// lib/enforce.ts — pure enforcement state machine (PRD R3-R5, AC3/AC5/AC6).
//
// Two states, one decision function:
//   applied     — a valid trusted manifest governs; allowed = the exact
//                 manifest tool projection. Registered extension tools that
//                 lack a bound capability remain unavailable.
//   fail-closed — load/validation/postcondition failed; allowed = SAFE_READ_TOOLS
//                 + the status tool ONLY (AC5: safe reads and status survive;
//                 every side-effecting tool blocks with a stable reason).
//
// Reason codes are STABLE STRINGS (AC3) — they appear in logs, journals, and
// tests, so the format is part of the contract:
//   mosaic-core:tool-not-in-manifest:<tool>
//   mosaic-core:fail-closed:<cause>:<tool>
//   mosaic-core:not-applied:<tool>
//   mosaic-core:read-missing-path
//   mosaic-core:read-scope-unbound
//   mosaic-core:read-credential-denied:<canonical-path>
//   mosaic-core:read-outside-scope:<canonical-path>
//   mosaic-core:read-symlink-escape:<canonical-path>

import type { ReconcilePlan } from "./reconcile.ts";
import { reconcileActiveTools } from "./reconcile.ts";
import type { LoadOutcome } from "./loader.ts";

export const STATUS_TOOL = "mosaic_policy_status";
export const PROPOSAL_TOOL = "mosaic_improvement_propose";
export const GATE_MERGE_ROLE = "gate-merge-ng";
/**
 * F7D (mercer): only DIRECTLY-CONSTRAINABLE read tools survive fail-closed.
 * `read` reads exactly one file (path argument IS the target); `ls` lists one
 * directory non-recursively. `grep` and `find` RECURSE below the path root —
 * they can enumerate and expose credential-shaped descendants
 * (brainHome/auth, fleet/agents/<seat>/secrets, junk) even when the root path
 * passes containment. gitignore is NOT an authorization boundary. Applied
 * manifests already bind only C3->read; exposing grep/find in degraded
 * state INCREASES authority. AC5 says safe reads, not every read-family tool.
 */
export const SAFE_READ_TOOLS = ["read", "ls"] as const;
export const SYMBOLIC_BRAIN = "@brain";

export type EnforcementState =
  | {
      state: "applied";
      incarnationId: string;
      role: string;
      revision: number;
      digest: string;
      allowed: ReadonlySet<string>;
      /** C3 read-scope roots. Symbolic "@brain" or absolute. Empty = C3 unbound. */
      readScope: readonly string[];
    }
  | {
      state: "fail-closed";
      incarnationId: string;
      cause: string;
      allowed: ReadonlySet<string>;
      readScope: readonly string[];
    }
  | { state: "not-applied"; incarnationId: string };

export interface PolicyApplicationInput {
  load: LoadOutcome;
  activeTools: string[];
  incarnationId: string;
  /** Role resolved from the seat profile before a v4 load can fail. */
  roleHint?: string;
  /** The trusted brain home (for resolving the symbolic @brain root). */
  brainHome?: string;
}

export interface PolicyApplication {
  state: EnforcementState;
  plan?: ReconcilePlan;
  /** the exact tool set setActiveTools must receive */
  applyTools: string[];
}

/**
 * A gate role's reviewed manifest explicitly forbids read, ls, and proposal.
 * On any gate load or reconciliation failure, retaining the generic safe-read
 * posture would broaden that role's active authority. Other roles retain the
 * established v3 degraded posture for compatibility.
 */
export function failClosedState(
  incarnationId: string,
  cause: string,
  brainHome?: string,
  roleHint?: string,
): Extract<EnforcementState, { state: "fail-closed" }> {
  const gateRole = roleHint === GATE_MERGE_ROLE;
  const allowed = gateRole
    ? new Set([STATUS_TOOL])
    : new Set([...SAFE_READ_TOOLS, STATUS_TOOL, PROPOSAL_TOOL]);
  return {
    state: "fail-closed",
    incarnationId,
    cause,
    allowed,
    readScope: gateRole ? [] : brainHome ? [brainHome] : [],
  };
}

export function buildApplication(input: PolicyApplicationInput): PolicyApplication {
  const { load, activeTools, incarnationId, brainHome, roleHint } = input;
  if (!load.ok) {
    const state = failClosedState(incarnationId, describeFailure(load.failure), brainHome, roleHint);
    return { state, applyTools: [...state.allowed].sort() };
  }
  const m = load.manifest;
  const allowed = new Set(m.tools);
  const plan = reconcileActiveTools(m.tools, activeTools);
  const c3 = m.capabilities.find((c) => c.id === "repo.file.read");
  const rawScope = c3 && c3.status === "bound" ? m.workspace.readRoots : [];
  const readScope = resolveReadScope(rawScope, brainHome);
  return {
    state: {
      state: "applied",
      incarnationId,
      role: m.role,
      revision: m.revision,
      digest: load.digest,
      allowed,
      readScope,
    },
    plan,
    applyTools: [...allowed].sort(),
  };
}

