// Copyright 2024 Dolthub, Inc.
//
// 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 functions

import (
	"strings"
	"unicode"

	"github.com/cockroachdb/errors"
)

// ioInputSections converts the input string for IoInput into a sectioned form according to the rules defined by Postgres:
// https://www.postgresql.org/docs/15/datatype-oid.html
func ioInputSections(input string) ([]string, error) {
	if len(input) == 0 {
		return nil, errors.Errorf("invalid name syntax")
	}
	runeInput := []rune(strings.TrimSpace(input))
	var sections []string
	var sectionBuilder strings.Builder
	var inQuotes bool

	for i := 0; i < len(runeInput); i++ {
		char := runeInput[i]
		switch char {
		case '"':
			if inQuotes {
				if i < len(runeInput)-1 && runeInput[i+1] == '"' {
					sectionBuilder.WriteRune(char)
					i++
				} else {
					inQuotes = false
					sectionBuilder.WriteRune(char)
					currentSection := sectionBuilder.String()
					sectionBuilder.Reset()
					// Handle "char" special case based on position
					if currentSection == `"char"` && (len(sections) == 0 || (len(sections) > 0 && sections[len(sections)-1] == ".")) {
						sections = append(sections, currentSection)
					} else {
						sections = append(sections, strings.Trim(currentSection, `"`))
					}
				}
			} else {
				if i < len(runeInput)-1 && runeInput[i+1] == '"' {
					return nil, errors.Errorf("invalid name syntax")
				}
				inQuotes = true
				sectionBuilder.WriteRune(char)
			}
		case '.':
			if inQuotes {
				sectionBuilder.WriteRune(char)
			} else {
				if sectionBuilder.Len() > 0 {
					sections = append(sections, sectionBuilder.String())
					sectionBuilder.Reset()
				}
				sections = append(sections, string(char))
			}
		case ' ':
			if inQuotes {
				sectionBuilder.WriteRune(char)
			} else {
				sectionBuilder.WriteRune(char)
			}
		case '[':
			sectionBuilder.WriteRune(char)
		case ']':
			sectionBuilder.WriteRune(char)
		default:
			if inQuotes {
				sectionBuilder.WriteRune(char)
			} else {
				if sectionBuilder.Len() == 0 && char == '"' {
					return nil, errors.Errorf("invalid name syntax")
				}
				sectionBuilder.WriteRune(unicode.ToLower(char))
			}
		}
	}

	if sectionBuilder.Len() > 0 {
		section := sectionBuilder.String()
		if inQuotes {
			// For some reason, you can have an unmatched double quote at the end, so we're duplicating that behavior
			if input[len(input)-1] != '"' {
				return nil, errors.Errorf("invalid name syntax")
			}
		}
		if len(sections) > 0 && sections[len(sections)-1] != "." {
			sections[len(sections)-1] += section
		} else {
			sections = append(sections, section)
		}
	}

	// Post-process to handle the specific "char" rule
	for i := 0; i < len(sections); i++ {
		if sections[i] == `"char"` && i == 0 && len(sections) > 1 {
			sections[i] = "char"
		}
	}

	return sections, nil
}