/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0.If a copy of the MPL was not distributed with this
 * file, You can obtain one at http ://mozilla.org/MPL/2.0/.
 */
#undef NDEBUG
#include <assert.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <intrin.h>
#include <ammintrin.h>

#include <io.h>

#include "zlib.h"

#include "ESPReader.h"

// 
// === CONSTANTS === 
//

#define STDOUT_FILENO 1

// timestamp field access
const uint16_t day_mask = 0x1F;
const uint16_t month_mask = 0xF;
const uint16_t year_mask = 0x7F;
const int month_offset = 5;
const int year_offset = 9;

// 
// === FORWARD DECLARATIONS === 
//

void asserts(void);

// Tree walkers
void walk_concat(SizedBuf *tree, struct walker_callbacks cb, void *from_parent);
void walk_group(SizedBuf *tree, struct walker_callbacks cb, void *from_parent);
void walk_record(SizedBuf *tree, struct walker_callbacks cb, void *from_parent);

// Header printers
void print_group_header(Group *header);
void print_record_header(Record *header);

// Printer helpers
void litcopy(struct str_buf *sb, struct str_lit lit);
void num_str(struct str_buf *sb, unsigned long num, int radix);
void type_str(struct str_buf *sb, Type4 type);
void timestamp_str(struct str_buf *sb, uint16_t timestamp);
void group_label_str(struct str_buf *sb, Group *header);
void record_flags_str(struct str_buf *sb, Record *header);
void sb_write(int fp, struct str_buf sb_pre, struct str_buf sb_post);

// Utilities
Timestamp convert_ts(uint16_t ts);

// Callbacks
void print_cb(
        Node n, 
        void *data, 
        void **carry_out, 
        void *from_parent,
        void **to_children
);
void stats_cb(
        Node n,
        void *data,
        void **carry_out,
        void *from_parent,
        void **to_children
);
void decompress_pre(
        Node n,
        void *decom_ptr,
        void **carry_out,
        void *from_parent,
        void **to_children
);
void decompress_post(
        Node n,
        void *data,
        void *carry_in
);
void create_tree_cb(
        Node n,
        void *data,
        void **carry_out,
        void *from_parent,
        void **to_children
);
void serialize_cb(MetaNode *m, void *data);

//
// === FUNCTIONS ===
//

void asserts(void)
{
        // binary overlay size checks
        assert(sizeof(Record) == 24); // Record struct incorrect size
        assert(sizeof(Group) == 24); // Group struct incorrect size
        assert(sizeof((Group) { 0 }.label) == 4); // Label union incorrect size
        assert(sizeof(Field) == 6); // Field struct incorrect size

        assert(sizeof(MetaNode) == 64); // 1 cache line

        // zlib compatability
        assert(sizeof(uLongf) == sizeof(uint32_t));
        assert(sizeof(Bytef) == sizeof(char));
}

void espr_walk(
        SizedBuf esp,
        struct walker_callbacks cb, 
        void *from_parent
) {
        // check assertions that cannot be checked at compile time
        asserts();

        // check that we are at the start of the file
        {
                Type4 *type = NULL;
                int err = sb_peek(esp, sizeof(Type4), &type);
                assert(err == 0);
                assert(type->uint == rt[TES4]);
        }

        walk_concat(&esp, cb, from_parent);
        assert(sb_empty(esp));
}

/* Unknown data will be some concatenation of groups and records.
 *
 * `walk_concat` will call the appropriate walking function
 * for each segment of unknown data in this concatenation.
 */
void walk_concat(SizedBuf *tree, struct walker_callbacks cb, void *from_parent)
{
        while (!sb_empty(*tree)) {
                const Type4 *type = NULL;
                int err = sb_peek(*tree, sizeof(Type4), &type);
                assert(err == 0);

                // check valid type
                assert(rt[rt_hash(type->uint)] == type->uint);

                // only need to distinguish between groups and records
                if (type->uint == rt[GRUP])
                        walk_group(tree, cb, from_parent);
                else
                        walk_record(tree, cb, from_parent);
        }
}

/* Walk a group record. Group records are containers for any other type of
 * record, including other group records.
 *
 * This function will also call `cb` with the node constructed from this group
 * record.
 */
void walk_group(SizedBuf *tree, struct walker_callbacks cb, void *from_parent)
{
        Group *header = NULL;
        {
                int err = sb_peek(*tree, sizeof(Group), &header);
                assert(err == 0);
        }

