using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;

namespace AcDream.Core.Spells;

/// <summary>
/// Loads + queries <see cref="SpellMetadata"/> from a CSV at startup.
/// Source: <c>docs/research/data/spells.csv</c> (RFC 4180-ish, 35
/// columns, 3,956 rows). Loaded once, used by panels + by
/// <c>EnchantmentMath</c> for buff stacking aggregation.
///
/// <para>
/// Hand-rolled CSV parser — the only complication is the
/// <c>Description</c> column which is double-quoted with embedded
/// commas. No external CsvHelper dependency.
/// </para>
///
/// <para>
/// Closes ISSUES.md #11. Required by ISSUES.md #6 for family-stacking
/// in vital-max enchantment aggregation.
/// </para>
/// </summary>
public sealed class SpellTable
{
    private readonly Dictionary<uint, SpellMetadata> _byId;

    /// <summary>Empty table (no spells loaded). Useful for tests +
    /// pre-load defaults.</summary>
    public static SpellTable Empty { get; } = new(new Dictionary<uint, SpellMetadata>());

    private SpellTable(Dictionary<uint, SpellMetadata> byId)
    {
        _byId = byId;
    }

    /// <summary>Number of spells loaded.</summary>
    public int Count => _byId.Count;

    /// <summary>Look up metadata by spell id. Returns <c>true</c> if
    /// found; <paramref name="meta"/> is the matching record.</summary>
    public bool TryGet(uint spellId, out SpellMetadata meta)
    {
        if (_byId.TryGetValue(spellId, out var v))
        {
            meta = v;
            return true;
        }
        meta = null!;
        return false;
    }

    /// <summary>All loaded spell IDs. Stable enumeration order is not
    /// guaranteed.</summary>
    public IEnumerable<uint> SpellIds => _byId.Keys;

    /// <summary>
    /// Load from a CSV file. Throws <see cref="FileNotFoundException"/>
    /// if the path doesn't exist; bad rows are silently skipped (the
    /// CSV is third-party data, not authored by us — be lenient).
    /// </summary>
    public static SpellTable LoadFromCsv(string csvPath)
    {
        if (!File.Exists(csvPath))
            throw new FileNotFoundException("spells.csv not found", csvPath);
        using var reader = new StreamReader(csvPath);
        return LoadFromReader(reader);
    }

    /// <summary>
    /// Load from any <see cref="TextReader"/>. Used by tests with
    /// <see cref="StringReader"/>; production loads via
    /// <see cref="LoadFromCsv"/>.
    /// </summary>
    public static SpellTable LoadFromReader(TextReader reader)
    {
        var byId = new Dictionary<uint, SpellMetadata>();

        string? header = reader.ReadLine();
        if (header is null) return new SpellTable(byId);

        // Map column-name → index. The CSV order is documented in
        // docs/research/data/README.md but we don't depend on it —
        // resolve every column we care about by name.
        var columns = ParseRow(header);
        var colIndex = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
        for (int i = 0; i < columns.Count; i++)
            colIndex[columns[i]] = i;

        int? Get(string name) => colIndex.TryGetValue(name, out int i) ? i : (int?)null;

        int? iSpellId     = Get("Spell ID");
        int? iName        = Get("Name");
        int? iSchool      = Get("School");
        int? iFamily      = Get("Family");
        int? iIconHex     = Get("IconId [Hex]");
        int? iWords       = Get("Spell Words");
        int? iDuration    = Get("Duration");
        int? iMana        = Get("Mana");
        int? iIsDebuff    = Get("IsDebuff");
        int? iIsFellow    = Get("IsFellowship");
        int? iDescription = Get("Description");

        if (iSpellId is null || iName is null) return new SpellTable(byId);

        string? line;
        while ((line = reader.ReadLine()) is not null)
        {
            if (string.IsNullOrWhiteSpace(line)) continue;
            var fields = ParseRow(line);
            if (fields.Count <= iSpellId.Value) continue;

            // Spell ID is the only non-optional column.
            if (!uint.TryParse(fields[iSpellId.Value], NumberStyles.Integer, CultureInfo.InvariantCulture, out uint spellId))
                continue;

            string name        = iName        is int n  && n  < fields.Count ? fields[n]  : "";
            string school      = iSchool      is int s  && s  < fields.Count ? fields[s]  : "";
            uint   family      = ParseUInt(fields, iFamily);
            uint   iconId      = ParseHexUInt(fields, iIconHex);
            string words       = iWords       is int w  && w  < fields.Count ? fields[w]  : "";
            float  duration    = ParseFloat(fields, iDuration);
            int    mana        = (int)ParseUInt(fields, iMana);
            bool   isDebuff    = ParseBool(fields, iIsDebuff);
            bool   isFellow    = ParseBool(fields, iIsFellow);
            string description = iDescription is int d  && d  < fields.Count ? fields[d]  : "";

            byId[spellId] = new SpellMetadata(
                spellId, name, school, family, iconId, words, duration,
                mana, isDebuff, isFellow, description);
        }

        return new SpellTable(byId);
    }

    private static uint ParseUInt(IList<string> fields, int? index)
    {
        if (index is not int i || i >= fields.Count) return 0;
        return uint.TryParse(fields[i], NumberStyles.Integer, CultureInfo.InvariantCulture, out uint v) ? v : 0u;
    }

    private static uint ParseHexUInt(IList<string> fields, int? index)
    {
        if (index is not int i || i >= fields.Count) return 0;
        string s = fields[i];
        if (s.StartsWith("0x", StringComparison.OrdinalIgnoreCase))
            s = s[2..];
        return uint.TryParse(s, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out uint v) ? v : 0u;
    }

    private static float ParseFloat(IList<string> fields, int? index)
    {
        if (index is not int i || i >= fields.Count) return 0f;
        return float.TryParse(fields[i], NumberStyles.Float, CultureInfo.InvariantCulture, out float v) ? v : 0f;
    }

    private static bool ParseBool(IList<string> fields, int? index)
    {
        if (index is not int i || i >= fields.Count) return false;
        return string.Equals(fields[i], "True", StringComparison.OrdinalIgnoreCase);
    }

    /// <summary>
    /// Hand-rolled RFC 4180-ish CSV row parser. Handles double-quoted
    /// fields with embedded commas (the Description column). Embedded
    /// double quotes are escaped by doubling (`""` → `"`). Public so
    /// callers (incl. tests) can reuse the parser without instantiating
    /// a full <see cref="SpellTable"/>.
    /// </summary>
    public static List<string> ParseRow(string row)
    {
        var fields = new List<string>();
        int i = 0;
        while (i < row.Length)
        {
            string field;
            if (row[i] == '"')
            {
                // Quoted field — consume until matching close-quote
                // (handle "" as an escaped quote within the field).
                i++; // skip opening
                var sb = new System.Text.StringBuilder();
                while (i < row.Length)
                {
                    if (row[i] == '"')
                    {
                        // Either a closing quote or an escaped "".
                        if (i + 1 < row.Length && row[i + 1] == '"')
                        {
                            sb.Append('"');
                            i += 2;
                            continue;
                        }
                        i++; // skip closing quote
                        break;
                    }
                    sb.Append(row[i]);
                    i++;
                }
                field = sb.ToString();
            }
            else
            {
                int start = i;
                while (i < row.Length && row[i] != ',')
                    i++;
                field = row[start..i];
            }
            fields.Add(field);
            // Skip the comma separator if present.
            if (i < row.Length && row[i] == ',')
                i++;
        }
        return fields;
    }
}