"""pull + push entry points + divergence detection.

Backend: restic-rest-server. URL form:
``rest:<scheme>://<id>:<password>@<host>/<id>/``

Password = HTTP basic auth ONLY. Restic repos are initialised with
``--insecure-no-password``; encryption-at-rest delegated to LUKS on the
host disk + TLS at the reverse proxy.

Divergence detection (pull only):

  1. Fetch remote latest snapshot id + time via ``snapshots --json --latest 1``.
  2. Read ``<pack>/.cloud-sync/state.json`` for the last-pulled snapshot id.
  3. Branches:
       - no state.json AND remote empty           → no-op
       - no state.json AND remote non-empty       → first-run restore
       - state.last_pulled == remote.id           → up to date, skip
       - state.last_pulled != remote.id, no local edits since
         state.last_pulled_at                     → fast-forward restore
       - state.last_pulled != remote.id, local edits since
         state.last_pulled_at                     → CONFLICT dialog
"""

from __future__ import annotations

import fnmatch
import json
import sys
import urllib.parse
from datetime import datetime, timezone
from pathlib import Path

from . import config as cfgmod, restic, scope as scopemod, state as statemod
from .cli import Args
from .creds import read_credentials
from .ui import HeadlessProgress, Progress


def pull(args: Args, progress: Progress | None = None) -> int:
    ui = progress or HeadlessProgress()

    # Opt-in gate: no sync.json → instance isn't sync-enabled, silent no-op.
    # This is the path the global Prism PreLaunch hook takes for instances
    # the player hasn't opted into sync.
    sync_cfg = cfgmod.read(args.pack_folder)
    if sync_cfg is None:
        return 0

    # First-run login. If the user declines, skip without blocking the
    # launch (return 0 — non-fatal for Prism PreLaunch).
    if not args.token_file.exists():
        if not _prompt_login_and_save(args, ui):
            ui.set_status("Sync skipped")
            print("instance-sync: no token; skipping pull")
            return 0

    ui.set_status("Reading credentials…")
    discord_id, password = read_credentials(args.token_file)

    ui.set_status("Resolving restic binary…")
    binary = restic.resolve_binary(args)
    repo = _restic_repo(sync_cfg.url, discord_id, password, sync_cfg.instance_id)
    env = _restic_env()
    label = cfgmod.resolve_label(args.instance_label, sync_cfg.instance_id)

    ui.set_status("Checking remote snapshots…")
    code, out = restic.run(
        binary,
        ["-r", repo, "--insecure-no-password", "snapshots", "--json", "--latest", "1"],
        env=env,
        cancel_check=ui.is_cancelled,
    )
    if code == -1:
        return 1
    if code != 0:
        print(
            f"instance-sync: failed to list snapshots (restic exit {code})",
            file=sys.stderr,
        )
        return 2

    snapshots = _parse_snapshots(out)
    if not snapshots:
        statemod.clear(args.pack_folder)
        ui.set_status("No snapshots yet — nothing to pull")
        print("instance-sync: no snapshots yet for this user; nothing to pull")
        return 0

    remote = snapshots[0]
    remote_id = remote["id"]
    remote_time = _parse_restic_time(remote["time"])

    local_state = statemod.read(args.pack_folder)
    scope = scopemod.load(args.pack_folder)

    decision: str
    if local_state is None:
        decision = "use_remote"
    elif local_state.last_pulled_snapshot_id == remote_id:
        ui.set_status("Cloud is up to date")
        print("instance-sync: already at latest snapshot")
        return 0
    else:
        modified = _find_modified_in_scope(
            args.pack_folder, scope, local_state.last_pulled_at
        )
        if not modified:
            decision = "use_remote"
        else:
            decision = _ask_conflict(modified, remote_time, label)
            if decision is None:
                # UI unavailable in headless mode → conservative: cancel
                ui.set_status("Conflict detected; no UI available")
                print(
                    "instance-sync: conflict detected (remote moved + local edits) "
                    "but headless mode can't prompt; aborting",
                    file=sys.stderr,
                )
                return 1

    if decision == "cancel":
        ui.set_status("Launch cancelled")
        return 1
    if decision == "keep_local":
        ui.set_status("Keeping local; push will overwrite cloud on exit")
        print("instance-sync: keeping local copy")
        return 0

