export type RendererProcessRssUnavailableReason =
    | 'renderer-os-pid-invalid'
    | 'renderer-process-identity-changed'
    | 'renderer-process-metric-ambiguous'
    | 'renderer-process-metric-creation-time-invalid'
    | 'renderer-process-metric-missing-at-start'
    | 'renderer-process-metric-missing-during-capture'
    | 'renderer-process-metric-type-invalid'
    | 'renderer-process-metric-working-set-invalid';

export interface RendererProcessIdentity {
    readonly creationTime: number;
    readonly pid: number;
}

export interface RendererProcessRssCapture {
    readonly identity: RendererProcessIdentity | null;
    readonly missingSampleCount: number;
    readonly peakRssBytes: number | null;
    readonly unavailableReason: RendererProcessRssUnavailableReason | null;
    readonly validSampleCount: number;
}

export interface RendererProcessRssCaptureApi {
    readonly create: (
        webContentsOsPid: unknown,
        processMetrics: readonly unknown[]
    ) => RendererProcessRssCapture;
    readonly sample: (
        capture: RendererProcessRssCapture,
        webContentsOsPid: unknown,
        processMetrics: readonly unknown[]
    ) => RendererProcessRssCapture;
}

export function createRendererProcessRssCaptureApi(): RendererProcessRssCaptureApi {
    type JsonRecord = Record<string, unknown>;

    const KIBIBYTE_BYTES = 1_024;
    const MAX_WORKING_SET_KIB = Math.floor(
        Number.MAX_SAFE_INTEGER / KIBIBYTE_BYTES
    );

    const helpers = {
        readRecord(value: unknown): JsonRecord | null {
            return typeof value === 'object' && value !== null
                ? (value as JsonRecord)
                : null;
        },

        isValidOsPid(value: unknown): value is number {
            return Number.isSafeInteger(value) && Number(value) > 0;
        },

        findPidCandidates(
            processMetrics: readonly unknown[],
            pid: number
        ): JsonRecord[] {
            return processMetrics
                .map((metric) => helpers.readRecord(metric))
                .filter(
                    (metric): metric is JsonRecord =>
                        metric !== null && metric['pid'] === pid
                );
        },

        readMetric(metric: JsonRecord):
            | {
                  readonly creationTime: number;
                  readonly rssBytes: number;
              }
            | RendererProcessRssUnavailableReason {
            if (metric['type'] !== 'Tab' && metric['type'] !== 'Renderer') {
                return 'renderer-process-metric-type-invalid';
            }

            const creationTime = metric['creationTime'];
            if (
                typeof creationTime !== 'number' ||
                !Number.isFinite(creationTime) ||
                creationTime < 0
            ) {
                return 'renderer-process-metric-creation-time-invalid';
            }

            const memory = helpers.readRecord(metric['memory']);
            const workingSetSize = memory?.['workingSetSize'];
            if (
                !Number.isSafeInteger(workingSetSize) ||
                Number(workingSetSize) <= 0 ||
                Number(workingSetSize) > MAX_WORKING_SET_KIB
            ) {
                return 'renderer-process-metric-working-set-invalid';
            }

            return {
                creationTime,
                rssBytes: Number(workingSetSize) * KIBIBYTE_BYTES,
            };
        },

        unavailableCapture(
            unavailableReason: RendererProcessRssUnavailableReason,
            options: {
                readonly identity?: RendererProcessIdentity | null;
                readonly missingSampleCount?: number;
                readonly validSampleCount?: number;
            } = {}
        ): RendererProcessRssCapture {
            return Object.freeze({
                identity: options.identity ?? null,
                missingSampleCount: options.missingSampleCount ?? 0,
                peakRssBytes: null,
                unavailableReason,
                validSampleCount: options.validSampleCount ?? 0,
            });
        },

