package matching

import (
	"context"

	"github.com/shopspring/decimal"

	"github.com/missionworkforce/missionmatch/internal/modules/matching/engine"
)

// compile-time assertion that ChainedResolver satisfies engine.SkillMatcher.
var _ engine.SkillMatcher = (*ChainedResolver)(nil)

// ChainedResolver runs the deterministic alias and relationship resolver first, then the semantic
// matcher, and satisfies the engine SkillMatcher interface so the engine code is unchanged.
// The resolver is consulted first because curated ontology knowledge (an alias is an exact
// equivalence; a verified substitution has a known strength) is more precise and auditable than a
// cosine similarity. The semantic matcher runs only when the resolver finds no match.
type ChainedResolver struct {
	resolver *DeterministicAliasResolver
	semantic engine.SkillMatcher
}

// NewChainedResolver builds a ChainedResolver from a DeterministicAliasResolver and a semantic
// SkillMatcher. Either may be nil: a nil resolver skips the alias step, a nil semantic falls back
// to resolver only (or no match when the resolver also misses).
func NewChainedResolver(resolver *DeterministicAliasResolver, semantic engine.SkillMatcher) *ChainedResolver {
	return &ChainedResolver{resolver: resolver, semantic: semantic}
}

// Match satisfies engine.SkillMatcher. It returns the best candidate skill satisfying the required
// skill. The alias resolver runs first; on a hit the result is returned immediately and the semantic
// matcher is never called. On a resolver miss, the semantic matcher runs at the given threshold.
// ctx carries the request deadline and cancellation to both the resolver and any semantic provider call.
func (c *ChainedResolver) Match(
	ctx context.Context,
	required engine.RequiredSkill,
	cands []engine.CandidateSkill,
	threshold decimal.Decimal,
) (engine.SkillMatch, bool) {
	if c.resolver != nil {
		if m, ok := c.resolver.ResolveAlias(ctx, required, cands); ok {
			return m, true
		}
	}
	if c.semantic == nil {
		return engine.SkillMatch{}, false
	}
	return c.semantic.Match(ctx, required, cands, threshold)
}