opencode/packages/core/src/snapshot.ts

export * as Snapshot from "./snapshot"

import { makeLocationNode } from "./effect/app-node"
import path from "path"
import { Context, Effect, Fiber, Layer, Schema, Scope } from "effect"
import { Config } from "./config"
import { File } from "./file"
import { FSUtil } from "./fs-util"
import { Git } from "./git"
import { Global } from "./global"
import { Location } from "./location"
import { AbsolutePath, RelativePath } from "./schema"
import { ID } from "@opencode-ai/schema/snapshot"
import { Hash } from "./util/hash"

export { ID }

export class Error extends Schema.TaggedErrorClass<Error>()("Snapshot.Error", {
  operation: Schema.Literals(["capture", "files", "diff", "preview", "restore"]),
  message: Schema.String,
  cause: Schema.optional(Schema.Defect()),
}) {}

export interface CompareInput {
  readonly from: ID
  readonly to: ID
}

export interface DiffInput extends CompareInput {
  readonly context?: number
  readonly paths?: readonly RelativePath[]
}

export interface RestoreInput {
  /** Paths are relative to the project root. */
  readonly files: ReadonlyMap<RelativePath, ID>
}

export interface PreviewInput extends RestoreInput {
  readonly context?: number
}

export interface Interface {
  /**
   * Capture the current Location-scoped filesystem state as a content-addressed
   * tree. Returns `undefined` when snapshots are disabled, unsupported, or the
   * best-effort capture fails.
   */
  readonly capture: () => Effect.Effect<ID | undefined>

  /**
   * List project-relative paths changed between two captured trees without
   * loading file contents or generating patches.
   */
  readonly files: (input: CompareInput) => Effect.Effect<readonly RelativePath[], Error>

  /**
   * Generate structured per-file diffs between two captured trees. `context`
   * controls unchanged lines around each unified diff hunk.
   */
  readonly diff: (input: DiffInput) => Effect.Effect<readonly File.Diff[], Error>

  /**
   * Preview the filesystem result of a selective restore without modifying the
   * worktree. Each project-relative path maps to the tree it would be restored
   * from.
   */
  readonly preview: (input: PreviewInput) => Effect.Effect<readonly File.Diff[], Error>

  /**
   * Restore selected project-relative paths from their associated trees. A path
   * absent from its selected tree is removed; paths outside the map are untouched.
   */
  readonly restore: (input: RestoreInput) => Effect.Effect<void, Error>

  /**
   * Replace the snapshot index with a captured tree and check out all its entries.
   * Files absent from the tree remain untouched. Prefer selective `restore` when
   * only known paths should change.
   */
  readonly checkout: (snapshot: ID) => Effect.Effect<void, Error>
}

export class Service extends Context.Service<Service, Interface>()("@opencode/v2/Snapshot") {}

const layer = Layer.effect(
  Service,
  Effect.gen(function* () {
    const config = yield* Config.Service
    const fs = yield* FSUtil.Service
    const git = yield* Git.Service
    const global = yield* Global.Service
    const location = yield* Location.Service
    const lifetime = yield* Scope.Scope
    // Cache a scope-owned fiber so caller cancellation stops waiting without poisoning shared initialization.
    const repositoryFiber = yield* Effect.cached(
      Effect.gen(function* () {
        const source = yield* git.repo.discover(location.project.directory)
        if (!source) return yield* new Error({ operation: "capture", message: "Project is not a Git repository" })
        const worktree = AbsolutePath.make(yield* fs.realPath(source.worktree).pipe(Effect.orDie))
        const gitDirectory = AbsolutePath.make(
          path.join(global.data, "snapshot", location.project.id, Hash.fast(worktree)),
        )
        const snapshotRepository = (yield* fs.existsSafe(path.join(gitDirectory, "HEAD")))
          ? new Git.Repository({ worktree, gitDirectory, commonDirectory: gitDirectory })
          : yield* git.repo
              .create({ worktree, gitDirectory, seed: source })
              .pipe(Effect.mapError((cause) => failure("capture", cause)))
        return { source, worktree, snapshotRepository }
      }).pipe(Effect.forkIn(lifetime)),
    )
    const repository = repositoryFiber.pipe(Effect.uninterruptible, Effect.flatMap(Fiber.join))

    const scope = Effect.fnUntraced(function* (worktree: AbsolutePath) {
      const relative = path.relative(worktree, location.directory)
      if (relative.startsWith("..") || path.isAbsolute(relative))
        return yield* new Error({ operation: "capture", message: "Location is outside the project" })
      return RelativePath.make(relative.replaceAll("\\", "/") || ".")
    })

    const enabled = Effect.fnUntraced(function* () {
      if (location.vcs?.type !== "git") return false
      return Config.latest(yield* config.entries(), "snapshots") !== false
    })

