"""Documented-vs-registered MCP tool inventory guard (#781).

The workflow documentation named a ``gitea_edit_issue`` tool that no namespace
had ever registered. Nothing compared the two lists, so an actor could plan a
mutation against a tool that did not exist and only discover it at execution
time — after the work was already scoped around it.

This module is that comparison, in two directions:

- :func:`assess_inventory_drift` compares the canonical inventory documented in
  ``docs/mcp-tool-inventory.md`` against the tools actually registered on the
  MCP server. Either list drifting fails the guard, so a new tool must be
  documented and a removed tool must be undocumented in the same change.
- :func:`assess_doc_references` catches the original defect directly: any tool
  name a workflow/skill document tells an actor to call must be registered.

Module and script names legitimately appear in the same prose (``gitea_auth``,
``offline_mcp_runner``), so :data:`NON_TOOL_IDENTIFIERS` names the known
non-tool identifiers explicitly rather than loosening the pattern.

This module performs no I/O — callers own reading the files.
"""

from __future__ import annotations

import re
from typing import Any, Iterable, Mapping

#: Canonical documented inventory, relative to the repository root.
INVENTORY_DOC_PATH = "docs/mcp-tool-inventory.md"

#: Delimiters around the generated inventory list in the doc.
INVENTORY_BEGIN_MARKER = "<!-- BEGIN REGISTERED TOOL INVENTORY -->"
INVENTORY_END_MARKER = "<!-- END REGISTERED TOOL INVENTORY -->"

#: Backticked identifiers that look like tool names but are modules/scripts.
#: Every entry is a real file in this repository, not an MCP tool.
NON_TOOL_IDENTIFIERS: frozenset[str] = frozenset(
    {
        "gitea_auth",
        "gitea_config",
        "gitea_mcp_server",
        "mcp_server",
        "offline_mcp_helper",
        "offline_mcp_runner",
    }
)

#: Prefixes that mark an identifier as a candidate MCP tool name.
TOOL_NAME_PREFIXES: tuple[str, ...] = ("gitea_", "mcp_")

_INVENTORY_ENTRY = re.compile(r"^-\s+`([A-Za-z_][A-Za-z0-9_]*)`")
_BACKTICKED = re.compile(r"`([A-Za-z_][A-Za-z0-9_]*)`")


def parse_documented_inventory(text: str) -> list[str]:
    """Return the tool names listed between the inventory markers.

    Raises ``ValueError`` when the markers are missing or out of order, so a
    mangled document fails the guard instead of silently documenting nothing.
    """
    start = text.find(INVENTORY_BEGIN_MARKER)
    end = text.find(INVENTORY_END_MARKER)
    if start == -1 or end == -1 or end < start:
        raise ValueError(
            f"{INVENTORY_DOC_PATH} must contain "
            f"'{INVENTORY_BEGIN_MARKER}' followed by "
            f"'{INVENTORY_END_MARKER}' (fail closed)."
        )
    block = text[start + len(INVENTORY_BEGIN_MARKER) : end]
    names: list[str] = []
    for line in block.splitlines():
        match = _INVENTORY_ENTRY.match(line.strip())
        if match:
            names.append(match.group(1))
    return names


def looks_like_tool_name(identifier: str) -> bool:
    """Return whether a backticked identifier is a candidate tool name."""
    if identifier in NON_TOOL_IDENTIFIERS:
        return False
    return identifier.startswith(TOOL_NAME_PREFIXES)


def extract_tool_references(text: str) -> set[str]:
    """Return candidate tool names a document tells an actor to call."""
    return {
        name
        for name in _BACKTICKED.findall(text)
        if looks_like_tool_name(name)
    }


def assess_inventory_drift(
    documented: Iterable[str],
    registered: Iterable[str],
) -> dict[str, Any]:
    """Compare the documented inventory against the registered tool set."""
    documented_list = list(documented)
    documented_set = set(documented_list)
    registered_set = set(registered)

    duplicates = sorted(
        {name for name in documented_list if documented_list.count(name) > 1}
    )
    documented_not_registered = sorted(documented_set - registered_set)
    registered_not_documented = sorted(registered_set - documented_set)
    unsorted = documented_list != sorted(documented_list)

    reasons: list[str] = []
    if documented_not_registered:
        reasons.append(
            "documented but not registered: "
            + ", ".join(documented_not_registered)
        )
    if registered_not_documented:
        reasons.append(
            "registered but not documented: "
            + ", ".join(registered_not_documented)
        )
    if duplicates:
        reasons.append("listed more than once: " + ", ".join(duplicates))
    if unsorted:
        reasons.append("inventory entries are not in sorted order")

    in_sync = not reasons
    return {
        "in_sync": in_sync,
        "documented_count": len(documented_set),
        "registered_count": len(registered_set),
        "documented_not_registered": documented_not_registered,
        "registered_not_documented": registered_not_documented,
        "duplicates": duplicates,
        "sorted": not unsorted,
        "reasons": reasons,
        "safe_next_action": (
            ""
            if in_sync
            else (
                f"Update {INVENTORY_DOC_PATH} so the block between the "
                "inventory markers lists exactly the registered tools, sorted, "
                "one '- `tool_name`' entry per line."
            )
        ),
    }


def assess_doc_references(
    references: Mapping[str, Iterable[str]],
    registered: Iterable[str],
) -> dict[str, Any]:
    """Verify every tool a document names is actually registered.

    *references* maps a document path to the candidate tool names it mentions.
    """
    registered_set = set(registered)
    unregistered: list[dict[str, Any]] = []
    checked = 0
    for path, names in sorted(references.items()):
        for name in sorted(set(names)):
            checked += 1
            if name not in registered_set:
                unregistered.append({"document": path, "tool": name})

    clean = not unregistered
    reasons = [
        f"{entry['document']} documents '{entry['tool']}', "
        "which no namespace registers"
        for entry in unregistered
    ]
    return {
        "clean": clean,
        "checked_count": checked,
        "unregistered": unregistered,
        "reasons": reasons,
        "safe_next_action": (
            ""
            if clean
            else (
                "Either register the named tool with @mcp.tool() or correct the "
                "document. Documentation must never name a tool an actor cannot "
                "reach. If the identifier is a module or script rather than a "
                "tool, add it to mcp_tool_inventory.NON_TOOL_IDENTIFIERS."
            )
        ),
    }


def render_inventory_block(registered: Iterable[str]) -> str:
    """Render the marker-delimited inventory block for the documentation."""
    lines = [INVENTORY_BEGIN_MARKER, ""]
    lines.extend(f"- `{name}`" for name in sorted(set(registered)))
    lines.extend(["", INVENTORY_END_MARKER])
    return "\n".join(lines)