using IntelligenceApi.Models;

namespace IntelligenceApi.Engines;

/// <summary>
/// Derives audience recommendations from raw census data for a ZCTA.
///
/// This logic was previously embedded in the Gateway's DemographicsController
/// as BuildMarketAnalysis(). It belongs here — IntelligenceApi owns all
/// recommendation and analysis logic; the Gateway is a thin proxy.
///
/// Registered as a singleton: stateless, no IO.
/// </summary>
public sealed class DemographicsAnalyzer
{
    public DemographicAnalysisResponse Analyze(DemographicAnalysisRequest request)
    {
        var c    = request.Census;
        var zcta = request.Zcta;

        // ── Age skew ──────────────────────────────────────────────────────────
        var youngPct  = c.Pct18to24 + c.Pct25to34;
        var maturePct = c.Pct55to64 + c.Pct65plus;

        string ageSkew;
        if      (youngPct  > maturePct + 10) ageSkew = "young";
        else if (maturePct > youngPct  + 10) ageSkew = "mature";
        else                                  ageSkew = "balanced";

        // ── Recommended age chips ─────────────────────────────────────────────
        // Include brackets with meaningful population share.
        var ageRanges = new List<string>();
        if (c.Pct18to24 >= 10) ageRanges.Add("AGE_18_24");
        if (c.Pct25to34 >= 12) ageRanges.Add("AGE_25_34");
        if (c.Pct35to44 >= 12) ageRanges.Add("AGE_35_44");
        if (c.Pct45to54 >= 12) ageRanges.Add("AGE_45_54");
        if (c.Pct55to64 >= 10) ageRanges.Add("AGE_55_64");
        if (c.Pct65plus >= 12) ageRanges.Add("AGE_65_UP");

        // Fallback: if no bracket clears the threshold, default to prime brackets
        if (ageRanges.Count == 0)
        {
            ageRanges.Add("AGE_25_34");
            ageRanges.Add("AGE_35_44");
        }

        // ── Recommended income chips ──────────────────────────────────────────
        var incomes = c.MedianIncome switch
        {
            > 100_000 => new List<string> { "TOP_10",    "TOP_11_20" },
            >  75_000 => new List<string> { "TOP_11_20", "TOP_21_30" },
            >  50_000 => new List<string> { "TOP_21_30", "TOP_31_40" },
            _         => new List<string> { "TOP_41_50", "LOWER_50"  }
        };

        // ── Human-readable insights ───────────────────────────────────────────
        var insights = new List<string>();

        if (c.TotalPopulation > 0) insights.Add($"{c.TotalPopulation:N0} people");
        if (c.MedianIncome    > 0) insights.Add($"Median income ${c.MedianIncome:N0}");
        if (c.PctBachelorPlus > 0) insights.Add($"{c.PctBachelorPlus}% college-educated");

        if      (c.PctOwnerOccupied  > 55) insights.Add($"{c.PctOwnerOccupied}% homeowners");
        else if (c.PctRenterOccupied > 55) insights.Add($"{c.PctRenterOccupied}% renters");

        if      (c.PctFamilyHouseholds > 60) insights.Add($"{c.PctFamilyHouseholds}% families");
        else if (c.PctLivingAlone      > 35) insights.Add($"{c.PctLivingAlone}% single-person households");

        insights.Add(ageSkew switch
        {
            "young"  => "Skews younger (18–34)",
            "mature" => "Skews older (55+)",
            _        => "Balanced age distribution"
        });

        return new DemographicAnalysisResponse
        {
            Ok     = true,
            Zcta   = zcta,
            Census = c,
            Recommendations = new AudienceRecommendations
            {
                AgeRanges   = ageRanges,
                Incomes     = incomes,
                AgeSkew     = ageSkew,
                MarketScope = "local"   // single ZIP is always local scope
            },
            Insights = insights
        };
    }
}