        SizedBuf group = { .size = header->size };
        {
                int err = sb_recast(tree, group.size, &group.data);
                assert(err == 0);
                err = sb_recast(&group, sizeof(Group), &header);
                assert(err == 0);
        }

        Node n = { 
                .header.group = header, 
                .data = group.data, 
                .type = NT_GROUP 
        };
        void *carry = NULL;
        void *to_children = NULL;

        // Pre-walk callback
        if (cb.pre)
                cb.pre(n, cb.data, &carry, from_parent, &to_children);

        // Walk through the concatenation of data inside the group.
        walk_concat(&group, cb, to_children);
        assert(sb_empty(group));

        // Post-walk callback
        if (cb.post)
                cb.post(n, cb.data, carry);
}

void walk_record(SizedBuf *tree, struct walker_callbacks cb, void *from_parent)
{
        Record *header = NULL;
        char *data = NULL;
        {
                int err = sb_recast(tree, sizeof(Record), &header);
                assert(err == 0);
                err = sb_recast(tree, header->size, &data);
                assert(err == 0);
        }

        assert(header->type.uint != rt[GRUP]);

        Node n = { 
                .header.record = header, 
                .data = data, 
                .type = NT_RECORD 
        };
        void *carry = NULL;
        void *to_children = NULL;

        /* Pre and post walk callbacks make less sense for record walking as 
         * records are leaf-ish, will still call both here for now as field 
         * walking may be added in the future.
         */

        // Pre-walk callback
        if (cb.pre)
                cb.pre(n, cb.data, &carry, from_parent, &to_children);

        // Post-walk callback
        if (cb.post)
                cb.post(n, cb.data, carry);
}

void espr_print(SizedBuf esp)
{
        struct walker_callbacks cb = { .pre = print_cb };
        espr_walk(esp, cb, NULL);
}

void print_cb(
        Node n, void *data, 
        void **carry_out, 
        void *from_parent,
        void **to_children
) {
        (void)data;
        (void)carry_out;
        (void)from_parent;
        (void)to_children;

        switch (n.type) {
        case NT_GROUP:
                print_group_header(n.header.group);
                break;
        case NT_RECORD:
                print_record_header(n.header.record);
                break;
        default:
                assert(false); // invalid node type
        }
}

ESPStats espr_stats(SizedBuf esp)
{
        ESPStats stats = { 0 };
        struct walker_callbacks cb = { .pre = stats_cb, .data = &stats };
        espr_walk(esp, cb, NULL);
        return stats;
}

/* Tallies up the group and record count. Calculates uncompressed size; groups
 * only need their header size tallied as their data size will be handled by
 * further walking of the tree.
 */
void stats_cb(
        Node n, 
        void *data, 
        void **carry_out, 
        void *from_parent,
        void **to_children
) {
        (void)carry_out;
        (void)from_parent;
        (void)to_children;

        struct esp_stats *stats = data;
        switch (n.type) {
        case NT_GROUP:
                stats->group_count++;
                stats->decompressed_size += sizeof(Group);
                break;
        case NT_RECORD:
                stats->record_count++;
                stats->decompressed_size += sizeof(Record);
                if (n.header.record->flags & COMPRESSED_FLAG) {
                        // uncompressed size is stored in the first 4 bytes of
                        // data
                        stats->decompressed_size += *((uint32_t *)n.data);
                } else {
                        stats->decompressed_size += n.header.record->size;
                }
                break;
        default:
                assert(false); // invalid node type
        }
}

void espr_decompress(SizedBuf esp, SizedBuf decom)
{
        struct walker_callbacks cb = { 
                .pre = decompress_pre, 
                .post = decompress_post, 
                .data = &decom
        };
        espr_walk(esp, cb, NULL);
}

/* Handles the copying of groups and records, and the decompression of
 * compressed record data.
 *
 * For groups it copies only the header as group data will be handled by further
 * walking. The destination prior to copying will also be saved to carry_out for
 * groups so that decompress_post can correctly update the size of the copied
 * group.
 *
 * For uncompressed records it simply copies the entirety of the record to the
 * destination. For compressed records in copies the header first and then
 * directly decompresses the compressed record into the destination.
 */
void decompress_pre(
        Node n, 
        void *out_buf, 
        void **carry_out,
        void *from_parent, 
        void **to_children
) {
        (void)from_parent;
        (void)to_children;

