#!/usr/bin/env bash
# Install technical-doc-flow for Claude Code, Codex, and Gemini CLI.
set -euo pipefail

PRODUCT="technical-doc-flow"
REPO_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
SKILL_SOURCE="$REPO_DIR/skills/$PRODUCT"
AGENTS_SOURCE="$REPO_DIR/agents"
CLAUDE_ROOT="${TECH_DOC_FLOW_CLAUDE_HOME:-${CLAUDE_HOME:-$HOME/.claude}}"
CODEX_ROOT="${TECH_DOC_FLOW_CODEX_HOME:-${CODEX_HOME:-$HOME/.codex}}"
PYTHON_BIN="${TECH_DOC_FLOW_PYTHON:-python3}"

MODE="symlink"
CLAUDE_MODE="auto"
CODEX_MODE="auto"
GEMINI_MODE="auto"
ONLY_PLATFORM=""
FORCE=0
DRY_RUN=0
BACKUP_STAMP="$(date +%Y%m%d-%H%M%S)"

usage() {
  cat <<'EOF'
Usage: ./install.sh [options]

With no platform option, installed CLIs or their configuration directories
are detected automatically. Claude and Codex install the exact same source
directory: skills/technical-doc-flow.

Options:
  --copy          Copy files instead of creating symlinks (Claude/Codex).
  --claude-only   Install Claude skill and root agents only.
  --codex-only    Install Codex skill only.
  --gemini-only   Link the Gemini extension only.
  --all           Select all three platforms explicitly.
  --no-claude     Skip Claude.
  --no-codex      Skip Codex.
  --no-gemini     Skip Gemini.
  --force         Back up a conflicting target as .bak.<timestamp> first.
  --dry-run       Print operations without changing files.
  -h, --help      Show this help.

Optional location overrides:
  TECH_DOC_FLOW_CLAUDE_HOME, TECH_DOC_FLOW_CODEX_HOME

Gemini always uses `gemini extensions link`; --copy never changes it.
EOF
}

die() {
  echo "error: $*" >&2
  exit 2
}

select_only() {
  local platform="$1"
  if [[ -n "$ONLY_PLATFORM" && "$ONLY_PLATFORM" != "$platform" ]]; then
    die "only one of --claude-only, --codex-only, --gemini-only may be used"
  fi
  ONLY_PLATFORM="$platform"
  CLAUDE_MODE="no"
  CODEX_MODE="no"
  GEMINI_MODE="no"
  case "$platform" in
    claude) CLAUDE_MODE="yes" ;;
    codex) CODEX_MODE="yes" ;;
    gemini) GEMINI_MODE="yes" ;;
  esac
}

while (($#)); do
  case "$1" in
    --copy) MODE="copy" ;;
    --claude-only) select_only claude ;;
    --codex-only) select_only codex ;;
    --gemini-only) select_only gemini ;;
    --all)
      [[ -z "$ONLY_PLATFORM" ]] || die "--all cannot be combined with --*-only"
      CLAUDE_MODE="yes"
      CODEX_MODE="yes"
      GEMINI_MODE="yes"
      ;;
    --no-claude) CLAUDE_MODE="no" ;;
    --no-codex) CODEX_MODE="no" ;;
    --no-gemini) GEMINI_MODE="no" ;;
    --force) FORCE=1 ;;
    --dry-run) DRY_RUN=1 ;;
    -h|--help) usage; exit 0 ;;
    *) die "unknown option: $1" ;;
  esac
  shift
done