    # decision == "use_remote"
    _, exclude_from = scopemod.materialize_for_restic(args.pack_folder, scope)
    ui.set_status("Restoring files…")
    code, _ = restic.run(
        binary,
        [
            "-r", repo, "--insecure-no-password",
            "restore", "latest",
            "--target", str(args.pack_folder),
            "--exclude-file", str(exclude_from),
        ],
        env=env,
        cancel_check=ui.is_cancelled,
    )
    if code == -1:
        return 1
    if code != 0:
        print(f"instance-sync: restic restore failed (exit {code})", file=sys.stderr)
        return 2

    statemod.write(
        args.pack_folder,
        statemod.State(
            instance_id=sync_cfg.instance_id,
            last_pulled_snapshot_id=remote_id,
            last_pulled_at=datetime.now(timezone.utc),
        ),
    )
    ui.set_status("Pull complete")
    print("instance-sync: pull ok")
    return 0


def push(args: Args, progress: Progress | None = None) -> int:
    ui = progress or HeadlessProgress()

    # Opt-in gate — see pull().
    sync_cfg = cfgmod.read(args.pack_folder)
    if sync_cfg is None:
        return 0

    if not args.token_file.exists():
        ui.set_status("No token; skipping push")
        print("instance-sync: no token; skipping push")
        return 0

    ui.set_status("Reading credentials…")
    discord_id, password = read_credentials(args.token_file)

    ui.set_status("Resolving restic binary…")
    binary = restic.resolve_binary(args)
    repo = _restic_repo(sync_cfg.url, discord_id, password, sync_cfg.instance_id)
    env = _restic_env()

    # First-push-on-a-new-instance: probe + init if the per-instance repo
    # doesn't exist yet. Idempotent on subsequent pushes.
    code = _ensure_repo_initialized(binary, repo, env, ui)
    if code != 0:
        return code

    scope = scopemod.load(args.pack_folder)
    files_from, exclude_from = scopemod.materialize_for_restic(args.pack_folder, scope)

    ui.set_status("Uploading snapshot…")
    code, out = restic.run(
        binary,
        [
            "-r", repo, "--insecure-no-password",
            "backup",
            "--files-from", str(files_from),
            "--exclude-file", str(exclude_from),
            "--host", "instance-sync",
            "--tag", "auto",
            "--json",
        ],
        env=env,
        cwd=args.pack_folder,
        cancel_check=ui.is_cancelled,
    )
    if code == -1:
        return 1
    if code != 0:
        print(f"instance-sync: restic backup failed (exit {code})", file=sys.stderr)
        return 2

    new_id = _parse_backup_summary(out)
    if new_id is not None:
        statemod.write(
            args.pack_folder,
            statemod.State(
                instance_id=sync_cfg.instance_id,
                last_pulled_snapshot_id=new_id,
                last_pulled_at=datetime.now(timezone.utc),
            ),
        )
    ui.set_status("Push complete")
    print("instance-sync: push ok")
    return 0


# ---------------------------------------------------------------------------
# divergence detection
# ---------------------------------------------------------------------------


def _find_modified_in_scope(
    pack_folder: Path, scope: scopemod.Scope, since: datetime
) -> list[tuple[Path, datetime]]:
    """Return (rel_path, mtime) for in-scope files newer than ``since``.

