import { existsSync } from "fs"
import { rm } from "fs/promises"
import { $ } from "bun"

/** Get the repo root from a working directory. */
export async function repoRoot(cwd?: string): Promise<string> {
  const result = await $`git rev-parse --show-toplevel`.cwd(cwd ?? ".").nothrow().quiet()
  if (result.exitCode !== 0) {
    throw new Error("Not a git repository. Run this command from inside a git repo.")
  }
  return result.text().trim()
}

/** Get the current branch name. */
export async function currentBranch(cwd?: string): Promise<string> {
  const result = await $`git rev-parse --abbrev-ref HEAD`.cwd(cwd ?? ".").nothrow().quiet()
  if (result.exitCode !== 0) {
    throw new Error("Could not determine current branch.")
  }
  return result.text().trim()
}

/** Check if a branch exists locally or remotely. Returns "local", "remote", or null. */
export async function branchExists(branch: string, cwd?: string, opts?: { fetch?: boolean }): Promise<"local" | "remote" | null> {
  const dir = cwd ?? "."
  const local = await $`git show-ref --verify --quiet refs/heads/${branch}`.cwd(dir).nothrow().quiet()
  if (local.exitCode === 0) return "local"

  if (opts?.fetch) {
    await $`git fetch origin`.cwd(dir).nothrow().quiet()
  }
  const remote = await $`git show-ref --verify --quiet refs/remotes/origin/${branch}`.cwd(dir).nothrow().quiet()
  if (remote.exitCode === 0) return "remote"

  return null
}

/** Create a worktree for the given branch. */
export async function createWorktree(branch: string, worktreePath: string, cwd: string): Promise<void> {
  // Clean up stale worktree path if it exists
  if (existsSync(worktreePath)) {
    await $`git worktree remove ${worktreePath} --force`.cwd(cwd).nothrow().quiet()
    if (existsSync(worktreePath)) {
      await rm(worktreePath, { recursive: true })
    }
  }
  await $`git worktree prune`.cwd(cwd).nothrow().quiet()

  const exists = await branchExists(branch, cwd, { fetch: true })

  let result
  if (exists === "local") {
    result = await $`git worktree add ${worktreePath} ${branch}`.cwd(cwd).nothrow().quiet()
  } else if (exists === "remote") {
    result = await $`git worktree add ${worktreePath} -b ${branch} origin/${branch}`.cwd(cwd).nothrow().quiet()
  } else {
    // New branch from current HEAD
    result = await $`git worktree add -b ${branch} ${worktreePath}`.cwd(cwd).nothrow().quiet()
  }
  if (result.exitCode !== 0) {
    throw new Error(`Failed to create worktree for "${branch}": ${result.stderr.toString().trim()}`)
  }
}

/** Remove a worktree. Silently succeeds if the worktree is already gone. */
export async function removeWorktree(worktreePath: string, cwd: string): Promise<void> {
  const result = await $`git worktree remove ${worktreePath} --force`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) {
    // Worktree may already be gone or stale — prune and clean up the directory
    await $`git worktree prune`.cwd(cwd).nothrow().quiet()
    if (existsSync(worktreePath)) {
      await rm(worktreePath, { recursive: true })
    }
  }
}

/** Delete a local branch. */
export async function deleteLocalBranch(branch: string, cwd: string): Promise<void> {
  await $`git branch -D ${branch}`.cwd(cwd).nothrow().quiet()
}

/** Checkout a branch. */
export async function checkout(branch: string, cwd: string): Promise<void> {
  const result = await $`git checkout ${branch}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) {
    throw new Error(`Failed to checkout branch "${branch}": ${result.stderr.toString().trim()}`)
  }
}

/** Merge a branch into the current branch. Returns conflicted file paths, or empty array if clean. */
export async function merge(branch: string, cwd: string, opts?: { squash?: boolean }): Promise<string[]> {
  const cmd = opts?.squash
    ? $`git merge --squash ${branch}`.cwd(cwd).nothrow().quiet()
    : $`git merge ${branch}`.cwd(cwd).nothrow().quiet()
  const result = await cmd
  if (result.exitCode === 0) return []

  // Check for unmerged (conflicted) files
  const unmerged = await $`git diff --name-only --diff-filter=U`.cwd(cwd).nothrow().quiet().text()
  const files = unmerged.trim().split("\n").filter(Boolean)
  if (files.length > 0) return files

  // Not a conflict — some other merge failure
  const label = opts?.squash ? "squash-merge" : "merge"
  throw new Error(`Failed to ${label} branch "${branch}": ${result.stderr.toString().trim()}`)
}

/** Return the staged diff as text. */
export async function diffStaged(cwd: string): Promise<string> {
  return await $`git diff --staged`.cwd(cwd).nothrow().quiet().text()
}

/** Commit staged changes with a message. */
export async function commit(message: string, cwd: string): Promise<void> {
  const result = await $`git commit -m ${message}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) {
    throw new Error(`Failed to commit: ${result.stderr.toString().trim()}`)
  }
}

