->items);
    free(list);
}

size_t pure_list_count(const PureList *list) { return list->count; }

PureList *pure_list_share(PureList *list, PureRetired *retired) {
    PureList *copy = malloc(sizeof(*copy));
    PureCell **items = list->count ? malloc(list->count * sizeof(*items)) : NULL;
    if (!copy || (list->count && !items)) {
        free(copy);
        free(items);
        return NULL;
    }
    if (list->count) memcpy(items, list->items, list->count * sizeof(*items));
    *copy = (PureList){.fields = list->fields, .items = items, .count = list->count, .capacity = list->count,
                       .id = list->id, .version = list->version, .refs = 1, .copy = true};
    memcpy(copy->text_fields, list->text_fields, sizeof(copy->text_fields));
    list->retired = retired;
    ++list->shares;
    return copy;
}

void pure_list_hold(PureList *copy) { __atomic_add_fetch(&copy->refs, 1, __ATOMIC_RELAXED); }

bool pure_list_current(const PureList *copy, const PureList *list) {
    return copy->id == list->id && copy->version == list->version;
}

static bool log_change(PureUndo *undo, Entry entry) {
    if (undo->count == undo->capacity) {
        size_t capacity = undo->capacity ? 2 * undo->capacity : 16;
        Entry *entries = realloc(undo->entries, capacity * sizeof(*entries));
        if (!entries) return false;
        undo->entries = entries;
        undo->capacity = capacity;
    }
    ((Entry *)undo->entries)[undo->count++] = entry;
    return true;
}

static bool copy_cell(const PureList *list, unsigned field, PureCell from, PureCell *to) {
    *to = (PureCell){.num = list->text_fields[field] ? 0 : from.num};
    if (!list->text_fields[field] || !from.size) return true;
    to->text = malloc(from.size);
    if (!to->text) return false;
    memcpy(to->text, from.text, from.size);
    to->size = from.size;
    return true;
}

/* ---- The stored form: each field in order, a number as its binary64 bits
 * (little-endian), a text as a u32le length and its bytes. */

static size_t cell_bytes(const PureList *list, unsigned field, PureCell cell) {
    return list->text_fields[field] ? 4 + cell.size : 8;
}

static size_t item_bytes(const PureList *list, const PureCell *item) {
    size_t size = 0;
    for (unsigned f = 0; f < list->fields; ++f) size += cell_bytes(list, f, item[f]);
    return size;
}

/* Where an item starts in the draft. Linear in the items before it. */
static size_t item_offset(const PureList *list, size_t at) {
    size_t offset = list->header;
    for (size_t i = 0; i < at; ++i) offset += item_bytes(list, list->items[i]);
    return offset;
}

static unsigned char *encode_cell(const PureList *list, unsigned field, PureCell cell, unsigned char *out) {
    uint64_t bits = cell.size;
    unsigned width = 4;
    if (!list->text_fields[field]) { memcpy(&bits, &cell.num, sizeof(bits)); width = 8; }
    for (unsigned i = 0; i < width; ++i) *out++ = (unsigned char)(bits >> (8 * i));
    if (list->text_fields[field] && cell.size) { memcpy(out, cell.text, cell.size); out += cell.size; }
    return out;
}

/* Replace remove bytes of the draft, within bytes into the item at `at` (or
 * after the last item), with bytes; nothing to do without a draft. */
static PureResult mirror(PureList *list, size_t at, size_t within, size_t remove, const unsigned char *bytes,
                         size_t size) {
    if (!list->draft) return PURE_OK;
    return pure_draft_splice(list->draft, item_offset(list, at) + within, remove, (PureSpan){bytes, size});
}

void pure_list_mirror(PureList *list, PureDraft *draft, size_t header) {
    list->draft = draft;
    list->header = header;
}

PURE_COLD PureResult pure_list_write(PureList *list) {
    size_t size = 0;
    for (size_t i = 0; i < list->count; ++i) size += item_bytes(list, list->items[i]);
    unsigned char *bytes = size ? malloc(size) : NULL, *at = bytes;
    if (size && !bytes) return PURE_ALLOCATION;
    for (size_t i = 0; i < list->count; ++i)
        for (unsigned f = 0; f < list->fields; ++f) at = encode_cell(list, f, list->items[i][f], at);
    PureResult result = mirror(list, 0, 0, 0, bytes, size);
    free(bytes);
    return result;
}