    Walks each include root, skips paths matching any exclude glob. Stops
    early at 50 hits (we only need to know "any" + sample some for the
    conflict dialog). False positives are safer than false negatives —
    a spurious conflict shows a dismissable dialog; a missed conflict
    silently overwrites the user's edits.
    """
    since_ts = since.timestamp()
    hits: list[tuple[Path, datetime]] = []
    for include in scope.include:
        root = pack_folder / include.rstrip("/")
        if not root.exists():
            continue
        candidates: list[Path] = [root] if root.is_file() else _walk_files(root)
        for f in candidates:
            try:
                mtime = f.stat().st_mtime
            except OSError:
                continue
            if mtime <= since_ts:
                continue
            rel = f.relative_to(pack_folder)
            if _matches_any(rel, scope.exclude):
                continue
            hits.append((rel, datetime.fromtimestamp(mtime, tz=timezone.utc)))
            if len(hits) >= 50:
                return hits
    return hits


def _walk_files(root: Path):
    try:
        for p in root.rglob("*"):
            if p.is_file():
                yield p
    except OSError:
        return


def _matches_any(rel: Path, patterns: list[str]) -> bool:
    """Restic-style glob match against the relative path.

    Subset of restic's exclude semantics that covers our default scope:
      ``foo/``         — foo itself OR anything under it
      ``**/foo/``      — any ancestor directory named foo, recursively
      ``foo/bar*``     — fnmatch against the full relative path
      ``**/*.log``     — fnmatch the basename (and any tail subpath)
    """
    rel_str = str(rel)
    parts = rel.parts
    for pat in patterns:
        if pat.endswith("/"):
            core = pat.rstrip("/")
            if core.startswith("**/"):
                tail = core[len("**/") :]
                if tail in parts:
                    return True
                continue
            if rel_str == core or rel_str.startswith(core + "/"):
                return True
            continue
        if fnmatch.fnmatch(rel_str, pat):
            return True
        if pat.startswith("**/"):
            suffix = pat[len("**/") :]
            if fnmatch.fnmatch(rel.name, suffix):
                return True
            for i in range(len(parts)):
                if fnmatch.fnmatch("/".join(parts[i:]), suffix):
                    return True
    return False


def _ask_conflict(
    modified: list[tuple[Path, datetime]],
    remote_time: datetime,
    label: str,
) -> str | None:
    """Show the conflict dialog. Returns choice or None if no UI available."""
    try:
        from .ui_qt import prompt_conflict_qt
    except ImportError:
        return None
    newest = max(modified, key=lambda h: h[1])
    return prompt_conflict_qt(
        local_modified=_format_dt(newest[1]),
        remote_modified=_format_dt(remote_time),
        save_label=label,
    )


def _prompt_login_and_save(args: Args, ui: Progress) -> bool:
    """First-run login. Returns True if a token was saved, False if skipped."""
    try:
        from .ui_qt import prompt_login_qt
    except ImportError:
        ui.set_status("No token and no UI; can't prompt")
        print(
            "instance-sync: no token at "
            f"{args.token_file} and no Qt UI available",
            file=sys.stderr,
        )
        return False
    token = prompt_login_qt()
    if token is None:
        return False
    args.token_file.parent.mkdir(parents=True, exist_ok=True)
    args.token_file.write_text(token + "\n", encoding="utf-8")
    args.token_file.chmod(0o600)
    return True


# ---------------------------------------------------------------------------
# restic output parsing
# ---------------------------------------------------------------------------


def _parse_snapshots(out: str) -> list[dict]:
    s = out.strip()
    if not s or s == "null":
        return []
    try:
        data = json.loads(s)
    except json.JSONDecodeError:
        return []
    return data if isinstance(data, list) else []


