import { KindGuard, Kind, type TSchema } from "@alkdev/typebox";

export interface TypeMismatch {
  path: string;
  expected: string;
  actual: string;
}

export interface TypeCompatResult {
  compatible: boolean;
  detail?: string;
  mismatches?: TypeMismatch[];
}

function schemaKind(schema: TSchema): string {
  return (schema as unknown as Record<typeof Kind, unknown>)[Kind] as string ?? "unknown";
}

function typeName(schema: TSchema): string {
  if (KindGuard.IsUnknown(schema)) return "unknown";
  if (KindGuard.IsAny(schema)) return "any";
  if (KindGuard.IsNull(schema)) return "null";
  if (KindGuard.IsString(schema)) return "string";
  if (KindGuard.IsNumber(schema)) return "number";
  if (KindGuard.IsInteger(schema)) return "integer";
  if (KindGuard.IsBoolean(schema)) return "boolean";
  if (KindGuard.IsLiteral(schema)) {
    const val = schema.const;
    return typeof val === "string" ? `"${val}"` : String(val);
  }
  if (KindGuard.IsArray(schema)) return "array";
  if (KindGuard.IsObject(schema)) return "object";
  if (KindGuard.IsUnion(schema)) {
    const anyOf = schema.anyOf as TSchema[] | undefined;
    if (anyOf) return anyOf.map(typeName).join(" | ");
    return "union";
  }
  if (KindGuard.IsRecord(schema)) return "record";
  if (KindGuard.IsTuple(schema)) return "tuple";
  if (KindGuard.IsNever(schema)) return "never";
  return schemaKind(schema);
}

function isUnknownType(schema: TSchema): boolean {
  if (KindGuard.IsUnknown(schema) || KindGuard.IsAny(schema)) return true;
  return false;
}

function unwrapOptional(schema: TSchema): TSchema {
  if (KindGuard.IsOptional(schema)) {
    return (schema as unknown as Record<string, unknown>)["type"] === "object"
      ? schema
      : ((schema as unknown as Record<string, unknown>)["anyOf"] as TSchema[] | undefined)?.[0] ?? schema;
  }
  return schema;
}

function unwrapReadonlyOptional(schema: TSchema): TSchema {
  let s = schema;
  if (KindGuard.IsReadonly(s)) {
    const inner = (s as unknown as Record<string, unknown>)["anyOf"] as TSchema[] | undefined;
    if (inner) s = inner[0]!;
  }
  return unwrapOptional(s);
}

function isOptionalField(schema: TSchema): boolean {
  if (KindGuard.IsOptional(schema)) return true;
  if (KindGuard.IsReadonly(schema)) {
    const inner = (schema as unknown as Record<string, unknown>)["anyOf"] as TSchema[] | undefined;
    if (inner && KindGuard.IsOptional(inner[0]!)) return true;
  }
  return false;
}

function isSupertypeOf(outer: TSchema, inner: TSchema): boolean {
  if (KindGuard.IsUnion(outer)) {
    const anyOf = outer.anyOf as TSchema[] | undefined;
    if (!anyOf) return false;
    return anyOf.some((variant) => isSupertypeOf(variant, inner));
  }
  if (KindGuard.IsUnion(inner)) {
    const anyOf = inner.anyOf as TSchema[] | undefined;
    if (!anyOf) return false;
    return anyOf.every((variant) => isSupertypeOf(outer, variant));
  }
  if (schemasEqual(outer, inner)) return true;
  if (KindGuard.IsLiteral(outer) && KindGuard.IsLiteral(inner)) {
    return outer.const === inner.const;
  }
  if (KindGuard.IsString(outer) && KindGuard.IsLiteral(inner) && typeof inner.const === "string") return true;
  if (KindGuard.IsNumber(outer) && KindGuard.IsLiteral(inner) && typeof inner.const === "number") return true;
  if (KindGuard.IsInteger(outer) && KindGuard.IsLiteral(inner) && typeof inner.const === "number") return true;
  if (KindGuard.IsBoolean(outer) && KindGuard.IsLiteral(inner) && typeof inner.const === "boolean") return true;
  return false;
}

