/**
 * PullService - Pull git operations without HTTP
 *
 * Encapsulates the full git pull workflow including:
 * - Branch name and detached HEAD detection
 * - Fetching from remote
 * - Status parsing and local change detection
 * - Stash push/pop logic
 * - Upstream verification (rev-parse / --verify)
 * - Pull execution and conflict detection
 * - Conflict file list collection
 *
 * Extracted from the worktree pull route to improve organization
 * and testability. Follows the same pattern as rebase-service.ts
 * and cherry-pick-service.ts.
 */

import { createLogger, getErrorMessage } from '@automaker/utils';
import { execGitCommand, getConflictFiles } from '@automaker/git-utils';
import { execGitCommandWithLockRetry, getCurrentBranch } from '../lib/git.js';

const logger = createLogger('PullService');

// ============================================================================
// Types
// ============================================================================

export interface PullOptions {
  /** Remote name to pull from (defaults to 'origin') */
  remote?: string;
  /** Specific remote branch to pull (e.g. 'main'). When provided, overrides the tracking branch and fetches this branch from the remote. */
  remoteBranch?: string;
  /** When true, automatically stash local changes before pulling and reapply after */
  stashIfNeeded?: boolean;
}

export interface PullResult {
  success: boolean;
  error?: string;
  branch?: string;
  pulled?: boolean;
  hasLocalChanges?: boolean;
  localChangedFiles?: string[];
  stashed?: boolean;
  stashRestored?: boolean;
  stashRecoveryFailed?: boolean;
  hasConflicts?: boolean;
  conflictSource?: 'pull' | 'stash';
  conflictFiles?: string[];
  message?: string;
  /** Whether the pull resulted in a merge commit (not fast-forward) */
  isMerge?: boolean;
  /** Whether the pull was a fast-forward (no merge commit needed) */
  isFastForward?: boolean;
  /** Files affected by the merge (only present when isMerge is true) */
  mergeAffectedFiles?: string[];
}

// ============================================================================
// Helper Functions
// ============================================================================

/**
 * Fetch the latest refs from a remote.
 *
 * @param worktreePath - Path to the git worktree
 * @param remote - Remote name (e.g. 'origin')
 */
export async function fetchRemote(worktreePath: string, remote: string): Promise<void> {
  await execGitCommand(['fetch', remote], worktreePath);
}

/**
 * Parse `git status --porcelain` output into a list of changed file paths.
 *
 * @param worktreePath - Path to the git worktree
 * @returns Object with hasLocalChanges flag and list of changed file paths
 */
export async function getLocalChanges(
  worktreePath: string
): Promise<{ hasLocalChanges: boolean; localChangedFiles: string[] }> {
  const statusOutput = await execGitCommand(['status', '--porcelain'], worktreePath);
  const hasLocalChanges = statusOutput.trim().length > 0;

  let localChangedFiles: string[] = [];
  if (hasLocalChanges) {
    localChangedFiles = statusOutput
      .trim()
      .split('\n')
      .filter((line) => line.trim().length > 0)
      .map((line) => {
        const entry = line.substring(3).trim();
        const arrowIndex = entry.indexOf(' -> ');
        return arrowIndex !== -1 ? entry.substring(arrowIndex + 4).trim() : entry;
      });
  }

  return { hasLocalChanges, localChangedFiles };
}

/**
 * Stash local changes with a descriptive message.
 *
 * @param worktreePath - Path to the git worktree
 * @param branchName - Current branch name (used in stash message)
 * @returns Promise<void> — resolves on success, throws on failure
 */
export async function stashChanges(worktreePath: string, branchName: string): Promise<void> {
  const stashMessage = `automaker-pull-stash: Pre-pull stash on ${branchName}`;
  await execGitCommandWithLockRetry(
    ['stash', 'push', '--include-untracked', '-m', stashMessage],
    worktreePath
  );
}

/**
 * Pop the top stash entry.
 *
 * @param worktreePath - Path to the git worktree
 * @returns The stdout from stash pop
 */
export async function popStash(worktreePath: string): Promise<string> {
  return await execGitCommandWithLockRetry(['stash', 'pop'], worktreePath);
}

/**
 * Try to pop the stash, returning whether the pop succeeded.
 *
 * @param worktreePath - Path to the git worktree
 * @returns true if stash pop succeeded, false if it failed
 */
async function tryPopStash(worktreePath: string): Promise<boolean> {
  try {
    await execGitCommandWithLockRetry(['stash', 'pop'], worktreePath);
    return true;
  } catch (stashPopError) {
    // Stash pop failed - leave it in stash list for manual recovery
    logger.error('Failed to reapply stash during error recovery', {
      worktreePath,
      error: getErrorMessage(stashPopError),
    });
    return false;
  }
}