        SizedBuf *d = out_buf;

        switch (n.type) {
        case NT_RECORD:
                // compressed record
                if (n.header.record->flags & COMPRESSED_FLAG) {
                        Record *copied_header = NULL;
                        {
                                // Acces for copied header
                                int err = sb_peek(*d, sizeof(Record), &copied_header);
                                assert(err == 0);
                                // copy header
                                err = sb_copyin(d, (char *)n.header.record, sizeof(Record));
                                assert(err == 0);
                        }

                        // decompress directly into buffer
                        // first 4 bytes are the decompressed size
                        const uint32_t dc_size = *((uint32_t *)n.data);
                        uint32_t to_copy = dc_size;
                        uint32_t cur_size = n.header.record->size - sizeof(uint32_t);
                        char *data_start = n.data + sizeof(uint32_t);

                        // check that we have enough space in the buffer
                        sb_check(*d, dc_size);

                        int ret = uncompress(
                                (Bytef *)d->data,
                                (uLongf *)&to_copy,
                                (Bytef *)data_start,
                                (uLong)cur_size
                        );
                        assert(ret == Z_OK);
                        assert(to_copy == dc_size);

                        // update the buffer
                        sb_update(d, dc_size);

                        // update header data size
                        copied_header->size = dc_size;

                        // unset compressed flag
                        copied_header->flags &= ~COMPRESSED_FLAG;
                } else {
                        // copy record
                        size_t record_size = sizeof(Record) 
                                + n.header.record->size;
                        sb_copyin(d, (char *)n.header.record, record_size);
                }
                break;
        case NT_GROUP:
                // save copied header location for post-walk group size recalc
                *carry_out = (void *)d->data;

                // copy header, contents will be copied while walking
                sb_copyin(d, (char *)n.header.group, sizeof(Group));

                break;
        default:
                assert(false); // invalid node type
        }
}

/* Handles recalculating group size after decompression. The location of the
 * the group's copied header will be passed in in carry_in and can be used both
 * to access the copied group header and calculate the new size of the group
 * based on the difference between the current destination pointer and the
 * group header pointer.
 */
void decompress_post(Node n, void *out, void *carry_in)
{
        SizedBuf *d = out;

        // only need to handle group resize
        if (n.type == NT_GROUP) {
                Group *g = (Group *)carry_in;
                uint32_t new_size = (uint32_t)((char *)d->data - (char *)g);
                g->size = new_size;
        }
}

void print_group_header(Group *header)
{
        assert(header->type < GTS_SIZE);

        // Guess at enough with significant margin
        char buf[1024] = { 0 };
        const struct str_buf sb_pre = { .buf = buf, .size = sizeof(buf) };
        struct str_buf sb = sb_pre;

        // literals
        struct str_lit
                l1 = STR_LIT("--- HEADER: GROUP ---"),
                l2 = STR_LIT("\nType: "),
                l3 = STR_LIT("\nSize: "),
                l4 = STR_LIT("\nLabel: "),
                l5 = STR_LIT("\nGroup type: "),
                l6 = STR_LIT("\nTimestamp: "),
                l7 = STR_LIT("\nVersion Control Info: "),
                l8 = STR_LIT("\nUnknown: "),
                l9 = STR_LIT("\n");

        struct str_lit gt = group_type_strings[header->type];

        // construct output
        litcopy(&sb, l1);
        litcopy(&sb, l2); type_str(&sb, header->grup);
        litcopy(&sb, l3); num_str(&sb, header->size, 10);
        litcopy(&sb, l4); group_label_str(&sb, header);
        litcopy(&sb, l5); litcopy(&sb, gt);
        litcopy(&sb, l6); timestamp_str(&sb, header->timestamp);
        litcopy(&sb, l7); num_str(&sb, header->vcinfo, 16);
        litcopy(&sb, l8); num_str(&sb, header->unknown, 16);
        litcopy(&sb, l9);