PURE_COLD PureResult pure_list_read(PureList *list, const unsigned char *bytes, size_t size) {
    PureCell cells[16];
    for (size_t at = 0; at < size;) {
        for (unsigned f = 0; f < list->fields; ++f) {
            size_t width = list->text_fields[f] ? 4 : 8;
            if (size - at < width) return PURE_STORE_ERROR;
            uint64_t bits = 0;
            for (size_t i = 0; i < width; ++i) bits |= (uint64_t)bytes[at + i] << (8 * i);
            at += width;
            if (!list->text_fields[f]) {
                cells[f] = (PureCell){0};
                memcpy(&cells[f].num, &bits, sizeof(bits));
                if (!isfinite(cells[f].num)) return PURE_STORE_ERROR;
                continue;
            }
            if (bits > size - at || !pure_utf8_valid((PureSpan){bytes + at, (size_t)bits}))
                return PURE_STORE_ERROR;
            cells[f] = (PureCell){0, (unsigned char *)bytes + at, (size_t)bits};
            at += (size_t)bits;
        }
        PureResult result = pure_list_insert(list, list->count, cells, NULL);
        if (result != PURE_OK) return result;
    }
    return PURE_OK;
}

static void place(PureList *list, size_t at, PureCell *item) {
    memmove(list->items + at + 1, list->items + at, (list->count - at) * sizeof(*list->items));
    list->items[at] = item;
    ++list->count;
    ++list->version;
}

static PureCell *take(PureList *list, size_t at) {
    PureCell *item = list->items[at];
    memmove(list->items + at, list->items + at + 1, (list->count - at - 1) * sizeof(*list->items));
    --list->count;
    ++list->version;
    return item;
}

PureResult pure_list_insert(PureList *list, size_t at, const PureCell *cells, PureUndo *undo) {
    if (at > list->count || list->count == PURE_LIST_ITEMS) return PURE_LIMIT;
    if (list->count == list->capacity) {
        size_t capacity = list->capacity ? 2 * list->capacity : 8;
        PureCell **items = realloc(list->items, capacity * sizeof(*items));
        if (!items) return PURE_ALLOCATION;
        list->items = items;
        list->capacity = capacity;
    }
    PureCell *item = new_item(list);
    if (!item) return PURE_ALLOCATION;
    for (unsigned f = 0; f < list->fields; ++f)
        if (!copy_cell(list, f, cells[f], &item[f])) { free_item(list, item); return PURE_ALLOCATION; }
    size_t size = list->draft ? item_bytes(list, item) : 0;
    unsigned char *bytes = size ? malloc(size) : NULL, *end = bytes;
    if (size && !bytes) { free_item(list, item); return PURE_ALLOCATION; }
    for (unsigned f = 0; bytes && f < list->fields; ++f) end = encode_cell(list, f, item[f], end);
    if (undo && !log_change(undo, (Entry){.change = INSERTED, .list = list, .at = at})) {
        free(bytes);
        free_item(list, item);
        return PURE_ALLOCATION;
    }
    PureResult result = mirror(list, at, 0, 0, bytes, size);
    free(bytes);
    if (result != PURE_OK) {
        if (undo) --undo->count;
        free_item(list, item);
        return result;
    }
    place(list, at, item);
    return PURE_OK;
}

PureResult pure_list_remove(PureList *list, size_t at, PureUndo *undo) {
    if (at >= list->count) return PURE_NOT_FOUND;
    if (!log_change(undo, (Entry){.change = REMOVED, .list = list, .at = at, .item = list->items[at]}))
        return PURE_ALLOCATION;
    PureResult result = mirror(list, at, 0, item_bytes(list, list->items[at]), NULL, 0);
    if (result != PURE_OK) { --undo->count; return result; }
    take(list, at);
    return PURE_OK;
}

/* A shared item's copy with every field but one (left empty). */
static PureCell *copy_item(const PureList *list, const PureCell *item, unsigned except) {
    PureCell *fresh = new_item(list);
    for (unsigned f = 0; fresh && f < list->fields; ++f)
        if (f != except && !copy_cell(list, f, item[f], &fresh[f])) {
            free_item(list, fresh);
            fresh = NULL;
        }
    return fresh;
}

PureResult pure_list_set(PureList *list, size_t at, unsigned field, PureCell value, PureUndo *undo) {
    if (at >= list->count) return PURE_NOT_FOUND;
    PureCell copy, *item = list->items[at];
    if (!copy_cell(list, field, value, &copy)) return PURE_ALLOCATION;
    PureCell *fresh = shared(list, item) ? copy_item(list, item, field) : item;
    size_t size = list->draft ? cell_bytes(list, field, copy) : 0;
    unsigned char *bytes = size ? malloc(size) : NULL;
    Entry entry = fresh == item ? (Entry){.change = CHANGED, .list = list, .at = at, .field = field, .old = item[field]} :
                                  (Entry){.change = REPLACED, .list = list, .at = at, .item = item};
    if (!fresh || (size && !bytes) || !log_change(undo, entry)) {
        free(bytes);
        free(copy.text);
        if (fresh != item) free_item(list, fresh);
        return PURE_ALLOCATION;
    }
    if (bytes) encode_cell(list, field, copy, bytes);
    size_t within = 0;
    for (unsigned f = 0; f < field; ++f) within += cell_bytes(list, f, item[f]);
    PureResult result = mirror(list, at, within, cell_bytes(list, field, item[field]), bytes, size);
    free(bytes);
    if (result != PURE_OK) {
        --undo->count;
        free(copy.text);
        if (fresh != item) free_item(list, fresh);
        return result;
    }
    fresh[field] = copy;
    list->items[at] = fresh;
    ++list->version;
    return PURE_OK;
}