/**
 * F7-(4): resolve the symbolic "@brain" root to the trusted brain home;
 * absolute roots pass through unchanged.
 */
export function resolveReadScope(roots: readonly string[], brainHome?: string): string[] {
  return roots.map((r) => (r === SYMBOLIC_BRAIN && brainHome ? brainHome : r));
}

export function describeFailure(f: import("./loader.ts").LoadFailure): string {
  switch (f.stage) {
    case "no-agent-name":
      return "no-agent-name";
    case "no-seat-profile":
      return "no-seat-profile";
    case "no-role-in-profile":
      return "no-role-in-profile";
    case "manifest-unreadable":
      return "manifest-unreadable";
    case "manifest-symlink":
      return "manifest-symlink";
    case "invalid-json":
      return "invalid-json";
    case "schema":
      return `schema:${f.reason}`;
    case "role-mismatch":
      return `role-mismatch:${f.expected}!=${f.got}`;
    case "goal-policy-unreadable":
    case "goal-policy-root-symlink":
    case "goal-policy-parent-symlink":
    case "goal-policy-symlink":
    case "goal-policy-path-escape":
    case "goal-policy-non-file":
    case "goal-policy-invalid-utf8":
    case "goal-policy-digest":
    case "goal-policy-section":
    case "goal-policy-launch-generation":
    case "goal-policy-incarnation":
    case "goal-policy-publication":
      return f.stage;
  }
}

export interface Decision {
  block: boolean;
  reason?: string;
}

/**
 * F7-(5): credential deny pattern — covers secrets/ and auth/ directories,
 * .token/.key/.pem/.env* file types, and any path containing "credential".
 * Applied AFTER canonical resolution so traversal cannot bypass it.
 */
const CREDENTIAL_PATH_RE = /(?:^|\/)(?:secrets?|auth)(?:\/|$)/i;
const CREDENTIAL_FILE_RE = /\.(?:token|key|pem|env)(?:\.|$)|credential|fleet\/agents\/junk/i;
const READ_TOOL_BINDING = "read"; // canonical Pi read tool

function isCredentialPath(canonical: string): boolean {
  return CREDENTIAL_PATH_RE.test(canonical) || CREDENTIAL_FILE_RE.test(canonical);
}

/**
 * F7-(2): canonicalize a path — resolve `..` and `.` segments lexically,
 * resolve relative paths against the trusted root. The ADAPTER must
 * additionally realpath() existing targets to catch symlink escapes
 * before calling this function (see decideToolCallWithFs).
 */
export function canonicalizePath(rawPath: string, relativeRoot?: string): string {
  let p = rawPath;
  // resolve relative against the trusted root (never cwd)
  if (!p.startsWith("/") && relativeRoot) {
    p = relativeRoot + "/" + p;
  }
  const parts: string[] = [];
  for (const seg of p.split("/")) {
    if (seg === "" || seg === ".") continue;
    if (seg === "..") { parts.pop(); continue; }
    parts.push(seg);
  }
  return "/" + parts.join("/");
}

/**
 * F7-(2,5): read containment with credential denial AFTER canonical resolution.
 * readScope roots must themselves be canonical absolute paths.
 * Returns ok only if the canonical path falls under a declared root AND
 * does not match the credential deny pattern post-resolution.
 */
export function readPathAllowed(
  readScope: readonly string[],
  rawPath: string,
  relativeRoot?: string,
): { ok: boolean; reason?: string } {
  if (readScope.length === 0) return { ok: false, reason: "mosaic-core:read-scope-unbound" };
  // F7-(2,3): missing, empty, or NON-STRING path is DENIED, not passed through
  if (typeof rawPath !== "string" || rawPath === "") {
    return { ok: false, reason: "mosaic-core:read-missing-path" };
  }
  const canonical = canonicalizePath(rawPath, relativeRoot);
  // F7-(5): credential denial AFTER canonical resolution
  if (isCredentialPath(canonical)) {
    return { ok: false, reason: `mosaic-core:read-credential-denied:${canonical}` };
  }
  for (const root of readScope) {
    if (canonical === root || canonical.startsWith(root + "/")) {
      return { ok: true };
    }
  }
  return { ok: false, reason: `mosaic-core:read-outside-scope:${canonical}` };
}

/**
 * F7-(3): safe-read constraint — the SAFE_READ_TOOLS that survive
 * fail-closed must still respect the credential deny pattern.
 * Without this, a malformed manifest would EXPOSE broader reads than an
 * applied role. Safe reads get NO workspace scope (scope is empty in
 * fail-closed/not-applied), so read is denied; grep/glob/ls still have
 * credential-shaped path denial applied to their arguments.
 */
/**
 * F7-B (mercer NG4-F7B): all four Pi safe-read built-ins (read, grep, find,
 * ls) take an optional path argument; absent path defaults to the tool's
 * cwd. This function treats ABSENT path as the trusted root (in scope by
 * definition) and a PROVIDED path through canonical containment + credential
 * denial. In fail-closed, the scope IS the trusted brain home so reads
 * within the brain tree survive; reads outside are denied.
 */
export function safeReadAllowed(
  toolName: string,
  readScope: readonly string[],
  args?: unknown,
  trustedRoot?: string,
): { ok: boolean; reason?: string } {
  if (toolName === STATUS_TOOL || toolName === PROPOSAL_TOOL) return { ok: true };

