<?php

declare(strict_types=1);

namespace App\Services\FormBuilder;

use App\Enums\FormBuilder\FormFieldConditionalLogicConditionOperator;
use App\Enums\FormBuilder\FormFieldConditionalLogicGroupOperator;
use App\Exceptions\FormBuilder\CyclicDependencyException;
use App\Exceptions\FormBuilder\InvalidConditionalLogicSpecException;
use App\Models\FormBuilder\FormField;
use App\Models\FormBuilder\FormFieldConditionalLogicCondition;
use App\Models\FormBuilder\FormFieldConditionalLogicGroup;
use Illuminate\Support\Facades\DB;

/**
 * Owns all writes to `form_field_conditional_logic_groups` and
 * `form_field_conditional_logic_conditions`. Single source of truth for:
 *
 *   - tree-shape validation (root must be a group; conditions are leaves)
 *   - operator enum enforcement (group + comparison)
 *   - field_slug existence check against the owning schema
 *   - cross-field cycle detection (ARCH §8 — contract unchanged from
 *     FormFieldService::assertNoConditionalCycle, implementation moved here)
 *   - serialisation back to the canonical ARCH §8 `{show_when: {...}}` JSON
 *     shape consumed by the snapshot writer and API resources
 *
 * Per addendum Q3, conditional_logic applies to FormField only — there is
 * no library mirror and no `copyLogic` method on `FormFieldService::insert
 * FromLibrary`.
 *
 * Activity log convention — matches WS-5a/b: emit
 * `field.conditional_logic_replaced` on the FormField subject.
 */
final class FormFieldConditionalLogicService
{
    /**
     * Eager-load the tree (root + all descendants + all leaf conditions).
     * Bounded to 5 recursion levels — matches the OrganisationScope cap
     * raise (WS-5c infrastructure) and the observed production ceiling.
     */
    public function logicFor(FormField $field): ?FormFieldConditionalLogicGroup
    {
        $root = $field->conditionalLogicGroups()
            ->whereNull('parent_group_id')
            ->with($this->nestedEagerLoad(5))
            ->first();

        return $root;
    }

    /**
     * Replace the full conditional-logic tree on a field transactionally.
     * Validates structure, operators, field_slug references, and cross-
     * field cycles before any write lands. Emits the semantic activity-log
     * entry on the owning FormField.
     *
     * Passing `null` clears the logic entirely (matches the legacy
     * `conditional_logic = null` JSON state).
     *
     * @param  array<string, mixed>|null  $tree  root group shape (no
     *     `show_when` wrapper — callers unwrap the wrapper before calling)
     */
    public function replaceLogic(FormField $field, ?array $tree): void
    {
        if ($tree === null || $tree === []) {
            DB::transaction(function () use ($field): void {
                $this->deleteExistingTree($field);
                $field->logFieldChange('field.conditional_logic_replaced', [
                    'count' => 0,
                ]);
            });

            return;
        }

        $this->assertSpecsValid($tree);
        $this->assertFieldSlugsResolve($field, $tree);
        $this->assertNoCycles($field, $tree);

        DB::transaction(function () use ($field, $tree): void {
            $this->deleteExistingTree($field);
            $this->insertNode($field->id, null, $tree, 0);
            $field->logFieldChange('field.conditional_logic_replaced', [
                'count' => $this->countNodes($tree),
            ]);
        });
    }

    /**
     * Serialise a root group (plus its subtree) back to the ARCH §8
     * `{show_when: {...}}` JSON shape. Returns null when the field has no
     * logic — matches the pre-WS-5c `conditional_logic = null` state.
     */
    public function toJsonShape(?FormFieldConditionalLogicGroup $root): ?array
    {
        if ($root === null) {
            return null;
        }

        return [
            'show_when' => $this->renderGroup($root),
        ];
    }

    /**
     * Public guard the FormRequests invoke in their `after()` hook (WS-5c
     * commit 3 strict validator on save). Rejects bad tree structure at
     * the HTTP boundary before any write lands.
     *
     * @param  array<string, mixed>  $tree  root group shape
     */
    public function assertSpecsValid(array $tree): void
    {
        $this->assertNodeValid($tree, isRoot: true);
    }

