import fs from 'node:fs';
import path from 'node:path';

import { STAGE_SEQUENCE } from './constants.js';
import { determineBriefClass, stagesForClass } from './brief-classifier.js';
import { mapStageToTask } from './stage-adapter.js';
import type {
  ForgeTask,
  PipelineOptions,
  PipelineResult,
  RunManifest,
  StageStatus,
  TaskExecutor,
} from './types.js';

/**
 * Generate a timestamp-based run ID.
 */
export function generateRunId(): string {
  const now = new Date();
  const pad = (n: number, w = 2) => String(n).padStart(w, '0');
  return [
    now.getUTCFullYear(),
    pad(now.getUTCMonth() + 1),
    pad(now.getUTCDate()),
    '-',
    pad(now.getUTCHours()),
    pad(now.getUTCMinutes()),
    pad(now.getUTCSeconds()),
  ].join('');
}

/**
 * Get the ISO timestamp for now.
 */
function nowISO(): string {
  return new Date().toISOString();
}

/**
 * Create and persist a run manifest.
 */
function createManifest(opts: {
  runId: string;
  briefPath: string;
  codebase: string;
  briefClass: RunManifest['briefClass'];
  classSource: RunManifest['classSource'];
  forceBoard: boolean;
  runDir: string;
}): RunManifest {
  const ts = nowISO();
  const manifest: RunManifest = {
    runId: opts.runId,
    brief: opts.briefPath,
    codebase: opts.codebase,
    briefClass: opts.briefClass,
    classSource: opts.classSource,
    forceBoard: opts.forceBoard,
    createdAt: ts,
    updatedAt: ts,
    currentStage: '',
    status: 'in_progress',
    stages: {},
  };
  saveManifest(opts.runDir, manifest);
  return manifest;
}

/**
 * Save a manifest to disk.
 */
export function saveManifest(runDir: string, manifest: RunManifest): void {
  manifest.updatedAt = nowISO();
  const manifestPath = path.join(runDir, 'manifest.json');
  fs.mkdirSync(path.dirname(manifestPath), { recursive: true });
  fs.writeFileSync(manifestPath, JSON.stringify(manifest, null, 2) + '\n', 'utf-8');
}

/**
 * Load a manifest from disk.
 */
export function loadManifest(runDir: string): RunManifest {
  const manifestPath = path.join(runDir, 'manifest.json');
  if (!fs.existsSync(manifestPath)) {
    throw new Error(`manifest.json not found: ${manifestPath}`);
  }
  return JSON.parse(fs.readFileSync(manifestPath, 'utf-8')) as RunManifest;
}

/**
 * Select and validate stages, optionally skipping to a specific stage.
 */
export function selectStages(stages?: string[], skipTo?: string): string[] {
  const selected = stages ?? [...STAGE_SEQUENCE];

  const unknown = selected.filter((s) => !STAGE_SEQUENCE.includes(s));
  if (unknown.length > 0) {
    throw new Error(`Unknown Forge stages requested: ${unknown.join(', ')}`);
  }

  if (!skipTo) return selected;

  if (!selected.includes(skipTo)) {
    throw new Error(`skip_to stage '${skipTo}' is not present in the selected stage list`);
  }
  const skipIndex = selected.indexOf(skipTo);
  return selected.slice(skipIndex);
}

/**
 * Run the Forge pipeline.
 *
 * 1. Classify the brief
 * 2. Generate a run ID and create run directory
 * 3. Map stages to tasks and submit to TaskExecutor
 * 4. Track manifest with stage statuses
 * 5. Return pipeline result
 */
export async function runPipeline(
  briefPath: string,
  projectRoot: string,
  options: PipelineOptions,
): Promise<PipelineResult> {
  const resolvedRoot = path.resolve(projectRoot);
  const resolvedBrief = path.resolve(briefPath);
  const briefContent = fs.readFileSync(resolvedBrief, 'utf-8');

  // Classify brief
  const { briefClass, classSource } = determineBriefClass(briefContent, options.briefClass);

  // Determine stages
  const classStages = options.stages ?? stagesForClass(briefClass, options.forceBoard);
  const selectedStages = selectStages(classStages, options.skipTo);

  // Create run directory
  const runId = generateRunId();
  const runDir = path.join(resolvedRoot, '.forge', 'runs', runId);
  fs.mkdirSync(runDir, { recursive: true });

  // Create manifest
  const manifest = createManifest({
    runId,
    briefPath: resolvedBrief,
    codebase: options.codebase ?? '',
    briefClass,
    classSource,
    forceBoard: options.forceBoard ?? false,
    runDir,
  });

  // Map stages to tasks
  const tasks: ForgeTask[] = [];
  for (let i = 0; i < selectedStages.length; i++) {
    const stageName = selectedStages[i]!;
    const task = mapStageToTask({
      stageName,
      briefContent,
      projectRoot: resolvedRoot,
      runId,
      runDir,
    });