        sb_write(STDOUT_FILENO, sb_pre, sb);
}

void litcopy(struct str_buf *sb, struct str_lit lit)
{
        assert(sb->size >= lit.size);
        memcpy(sb->buf, lit.lit, lit.size);
        sb->size -= lit.size;
        sb->buf += lit.size;
}

void num_str(struct str_buf *sb, unsigned long num, int radix)
{
        errno_t ret = _ultoa_s(num, sb->buf, sb->size, radix);
        assert(ret == 0);
        int len = (int)strlen(sb->buf);
        sb->size -= len;
        sb->buf += len;
}

void type_str(struct str_buf *sb, Type4 type)
{
        assert(sb->size >= 4);
        for (size_t i = 0; i != 4; i++)
                sb->buf[i] = type.bytes[i];
        sb->buf += 4;
        sb->size -= 4;
}

void group_label_str(struct str_buf *sb, Group *header)
{
        switch (header->type) {
        case GT_TOP:
                type_str(sb, header->label.type);
                break;
        case GT_INTERIOR_CELL_BLOCK:
        case GT_INTERIOR_CELL_SUBBLOCK:
                num_str(sb, header->label.number, 10);
                break;
        case GT_EXTERIOR_CELL_BLOCK:
        case GT_EXTERIOR_CELL_SUBBLOCK:
                uint16_t x = header->label.coord[1], y = header->label.coord[0];
                litcopy(sb, LIT("X: ")); num_str(sb, x, 10);
                litcopy(sb, LIT("Y: ")); num_str(sb, y, 10);
                break;
        case GT_WORLD_CHILDREN:
        case GT_CELL_CHILDREN:
        case GT_TOPIC_CHILDREN:
        case GT_CELL_PERSISTENT_CHILDREN:
        case GT_CELL_TEMPORARY_CHILDREN:
                litcopy(sb, LIT("FormID["));
                num_str(sb, header->label.formid, 16);
                litcopy(sb, LIT("]"));
                break;
        default:
                assert(false); // invalid group type
        }
}

void timestamp_str(struct str_buf *sb, uint16_t timestamp)
{
        Timestamp ts = convert_ts(timestamp);
        litcopy(sb, LIT("20x")); 
        num_str(sb, ts.year, 10); 
        litcopy(sb, LIT("-"));
        num_str(sb, ts.month, 10); 
        litcopy(sb, LIT("-")); 
        num_str(sb, ts.day, 10);
}

void sb_write(int fp, struct str_buf sb_pre, struct str_buf sb_post)
{
        int size = sb_pre.size - sb_post.size;
        assert(size >= 0);
        int ret = _write(fp, sb_pre.buf, size);
        assert(ret == size);
}

void print_record_header(Record *header)
{
        char buf[1024] = { 0 };
        const struct str_buf sb_pre = { .buf = buf, .size = sizeof(buf) };
        struct str_buf sb = sb_pre;

        const struct str_lit
                l1 = LIT("--- HEADER: RECORD ---"),
                l2 = LIT("\nType: "),
                l3 = LIT("\nFlags: "),
                l4 = LIT("\nFormID: "),
                l5 = LIT("\nTimestamp: "),
                l6 = LIT("\nVersion Control Info: "),
                l7 = LIT("\nVersion: "),
                l8 = LIT("\nUnknown: "),
                l9 = LIT("\n");

        litcopy(&sb, l1);
        litcopy(&sb, l2); type_str(&sb, header->type);
        litcopy(&sb, l3); record_flags_str(&sb, header);
        litcopy(&sb, l4); num_str(&sb, header->formid, 16);
        litcopy(&sb, l5); timestamp_str(&sb, header->timestamp);
        litcopy(&sb, l6); num_str(&sb, header->vcinfo, 16);
        litcopy(&sb, l7); num_str(&sb, header->version, 10);
        litcopy(&sb, l8); num_str(&sb, header->unknown, 16);
        litcopy(&sb, l9);

        sb_write(STDOUT_FILENO, sb_pre, sb);
}

void record_flags_str(struct str_buf *sb, Record *header)
{
        uint32_t flags = header->flags;
        const uint32_t type = header->type.uint;

        // print flags
        if (type == rt[REFR]) {
            // TODO
            // REFR requires FormID lookup
                flags = 0;
        } else {
                rfs_inner *const flag_lut = rfs[rt_hash(type)];
                if (flag_lut) {
                        while (flags != 0) {
                                // get next flag, from lowest bit to highest
                                // will always be >= 0 as flags is not 0
                                int lowest = _tzcnt_u32(flags);
                                assert(lowest < 32);