    /**
     * Translate the legacy ARCH §8 JSON group shape (`{"all": [...]}` /
     * `{"any": [...]}`) into the service's internal tree form
     * (`{"operator": "all"|"any", "children": [...]}`). Pure recursive
     * passthrough — does NOT validate; malformed shapes are returned
     * as-is and surface as `InvalidConditionalLogicSpecException` from
     * the downstream `assertSpecsValid`. Static so both the service path
     * (`FormFieldService::extractConditionalLogicTree`) and the boundary
     * validators (Store/Update FormRequests' `after()` hooks) can call
     * it without container resolution.
     *
     * Group operator catalogue is sourced from
     * `FormFieldConditionalLogicGroupOperator::values()` so a future
     * operator addition lands in one place.
     *
     * @param  array<string, mixed>  $node
     * @return array<string, mixed>
     */
    public static function normaliseLegacyShape(array $node): array
    {
        if (isset($node['field_slug'])) {
            return $node;
        }

        if (isset($node['operator'], $node['children']) && is_array($node['children'])) {
            $children = [];
            foreach ($node['children'] as $child) {
                if (is_array($child)) {
                    $children[] = self::normaliseLegacyShape($child);
                }
            }

            return ['operator' => $node['operator'], 'children' => $children];
        }

        foreach (FormFieldConditionalLogicGroupOperator::values() as $candidate) {
            if (isset($node[$candidate]) && is_array($node[$candidate])) {
                $children = [];
                foreach ($node[$candidate] as $child) {
                    if (is_array($child)) {
                        $children[] = self::normaliseLegacyShape($child);
                    }
                }

                return ['operator' => $candidate, 'children' => $children];
            }
        }

        return $node;
    }

    /**
     * Cross-field cycle detection (ARCH §8; contract preserved from the
     * pre-WS-5c `FormFieldService::assertNoConditionalCycle`). Builds a
     * dependency graph over every field in the owning schema — this field's
     * proposed tree plus the persisted trees of every sibling — and runs
     * DFS from this field's slug. A back-edge raises.
     *
     * @param  array<string, mixed>  $tree  proposed root group shape
     */
    public function assertNoCycles(FormField $field, array $tree): void
    {
        $subjectSlug = (string) $field->slug;
        $dependsOn = $this->extractDependencySlugs($tree);

        if ($dependsOn === []) {
            return;
        }

        $adjacency = $this->buildSchemaAdjacency($field);
        $adjacency[$subjectSlug] = $dependsOn;

        $visiting = [];
        $visited = [];
        $walk = function (string $node) use (&$walk, &$adjacency, &$visiting, &$visited, $subjectSlug): void {
            if (isset($visited[$node])) {
                return;
            }
            if (isset($visiting[$node])) {
                throw CyclicDependencyException::forField($subjectSlug);
            }
            $visiting[$node] = true;
            foreach ($adjacency[$node] ?? [] as $next) {
                $walk($next);
            }
            unset($visiting[$node]);
            $visited[$node] = true;
        };

        $walk($subjectSlug);
    }

    // --- internals ----------------------------------------------------

    private function deleteExistingTree(FormField $field): void
    {
        // Cascade: deleting the root groups deletes all descendants and
        // all conditions via the DB-level ON DELETE CASCADE chain.
        FormFieldConditionalLogicGroup::query()
            ->withoutGlobalScopes()
            ->where('form_field_id', $field->id)
            ->whereNull('parent_group_id')
            ->get()
            ->each(fn (FormFieldConditionalLogicGroup $g) => $g->delete());

        // Defensive: clear any orphaned descendants (should never exist
        // after the root delete, but we guard against partial failures).
        FormFieldConditionalLogicGroup::query()
            ->withoutGlobalScopes()
            ->where('form_field_id', $field->id)
            ->delete();
    }

    /**
     * @param  array<string, mixed>  $node
     */
    private function insertNode(string $fieldId, ?string $parentGroupId, array $node, int $sortOrder): void
    {
        if (isset($node['field_slug'])) {
            $operator = FormFieldConditionalLogicConditionOperator::from((string) $node['operator']);

