import { z } from "zod";
import type { CTPDocument } from "./schema";

// ─── Sub-schemas ──────────────────────────────────────────────────────────────

const TimeSignatureSchema = z.object({
  numerator: z.number().int().min(1).max(32),
  denominator: z
    .number()
    .int()
    .refine((n) => [1, 2, 4, 8, 16, 32].includes(n), {
      message: "denominator must be a power of 2 (1, 2, 4, 8, 16, or 32)",
    }),
});

const StepSectionSchema = z.object({
  label: z.string().min(1).max(64),
  start_bar: z.number().int().min(1),
  bpm: z.number().min(20).max(400),
  time_signature: TimeSignatureSchema,
  transition: z.literal("step"),
});

const RampSectionSchema = z.object({
  label: z.string().min(1).max(64),
  start_bar: z.number().int().min(1),
  bpm_start: z.number().min(20).max(400),
  bpm_end: z.number().min(20).max(400),
  time_signature: TimeSignatureSchema,
  transition: z.literal("ramp"),
});

const CTPSectionSchema = z.discriminatedUnion("transition", [
  StepSectionSchema,
  RampSectionSchema,
]);

const CountInSchema = z.object({
  enabled: z.boolean(),
  bars: z.number().int().min(1).max(8),
  use_first_section_tempo: z.boolean(),
});

const CTPMetadataSchema = z.object({
  title: z.string().min(1).max(256),
  artist: z.string().min(1).max(256),
  mbid: z
    .string()
    .uuid()
    .nullable()
    .default(null),
  duration_seconds: z.number().positive(),
  contributed_by: z.string().min(1).max(64),
  verified: z.boolean(),
  created_at: z.string().datetime(),
});

// ─── Root schema ──────────────────────────────────────────────────────────────

export const CTPDocumentSchema = z
  .object({
    version: z.literal("1.0"),
    metadata: CTPMetadataSchema,
    count_in: CountInSchema,
    sections: z.array(CTPSectionSchema).min(1),
  })
  .superRefine((doc, ctx) => {
    const sections = doc.sections;

    // First section must start at bar 1
    if (sections[0].start_bar !== 1) {
      ctx.addIssue({
        code: z.ZodIssueCode.custom,
        path: ["sections", 0, "start_bar"],
        message: "The first section must start at bar 1",
      });
    }

    // Sections must be sorted by start_bar (strictly ascending)
    for (let i = 1; i < sections.length; i++) {
      if (sections[i].start_bar <= sections[i - 1].start_bar) {
        ctx.addIssue({
          code: z.ZodIssueCode.custom,
          path: ["sections", i, "start_bar"],
          message: `Section start_bar must be strictly greater than the previous section's start_bar (got ${sections[i].start_bar} after ${sections[i - 1].start_bar})`,
        });
      }
    }
  });

// ─── Exported validator ───────────────────────────────────────────────────────

export type CTPValidationResult =
  | { success: true; data: CTPDocument }
  | { success: false; errors: z.ZodError };

/**
 * Validates an unknown value as a CTPDocument.
 * Returns a typed result union instead of throwing.
 */
export function validateCTP(input: unknown): CTPValidationResult {
  const result = CTPDocumentSchema.safeParse(input);
  if (result.success) {
    return { success: true, data: result.data as CTPDocument };
  }
  return { success: false, errors: result.error };
}

/**
 * Validates and throws a descriptive error if the document is invalid.
 * Useful in scripts/CLI contexts.
 */
export function parseCTP(input: unknown): CTPDocument {
  return CTPDocumentSchema.parse(input) as CTPDocument;
}