[[ -f "$SKILL_SOURCE/SKILL.md" ]] \
  || die "canonical skill not found: $SKILL_SOURCE/SKILL.md"

shopt -s nullglob
AGENT_FILES=("$AGENTS_SOURCE"/*.md)
OBSOLETE_CLAUDE_AGENT_NAMES=("doc-visual-planner.md")

if [[ "$MODE" == "copy" && "$CLAUDE_MODE" == "no" \
  && "$CODEX_MODE" == "no" && "$GEMINI_MODE" != "no" ]]; then
  echo "note: --copy does not apply to Gemini; using extension link"
fi

run() {
  printf '+'
  printf ' %q' "$@"
  printf '\n'
  if ((DRY_RUN == 0)); then
    "$@"
  fi
}

next_backup_path() {
  local destination="$1"
  local candidate="$destination.bak.$BACKUP_STAMP"
  local suffix=1
  while [[ -e "$candidate" || -L "$candidate" ]]; do
    candidate="$destination.bak.$BACKUP_STAMP.$suffix"
    ((suffix += 1))
  done
  printf '%s\n' "$candidate"
}

# Rename a staged or existing entry only when the destination name is still
# unused. A preflight path check cannot provide that guarantee because another
# process may create the destination before the rename.
#
# Return codes:
#   0: renamed
#   3: destination is occupied
#   4: this platform/filesystem cannot provide atomic no-clobber rename
#   5: another rename error occurred
atomic_rename_noreplace() {
  local source="$1" destination="$2" rc=0
  printf '+ atomic-mv-noreplace %q %q\n' "$source" "$destination"
  if ((DRY_RUN)); then
    return 0
  fi

  "$PYTHON_BIN" - "$source" "$destination" <<'PY' || rc=$?
import ctypes
import errno
import os
import sys


source = os.fsencode(sys.argv[1])
destination = os.fsencode(sys.argv[2])
libc = ctypes.CDLL(None, use_errno=True)

if sys.platform.startswith("linux"):
    try:
        renameat2 = libc.renameat2
    except AttributeError:
        raise SystemExit(4)
    renameat2.argtypes = [
        ctypes.c_int,
        ctypes.c_char_p,
        ctypes.c_int,
        ctypes.c_char_p,
        ctypes.c_uint,
    ]
    renameat2.restype = ctypes.c_int
    result = renameat2(-100, source, -100, destination, 1)  # RENAME_NOREPLACE
elif sys.platform == "darwin":
    try:
        renamex_np = libc.renamex_np
    except AttributeError:
        raise SystemExit(4)
    renamex_np.argtypes = [ctypes.c_char_p, ctypes.c_char_p, ctypes.c_uint]
    renamex_np.restype = ctypes.c_int
    result = renamex_np(source, destination, 0x00000004)  # RENAME_EXCL
else:
    raise SystemExit(4)

if result == 0:
    raise SystemExit(0)

error_number = ctypes.get_errno()
if error_number in (errno.EEXIST, errno.ENOTEMPTY):
    raise SystemExit(3)
if error_number in {
    errno.EINVAL,
    errno.ENOSYS,
    getattr(errno, "ENOTSUP", errno.EINVAL),
    getattr(errno, "EOPNOTSUPP", errno.EINVAL),
}:
    raise SystemExit(4)

print(
    f"atomic no-clobber rename failed: {os.strerror(error_number)}",
    file=sys.stderr,
)
raise SystemExit(5)
PY
  return "$rc"
}

backup_destination_noreplace() {
  local destination="$1" backup="$2" rc
  if atomic_rename_noreplace "$destination" "$backup"; then
    return 0
  else
    rc=$?
  fi

  case "$rc" in
    3)
      die "backup target became occupied after preflight: $backup; $destination was not moved"
      ;;
    4)
      die "atomic no-clobber backup is unsupported on this platform/filesystem; $destination was not moved"
      ;;
    *)
      die "could not back up $destination without replacing $backup"
      ;;
  esac
}

publish_copy_noreplace() {
  local source="$1" destination="$2" parent base stage_root stage rc
  parent="$(dirname "$destination")"
  base="$(basename "$destination")"

  if ((DRY_RUN)); then
    printf '+ cp -RL %q %q\n' "$source" "<staged beside $destination>"
    printf '+ atomic-mv-noreplace %q %q\n' \
      "<staged beside $destination>" "$destination"
    return 0
  fi