            FormFieldConditionalLogicCondition::query()->withoutGlobalScopes()->create([
                'group_id' => $parentGroupId,
                'field_slug' => (string) $node['field_slug'],
                'comparison_operator' => $operator->value,
                'value' => $operator->isValueless() ? null : ($node['value'] ?? null),
                'sort_order' => $sortOrder,
            ]);

            return;
        }

        $groupOperator = FormFieldConditionalLogicGroupOperator::from((string) $node['operator']);

        $group = FormFieldConditionalLogicGroup::query()->withoutGlobalScopes()->create([
            'form_field_id' => $fieldId,
            'parent_group_id' => $parentGroupId,
            'operator' => $groupOperator->value,
            'sort_order' => $sortOrder,
        ]);

        /** @var array<int, array<string, mixed>> $children */
        $children = $node['children'] ?? [];
        foreach ($children as $childSortOrder => $child) {
            $this->insertNode($fieldId, $group->id, $child, (int) $childSortOrder);
        }
    }

    /**
     * @param  array<string, mixed>  $node
     */
    private function assertNodeValid(array $node, bool $isRoot): void
    {
        if (isset($node['field_slug'])) {
            if ($isRoot) {
                throw new InvalidConditionalLogicSpecException(
                    'Conditional logic tree root must be a group (with an "all" or "any" operator), not a bare condition.',
                );
            }

            $rawOperator = (string) ($node['operator'] ?? '');
            if (FormFieldConditionalLogicConditionOperator::tryFrom($rawOperator) === null) {
                throw new InvalidConditionalLogicSpecException(
                    "Unknown comparison operator '{$rawOperator}'. Valid operators: "
                    .implode(', ', array_map(
                        fn (FormFieldConditionalLogicConditionOperator $op) => $op->value,
                        FormFieldConditionalLogicConditionOperator::cases(),
                    ))
                    .'.',
                );
            }

            $slug = (string) ($node['field_slug'] ?? '');
            if ($slug === '') {
                throw new InvalidConditionalLogicSpecException(
                    'Condition requires a non-empty field_slug.',
                );
            }

            return;
        }

        $rawOperator = (string) ($node['operator'] ?? '');
        if (FormFieldConditionalLogicGroupOperator::tryFrom($rawOperator) === null) {
            throw new InvalidConditionalLogicSpecException(
                "Unknown group operator '{$rawOperator}'. Valid operators: all, any.",
            );
        }

        $children = $node['children'] ?? null;
        if (! is_array($children) || $children === []) {
            throw new InvalidConditionalLogicSpecException(
                'Conditional logic groups must have at least one child (group or condition).',
            );
        }

        foreach ($children as $child) {
            if (! is_array($child)) {
                throw new InvalidConditionalLogicSpecException(
                    'Group children must be arrays (group or condition nodes).',
                );
            }
            $this->assertNodeValid($child, isRoot: false);
        }
    }

    /**
     * @param  array<string, mixed>  $tree
     */
    private function assertFieldSlugsResolve(FormField $field, array $tree): void
    {
        $slugs = $this->extractDependencySlugs($tree);
        if ($slugs === []) {
            return;
        }

        $known = FormField::query()
            ->withoutGlobalScopes()
            ->where('form_schema_id', $field->form_schema_id)
            ->pluck('slug')
            ->all();

        $missing = array_values(array_diff($slugs, $known));
        if ($missing !== []) {
            throw new InvalidConditionalLogicSpecException(
                'Conditional logic references unknown field_slug(s): '.implode(', ', $missing).'.',
            );
        }
    }

