/*
 * meow_ui_scroll.c — 滚动物理（§12.3）。
 *
 * 速度采样：track 时把 (pos, t) 记进定长环形（≤MEOW_SCROLL_SAMPLES），fling 时取
 * 最近 MEOW_SCROLL_WINDOW ms 窗口，按「间隔速度 × 近者权重」加权得出初速（px/s）。
 * 位置模型：ease-out quad 的位移曲线（末速恰为 0），初速与输入 v 对齐，时长 = 2×tau。
 * 边界：free 目标越界 → clamp 到 [0,max]；若越界速度大 → 补两段短 IN_OUT 回弹
 * （overshoot 超过边界方向的内侧再回位），不做弹簧。停止后可选 snap 到 step 倍数。
 *
 * 不引 libm（SDK 约定，免 -lm）；只用整数 + 纯浮点四则。
 */
#include "meow_ui.h"
#include "include/meow_ui_scroll.h"
#include "meow_ui_internal.h"   /* meow_widget_rect（定位 redraw 视口区） */
#include "include/meow_ui_anim.h"
#include <string.h>

#define MEOW_SCROLL_POOL      8
#define MEOW_SCROLL_SAMPLES   8            /* 速度采样点数（最近 N 加权） */
#define MEOW_SCROLL_WINDOW    110          /* 速度窗口（ms） */
#define MEOW_SCROLL_TAU       180          /* 默认摩擦时间常数（ms） */
#define MEOW_SCROLL_MIN_SPEED 60           /* 低于此的初速不 fling（px/s） */
#define MEOW_SCROLL_MAX_DUR   900          /* fling 时长上限（ms） */
#define MEOW_SCROLL_BOUNCE_MS 110          /* 每段回弹时长（ms） */
#define MEOW_SCROLL_SNAP_MS   120

typedef enum {
    MEOW_SCROLL_IDLE = 0,
    MEOW_SCROLL_FLING,
    MEOW_SCROLL_BOUNCE1,
    MEOW_SCROLL_BOUNCE2,
    MEOW_SCROLL_SNAP,
} meow_scroll_phase;

struct meow_scroll {
    meow_scroll_set_fn    set;
    meow_scroll_max_fn    max;
    meow_scroll_get_fn    get;
    meow_scroll_redraw_fn redraw;
    void                 *ctx;

    int snap_step;          /* >0 = 吸附步长 */
    int tau_ms;             /* 摩擦时间常数 */
    /* 速度采样（顺序数组，满则前移，≤SAMPLES） */
    int      v_pos[MEOW_SCROLL_SAMPLES];
    uint64_t v_t[MEOW_SCROLL_SAMPLES];
    int      v_n;

    meow_scroll_phase phase;
    meow_anim        *anim;
    int               maxv;         /* fling 开始时缓存 max_scroll */
    int               bounce;       /* fling 边界回弹幅度（带符号；0=不回弹） */
    int               bounce_start; /* 回弹回位起点（= clamp 边界） */
    int               snap_to;      /* snap 目标 */
};

static meow_scroll g_pool[MEOW_SCROLL_POOL];
static unsigned char g_used[MEOW_SCROLL_POOL];

/* ---- 生命周期 ---- */
meow_scroll *meow_scroll_create(meow_scroll_set_fn set, meow_scroll_max_fn max,
                                meow_scroll_get_fn get, meow_scroll_redraw_fn redraw,
                                void *ctx)
{
    if (!set || !max || !get) return NULL;
    for (int i = 0; i < MEOW_SCROLL_POOL; i++) {
        if (!g_used[i]) {
            g_used[i] = 1;
            meow_scroll *s = &g_pool[i];
            memset(s, 0, sizeof *s);
            s->set = set; s->max = max; s->get = get; s->redraw = redraw; s->ctx = ctx;
            s->tau_ms = MEOW_SCROLL_TAU;
            return s;
        }
    }
    return NULL;
}
void meow_scroll_free(meow_scroll *s)
{
    if (!s) return;
    if (s->anim) meow_anim_cancel(s->anim);
    s->anim = NULL;
    for (int i = 0; i < MEOW_SCROLL_POOL; i++)
        if (&g_pool[i] == s) { g_used[i] = 0; return; }
}

