#include "line_index.h"
#include <stdlib.h>
#include <string.h>

#define LINE_IX_DYNAMIC_INIT 256

static size_t scan_line_end(const char *input, size_t len, size_t pos)
{
    const char *hit = memchr(input + pos, '\n', len - pos);
    return hit ? (size_t)(hit - input) : len;
}

static size_t scan_skip_line(const char *input, size_t len, size_t pos)
{
    pos = scan_line_end(input, len, pos);
    if (pos < len)
        pos++;
    return pos;
}

static int line_index_ensure(line_index_t *ix, uint32_t need_slots)
{
    if (need_slots <= ix->cap)
        return 0;
    if (!ix->owned) {
        ix->valid = 0;
        return -1;
    }
    uint32_t cap = ix->cap ? ix->cap : LINE_IX_DYNAMIC_INIT;
    while (cap < need_slots)
        cap *= 2;
    uint32_t *p = (uint32_t *)realloc(ix->off, (size_t)cap * sizeof(uint32_t));
    if (!p) {
        ix->valid = 0;
        return -1;
    }
    ix->off = p;
    ix->cap = cap;
    return 0;
}

int line_index_init_dynamic(line_index_t *ix, uint32_t initial_cap)
{
    if (!ix)
        return -1;
    if (initial_cap < 2)
        initial_cap = LINE_IX_DYNAMIC_INIT;
    uint32_t *off = (uint32_t *)malloc((size_t)initial_cap * sizeof(uint32_t));
    if (!off)
        return -1;
    ix->off = off;
    ix->cap = initial_cap;
    ix->n = 1;
    ix->off[0] = 0;
    ix->off[1] = 0;
    ix->cur = 0;
    ix->valid = 1;
    ix->owned = 1;
    return 0;
}

void line_index_free(line_index_t *ix)
{
    if (!ix)
        return;
    if (ix->owned) {
        free(ix->off);
        ix->off = NULL;
        ix->owned = 0;
        ix->cap = 0;
    }
}

void line_index_build(const char *input, size_t len, line_index_t *ix)
{
    ix->n = 1;
    ix->off[0] = 0;
    ix->cur = 0;
    ix->valid = 1;

    const char *start = input;
    const char *end = input + len;
    const char *hit;
    while ((hit = memchr(start, '\n', (size_t)(end - start))) != NULL) {
        if (ix->n + 1 >= ix->cap) {
            if (line_index_ensure(ix, ix->n + 2) != 0)
                return;
        }
        ix->off[ix->n++] = (uint32_t)(hit - input) + 1;
        start = hit + 1;
    }
    if (ix->n >= ix->cap) {
        if (line_index_ensure(ix, ix->n + 1) != 0)
            return;
    }
    ix->off[ix->n] = (uint32_t)len;
}

size_t line_index_extend(line_index_t *ix, const char *input,
                         size_t old_len, size_t new_len)
{
    if (!ix || !ix->valid || new_len <= old_len)
        return 0;

    size_t last_nl = 0;
    const char *start = input + old_len;
    const char *end = input + new_len;
    const char *hit;
    while ((hit = memchr(start, '\n', (size_t)(end - start))) != NULL) {
        if (ix->n + 1 >= ix->cap) {
            if (line_index_ensure(ix, ix->n + 2) != 0)
                return last_nl;
        }
        last_nl = (size_t)(hit - input) + 1;
        ix->off[ix->n++] = (uint32_t)last_nl;
        start = hit + 1;
    }
    if (ix->n >= ix->cap) {
        if (line_index_ensure(ix, ix->n + 1) != 0)
            return last_nl;
    }
    ix->off[ix->n] = (uint32_t)new_len;
    return last_nl;
}

static uint32_t line_no(const line_index_t *ix, size_t pos)
{
    uint32_t lo = 0;
    uint32_t hi = ix->n;
    while (lo + 1 < hi) {
        uint32_t mid = (lo + hi) / 2;
        if (ix->off[mid] <= pos)
            lo = mid;
        else
            hi = mid;
    }
    return lo;
}

void line_index_seek(line_index_t *ix, size_t pos)
{
    if (!ix || !ix->valid)
        return;
    ix->cur = line_no(ix, pos);
}

static uint32_t resolve_line(line_index_t *ix, size_t pos)
{
    /* Sequential hot path: render walks lines in order. */
    if (ix->cur < ix->n && ix->off[ix->cur] == (uint32_t)pos)
        return ix->cur;
    if (ix->cur + 1 < ix->n && ix->off[ix->cur + 1] == (uint32_t)pos) {
        ix->cur++;
        return ix->cur;
    }
    ix->cur = line_no(ix, pos);
    return ix->cur;
}

size_t line_end_ix(line_index_t *ix, const char *input, size_t len, size_t pos)
{
    if (!ix || !ix->valid)
        return scan_line_end(input, len, pos);

    uint32_t k = resolve_line(ix, pos);
    size_t next = (size_t)ix->off[k + 1];
    if (next > 0 && next <= len && input[next - 1] == '\n')
        return next - 1;
    return next <= len ? next : len;
}

size_t skip_line_ix(line_index_t *ix, const char *input, size_t len, size_t pos)
{
    if (!ix || !ix->valid)
        return scan_skip_line(input, len, pos);

    uint32_t k = resolve_line(ix, pos);
    size_t next = (size_t)ix->off[k + 1];
    if (next > len)
        return len;
    /* Advance cursor to the next line start (may equal n at EOF). */
    ix->cur = k + 1;
    return next;
}