import type {
  SessionsListInput,
  SessionsListOutput,
  SessionsCreateInput,
  SessionsCreateOutput,
  SessionsGetInput,
  SessionsGetOutput,
  SessionsSwitchAgentInput,
  SessionsSwitchAgentOutput,
  SessionsSwitchModelInput,
  SessionsSwitchModelOutput,
  SessionsPromptInput,
  SessionsPromptOutput,
  SessionsCompactInput,
  SessionsCompactOutput,
  SessionsWaitInput,
  SessionsWaitOutput,
  SessionsStageInput,
  SessionsStageOutput,
  SessionsClearInput,
  SessionsClearOutput,
  SessionsCommitInput,
  SessionsCommitOutput,
  SessionsContextInput,
  SessionsContextOutput,
} from "./types"
import { ClientError } from "./client-error"

export interface ClientOptions {
  readonly baseUrl: string
  readonly fetch?: typeof globalThis.fetch
  readonly headers?: HeadersInit
}

export interface RequestOptions {
  readonly signal?: AbortSignal
  readonly headers?: HeadersInit
}

interface RequestDescriptor {
  readonly method: string
  readonly path: string
  readonly query?: Record<string, unknown>
  readonly headers?: Record<string, unknown>
  readonly body?: unknown
  readonly successStatus: number
  readonly declaredStatuses: ReadonlyArray<number>
  readonly empty: boolean
}

export function make(options: ClientOptions) {
  const fetch = options.fetch ?? globalThis.fetch

  const prepare = (descriptor: RequestDescriptor, requestOptions?: RequestOptions) => {
    const url = new URL(descriptor.path, options.baseUrl)
    for (const [key, value] of Object.entries(descriptor.query ?? {})) appendQuery(url.searchParams, key, value)
    const headers = new Headers(options.headers)
    for (const [key, value] of Object.entries(descriptor.headers ?? {})) {
      if (value !== undefined && value !== null) headers.set(key, String(value))
    }
    for (const [key, value] of new Headers(requestOptions?.headers)) headers.set(key, value)
    if (descriptor.body !== undefined && !headers.has("content-type")) headers.set("content-type", "application/json")
    return {
      url,
      init: {
        method: descriptor.method,
        signal: requestOptions?.signal,
        headers,
        body: descriptor.body === undefined ? undefined : JSON.stringify(descriptor.body),
      } satisfies RequestInit,
    }
  }

  const execute = async (descriptor: RequestDescriptor, requestOptions?: RequestOptions) => {
    try {
      const prepared = prepare(descriptor, requestOptions)
      return await fetch(prepared.url, prepared.init)
    } catch (cause) {
      throw new ClientError("Transport", { cause })
    }
  }

  const responseError = async (response: Response, descriptor: RequestDescriptor): Promise<never> => {
    if (descriptor.declaredStatuses.includes(response.status)) throw await json(response)
    try {
      await response.body?.cancel()
    } catch {}
    throw new ClientError("UnexpectedStatus", { cause: { status: response.status } })
  }

  const request = async <A>(descriptor: RequestDescriptor, requestOptions?: RequestOptions): Promise<A> => {
    const response = await execute(descriptor, requestOptions)
    if (response.status !== descriptor.successStatus) return responseError(response, descriptor)
    if (descriptor.empty) {
      try {
        await response.body?.cancel()
      } catch {}
      return undefined as A
    }
    return (await json(response)) as A
  }

  const sse = <A>(descriptor: RequestDescriptor, requestOptions?: RequestOptions): AsyncIterable<A> => ({
    async *[Symbol.asyncIterator]() {
      const response = await execute(descriptor, requestOptions)
      if (response.status !== descriptor.successStatus) await responseError(response, descriptor)
      if (!isContentType(response, "text/event-stream")) {
        try {
          await response.body?.cancel()
        } catch {}
        throw new ClientError("UnsupportedContentType")
      }
      if (response.body === null) throw new ClientError("MalformedResponse")
      const reader = response.body.getReader()
      const decoder = new TextDecoder()
      let buffer = ""
      try {
        while (true) {
          let next
          try {
            next = await reader.read()
          } catch (cause) {
            throw new ClientError("Transport", { cause })
          }
          buffer += decoder.decode(next.value, { stream: !next.done })
          if (buffer.length > 1_048_576) throw new ClientError("MalformedResponse")
          const trailingCarriageReturn = !next.done && buffer.endsWith("\r")
          if (trailingCarriageReturn) buffer = buffer.slice(0, -1)
          buffer = buffer.replaceAll("\r\n", "\n").replaceAll("\r", "\n")
          if (trailingCarriageReturn) buffer += "\r"
          if (next.done && buffer !== "") buffer += "\n\n"
          let boundary = buffer.indexOf("\n\n")
          while (boundary >= 0) {
            const block = buffer.slice(0, boundary)
            buffer = buffer.slice(boundary + 2)
            const data = block
              .split("\n")
              .flatMap((line) => (line.startsWith("data:") ? [line.slice(5).trimStart()] : []))
              .join("\n")
            if (data !== "") {
              try {
                yield JSON.parse(data) as A
              } catch (cause) {
                throw new ClientError("MalformedResponse", { cause })
              }
            }
            boundary = buffer.indexOf("\n\n")
          }
          if (next.done) return
        }
      } finally {
        try {
          await reader.cancel()
        } catch {}
        reader.releaseLock()
      }
    },
  })

