"""
ragstudio backend.

Single long-running HTTP server that owns the searchers (and therefore the
loaded model weights). Both the UI and the CLI talk to it over HTTP.

Routes:
  GET /                            -> ui/static/index.html
  GET /static/<file>               -> ui static asset
  GET /api/modalities              -> {"modalities": [...], "groups": {...}}
  GET /api/search/<modality>?q=&k= -> {modality, kind, query, hits:[{score,path}]}
  GET /api/file?path=              -> serve a file referenced in any index's
                                      *_meta.json (with stale-path healing)

Usage:
    python backend/server.py [--host 127.0.0.1] [--port 8000]
"""

import argparse
import json
import mimetypes
import os
import re
import sys
import threading
import time
import urllib.parse
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
from pathlib import Path

SYNC_INTERVAL_S = 30

# Video meta entries are stored as "<path> @ <t>s"; strip the timestamp so the
# allow-list contains the underlying file path.
_VIDEO_FRAME_SUFFIX = re.compile(r" @ \d+(?:\.\d+)?s$")


def _strip_frame_suffix(entry: str) -> str:
    return _VIDEO_FRAME_SUFFIX.sub("", entry)

REPO_ROOT = Path(__file__).resolve().parent.parent
INDEXING_DIR = REPO_ROOT / "indexing"
INDEX_DATA_DIR = INDEXING_DIR / "index_data"
UI_STATIC_DIR = REPO_ROOT / "ui" / "static"


def _source_root() -> Path | None:
    """Folder originally passed to build_index(), recorded by index.py."""
    manifest = INDEX_DATA_DIR / "_source.txt"
    if not manifest.exists():
        return None
    p = Path(manifest.read_text().strip())
    return p if p.is_dir() else None

# Searchers use relative `index_data/`; cd into indexing/ so paths resolve.
os.chdir(INDEXING_DIR)
sys.path.insert(0, str(INDEXING_DIR))

from searchers import GROUPS, SEARCHERS  # noqa: E402


def _modality_kind(name: str) -> str:
    if name == "image":
        return "image"
    if name == "video":
        return "video"
    return "text"


def _load_allowed_paths() -> set[str]:
    """Union of every path referenced in any *_meta.json — the file allow-list."""
    allowed: set[str] = set()
    for meta in (INDEXING_DIR / "index_data").glob("*_meta.json"):
        try:
            data = json.loads(meta.read_text())
        except Exception:
            continue
        if isinstance(data, list):
            for entry in data:
                if isinstance(entry, str):
                    allowed.add(_strip_frame_suffix(entry))
                elif isinstance(entry, dict) and "path" in entry:
                    allowed.add(_strip_frame_suffix(entry["path"]))
    return allowed


ALLOWED_PATHS = _load_allowed_paths()

# basename -> actual filesystem path, for healing stale absolute paths when
# indexed files have since been moved. Built lazily on first miss.
_BASENAME_INDEX: dict[str, str] | None = None


def _build_basename_index() -> dict[str, str]:
    needed = {Path(p).name for p in ALLOWED_PATHS}
    out: dict[str, str] = {}
    seen: set[Path] = set()
    for root in (INDEXING_DIR, REPO_ROOT):
        try:
            root = root.resolve()
        except Exception:
            continue
        if root in seen:
            continue
        seen.add(root)
        for path in root.rglob("*"):
            if not path.is_file():
                continue
            name = path.name
            if name in needed and name not in out:
                out[name] = str(path)
    return out


_EXCERPT_CONTEXT_LINES = 4
_EXCERPT_LINE_CHARS = 240
_EXCERPT_TOKEN_RE = re.compile(r"\w+")
# Split text into sentence-ish candidate units. Falls back to whole lines if
# the file already uses line breaks meaningfully.
_SENTENCE_SPLIT_RE = re.compile(r"(?<=[.!?])\s+(?=[A-Za-z0-9])")


def _split_candidates(text: str) -> list[str]:
    by_line = [line.strip() for line in text.splitlines() if line.strip()]
    # If newlines already chop the text into multiple pieces, trust them.
    if len(by_line) >= 4:
        return by_line
    # Otherwise treat each line as a paragraph and split it into sentences.
    out: list[str] = []
    for line in by_line:
        out.extend(s.strip() for s in _SENTENCE_SPLIT_RE.split(line) if s.strip())
    return out


def _cap_line(s: str) -> str:
    return s if len(s) <= _EXCERPT_LINE_CHARS else s[: _EXCERPT_LINE_CHARS] + "…"


