Get mod name and relative ID for Skyrim mod (using Skyrim Platform)

ExampleUsage.ts

import { printConsole, Game } from "skyrimPlatform"
import { getFormInfo } from "./FormInfo"

export default function StartRuntime() {
    // ESPFE
    const justDesserts = Game.getFormFromFile(0x801, "JustDesserts.esp")
    const justDessertsInfo = getFormInfo(justDesserts!)
    printConsole(JSON.stringify(justDessertsInfo))
    // Prints out: {"modName":"JustDesserts.esp","relativeFormId":2049}

    // ESP
    const hailOfThorns = Game.getFormFromFile(0x800, "AdventurerLikeYou.esp")
    const hailOfThornsInfo = getFormInfo(hailOfThorns!)
    printConsole(JSON.stringify(hailOfThornsInfo))
    // Prints out: {"modName":"AdventurerLikeYou.esp","relativeFormId":2048}
}

FormInfo.ts

import { Game, Form } from "skyrimPlatform"

export interface FormInfo {
    modName: string,
    relativeFormId: number
}

export function getFormInfo(form: Form) {
    return getFormInfoFromId(form.getFormID())
}

export function getFormInfoFromId(formId: number): FormInfo | undefined {
    const hex = formId.toString(16)
    if (hex.toLowerCase().startsWith('ff')) {
        // FF are forms which were created at runtime (no source ESP/ESM/ESL)
        return
    } else if (hex.toLowerCase().startsWith('fe')) {
        // FExxxYYY
        const index = parseInt(hex.substr(2, 3), 16)
        const relativeId = parseInt(hex.substr(5, 3), 16)
        const modName = Game.getLightModName(index)
        return {
            modName: modName,
            relativeFormId: relativeId
        }
    } else {
        // xxYYYYYY
        const index = parseInt(hex.substr(0, 2), 16)
        const relativeId = parseInt(hex.substr(2, 6), 16)
        const modName = Game.getModName(index)
        return {
            modName: modName,
            relativeFormId: relativeId
        }
    }
}

FormInfoWithCache.ts

// If you have LOTS and LOTS of forms and you want to make fewer native function invocations
// then you could cache the mod names for each mod index.
//
// I haven't tested this version, but it uses a cache so you'll only ever make a `Game.*` native
// invocation *ONCE* per each unique mod.

import { Game, Form } from "skyrimPlatform"

const lightMods = new Map<number, string>() // I forget whether the IDs can collide,
const fullMods  = new Map<number, string>() // I don't actually know why Game has getLightModName
                                            // There is no reason to have 2 separate maps but 🤷‍♀️

export interface FormInfo {
    modName: string,
    relativeFormId: number
}

export function getFormInfo(form: Form) {
    return getFormInfoFromId(form.getFormID())
}

export function getFormInfoFromId(formId: number): FormInfo | undefined {
    const hex = formId.toString(16)
    if (hex.toLowerCase().startsWith('ff')) {
        // FF are forms which were created at runtime (no source ESP/ESM/ESL)
        return
    } else if (hex.toLowerCase().startsWith('fe')) {
        // FExxxYYY
        const index = parseInt(hex.substr(2, 3), 16)
        const relativeId = parseInt(hex.substr(5, 3), 16)
        let modName = "" 
        if (lightMods.has(index)) {
          modName = lightMods.get(index)
        } else {
          modName = Game.getLightModName(index)
          lightMods.set(index, modName)
        }
        return {
            modName: modName,
            relativeFormId: relativeId
        }
    } else {
        // xxYYYYYY
        const index = parseInt(hex.substr(0, 2), 16)
        const relativeId = parseInt(hex.substr(2, 6), 16)
        let modName = "" 
        if (fullMods.has(index)) {
          modName = fullMods.get(index)
        } else {
          modName = Game.getModName(index)
          fullMods.set(index, modName)
        }
        return {
            modName: modName,
            relativeFormId: relativeId
        }
    }
}