/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import {
  Config,
  ToolCallRequestInfo,
  ToolCallResponseInfo,
  ToolConfirmationOutcome,
  Tool,
} from '@gemini-code/server';
import { Part } from '@google/genai';
import { useCallback, useEffect, useState } from 'react';
import {
  HistoryItemToolGroup,
  IndividualToolCallDisplay,
  ToolCallStatus,
} from '../types.js';

type ScheduledToolCall = {
  status: 'scheduled';
  request: ToolCallRequestInfo;
  tool: Tool;
};

type ErroredToolCall = {
  status: 'error';
  request: ToolCallRequestInfo;
  response: ToolCallResponseInfo;
};

type SuccessfulToolCall = {
  status: 'success';
  request: ToolCallRequestInfo;
  tool: Tool;
  response: ToolCallResponseInfo;
};

type ExecutingToolCall = {
  status: 'executing';
  request: ToolCallRequestInfo;
  tool: Tool;
};

type CancelledToolCall = {
  status: 'cancelled';
  request: ToolCallRequestInfo;
  response: ToolCallResponseInfo;
  tool: Tool;
};

type WaitingToolCall = {
  status: 'awaiting_approval';
  request: ToolCallRequestInfo;
  tool: Tool;
  confirm: (outcome: ToolConfirmationOutcome) => Promise<void>;
};

export type Status = ToolCall['status'];

export type ToolCall =
  | ScheduledToolCall
  | ErroredToolCall
  | SuccessfulToolCall
  | ExecutingToolCall
  | CancelledToolCall
  | WaitingToolCall;

export type ScheduleFn = (
  request: ToolCallRequestInfo | ToolCallRequestInfo[],
) => void;
export type CancelFn = () => void;
export type CompletedToolCall =
  | SuccessfulToolCall
  | CancelledToolCall
  | ErroredToolCall;

export function useToolScheduler(
  onComplete: (tools: CompletedToolCall[]) => void,
  config: Config,
): [ToolCall[], ScheduleFn, CancelFn] {
  const [toolRegistry] = useState(() => config.getToolRegistry());
  const [toolCalls, setToolCalls] = useState<ToolCall[]>([]);
  const [abortController, setAbortController] = useState<AbortController>(
    () => new AbortController(),
  );

  const isRunning = toolCalls.some(
    (t) => t.status === 'executing' || t.status === 'awaiting_approval',
  );
  // Note: request array[] typically signal pending tool calls
  const schedule = useCallback(
    async (request: ToolCallRequestInfo | ToolCallRequestInfo[]) => {
      if (isRunning) {
        throw new Error(
          'Cannot schedule tool calls while other tool calls are running',
        );
      }
      const requests = Array.isArray(request) ? request : [request];
      const newCalls: ToolCall[] = await Promise.all(
        requests.map(async (r): Promise<ToolCall> => {
          const tool = toolRegistry.getTool(r.name);
          if (!tool) {
            return {
              status: 'error',
              request: r,
              response: toolErrorResponse(
                r,
                new Error(`tool ${r.name} does not exist`),
              ),
            };
          }

          const userApproval = await tool.shouldConfirmExecute(r.args);
          if (userApproval) {
            return {
              status: 'awaiting_approval',
              request: r,
              tool,
              confirm: async (outcome) => {
                await userApproval.onConfirm(outcome);
                setToolCalls(
                  outcome === ToolConfirmationOutcome.Cancel
                    ? setStatus(
                        r.callId,
                        'cancelled',
                        'User did not allow tool call',
                      )
                    : setStatus(r.callId, 'scheduled'),
                );
              },
            };
          }

          return {
            status: 'scheduled',
            request: r,
            tool,
          };
        }),
      );
      setToolCalls((t) => t.concat(newCalls));
    },
    [isRunning, setToolCalls, toolRegistry],
  );