  return {
    sessions: {
      list: (input?: SessionsListInput, requestOptions?: RequestOptions) =>
        request<SessionsListOutput>(
          {
            method: "GET",
            path: `/api/session`,
            query: {
              workspace: input?.workspace,
              limit: input?.limit,
              order: input?.order,
              search: input?.search,
              directory: input?.directory,
              project: input?.project,
              subpath: input?.subpath,
              cursor: input?.cursor,
            },
            successStatus: 200,
            declaredStatuses: [400, 401],
            empty: false,
          },
          requestOptions,
        ),
      create: (input?: SessionsCreateInput, requestOptions?: RequestOptions) =>
        request<{ readonly data: SessionsCreateOutput }>(
          {
            method: "POST",
            path: `/api/session`,
            body: { id: input?.id, agent: input?.agent, model: input?.model, location: input?.location },
            successStatus: 200,
            declaredStatuses: [401, 400],
            empty: false,
          },
          requestOptions,
        ).then((value) => value.data),
      get: (input: SessionsGetInput, requestOptions?: RequestOptions) =>
        request<{ readonly data: SessionsGetOutput }>(
          {
            method: "GET",
            path: `/api/session/${encodeURIComponent(input.sessionID)}`,
            successStatus: 200,
            declaredStatuses: [404, 400, 401],
            empty: false,
          },
          requestOptions,
        ).then((value) => value.data),
      switchAgent: (input: SessionsSwitchAgentInput, requestOptions?: RequestOptions) =>
        request<SessionsSwitchAgentOutput>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/agent`,
            body: { agent: input.agent },
            successStatus: 204,
            declaredStatuses: [404, 400, 401],
            empty: true,
          },
          requestOptions,
        ),
      switchModel: (input: SessionsSwitchModelInput, requestOptions?: RequestOptions) =>
        request<SessionsSwitchModelOutput>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/model`,
            body: { model: input.model },
            successStatus: 204,
            declaredStatuses: [404, 400, 401],
            empty: true,
          },
          requestOptions,
        ),
      prompt: (input: SessionsPromptInput, requestOptions?: RequestOptions) =>
        request<{ readonly data: SessionsPromptOutput }>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/prompt`,
            body: { id: input.id, prompt: input.prompt, delivery: input.delivery, resume: input.resume },
            successStatus: 200,
            declaredStatuses: [409, 404, 400, 401],
            empty: false,
          },
          requestOptions,
        ).then((value) => value.data),
      compact: (input: SessionsCompactInput, requestOptions?: RequestOptions) =>
        request<SessionsCompactOutput>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/compact`,
            successStatus: 204,
            declaredStatuses: [404, 503, 400, 401],
            empty: true,
          },
          requestOptions,
        ),
      wait: (input: SessionsWaitInput, requestOptions?: RequestOptions) =>
        request<SessionsWaitOutput>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/wait`,
            successStatus: 204,
            declaredStatuses: [404, 503, 400, 401],
            empty: true,
          },
          requestOptions,
        ),
      stage: (input: SessionsStageInput, requestOptions?: RequestOptions) =>
        request<{ readonly data: SessionsStageOutput }>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/revert/stage`,
            body: { messageID: input.messageID, files: input.files },
            successStatus: 200,
            declaredStatuses: [404, 500, 400, 401],
            empty: false,
          },
          requestOptions,
        ).then((value) => value.data),
      clear: (input: SessionsClearInput, requestOptions?: RequestOptions) =>
        request<SessionsClearOutput>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/revert/clear`,
            successStatus: 204,
            declaredStatuses: [404, 500, 400, 401],
            empty: true,
          },
          requestOptions,
        ),
      commit: (input: SessionsCommitInput, requestOptions?: RequestOptions) =>
        request<SessionsCommitOutput>(
          {
            method: "POST",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/revert/commit`,
            successStatus: 204,
            declaredStatuses: [404, 400, 401],
            empty: true,
          },
          requestOptions,
        ),
      context: (input: SessionsContextInput, requestOptions?: RequestOptions) =>
        request<{ readonly data: SessionsContextOutput }>(
          {
            method: "GET",
            path: `/api/session/${encodeURIComponent(input.sessionID)}/context`,
            successStatus: 200,
            declaredStatuses: [404, 500, 400, 401],
            empty: false,
          },
          requestOptions,
        ).then((value) => value.data),
    },
  }
}

function appendQuery(params: URLSearchParams, key: string, value: unknown): void {
  if (value === undefined || value === null) return
  if (Array.isArray(value)) {
    for (const item of value) appendQuery(params, key, item)
    return
  }
  if (typeof value === "object") {
    for (const [child, item] of Object.entries(value)) appendQuery(params, `${key}[${child}]`, item)
    return
  }
  params.append(key, String(value))
}

async function json(response: Response): Promise<unknown> {
  if (!isContentType(response, "application/json") && !response.headers.get("content-type")?.includes("+json")) {
    try {
      await response.body?.cancel()
    } catch {}
    throw new ClientError("UnsupportedContentType")
  }
  let text: string
  try {
    text = await response.text()
  } catch (cause) {
    throw new ClientError("Transport", { cause })
  }
  if (text === "") throw new ClientError("MalformedResponse")
  try {
    return JSON.parse(text)
  } catch (cause) {
    throw new ClientError("MalformedResponse", { cause })
  }
}

function isContentType(response: Response, expected: string) {
  return response.headers.get("content-type")?.split(";", 1)[0]?.trim().toLowerCase() === expected
}