package fejkdata

import (
	"errors"
	"fmt"
)

// DataType is what a record column holds, which decides how a record writes its value.
type DataType int

// The datatypes a column declares with "datatype"; a column without one is a string.
const (
	DataTypeString DataType = iota
	DataTypeInteger
	DataTypeNumber
	DataTypeBoolean
)

var (
	dataTypeNames = [...]string{"string", "integer", "number", "boolean"}
	dataTypeNouns = [...]string{"text", "an integer", "a number", "a boolean"}
)

// String is the datatype as data spells it.
func (d DataType) String() string {
	if d < 0 || int(d) >= len(dataTypeNames) {
		return fmt.Sprintf("DataType(%d)", int(d))
	}
	return dataTypeNames[d]
}

// position is where a JSON value sits, which decides whether it may carry a datatype or
// be null.
type position int

const (
	inFormat position = iota // rendered by a format, so neither
	atTop                    // a category or an inline template, whose fields may be columns
	inColumn                 // a column, or a choice item standing in for one
)

// datatypeOf reads a template's "datatype" (default DataTypeString).
func datatypeOf(m map[string]any, pos position) (DataType, error) {
	v, ok := m["datatype"]
	if !ok {
		return DataTypeString, nil
	}
	name, ok := v.(string)
	if !ok {
		return 0, fmt.Errorf("datatype must be a string, got %T", v)
	}
	if name == DataTypeString.String() {
		return 0, fmt.Errorf("datatype %q is the default, so it has no effect; drop it", name)
	}
	for d := DataTypeInteger; d <= DataTypeBoolean; d++ {
		if name != d.String() {
			continue
		}
		if pos != inColumn {
			return 0, errors.New("datatype only types a record column — a field of the top-level template — so it has no effect here")
		}
		return d, nil
	}
	return 0, fmt.Errorf(`datatype takes "integer", "number" or "boolean", got %q`, name)
}

// columnDatatype is the datatype a column's items declare. They must agree, since a
// column holds one; a column only ever null is a string.
func columnDatatype(n node) (DataType, error) {
	var items []*template
	var collect func(node)
	collect = func(n node) {
		switch n := n.(type) {
		case *choice:
			for _, it := range n.items {
				collect(it)
			}
		case *template:
			items = append(items, n)
		}
	}
	collect(n)
	if len(items) == 0 {
		return DataTypeString, nil
	}
	for _, t := range items[1:] {
		if t.datatype != items[0].datatype {
			return items[0].datatype, disagreement(items[0], t)
		}
	}
	return items[0].datatype, nil
}

// disagreement names the fix for two items of one column declaring different datatypes.
func disagreement(a, b *template) error {
	typed, bare := a, b
	if typed.datatype == DataTypeString {
		typed, bare = b, a
	}
	switch {
	case bare.datatype != DataTypeString:
		return fmt.Errorf("its items declare %s and %s; a column holds one datatype", a.datatype, b.datatype)
	case len(bare.fields) == 0 && bare.repeat == 1:
		return fmt.Errorf(`item %q declares no datatype, and a column holds one; write it as {"format":%q,"datatype":%q}`, bare.format, bare.format, typed.datatype)
	}
	return fmt.Errorf(`an item declares no datatype beside one declaring %s; a column holds one, so give it "datatype": %q`, typed.datatype, typed.datatype)
}