import { positionAt } from '../GPS/actions/arena/worldline.js'
import { Frustum } from './frustum.js'

export class RequestorRegistry {

    constructor(reader, getNow, scanIntervalMs, onPush, debug = false) {
        this.reader = reader
        this.getNow = getNow
        this.scanIntervalMs = scanIntervalMs
        this.onPush = onPush
        this.debug = debug
        this.requestors = new Map()
    }

    #tickTimer = null
    #scanInFlight = false

    #adjustFrequency(requestedMs) {
        if(typeof(requestedMs) !== 'number' || Number.isNaN(requestedMs)) return(null)
        if(requestedMs < 300 || requestedMs > 10000) return(null)
        const tickMs = this.scanIntervalMs
        const ticks = Math.round(requestedMs / tickMs)
        const minTicks = Math.ceil(300 / tickMs)
        const maxTicks = Math.floor(10000 / tickMs)
        const clampedTicks = Math.max(minTicks, Math.min(maxTicks, ticks))
        return(clampedTicks * tickMs)
    }

    async subscribeFrustum(id, { planes, frequency }) {
        if(!id || typeof(id) !== 'string') return({ ok: false, err: 'Invalid requestor id' })
        const frustum = Frustum.fromPlanes(planes)
        if(!frustum) return({ ok: false, err: 'Invalid frustum planes' })

        const frequencyMs = this.#adjustFrequency(frequency)
        if(frequencyMs === null) {
            return({ ok: false, err: 'Invalid frequency (expected 300–10000 ms)' })
        }

        const t = this.getNow()
        if(t === null) return({ ok: false, err: 'Simulation not live' })

        const agents = await this.reader.loadAllAgents()
        const matching = this.#matchAgents(agents, frustum, t)
        const pushEveryNTicks = frequencyMs / this.scanIntervalMs

        this.requestors.set(id, {
            id,
            frustum,
            tMode: 'live',
            subscription: true,
            frequencyMs,
            pushEveryNTicks,
            tickCounter: 0,
            agents: matching,
            t,
            updatedAt: Date.now(),
        })
        this.#ensureTick()

        return({
            ok: true,
            frequency: frequencyMs,
            agents: matching,
            t,
        })
    }

    updateRequestor(id, spec) {
        const requestor = this.requestors.get(id)
        if(!requestor) return({ ok: false, err: 'Unknown requestor' })
        if(Array.isArray(spec?.planes)) {
            const frustum = Frustum.fromPlanes(spec.planes)
            if(!frustum) return({ ok: false, err: 'Invalid frustum planes' })
            requestor.frustum = frustum
        }
        if(typeof(spec?.frequency) === 'number') {
            const frequencyMs = this.#adjustFrequency(spec.frequency)
            if(frequencyMs === null) return({ ok: false, err: 'Invalid frequency (expected 300–10000 ms)' })
            requestor.frequencyMs = frequencyMs
            requestor.pushEveryNTicks = frequencyMs / this.scanIntervalMs
            requestor.tickCounter = 0
        }
        return({ ok: true, frequency: requestor.frequencyMs })
    }

    unregisterRequestor(id) {
        this.requestors.delete(id)
        if(this.requestors.size === 0) this.#stopTick()
        return({ ok: true })
    }

    getRequestorAgents(id) {
        const requestor = this.requestors.get(id)
        if(!requestor) return(null)
        return({
            agents: [...requestor.agents],
            t: requestor.t,
            frequency: requestor.frequencyMs ?? null,
            updatedAt: requestor.updatedAt,
        })
    }

    clear() {
        this.requestors.clear()
        this.#stopTick()
    }

    async evaluateOnce({ frustum, t }) {
        if(!frustum || !(frustum instanceof Frustum)) {
            return({ ok: false, err: 'Invalid frustum', agents: [] })
        }
        if(typeof(t) !== 'number' || Number.isNaN(t)) return({ ok: false, err: 'Invalid simulation time', agents: [] })
        const agents = await this.reader.loadAllAgents()
        const matching = this.#matchAgents(agents, frustum, t)
        return({ ok: true, agents: matching, t })
    }

    #resolveT(requestor) {
        if(requestor.tMode === 'fixed') return(requestor.fixedT)
        return(this.getNow())
    }

    #matchAgents(agents, frustum, t) {
        const matching = []
        for(const agent of agents.values()) {
            const position = positionAt(agent, t)
            if(!frustum.containsPoint(position)) continue
            matching.push(this.reader.buildAgentSnapshot(agent, t))
        }
        return(matching)
    }

    #pushUpdate(requestor) {
        if(typeof(this.onPush) !== 'function') return
        this.onPush(requestor.id, {
            agents: [...requestor.agents],
            t: requestor.t,
        })
    }

    async #scanAll() {
        if(this.#scanInFlight || this.requestors.size === 0) return
        this.#scanInFlight = true
        try {
            const agents = await this.reader.loadAllAgents()
            for(const requestor of this.requestors.values()) {
                const t = this.#resolveT(requestor)
                if(t === null) {
                    requestor.agents = []
                    requestor.t = null
                    requestor.updatedAt = Date.now()
                    continue
                }
                requestor.agents = this.#matchAgents(agents, requestor.frustum, t)
                requestor.t = t
                requestor.updatedAt = Date.now()

                if(!requestor.subscription) continue

                requestor.tickCounter++
                if(requestor.tickCounter >= requestor.pushEveryNTicks) {
                    requestor.tickCounter = 0
                    this.#pushUpdate(requestor)
                }
            }
            if(this.debug) console.log(`[Observer] Scanned ${agents.size} agent(s) for ${this.requestors.size} requestor(s)`)
        } catch(err) {
            console.error('[Observer] Requestor scan failed:', err)
        } finally {
            this.#scanInFlight = false
        }
    }

    #ensureTick() {
        if(this.#tickTimer) return
        this.#tickTimer = setInterval(() => {
            this.#scanAll()
        }, this.scanIntervalMs)
    }

    #stopTick() {
        if(!this.#tickTimer) return
        clearInterval(this.#tickTimer)
        this.#tickTimer = null
    }

}