/**
 * Result of the upstream/remote branch check.
 * - 'tracking': the branch has a configured upstream tracking ref
 * - 'remote': no tracking ref, but the remote branch exists
 * - 'none': neither a tracking ref nor a remote branch was found
 */
export type UpstreamStatus = 'tracking' | 'remote' | 'none';

/**
 * Check whether the branch has an upstream tracking ref, or whether
 * the remote branch exists.
 *
 * @param worktreePath - Path to the git worktree
 * @param branchName - Current branch name
 * @param remote - Remote name
 * @returns UpstreamStatus indicating tracking ref, remote branch, or neither
 */
export async function hasUpstreamOrRemoteBranch(
  worktreePath: string,
  branchName: string,
  remote: string
): Promise<UpstreamStatus> {
  try {
    await execGitCommand(['rev-parse', '--abbrev-ref', `${branchName}@{upstream}`], worktreePath);
    return 'tracking';
  } catch {
    // No upstream tracking - check if the remote branch exists
    try {
      await execGitCommand(['rev-parse', '--verify', `${remote}/${branchName}`], worktreePath);
      return 'remote';
    } catch {
      return 'none';
    }
  }
}

/**
 * Check whether an error output string indicates a merge conflict.
 */
function isConflictError(errorOutput: string): boolean {
  return errorOutput.includes('CONFLICT') || errorOutput.includes('Automatic merge failed');
}

/**
 * Determine whether the current HEAD commit is a merge commit by checking
 * whether it has two or more parent hashes.
 *
 * Runs `git show -s --pretty=%P HEAD` which prints the parent SHAs separated
 * by spaces.  A merge commit has at least two parents; a regular commit has one.
 *
 * @param worktreePath - Path to the git worktree
 * @returns true if HEAD is a merge commit, false otherwise
 */
async function isMergeCommit(worktreePath: string): Promise<boolean> {
  try {
    const output = await execGitCommand(['show', '-s', '--pretty=%P', 'HEAD'], worktreePath);
    // Each parent SHA is separated by a space; two or more means it's a merge
    const parents = output
      .trim()
      .split(/\s+/)
      .filter((p) => p.length > 0);
    return parents.length >= 2;
  } catch {
    // If the check fails for any reason, assume it is not a merge commit
    return false;
  }
}

/**
 * Check whether an output string indicates a stash conflict.
 */
function isStashConflict(output: string): boolean {
  return output.includes('CONFLICT') || output.includes('Merge conflict');
}

// ============================================================================
// Main Service Function
// ============================================================================

/**
 * Perform a full git pull workflow on the given worktree.
 *
 * The workflow:
 * 1. Get current branch name (detect detached HEAD)
 * 2. Fetch from remote
 * 3. Check for local changes
 * 4. If local changes and stashIfNeeded, stash them
 * 5. Verify upstream tracking or remote branch exists
 * 6. Execute `git pull`
 * 7. If stash was created and pull succeeded, reapply stash
 * 8. Detect and report conflicts from pull or stash reapplication
 *
 * @param worktreePath - Path to the git worktree
 * @param options - Pull options (remote, stashIfNeeded)
 * @returns PullResult with detailed status information
 */
export async function performPull(
  worktreePath: string,
  options?: PullOptions
): Promise<PullResult> {
  const targetRemote = options?.remote || 'origin';
  const stashIfNeeded = options?.stashIfNeeded ?? false;
  const targetRemoteBranch = options?.remoteBranch;

  // 1. Get current branch name
  let branchName: string;
  try {
    branchName = await getCurrentBranch(worktreePath);
  } catch (err) {
    return {
      success: false,
      error: `Failed to get current branch: ${getErrorMessage(err)}`,
    };
  }

  // 2. Check for detached HEAD state
  if (branchName === 'HEAD') {
    return {
      success: false,
      error: 'Cannot pull in detached HEAD state. Please checkout a branch first.',
    };
  }

  // 3. Fetch latest from remote
  try {
    await fetchRemote(worktreePath, targetRemote);
  } catch (fetchError) {
    return {
      success: false,
      error: `Failed to fetch from remote '${targetRemote}': ${getErrorMessage(fetchError)}`,
    };
  }