/** Stage a file. */
export async function stageFile(file: string, cwd: string): Promise<void> {
  await $`git add ${file}`.cwd(cwd).nothrow().quiet()
}

/** Finalize a merge commit after resolving conflicts. */
export async function commitMerge(cwd: string): Promise<void> {
  const result = await $`git commit --no-edit`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) {
    throw new Error(`Failed to commit merge: ${result.stderr.toString().trim()}`)
  }
}

/** Abort an in-progress merge. */
export async function abortMerge(cwd: string): Promise<void> {
  await $`git merge --abort`.cwd(cwd).nothrow().quiet()
}

/** Rebase the current branch onto another. Returns conflicted file paths, or empty array if clean. */
export async function rebase(onto: string, cwd: string): Promise<string[]> {
  // Bail early if a rebase is already in progress
  const inProgress = await $`git -C ${cwd} rev-parse --verify --quiet REBASE_HEAD`.nothrow().quiet()
  if (inProgress.exitCode === 0) {
    throw new Error(`A rebase is already in progress. Run "git -C ${cwd} rebase --abort" to cancel it first.`)
  }

  const result = await $`git rebase ${onto}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode === 0) return []

  const unmerged = await $`git diff --name-only --diff-filter=U`.cwd(cwd).nothrow().quiet().text()
  const files = unmerged.trim().split("\n").filter(Boolean)
  if (files.length > 0) return files

  // No conflicts but rebase still failed — include stderr for diagnostics
  const stderr = result.stderr.toString().trim()
  throw new Error(`Rebase onto "${onto}" failed: ${stderr || "(no output from git)"}`)
}

/** Continue a rebase after resolving conflicts. Returns conflicted files for the next commit, or empty if done. */
export async function rebaseContinue(cwd: string): Promise<string[]> {
  const result = await $`git -c core.editor=true rebase --continue`.cwd(cwd).nothrow().quiet()
  if (result.exitCode === 0) return []

  const unmerged = await $`git diff --name-only --diff-filter=U`.cwd(cwd).nothrow().quiet().text()
  const files = unmerged.trim().split("\n").filter(Boolean)
  if (files.length > 0) return files

  throw new Error(`Rebase --continue failed: ${result.stderr.toString().trim()}`)
}

/** Abort an in-progress rebase. */
export async function rebaseAbort(cwd: string): Promise<void> {
  await $`git rebase --abort`.cwd(cwd).nothrow().quiet()
}

/** Check if a worktree has uncommitted changes. */
export async function isDirty(worktreePath: string): Promise<boolean> {
  const result = await $`git -C ${worktreePath} status --porcelain`.nothrow().quiet()
  if (result.exitCode !== 0) return false
  return result.text().trim().length > 0
}

/** Find the merge base (common ancestor) between two refs. */
export async function mergeBase(ref1: string, ref2: string, cwd: string): Promise<string> {
  const result = await $`git merge-base ${ref1} ${ref2}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) {
    throw new Error(`Could not find merge base between "${ref1}" and "${ref2}"`)
  }
  return result.text().trim()
}

/** Get a one-line-per-commit log for a revision range. Returns empty string on failure. */
export async function commitLog(range: string, cwd: string): Promise<string> {
  const result = await $`git log --oneline ${range}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) return ""
  return result.text().trim()
}

/** Get a diff stat summary for a revision range. Returns empty string on failure. */
export async function diffStat(range: string, cwd: string): Promise<string> {
  const result = await $`git diff --stat ${range}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) return ""
  return result.text().trim()
}

/** Get the diff for a specific file between two refs. Returns empty string on failure. */
export async function fileDiff(ref1: string, ref2: string, file: string, cwd: string): Promise<string> {
  const result = await $`git diff ${ref1} ${ref2} -- ${file}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) return ""
  return result.text().trim()
}

/** Check if a branch has commits beyond main. */
export async function hasNewCommits(worktreePath: string): Promise<boolean> {
  const main = await mainBranch(worktreePath)
  const result = await $`git -C ${worktreePath} rev-list ${main}..HEAD --count`.nothrow().quiet()
  if (result.exitCode !== 0) return false
  return parseInt(result.text().trim(), 10) > 0
}

/** Get the full unified diff of a branch vs main as a string. */
export async function branchDiff(branch: string, cwd: string): Promise<string> {
  const main = await mainBranch(cwd)
  const result = await $`git diff ${main}...${branch}`.cwd(cwd).nothrow().quiet()
  if (result.exitCode !== 0) return ""
  return result.text()
}

/** Detect the main branch name (main or master). */
export async function mainBranch(cwd?: string): Promise<string> {
  const dir = cwd ?? "."
  const result = await $`git -C ${dir} rev-parse --verify --quiet refs/heads/main`.nothrow().quiet()
  return result.exitCode === 0 ? "main" : "master"
}