paradox-save-parser-frontend/src/services/SaveParserBackendService.ts

import { PROXY_PATHS } from '@/app/api/proxy/paths'
import type { SaveUploadConfig } from '@/config/AppConfig'
import { GameEnum } from '@/config/games'
import { packSaveForUpload, StageCallback } from '@/lib/saveArchive/client'
import { OriginalFileType } from '@/lib/saveArchive/messages'
import { createZstdDecompressStream } from '@/lib/saveArchive/zstdStream'

export interface UploadSaveResponse {
    id: string
}

export interface SaveStatusResponse {
    id: string
    game: string
    status: string
    uploadDateTime: string
    // Shape the save had when it was uploaded, needed to rebuild a file the
    // game can load again.
    originalFileType: OriginalFileType
    originalFileName: string
}

// Tries to read  the response body as string, returning an empty string if that fails.
async function getBodyTextOrEmpty(res: Response): Promise<string> {
    try {
        return await res.text()
    } catch {
        return ''
    }
}

export class SaveParserBackendService {
    private API_BASE = PROXY_PATHS.saveParserBackend

    /**
     * Re-compresses a save file and uploads it, returning its assigned id.
     *
     * Saves are not uploaded as the game wrote them. Plain text and archived
     * saves are both packed into a tar inside a zstd frame, which is a lot
     * smaller than the game's own zip and cheap for the backend to unpack.
     * The shape the file originally had travels along, so it can be rebuilt
     * when someone downloads the save later.
     */
    async uploadSave(
        game: GameEnum,
        file: File,
        config: SaveUploadConfig,
        onStage: StageCallback
    ): Promise<UploadSaveResponse> {
        const save = await packSaveForUpload(game, file, config, onStage)
        onStage('uploading')

        const url =
            `${this.API_BASE}/uploadSave?game=${encodeURIComponent(game)}` +
            `&originalFileType=${encodeURIComponent(save.originalFileType)}` +
            `&originalFileName=${encodeURIComponent(save.originalFileName)}`
        const response = await fetch(url, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/zstd',
            },
            body: save.data,
        })

        if (!response.ok) {
            throw new Error(
                `Failed to upload save: ${response.statusText} ` +
                    (await getBodyTextOrEmpty(response))
            )
        }

        return await response.json()
    }

    // Fetches the current parsing status of a previously uploaded save.
    async getSaveStatus(id: string): Promise<SaveStatusResponse> {
        const url = `${this.API_BASE}/getSaveStatus?id=${encodeURIComponent(id)}`
        const response = await fetch(url)

        if (!response.ok) {
            throw new Error(
                `Failed to get save status: ${response.statusText} ` +
                    (await getBodyTextOrEmpty(response))
            )
        }

        return await response.json()
    }

    /**
     * Fetches the fully parsed data for a save once its parsing is done.
     *
     * The backend stores and serves that data as zstd compressed json, so the
     * body is decompressed on the way in rather than read as text first.
     */
    async getSaveData(id: string): Promise<Record<string, unknown>> {
        const url = `${this.API_BASE}/getSaveData?id=${encodeURIComponent(id)}`
        const response = await fetch(url)

        if (!response.ok) {
            throw new Error(
                `Failed to get parsed save: ${response.statusText} ` +
                    (await getBodyTextOrEmpty(response))
            )
        }
        // A body is only missing on a response that cannot carry one, which a
        // successful getSaveData never is.
        if (!response.body) {
            throw new Error('Failed to get parsed save: response has no body')
        }

        // Decompresses as the bytes arrive, so the compressed json is never
        // held whole; only the parsed object stays in memory.
        const json = response.body.pipeThrough(createZstdDecompressStream())
        return await new Response(json).json()
    }

    /**
     * Fetches the stored save archive, exactly as it was uploaded. Turning it
     * back into a file the game can load is done in the browser.
     */
    async getSaveFile(id: string): Promise<Blob> {
        const url = `${this.API_BASE}/getSaveFile?id=${encodeURIComponent(id)}`
        const response = await fetch(url)

        if (!response.ok) {
            throw new Error(
                `Failed to get save file: ${response.statusText} ` +
                    (await getBodyTextOrEmpty(response))
            )
        }

        return await response.blob()
    }
}

export const saveParserBackendService = new SaveParserBackendService()