def _parse_restic_time(s: str) -> datetime:
    """Restic emits e.g. ``2026-06-04T18:33:21.123456789Z``."""
    if s.endswith("Z"):
        s = s[:-1] + "+00:00"
    # Python's fromisoformat doesn't accept nanosecond precision — trim to micro.
    if "." in s:
        head, _, tail = s.partition(".")
        frac, _, tz = tail.partition("+")
        if tz:
            tz = "+" + tz
        else:
            frac, _, tz = tail.partition("-")
            if tz:
                tz = "-" + tz
        s = f"{head}.{frac[:6]}{tz}"
    return datetime.fromisoformat(s).astimezone(timezone.utc)


def _parse_backup_summary(out: str) -> str | None:
    """restic backup --json emits one JSON line per event; the final
    ``summary`` event carries ``snapshot_id``."""
    for line in reversed(out.splitlines()):
        line = line.strip()
        if not line:
            continue
        try:
            ev = json.loads(line)
        except json.JSONDecodeError:
            continue
        if ev.get("message_type") == "summary" and "snapshot_id" in ev:
            return str(ev["snapshot_id"])
    return None


# ---------------------------------------------------------------------------
# misc helpers
# ---------------------------------------------------------------------------


def _format_dt(dt: datetime) -> str:
    """Format a tz-aware datetime as 'Thursday, October 21, 2021 at 7:12 PM'.

    Hand-rolled instead of ``strftime("%-d")`` because GNU strftime's
    leading-zero stripping syntax is platform-specific (``%-d`` vs ``%#d``).
    """
    local = dt.astimezone()
    weekday = local.strftime("%A")
    month = local.strftime("%B")
    hour = local.hour % 12 or 12
    ampm = local.strftime("%p")
    return f"{weekday}, {month} {local.day}, {local.year} at {hour}:{local.minute:02d} {ampm}"


def _restic_repo(
    base_url: str, discord_id: str, password: str, instance_id: str
) -> str:
    """Build ``rest:<scheme>://<id>:<pw>@<host>/<id>/<instance_id>/``.

    Per-instance subpath under the user's namespace. ``--private-repos``
    on restic-rest-server only enforces the FIRST path segment (the
    username); deeper segments are user-controlled, so each instance
    gets its own isolated restic repo without server-side coordination.
    """
    raw = base_url.strip()
    if raw.startswith("rest:"):
        raw = raw[len("rest:"):]
    raw = raw.rstrip("/")
    scheme_end = raw.find("://")
    if scheme_end <= 0:
        raise ValueError(
            f"url must include scheme (http:// or https://): {base_url!r}"
        )
    scheme = raw[: scheme_end + 3]
    host_and_path = raw[scheme_end + 3 :]
    u = urllib.parse.quote(discord_id, safe="")
    p = urllib.parse.quote(password, safe="")
    iid = urllib.parse.quote(instance_id, safe="")
    return f"rest:{scheme}{u}:{p}@{host_and_path}/{discord_id}/{iid}/"


def _ensure_repo_initialized(
    binary: Path, repo: str, env: dict[str, str], ui: "Progress"
) -> int:
    """`restic cat config` to probe; `restic init` if absent. Returns 0/1/2.

    Cheap to call before every push — `cat config` is a single HTTP GET.
    Idempotent: if the repo already exists, init is skipped.
    """
    code, _ = restic.run(
        binary,
        ["-r", repo, "--insecure-no-password", "cat", "config"],
        env=env,
        cancel_check=ui.is_cancelled,
    )
    if code == 0:
        return 0
    if code == -1:
        return 1
    # cat config failed → assume not initialized; init it.
    ui.set_status("Initializing remote repo…")
    code, _ = restic.run(
        binary,
        ["-r", repo, "--insecure-no-password", "init"],
        env=env,
        cancel_check=ui.is_cancelled,
    )
    if code == -1:
        return 1
    if code != 0:
        print(
            f"instance-sync: restic init failed (exit {code})", file=sys.stderr
        )
        return 2
    return 0


def _restic_env() -> dict[str, str]:
    return {
        # No RESTIC_PASSWORD — repos use --insecure-no-password.
        "RESTIC_PROGRESS_FPS": "0",
    }