from __future__ import annotations

import os
from pathlib import Path

from .db import connect
from .hashing import sha256


def confirm_sha256(conn, row) -> str | None:
    path = Path(row["file_path"])
    try:
        st = path.stat()
    except FileNotFoundError:
        return None
    if st.st_size != row["file_size"]:
        return None
    # If the file changed after indexing, refresh the fast hash first and refuse
    # this pass. The next incremental/reconcile pass will safely retry it.
    digest = sha256(path)
    conn.execute(
        "UPDATE audio_tracks SET sha256=?, updated_at=CURRENT_TIMESTAMP WHERE id=?",
        (digest, row["id"]),
    )
    return digest


def hardlink_duplicate(conn, loser: Path, winner: Path) -> None:
    """Make loser a hard link to winner, atomically replacing loser."""
    tmp = loser.with_name(loser.name + ".dedupe-linking")
    if tmp.exists():
        tmp.unlink()
    os.link(winner, tmp)
    os.replace(tmp, loser)


def choose_winner(rows):
    """Prefer public admin paths, then older records, then lexical path."""
    def key(r):
        path = r["file_path"]
        is_admin = "/admin/" in path or path.endswith("/admin")
        return (0 if is_admin else 1, r["created_at"], path)
    return min(rows, key=key)


def exact_dedupe(db_path: Path, root: Path) -> list[tuple[str, str]]:
    """Hard-link byte-identical files while preserving every logical user path."""
    actions = []
    with connect(db_path) as conn:
        candidates = conn.execute(
            """
            SELECT * FROM audio_tracks
            WHERE status='active'
            ORDER BY id
            """
        ).fetchall()
        # Only full-hash files that share the cheap L1 key need to be compared.
        groups = {}
        for row in candidates:
            groups.setdefault((row["file_size"], row["fast_hash"]), []).append(row)
        for rows in groups.values():
            if len(rows) < 2:
                # L1 has no collision candidate. Do not read the whole file;
                # the full SHA-256 will be computed only when a future file
                # lands in the same L1 bucket.
                continue
            for row in rows:
                if row["sha256"] is None:
                    confirm_sha256(conn, row)
            refreshed = conn.execute(
                "SELECT * FROM audio_tracks WHERE id IN (%s)" % ",".join("?" * len(rows)),
                [r["id"] for r in rows],
            ).fetchall()
            by_hash = {}
            for row in refreshed:
                if row["sha256"]:
                    by_hash.setdefault(row["sha256"], []).append(row)
            for same in by_hash.values():
                if len(same) < 2:
                    continue
                winner = choose_winner(same)
                winpath = Path(winner["file_path"])
                if not winpath.exists():
                    continue
                for row in same:
                    if row["id"] == winner["id"]:
                        continue
                    loser = Path(row["file_path"])
                    if not loser.exists():
                        continue
                    # Preserve the user's logical path. Exact duplicates are NOT
                    # moved to trash: all users should continue seeing/downloading
                    # their own path, while the inode/data is shared.
                    if loser.stat().st_ino != winpath.stat().st_ino:
                        hardlink_duplicate(conn, loser, winpath)
                    conn.execute(
                        "UPDATE audio_tracks SET status='hardlinked', updated_at=CURRENT_TIMESTAMP WHERE id=?",
                        (row["id"],),
                    )
                    actions.append((str(loser), str(winpath)))
    return actions