"""OKF (Open Knowledge Format) bundle navigation — framework-neutral, D7-portable context seam.

Reads a bundle the way OKF intends (progressive disclosure): start at ``index.md``, follow
intra-bundle cross-links, parse each file's YAML frontmatter, classify by the one required
``type`` field. **NO** ``agent_framework``, **NO** ``mcp`` — pure stdlib, so the SAME navigation
serves both the MAF and the Claude-SDK implementations unchanged (målbilde §4 vendor-neutrality).

Robustness is part of the spec (OKF SPEC §4): consumers MUST tolerate broken links and unknown
fields. A link to a missing file — or one escaping the bundle — is silently skipped, never raised.
Path-safety reuses ``retrieval.safe_resolve`` (also pure stdlib): each cross-link is canonicalised
and boundary-checked against the bundle dir, fail-closed.
"""

from __future__ import annotations

import json
import re
from dataclasses import dataclass
from pathlib import Path
from typing import Any

from portfolio_optimiser.retrieval import PathSecurityError, safe_resolve

_INDEX_NAME = "index.md"
_IR_PROJECTION = "validator-input.json"
# Intra-bundle markdown cross-links: ``](target.md)``. Targets with a path separator (``/``) are
# treated as out-of-bundle and skipped (only same-dir bundle files are navigated).
_LINK_RE = re.compile(r"\]\(([^)]+\.md)\)")


def parse_frontmatter(path: str | Path) -> dict[str, str]:
    """Read the leading ``---``-delimited YAML frontmatter block as key:value strings.

    Minimal by design (no ``yaml`` dependency): enough for the one required ``type`` field and the
    verdict's scalar fields. List values (``tags: [...]``) are kept verbatim; unknown fields are
    preserved (OKF SPEC §4). Returns ``{}`` when there is no frontmatter block."""
    lines = Path(path).read_text(encoding="utf-8").splitlines()
    if not lines or lines[0].strip() != "---":
        return {}
    fm: dict[str, str] = {}
    for line in lines[1:]:
        if line.strip() == "---":
            break
        key, sep, val = line.partition(":")
        if sep:
            fm[key.strip()] = val.strip()
    return fm


def _read_body(path: Path) -> str:
    """The markdown body after the frontmatter block (or the whole file if there is none)."""
    lines = path.read_text(encoding="utf-8").splitlines(keepends=True)
    if lines and lines[0].strip() == "---":
        for i in range(1, len(lines)):
            if lines[i].strip() == "---":
                return "".join(lines[i + 1 :]).lstrip("\n")
    return "".join(lines)


@dataclass(frozen=True)
class BundleFile:
    """One OKF file: its name, declared ``type`` (``""`` if absent), frontmatter, and body."""

    name: str
    type: str
    frontmatter: dict[str, str]
    body: str


@dataclass(frozen=True)
class Bundle:
    """A navigated OKF bundle: ``index.md`` plus every cross-linked file that resolves."""

    dir: str
    files: tuple[BundleFile, ...]

    @property
    def index_summary(self) -> str:
        """The index body — the progressive-disclosure entry point (not whole-bundle stuffing)."""
        return next((f.body for f in self.files if f.name == _INDEX_NAME), "")

    @property
    def verdicts(self) -> list[BundleFile]:
        """Every ``type: verdict`` file (the ExpeL seeds the Step-1 wiring retrieves)."""
        return [f for f in self.files if f.type == "verdict"]

    @property
    def context_files(self) -> list[BundleFile]:
        """The non-index, non-``verdict`` concept files — the bodies that form the agent context.
        The verdict layer is deliberately EXCLUDED: prior verdicts reach the hypothesis prompt only
        through the gated ExpeL fold, never by stuffing them into the read-context (målbilde §4)."""
        return [f for f in self.files if f.name != _INDEX_NAME and f.type != "verdict"]

    @property
    def hypothesis(self) -> BundleFile | None:
        """The candidate ``type: hypothesis`` file, if present."""
        return next((f for f in self.files if f.type == "hypothesis"), None)


def _load_file(bundle_dir: str, name: str) -> BundleFile | None:
    """Resolve ``name`` within ``bundle_dir`` and read it, or ``None`` if missing / escaping the
    bundle (OKF §4 broken-link tolerance + fail-closed path-safety)."""
    try:
        resolved = Path(safe_resolve(bundle_dir, name))
    except PathSecurityError:
        return None
    if not resolved.is_file():
        return None
    fm = parse_frontmatter(resolved)
    return BundleFile(name=name, type=fm.get("type", ""), frontmatter=fm, body=_read_body(resolved))