function schemasEqual(a: TSchema, b: TSchema): boolean {
  const aKind = (a as unknown as Record<typeof Kind, unknown>)[Kind];
  const bKind = (b as unknown as Record<typeof Kind, unknown>)[Kind];
  if (aKind !== bKind) return false;
  if (KindGuard.IsString(a) && KindGuard.IsString(b)) return true;
  if (KindGuard.IsNumber(a) && KindGuard.IsNumber(b)) return true;
  if (KindGuard.IsInteger(a) && KindGuard.IsInteger(b)) return true;
  if (KindGuard.IsBoolean(a) && KindGuard.IsBoolean(b)) return true;
  if (KindGuard.IsNull(a) && KindGuard.IsNull(b)) return true;
  if (KindGuard.IsUnknown(a) && KindGuard.IsUnknown(b)) return true;
  if (KindGuard.IsAny(a) && KindGuard.IsAny(b)) return true;
  if (KindGuard.IsLiteral(a) && KindGuard.IsLiteral(b)) return a.const === b.const;
  return false;
}

function checkCompat(output: TSchema, input: TSchema, path: string, mismatches: TypeMismatch[]): void {
  const outUnwrapped = unwrapReadonlyOptional(output);
  const inUnwrapped = unwrapReadonlyOptional(input);

  if (isUnknownType(outUnwrapped) || isUnknownType(inUnwrapped)) {
    mismatches.push({
      path,
      expected: typeName(inUnwrapped),
      actual: typeName(outUnwrapped),
    });
    return;
  }

  if (KindGuard.IsNull(outUnwrapped) && KindGuard.IsNull(inUnwrapped)) return;
  if (KindGuard.IsString(outUnwrapped) && KindGuard.IsString(inUnwrapped)) return;
  if (KindGuard.IsNumber(outUnwrapped) && KindGuard.IsNumber(inUnwrapped)) return;
  if (KindGuard.IsInteger(outUnwrapped) && KindGuard.IsInteger(inUnwrapped)) return;
  if (KindGuard.IsInteger(outUnwrapped) && KindGuard.IsNumber(inUnwrapped)) return;
  if (KindGuard.IsBoolean(outUnwrapped) && KindGuard.IsBoolean(inUnwrapped)) return;
  if (KindGuard.IsLiteral(outUnwrapped) && KindGuard.IsLiteral(inUnwrapped)) {
    if (outUnwrapped.const !== inUnwrapped.const) {
      mismatches.push({
        path,
        expected: typeName(inUnwrapped),
        actual: typeName(outUnwrapped),
      });
    }
    return;
  }

  if (KindGuard.IsLiteral(outUnwrapped)) {
    if (!isSupertypeOf(inUnwrapped, outUnwrapped)) {
      mismatches.push({
        path,
        expected: typeName(inUnwrapped),
        actual: typeName(outUnwrapped),
      });
    }
    return;
  }

  if (KindGuard.IsUnion(inUnwrapped) && !KindGuard.IsUnion(outUnwrapped)) {
    if (!isSupertypeOf(inUnwrapped, outUnwrapped)) {
      mismatches.push({
        path,
        expected: typeName(inUnwrapped),
        actual: typeName(outUnwrapped),
      });
    }
    return;
  }

  if (KindGuard.IsUnion(outUnwrapped) && !KindGuard.IsUnion(inUnwrapped)) {
    const anyOf = outUnwrapped.anyOf as TSchema[] | undefined;
    if (anyOf) {
      const allCompat = anyOf.every((variant) => {
        const subMismatches: TypeMismatch[] = [];
        checkCompat(variant, inUnwrapped, path, subMismatches);
        return subMismatches.length === 0;
      });
      if (!allCompat) {
        mismatches.push({
          path,
          expected: typeName(inUnwrapped),
          actual: typeName(outUnwrapped),
        });
      }
    }
    return;
  }