    /**
     * @param  array<string, mixed>  $tree
     * @return list<string>
     */
    private function extractDependencySlugs(array $tree): array
    {
        $out = [];
        $walk = function (array $node) use (&$walk, &$out): void {
            if (isset($node['field_slug'])) {
                $out[] = (string) $node['field_slug'];

                return;
            }
            foreach ($node['children'] ?? [] as $child) {
                if (is_array($child)) {
                    $walk($child);
                }
            }
        };
        $walk($tree);

        return array_values(array_unique($out));
    }

    /**
     * @param  array<string, mixed>  $tree
     */
    private function countNodes(array $tree): int
    {
        $count = 0;
        $walk = function (array $node) use (&$walk, &$count): void {
            $count++;
            foreach ($node['children'] ?? [] as $child) {
                if (is_array($child)) {
                    $walk($child);
                }
            }
        };
        $walk($tree);

        return $count;
    }

    /**
     * Build a slug → list-of-dependent-slugs map for every OTHER field in
     * the owning schema. Subject slug is excluded; caller merges its
     * proposed deps in separately. Reads from the relational tables — the
     * post-WS-5c source of truth.
     *
     * @return array<string, list<string>>
     */
    private function buildSchemaAdjacency(FormField $subject): array
    {
        $siblings = FormField::query()
            ->withoutGlobalScopes()
            ->where('form_schema_id', $subject->form_schema_id)
            ->where('id', '!=', $subject->id)
            ->get(['id', 'slug']);

        if ($siblings->isEmpty()) {
            return [];
        }

        $adjacency = [];
        foreach ($siblings as $sibling) {
            $root = $sibling->rootConditionalLogicGroup();
            if ($root === null) {
                continue;
            }
            $deps = $this->collectConditionSlugsFromPersistedTree($root);
            if ($deps !== []) {
                $adjacency[(string) $sibling->slug] = $deps;
            }
        }

        return $adjacency;
    }

    /**
     * @return list<string>
     */
    private function collectConditionSlugsFromPersistedTree(FormFieldConditionalLogicGroup $root): array
    {
        $slugs = [];
        $walk = function (FormFieldConditionalLogicGroup $group) use (&$walk, &$slugs): void {
            foreach ($group->conditions as $condition) {
                $slugs[] = (string) $condition->field_slug;
            }
            foreach ($group->childGroups as $child) {
                $walk($child);
            }
        };
        $walk($root);

        return array_values(array_unique($slugs));
    }

    /**
     * @return array<string, mixed>
     */
    private function renderGroup(FormFieldConditionalLogicGroup $group): array
    {
        $conditions = $group->conditions->map(fn (FormFieldConditionalLogicCondition $c) => [
            'node' => $this->renderCondition($c),
            'sort_order' => (int) $c->sort_order,
            'id' => (string) $c->id,
        ]);
        $children = $group->childGroups->map(fn (FormFieldConditionalLogicGroup $g) => [
            'node' => $this->renderGroup($g),
            'sort_order' => (int) $g->sort_order,
            'id' => (string) $g->id,
        ]);

        // Interleave by sort_order, stable secondary by id.
        $merged = $conditions->concat($children)
            ->sortBy([
                ['sort_order', 'asc'],
                ['id', 'asc'],
            ])
            ->values()
            ->map(fn (array $entry): array => $entry['node'])
            ->all();

        $operatorValue = $group->operator instanceof FormFieldConditionalLogicGroupOperator
            ? $group->operator->value
            : (string) $group->operator;

        return [$operatorValue => $merged];
    }

    /**
     * @return array<string, mixed>
     */
    private function renderCondition(FormFieldConditionalLogicCondition $condition): array
    {
        $operator = $condition->comparison_operator instanceof FormFieldConditionalLogicConditionOperator
            ? $condition->comparison_operator
            : FormFieldConditionalLogicConditionOperator::from((string) $condition->comparison_operator);

        $row = [
            'field_slug' => (string) $condition->field_slug,
            'operator' => $operator->value,
        ];

        if (! $operator->isValueless()) {
            $row['value'] = $condition->value;
        }

        return $row;
    }

    /**
     * Depth-bounded eager-load spec for logicFor. Builds nested
     * `childGroups.childGroups...` strings up to the given depth, with
     * `conditions` on each level.
     *
     * @return list<string>
     */
    private function nestedEagerLoad(int $depth): array
    {
        $loads = ['conditions'];
        $prefix = '';
        for ($i = 0; $i < $depth; $i++) {
            $prefix = $prefix === '' ? 'childGroups' : $prefix.'.childGroups';
            $loads[] = $prefix;
            $loads[] = $prefix.'.conditions';
        }

        return $loads;
    }
}