    const capture = Effect.fn("Snapshot.capture")(function* () {
      if (!(yield* enabled())) return undefined
      return yield* Effect.gen(function* () {
        const repo = yield* repository
        return ID.make(
          yield* git.tree.capture({
            repository: repo.snapshotRepository,
            scopes: [yield* scope(repo.worktree)],
            ignores: repo.source,
            maximumUntrackedFileBytes: 2 * 1024 * 1024,
          }),
        )
      }).pipe(
        Effect.catch((cause) => Effect.logWarning("failed to capture snapshot", { cause }).pipe(Effect.as(undefined))),
      )
    })

    const compare = Effect.fnUntraced(function* (operation: "files" | "diff", input: CompareInput) {
      const repo = yield* repository.pipe(Effect.mapError((cause) => failure(operation, cause)))
      return {
        source: repo.source,
        input: {
          repository: repo.snapshotRepository,
          from: Git.TreeID.make(input.from),
          to: Git.TreeID.make(input.to),
        },
      }
    })

    const files = Effect.fn("Snapshot.files")(function* (input: CompareInput) {
      const comparison = yield* compare("files", input)
      const files = yield* git.tree.files(comparison.input).pipe(Effect.mapError((cause) => failure("files", cause)))
      const ignored = yield* git.index
        .ignored({ repository: comparison.source, paths: files })
        .pipe(Effect.mapError((cause) => failure("files", cause)))
      return files.filter((file) => !ignored.has(file))
    })

    const diff = Effect.fn("Snapshot.diff")(function* (input: DiffInput) {
      const comparison = yield* compare("diff", input)
      const files = yield* git.tree.files(comparison.input).pipe(Effect.mapError((cause) => failure("diff", cause)))
      const ignored = yield* git.index
        .ignored({ repository: comparison.source, paths: files })
        .pipe(Effect.mapError((cause) => failure("diff", cause)))
      return yield* git.tree
        .diff({
          ...comparison.input,
          context: input.context,
          paths: (input.paths ?? files).filter((file) => !ignored.has(file)),
        })
        .pipe(Effect.mapError((cause) => failure("diff", cause)))
    })

    const plan = Effect.fnUntraced(function* (
      operation: "preview" | "restore",
      worktree: AbsolutePath,
      input: RestoreInput,
    ) {
      const files = new Map<RelativePath, Git.TreeID>()
      for (const [file, snapshot] of input.files) {
        const absolute = path.resolve(worktree, file)
        if (!FSUtil.contains(worktree, absolute))
          return yield* new Error({ operation, message: `Path escapes the project: ${file}` })
        files.set(file, Git.TreeID.make(snapshot))
      }
      return files
    })

    const preview = Effect.fn("Snapshot.preview")(function* (input: PreviewInput) {
      if (!(yield* enabled())) return yield* new Error({ operation: "preview", message: "Snapshots are disabled" })
      const repo = yield* repository.pipe(Effect.mapError((cause) => failure("preview", cause)))
      const files = yield* plan("preview", repo.worktree, input)
      const current = yield* git.tree
        .capture({
          repository: repo.snapshotRepository,
          scopes: Array.from(files.keys()),
          ignores: repo.source,
          maximumUntrackedFileBytes: 2 * 1024 * 1024,
        })
        .pipe(Effect.mapError((cause) => failure("preview", cause)))
      return yield* git.tree
        .preview({
          repository: repo.snapshotRepository,
          current,
          files,
          context: input.context,
        })
        .pipe(Effect.mapError((cause) => failure("preview", cause)))
    })

    const restore = Effect.fn("Snapshot.restore")(function* (input: RestoreInput) {
      if (!(yield* enabled())) return yield* new Error({ operation: "restore", message: "Snapshots are disabled" })
      const repo = yield* repository.pipe(Effect.mapError((cause) => failure("restore", cause)))
      yield* git.tree
        .restore({ repository: repo.snapshotRepository, files: yield* plan("restore", repo.worktree, input) })
        .pipe(Effect.mapError((cause) => failure("restore", cause)))
    })

    const checkout = Effect.fn("Snapshot.checkout")(function* (snapshot: ID) {
      const repo = yield* repository.pipe(Effect.mapError((cause) => failure("restore", cause)))
      yield* git.tree
        .checkout({ repository: repo.snapshotRepository, tree: Git.TreeID.make(snapshot) })
        .pipe(Effect.mapError((cause) => failure("restore", cause)))
    })

    return Service.of({ capture, files, diff, preview, restore, checkout })
  }).pipe(Effect.withSpan("Snapshot.boot")),
)

export const node = makeLocationNode({
  service: Service,
  layer,
  deps: [Config.node, FSUtil.node, Git.node, Global.node, Location.node],
})

export const noopLayer = Layer.succeed(
  Service,
  Service.of({
    capture: () => Effect.succeed(undefined),
    files: () => Effect.succeed([]),
    diff: () => Effect.succeed([]),
    preview: () => Effect.succeed([]),
    restore: () => Effect.void,
    checkout: () => Effect.void,
  }),
)

function failure(operation: Error["operation"], cause: unknown) {
  if (cause instanceof Error && cause.operation === operation) return cause
  return new Error({
    operation,
    message: cause instanceof globalThis.Error ? cause.message : String(cause),
    cause,
  })
}