opencode/packages/cli/src/mini/variant.shared.ts

// Model variant resolution and persistence.
//
// Variants are provider-specific reasoning effort levels (e.g., "high", "max").
// Resolution priority: CLI --variant flag > saved preference > session history.
//
// The saved variant persists across sessions in ~/.local/state/opencode/model.json
// so your last-used variant sticks. Cycling (ctrl+t) updates both the active
// variant and the persisted file.
import path from "path"
import { FSUtil } from "@opencode-ai/core/fs-util"
import { AppNodeBuilder } from "@opencode-ai/core/effect/app-node-builder"
import { Context, Effect, Layer } from "effect"
import { LayerNode } from "@opencode-ai/core/effect/layer-node"
import { makeGlobalNode } from "@opencode-ai/core/effect/app-node"
import { makeRuntime } from "@opencode-ai/core/effect/runtime"
import { Global } from "@opencode-ai/core/global"
import { createSession, sessionVariant, type RunSession, type SessionMessages } from "./session.shared"
import type { RunInput, RunProvider } from "./types"

const MODEL_FILE = path.join(Global.Path.state, "model.json")

type ModelState = Record<string, unknown> & {
  variant?: Record<string, string | undefined>
}
type VariantService = {
  readonly resolveSavedVariant: (model: RunInput["model"]) => Effect.Effect<string | undefined>
  readonly saveVariant: (model: RunInput["model"], variant: string | undefined) => Effect.Effect<void>
}
type VariantRuntime = {
  resolveSavedVariant(model: RunInput["model"]): Promise<string | undefined>
  saveVariant(model: RunInput["model"], variant: string | undefined): Promise<void>
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return !!value && typeof value === "object" && !Array.isArray(value)
}

class Service extends Context.Service<Service, VariantService>()("@opencode/RunVariant") {}

function modelKey(provider: string, model: string): string {
  return `${provider}/${model}`
}

function variantKey(model: NonNullable<RunInput["model"]>): string {
  return modelKey(model.providerID, model.modelID)
}

export function modelInfo(providers: RunProvider[] | undefined, model: NonNullable<RunInput["model"]>) {
  const provider = providers?.find((item) => item.id === model.providerID)
  return {
    provider: provider?.name ?? model.providerID,
    model: provider?.models[model.modelID]?.name ?? model.modelID,
  }
}

export function formatModelLabel(
  model: NonNullable<RunInput["model"]>,
  variant: string | undefined,
  providers?: RunProvider[],
): string {
  const names = modelInfo(providers, model)
  const label = variant ? ` · ${variant}` : ""
  return `${names.model} · ${names.provider}${label}`
}

export function cycleVariant(current: string | undefined, variants: string[]): string | undefined {
  if (variants.length === 0) {
    return undefined
  }

  if (!current) {
    return variants[0]
  }

  const idx = variants.indexOf(current)
  if (idx === -1 || idx === variants.length - 1) {
    return undefined
  }

  return variants[idx + 1]
}

export function pickVariant(model: RunInput["model"], input: RunSession | SessionMessages): string | undefined {
  return sessionVariant(Array.isArray(input) ? createSession(input) : input, model)
}

function fitVariant(value: string | undefined, variants: string[]): string | undefined {
  if (!value) {
    return undefined
  }

  if (variants.length === 0 || variants.includes(value)) {
    return value
  }

  return undefined
}

// Picks the active variant. CLI flag wins, then saved preference, then session
// history. fitVariant() checks saved and session values against the available
// variants list -- if the provider doesn't offer a variant, it drops.
export function resolveVariant(
  input: string | undefined,
  session: string | undefined,
  saved: string | undefined,
  variants: string[],
): string | undefined {
  if (input !== undefined) {
    return input
  }

  const fallback = fitVariant(saved, variants)
  const current = fitVariant(session, variants)
  if (current !== undefined) {
    return current
  }

  return fallback
}

function state(value: unknown): ModelState {
  if (!isRecord(value)) {
    return {}
  }

  const variant = isRecord(value.variant)
    ? Object.fromEntries(
        Object.entries(value.variant).flatMap(([key, item]) => {
          if (typeof item !== "string") {
            return []
          }

          return [[key, item] as const]
        }),
      )
    : undefined

  return {
    ...value,
    variant,
  }
}

const layer = Layer.fresh(
  Layer.effect(
    Service,
    Effect.gen(function* () {
      const file = yield* FSUtil.Service

      const read = Effect.fn("RunVariant.read")(function* () {
        return yield* file.readJson(MODEL_FILE).pipe(
          Effect.map(state),
          Effect.catchCause(() => Effect.succeed(state(undefined))),
        )
      })

      const resolveSavedVariant = Effect.fn("RunVariant.resolveSavedVariant")(function* (model: RunInput["model"]) {
        if (!model) {
          return undefined
        }

        return (yield* read()).variant?.[variantKey(model)]
      })

      const saveVariant = Effect.fn("RunVariant.saveVariant")(function* (
        model: RunInput["model"],
        variant: string | undefined,
      ) {
        if (!model) {
          return
        }

        const current = yield* read()
        const next = {
          ...current.variant,
        }
        const key = variantKey(model)
        if (variant) {
          next[key] = variant
        }

        if (!variant) {
          delete next[key]
        }

        yield* file
          .writeJson(MODEL_FILE, {
            ...current,
            variant: next,
          })
          .pipe(Effect.orElseSucceed(() => undefined))
      })

      return Service.of({
        resolveSavedVariant,
        saveVariant,
      })
    }),
  ),
)

const node = makeGlobalNode({ service: Service, layer, deps: [FSUtil.node] })

/** @internal Exported for testing. */
export function createVariantRuntime(replacements?: readonly LayerNode.Replacement[]): VariantRuntime {
  const runtime = makeRuntime(Service, AppNodeBuilder.build(node, replacements))
  return {
    resolveSavedVariant: (model) => runtime.runPromise((svc) => svc.resolveSavedVariant(model)).catch(() => undefined),
    saveVariant: (model, variant) => runtime.runPromise((svc) => svc.saveVariant(model, variant)).catch(() => {}),
  }
}

const runtime = createVariantRuntime()

export async function resolveSavedVariant(model: RunInput["model"]): Promise<string | undefined> {
  return runtime.resolveSavedVariant(model)
}

export function saveVariant(model: RunInput["model"], variant: string | undefined): void {
  void runtime.saveVariant(model, variant)
}