import type { ModuleMigrationAggregate } from "../modules/index.js";
import type {
  MigrationApplyResult,
  MigrationPlanResult,
  RetainedMigrationHistory,
} from "../migrations/index.js";

function plural(count: number, singular: string): string {
  return count === 1 ? singular : `${singular}s`;
}

export function formatMigrationValidationReport(
  aggregate: ModuleMigrationAggregate,
): readonly string[] {
  const moduleCount = aggregate.modules.length;
  const migrationCount = aggregate.migrations.length;
  const header = `Migration validation passed (${moduleCount} ${plural(moduleCount, "module")}, ${migrationCount} ${plural(migrationCount, "migration")})${moduleCount === 0 ? "." : ":"}`;
  const lines = [header];

  for (const module of aggregate.modules) {
    if (module.migrations.length === 0) {
      lines.push(`- ${module.moduleId} (no migrations)`);
      continue;
    }
    for (const migration of module.migrations) {
      lines.push(
        `- ${migration.identity} sha256=${migration.checksum} destructive=${migration.destructive.mode}`,
      );
    }
  }

  return Object.freeze(lines);
}

/** An absent module's applied history (ADR 0048): kept, reported, and never a reason to stop. */
function retainedLines(retained: readonly RetainedMigrationHistory[]): readonly string[] {
  return retained.map(
    (module) =>
      `- [retained] ${module.moduleId}: ${module.appliedCount} applied ${plural(module.appliedCount, "migration")} kept; the module is not installed`,
  );
}

export function formatMigrationPlanReport(plan: MigrationPlanResult): readonly string[] {
  const readyCount = plan.pendingCount - plan.approvalRequiredCount;
  const retainedSummary = plan.retained.length === 0 ? "" : `, ${plan.retained.length} retained`;
  const lines = [
    `Migration plan (${plan.appliedCount} applied, ${readyCount} pending, ${plan.approvalRequiredCount} approval-blocked${retainedSummary}):`,
  ];

  for (const entry of plan.entries) {
    lines.push(`- [${entry.status}] ${entry.identity} sha256=${entry.checksum}`);
  }
  if (plan.entries.length === 0) {
    lines.push("- No installed module migrations.");
  }
  lines.push(...retainedLines(plan.retained));
  lines.push(
    "Informational only: this plan is read-only and may become stale; apply revalidates history under the migration lock.",
  );

  return Object.freeze(lines);
}

export function formatMigrationApplyReport(result: MigrationApplyResult): readonly string[] {
  if (result.noOp) {
    return Object.freeze([
      "Migration apply completed: database is already current (no changes).",
      ...retainedLines(result.retained),
    ]);
  }

  const lines = [
    `Migration apply completed (${result.appliedCount} ${plural(result.appliedCount, "migration")} applied):`,
  ];
  for (const migration of result.applied) {
    lines.push(`- ${migration.identity} sha256=${migration.checksum}`);
  }
  lines.push(...retainedLines(result.retained));
  return Object.freeze(lines);
}