/* ---- wrap：包一个 meow_widget 列表 ---- */
typedef struct { meow_widget *w; int lv; } wrap_ctx;
static void wrap_set(void *c, int off)
{ wrap_ctx *wc = c; if (wc->lv) meow_listview_set_scroll(wc->w, off); else meow_list_set_scroll(wc->w, off); }
static int  wrap_max(void *c)
{ wrap_ctx *wc = c; return wc->lv ? meow_listview_max_scroll(wc->w) : meow_list_max_scroll(wc->w); }
static int  wrap_get(void *c)
{ wrap_ctx *wc = c; return wc->lv ? meow_listview_scroll(wc->w) : meow_list_scroll(wc->w); }
static void wrap_redraw(void *c)
{
    wrap_ctx *wc = c;
    if (!wc->w) return;
    int r[4]; meow_widget_rect(wc->w, r);
    if (r[2] > 0 && r[3] > 0) meow_ui_flush_region(r[0], r[1], r[2], r[3]);   /* 只刷视口区 */
}

static wrap_ctx g_wrap_ctx[MEOW_SCROLL_POOL];
static int g_wrap_used[MEOW_SCROLL_POOL];

meow_scroll *meow_scroll_wrap(meow_widget *list, int is_listview)
{
    if (!list) return NULL;
    meow_scroll *s = meow_scroll_create(wrap_set, wrap_max, wrap_get, wrap_redraw, NULL);
    if (!s) return NULL;
    for (int i = 0; i < MEOW_SCROLL_POOL; i++) {
        if (!g_wrap_used[i]) {
            g_wrap_used[i] = 1;
            g_wrap_ctx[i].w = list; g_wrap_ctx[i].lv = is_listview ? 1 : 0;
            s->ctx = &g_wrap_ctx[i];
            return s;
        }
    }
    meow_scroll_free(s);
    return NULL;
}

/* ---- 速度采样 ---- */
static void sample_push(meow_scroll *s, int pos, uint64_t t)
{
    if (s->v_n >= MEOW_SCROLL_SAMPLES) {   /* 满：前移丢弃最旧 */
        for (int i = 1; i < s->v_n; i++) { s->v_pos[i - 1] = s->v_pos[i]; s->v_t[i - 1] = s->v_t[i]; }
        s->v_n--;
    }
    s->v_pos[s->v_n] = pos; s->v_t[s->v_n] = t; s->v_n++;
}

/* 加权初速：取窗口内采样，按间隔速度 × 近者权重加权平均（px/s）。 */
static int sample_velocity(meow_scroll *s, uint64_t now)
{
    int lo = 0;
    while (lo < s->v_n && now > s->v_t[lo] && (now - s->v_t[lo]) > MEOW_SCROLL_WINDOW) lo++;
    if (s->v_n - lo < 2) return 0;
    long long sum_w = 0, sum_vw = 0;
    for (int i = lo; i < s->v_n - 1; i++) {
        uint64_t dt = s->v_t[i + 1] - s->v_t[i];
        if (dt == 0) continue;
        long long v = (long long)(s->v_pos[i + 1] - s->v_pos[i]) * 1000LL / (long long)dt;
        long long w = (i - lo + 1);   /* 近者权重高 */
        sum_vw += v * w; sum_w += w;
    }
    if (sum_w == 0) return 0;
    return (int)(sum_vw / sum_w);
}

int meow_scroll_velocity(meow_scroll *s)
{
    if (!s) return 0;
    return sample_velocity(s, meow_ui_time_ms());
}

void meow_scroll_track(meow_scroll *s, int dy, uint64_t t_ms)
{
    if (!s || dy == 0) return;
    int off = s->get(s->ctx) + dy;   /* set 会 clamp 到 [0,max]（与 scroll_by 一致） */
    s->set(s->ctx, off);
    int got = s->get(s->ctx);        /* clamp 后的真实 offset */
    sample_push(s, got, t_ms);
}

/* ---- 动画驱动回调 ---- */
static void fling_update(meow_anim *a, float v, void *ctx)
{
    (void)a;
    meow_scroll *s = (meow_scroll *)ctx;
    s->set(s->ctx, (int)v);
    if (s->redraw) s->redraw(s->ctx);
}
static void fling_done(meow_anim *a, int canceled, void *ctx)
{
    (void)a;
    meow_scroll *s = (meow_scroll *)ctx;
    s->anim = NULL;
    if (canceled) { s->phase = MEOW_SCROLL_IDLE; return; }
    if (s->phase == MEOW_SCROLL_FLING) {
        if (s->bounce != 0) {
            /* 边界回弹段1：向内侧过冲 → 段2 回位（bounce 已带符号；顶界 +，底界 -） */
            int from = s->get(s->ctx);
            int to = from + s->bounce;        /* bounce 已带符号 */
            if (to < 0) to = 0;
            if (to > s->maxv) to = s->maxv;
            if (to == from) { s->phase = MEOW_SCROLL_IDLE; return; }
            s->phase = MEOW_SCROLL_BOUNCE1;
            meow_anim_desc d; memset(&d, 0, sizeof d);
            d.from = (float)from; d.to = (float)to; d.duration_ms = MEOW_SCROLL_BOUNCE_MS;
            d.ease = MEOW_EASE_IN_OUT; d.update = fling_update; d.done = fling_done; d.ctx = s;
            s->anim = meow_anim_start(&d);
            return;
        }
        /* 无回弹 → snap 或收尾 */
        if (s->snap_step > 0 && s->get(s->ctx) != s->snap_to) {
            int from = s->get(s->ctx);
            int to = s->snap_to;
            if (to < 0) to = 0;
            if (to > s->maxv) to = s->maxv;
            if (to != from) {
                s->phase = MEOW_SCROLL_SNAP;
                meow_anim_desc d; memset(&d, 0, sizeof d);
                d.from = (float)from; d.to = (float)to; d.duration_ms = MEOW_SCROLL_SNAP_MS;
                d.ease = MEOW_EASE_IN_OUT; d.update = fling_update; d.done = fling_done; d.ctx = s;
                s->anim = meow_anim_start(&d);
                return;
            }
        }
        s->phase = MEOW_SCROLL_IDLE;
        return;
    }
    if (s->phase == MEOW_SCROLL_BOUNCE1) {
        int from = s->get(s->ctx);
        /* 回位到 bounce 起点（= clamp 边界） */
        int to = s->bounce_start;
        if (to < 0) to = 0;
        if (to > s->maxv) to = s->maxv;
        s->phase = MEOW_SCROLL_BOUNCE2;
        if (to == from) { s->phase = MEOW_SCROLL_IDLE; return; }
        meow_anim_desc d; memset(&d, 0, sizeof d);
        d.from = (float)from; d.to = (float)to; d.duration_ms = MEOW_SCROLL_BOUNCE_MS;
        d.ease = MEOW_EASE_IN_OUT; d.update = fling_update; d.done = fling_done; d.ctx = s;
        s->anim = meow_anim_start(&d);
        return;
    }
    if (s->phase == MEOW_SCROLL_BOUNCE2 || s->phase == MEOW_SCROLL_SNAP) {
        s->phase = MEOW_SCROLL_IDLE;
        return;
    }
    s->phase = MEOW_SCROLL_IDLE;
}

