/* logic/reader/nav.c — 阅读导航纯逻辑实现（见 nav.h 的方向语义说明）。 */
#include "logic/reader/nav.h"

int mr_nav_tap_zone(int x, int view_w)
{
    if (view_w <= 0) return MR_ZONE_MIDDLE;
    if (x < view_w / 3) return MR_ZONE_LEFT;
    if (x >= (view_w * 2) / 3) return MR_ZONE_RIGHT;
    return MR_ZONE_MIDDLE;
}

int mr_nav_tap_delta(int rtl, int zone)
{
    if (zone == MR_ZONE_MIDDLE) return 0;
    if (rtl) return (zone == MR_ZONE_LEFT) ? 1 : -1;    /* RTL：左进右退 */
    return (zone == MR_ZONE_LEFT) ? -1 : 1;             /* LTR：右进左退 */
}

int mr_nav_swipe_delta(int rtl, int dx)
{
    if (dx == 0) return 0;
    if (rtl) return dx > 0 ? 1 : -1;
    return dx > 0 ? -1 : 1;
}

int mr_nav_clamp_page(int page, int count)
{
    if (count <= 0) return -1;
    if (page < 0) return 0;
    if (page >= count) return count - 1;
    return page;
}

int mr_nav_commit_dist(int view_w)
{
    int t = view_w / 4;
    if (t < 60) t = 60;
    if (t > 160) t = 160;
    return t;
}

int mr_nav_commit(int dx, int view_w)
{
    int adx = dx < 0 ? -dx : dx;
    return adx >= mr_nav_commit_dist(view_w);
}

int mr_nav_fit_size(int fit, int src_w, int src_h, int vw, int vh,
                    int *out_w, int *out_h)
{
    if (!out_w || !out_h || src_w <= 0 || src_h <= 0 || vw <= 0 || vh <= 0) return -1;
    long long w, h;
    if (fit == MR_FIT_ORIGINAL) {
        w = src_w;
        h = src_h;
    } else if (fit == MR_FIT_HEIGHT) {
        h = vh;
        w = (long long)src_w * vh / src_h;
    } else {
        w = vw;
        h = (long long)src_h * vw / src_w;
    }
    if (w < 1) w = 1;
    if (h < 1) h = 1;
    *out_w = (int)w;
    *out_h = (int)h;
    return 0;
}

int mr_nav_zoom_size(int w, int h, int zoom_pct, int *out_w, int *out_h)
{
    if (!out_w || !out_h || w <= 0 || h <= 0 || zoom_pct <= 0) return -1;
    long long ww = (long long)w * zoom_pct / 100;
    long long hh = (long long)h * zoom_pct / 100;
    if (ww < 1) ww = 1;
    if (hh < 1) hh = 1;
    *out_w = (int)ww;
    *out_h = (int)hh;
    return 0;
}

void mr_nav_pan_limit(int content_w, int content_h, int vw, int vh,
                      int *lim_x, int *lim_y)
{
    int lx = content_w - vw;
    int ly = content_h - vh;
    if (lx < 0) lx = 0;
    if (ly < 0) ly = 0;
    /* 平移量是「中心偏移」：可左右各移动溢出量的一半，两边才都看得到。 */
    if (lim_x) *lim_x = lx / 2;
    if (lim_y) *lim_y = ly / 2;
}

void mr_nav_pan_clamp(int content_w, int content_h, int vw, int vh,
                      int *pan_x, int *pan_y)
{
    int lx, ly;
    mr_nav_pan_limit(content_w, content_h, vw, vh, &lx, &ly);
    if (pan_x) {
        if (*pan_x > lx) *pan_x = lx;
        if (*pan_x < -lx) *pan_x = -lx;
    }
    if (pan_y) {
        if (*pan_y > ly) *pan_y = ly;
        if (*pan_y < -ly) *pan_y = -ly;
    }
}

int mr_nav_slide_from(int rtl, int delta, int view_w)
{
    if (!delta) return 0;
    int from = rtl ? -delta : delta;
    return from * view_w;
}

int mr_nav_fit_next(int fit)
{
    if (fit < 0 || fit >= MR_FIT_COUNT) return MR_FIT_WIDTH;
    return (fit + 1) % MR_FIT_COUNT;
}