package mock

import (
	_ "embed"
	"encoding/json"
	"errors"
	"fmt"
	"math/rand"
	"sort"
	"strings"

	"git.avsdev.uk/Go/job-search/internal/mock/findatender/ocds"
)

// Method is a procurement method and its details, as published on a tender.
type Method struct {
	Method  string `json:"procurementMethod"`
	Details string `json:"procurementMethodDetails,omitempty"`
}

// embeddedCatalog is data/catalog.json, compiled into the binary. Rebuild after
// changing the file.
//
//go:embed data/catalog.json
var embeddedCatalog []byte

// Catalog is the pool the generator draws from. It is read from
// ./data/catalog.json. Classifications holds every classification the subjects
// use, keyed "{scheme}-{id}" (e.g. "CPV-90513000"), and subjects and their
// items refer to entries by that key.
type Catalog struct {
	Buyers          []ocds.Organization            `json:"buyers"`
	Suppliers       []ocds.Organization            `json:"suppliers"`
	Subjects        []Subject                      `json:"subjects"`
	Methods         []Method                       `json:"methods"`
	Classifications map[string]ocds.Classification `json:"classifications"`
}

// Subject is a tender as stored in the catalog: an ocds.Tender whose main
// classification and additionalClassifications, on the tender and on each
// item, are keys into Catalog.Classifications. The outer fields shadow the
// embedded ones of the same JSON name, so everything else is read as
// ocds.Tender.
type Subject struct {
	ocds.Tender
	Classification            string        `json:"classification,omitempty"`
	AdditionalClassifications []string      `json:"additionalClassifications,omitempty"`
	Items                     []SubjectItem `json:"items,omitempty"`
}

// SubjectItem is an ocds.Item whose additionalClassifications are keys into
// Catalog.Classifications.
type SubjectItem struct {
	ocds.Item
	AdditionalClassifications []string `json:"additionalClassifications,omitempty"`
}

// LoadCatalog parses the embedded catalog and checks it is usable: every
// pool has at least one entry and every classification key resolves.
func LoadCatalog() (*Catalog, error) {
	return parseCatalog(embeddedCatalog, "embedded catalog")
}

// parseCatalog decodes and validates catalog JSON; name labels any error.
func parseCatalog(data []byte, name string) (*Catalog, error) {
	var catalog Catalog
	if err := json.Unmarshal(data, &catalog); err != nil {
		return nil, fmt.Errorf("decoding %s: %w", name, err)
	}
	if err := catalog.validate(); err != nil {
		return nil, fmt.Errorf("invalid %s: %w", name, err)
	}
	return &catalog, nil
}

// validate checks that every pool has at least one entry and that every
// classification key used by a subject or its items is in Classifications.
// It reports all the problems found, listing at most five missing keys.
func (c *Catalog) validate() error {
	var errs []error

	pools := []struct {
		name  string
		count int
	}{
		{name: "buyers", count: len(c.Buyers)},
		{name: "suppliers", count: len(c.Suppliers)},
		{name: "subjects", count: len(c.Subjects)},
		{name: "methods", count: len(c.Methods)},
		{name: "classifications", count: len(c.Classifications)},
	}
	for _, pool := range pools {
		if pool.count == 0 {
			errs = append(errs, fmt.Errorf("mock: no %s", pool.name))
		}
	}

	missing := map[string]bool{}
	check := func(keys ...string) {
		for _, key := range keys {
			if _, ok := c.Classifications[key]; key != "" && !ok {
				missing[key] = true
			}
		}
	}

	for _, subject := range c.Subjects {
		check(subject.Classification)
		check(subject.AdditionalClassifications...)
		for _, item := range subject.Items {
			check(item.AdditionalClassifications...)
		}
	}

	if len(missing) > 0 {
		keys := make([]string, 0, len(missing))
		for key := range missing {
			keys = append(keys, key)
		}
		sort.Strings(keys)
		if len(keys) > 5 {
			keys = append(keys[:5], "...")
		}
		errs = append(errs, fmt.Errorf(
			"mock: %d classification key(s) not found in classifications: %s",
			len(missing),
			strings.Join(keys, ", "),
		))
	}

	return errors.Join(errs...)
}

// ---------- picking (always returns a copy the caller may modify) ----------

func (c *Catalog) buyer(rng *rand.Rand) ocds.Organization {
	return clone(c.Buyers[rng.Intn(len(c.Buyers))])
}

func (c *Catalog) supplier(rng *rand.Rand) ocds.Organization {
	return clone(c.Suppliers[rng.Intn(len(c.Suppliers))])
}

func (c *Catalog) method(rng *rand.Rand) Method {
	return c.Methods[rng.Intn(len(c.Methods))]
}

// subject picks a subject and returns it as an ocds.Tender, with its
// classification keys resolved to full classifications.
func (c *Catalog) subject(rng *rand.Rand) ocds.Tender {
	subject := clone(c.Subjects[rng.Intn(len(c.Subjects))])
	tender := subject.Tender
	tender.Classification = c.resolveOne(subject.Classification)
	tender.AdditionalClassifications = c.resolve(
		subject.AdditionalClassifications,
	)

	tender.Items = nil
	for _, subjectItem := range subject.Items {
		item := subjectItem.Item
		item.AdditionalClassifications = c.resolve(
			subjectItem.AdditionalClassifications,
		)
		tender.Items = append(tender.Items, item)
	}

	return tender
}

// resolveOne returns a copy of the classification with key, or nil if there
// is none.
func (c *Catalog) resolveOne(key string) *ocds.Classification {
	if classification, ok := c.Classifications[key]; ok {
		return &classification
	}
	return nil
}

// resolve returns copies of the classifications with keys, skipping keys
// that have none.
func (c *Catalog) resolve(keys []string) []ocds.Classification {
	var out []ocds.Classification
	for _, key := range keys {
		if classification, ok := c.Classifications[key]; ok {
			out = append(out, classification)
		}
	}
	return out
}

// clone deep-copies a value through JSON, which is all the generated types
// need.
func clone[T any](value T) T {
	var out T
	data, err := json.Marshal(value)
	if err == nil {
		json.Unmarshal(data, &out) //nolint:errcheck,gosec // data was just marshalled from a T
	}
	return out
}