// Cthulhu screen reader.
// Copyright (c) 2026 Storm Dragon
// Authors: Storm Dragon, Angus Kola
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.

package parity

import (
	"encoding/csv"
	"errors"
	"fmt"
	"io"
)

var ErrSchema = errors.New("parity ledger schema")

const (
	StatusPending          = "pending"
	StatusInProgress       = "in-progress"
	StatusImplemented      = "implemented"
	StatusAuditRequired    = "audit-required"
	StatusAcceptedOmission = "accepted-omission"
)

var allowedStatuses = map[string]struct{}{
	StatusPending:          {},
	StatusInProgress:       {},
	StatusImplemented:      {},
	StatusAuditRequired:    {},
	StatusAcceptedOmission: {},
}

var columns = []string{
	"id",
	"python_source",
	"subsystem",
	"behavior",
	"owner",
	"go_destination",
	"status",
	"automated_evidence",
	"x11_evidence",
	"wayland_evidence",
	"speech_evidence",
	"braille_evidence",
	"notes",
}

type Record struct {
	ID                string
	PythonSource      string
	Subsystem         string
	Behavior          string
	Owner             string
	GoDestination     string
	Status            string
	AutomatedEvidence string
	X11Evidence       string
	WaylandEvidence   string
	SpeechEvidence    string
	BrailleEvidence   string
	Notes             string
}

type ParseError struct {
	Row int
	Err error
}

func (parseError *ParseError) Error() string {
	return fmt.Sprintf("row %d: %v", parseError.Row, parseError.Err)
}

func (parseError *ParseError) Unwrap() error {
	return parseError.Err
}

func Load(reader io.Reader) ([]Record, error) {
	csvReader := csv.NewReader(reader)
	csvReader.FieldsPerRecord = len(columns)
	csvReader.TrimLeadingSpace = true

	header, err := csvReader.Read()
	if err != nil {
		return nil, &ParseError{Row: 1, Err: fmt.Errorf("%w: read header: %w", ErrSchema, err)}
	}
	for index, column := range header {
		if column != columns[index] {
			return nil, &ParseError{
				Row: 1,
				Err: fmt.Errorf("%w: column %d is %q, want %q", ErrSchema, index+1, column, columns[index]),
			}
		}
	}

	ids := make(map[string]struct{})
	var records []Record
	for row := 2; ; row++ {
		fields, readErr := csvReader.Read()
		if errors.Is(readErr, io.EOF) {
			break
		}
		if readErr != nil {
			return nil, &ParseError{Row: row, Err: fmt.Errorf("read record: %w", readErr)}
		}
		record := Record{
			ID:                fields[0],
			PythonSource:      fields[1],
			Subsystem:         fields[2],
			Behavior:          fields[3],
			Owner:             fields[4],
			GoDestination:     fields[5],
			Status:            fields[6],
			AutomatedEvidence: fields[7],
			X11Evidence:       fields[8],
			WaylandEvidence:   fields[9],
			SpeechEvidence:    fields[10],
			BrailleEvidence:   fields[11],
			Notes:             fields[12],
		}
		if err := validate(record, row, ids); err != nil {
			return nil, err
		}
		records = append(records, record)
	}
	return records, nil
}

func validate(record Record, row int, ids map[string]struct{}) error {
	for field, value := range map[string]string{
		"id":            record.ID,
		"python_source": record.PythonSource,
		"subsystem":     record.Subsystem,
		"behavior":      record.Behavior,
		"status":        record.Status,
	} {
		if value == "" {
			return &ParseError{Row: row, Err: fmt.Errorf("%w: %s is empty", ErrSchema, field)}
		}
	}
	if _, exists := allowedStatuses[record.Status]; !exists {
		return &ParseError{
			Row: row,
			Err: fmt.Errorf("%w: invalid status %q", ErrSchema, record.Status),
		}
	}
	if _, exists := ids[record.ID]; exists {
		return &ParseError{
			Row: row,
			Err: fmt.Errorf("%w: duplicate id %q", ErrSchema, record.ID),
		}
	}
	if record.GoDestination == "" && record.Status != StatusAcceptedOmission {
		return &ParseError{
			Row: row,
			Err: fmt.Errorf("%w: go_destination is empty for status %q", ErrSchema, record.Status),
		}
	}
	ids[record.ID] = struct{}{}
	return nil
}

func FormatStatuses() string {
	return "pending, in-progress, implemented, audit-required, accepted-omission"
}