// Copyright 2020 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
//
//     http://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 pkg

import (
	"encoding/json"
	"fmt"

	"cuelang.org/go/cue/errors"
	"cuelang.org/go/cue/parser"
	"cuelang.org/go/internal/core/adt"
	"cuelang.org/go/internal/core/compile"
	"cuelang.org/go/internal/core/convert"
)

// A Builtin is a Builtin function or constant.
//
// A function may return and a constant may be any of the following types:
//
//	error (translates to bottom)
//	nil   (translates to null)
//	bool
//	int*
//	uint*
//	float64
//	string
//	*big.Float
//	*big.Int
//
//	For any of the above, including interface{} and these types recursively:
//	[]T
//	map[string]T
type Builtin struct {
	Name        string
	Pkg         adt.Feature
	Params      []Param
	Result      adt.Kind
	NonConcrete bool
	Func        func(c *CallCtxt)
	Const       string
}

type Param struct {
	Kind  adt.Kind
	Value adt.Value // input constraint (may be nil)
}

type Package struct {
	Native []*Builtin
	CUE    string
}

func (p *Package) MustCompile(ctx *adt.OpContext, importPath string) *adt.Vertex {
	obj := &adt.Vertex{}
	pkgLabel := ctx.StringLabel(importPath)
	st := &adt.StructLit{}
	if len(p.Native) > 0 {
		obj.AddConjunct(adt.MakeRootConjunct(nil, st))
	}
	for _, bref := range p.Native {
		// Make a copy of each Builtin object; otherwise concurrent use by separate
		// contexts will lead to data races when setting [Builtin.Pkg] below.
		// TODO(perf): avoid copying the builtins, e.g. by using a sync.Once.
		b := *bref

		b.Pkg = pkgLabel

		f := ctx.StringLabel(b.Name) // never starts with _
		// n := &node{baseValue: newBase(imp.Path)}
		var v adt.Expr
		if b.Const != "" {
			v = mustParseConstBuiltin(ctx, b.Name, b.Const)
		} else {
			v = ToBuiltin(&b)
		}
		st.Decls = append(st.Decls, &adt.Field{
			Label: f,
			Value: v,
		})
	}

	// Parse builtin CUE
	if p.CUE != "" {
		expr, err := parser.ParseExpr(importPath, p.CUE)
		if err != nil {
			panic(fmt.Errorf("could not parse %v: %v", p.CUE, err))
		}
		c, err := compile.Expr(nil, ctx.Runtime, importPath, expr)
		if err != nil {
			panic(fmt.Errorf("could compile parse %v: %v", p.CUE, err))
		}
		obj.AddConjunct(c)
	}

	// We could compile lazily, but this is easier for debugging.
	obj.Finalize(ctx)
	if err := obj.Err(ctx); err != nil {
		panic(err.Err)
	}

	return obj
}

// ToBuiltin converts a Builtin into an adt.Builtin.
func ToBuiltin(b *Builtin) *adt.Builtin {
	params := make([]adt.Param, len(b.Params))
	for i, p := range b.Params {
		params[i].Value = p.Value
		if params[i].Value == nil {
			params[i].Value = &adt.BasicType{K: p.Kind}
		}
	}

	x := &adt.Builtin{
		Params:      params,
		Result:      b.Result,
		NonConcrete: b.NonConcrete,
		Package:     b.Pkg,
		Name:        b.Name,
	}
	x.Func = func(call adt.BuiltinCallContext) (ret adt.Expr) {
		ctx := call.OpContext()

		// call, _ := ctx.Source().(*ast.CallExpr)
		c := &CallCtxt{
			BuiltinCallContext: call,
			ctx:                ctx,
			builtin:            b,
		}
		defer func() {
			var errVal interface{} = c.Err
			if err := recover(); err != nil {
				errVal = err
			}
			ret = processErr(c, errVal, ret)
		}()
		b.Func(c)
		switch v := c.Ret.(type) {
		case nil:
			// Validators may return a nil in case validation passes.
			return nil
		case *adt.Bottom:
			// deal with API limitation: catch nil interface issue.
			if v != nil {
				return v
			}
			return nil
		case adt.Value:
			return v
		case Bottomer:
			// deal with API limitation: catch nil interface issue.
			if b := v.Bottom(); b != nil {
				return b
			}
			return nil
		}
		if c.Err != nil {
			if _, ok := c.Err.(ValidationError); !ok || c.ctx.IsValidator {
				return nil
			}
		}
		return convert.FromGoValue(ctx, c.Ret, true)
	}
	return x
}

// newConstBuiltin parses and creates any CUE expression that does not have
// fields.
func mustParseConstBuiltin(ctx adt.Runtime, name, val string) adt.Expr {
	expr, err := parser.ParseExpr("<builtin:"+name+">", val)
	if err != nil {
		panic(err)
	}
	c, err := compile.Expr(nil, ctx, "_", expr)
	if err != nil {
		panic(err)
	}
	return c.Expr()

}

func processErr(call *CallCtxt, errVal interface{}, ret adt.Expr) adt.Expr {
	switch err := errVal.(type) {
	case nil:
	case ValidationError:
		if call.ctx.IsValidator {
			ret = err.B
		}
	case *adt.Bottom:
		ret = err
	case *callError:
		ret = err.b
	case *json.MarshalerError:
		if err, ok := err.Err.(Bottomer); ok {
			if b := err.Bottom(); b != nil {
				ret = b
			}
		}
	case Bottomer:
		ret = err.Bottom()

	case errors.Error:
		// Convert lists of errors to a combined Bottom error.
		if list := errors.Errors(err); len(list) != 0 && list[0] != errVal {
			var errs *adt.Bottom
			for _, err := range list {
				if b, ok := processErr(call, err, nil).(*adt.Bottom); ok {
					errs = adt.CombineErrors(nil, errs, b)
				}
			}
			if errs != nil {
				return errs
			}
		}

		ret = &adt.Bottom{Err: err}
	case error:
		// TODO: store the underlying error explicitly
		ret = &adt.Bottom{Err: errors.Promote(err, "")}
	case string, fmt.Stringer:
		// A string or a stringer likely used as a panic value.
		ret = &adt.Bottom{
			Err: errors.Newf(call.ctx.Pos(), "%s", err),
		}
	default:
		// Some other value used when panicking; likely a bug.
		ret = &adt.Bottom{
			Err: errors.Newf(call.ctx.Pos(), "BUG: non-stringifiable %T", err),
		}
	}
	return ret
}
