import {
  copyFile,
  mkdir,
  readFile,
  rm,
  unlink,
} from 'node:fs/promises';
import path from 'node:path';
import type { ProductModelRef } from '../coding-runtime/contracts';
import {
  buildLegacyProjectAgentManifest,
  normalizeLegacyProjectConfigV1,
} from './legacy-v1';
import type { ProjectAgentConfig, ProjectConfig } from '../../shared/project-config';
import {
  atomicWriteJson,
  atomicWriteText,
  type JsonFileWriter,
} from './atomic-json';
import {
  CODING_PROJECT_CONFIG_PATH,
  normalizeCodingProjectConfigV2,
  type CodingProjectAgentV2,
  type CodingProjectConfigV2,
} from './project-config';
import {
  CODING_CONVERSATIONS_PATH,
  createEmptyConversationFileV2,
} from './conversation-store';

export interface LegacyModelResolutionInput {
  agentId: string;
  legacyModel: string;
}

export type LegacyModelResolver = (
  input: LegacyModelResolutionInput,
) => Promise<ProductModelRef | null>;

export interface CodingProjectMigrationDependencies {
  resolveLegacyModel: LegacyModelResolver;
  now?: () => string;
  writeJson?: JsonFileWriter;
  copyFile?: typeof copyFile;
}

export type CodingProjectMigrationResult =
  | {
      status: 'already-current';
      config: CodingProjectConfigV2;
    }
  | {
      status: 'migrated';
      config: CodingProjectConfigV2;
      backupDirectory: string;
      removedGeneratedAgents: string[];
      backedUpUncertainAgents: string[];
    };

type AgentFileSnapshot = {
  fileName: string;
  filePath: string;
  content: string;
  generated: boolean;
  backupPath?: string;
};

function isMissing(error: unknown): boolean {
  return (error as NodeJS.ErrnoException).code === 'ENOENT';
}

function timestampKey(value: string): string {
  return value.replace(/[^0-9A-Za-z_-]/g, '-');
}

async function readOptionalText(filePath: string): Promise<string | null> {
  try {
    return await readFile(filePath, 'utf8');
  } catch (error) {
    if (isMissing(error)) return null;
    throw error;
  }
}

async function snapshotLegacyAgentFiles(
  projectPath: string,
  config: ProjectConfig,
  backupDirectory: string,
  copy: typeof copyFile,
): Promise<AgentFileSnapshot[]> {
  const agentDirectory = path.join(projectPath, '.opencode', 'agent');
  const expected = new Map(buildLegacyProjectAgentManifest(config).map((entry) => [
    path.basename(entry.relativePath),
    entry.content,
  ]));
  const snapshots: AgentFileSnapshot[] = [];
  for (const [fileName, expectedContent] of expected) {
    const filePath = path.join(agentDirectory, fileName);
    const content = await readOptionalText(filePath);
    if (content === null) continue;
    const generated = expectedContent === content;
    if (generated) {
      snapshots.push({ fileName, filePath, content, generated });
      continue;
    }
    const backupPath = path.join(backupDirectory, '.opencode', 'agent', fileName);
    await mkdir(path.dirname(backupPath), { recursive: true });
    await copy(filePath, backupPath);
    snapshots.push({ fileName, filePath, content, generated, backupPath });
  }
  return snapshots;
}

function legacyModelForAgent(config: ProjectConfig, agent: ProjectAgentConfig): string | null {
  const direct = typeof agent.model === 'string' ? agent.model.trim() : '';
  const fallback = typeof config.defaultModel === 'string' ? config.defaultModel.trim() : '';
  return direct || fallback || null;
}

function preserveLegacyAgentFields(
  rawProject: unknown,
  normalized: ProjectConfig,
): ProjectConfig {
  if (!rawProject || typeof rawProject !== 'object' || Array.isArray(rawProject)) return normalized;
  const rawAgents = (rawProject as { agents?: unknown }).agents;
  if (!Array.isArray(rawAgents)) return normalized;
  const rawById = new Map<string, { prompt?: unknown; skillIds?: unknown }>();
  for (const value of rawAgents) {
    if (!value || typeof value !== 'object' || Array.isArray(value)) continue;
    const record = value as { id?: unknown; prompt?: unknown; skillIds?: unknown };
    const id = typeof record.id === 'string' ? record.id.trim() : '';
    if (id) rawById.set(id, record);
  }
  return {
    ...normalized,
    agents: normalized.agents.map((agent) => {
      const raw = rawById.get(agent.id);
      const rawSkillIds = Array.isArray(raw?.skillIds)
        ? [...new Set(raw.skillIds
            .filter((item): item is string => typeof item === 'string')
            .map((item) => item.trim())
            .filter(Boolean))]
        : agent.skillIds;
      return {
        ...agent,
        prompt: typeof raw?.prompt === 'string' ? raw.prompt : agent.prompt,
        skillIds: rawSkillIds,
      };
    }),
  };
}