def _bm25_match_idx(query: str, lines: list[str]) -> int:
    q_tokens = set(_EXCERPT_TOKEN_RE.findall(query.lower()))
    if not q_tokens:
        return 0
    best_i, best_count = 0, -1
    for i, line in enumerate(lines):
        tokens = _EXCERPT_TOKEN_RE.findall(line.lower())
        count = sum(1 for t in tokens if t in q_tokens)
        if count > best_count:
            best_i, best_count = i, count
    return best_i


def _semantic_match_idx(query: str, lines: list[str]) -> int:
    # Reuse the model already loaded by the semantic-text searcher so we don't
    # double the VRAM/load time. This is a private import on purpose.
    from searchers.semantic_text import _get_model

    import numpy as np

    model = _get_model()
    q_emb = model.encode([query], convert_to_numpy=True, normalize_embeddings=True)
    line_emb = model.encode(
        lines,
        convert_to_numpy=True,
        normalize_embeddings=True,
        batch_size=64,
        show_progress_bar=False,
    )
    sims = (line_emb @ q_emb.T).flatten()
    return int(np.argmax(sims))


def _text_excerpt(modality: str, query: str, requested: str) -> dict | None:
    """Three-part snippet ({before, match, after}) centered on the line most
    relevant to the query for this modality."""
    resolved = _resolve_path(requested)
    if resolved is None:
        return None
    try:
        raw = resolved.read_text(encoding="utf-8", errors="replace")
    except OSError:
        return None
    candidates = _split_candidates(raw)
    if not candidates:
        return None

    if modality == "semantic-text":
        center = _semantic_match_idx(query, candidates)
    else:
        center = _bm25_match_idx(query, candidates)

    start = max(0, center - _EXCERPT_CONTEXT_LINES)
    end = min(len(candidates), center + _EXCERPT_CONTEXT_LINES + 1)
    return {
        "before": "\n".join(_cap_line(c) for c in candidates[start:center]),
        "match": _cap_line(candidates[center]),
        "after": "\n".join(_cap_line(c) for c in candidates[center + 1 : end]),
    }


def _resolve_path(requested: str) -> Path | None:
    p = Path(requested)
    if p.is_absolute() and p.is_file():
        return p

    # Indexer stores paths relative to the original source folder. Try:
    #   1. <INDEX_DATA_DIR>/source/<rel> -- copy pulled from the bucket
    #   2. <_source.txt>/<rel>            -- original folder on this machine
    if not p.is_absolute():
        bucket_copy = INDEX_DATA_DIR / "source" / p
        if bucket_copy.is_file():
            return bucket_copy
        src = _source_root()
        if src is not None:
            local_copy = src / p
            if local_copy.is_file():
                return local_copy

    # Last-resort: basename match anywhere under the repo, for indexes that
    # still hold stale absolute paths or whose source folder has moved.
    global _BASENAME_INDEX
    if _BASENAME_INDEX is None:
        _BASENAME_INDEX = _build_basename_index()
    hit = _BASENAME_INDEX.get(p.name)
    return Path(hit) if hit else None


class Handler(BaseHTTPRequestHandler):
    def handle(self):
        try:
            super().handle()
        except BrokenPipeError:
            pass

    def log_message(self, fmt, *args):
        sys.stderr.write(f"[backend] {self.address_string()} - {fmt % args}\n")

    def _send_json(self, status: int, payload):
        body = json.dumps(payload).encode("utf-8")
        self.send_response(status)
        self.send_header("Content-Type", "application/json; charset=utf-8")
        self.send_header("Content-Length", str(len(body)))
        self.send_header("Cache-Control", "no-store")
        self.end_headers()
        self.wfile.write(body)

    def _send_file(self, path: Path, status: int = 200):
        if not path.is_file():
            self._send_json(404, {"error": f"not found: {path}"})
            return
        ctype, _ = mimetypes.guess_type(str(path))
        ctype = ctype or "application/octet-stream"
        size = path.stat().st_size
        range_hdr = self.headers.get("Range")
        if range_hdr and range_hdr.startswith("bytes="):
            # Parse byte range (only single ranges supported).
            spec = range_hdr[len("bytes="):]
            start_s, _, end_s = spec.partition("-")
            start = int(start_s) if start_s else 0
            end = int(end_s) if end_s else size - 1
            end = min(end, size - 1)
            length = end - start + 1
            with open(path, "rb") as f:
                f.seek(start)
                data = f.read(length)
            self.send_response(206)
            self.send_header("Content-Type", ctype)
            self.send_header("Content-Range", f"bytes {start}-{end}/{size}")
            self.send_header("Content-Length", str(length))
            self.send_header("Accept-Ranges", "bytes")
            self.end_headers()
            self.wfile.write(data)
        else:
            data = path.read_bytes()
            self.send_response(status)
            self.send_header("Content-Type", ctype)
            self.send_header("Content-Length", str(len(data)))
            self.send_header("Accept-Ranges", "bytes")
            self.end_headers()
            self.wfile.write(data)

