"""Enforced PR review/merge workflow state machine (#290).

Review and merge must advance through explicit states. Any failed upstream
gate forbids downstream approve/merge mutations until the full workflow is
restarted after blockers clear.
"""

from __future__ import annotations

import re
from typing import Any

REVIEW_MERGE_STATES: tuple[str, ...] = (
    "PRECHECK",
    "INVENTORY",
    "SELECT_PR",
    "PIN_HEAD_SHA",
    "CREATE_BRANCHES_WORKTREE",
    "VALIDATE",
    "REVIEW_DECISION",
    "APPROVE_OR_REQUEST_CHANGES",
    "PRE_MERGE_RECHECK",
    "MERGE",
    "POST_MERGE_REPORT",
)

TERMINAL_BLOCKED_HEADING = (
    "PR review/merge workflow blocked. Restart the full workflow after blockers clear."
)

_FORBIDDEN_RECOVERY_REPLAY_RE = re.compile(
    r"\b(?:approve(?:\s+pr)?\s*#?\d+|merge(?:\s+pr)?\s*#?\d+|gitea_merge_pr|"
    r"gitea_submit_pr_review|submit\s+approve|run\s+merge)\b",
    re.IGNORECASE,
)
_RESTART_WORKFLOW_RE = re.compile(
    r"restart(?:\s+the)?\s+full\s+workflow|rerun\s+the\s+full\s+workflow",
    re.IGNORECASE,
)
_READY_TO_MERGE_RE = re.compile(
    r"\bready\s+to\s+merge\b",
    re.IGNORECASE,
)
_REVIEWED_VALIDATED_RE = re.compile(
    r"\b(?:reviewed|validated|approval\s+submitted)\b",
    re.IGNORECASE,
)

_PRE_MERGE_REQUIRED_GATES = (
    "whoami_verified",
    "profile_runtime_verified",
    "merge_capability_verified",
    "pr_refetched",
    "reviewed_head_sha_unchanged",
    "pr_mergeable",
    "checks_passed",
    "reviewer_not_author",
    "worktree_clean",
)


def _clean(value: str | None) -> str:
    return (value or "").strip()


def state_index(state: str) -> int:
    name = _clean(state).upper()
    try:
        return REVIEW_MERGE_STATES.index(name)
    except ValueError as exc:
        raise ValueError(f"unknown review/merge state '{state}' (fail closed)") from exc


def downstream_states(from_state: str) -> list[str]:
    idx = state_index(from_state)
    return list(REVIEW_MERGE_STATES[idx + 1 :])


def _completed_through(state_completion: dict[str, bool], state: str) -> bool:
    return bool(state_completion.get(state))


def _first_incomplete_state(state_completion: dict[str, bool]) -> str | None:
    for state in REVIEW_MERGE_STATES:
        if not _completed_through(state_completion, state):
            return state
    return None


def assess_workflow_blockers(
    *,
    infra_stop: bool = False,
    capability_blocked: bool = False,
    mcp_reconnect_failed: bool = False,
    stale_capability_state: bool = False,
) -> dict[str, Any]:
    """Return hard blockers that forbid all PR queue work (#290 AC3)."""
    reasons: list[str] = []
    if infra_stop:
        reasons.append("infra_stop is active; PR selection/review/merge is forbidden")
    if capability_blocked:
        reasons.append("gitea_resolve_task_capability returned blocked/stop_required")
    if mcp_reconnect_failed:
        reasons.append("MCP reconnect failed; stale session state cannot be reused")
    if stale_capability_state:
        reasons.append("stale MCP capability state detected after reconnect failure")
    return {
        "block": bool(reasons),
        "reasons": reasons,
        "forbidden_states": list(REVIEW_MERGE_STATES) if reasons else [],
        "safe_next_action": (
            TERMINAL_BLOCKED_HEADING if reasons else "proceed with PRECHECK"
        ),
    }


def assess_state_advancement(
    state_completion: dict[str, bool] | None,
    *,
    target_state: str,
    infra_stop: bool = False,
    capability_blocked: bool = False,
) -> dict[str, Any]:
    """Fail closed when *target_state* is requested before upstream gates pass."""
    completion = dict(state_completion or {})
    target = _clean(target_state).upper()
    blockers = assess_workflow_blockers(
        infra_stop=infra_stop,
        capability_blocked=capability_blocked,
    )
    reasons = list(blockers["reasons"])

    try:
        target_idx = state_index(target)
    except ValueError as exc:
        return {
            "target_state": target,
            "allowed": False,
            "block": True,
            "reasons": [str(exc)],
            "next_allowed_state": None,
            "safe_next_action": TERMINAL_BLOCKED_HEADING,
        }

    if blockers["block"]:
        return {
            "target_state": target,
            "allowed": False,
            "block": True,
            "reasons": reasons,
            "next_allowed_state": None,
            "safe_next_action": blockers["safe_next_action"],
        }

    next_allowed = _first_incomplete_state(completion)
    if next_allowed is None:
        allowed = target_idx == len(REVIEW_MERGE_STATES) - 1
        if not allowed:
            reasons.append("workflow already completed through POST_MERGE_REPORT")
    else:
        allowed = state_index(next_allowed) >= target_idx
        if not allowed:
            reasons.append(
                f"state '{target}' is forbidden until '{next_allowed}' completes"
            )