PureCell pure_list_get(const PureList *list, size_t at, unsigned field) {
    return list->items[at][field];
}

/* How two cells of a field order: numbers by value (-0 and +0 are one key),
 * texts by their bytes. */
static int order(const PureList *list, unsigned field, PureCell a, PureCell b) {
    if (!list->text_fields[field]) return (a.num > b.num) - (a.num < b.num);
    size_t shorter = a.size < b.size ? a.size : b.size;
    int bytes = shorter ? memcmp(a.text, b.text, shorter) : 0;
    return bytes ? (bytes > 0) - (bytes < 0) : (a.size > b.size) - (a.size < b.size);
}

size_t pure_list_seek(const PureList *list, unsigned field, PureCell key, bool *found) {
    size_t low = 0, high = list->count;
    while (low < high) {
        size_t middle = low + (high - low) / 2;
        if (order(list, field, list->items[middle][field], key) < 0) low = middle + 1;
        else high = middle;
    }
    *found = low < list->count && !order(list, field, list->items[low][field], key);
    return low;
}

/* Positions sorted by their items' field, stably (spare holds count). */
PURE_COLD static void merge_sort(const PureList *list, unsigned field, size_t *at, size_t *spare, size_t count) {
    if (count < 2) return;
    size_t half = count / 2, i = 0, j = half, k = 0;
    merge_sort(list, field, at, spare, half);
    merge_sort(list, field, at + half, spare, count - half);
    while (i < half && j < count)
        spare[k++] = order(list, field, list->items[at[j]][field], list->items[at[i]][field]) < 0 ? at[j++] : at[i++];
    while (i < half) spare[k++] = at[i++];
    while (j < count) spare[k++] = at[j++];
    memcpy(at, spare, count * sizeof(*at));
}

PURE_COLD PureResult pure_list_sorted(const PureList *list, unsigned field, PureList **out, size_t *moved) {
    *out = NULL;
    bool ordered = true;
    for (size_t i = 1; i < list->count && ordered; ++i)
        ordered = order(list, field, list->items[i - 1][field], list->items[i][field]) < 0;
    if (ordered) return PURE_OK;
    size_t *at = malloc(2 * list->count * sizeof(*at));
    if (!at) return PURE_ALLOCATION;
    for (size_t i = 0; i < list->count; ++i) at[i] = i;
    merge_sort(list, field, at, at + list->count, list->count);
    PureResult result = PURE_OK;
    for (size_t i = 1; i < list->count && result == PURE_OK; ++i)
        if (!order(list, field, list->items[at[i - 1]][field], list->items[at[i]][field])) result = PURE_CONFLICT;
    PureList *sorted = result == PURE_OK ? pure_list_new(list->fields, list->text_fields) : NULL;
    if (result == PURE_OK && !sorted) result = PURE_ALLOCATION;
    for (size_t i = 0; result == PURE_OK && i < list->count; ++i) {
        result = pure_list_insert(sorted, i, list->items[at[i]], NULL);
        moved[at[i]] = i;
    }
    free(at);
    if (result != PURE_OK) {
        pure_list_free(sorted);
        return result;
    }
    *out = sorted;
    return PURE_OK;
}

void pure_undo_rollback(PureUndo *undo, size_t mark) {
    Entry *entries = undo->entries;
    for (size_t i = undo->count; i-- > mark;) {
        Entry *e = &entries[i];
        if (e->change == INSERTED) free_item(e->list, take(e->list, e->at));
        else if (e->change == REMOVED) place(e->list, e->at, e->item); /* capacity is still there */
        else if (e->change == REPLACED) {
            free_item(e->list, e->list->items[e->at]);
            e->list->items[e->at] = e->item;
            ++e->list->version;
        } else {
            if (e->list->text_fields[e->field]) free(e->list->items[e->at][e->field].text);
            e->list->items[e->at][e->field] = e->old;
            ++e->list->version;
        }
    }
    undo->count = mark;
}

void pure_undo_commit(PureUndo *undo) {
    Entry *entries = undo->entries;
    for (size_t i = 0; i < undo->count; ++i) {
        Entry *e = &entries[i];
        if (e->change == REMOVED || e->change == REPLACED) let_go(e->list, e->item);
        else if (e->change == CHANGED && e->list->text_fields[e->field]) free(e->old.text);
    }
    undo->count = 0;
}

void pure_undo_free(PureUndo *undo) {
    free(undo->entries);
    *undo = (PureUndo){0};
}