    def _run_search(self, modality: str, query: str, top_k: int):
        fn = SEARCHERS.get(modality)
        if fn is None:
            self._send_json(404, {"error": f"unknown modality: {modality}"})
            return
        kind = _modality_kind(modality)
        try:
            hits = fn(query, top_k)
        except Exception as exc:
            self._send_json(
                500,
                {
                    "modality": modality,
                    "kind": kind,
                    "query": query,
                    "error": str(exc),
                    "hits": [],
                },
            )
            return
        out = []
        for s, p in hits:
            entry = {"score": float(s), "path": p}
            if kind == "text":
                excerpt = _text_excerpt(modality, query, p)
                if excerpt:
                    entry["excerpt"] = excerpt
            out.append(entry)
        self._send_json(
            200,
            {
                "modality": modality,
                "kind": kind,
                "query": query,
                "hits": out,
            },
        )

    def do_GET(self):
        parsed = urllib.parse.urlparse(self.path)
        route = parsed.path
        qs = urllib.parse.parse_qs(parsed.query)

        # static UI
        if route in ("/", "/index.html"):
            self._send_file(UI_STATIC_DIR / "index.html")
            return
        if route.startswith("/static/"):
            target = (UI_STATIC_DIR / route[len("/static/") :]).resolve()
            root = UI_STATIC_DIR.resolve()
            if root != target and root not in target.parents:
                self._send_json(403, {"error": "forbidden"})
                return
            self._send_file(target)
            return

        # API
        if route == "/api/modalities":
            self._send_json(
                200,
                {
                    "modalities": sorted(SEARCHERS.keys()),
                    "groups": {k: list(v) for k, v in GROUPS.items()},
                },
            )
            return

        if route.startswith("/api/search/"):
            modality = route[len("/api/search/") :]
            query = (qs.get("q", [""])[0] or "").strip()
            if not query:
                self._send_json(400, {"error": "missing q"})
                return
            top_k = int(qs.get("k", ["8"])[0])
            self._run_search(modality, query, top_k)
            return

        if route == "/api/file":
            path = qs.get("path", [""])[0]
            if not path:
                self._send_json(400, {"error": "missing path"})
                return
            global ALLOWED_PATHS
            if path not in ALLOWED_PATHS:
                ALLOWED_PATHS = _load_allowed_paths()
            if path not in ALLOWED_PATHS:
                self._send_json(403, {"error": "path not in any index"})
                return
            resolved = _resolve_path(path)
            if resolved is None:
                self._send_json(404, {"error": f"file missing on disk: {path}"})
                return
            self._send_file(resolved)
            return

        self._send_json(404, {"error": f"no route for {route}"})


def _sync_loop() -> None:
    """Pull the shared index bucket into index_data/ every SYNC_INTERVAL_S."""
    # `sync` lives in INDEXING_DIR which is already on sys.path.
    import sync as sync_mod

    while True:
        try:
            sync_mod.sync(pull=True)
        except Exception as exc:
            print(f"[sync] pull failed: {exc}", file=sys.stderr)
        time.sleep(SYNC_INTERVAL_S)


def main() -> None:
    parser = argparse.ArgumentParser(description=__doc__.strip())
    parser.add_argument("--host", default="127.0.0.1")
    parser.add_argument("--port", type=int, default=8000)
    args = parser.parse_args()

    threading.Thread(target=_sync_loop, daemon=True).start()

    server = ThreadingHTTPServer((args.host, args.port), Handler)
    print(f"ragstudio backend on http://{args.host}:{args.port}")
    print(f"  cwd:        {os.getcwd()}")
    print(f"  searchers:  {sorted(SEARCHERS)}")
    print(f"  static UI:  {UI_STATIC_DIR}")
    print(f"  index files: {len(ALLOWED_PATHS)}")
    print(f"  sync:       pull every {SYNC_INTERVAL_S}s")
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        print("\nshutting down")
        server.server_close()


if __name__ == "__main__":
    main()