    return {
        "target_state": target,
        "allowed": allowed and not reasons,
        "block": bool(reasons),
        "reasons": reasons,
        "next_allowed_state": next_allowed,
        "completed_states": [s for s in REVIEW_MERGE_STATES if completion.get(s)],
        "safe_next_action": (
            f"complete state '{next_allowed}' before advancing"
            if next_allowed and not allowed
            else (
                TERMINAL_BLOCKED_HEADING
                if reasons
                else f"advance to {target}"
            )
        ),
    }


def can_approve(state_completion: dict[str, bool] | None, **blocker_kwargs) -> dict[str, Any]:
    """Approval requires all states through REVIEW_DECISION (#290 AC)."""
    required = REVIEW_MERGE_STATES[: REVIEW_MERGE_STATES.index("REVIEW_DECISION") + 1]
    completion = dict(state_completion or {})
    advance = assess_state_advancement(
        completion,
        target_state="APPROVE_OR_REQUEST_CHANGES",
        **blocker_kwargs,
    )
    missing = [s for s in required if not completion.get(s)]
    reasons = list(advance["reasons"])
    if missing:
        reasons.append(
            "approval blocked: incomplete states: " + ", ".join(missing)
        )
    block = bool(reasons) or advance["block"]
    return {
        "allowed": not block,
        "block": block,
        "reasons": reasons,
        "missing_states": missing,
        "safe_next_action": advance["safe_next_action"],
    }


def can_merge(
    state_completion: dict[str, bool] | None,
    *,
    pre_merge_gates: dict[str, bool] | None = None,
    **blocker_kwargs,
) -> dict[str, Any]:
    """Merge requires approve path plus fresh PRE_MERGE_RECHECK gates (#290 AC6)."""
    completion = dict(state_completion or {})
    approve = can_approve(completion, **blocker_kwargs)
    reasons = list(approve["reasons"])

    if not completion.get("APPROVE_OR_REQUEST_CHANGES"):
        reasons.append("merge blocked: APPROVE_OR_REQUEST_CHANGES not completed")

    gate_map = dict(pre_merge_gates or {})
    missing_gates = [g for g in _PRE_MERGE_REQUIRED_GATES if not gate_map.get(g)]
    if missing_gates:
        reasons.append(
            "merge blocked: pre-merge gates incomplete: " + ", ".join(missing_gates)
        )

    advance = assess_state_advancement(
        completion,
        target_state="MERGE",
        **blocker_kwargs,
    )
    reasons.extend(advance["reasons"])

    block = bool(reasons)
    return {
        "allowed": not block,
        "block": block,
        "reasons": reasons,
        "missing_pre_merge_gates": missing_gates,
        "safe_next_action": (
            "complete PRE_MERGE_RECHECK with fresh whoami/capability/PR re-fetch "
            "before merge"
            if block
            else "merge allowed"
        ),
    }


def assess_blocked_recovery_handoff(report_text: str) -> dict[str, Any]:
    """Blocked handoffs must not replay approve/merge commands (#290 AC4)."""
    text = report_text or ""
    reasons: list[str] = []
    if _FORBIDDEN_RECOVERY_REPLAY_RE.search(text):
        reasons.append(
            "blocked recovery handoff contains direct approve/merge replay command"
        )
    if reasons and not _RESTART_WORKFLOW_RE.search(text):
        reasons.append(
            "blocked recovery handoff must direct operator to restart full workflow"
        )
    return {
        "block": bool(reasons),
        "allowed": not reasons,
        "reasons": reasons,
        "safe_next_action": (
            "remove approve/merge replay commands and say to restart full workflow "
            "after blockers clear"
            if reasons
            else "recovery handoff wording acceptable"
        ),
    }


def assess_final_report_state_claims(
    report_text: str,
    *,
    state_completion: dict[str, bool] | None = None,
    approve_completed: bool = False,
    merge_completed: bool = False,
) -> dict[str, Any]:
    """Reports must not claim reviewed/ready-to-merge without gate proof (#290 AC10)."""
    text = report_text or ""
    completion = dict(state_completion or {})
    reasons: list[str] = []

    if _READY_TO_MERGE_RE.search(text) and not (
        merge_completed or completion.get("PRE_MERGE_RECHECK")
    ):
        reasons.append(
            "report claims ready-to-merge without PRE_MERGE_RECHECK completion"
        )

    if _REVIEWED_VALIDATED_RE.search(text):
        if not (approve_completed or completion.get("VALIDATE")):
            reasons.append(
                "report claims reviewed/validated without VALIDATE/APPROVE proof"
            )

    return {
        "block": bool(reasons),
        "allowed": not reasons,
        "reasons": reasons,
        "safe_next_action": (
            "remove stale reviewed/ready-to-merge claims unless gates passed"
            if reasons
            else "final report state claims consistent with workflow"
        ),
    }


def workflow_status(
    state_completion: dict[str, bool] | None,
    **blocker_kwargs,
) -> dict[str, Any]:
    """Summarize current state-machine position for MCP/runtime reporting."""
    completion = dict(state_completion or {})
    blockers = assess_workflow_blockers(**blocker_kwargs)
    next_state = _first_incomplete_state(completion)
    return {
        "states": list(REVIEW_MERGE_STATES),
        "completed_states": [s for s in REVIEW_MERGE_STATES if completion.get(s)],
        "next_required_state": next_state,
        "workflow_complete": next_state is None,
        "approve_allowed": can_approve(completion, **blocker_kwargs)["allowed"],
        "merge_allowed": can_merge(completion, **blocker_kwargs)["allowed"],
        "blockers": blockers,
    }