    // Override dependency chain for selected (possibly filtered) stages
    if (i > 0) {
      task.dependsOn = [tasks[i - 1]!.id];
    } else {
      delete task.dependsOn;
    }

    tasks.push(task);
  }

  // Execute stages
  const { executor } = options;
  for (let i = 0; i < tasks.length; i++) {
    const task = tasks[i]!;
    const stageName = selectedStages[i]!;

    // Update manifest: stage in progress
    manifest.currentStage = stageName;
    manifest.stages[stageName] = {
      status: 'in_progress',
      startedAt: nowISO(),
    };
    saveManifest(runDir, manifest);

    try {
      await executor.submitTask(task);
      const result = await executor.waitForCompletion(task.id, task.timeoutSeconds * 1000);

      // Update manifest: stage completed or failed
      const stageStatus: StageStatus = {
        status: result.status === 'completed' ? 'passed' : 'failed',
        startedAt: manifest.stages[stageName]!.startedAt,
        completedAt: nowISO(),
      };
      manifest.stages[stageName] = stageStatus;

      if (result.status !== 'completed') {
        manifest.status = 'failed';
        saveManifest(runDir, manifest);
        throw new Error(`Stage ${stageName} failed with status: ${result.status}`);
      }

      saveManifest(runDir, manifest);
    } catch (error) {
      if (!manifest.stages[stageName]?.completedAt) {
        manifest.stages[stageName] = {
          status: 'failed',
          startedAt: manifest.stages[stageName]?.startedAt,
          completedAt: nowISO(),
        };
      }
      manifest.status = 'failed';
      saveManifest(runDir, manifest);
      throw error;
    }
  }

  // All stages passed
  manifest.status = 'completed';
  saveManifest(runDir, manifest);

  return {
    runId,
    briefPath: resolvedBrief,
    projectRoot: resolvedRoot,
    runDir,
    taskIds: tasks.map((t) => t.id),
    stages: selectedStages,
    manifest,
  };
}

/**
 * Resume a pipeline from the last incomplete stage.
 */
export async function resumePipeline(
  runDir: string,
  executor: TaskExecutor,
): Promise<PipelineResult> {
  const manifest = loadManifest(runDir);
  const resolvedRoot = path.dirname(path.dirname(path.dirname(runDir))); // .forge/runs/{id} → project root

  const briefContent = fs.readFileSync(manifest.brief, 'utf-8');
  const allStages = stagesForClass(manifest.briefClass, manifest.forceBoard);

  // Find first non-passed stage
  const resumeFrom = allStages.find((s) => manifest.stages[s]?.status !== 'passed');
  if (!resumeFrom) {
    manifest.status = 'completed';
    saveManifest(runDir, manifest);
    return {
      runId: manifest.runId,
      briefPath: manifest.brief,
      projectRoot: resolvedRoot,
      runDir,
      taskIds: [],
      stages: allStages,
      manifest,
    };
  }

  const remainingStages = selectStages(allStages, resumeFrom);
  manifest.status = 'in_progress';

  const tasks: ForgeTask[] = [];
  for (let i = 0; i < remainingStages.length; i++) {
    const stageName = remainingStages[i]!;
    const task = mapStageToTask({
      stageName,
      briefContent,
      projectRoot: resolvedRoot,
      runId: manifest.runId,
      runDir,
    });

    if (i > 0) {
      task.dependsOn = [tasks[i - 1]!.id];
    } else {
      delete task.dependsOn;
    }
    tasks.push(task);
  }

  for (let i = 0; i < tasks.length; i++) {
    const task = tasks[i]!;
    const stageName = remainingStages[i]!;

    manifest.currentStage = stageName;
    manifest.stages[stageName] = {
      status: 'in_progress',
      startedAt: nowISO(),
    };
    saveManifest(runDir, manifest);

    try {
      await executor.submitTask(task);
      const result = await executor.waitForCompletion(task.id, task.timeoutSeconds * 1000);

      manifest.stages[stageName] = {
        status: result.status === 'completed' ? 'passed' : 'failed',
        startedAt: manifest.stages[stageName]!.startedAt,
        completedAt: nowISO(),
      };

      if (result.status !== 'completed') {
        manifest.status = 'failed';
        saveManifest(runDir, manifest);
        throw new Error(`Stage ${stageName} failed with status: ${result.status}`);
      }

      saveManifest(runDir, manifest);
    } catch (error) {
      if (!manifest.stages[stageName]?.completedAt) {
        manifest.stages[stageName] = {
          status: 'failed',
          startedAt: manifest.stages[stageName]?.startedAt,
          completedAt: nowISO(),
        };
      }
      manifest.status = 'failed';
      saveManifest(runDir, manifest);
      throw error;
    }
  }

  manifest.status = 'completed';
  saveManifest(runDir, manifest);

  return {
    runId: manifest.runId,
    briefPath: manifest.brief,
    projectRoot: resolvedRoot,
    runDir,
    taskIds: tasks.map((t) => t.id),
    stages: remainingStages,
    manifest,
  };
}

/**
 * Get the status of a pipeline run.
 */
export function getPipelineStatus(runDir: string): RunManifest {
  return loadManifest(runDir);
}