                                // get flag string
                                const struct str_lit lit = (*flag_lut)[lowest];

                                // not a valid flag
                                if (!lit.lit)
                                        break;

                                // copy flag string
                                litcopy(sb, LIT("\n - ")); litcopy(sb, lit);
                                // remove flag from to be processed
                                flags ^= ((uint32_t)1) << lowest;
                        }
                }
        }

        // slow path
        if (flags != 0) {
                printf("\n\nOriginal flags: %08x\n", header->flags);
                printf("Unhandled flags: %08x\n", flags);
                assert(false); // unhandled flags
        }
}

/* Converts the bit-packed/encoded timestamp used in esp/esm files into day,
 * month and year. See UESP for further explanation.
 *
 * This currently handles the timestamp format used in Skyrim.esm, but newer
 * files apparently use a different format. This will need to be handled later.
 */
Timestamp convert_ts(uint16_t ts)
{
        /*
        const uint8_t day = (uint8_t)(ts & day_mask);
        const uint8_t month = (uint8_t)((ts >> month_offset) & month_mask);
        const uint16_t year = (ts >> year_offset) & year_mask;
        */

        const uint8_t day = ts & 0xff;
        const uint8_t hb = (ts >> 8) & 0xff;
        const uint8_t month = ((hb - 1) % 12) + 1;
        const uint8_t year = ((hb - 1) / 12 + 3) % 10;

        return (Timestamp) { year, month, day };
}

MetaTree espr_create_tree(SizedBuf in, SizedBuf tree)
{
        // create root node
        MetaNode *root = NULL;
        {
                int err = sb_recast(&tree, sizeof(MetaNode), &root);
                assert(err == 0);
        }
        *root = (MetaNode){ 0 };

        // walk
        struct walker_callbacks cb = { .pre = create_tree_cb, .data = &tree };
        espr_walk(in, cb, root);

        return (MetaTree) { .root = root, .size = in.size };
}

void create_tree_cb(
        const Node n,
        void *data,
        void **carry_out,
        void *from_parent,
        void **to_children
) {
        (void)carry_out;

        // add new metanode to tree
        SizedBuf *tree = data;
        MetaNode *m = NULL;
        {
                int err = sb_recast(tree, sizeof(MetaNode), &m);
                assert(err == 0);
        }

        // parent passes their MetaNode to children
        MetaNode *p = from_parent;

        // construct new node
        *m = (MetaNode){ 0 }; // zero/null unused
        m->n = n;
        m->parent = p;
        m->prev = p->last_child;
        // the linked list of children may not already exist
        if (p->last_child)
                p->last_child->next = m;
        else
                p->first_child = m;
        p->last_child = m;

        // send self to children
        *to_children = m;
}

void espr_meta_walk(MetaTree tree, struct meta_callbacks cb) {
        espr_meta_node_walk(tree.root, cb);
}

void espr_meta_node_walk(MetaNode *m, struct meta_callbacks cb) {
        cb.pre(m, cb.data);
        MetaNode *child = m->first_child;
        while (child) {
                espr_meta_node_walk(child, cb);
                child = child->next;
        }
}

void espr_serialize(MetaTree tree, SizedBuf out) {
        struct meta_callbacks cb = { .pre = serialize_cb, .data = &out };
        espr_meta_walk(tree, cb);
}

void serialize_cb(MetaNode *m, void *data) {
        SizedBuf *out = data;

        // exit on empty node
        if (!m->n.data)
                return;

        switch (m->n.type) {
        case NT_GROUP:
                // only serialize the header of groups
        {
                int err = sb_copyin(out, (char *)m->n.header.group, sizeof(Group));
                assert(err == 0);
        }
        break;
        case NT_RECORD:
                size_t data_size = m->n.header.record->size;
                char *header = (char *)m->n.header.record;
                // serialize header and data separately as they may be 
                // discontiguous
        {
                int err = sb_copyin(out, header, sizeof(Record));
                assert(err == 0);
                err = sb_copyin(out, m->n.data, data_size);
                assert(err == 0);
        }
                break;
        default:
                assert(false);
        }
}