/* ---- fling ---- */
void meow_scroll_fling(meow_scroll *s)
{
    if (!s) return;
    if (s->anim) { meow_anim_cancel(s->anim); s->anim = NULL; }
    s->phase = MEOW_SCROLL_IDLE;
    int v = sample_velocity(s, meow_ui_time_ms());
    if (v > -MEOW_SCROLL_MIN_SPEED && v < MEOW_SCROLL_MIN_SPEED) return;   /* 太慢不 fling */
    int max = s->max(s->ctx);
    if (max < 0) max = 0;
    s->maxv = max;
    int pos0 = s->get(s->ctx);
    int dist = (int)((long long)v * s->tau_ms / 1000LL);   /* 摩擦滑行总位移（px） */
    int free_target = pos0 + dist;
    int clamped = free_target, over = 0;
    if (clamped > max) { over = clamped - max; clamped = max; }
    if (clamped < 0)   { over = -clamped; clamped = 0; }
    if (clamped == pos0) return;   /* 无位移 */

    int dir;                          /* 回弹方向：底界向 -1（往内上），顶界向 +1（往内下） */
    if (free_target > max) dir = -1;
    else if (free_target < 0) dir = 1;
    else dir = 0;

    int dur = 2 * s->tau_ms;          /* ease-out quad：初速与 v 对齐，末速为 0 */
    if (dur > MEOW_SCROLL_MAX_DUR) dur = MEOW_SCROLL_MAX_DUR;

    s->bounce = 0;
    s->snap_to = pos0;
    if (s->snap_step > 0) {
        int half = s->snap_step / 2;
        s->snap_to = ((pos0 + half) / s->snap_step) * s->snap_step;
        if (s->snap_to > max) s->snap_to = max;
    }
    if (over > 12) {                 /* 快速撞墙：clamp + 简单回弹 */
        int amt = over / 10; if (amt < 3) amt = 3; if (amt > 14) amt = 14;
        s->bounce = dir * amt;       /* 带符号的向内幅度 */
        /* 记录回位起点 = clamp 边界 */
        s->bounce_start = clamped;
    }

    s->phase = MEOW_SCROLL_FLING;
    meow_anim_desc d; memset(&d, 0, sizeof d);
    d.from = (float)pos0; d.to = (float)clamped; d.duration_ms = (uint32_t)dur;
    d.ease = MEOW_EASE_OUT; d.update = fling_update; d.done = fling_done; d.ctx = s;
    s->anim = meow_anim_start(&d);
}

void meow_scroll_stop(meow_scroll *s)
{
    if (!s) return;
    if (s->anim) { meow_anim_cancel(s->anim); s->anim = NULL; }
    s->phase = MEOW_SCROLL_IDLE;
}

int  meow_scroll_active(meow_scroll *s) { return (s && s->phase != MEOW_SCROLL_IDLE) ? 1 : 0; }
int  meow_scroll_offset(meow_scroll *s) { return s ? s->get(s->ctx) : 0; }
void meow_scroll_set_snap(meow_scroll *s, int step) { if (s) s->snap_step = step > 0 ? step : 0; }
void meow_scroll_set_friction(meow_scroll *s, int tau_ms)
{ if (s) s->tau_ms = (tau_ms > 20 && tau_ms <= 2000) ? tau_ms : MEOW_SCROLL_TAU; }