  if (KindGuard.IsUnion(outUnwrapped) && KindGuard.IsUnion(inUnwrapped)) {
    const outAnyOf = outUnwrapped.anyOf as TSchema[] | undefined;
    const inAnyOf = inUnwrapped.anyOf as TSchema[] | undefined;
    if (outAnyOf && inAnyOf) {
      for (const outVariant of outAnyOf) {
        const covered = inAnyOf.some((inVariant) => {
          const sub: TypeMismatch[] = [];
          checkCompat(outVariant, inVariant, path, sub);
          return sub.length === 0;
        });
        if (!covered) {
          mismatches.push({
            path,
            expected: typeName(inUnwrapped),
            actual: typeName(outUnwrapped),
          });
          return;
        }
      }
    }
    return;
  }

  if (KindGuard.IsArray(outUnwrapped) && KindGuard.IsArray(inUnwrapped)) {
    const outItems = outUnwrapped.items as TSchema | undefined;
    const inItems = inUnwrapped.items as TSchema | undefined;
    if (outItems && inItems) {
      checkCompat(outItems, inItems, `${path}[]`, mismatches);
    }
    return;
  }

  if (KindGuard.IsObject(outUnwrapped) && KindGuard.IsObject(inUnwrapped)) {
    const outProps = outUnwrapped.properties as Record<string, TSchema> | undefined;
    const inProps = inUnwrapped.properties as Record<string, TSchema> | undefined;
    if (inProps) {
      for (const key of Object.keys(inProps)) {
        const inField = inProps[key]!;
        const isOpt = isOptionalField(inField);
        if (outProps && key in outProps) {
          checkCompat(outProps[key]!, inField, `${path}/${key}`, mismatches);
        } else if (!isOpt) {
          mismatches.push({
            path: `${path}/${key}`,
            expected: typeName(inField),
            actual: "missing",
          });
        }
      }
    }
    return;
  }

  if (KindGuard.IsRecord(outUnwrapped) && KindGuard.IsRecord(inUnwrapped)) {
    const outVal = outUnwrapped.additionalProperties as TSchema | undefined;
    const inVal = inUnwrapped.additionalProperties as TSchema | undefined;
    if (outVal && inVal) {
      checkCompat(outVal, inVal, `${path}{}`, mismatches);
    }
    return;
  }

  if (!schemasEqual(outUnwrapped, inUnwrapped) && !isSupertypeOf(inUnwrapped, outUnwrapped)) {
    mismatches.push({
      path,
      expected: typeName(inUnwrapped),
      actual: typeName(outUnwrapped),
    });
  }
}

export function typeCompat(outputSchema: TSchema, inputSchema: TSchema): TypeCompatResult | undefined {
  if (isUnknownType(outputSchema) || isUnknownType(inputSchema)) return undefined;

  const mismatches: TypeMismatch[] = [];
  checkCompat(outputSchema, inputSchema, "", mismatches);

  if (mismatches.length === 0) {
    const outUnwrapped = unwrapReadonlyOptional(outputSchema);
    const inUnwrapped = unwrapReadonlyOptional(inputSchema);
    if (KindGuard.IsObject(outUnwrapped) && KindGuard.IsObject(inUnwrapped)) {
      const outProps = outUnwrapped.properties as Record<string, TSchema> | undefined;
      const inProps = inUnwrapped.properties as Record<string, TSchema> | undefined;
      if (outProps && inProps) {
        const hasExtra = Object.keys(outProps).some((k) => !(k in inProps));
        if (hasExtra) {
          return { compatible: true, detail: "output has extra fields beyond input requirements" };
        }
      }
    }
    return { compatible: true };
  }

  return { compatible: false, mismatches };
}