/** 运动帧间隔窗口（票 59 采样口径修正）。
 *
 * 为什么需要：导出里的 movingFrameIntervals 曾把"静止→运动"的第一段也收进窗口，
 * 而这一段包含按需渲染（requestRenderMode）的空档，几百毫秒的假尖峰正是这样来的；
 * 反过来，真正的长停顿又因 1000ms 上限被静默丢弃、连计数都没有。
 *
 * 现在的口径：只收**连续运动帧之间**的间隔（上一帧也在运动）。起步段、隐藏期、
 * 以及 >=maxGapMs 的空档都不进窗口，但都会被**计数**并保留最大被排除值，
 * 所以既去掉起步空档，也不会把长停顿藏起来。
 */
export const MOTION_WINDOW_DEFAULTS = { maxSamples: 240, maxGapMs: 1000 }

/**
 * @param {{maxSamples?: number, maxGapMs?: number}} [options]
 * @returns {{push: (tMs: number, moving: boolean) => string, markGap: (tMs: number) => void,
 *   reset: () => void, snapshot: () => object}}
 */
export function createMotionIntervalWindow(options = {}) {
    const configured = Number(options.maxSamples)
    const maxSamples = Number.isFinite(configured) && configured >= 1
        ? Math.trunc(configured)
        : MOTION_WINDOW_DEFAULTS.maxSamples
    const ceiling = Number(options.maxGapMs)
    const maxGapMs = Number.isFinite(ceiling) ? ceiling : MOTION_WINDOW_DEFAULTS.maxGapMs
    let intervals = []
    let previous = null
    let restartGapsExcluded = 0
    let longGapsExcluded = 0
    let maxExcludedMs = null
    const exclude = (kind, dt) => {
        if (kind === 'restart-gap') restartGapsExcluded += 1
        else longGapsExcluded += 1
        if (maxExcludedMs === null || dt > maxExcludedMs) maxExcludedMs = dt
        return kind
    }
    return {
        /** @returns {'first'|'sampled'|'restart-gap'|'long-gap'|'idle'} */
        push(tMs, moving) {
            const at = Number(tMs)
            if (!Number.isFinite(at)) return 'idle'
            const isMoving = !!moving
            if (previous === null) { previous = { at, moving: isMoving }; return 'first' }
            const dt = at - previous.at
            const wasMoving = previous.moving
            previous = { at, moving: isMoving }
            if (!isMoving || dt <= 0) return 'idle'
            if (!wasMoving) return exclude('restart-gap', dt)
            if (dt >= maxGapMs) return exclude('long-gap', dt)
            intervals.push(dt)
            if (intervals.length > maxSamples) intervals.shift()
            return 'sampled'
        },
        /** 隐藏期间的帧不采样，但必须打断"连续运动"，否则恢复可见的首段会被当成连续帧。 */
        markGap(tMs) {
            const at = Number(tMs)
            if (Number.isFinite(at)) previous = { at, moving: false }
        },
        reset() {
            intervals = []
            previous = null
            restartGapsExcluded = 0
            longGapsExcluded = 0
            maxExcludedMs = null
        },
        snapshot() {
            const sorted = [...intervals].sort((a, b) => a - b)
            return {
                samples: sorted.length,
                p50Ms: sorted.length ? +sorted[Math.floor(sorted.length * .5)].toFixed(2) : null,
                p95Ms: sorted.length ? +sorted[Math.min(sorted.length - 1, Math.floor(sorted.length * .95))].toFixed(2) : null,
                maxMs: sorted.length ? +sorted[sorted.length - 1].toFixed(2) : null,
                over50Ms: sorted.filter(n => n > 50).length,
                restartGapsExcluded,
                longGapsExcluded,
                maxExcludedMs: maxExcludedMs === null ? null : +maxExcludedMs.toFixed(2),
            }
        },
    }
}