  const cancel = useCallback(
    (reason: string = 'unspecified') => {
      abortController.abort();
      setAbortController(new AbortController());
      setToolCalls((tc) =>
        tc.map((c) =>
          c.status !== 'error'
            ? {
                ...c,
                status: 'cancelled',
                response: {
                  callId: c.request.callId,
                  responsePart: {
                    functionResponse: {
                      id: c.request.callId,
                      name: c.request.name,
                      response: {
                        error: `[Operation Cancelled] Reason: ${reason}`,
                      },
                    },
                  },
                  resultDisplay: undefined,
                  error: undefined,
                },
              }
            : c,
        ),
      );
    },
    [abortController],
  );

  useEffect(() => {
    // effect for executing scheduled tool calls
    const scheduledCalls = toolCalls.filter((t) => t.status === 'scheduled');
    const awaitingConfirmation = toolCalls.some(
      (t) => t.status === 'awaiting_approval',
    );
    if (!awaitingConfirmation && scheduledCalls.length) {
      scheduledCalls.forEach(async (c) => {
        const callId = c.request.callId;
        try {
          setToolCalls(setStatus(c.request.callId, 'executing'));
          const result = await c.tool.execute(
            c.request.args,
            abortController.signal,
          );
          const functionResponse: Part = {
            functionResponse: {
              name: c.request.name,
              id: callId,
              response: { output: result.llmContent },
            },
          };
          const response: ToolCallResponseInfo = {
            callId,
            responsePart: functionResponse,
            resultDisplay: result.returnDisplay,
            error: undefined,
          };
          setToolCalls(setStatus(callId, 'success', response));
        } catch (e: unknown) {
          setToolCalls(
            setStatus(
              callId,
              'error',
              toolErrorResponse(
                c.request,
                e instanceof Error ? e : new Error(String(e)),
              ),
            ),
          );
        }
      });
    }
  }, [toolCalls, toolRegistry, abortController.signal]);

  useEffect(() => {
    const completedTools = toolCalls.filter(
      (t) =>
        t.status === 'success' ||
        t.status === 'error' ||
        t.status === 'cancelled',
    );
    const allDone = completedTools.length === toolCalls.length;
    if (toolCalls.length && allDone) {
      onComplete(completedTools);
      setToolCalls([]);
      setAbortController(new AbortController());
    }
  }, [toolCalls, onComplete]);

  return [toolCalls, schedule, cancel];
}

function setStatus(
  targetCallId: string,
  status: 'success',
  response: ToolCallResponseInfo,
): (t: ToolCall[]) => ToolCall[];
function setStatus(
  targetCallId: string,
  status: 'awaiting_approval',
  confirm: (t: ToolConfirmationOutcome) => Promise<void>,
): (t: ToolCall[]) => ToolCall[];
function setStatus(
  targetCallId: string,
  status: 'error',
  response: ToolCallResponseInfo,
): (t: ToolCall[]) => ToolCall[];
function setStatus(
  targetCallId: string,
  status: 'cancelled',
  reason: string,
): (t: ToolCall[]) => ToolCall[];
function setStatus(
  targetCallId: string,
  status: 'executing' | 'scheduled',
): (t: ToolCall[]) => ToolCall[];
function setStatus(
  targetCallId: string,
  status: Status,
  auxiliaryData?: unknown,
): (t: ToolCall[]) => ToolCall[] {
  return function (tc: ToolCall[]): ToolCall[] {
    return tc.map((t) => {
      if (t.request.callId !== targetCallId || t.status === 'error') {
        return t;
      }
      switch (status) {
        case 'success': {
          const next: SuccessfulToolCall = {
            ...t,
            status: 'success',
            response: auxiliaryData as ToolCallResponseInfo,
          };
          return next;
        }
        case 'error': {
          const next: ErroredToolCall = {
            ...t,
            status: 'error',
            response: auxiliaryData as ToolCallResponseInfo,
          };
          return next;
        }
        case 'awaiting_approval': {
          const next: WaitingToolCall = {
            ...t,
            status: 'awaiting_approval',
            confirm: auxiliaryData as (
              o: ToolConfirmationOutcome,
            ) => Promise<void>,
          };
          return next;
        }
        case 'scheduled': {
          const next: ScheduledToolCall = {
            ...t,
            status: 'scheduled',
          };
          return next;
        }
        case 'cancelled': {
          const next: CancelledToolCall = {
            ...t,
            status: 'cancelled',
            response: {
              callId: t.request.callId,
              responsePart: {
                functionResponse: {
                  id: t.request.callId,
                  name: t.request.name,
                  response: {
                    error: `[Operation Cancelled] Reason: ${auxiliaryData}`,
                  },
                },
              },
              resultDisplay: undefined,
              error: undefined,
            },
          };
          return next;
        }
        case 'executing': {
          const next: ExecutingToolCall = {
            ...t,
            status: 'executing',
          };
          return next;
        }
        default: {
          // ensures every case is checked for above
          const exhaustiveCheck: never = status;
          return exhaustiveCheck;
        }
      }
    });
  };
}