def navigate_bundle(bundle_dir: str) -> Bundle:
    """Navigate the OKF bundle from ``index.md``: parse the index, follow its intra-bundle ``.md``
    cross-links, and read each linked file's frontmatter + body. Deterministic: index first, then
    links in first-seen order, de-duplicated. Broken / escaping links are skipped (§4). Raises
    ``ValueError`` only when ``index.md`` itself is unreadable (a bundle has no entry point)."""
    index = _load_file(bundle_dir, _INDEX_NAME)
    if index is None:
        raise ValueError(f"OKF bundle has no readable {_INDEX_NAME}: {bundle_dir!r}")
    files: list[BundleFile] = [index]
    seen = {_INDEX_NAME}
    for target in _LINK_RE.findall(index.body):
        if "/" in target or target in seen:
            continue  # only same-dir bundle files; de-dup repeated links
        seen.add(target)
        linked = _load_file(bundle_dir, target)
        if linked is not None:
            files.append(linked)
    return Bundle(dir=bundle_dir, files=tuple(files))


def bundle_context(bundle: Bundle, *, dimension: str | None = None) -> str:
    """Render a navigated bundle as agent read-context via progressive disclosure: the ``index.md``
    summary, then each concept file as ``## {type}: {title}\\n{body}``. ``type: verdict`` files are
    EXCLUDED (målbilde §2 step 1 / §4: navigation, not chunk-stuffing — the verdict layer folds in
    only via the gated ExpeL retrieval). Deterministic: index first, then context files in
    navigation order; empty sections are dropped.

    When ``dimension`` is given, only concept files whose frontmatter ``dimension`` matches — or that
    carry no ``dimension`` at all (un-scoped knowledge is never dropped) — are rendered; the default
    ``dimension=None`` renders every concept file, byte-identical to the prior behavior. ``dimension``
    is a plain ``str`` (not the ``Dimension`` type) so ``okf`` stays MAF-free and import-cycle-free."""
    sections = [bundle.index_summary]
    for f in bundle.context_files:
        if dimension is not None:
            file_dim = f.frontmatter.get("dimension")
            if file_dim is not None and file_dim != dimension:
                continue
        title = f.frontmatter.get("title", f.name).strip('"')
        sections.append(f"## {f.type or 'document'}: {title}\n{f.body}")
    return "\n\n".join(s for s in sections if s.strip())


def render_frontmatter(frontmatter: dict[str, str]) -> str:
    """Render a frontmatter dict as ``key: value`` lines (the inverse direction of
    ``parse_frontmatter``, used by the Step-8 promotion writer). Scalar values are **single-lined**
    (every newline/CR collapses to a space) because ``parse_frontmatter`` is line-oriented and stops
    at the first ``---`` line — a multi-line value would otherwise corrupt the block or terminate it
    early. NOT a bijection: this only guarantees that the single-line fields it writes re-parse to
    the same strings; ``parse_frontmatter`` keeps quotes and treats ``tags: [...]`` as a literal
    string, so callers pass already-formatted values. Keys are emitted in insertion order."""
    return "\n".join(f"{key}: {' '.join(str(value).split())}" for key, value in frontmatter.items())


def write_concept_file(bundle_dir: str, name: str, frontmatter: dict[str, str], body: str) -> Path:
    """Write a typed OKF concept file (``---`` frontmatter + markdown body) into ``bundle_dir``,
    path-safe via ``safe_resolve`` (fail-closed: a ``name`` escaping the bundle raises
    ``PathSecurityError``). Pure stdlib — the D7-portable counterpart of ``navigate_bundle``'s read.
    Returns the written path."""
    resolved = Path(safe_resolve(bundle_dir, name))
    resolved.parent.mkdir(parents=True, exist_ok=True)
    resolved.write_text(f"---\n{render_frontmatter(frontmatter)}\n---\n\n{body}", encoding="utf-8")
    return resolved


def link_in_index(bundle_dir: str, target_name: str, label: str) -> bool:
    """Append an intra-bundle cross-link ``- [label](target_name)`` to ``index.md`` so
    ``navigate_bundle`` (which follows ONLY index cross-links) reaches a newly written file.
    Idempotent: if a link to ``target_name`` already exists the index is left untouched. Returns
    whether a link was added. ``label`` is supplied by the caller and ends up in ``index_summary``
    (hence ``bundle_context``) verbatim, so the promotion policy passes a NEUTRAL label carrying no
    verdict signal (målbilde §3/§6). Known MVP limitation: the read-modify-write is not atomic."""
    resolved = Path(safe_resolve(bundle_dir, _INDEX_NAME))
    body = resolved.read_text(encoding="utf-8")
    if f"]({target_name})" in body:
        return False
    prefix = body if body.endswith("\n") else body + "\n"
    resolved.write_text(f"{prefix}- [{label}]({target_name})\n", encoding="utf-8")
    return True


def load_ir_projection(bundle_dir: str, name: str = _IR_PROJECTION) -> dict[str, Any]:
    """Load the bundle's IR projection (``validator-input.json`` by default): the candidate
    measure's cost-IR (``measure``, ``affected_items``, ``claimed_saving_nok``) — the
    pre-hypothesis ExpeL query-key source. Raises if missing / escaping the bundle (fail-fast: it
    is required input, not an optional cross-link)."""
    resolved = Path(safe_resolve(bundle_dir, name))
    if not resolved.is_file():
        raise FileNotFoundError(f"IR projection not found in bundle: {name!r}")
    data: dict[str, Any] = json.loads(resolved.read_text(encoding="utf-8"))
    return data