  stage_root="$(mktemp -d "$parent/.${base}.install.XXXXXXXX")" \
    || die "could not create a staging directory beside $destination"
  stage="$stage_root/payload"

  printf '+ cp -RL %q %q\n' "$source" "$stage"
  if ! cp -RL -- "$source" "$stage"; then
    rm -rf -- "$stage_root"
    die "could not stage copy for $destination"
  fi

  if atomic_rename_noreplace "$stage" "$destination"; then
    rmdir -- "$stage_root"
    return 0
  else
    rc=$?
  fi

  rm -rf -- "$stage_root"
  case "$rc" in
    3)
      die "target appeared after preflight: $destination; the competing entry was preserved"
      ;;
    4)
      die "atomic no-clobber copy publish is unsupported on this platform/filesystem"
      ;;
    *)
      die "could not publish staged copy without replacing $destination"
      ;;
  esac
}

publish_symlink_noreplace() {
  local source="$1" destination="$2" parent base stage_root stage rc
  parent="$(dirname "$destination")"
  base="$(basename "$destination")"

  if ((DRY_RUN)); then
    printf '+ ln -s -- %q %q\n' "$source" "<staged beside $destination>"
    printf '+ atomic-mv-noreplace %q %q\n' \
      "<staged beside $destination>" "$destination"
    return 0
  fi

  stage_root="$(mktemp -d "$parent/.${base}.install.XXXXXXXX")" \
    || die "could not create a staging directory beside $destination"
  stage="$stage_root/payload"

  printf '+ ln -s -- %q %q\n' "$source" "$stage"
  if ! ln -s -- "$source" "$stage"; then
    rmdir -- "$stage_root"
    die "could not stage symlink for $destination"
  fi

  if atomic_rename_noreplace "$stage" "$destination"; then
    rmdir -- "$stage_root"
    return 0
  else
    rc=$?
  fi

  rm -- "$stage"
  rmdir -- "$stage_root"
  case "$rc" in
    3)
      die "target appeared after preflight: $destination; the competing entry was preserved"
      ;;
    4)
      die "atomic no-clobber symlink publish is unsupported on this platform/filesystem"
      ;;
    *)
      die "could not publish staged symlink without replacing $destination"
      ;;
  esac
}

# Installation is planned in memory first. No mkdir, backup, symlink, or copy
# may happen until every selected local target and required command passes this
# preflight.
PLAN_PLATFORMS=()
PLAN_SOURCES=()
PLAN_DESTINATIONS=()
PLAN_ACTIONS=()
PLAN_BACKUPS=()
MIGRATION_PLAN_ACTIONS=()
MIGRATION_PLAN_DESTINATIONS=()
MIGRATION_PLAN_SOURCES=()
MIGRATION_PLAN_MESSAGES=()

preflight_parent() {
  local destination="$1" cursor
  cursor="$(dirname "$destination")"
  while [[ "$cursor" != "/" && ! -e "$cursor" && ! -L "$cursor" ]]; do
    cursor="$(dirname "$cursor")"
  done
  [[ -d "$cursor" ]] \
    || die "destination parent is not a directory: $cursor (for $destination)"
}

plan_target() {
  local platform="$1" source="$2" destination="$3"
  local action="install" backup="" existing

  [[ -e "$source" || -L "$source" ]] \
    || die "installation source not found: $source"
  preflight_parent "$destination"

  for existing in "${PLAN_DESTINATIONS[@]}"; do
    [[ "$existing" != "$destination" ]] \
      || die "duplicate installation destination: $destination"
  done

  if [[ -L "$destination" && "$(readlink "$destination")" == "$source" ]]; then
    if [[ "$MODE" == "symlink" ]]; then
      action="skip"
    elif ((FORCE == 0)); then
      die "$destination is currently symlinked; use --copy --force to convert it"
    fi
  fi

  if [[ "$action" != "skip" && ( -e "$destination" || -L "$destination" ) ]]; then
    if ((FORCE == 0)); then
      die "target already exists: $destination (use --force to back it up)"
    fi
    backup="$(next_backup_path "$destination")"
  fi