  // 4. Check for local changes
  let hasLocalChanges: boolean;
  let localChangedFiles: string[];
  try {
    ({ hasLocalChanges, localChangedFiles } = await getLocalChanges(worktreePath));
  } catch (err) {
    return {
      success: false,
      error: `Failed to get local changes: ${getErrorMessage(err)}`,
    };
  }

  // 5. If there are local changes and stashIfNeeded is not requested, return info
  if (hasLocalChanges && !stashIfNeeded) {
    return {
      success: true,
      branch: branchName,
      pulled: false,
      hasLocalChanges: true,
      localChangedFiles,
      message:
        'Local changes detected. Use stashIfNeeded to automatically stash and reapply changes.',
    };
  }

  // 6. Stash local changes if needed
  let didStash = false;
  if (hasLocalChanges && stashIfNeeded) {
    try {
      await stashChanges(worktreePath, branchName);
      didStash = true;
    } catch (stashError) {
      return {
        success: false,
        error: `Failed to stash local changes: ${getErrorMessage(stashError)}`,
      };
    }
  }

  // 7. Verify upstream tracking or remote branch exists
  // Skip this check when a specific remote branch is provided - we always use
  // explicit 'git pull <remote> <branch>' args in that case.
  let upstreamStatus: UpstreamStatus = 'tracking';
  if (!targetRemoteBranch) {
    upstreamStatus = await hasUpstreamOrRemoteBranch(worktreePath, branchName, targetRemote);
    if (upstreamStatus === 'none') {
      let stashRecoveryFailed = false;
      if (didStash) {
        const stashPopped = await tryPopStash(worktreePath);
        stashRecoveryFailed = !stashPopped;
      }
      return {
        success: false,
        error: `Branch '${branchName}' has no upstream branch on remote '${targetRemote}'. Push it first or set upstream with: git branch --set-upstream-to=${targetRemote}/${branchName}${stashRecoveryFailed ? ' Local changes remain stashed and need manual recovery (run: git stash pop).' : ''}`,
        stashRecoveryFailed: stashRecoveryFailed ? stashRecoveryFailed : undefined,
      };
    }
  }

  // 8. Pull latest changes
  // When a specific remote branch is requested, always use explicit remote + branch args.
  // When the branch has a configured upstream tracking ref, let Git use it automatically.
  // When only the remote branch exists (no tracking ref), explicitly specify remote and branch.
  const pullArgs = targetRemoteBranch
    ? ['pull', targetRemote, targetRemoteBranch]
    : upstreamStatus === 'tracking'
      ? ['pull']
      : ['pull', targetRemote, branchName];
  let pullConflict = false;
  let pullConflictFiles: string[] = [];

  // Declare merge detection variables before the try block so they are accessible
  // in the stash reapplication path even when didStash is true.
  let isMerge = false;
  let isFastForward = false;
  let mergeAffectedFiles: string[] = [];

  try {
    const pullOutput = await execGitCommand(pullArgs, worktreePath);

    const alreadyUpToDate = pullOutput.includes('Already up to date');
    // Detect fast-forward from git pull output
    isFastForward = pullOutput.includes('Fast-forward') || pullOutput.includes('fast-forward');
    // Detect merge by checking whether the new HEAD has two parents (more reliable
    // than string-matching localised pull output which may not contain 'Merge').
    isMerge = !alreadyUpToDate && !isFastForward ? await isMergeCommit(worktreePath) : false;

    // If it was a real merge (not fast-forward), get the affected files
    if (isMerge) {
      try {
        // Get files changed in the merge commit
        const diffOutput = await execGitCommand(
          ['diff', '--name-only', 'HEAD~1', 'HEAD'],
          worktreePath
        );
        mergeAffectedFiles = diffOutput
          .trim()
          .split('\n')
          .filter((f: string) => f.trim().length > 0);
      } catch {
        // Ignore errors - this is best-effort
      }
    }

    // If no stash to reapply, return success
    if (!didStash) {
      return {
        success: true,
        branch: branchName,
        pulled: !alreadyUpToDate,
        hasLocalChanges: false,
        stashed: false,
        stashRestored: false,
        message: alreadyUpToDate ? 'Already up to date' : 'Pulled latest changes',
        ...(isMerge ? { isMerge: true, mergeAffectedFiles } : {}),
        ...(isFastForward ? { isFastForward: true } : {}),
      };
    }
  } catch (pullError: unknown) {
    const err = pullError as { stderr?: string; stdout?: string; message?: string };
    const errorOutput = `${err.stderr || ''} ${err.stdout || ''} ${err.message || ''}`;

    if (isConflictError(errorOutput)) {
      pullConflict = true;
      try {
        pullConflictFiles = await getConflictFiles(worktreePath);
      } catch {
        pullConflictFiles = [];
      }
    } else {
      // Non-conflict pull error
      let stashRecoveryFailed = false;
      if (didStash) {
        const stashPopped = await tryPopStash(worktreePath);
        stashRecoveryFailed = !stashPopped;
      }