        invalidateCapture(
            capture: RendererProcessRssCapture,
            unavailableReason: RendererProcessRssUnavailableReason,
            missingSampleCount = capture.missingSampleCount
        ): RendererProcessRssCapture {
            return helpers.unavailableCapture(unavailableReason, {
                identity: capture.identity,
                missingSampleCount,
                validSampleCount: capture.validSampleCount,
            });
        },

        create(
            webContentsOsPid: unknown,
            processMetrics: readonly unknown[]
        ): RendererProcessRssCapture {
            if (!helpers.isValidOsPid(webContentsOsPid)) {
                return helpers.unavailableCapture('renderer-os-pid-invalid');
            }

            const candidates = helpers.findPidCandidates(
                processMetrics,
                webContentsOsPid
            );
            if (candidates.length === 0) {
                return helpers.unavailableCapture(
                    'renderer-process-metric-missing-at-start',
                    {
                        missingSampleCount: 1,
                    }
                );
            }
            if (candidates.length !== 1) {
                return helpers.unavailableCapture(
                    'renderer-process-metric-ambiguous'
                );
            }

            const metric = helpers.readMetric(candidates[0] as JsonRecord);
            if (typeof metric === 'string') {
                return helpers.unavailableCapture(metric);
            }

            return Object.freeze({
                identity: Object.freeze({
                    creationTime: metric.creationTime,
                    pid: webContentsOsPid,
                }),
                missingSampleCount: 0,
                peakRssBytes: metric.rssBytes,
                unavailableReason: null,
                validSampleCount: 1,
            });
        },

        sample(
            capture: RendererProcessRssCapture,
            webContentsOsPid: unknown,
            processMetrics: readonly unknown[]
        ): RendererProcessRssCapture {
            if (capture.unavailableReason !== null) {
                return capture;
            }
            if (!helpers.isValidOsPid(webContentsOsPid)) {
                return helpers.invalidateCapture(
                    capture,
                    'renderer-os-pid-invalid'
                );
            }

            const identity = capture.identity;
            if (identity === null || webContentsOsPid !== identity.pid) {
                return helpers.invalidateCapture(
                    capture,
                    'renderer-process-identity-changed'
                );
            }

            const candidates = helpers.findPidCandidates(
                processMetrics,
                webContentsOsPid
            );
            if (candidates.length === 0) {
                return helpers.invalidateCapture(
                    capture,
                    'renderer-process-metric-missing-during-capture',
                    capture.missingSampleCount + 1
                );
            }
            if (candidates.length !== 1) {
                return helpers.invalidateCapture(
                    capture,
                    'renderer-process-metric-ambiguous'
                );
            }

            const metric = helpers.readMetric(candidates[0] as JsonRecord);
            if (typeof metric === 'string') {
                return helpers.invalidateCapture(capture, metric);
            }
            if (metric.creationTime !== identity.creationTime) {
                return helpers.invalidateCapture(
                    capture,
                    'renderer-process-identity-changed'
                );
            }

            return Object.freeze({
                identity,
                missingSampleCount: capture.missingSampleCount,
                peakRssBytes: Math.max(
                    capture.peakRssBytes ?? metric.rssBytes,
                    metric.rssBytes
                ),
                unavailableReason: null,
                validSampleCount: capture.validSampleCount + 1,
            });
        },
    };

    return Object.freeze({
        create: helpers.create,
        sample: helpers.sample,
    });
}

const rendererProcessRssCaptureApi = createRendererProcessRssCaptureApi();

export function createRendererProcessRssCapture(
    webContentsOsPid: unknown,
    processMetrics: readonly unknown[]
): RendererProcessRssCapture {
    return rendererProcessRssCaptureApi.create(
        webContentsOsPid,
        processMetrics
    );
}

export function captureRendererProcessRssSample(
    capture: RendererProcessRssCapture,
    webContentsOsPid: unknown,
    processMetrics: readonly unknown[]
): RendererProcessRssCapture {
    return rendererProcessRssCaptureApi.sample(
        capture,
        webContentsOsPid,
        processMetrics
    );
}