  PLAN_PLATFORMS+=("$platform")
  PLAN_SOURCES+=("$source")
  PLAN_DESTINATIONS+=("$destination")
  PLAN_ACTIONS+=("$action")
  PLAN_BACKUPS+=("$backup")
}

append_migration_plan() {
  MIGRATION_PLAN_ACTIONS+=("$1")
  MIGRATION_PLAN_DESTINATIONS+=("$2")
  MIGRATION_PLAN_SOURCES+=("$3")
  MIGRATION_PLAN_MESSAGES+=("$4")
}

plan_obsolete_claude_agent() {
  local name="$1" destination source target
  destination="$CLAUDE_ROOT/agents/$name"
  source="$AGENTS_SOURCE/$name"

  # If a future release restores this source name, it is no longer obsolete
  # and the normal installation plan owns it.
  if [[ -e "$source" || -L "$source" ]]; then
    return 0
  fi

  if [[ -L "$destination" ]]; then
    if ! target="$(readlink "$destination")"; then
      die "could not inspect obsolete Claude agent candidate: $destination"
    fi
    if [[ "$target" == "$source" ]]; then
      append_migration_plan remove "$destination" "$source" ""
    else
      append_migration_plan preserve "$destination" "" \
        "preserve (obsolete agent path has a different symlink target): $destination -> $target"
    fi
  elif [[ -e "$destination" ]]; then
    append_migration_plan preserve "$destination" "" \
      "preserve (obsolete agent copy or user-managed entry): $destination"
  fi
}

revalidate_migration_removal() {
  local destination="$1" source="$2" target
  if [[ ! -L "$destination" ]]; then
    die "obsolete managed agent changed type or disappeared: $destination; nothing at this path was removed"
  fi
  if ! target="$(readlink "$destination")"; then
    die "could not re-read obsolete managed agent symlink: $destination; nothing at this path was removed"
  fi
  if [[ "$target" != "$source" ]]; then
    die "obsolete managed agent changed target: $destination -> $target; expected $source"
  fi
}

revalidate_migration_plan() {
  local index
  for index in "${!MIGRATION_PLAN_DESTINATIONS[@]}"; do
    [[ "${MIGRATION_PLAN_ACTIONS[$index]}" == "remove" ]] || continue
    revalidate_migration_removal \
      "${MIGRATION_PLAN_DESTINATIONS[$index]}" \
      "${MIGRATION_PLAN_SOURCES[$index]}"
  done
}

execute_migration_plan() {
  local index destination source
  for index in "${!MIGRATION_PLAN_DESTINATIONS[@]}"; do
    if [[ "${MIGRATION_PLAN_ACTIONS[$index]}" == "preserve" ]]; then
      echo "${MIGRATION_PLAN_MESSAGES[$index]}"
      continue
    fi

    destination="${MIGRATION_PLAN_DESTINATIONS[$index]}"
    source="${MIGRATION_PLAN_SOURCES[$index]}"
    printf '+ rm -- %q\n' "$destination"
    if ((DRY_RUN == 0)); then
      revalidate_migration_removal "$destination" "$source"
      rm -- "$destination"
      echo "removed obsolete managed agent: $destination"
    fi
  done
}

install_planned_platform() {
  local platform="$1" index source destination action backup
  for index in "${!PLAN_DESTINATIONS[@]}"; do
    [[ "${PLAN_PLATFORMS[$index]}" == "$platform" ]] || continue
    source="${PLAN_SOURCES[$index]}"
    destination="${PLAN_DESTINATIONS[$index]}"
    action="${PLAN_ACTIONS[$index]}"
    backup="${PLAN_BACKUPS[$index]}"

    if [[ "$action" == "skip" ]]; then
      echo "ok (already linked): $destination"
      continue
    fi

