// Copyright 2025 CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package yaml

import (
	"errors"
	"io"

	"cuelang.org/go/cue"
	cueerrors "cuelang.org/go/cue/errors"
	"cuelang.org/go/internal/core/adt"
	"cuelang.org/go/internal/pkg"
	"cuelang.org/go/internal/value"
)

// Validate validates YAML and confirms it is an instance of schema.
// If the YAML source is a stream, every object must match v.
//
// If Validate is called in a broader context, like a validation or function
// call, the cycle context of n should be accumulated in c before this call.
// This can be done by using the Expr method on the BuiltinCallContext.
func Validate(c *adt.OpContext, b []byte, v cue.Value) (bool, error) {
	d := NewDecoder("yaml.Validate", b)
	r := v.Context()
	for {
		expr, err := d.Decode()
		if err != nil {
			if err == io.EOF {
				return true, nil
			}
			return false, err
		}

		x := r.BuildExpr(expr)
		if err := x.Err(); err != nil {
			return false, err
		}

		// TODO: consider using subsumption again here.
		// Alternatives:
		// - allow definition of non-concrete list,
		//   like list.Of(int), or []int.
		// - Introduce ! in addition to ?, allowing:
		//   list!: [...]
		// if err := v.Subsume(inst.Value(), cue.Final()); err != nil {
		// 	return false, err
		// }
		vx := adt.Unify(c, value.Vertex(x), value.Vertex(v))
		x = value.Make(c, vx)

		// Note that we do not return early on x.Err here: doing so would only
		// report the single top-level error, whereas Validate descends into all
		// arcs and reports every conflict.
		if err := x.Validate(cue.Concrete(true)); err != nil {
			// Strip error codes: incomplete errors are terminal in this case.
			// Validate may report several conflicts as a list of errors, so
			// strip each one individually rather than collapsing the whole list
			// down to a single error.
			var errs cueerrors.Error
			for _, e := range cueerrors.Errors(err) {
				var b pkg.Bottomer
				if errors.As(e, &b) {
					e = b.Bottom().Err
				}
				errs = cueerrors.Append(errs, e)
			}
			return false, errs
		}
	}
}

// ValidatePartial validates YAML and confirms it matches the constraints
// specified by v using unification. This means that b must be consistent with,
// but does not have to be an instance of v. If the YAML source is a stream,
// every object must match v.
func ValidatePartial(c *adt.OpContext, b []byte, v cue.Value) (bool, error) {
	d := NewDecoder("yaml.ValidatePartial", b)
	r := v.Context()
	for {
		expr, err := d.Decode()
		if err != nil {
			if err == io.EOF {
				return true, nil
			}
			return false, err
		}

		x := r.BuildExpr(expr)
		if err := x.Err(); err != nil {
			return false, err
		}

		vx := adt.Unify(c, value.Vertex(x), value.Vertex(v))
		x = value.Make(c, vx)

		// Use Validate rather than Err so that every conflict is reported, not
		// just the single top-level error. No options are passed as partial
		// validation must not require values to be concrete.
		if err := x.Validate(); err != nil {
			return false, err
		}
	}
}
