#include <string.h>
#include "block-iter.h"
#include "util/debug.h"
#include "util/utf8.h"
#include "util/xmalloc.h"

void block_iter_normalize(BlockIter *bi)
{
    const Block *blk = bi->blk;
    if (bi->offset == blk->size && blk->node.next != bi->head) {
        bi->blk = BLOCK(blk->node.next);
        bi->offset = 0;
    }
}

/*
 * Move after next newline (beginning of next line or end of file).
 * Returns number of bytes iterator advanced.
 */
size_t block_iter_eat_line(BlockIter *bi)
{
    block_iter_normalize(bi);
    const size_t offset = bi->offset;
    if (unlikely(offset == bi->blk->size)) {
        return 0;
    }

    // There must be at least one newline
    if (bi->blk->nl == 1) {
        bi->offset = bi->blk->size;
    } else {
        const unsigned char *end;
        end = memchr(bi->blk->data + offset, '\n', bi->blk->size - offset);
        BUG_ON(!end);
        bi->offset = (size_t)(end + 1 - bi->blk->data);
    }

    return bi->offset - offset;
}

/*
 * Move to beginning of next line.
 * If there is no next line, iterator is not advanced.
 * Returns number of bytes iterator advanced.
 */
size_t block_iter_next_line(BlockIter *bi)
{
    block_iter_normalize(bi);
    const size_t offset = bi->offset;
    if (unlikely(offset == bi->blk->size)) {
        return 0;
    }

    // There must be at least one newline
    size_t new_offset;
    if (bi->blk->nl == 1) {
        new_offset = bi->blk->size;
    } else {
        const unsigned char *end;
        end = memchr(bi->blk->data + offset, '\n', bi->blk->size - offset);
        BUG_ON(!end);
        new_offset = (size_t)(end + 1 - bi->blk->data);
    }
    if (new_offset == bi->blk->size && bi->blk->node.next == bi->head) {
        return 0;
    }

    bi->offset = new_offset;
    return bi->offset - offset;
}

/*
 * Move to beginning of previous line.
 * Returns number of bytes moved, which is zero if there's no previous line.
 */
size_t block_iter_prev_line(BlockIter *bi)
{
    Block *blk = bi->blk;
    size_t offset = bi->offset;
    size_t start = offset;

    while (offset && blk->data[offset - 1] != '\n') {
        offset--;
    }

    if (!offset) {
        if (blk->node.prev == bi->head) {
            return 0;
        }
        bi->blk = blk = BLOCK(blk->node.prev);
        offset = blk->size;
        start += offset;
    }

    offset--;
    while (offset && blk->data[offset - 1] != '\n') {
        offset--;
    }
    bi->offset = offset;
    return start - offset;
}

size_t block_iter_get_char(const BlockIter *bi, CodePoint *up)
{
    BlockIter tmp = *bi;
    return block_iter_next_char(&tmp, up);
}

size_t block_iter_next_char(BlockIter *bi, CodePoint *up)
{
    size_t offset = bi->offset;
    if (unlikely(offset == bi->blk->size)) {
        if (unlikely(bi->blk->node.next == bi->head)) {
            return 0;
        }
        bi->blk = BLOCK(bi->blk->node.next);
        bi->offset = offset = 0;
    }

    // Note: this block can't be empty
    *up = bi->blk->data[offset];
    if (likely(*up < 0x80)) {
        bi->offset++;
        return 1;
    }

    *up = u_get_nonascii(bi->blk->data, bi->blk->size, &bi->offset);
    return bi->offset - offset;
}

size_t block_iter_prev_char(BlockIter *bi, CodePoint *up)
{
    size_t offset = bi->offset;
    if (unlikely(offset == 0)) {
        if (unlikely(bi->blk->node.prev == bi->head)) {
            return 0;
        }
        bi->blk = BLOCK(bi->blk->node.prev);
        bi->offset = offset = bi->blk->size;
    }

    // Note: this block can't be empty
    *up = bi->blk->data[offset - 1];
    if (likely(*up < 0x80)) {
        bi->offset--;
        return 1;
    }