    run mkdir -p -- "$(dirname "$destination")"
    if [[ -n "$backup" ]]; then
      backup_destination_noreplace "$destination" "$backup"
    fi

    if [[ "$MODE" == "symlink" ]]; then
      publish_symlink_noreplace "$source" "$destination"
    else
      publish_copy_noreplace "$source" "$destination"
    fi
    echo "installed: $destination"
  done
}

is_selected() {
  local mode="$1" command_name="$2" config_root="$3"
  case "$mode" in
    yes) return 0 ;;
    no) return 1 ;;
    auto) command -v "$command_name" >/dev/null 2>&1 || [[ -d "$config_root" ]] ;;
  esac
}

CLAUDE_SELECTED=0
CODEX_SELECTED=0
GEMINI_SELECTED=0
is_selected "$CLAUDE_MODE" claude "$CLAUDE_ROOT" && CLAUDE_SELECTED=1
is_selected "$CODEX_MODE" codex "$CODEX_ROOT" && CODEX_SELECTED=1
is_selected "$GEMINI_MODE" gemini "${TECH_DOC_FLOW_GEMINI_HOME:-$HOME/.gemini}" \
  && GEMINI_SELECTED=1

if ((CLAUDE_SELECTED)); then
  ((${#AGENT_FILES[@]} > 0)) \
    || die "Claude agent definitions not found: $AGENTS_SOURCE/*.md"
  plan_target claude "$SKILL_SOURCE" "$CLAUDE_ROOT/skills/$PRODUCT"
  for agent in "${AGENT_FILES[@]}"; do
    plan_target claude "$agent" "$CLAUDE_ROOT/agents/$(basename "$agent")"
  done
  for obsolete_name in "${OBSOLETE_CLAUDE_AGENT_NAMES[@]}"; do
    plan_obsolete_claude_agent "$obsolete_name"
  done
fi

if ((CODEX_SELECTED)); then
  plan_target codex "$SKILL_SOURCE" "$CODEX_ROOT/skills/$PRODUCT"
fi

if ((GEMINI_SELECTED && DRY_RUN == 0)) && ! command -v gemini >/dev/null 2>&1; then
  die "gemini command not found; install Gemini CLI or skip with --no-gemini"
fi

ATOMIC_RENAME_REQUIRED=0
for index in "${!PLAN_DESTINATIONS[@]}"; do
  [[ "${PLAN_ACTIONS[$index]}" == "skip" ]] && continue
  ATOMIC_RENAME_REQUIRED=1
  break
done
if ((ATOMIC_RENAME_REQUIRED && DRY_RUN == 0)) \
  && ! command -v "$PYTHON_BIN" >/dev/null 2>&1; then
  die "$PYTHON_BIN is required for atomic no-clobber install operations"
fi

# Revalidate every proven obsolete symlink after all selected targets and
# command prerequisites pass, but before the first installation mutation.
revalidate_migration_plan

# All predictable collisions and command prerequisites have passed. Only now
# may the installer mutate any destination.
if ((CLAUDE_SELECTED)); then
  echo "== Claude Code =="
  execute_migration_plan
  install_planned_platform claude
else
  echo "== Claude Code: skipped =="
fi

if ((CODEX_SELECTED)); then
  echo "== Codex =="
  install_planned_platform codex
else
  echo "== Codex: skipped =="
fi

if ((GEMINI_SELECTED)); then
  echo "== Gemini CLI =="
  if ((DRY_RUN)); then
    printf '+ gemini extensions link %q\n' "$REPO_DIR"
  elif ! printf 'Y\n' | gemini extensions link "$REPO_DIR"; then
    die "Gemini extension link failed"
  else
    echo "installed: Gemini extension ($PRODUCT)"
  fi
else
  echo "== Gemini CLI: skipped =="
fi

echo "installation complete (claude_codex_mode=$MODE, gemini_mode=extension-link, dry_run=$DRY_RUN)"