const toolErrorResponse = (
  request: ToolCallRequestInfo,
  error: Error,
): ToolCallResponseInfo => ({
  callId: request.callId,
  error,
  responsePart: {
    functionResponse: {
      id: request.callId,
      name: request.name,
      response: { error: error.message },
    },
  },
  resultDisplay: error.message,
});

function mapStatus(status: Status): ToolCallStatus {
  switch (status) {
    case 'awaiting_approval':
      return ToolCallStatus.Confirming;
    case 'executing':
      return ToolCallStatus.Executing;
    case 'success':
      return ToolCallStatus.Success;
    case 'cancelled':
      return ToolCallStatus.Canceled;
    case 'error':
      return ToolCallStatus.Error;
    case 'scheduled':
      return ToolCallStatus.Pending;
    default: {
      // ensures every case is checked for above
      const exhaustiveCheck: never = status;
      return exhaustiveCheck;
    }
  }
}

// convenient function for callers to map ToolCall back to a HistoryItem
export function mapToDisplay(
  tool: ToolCall[] | ToolCall,
): HistoryItemToolGroup {
  const tools = Array.isArray(tool) ? tool : [tool];
  const toolsDisplays = tools.map((t): IndividualToolCallDisplay => {
    switch (t.status) {
      case 'success':
        return {
          callId: t.request.callId,
          name: t.tool.displayName,
          description: t.tool.getDescription(t.request.args),
          resultDisplay: t.response.resultDisplay,
          status: mapStatus(t.status),
          confirmationDetails: undefined,
        };
      case 'error':
        return {
          callId: t.request.callId,
          name: t.request.name,
          description: '',
          resultDisplay: t.response.resultDisplay,
          status: mapStatus(t.status),
          confirmationDetails: undefined,
        };
      case 'cancelled':
        return {
          callId: t.request.callId,
          name: t.tool.displayName,
          description: t.tool.getDescription(t.request.args),
          resultDisplay: t.response.resultDisplay,
          status: mapStatus(t.status),
          confirmationDetails: undefined,
        };
      case 'awaiting_approval':
        return {
          callId: t.request.callId,
          name: t.tool.displayName,
          description: t.tool.getDescription(t.request.args),
          resultDisplay: undefined,
          status: mapStatus(t.status),
          confirmationDetails: {
            title: t.request.name,
            onConfirm: t.confirm,
          },
        };
      case 'executing':
        return {
          callId: t.request.callId,
          name: t.tool.displayName,
          description: t.tool.getDescription(t.request.args),
          resultDisplay: undefined,
          status: mapStatus(t.status),
          confirmationDetails: undefined,
        };
      case 'scheduled':
        return {
          callId: t.request.callId,
          name: t.tool.displayName,
          description: t.tool.getDescription(t.request.args),
          resultDisplay: undefined,
          status: mapStatus(t.status),
          confirmationDetails: undefined,
        };
      default: {
        // ensures every case is checked for above
        const exhaustiveCheck: never = t;
        return exhaustiveCheck;
      }
    }
  });
  const historyItem: HistoryItemToolGroup = {
    type: 'tool_group',
    tools: toolsDisplays,
  };
  return historyItem;
}