      // Check for common errors
      const errorMsg = err.stderr || err.message || 'Pull failed';
      if (errorMsg.includes('no tracking information')) {
        return {
          success: false,
          error: `Branch '${branchName}' has no upstream branch. Push it first or set upstream with: git branch --set-upstream-to=${targetRemote}/${branchName}${stashRecoveryFailed ? ' Local changes remain stashed and need manual recovery (run: git stash pop).' : ''}`,
          stashRecoveryFailed: stashRecoveryFailed ? stashRecoveryFailed : undefined,
        };
      }

      return {
        success: false,
        error: `${errorMsg}${stashRecoveryFailed ? ' Local changes remain stashed and need manual recovery (run: git stash pop).' : ''}`,
        stashRecoveryFailed: stashRecoveryFailed ? stashRecoveryFailed : undefined,
      };
    }
  }

  // 9. If pull had conflicts, return conflict info (don't try stash pop)
  if (pullConflict) {
    return {
      success: false,
      branch: branchName,
      pulled: true,
      hasConflicts: true,
      conflictSource: 'pull',
      conflictFiles: pullConflictFiles,
      stashed: didStash,
      stashRestored: false,
      message:
        `Pull resulted in merge conflicts. ${didStash ? 'Your local changes are still stashed.' : ''}`.trim(),
    };
  }

  // 10. Pull succeeded, now try to reapply stash
  if (didStash) {
    return await reapplyStash(worktreePath, branchName, {
      isMerge,
      isFastForward,
      mergeAffectedFiles,
    });
  }

  // Shouldn't reach here, but return a safe default
  return {
    success: true,
    branch: branchName,
    pulled: true,
    message: 'Pulled latest changes',
  };
}

/**
 * Attempt to reapply stashed changes after a successful pull.
 * Handles both clean reapplication and conflict scenarios.
 *
 * @param worktreePath - Path to the git worktree
 * @param branchName - Current branch name
 * @param mergeInfo - Merge/fast-forward detection info from the pull step
 * @returns PullResult reflecting stash reapplication status
 */
async function reapplyStash(
  worktreePath: string,
  branchName: string,
  mergeInfo: { isMerge: boolean; isFastForward: boolean; mergeAffectedFiles: string[] }
): Promise<PullResult> {
  const mergeFields: Partial<PullResult> = {
    ...(mergeInfo.isMerge
      ? { isMerge: true, mergeAffectedFiles: mergeInfo.mergeAffectedFiles }
      : {}),
    ...(mergeInfo.isFastForward ? { isFastForward: true } : {}),
  };

  try {
    await popStash(worktreePath);

    // Stash pop succeeded cleanly (popStash throws on non-zero exit)
    return {
      success: true,
      branch: branchName,
      pulled: true,
      hasConflicts: false,
      stashed: true,
      stashRestored: true,
      ...mergeFields,
      message: 'Pulled latest changes and restored your stashed changes.',
    };
  } catch (stashPopError: unknown) {
    const err = stashPopError as { stderr?: string; stdout?: string; message?: string };
    const errorOutput = `${err.stderr || ''} ${err.stdout || ''} ${err.message || ''}`;

    // Check if stash pop failed due to conflicts
    // The stash remains in the stash list when conflicts occur, so stashRestored is false
    if (isStashConflict(errorOutput)) {
      let stashConflictFiles: string[] = [];
      try {
        stashConflictFiles = await getConflictFiles(worktreePath);
      } catch {
        stashConflictFiles = [];
      }

      return {
        success: true,
        branch: branchName,
        pulled: true,
        hasConflicts: true,
        conflictSource: 'stash',
        conflictFiles: stashConflictFiles,
        stashed: true,
        stashRestored: false,
        ...mergeFields,
        message: 'Pull succeeded but reapplying your stashed changes resulted in merge conflicts.',
      };
    }

    // Non-conflict stash pop error - stash is still in the stash list
    logger.warn('Failed to reapply stash after pull', { worktreePath, error: errorOutput });

    return {
      success: true,
      branch: branchName,
      pulled: true,
      hasConflicts: false,
      stashed: true,
      stashRestored: false,
      ...mergeFields,
      message:
        'Pull succeeded but failed to reapply stashed changes. Your changes are still in the stash list.',
    };
  }
}