import { generateText, type ModelMessage } from "ai"
import { Session } from "."
import { Identifier } from "../id/id"
import { Instance } from "../project/instance"
import { Provider } from "../provider/provider"
import { defer } from "../util/defer"
import { MessageV2 } from "./message-v2"
import { SystemPrompt } from "./system"
import { Bus } from "../bus"
import z from "zod"
import type { ModelsDev } from "../provider/models"
import { SessionPrompt } from "./prompt"

export namespace SessionCompaction {
  export const Event = {
    Compacted: Bus.event(
      "session.compacted",
      z.object({
        sessionID: z.string(),
      }),
    ),
  }

  export function isOverflow(input: { tokens: MessageV2.Assistant["tokens"]; model: ModelsDev.Model }) {
    const count = input.tokens.input + input.tokens.cache.read + input.tokens.output
    const output = Math.min(input.model.limit.output, SessionPrompt.OUTPUT_TOKEN_MAX) || SessionPrompt.OUTPUT_TOKEN_MAX
    const usable = input.model.limit.context - output
    return count > usable
  }

  export async function run(input: { sessionID: string; providerID: string; modelID: string }) {
    await Session.update(input.sessionID, (draft) => {
      draft.time.compacting = Date.now()
    })
    await using _ = defer(async () => {
      await Session.update(input.sessionID, (draft) => {
        draft.time.compacting = undefined
      })
    })
    const toSummarize = await Session.messages(input.sessionID).then(MessageV2.filterSummarized)
    const model = await Provider.getModel(input.providerID, input.modelID)
    const system = [
      ...SystemPrompt.summarize(model.providerID),
      ...(await SystemPrompt.environment()),
      ...(await SystemPrompt.custom()),
    ]

    const msg = (await Session.updateMessage({
      id: Identifier.ascending("message"),
      role: "assistant",
      sessionID: input.sessionID,
      system,
      mode: "build",
      path: {
        cwd: Instance.directory,
        root: Instance.worktree,
      },
      cost: 0,
      tokens: {
        output: 0,
        input: 0,
        reasoning: 0,
        cache: { read: 0, write: 0 },
      },
      modelID: input.modelID,
      providerID: model.providerID,
      time: {
        created: Date.now(),
      },
    })) as MessageV2.Assistant
    const generated = await generateText({
      maxRetries: 10,
      model: model.language,
      messages: [
        ...system.map(
          (x): ModelMessage => ({
            role: "system",
            content: x,
          }),
        ),
        ...MessageV2.toModelMessage(toSummarize),
        {
          role: "user",
          content: [
            {
              type: "text",
              text: "Provide a detailed but concise summary of our conversation above. Focus on information that would be helpful for continuing the conversation, including what we did, what we're doing, which files we're working on, and what we're going to do next.",
            },
          ],
        },
      ],
    })
    const usage = Session.getUsage(model.info, generated.usage, generated.providerMetadata)
    msg.cost += usage.cost
    msg.tokens = usage.tokens
    msg.summary = true
    msg.time.completed = Date.now()
    await Session.updateMessage(msg)
    const part = await Session.updatePart({
      type: "text",
      sessionID: input.sessionID,
      messageID: msg.id,
      id: Identifier.ascending("part"),
      text: generated.text,
      time: {
        start: Date.now(),
        end: Date.now(),
      },
    })

    Bus.publish(Event.Compacted, {
      sessionID: input.sessionID,
    })

    return {
      info: msg,
      parts: [part],
    }
  }
}