async function migrateAgent(
  config: ProjectConfig,
  agent: ProjectAgentConfig,
  resolveLegacyModel: LegacyModelResolver,
  fallbackTimestamp: string,
): Promise<CodingProjectAgentV2> {
  const legacyModel = legacyModelForAgent(config, agent);
  const model = legacyModel
    ? await resolveLegacyModel({ agentId: agent.id, legacyModel })
    : null;
  return {
    id: agent.id,
    avatarId: agent.avatarId,
    ...(agent.avatarDataUrl ? { avatarDataUrl: agent.avatarDataUrl } : {}),
    roleName: agent.roleName,
    name: agent.name,
    builtIn: agent.builtIn,
    enabled: agent.enabled,
    model,
    modelResolution: model ? 'resolved' : 'required',
    skillIds: [...agent.skillIds],
    responsibility: {
      mission: agent.responsibility.mission,
      owns: [...agent.responsibility.owns],
      boundaries: [...agent.responsibility.boundaries],
      collaborators: [...agent.responsibility.collaborators],
      principles: [...agent.responsibility.principles],
    },
    prompt: agent.prompt,
    archivedAt: agent.archivedAt ?? null,
    pinned: agent.pinned === true,
    createdAt: agent.createdAt ?? fallbackTimestamp,
    updatedAt: agent.updatedAt ?? fallbackTimestamp,
  };
}

async function restoreOriginalState(
  projectConfigPath: string,
  projectSource: string,
  conversationsPath: string,
  conversationsSource: string | null,
  agentFiles: AgentFileSnapshot[],
): Promise<void> {
  const failures: string[] = [];
  const restore = async (label: string, operation: () => Promise<void>) => {
    try {
      await operation();
    } catch (error) {
      failures.push(`${label}: ${error instanceof Error ? error.message : String(error)}`);
    }
  };
  await restore('project config', () => atomicWriteText(projectConfigPath, projectSource));
  if (conversationsSource === null) {
    await restore('Conversation metadata', () => rm(conversationsPath, { force: true }));
  } else {
    await restore('Conversation metadata', () => atomicWriteText(conversationsPath, conversationsSource));
  }
  for (const agent of agentFiles) {
    await restore(`Agent ${agent.fileName}`, () => atomicWriteText(agent.filePath, agent.content));
  }
  if (failures.length > 0) {
    throw new Error(`Pi cutover rollback was incomplete: ${failures.join('; ')}`);
  }
}

export async function migrateCodingProjectToV2(
  projectPath: string,
  dependencies: CodingProjectMigrationDependencies,
): Promise<CodingProjectMigrationResult> {
  const projectConfigPath = path.join(projectPath, CODING_PROJECT_CONFIG_PATH);
  const conversationsPath = path.join(projectPath, CODING_CONVERSATIONS_PATH);
  const projectSource = await readFile(projectConfigPath, 'utf8');
  const rawProject = JSON.parse(projectSource) as unknown;
  if (rawProject && typeof rawProject === 'object' && !Array.isArray(rawProject)
    && (rawProject as { schemaVersion?: unknown }).schemaVersion === 2) {
    return {
      status: 'already-current',
      config: normalizeCodingProjectConfigV2(rawProject),
    };
  }
  const normalizedLegacyConfig = normalizeLegacyProjectConfigV1(rawProject);
  const legacyConfig = preserveLegacyAgentFields(rawProject, normalizedLegacyConfig);
  const conversationsSource = await readOptionalText(conversationsPath);
  const migrationTimestamp = dependencies.now?.() ?? new Date().toISOString();
  const backupDirectory = path.join(
    projectPath,
    '.niancode',
    'migration-backups',
    `pi-cutover-${timestampKey(migrationTimestamp)}`,
  );
  const copy = dependencies.copyFile ?? copyFile;
  const writeJson = dependencies.writeJson ?? atomicWriteJson;

  await mkdir(path.dirname(backupDirectory), { recursive: true });
  await mkdir(backupDirectory, { recursive: false });
  await copy(projectConfigPath, path.join(backupDirectory, 'project.json'));
  if (conversationsSource !== null) {
    await copy(conversationsPath, path.join(backupDirectory, 'conversations.json'));
  }
  const agentFiles = await snapshotLegacyAgentFiles(
    projectPath,
    normalizedLegacyConfig,
    backupDirectory,
    copy,
  );

  const agents = await Promise.all(legacyConfig.agents.map((agent) => migrateAgent(
    legacyConfig,
    agent,
    dependencies.resolveLegacyModel,
    migrationTimestamp,
  )));
  const migratedConfig = normalizeCodingProjectConfigV2({
    schemaVersion: 2,
    projectType: legacyConfig.projectType,
    initialized: legacyConfig.initialized,
    agents,
    knowledgeDirectory: 'knowledge',
    legacyConversationNotice: 'pending',
    createdAt: legacyConfig.createdAt,
    updatedAt: migrationTimestamp,
  });

  try {
    await writeJson(conversationsPath, createEmptyConversationFileV2());
    await writeJson(projectConfigPath, migratedConfig);
    for (const agent of agentFiles) await unlink(agent.filePath);
  } catch (error) {
    try {
      await restoreOriginalState(
        projectConfigPath,
        projectSource,
        conversationsPath,
        conversationsSource,
        agentFiles,
      );
    } catch (rollbackError) {
      const rollbackMessage = rollbackError instanceof Error
        ? rollbackError.message
        : String(rollbackError);
      const migrationMessage = error instanceof Error ? error.message : String(error);
      throw new Error(
        `Pi project migration failed (${migrationMessage}) and rollback was incomplete: ${rollbackMessage}`,
        { cause: rollbackError },
      );
    }
    throw error;
  }

  return {
    status: 'migrated',
    config: migratedConfig,
    backupDirectory,
    removedGeneratedAgents: agentFiles.filter((agent) => agent.generated).map((agent) => agent.fileName),
    backedUpUncertainAgents: agentFiles.filter((agent) => !agent.generated).map((agent) => agent.fileName),
  };
}