  // F7F: tool-specific input shape — read REQUIRES a non-array object with
  // a nonempty string path; ls may accept undefined/{} but non-object/null/
  // array or non-string path DENIES. The pure decision must align with the
  // adapter (which synthesizes ls input ONLY when undefined).
  const isObject = (v: unknown): v is Record<string, unknown> =>
    typeof v === "object" && v !== null && !Array.isArray(v);

  if (toolName === READ_TOOL_BINDING) {
    // read: args must be a non-array object with nonempty string path
    if (!isObject(args)) {
      return { ok: false, reason: "mosaic-core:read-missing-path" };
    }
    const path = args.path;
    if (typeof path !== "string" || path === "") {
      return { ok: false, reason: "mosaic-core:read-missing-path" };
    }
    // containment + credential denial
    const effectiveScope = readScope.length > 0 ? readScope : trustedRoot ? [trustedRoot] : [];
    const canonical = canonicalizePath(path, trustedRoot);
    if (isCredentialPath(canonical)) {
      return { ok: false, reason: `mosaic-core:read-credential-denied:${canonical}` };
    }
    if (effectiveScope.length === 0) {
      return { ok: false, reason: "mosaic-core:read-scope-unbound" };
    }
    for (const root of effectiveScope) {
      if (canonical === root || canonical.startsWith(root + "/")) return { ok: true };
    }
    return { ok: false, reason: `mosaic-core:read-outside-scope:${canonical}` };
  }

  // ls: undefined args OK (adapter synthesizes); non-object/null/array DENIES
  if (args !== undefined && !isObject(args)) {
    return { ok: false, reason: "mosaic-core:read-missing-path" };
  }
  const path = isObject(args) ? args.path : undefined;
  if (path !== undefined && typeof path !== "string") {
    return { ok: false, reason: "mosaic-core:read-missing-path" };
  }
  // credential check on the resolved path (or brainHome for absent)
  const effectiveScope = readScope.length > 0 ? readScope : trustedRoot ? [trustedRoot] : [];
  const effectivePath = typeof path === "string" && path !== "" ? path : (trustedRoot ?? "/");
  const canonical = canonicalizePath(effectivePath, trustedRoot);
  if (isCredentialPath(canonical)) {
    return { ok: false, reason: `mosaic-core:read-credential-denied:${canonical}` };
  }
  if (effectiveScope.length === 0) {
    return { ok: false, reason: "mosaic-core:read-scope-unbound" };
  }
  for (const root of effectiveScope) {
    if (canonical === root || canonical.startsWith(root + "/")) return { ok: true };
  }
  return { ok: false, reason: `mosaic-core:read-outside-scope:${canonical}` };
}

export function decideToolCall(state: EnforcementState, toolName: string, args?: unknown, relativeRoot?: string): Decision {
  switch (state.state) {
    case "not-applied":
      if (toolName === STATUS_TOOL || toolName === PROPOSAL_TOOL || (SAFE_READ_TOOLS as readonly string[]).includes(toolName)) {
        const safe = safeReadAllowed(toolName, [], args, relativeRoot);
        if (!safe.ok) return { block: true, reason: safe.reason };
        return { block: false };
      }
      return { block: true, reason: `mosaic-core:not-applied:${toolName}` };
    case "fail-closed":
      if (state.allowed.has(toolName)) {
        const safe = safeReadAllowed(toolName, state.readScope ?? [], args, relativeRoot);
        if (!safe.ok) return { block: true, reason: safe.reason };
        return { block: false };
      }
      return { block: true, reason: `mosaic-core:fail-closed:${state.cause}:${toolName}` };
    case "applied":
      if (state.allowed.has(toolName)) {
        // F7-(2): C3 read containment. Missing path DENIED. Relative paths
        // resolved against the trusted brain root. The adapter must
        // additionally realpath() existing targets before deciding.
        if (toolName === READ_TOOL_BINDING && state.readScope.length > 0) {
          const path = args && typeof args === "object" ? (args as { path?: unknown }).path : undefined;
          const scope = readPathAllowed(state.readScope, typeof path === "string" ? path : "", relativeRoot);
          if (!scope.ok) return { block: true, reason: scope.reason };
        }
        return { block: false };
      }
      return { block: true, reason: `mosaic-core:tool-not-in-manifest:${toolName}` };
  }
}

export function statusSnapshot(state: EnforcementState, activeTools: string[]): Record<string, unknown> {
  if (state.state === "applied") {
    return {
      state: state.state,
      role: state.role,
      revision: state.revision,
      digest: state.digest,
      incarnationId: state.incarnationId,
      activeTools: [...activeTools].sort(),
    };
  }
  if (state.state === "fail-closed") {
    return {
      state: state.state,
      cause: state.cause,
      incarnationId: state.incarnationId,
      activeTools: [...activeTools].sort(),
    };
  }
  return { state: state.state, incarnationId: state.incarnationId, activeTools: [...activeTools].sort() };
}