    *up = u_prev_char(bi->blk->data, &bi->offset);
    return offset - bi->offset;
}

size_t block_iter_next_column(BlockIter *bi)
{
    CodePoint u;
    size_t size = block_iter_next_char(bi, &u);
    while (block_iter_get_char(bi, &u) && u_is_zero_width(u)) {
        size += block_iter_next_char(bi, &u);
    }
    return size;
}

size_t block_iter_prev_column(BlockIter *bi)
{
    CodePoint u;
    size_t skip, total = 0;
    do {
        skip = block_iter_prev_char(bi, &u);
        total += skip;
    } while (skip && u_is_zero_width(u));
    return total;
}

size_t block_iter_bol(BlockIter *bi)
{
    block_iter_normalize(bi);
    size_t offset = bi->offset;
    if (offset == 0 || offset == bi->blk->size) {
        return 0;
    }

    if (bi->blk->nl == 1) {
        offset = 0;
    } else {
        while (offset && bi->blk->data[offset - 1] != '\n') {
            offset--;
        }
    }

    const size_t ret = bi->offset - offset;
    bi->offset = offset;
    return ret;
}

size_t block_iter_eol(BlockIter *bi)
{
    block_iter_normalize(bi);
    const Block *blk = bi->blk;
    const size_t offset = bi->offset;
    if (unlikely(offset == blk->size)) {
        // Cursor at end of last block
        return 0;
    }
    if (blk->nl == 1) {
        bi->offset = blk->size - 1;
        return bi->offset - offset;
    }
    const unsigned char *end = memchr(blk->data + offset, '\n', blk->size - offset);
    BUG_ON(!end);
    bi->offset = (size_t)(end - blk->data);
    return bi->offset - offset;
}

void block_iter_back_bytes(BlockIter *bi, size_t count)
{
    while (count > bi->offset) {
        count -= bi->offset;
        bi->blk = BLOCK(bi->blk->node.prev);
        bi->offset = bi->blk->size;
    }
    bi->offset -= count;
}

void block_iter_skip_bytes(BlockIter *bi, size_t count)
{
    size_t avail = bi->blk->size - bi->offset;
    while (count > avail) {
        count -= avail;
        bi->blk = BLOCK(bi->blk->node.next);
        bi->offset = 0;
        avail = bi->blk->size;
    }
    bi->offset += count;
}

void block_iter_goto_offset(BlockIter *bi, size_t offset)
{
    Block *blk;
    block_for_each(blk, bi->head) {
        if (offset <= blk->size) {
            bi->blk = blk;
            bi->offset = offset;
            return;
        }
        offset -= blk->size;
    }
}

void block_iter_goto_line(BlockIter *bi, size_t line)
{
    Block *blk = BLOCK(bi->head->next);
    size_t nl = 0;
    while (blk->node.next != bi->head && nl + blk->nl < line) {
        nl += blk->nl;
        blk = BLOCK(blk->node.next);
    }

    bi->blk = blk;
    bi->offset = 0;
    while (nl < line) {
        if (!block_iter_eat_line(bi)) {
            break;
        }
        nl++;
    }
}

size_t block_iter_get_offset(const BlockIter *bi)
{
    const Block *blk;
    size_t offset = 0;
    block_for_each(blk, bi->head) {
        if (blk == bi->blk) {
            break;
        }
        offset += blk->size;
    }
    return offset + bi->offset;
}

char *block_iter_get_bytes(const BlockIter *bi, size_t len)
{
    if (len == 0) {
        return NULL;
    }

    const Block *blk = bi->blk;
    size_t offset = bi->offset;
    size_t pos = 0;
    char *buf = xmalloc(len);

    while (pos < len) {
        const size_t avail = blk->size - offset;
        size_t count = MIN(len - pos, avail);
        memcpy(buf + pos, blk->data + offset, count);
        pos += count;
        BUG_ON(pos < len && blk->node.next == bi->head);
        blk = BLOCK(blk->node.next);
        offset = 0;
    }

    return buf;
}

// bi should be at bol
void fill_line_nl_ref(BlockIter *bi, StringView *line)
{
    block_iter_normalize(bi);
    line->data = bi->blk->data + bi->offset;
    const size_t max = bi->blk->size - bi->offset;
    if (unlikely(max == 0)) {
        // Cursor at end of last block
        line->length = 0;
        return;
    }
    if (bi->blk->nl == 1) {
        BUG_ON(line->data[max - 1] != '\n');
        line->length = max;
        return;
    }
    const unsigned char *nl = memchr(line->data, '\n', max);
    BUG_ON(!nl);
    line->length = (size_t)(nl - line->data + 1);
    BUG_ON(line->length == 0);
}

void fill_line_ref(BlockIter *bi, StringView *line)
{
    fill_line_nl_ref(bi, line);
    // Trim the newline
    line->length -= (line->length > 0);
}

// Set the `line` argument to point to the current line and return
// the offset of the cursor, relative to the start of the line
// (zero means cursor is at bol)
size_t fetch_this_line(const BlockIter *bi, StringView *line)
{
    BlockIter tmp = *bi;
    size_t count = block_iter_bol(&tmp);
    fill_line_ref(&tmp, line);
    return count;
}