"""Backfill canonical record ids onto existing task rows (STATE-WP-0083-T06).

Only the repository files hold the mapping. A file task declares both its
canonical id and the projection UUID it was registered under:

    ```task
    id: CUST-WP-0067-T01
    state_hub_task_id: "f3608db4-..."
    ```

so the pairing can be read directly rather than guessed from titles. Anything a
file does not claim is left alone: a task row whose canonical id cannot be
established keeps `record_id` null, and the reset continues to refuse to act on
it. An unknown identity must stay unknown rather than be inferred.
"""

from __future__ import annotations

import re
from dataclasses import dataclass, field
from pathlib import Path
from typing import Any

_TASK_BLOCK_RE = re.compile(r"```task\s*\n(.*?)\n```", re.DOTALL)
_ID_RE = re.compile(r"^id:\s*(\S+)", re.MULTILINE)
_UUID_RE = re.compile(r'state_hub_task_id:\s*"?([0-9a-f-]{36})"?')


@dataclass
class BackfillReport:
    scanned_files: int = 0
    pairs_found: int = 0
    updated: int = 0
    already_set: int = 0
    conflicts: list[dict[str, str]] = field(default_factory=list)
    unmatched_uuids: int = 0

    def to_dict(self) -> dict[str, Any]:
        return {
            "schema": "state-hub.task-record-id-backfill.v1",
            "scanned_files": self.scanned_files,
            "pairs_found": self.pairs_found,
            "updated": self.updated,
            "already_set": self.already_set,
            "unmatched_uuids": self.unmatched_uuids,
            "conflicts": self.conflicts,
        }


def collect_pairs(roots: list[Path]) -> tuple[dict[str, str], BackfillReport]:
    """Map projection UUID -> canonical record id, from workplan files."""
    report = BackfillReport()
    pairs: dict[str, str] = {}
    for root in roots:
        wp_dir = root / "workplans"
        if not wp_dir.is_dir():
            continue
        for path in sorted(wp_dir.rglob("*.md")):
            if path.name.startswith("."):
                continue
            try:
                text = path.read_text(encoding="utf-8")
            except (OSError, UnicodeDecodeError):
                continue
            report.scanned_files += 1
            for block in _TASK_BLOCK_RE.finditer(text):
                body = block.group(1)
                rid = _ID_RE.search(body)
                uid = _UUID_RE.search(body)
                if not rid or not uid:
                    continue
                record_id, task_uuid = rid.group(1).strip(), uid.group(1)
                prior = pairs.get(task_uuid)
                if prior and prior != record_id:
                    # One UUID claimed by two canonical ids: a duplicate
                    # registration. Recording it and skipping is the only safe
                    # option — picking one would fabricate an identity.
                    report.conflicts.append(
                        {"uuid": task_uuid, "first": prior, "second": record_id}
                    )
                    continue
                pairs[task_uuid] = record_id
    report.pairs_found = len(pairs)
    return pairs, report


async def backfill_task_record_ids(
    session: Any, roots: list[Path], *, dry_run: bool = True
) -> BackfillReport:
    from sqlalchemy import select

    from api.models.task import Task

    pairs, report = collect_pairs(roots)
    if not pairs:
        return report

    rows = list((await session.execute(select(Task))).scalars())
    by_id = {str(r.id): r for r in rows}
    for task_uuid, record_id in pairs.items():
        row = by_id.get(task_uuid)
        if row is None:
            report.unmatched_uuids += 1
            continue
        if row.record_id == record_id:
            report.already_set += 1
            continue
        if row.record_id and row.record_id != record_id:
            report.conflicts.append(
                {"uuid": task_uuid, "first": row.record_id, "second": record_id}
            )
            continue
        report.updated += 1
        if not dry_run:
            row.record_id = record_id
    return report


async def backfill_from_forge(
    session: Any,
    repo_slugs: list[str],
    *,
    forge_base: str | None = None,
    dry_run: bool = True,
) -> BackfillReport:
    """Backfill from repositories cloned out of the forge.

    The local-path variant above needs a workstation checkout, which central
    does not have and should not depend on: `ADR-012` decision 1 makes the forge
    the projection source, and a backfill sourced from someone's laptop would
    reintroduce exactly the coupling that ADR removes.

    Central can clone the forge directly, so it reads the pairing from the same
    place it derives everything else.
    """
    import tempfile

    from api.services.forge_projection import (
        DEFAULT_FORGE_BASE,
        ForgeDeriveError,
        _run_git,
    )

    base = forge_base or DEFAULT_FORGE_BASE
    report = BackfillReport()
    pairs: dict[str, str] = {}

    for slug in repo_slugs:
        url = f"{base.rstrip('/')}/{slug}.git"
        with tempfile.TemporaryDirectory(prefix=f"backfill-{slug}-") as tmp:
            try:
                _run_git("clone", "--depth", "1", "--quiet", url, tmp)
            except (ForgeDeriveError, Exception):
                # A repository that cannot be read contributes nothing. It must
                # not silently reduce what the rest can identify.
                continue
            repo_pairs, repo_report = collect_pairs([Path(tmp)])
            report.scanned_files += repo_report.scanned_files
            report.conflicts.extend(repo_report.conflicts)
            for uid, rid in repo_pairs.items():
                prior = pairs.get(uid)
                if prior and prior != rid:
                    report.conflicts.append({"uuid": uid, "first": prior, "second": rid})
                    continue
                pairs[uid] = rid

    report.pairs_found = len(pairs)
    if not pairs:
        return report

    from sqlalchemy import select

    from api.models.task import Task

    rows = list((await session.execute(select(Task))).scalars())
    by_id = {str(r.id): r for r in rows}
    for uid, rid in pairs.items():
        row = by_id.get(uid)
        if row is None:
            report.unmatched_uuids += 1
            continue
        if row.record_id == rid:
            report.already_set += 1
            continue
        if row.record_id and row.record_id != rid:
            report.conflicts.append({"uuid": uid, "first": row.record_id, "second": rid})
            continue
        report.updated += 1
        if not dry_run:
            row.record_id = rid
    return report